HYDROGENATION OF SULPHUR CONTAINING GASES WITH PHOSPHIDE NANOPARTICLES
20230226528 · 2023-07-20
Inventors
- Yasser ALWAHEDI (Abu Dhabi, AE)
- Kyriaki POLYCHRONOPOULOU (Abu Dhabi, AE)
- Xinnan LU (Abu Dhabi, AE)
- Safa GABER (Abu Dhabi, AE)
- Dina GABER (Abu Dhabi, AE)
- Georgia BASINA (Abu Dhabi, AE)
- Malathe SAMIR (Abu Dhabi, AE)
Cpc classification
B01J37/0209
PERFORMING OPERATIONS; TRANSPORTING
B01J37/0018
PERFORMING OPERATIONS; TRANSPORTING
International classification
B01J27/185
PERFORMING OPERATIONS; TRANSPORTING
B01J35/00
PERFORMING OPERATIONS; TRANSPORTING
B01J37/03
PERFORMING OPERATIONS; TRANSPORTING
B01J37/02
PERFORMING OPERATIONS; TRANSPORTING
Abstract
Embodiments include hydrogenating catalysts and methods of making the same. The catalyst includes nanoparticles of a metal phosphide, such as nickel phosphide with a Ni.sub.5P.sub.4 phase. Also included are methods of hydrogenating a gas that contains sulfur. The methods include directing the gas containing sulfur to a catalyst that includes nanoparticles of a metal phosphide, and contacting the catalyst with the gas containing sulfur to produce a hydrogenated gas.
Claims
1. A method of making a hydrogenation catalyst, the method comprising: dispersing Ni in a mesoporous SiO.sub.2 to form a Ni@meso-SiO.sub.2 composite; contacting the Ni@meso-SiO.sub.2 composite with a P source to provide a Ni.sub.xP.sub.y@meso-SiO.sub.2 composite, wherein contact between the Ni@meso-SiO.sub.2 composite and the P source occurs as a temperature between 225° C. and 375° C., and wherein the Ni.sub.xP.sub.y@meso-SiO.sub.2 composite includes Ni.sub.xP.sub.y nanoparticles that are less than 5 nm in size and are embedded within the mesoporous SiO.sub.2.
2. The method of claim 1, wherein dispersing Ni in mesoporous SiO.sub.2 includes forming a mixture of Ni precursor, a solvent, a surfactant, and a SiO.sub.2 source.
3. The method of claim 2, wherein the mixture includes a Ni:Si atomic ratio of 5% or less.
4. The method of claim 2, wherein the Ni precursor is Ni(acac).sub.2, the solvent is water, the surfactant is CTAB, and the SiO2 source is Na.sub.2SiO.sub.3; and wherein dispersing Ni in mesoporous SiO.sub.2 includes forming particles of Ni@meso-SiO.sub.2 composite suspended in a liquid phase and separating the particles of Ni@SiO.sub.2 composite from the liquid phase; and further including removing excess Ni precursor from the mixture; and further stirring the mixture at a temperature of between about 15° C. and 60° C. for a time of between 1 hour and 24 hours.
5.-7. (canceled)
8. The method of claim 1, wherein contacting the Ni@meso-SiO.sub.2 composite with a P source includes dissolving the P source in OA.
9. The method of claim 1, wherein the P source is TOP.
10. The method of claim 1, wherein the Ni@meso-SiO.sub.2 composite is contacted with the P source for at least 2 hours.
11. The method of claim 1, wherein the Ni.sub.xP.sub.y@meso-SiO.sub.2 composite is substantially free of amorphous phase Ni.
12. The method of claim 1, wherein contact between the Ni@meso-SiO.sub.2 composite and the P source occurs as a temperature between 225° C. and 275° C., and wherein the Ni.sub.xP.sub.y@meso-SiO.sub.2 composite is a Ni.sub.12P.sub.5@meso-SiO.sub.2 composite and includes Ni.sub.12P.sub.5 nanoparticles that are less than 5 nm in size and are embedded within the mesoporous SiO.sub.2.
13. The method of claim 1, wherein contact between the Ni@meso-SiO.sub.2 composite and the P source occurs as a temperature between 275° C. and 325° C., and wherein the Ni.sub.xP.sub.y@meso-SiO.sub.2 composite is a Ni.sub.2P@meso-SiO.sub.2 composite and includes Ni.sub.2P nanoparticles that are less than 5 nm in size and are embedded within the mesoporous SiO.sub.2.
14. The method of claim 1, wherein contact between the Ni@meso-SiO.sub.2 composite and the P source occurs as a temperature between 325° C. and 375° C., and wherein the Ni.sub.xP.sub.y@meso-SiO.sub.2 composite is a Ni.sub.5P.sub.4@meso-SiO.sub.2 composite and includes Ni.sub.5P.sub.4 nanoparticles that are less than 5 nm in size and are embedded within the mesoporous SiO.sub.2.
15. The method of claim 1, wherein the Ni.sub.2P nanoparticles are less than 2 nm in size.
16. A method of making a hydrogenation catalyst, the method comprising: dissolving Ni in a solvent at a temperature between 15° C. and 100° C. to form a first mixture, wherein the solvent has a boiling point that is above 400° C.; heating the mixture to a temperature of between 325° C. and 375° C. to provide a heated mixture; adding a P source to the heated mixture while maintaining the temperature between 325° C. and 375° C. to allow the P source to phosphorize the Ni and to produce Ni.sub.5P.sub.4 nanoparticles.
17. The method of claim 16, wherein the solvent is TOPO.
18. The method of claim 17, wherein the Ni precursor is Ni(acac).sub.2.
19. The method of claim 18, where the P source is TOP or TOPO.
20. The method of claim 16, wherein the Ni.sub.5P.sub.4 nanocrystals are between 25 nm and 125 nm in size.
21. A hydrogenation catalyst, comprising: Ni.sub.2P nanoparticles that are less than 5 nm in size; and mesoporous SiO.sub.2, wherein the Ni.sub.2P nanoparticles are embedded within the mesoporous SiO.sub.2.
22. The hydrogenation catalyst of claim 21, wherein the Ni.sub.2P nanoparticles that are less than 2 nm in size.
23. A hydrogenation catalyst comprising Ni.sub.5P.sub.4 nanoparticles that are between 25 nm and 125 nm in size.
24. (canceled)
Description
BRIEF DESCRIPTION OF THE DRAWINGS
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DETAILED DESCRIPTION
Definitions
[0066] As used herein, the term “Co(acac).sub.2” refers to cobalt (II) acetylacetonate.
[0067] As used herein, the term “CTAB” refers to hexadecyl trimethyl ammonium bromide. Examples of suitable CTAB include 98% CTAB, available from Millipore Sigma of Burlington, Mass.
[0068] As used herein, the term “Fe(acac).sub.3” refers to iron (III) acetylacetonate.
[0069] As used herein, the term “GHSV” refers to gas hourly space velocity.
[0070] As used herein, the term “Mo(CO).sub.6” refers to molybdenumhexacarbonyl.
[0071] As used herein, the term “(NH.sub.4).sub.6M.sub.o7O.sub.24 4H.sub.2O” refers to ammonium molybdate tetrahydrate.
[0072] As used herein, the term “Ni(acac).sub.2” refers to nickel (II) acetylacetonate (Ni(acac).sub.2).
[0073] As used herein, the term “Ni(NO.sub.3).sub.2” refers to nickel (II) nitrate hexahydrate (Ni(NO.sub.3).sub.2 6H.sub.2O. Examples of suitable Ni(NO.sub.3).sub.2 include 95% Ni(NO.sub.3).sub.2, available from Millipore Sigma of Burlington, Mass.
[0074] As used herein, the terms “phosphorizing”, “phosphorate”, or the like mean to combine or impregnate with phosphorus.
[0075] As used herein, the term “OA” refers to oleylamine. Examples of suitable OA include ≥98% OA with a b.p. 348° C., available from Millipore Sigma of Burlington, Mass.
[0076] As used herein, the term “TEM” refers to high-resolution transmission electron microscopy.
[0077] As used herein, the term “TEOS” refers to tetraethyl orthosilicate. Examples of suitable TEOS include ≥99% GC TEOS, available from Millipore Sigma of Burlington, Mass.
[0078] As used herein, the term “TOP” refers to trioctylphosphine. Examples of suitable TOP include 97% TOP, available from Millipore Sigma of Burlington, Mass.
[0079] As used herein, the term “TOPO” refers to trioctylphosphine oxide. Examples of suitable TOPO include 99% TOPO, available from Millipore Sigma of Burlington, Mass.
[0080] As used herein, the term “WCl.sub.4” refers to tungsten (IV) chloride.
[0081] As used herein, the term “XRD” refers to x-ray diffraction.
DISCUSSION
[0082] The present disclosure provides novel catalytic materials and methods useful for hydrogenating sulfur-containing gases. It has been surprisingly found that metallic phosphide nanoparticles are useful catalytic materials for the hydrogenation of sulfur compounds and offer improved performance over prior art catalytic materials. In some embodiments, the present invention includes catalytic materials that outperform prior art catalysts in terms of hydrogen sulfide conversion rates and operating temperature. Further, in some embodiments, the present inventive catalytic materials meet or exceed the performance of prior art catalysts while using significantly less catalytic mass (e.g., 1/20 as much catalytic mass). Hence, the present invention provides substantial cost savings.
[0083] In some embodiments, the present invention includes a hydrodesulphurization catalyst or catalytic material that includes nanoparticles of a metal phosphide. For example, the metal phosphide can be a nickel phosphide, a cobalt phosphide, a molybdenum phosphide, or mixtures thereof. In some embodiments the metal phosphide is a nickel phosphide with a Ni.sub.5P.sub.4 phase structure, a nickel phosphide with a NiP.sub.2 phase structure, a nickel phosphide with a Ni.sub.2P phase structure, a nickel phosphide with a Ni.sub.12P.sub.5 phase structure, or mixtures thereof. In some embodiments, the metal phosphide is a cobalt phosphide (e.g., a cobalt phosphide in a CoP phase or a Co.sub.2P phase), an iron phosphide (e.g., an iron phosphide in a FeP.sub.4 phase), a molybdenum phosphide, a tungsten phosphide, or combinations thereof. In some embodiments, the catalyst or catalytic material of the present invention includes two or more of the above-described metal phosphides (e.g., 3, 4, 5, or more than 5). In some embodiments, the catalyst or catalytic material of the present invention includes two or more of the above-described metal phosphides and one or more of the phosphides acts as a co-catalytic material. In some embodiments, the metal phosphide(s) of the nanoparticles are each in a sing phase (e.g., Ni.sub.2P and/or Ni.sub.5P.sub.4 phases). In other embodiments, the nanoparticles are in two or more phases (e.g., Ni.sub.2P and/or Ni.sub.5P.sub.4 phases). In some embodiments, the nanoparticles are devoid of metal phosphides that are in an amorphous phase.
[0084] In some embodiments, the nanoparticles have a mean or average particle size of between about 0.1 nm to about 1,000 nm or higher, such as about 5 nm, about 10 nm, about 20 nm, about 30 nm, about 40 nm, about 50 nm, about 60, about 70, about 75 nm, about 80, about 90, about 100 nm, about 150 nm, about 200 nm, about 250 nm, about 300 nm, about 350 nm, about 400 nm, about 450 nm, about 500 nm, about 550 nm, about 600 nm, about 650 nm, about 700 nm, about 750 nm, about 800 nm, about 850 nm, about 900 nm, about 950 nm, about 1000 nm or higher, or any incremental value or subrange between the provided particle sizes. In some embodiments, the nanoparticles have a mean or average particle size of between about 0.1 nm and about 20 nm or less than 20 nm, such as between about 0.1 nm and about 15 nm or lower, such as about 12 nm, about 10 nm, about 9 nm, about 8 nm, about 7 nm, about 6 nm, about 5 nm, about 4 nm, about 3 nm, about 2 nm, about 1 nm, about 0.5 nm, or any incremental value or subrange between the provided particle sizes.
[0085] In some embodiments, the nanoparticles include one or more coating or “support” layers. For example, in some embodiments, the nanoparticles include a coating of CTAB, silicon dioxide (e.g., mesoporous silicon dioxide or a silicon dioxide coating that has pores with diameters between 2 and 50 nm), a cerium oxide (e.g., cerium (III) oxide, cerium (III, IV) oxide, or cerium (IV) oxide), an aluminum oxide (e.g., aluminum (III) oxide, aluminum (II) oxide, or aluminum (I) oxide), or combinations thereof (e.g., an inner coating of CTAB and an outer coating of silicon dioxide). The coating layers on the nanoparticles may cover only a portion of a nanoparticle, such that at least a portion of the metal phosphide surface of the nanoparticles is not in direct contact with the coating material. In some embodiments, the one or more coating layers may completely engulf some or all of the nanoparticles such that the some or all of the nanoparticles are completely embedded within the coating material. In some embodiments, the one or more coating layers protect the metal phosphide nanoparticles from sintering during use.
[0086] In some embodiments, the present invention includes one or more of the inventive catalytic materials arranged on or secured to a solid support. For example, some embodiments of the present invention include nanoparticles of metal phosphide that are arranged on or secured to an alumina support (e.g., a gamma alumina support).
[0087] In some embodiments, the present invention includes methods of using the inventive catalysts or catalytic materials to hydrogenate a gas that includes sulfur.
[0088] As shown in
[0089] Catalytic bed 302 includes at least one of the inventive catalysts or catalytic materials of the present invention described herein. For example, catalytic bed 302 could be a catalysis unit that include nanoparticles of nickel phosphide with a Ni.sub.5P.sub.4 phase structure mounted on a gamma alumina solid support.
[0090] Separation unit 304 could be one or more separation units suitable for separating chemical species of interest from separation unit feed line 314. For example, separation unit 304 could include one or more distillation columns, absorption columns, or gas separator tanks.
[0091] Sulfur-containing gas feed line 306 directs a sulfur-containing gas to catalytic bed 302 and into contact with the inventive catalyst or catalytic material therein. The sulfur-containing gas might be, for example, a Claus tail gas that contains sulfur compounds such SO.sub.2, COS, and/or CS.sub.2.
[0092] If given application requires additional hydrogen for the hydrogenation reaction, optional hydrogen-containing gas feed line 308 directs a flow of a hydrogen-containing gas into catalytic bed 302 and into contact with the inventive catalyst or catalytic material therein.
[0093] While not illustrated in
[0094] Once in catalytic bed 302, the sulfur-containing gas and, if used, the hydrogen-containing gas come into contact with the inventive catalysts or catalytic material inside bed 302. The inventive catalysts or catalytic material catalyze the hydrogenation reaction and portions of the sulfur compounds in the sulfur-containing gas are hydrogenated to the desired catalytic products (e.g., H.sub.2S), thereby producing a hydrogenated gas.
[0095] The sulfur-containing gas and/or the hydrogen-containing gas may contact the inventive catalyst or catalytic material at any desired temperature. In some embodiments of the invention, the sulfur-containing gas and/or the hydrogen-containing gas contact the inventive catalyst or catalytic material at a temperature of between about 200° C. and about 500° C. or higher, such as about 210° C., about 220° C., about 230° C., about 240° C., about 250° C., about 260° C., about 270° C., about 280° C., about 290° C., about 300° C., about 310° C., about 320° C., about 330° C., about 340° C., about 350° C., about 360° C., about 370° C., about 380° C., about 390° C., about 400° C., about 410° C., about 420° C., about 430° C., about 440° C., about 450° C., about 460° C., about 470° C., about 480° C., about 490° C., about 500° C. or higher, or any incremental value or subrange between the provided temperatures.
[0096] The sulfur-containing gas and/or the hydrogen-containing gas may contact the inventive catalyst or catalytic material at any desired pressure. In some embodiments of the invention, the sulfur-containing gas and/or the hydrogen-containing gas contact the inventive catalyst or catalytic material at a pressure that is between about 1 atmosphere and about 150 atmospheres or higher, such as about 2 atmospheres, about 3 atmospheres, about 4 atmospheres, about 5 atmospheres, about 6 atmospheres, about 7 atmospheres, about 8 atmospheres, about 9 atmospheres, about 10 atmospheres, about 15 atmospheres, about 20 atmospheres, about 25 atmospheres, about 30 atmospheres, about 35 atmospheres, about 40 atmospheres, about 45 atmospheres, about 50 atmospheres, about 55 atmospheres, about 60 atmospheres, about 65 atmospheres, about 70 atmospheres, about 75 atmospheres, about 80 atmospheres, about 85 atmospheres, about 90 atmospheres, about 95 atmospheres, about 100 atmospheres, about 105 atmospheres, about 110 atmospheres, about 115 atmospheres, about 120 atmospheres, about 125 atmospheres, about 130 atmospheres, about 135 atmospheres, about 140 atmospheres, about 145 atmospheres, about 150 atmospheres or higher, or any incremental value or subrange between the provided pressures.
[0097] After contacting the inventive catalysts or catalytic material in catalytic bed 302, the hydrogenated gas, including catalytic reaction products such as H.sub.2S, are directed from catalytic bed 302 to separation unit 304 via separation unit feed line 314. Optionally, separation unit feed line 314 may direct the hydrogenated gas through one or more unit operations to condition the catalytic reaction products prior to directing the hydrogenated gas to separation unit 304. For example, line 314 may pass hydrogenated gas through one or more heat exchangers, furnaces, chillers, humidifiers, dryers, pumps, compressors, or pressure reduction valves.
[0098] Once in separation unit 304, the catalytic reaction products in the hydrogenated gas are separated into one or more product and/or waste streams. The products of interest (e.g., H.sub.2S) are directed from separation unit 304 via separation unit product line 312, while unreacted or undesired chemical species are directed from separation unit 304 via separation unit waste line 310.
[0099] The present invention includes methods of making a hydrogenation catalyst.
[0100] In some embodiments, the methods of making a hydrogenation catalyst include dispersing Ni in a mesoporous SiO.sub.2 to form a Ni@meso-SiO.sub.2 composite and then contacting the Ni@meso-SiO.sub.2 composite with a P source to provide a Ni.sub.xP.sub.y@meso-SiO.sub.2 composite.
[0101] Dispersing Ni in a mesoporous SiO.sub.2 can include dissolving a Ni precursor in a solvent to form a mixture of dissolved Ni and/or dispersing Ni-containing nanoparticle compounds within the mixture (e.g., dispersing nanoparticles of Ni(acac).sub.2 and/or Ni.sub.xP.sub.y nanoparticles such as Ni.sub.2P or Ni.sub.12P.sub.5 nanoparticles). The solvent could be, for example, water, OA, TOP, TOPO, or mixtures of one or more of those materials. The Ni precursor can be, for example, Ni(acac).sub.2. Additional components can also be utilized during the dispersion; for example, the mixture could include a surfactant and/or a source of SiO.sub.2. For example, the surfactant could be CTAB, OA, TOP, or TOPO and/or the source of SiO.sub.2 could be Na.sub.2SiO.sub.3. NaOH or other bases or acids could be included in the mixture to facilitate the dispersion of the Ni in the mesoporous SiO.sub.2.
[0102] The dispersion of Ni in the solvent can be conducted at a temperature that is between ˜15° C. and ˜250° C., such as ˜20° C., ˜25° C., ˜30° C., ˜35° C., ˜40° C., ˜45° C., ˜50° C., ˜55° C., ˜60° C., ˜65° C., ˜70° C., ˜75° C., ˜80° C., ˜85° C., ˜90° C., ˜95° C., ˜100° C., ˜125° C., ˜150° C., ˜175° C., ˜200° C., ˜225° C., ˜250° C., of any incremental value or subrange between these provided temperatures.
[0103] Dispersing Ni in a mesoporous SiO.sub.2 can include removing excess Ni from the solution. For example, any undissolved Ni solids can be removed by filtration and/or centrifugation. In some embodiments, the final Ni content in the dispersed mixture can be such that the Ni to Si atomic ratio is 5% or less.
[0104] The Ni@meso-SiO.sub.2 composite produced can take the form of nanoparticles of nickel compounds (e.g., Ni(acac).sub.2 and/or Ni.sub.xP.sub.y nanoparticles such as Ni.sub.2P or Ni.sub.12P.sub.5 nanoparticles) embedded, constrained, or encased within mesoporous SiO.sub.2. In some embodiments, dispersing Ni in a mesoporous SiO.sub.2 includes removing these composite nanoparticles from the solvent mixture in which they are dispersed (e.g., by centrifugation, filtration, and/or drying and/or washing).
[0105] In some embodiments, the P source is one or more of TOP or TOPO. Contacting the Ni@meso-SiO.sub.2 composite with the P source can include dissolving or mixing TOP or TOPO into OA.
[0106] In some embodiments the P source and Ni@meso-SiO.sub.2 composite are contacted for a period of time and at a temperature necessary to phosphorilize the Ni@meso-SiO.sub.2 composite to a desired extent and produce the desired Ni.sub.xP.sub.y phase in the resulting Ni.sub.xP.sub.y@meso-SiO.sub.2 composite. For example, the P source and Ni@meso-SiO.sub.2 composite may be contacted for up to about 5 minutes, 10 minutes, 20 minutes, 30 minutes, 40 minutes, 50 minutes, 60 minutes, 75 minutes, 90 minutes, 105 minutes, 120 minutes, 150 minutes, 180 minutes, 210 minutes, 240 minutes, 270 minutes, 300 minutes, 330 minutes 360 minutes, 390 minutes, 420 minutes, 450 minutes, 480 minutes, 510 minutes, 540 minutes, 570 minutes, 10 hours, 12 hours, 18 hours, 24 hours, 2 days, 3 days, 4 days, 7 days, or any incremental value or subrange between these provided times. The temperature at which the P source and Ni@meso-SiO.sub.2 composite are contacted may be between about 180° C. and about 500° C., such as about 180° C., about 190° C., about 200° C., about 210° C., about 220° C., about 225° C., about 230° C., about 240° C., about 250° C., about 260° C., about 270° C., about 275° C., about 280° C., about 290° C., about 300° C., about 310° C., about 320° C., about 325° C., about 330° C., about 340° C., about 350° C., about 360° C., about 370° C., about 375° C., about 380° C., about 390° C., about 400° C., about 410° C., about 420° C., about 425° C., about 430° C., about 440° C., about 450° C., about 460° C., about 470° C., about 475° C., about 480° C., about 490° C., about 500° C., or any incremental value or subrange between these provided temperatures. In some embodiments, the contact between the Ni@meso-SiO.sub.2 composite and the P source occurs as a temperature between 225° C. and 275° C. and the resulting Ni.sub.xP.sub.y@meso-SiO.sub.2 composite is a Ni.sub.12P.sub.5@meso-SiO.sub.2 composite that includes Ni.sub.12P.sub.5 nanoparticles less than 5 nm in size embedded within the mesoporous SiO.sub.2. In some embodiments, the contact between the Ni@meso-SiO.sub.2 composite and the P source occurs as a temperature between 275° C. and 325° C. and the resulting Ni.sub.xP.sub.y@meso-SiO.sub.2 composite is a Ni.sub.2P@meso-SiO.sub.2 composite and includes Ni.sub.2P nanoparticles less than 5 nm in size embedded within the mesoporous SiO.sub.2. In some embodiments, the contact between the Ni@meso-SiO.sub.2 composite and the P source occurs as a temperature between 325° C. and 375° C. and the resulting Ni.sub.xP.sub.y@meso-SiO.sub.2 composite is a Ni.sub.5P.sub.4@meso-SiO.sub.2 composite and includes Ni.sub.5P.sub.4 nanoparticles less than 5 nm in size embedded within the mesoporous SiO.sub.2.
[0107] In some embodiments, the present invention includes methods of making a hydrogenation catalyst, where the method includes forming a first mixture by dissolving Ni (e.g., a Ni precursor such as Ni(acac).sub.2) in a solvent that has a boiling point that is higher than the temperatures needed to phosphoralize the Ni. For example, the solvent may have a boiling point that is above 400° C., such as TOPO which has a boiling point of about 411.2° C. The temperature at which the Ni is dissolved in the solvent is below the nucleation temperature of the Ni in that solvent. For example, the temperature at which the Ni is dissolved in the solvent could be between ˜15° C. and ˜250° C., such as ˜20° C., ˜25° C., ˜30° C., ˜35° C., ˜40° C., ˜45° C., ˜50° C., ˜55° C., ˜60° C., ˜65° C., ˜70° C., ˜75° C., ˜80° C., ˜85° C., ˜90° C., ˜95° C., 100° C., 125° C., −150° C., −175° C., −200° C., −225° C., −250° C., of any incremental value or subrange between these provided temperatures.
[0108] After forming the first mixture, the first mixture is heated to a temperature at which the Ni will be phosphoralized and the P source is added while maintaining that temperature. For example, the first mixture could be heated to a temperature of between 325° C. and 375° C. to provide a heated mixture, and then a P source (e.g., TOP or TOPO) is added to the heated mixture while maintaining the temperature between 325° C. and 375° C. to allow the P source to phosphorize the Ni to produce Ni.sub.5P.sub.4 nanoparticles. In other examples, the temperature to which the first mixture is heated and the phosphorylation process conducted is between about 225° C. and about 375° C., such as about 225° C., about 230° C., about 240° C., about 250° C., about 260° C., about 270° C., about 275° C., about 280° C., about 290° C., about 300° C., about 310° C., about 320° C., about 325° C., about 330° C., about 340° C., about 350° C., about 360° C., about 370° C., about 375° C., or any incremental value or subrange between these provided temperatures
Example 1
Ni.SUB.x.P.SUB.y .Catalyst Synthesis
[0109] A systematic methodology of synthesizing catalysts was followed to produce various types of Ni.sub.xP.sub.y catalysts. Flow charts illustrating some aspects of the methodologies are provided in
1. Ni.sub.xP.sub.y Phase Control
[0110] Ni.sub.xP.sub.y nanoparticles having various types of phases and a mesoporous coating were produced using the methodologies of group “A” in
Synthesis of Ni.sub.xP.sub.y, Nanoparticles
[0111] Ni.sub.xP.sub.y nanoparticles were synthesized in a N.sub.2 atmosphere via thermal decomposition of nickel precursor in organic mixtures using OA and TOP or TOPO. In a typical preparation of Ni.sub.xP.sub.y nanoparticles, 2 mmol of nickel precursor Ni(acac).sub.2 was first dissolved in the reaction mixture of 10 mL OA and 5 mL TOP under magnetic stirring for 5 min at 80° C. After the stirring, the mixture was heated to 230° C. for 1 hour, and then another 5 mL TOP was injected into the mixture and stirred at the following reaction temperatures T for another 2 hours to produce the following types of nanoparticle samples: [0112] Sample of 1-Ni.sub.5P.sub.4: T=350° C. [0113] Sample of n-Ni.sub.2P: T=300° C. [0114] Sample of n-Ni.sub.2P.sub.5: T=250° C.
The above operations were carried out in a fume hood.
[0115] After cooling to room temperature, the Ni.sub.xP.sub.y particles were precipitated by addition of ethanol (≥99.8% for HPLC; available from Millipore Sigma) and subsequently centrifuged for 10 min at 4500 rpm. The supernatant was then discarded and the nanoparticles retained. To remove excess surfactants, the nanoparticles were washed three times by dispersion in n-hexane (95% anhydrous; available from Millipore Sigma), then precipitated with ethanol and isolated by centrifugation. The resulting nanoparticles were dried at room temperature.
[0116] The resulting 1-Ni.sub.5P.sub.4 sample comprised Ni.sub.5P.sub.4 phase particles with a relatively large particle size of >500 nm. The resulting n-Ni.sub.2P sample comprised Ni.sub.2P phase particles with a particle size of about 11 nm. The n-Ni.sub.12P.sub.5 sample comprised Ni.sub.12P.sub.5 phase particles with a particle size of about 12 nm.
Coating Ni.sub.xP.sub.y, Nanoparticles with Mesoporous Silica
[0117] The Ni.sub.xP.sub.y nanoparticles described above were coated with mesoporous silica to produce Ni.sub.xP.sub.y@meso-SiO.sub.2 coated catalytic nanoparticles. Prior to the dispersion in water, the previously obtained nanoparticles were dispersed in hexane. Specifically, 100 mg of the previously obtained Ni.sub.xP.sub.y nanoparticles were dispersed in 5 mL n-hexane and then mixed with 50 ml of an aqueous solution (1% w/v) of CTAB. The mixture of nanoparticles, hexane, and CTAB was sonicated for 30 min and then stirred overnight at room temperature. The nanoparticles were isolated from the solution using centrifugation. The resulting CTAB-coated Ni.sub.xP.sub.y particles were washed and recovered again by centrifugation, followed by dispersion in 50 ml of deionized water to form a stable hydrosol.
[0118] The coated catalyst, Ni.sub.xP.sub.y@meso-SiO.sub.2, was synthesized by hydrolysis of the silica source TEOS in the presence of base, then the resultant silanol groups were condensed prior to extraction of surfactant. Specifically, 0.5 mL of TEOS was added dropwise into 50 ml of the previously obtained CTAB-coated Ni.sub.xP.sub.y hydrosol with vigorous stirring for 15 minutes. To this mixture, 70 μL of aqueous ammonia solution (26 wt % NH.sub.4OH) was then added and the reaction proceeded at room temperature for 24 hours. Afterwards, the Ni.sub.xP.sub.y/coated-CTAB/SiO.sub.2 particles were recovered by centrifugation, washed in H.sub.2O, and then washed in ethanol. The CTAB was removed by stirring the sample in a diluted HCl/ethanol solution (0.4 ml 1M HCl in 40 mL ethanol) at room temperature for 1 hour. After three extractions, the final product was washed with ethanol, recovered by centrifugation, and dried at room temperature to obtain the Ni.sub.xP.sub.y@meso-SiO.sub.2 nanoparticles. The SiO.sub.2 coated samples derived the 1-Ni.sub.5P.sub.4 sample, the n-Ni.sub.2P sample, and the n-Ni.sub.12P.sub.5 sample were denoted as the 1-Ni.sub.5P.sub.4@SiO.sub.2 sample, the n-Ni.sub.2P@SiO.sub.2 sample, and the n-Ni.sub.12P.sub.5@SiO.sub.2 sample, respectively.
2. Ni.sub.5P.sub.4 Morphology Control by Use of TOP or TOPO
[0119] Samples of Ni.sub.5P.sub.4 with various morphologies were synthesized using TOP or TOPO using the methodologies of group “B” in
Synthesis of m-Ni.sub.5P.sub.4 Nanoparticles
[0120] Medium sized nanoparticles, having particle sizes of about 20 to about 50 nm, were prepared and designated “m-Ni.sub.5P.sub.4”. The procedure used to create the m-Ni5P4 particles included first dissolving 2 mmol of Ni(acac).sub.2 precursor in 5 g TOPP under a N.sub.2 atmosphere. The reaction mixture was magnetically stirred for 10 min at 80° C. The temperature was raised to 350° C., 5 mL TOP was added, and the mixture stirred at 350° C. for another 2 hours.
Synthesis of h-Ni.sub.5P.sub.4 Nanoparticles
[0121] Hollow Ni.sub.5P.sub.4 nanoparticles having a particle size of about 50 nm were prepared and designated “h-Ni.sub.5P.sub.4”. The procedure used to create the h-Ni.sub.5P.sub.4 particles included first dissolving 2 mmol of Ni(acac).sub.2 precursor in 10 mL OA under a N.sub.2 atmosphere and magnetically stirring for 10 min at 80° C. The temperature was then raised to 230° C. for 1 hour while the stirring continued. Then 5 mL TOP was added and the mixture stirred for another 2 hours at 230° C.
Synthesis of p-Ni.sub.5P.sub.4 nanoparticles
[0122] Porous networks of Ni.sub.5P.sub.4 nanoparticles having a particle size of about 50 to about 100 nm were prepared and designated “p-Ni.sub.5P.sub.4”. The procedure used to create the p-Ni.sub.5P.sub.4 particles included first dissolving 2 mmol of Ni(acac).sub.2 precursor in 10 mL OA and 5 mL TOP under a N.sub.2 atmosphere and magnetically stirring for 10 min at 80° C. The temperature was then raised to 230° C. for 1 hour while the stirring continued. Then 5 mL TOPO was added and the mixture stirred for another 2 hours at 350° C. 3. Ni.sub.5P.sub.4 morphology control by the confinement of SiO.sub.2:
[0123] Samples of Ni.sub.5P.sub.4 nanoparticles were synthesized using the SiO.sub.2 confinement methodologies of group “C” in
Synthesis of n-Ni.sub.5P.sub.4@SiO.sub.2
[0124] About 0.1 g of the previously prepared n-Ni.sub.2P@SiO.sub.2 nanoparticles were first dispersed in 10 mL OA and 5 mL TOP. The reaction mixture was magnetically stirred for 30 minutes at 100° C. and then stirred for another 2 hours at a temperature of 350° C. The result were nanoparticles of Ni.sub.5P.sub.4 that had a size of about 11 nm and a coating of SiO.sub.2 and were denoted as n-Ni.sub.5P.sub.4@SiO.sub.2.
Synthesis of u-Ni.sub.5P.sub.4@SiO.sub.2
[0125] Clusters of nanoparticles of Ni.sub.5P.sub.4 having an ultra-fine particle size of less than 2 nm and fined within mesoporous SiO.sub.2 were created and denoted as u-Ni.sub.5P.sub.4@SiO.sub.2.
[0126] First, a solution of Na.sub.2SiO.sub.3 was prepared by dissolving 32.0 g Na(OH) in 800 mL deionized water. About 187 mL Ludox (40 wt. %) was added into the NaOH solution and the mixture stirred at 40° C. overnight to provide a transparent solution. This Na.sub.2SiO.sub.3 solution can be stored in a sealed Teflon bottle at room temperature for several weeks and used so long as it remains clear.
[0127] 1.0 g CTAB and 1 mmol of Ni(acac).sub.2 precursor were dissolved in 35 mL deionized water followed by slowly stirred (to avoid creating bubbles) at a temperature 60° C. for 1 hour until dissolution of the surfactant is complete and a clear viscous solution is formed (the precipitate was removed by centrifugation). In a synchronous mode, 25 g of the above Na.sub.2SiO.sub.3 solution were stirred at 60° C. for 1 hour and the CTAB solution was subsequently added dropwise into the Na.sub.2SiO.sub.3 solution. The resulting mixture was vigorously stirred for 1 hour at a temperature of 60° C., followed by overnight stirring at room temperature. The mixture was then centrifuged for 10 min at 4500 rpm to collect the precipitated powder. The excess of the surfactants was removed by washing the obtained powder three times in H.sub.2O, then two times in ethanol. The powder was then collected by centrifugation. The solid was dried in an oven at 80° C. overnight to obtain a bout 1.5 g of a light green powder.
[0128] In an N.sub.2 atmosphere, 0.5 g obtain the light green powder was first dissolved in 10 mL OA and 5 mL TOP. The reaction mixture was magnetically stirred for 10 minutes at 80° C. and then stirred for another 2 hours at a temperature of 350° C. After cooling at room temperature, precipitation of a powder was achieved by addition of ethanol followed by centrifugation for 10 min at 4500 rpm. The supernatant was discarded and the retained nanoparticle powder was washed three times in hexane to remove excess surfactants, precipitated with ethanol, and isolated by centrifugation. The resulting black nanoparticle powder was dried in an oven at 80° C. overnight.
Synthesis of u-Ni.sub.5P.sub.4@SiO.sub.2-l
[0129] A sample denoted as u-Ni.sub.5P.sub.4@SiO.sub.2-1 was prepared using the same synthesis method as described above for the synthesis of u-Ni.sub.5P.sub.4@SiO.sub.2, with the exception that the 350° C. heating step lasted for 4 hours instead of 2 hours. The resulting catalysts comprised clusters of ultra-fine nanoparticles of Ni.sub.5P.sub.4 having an average particle size of <2 nm and confined within mesoporous SiO.sub.2.
Example 2
[0130] Characterization and Testing of Ni.sub.xP.sub.y Nanoparticles
Characterization Equipment and Methodology
[0131] The XRD patterns of the calcined catalysts were collected with a Panalytical X′Pert PRO powder diffractometer (available from Malvern Panalytical Ltd of Malvern, United Kingdom) using Cu-Ka radiation (λ=1.5406 Å) operated at 40 mA and 40 kV. The mean particle size and morphology were determined using high resolution transmission electron microscopy (HR-TEM; 200 kV FEI Tecnai, available from FEI Company of Hillsboro, Oreg.). Elemental analysis was conducted in a FEI Quanta 250 FEG scanning microscope (available from FEI Company). The electron source of this instrument is a Schottky field emission gun, possessing a spatial resolution of approximately 1 nm at 30 KV (SE) and 3.0 nm at 1 KV (SE). Elemental analysis was conducted using an equipped Apollo silicon drift detector (SDD) integrated with the EDAX Genesis software (available from EDAX of Ametek, Inc. of Berwyn, Pa.).
[0132] Selected catalysts were studied using HR-TEM technique in a Titan 80-300 ST electron microscope, operated at 300 kV. A spherical aberration (Cs) corrector for the image (CEOS CETCOR), and an energy filter (model GIF Quantum 963, Gatan, Inc.) complement the microscope. Additionally, nanoscale elemental mapping was performed using the STEM mode. The TEM data acquisition and processing was performed using Gatan Microscopy Suite (GMS, version 3.2).
[0133] The atomic percentages of the components were calculated from multiple measurements done at various locations and magnifications (average values are herein provided from 5 measurements, error range about 2%).
[0134] Porosimetry studies were conducted using nitrogen adsorption-desorption isotherms at 77 K in a 3Flex Micromeritics (Atlanta, USA) instrument. Samples (˜90 mg) were degassed at 130° C. in vacuum overnight prior to any measurement.
[0135] An ESCALAB Thermo Scientific Theta Probe Angle-Resolved X-ray Photoelectron Spectrometer (East Grinstead, UK) was used for the photoelectron spectroscopic studies. A monochromatic A1 Kα X-ray source (hv=1486.6 eV) was used. Pass energy of 300 eV and 50 eV were used to collect the survey spectra, and the high-resolution core level spectra, respectively. The C 1 s peak at 285.0 eV was used as internal reference for all the spectra. The redox properties of the Nickel phosphide catalysts were investigated using H.sub.2 temperature-programmed reduction (H.sub.2-TPR). Autochem 2920, (Micromeritics Instruments Corporation, Norcross, Ga., USA) instrument equipped with a thermal conductivity detector (TCD) was used. A catalyst sample of 120 mg was loaded on the U-shaped quartz tube and pretreated at 100° C. for 1 h under He flow (30 ml/min). After cooling the sample at 35° C., 10% H.sub.2/Ar gas mixture was passed at 30 ml/min flow rate. After signal stabilization, the temperature was raised up to 800° C. at a heating rate of 5° C./min while the TCD signal was recorded every 1 second. A cold trap was used to remove any condensable from the gas stream. The .sup.31P Magic Angle Spinning (MAS) solid-state nuclear magnetic resonance (ssNMR) spectrum were collected on a Bruker Avance III 400 spectrometer operating at magnetic fields of 9.4T with a .sup.31P Larmor frequency of 162.066 MHz, at spinning speeds of 14.00 kHz. For acquisition, a rotor synchronized Hahn echo pulse sequence was employed for acquisition, with a π/2 excitation pulse of 2 ps, which corresponds to a rf field strength of 125 kHz. All NMR shifts were referenced to H.sub.3PO.sub.4 85% wt at 0 ppm. NMR Knight shift calculations were performed on bulk Ni.sub.5P.sub.4, by using the full-potential linearized augmented plane-wave method, as implemented in the Wien2k DFT software package within the LDA formalism. The k-mesh convergence was checked up to 50,000. Other computational parameters, such as atomic sphere radii as well as potentials and wave functions inside the atomic spheres, were as set by Wien2k defaults.
Catalytic Assessment: Reaction Metrics
[0136] Experiments to measure the selective hydrogenation of SO.sub.2 were conducted at atmospheric pressure in a fixed bed U-shaped quartz reactor. Forty milligrams of a given catalyst was diluted with 180 mg of quartz particles (125 to 250 μm) and then placed in the quartz reaction tube which had a 4 mm internal diameter. The catalyst bed was initially pretreated for 1 hours at 100° C. by introducing a stream of argon at 40 ml/min. Then, a feed gas consists of 103 ppm SO.sub.2 at 20 mL/min and a feed gas of 2% H.sub.2 in N.sub.2 at 20 mL/min were fed into the reactor (total feed gas at 40 mL/min; a GHSV of ˜50000 h.sup.−1), and the reaction was run at a temperature range of 100-320° C. The effluent stream (reactants and reaction products) was analyzed using a PerkinElmer Clarus 580 Gas Chromatograph (GC)-Model Arnel 4025 PPC and Model Arnel 4016 PPC Sulphur Chemiluminescence Detector (SCD) (both available from PerkinElmer, Inc. of Waltham, Mass.).
[0137] The conversion of SO.sub.2 can be described based on the following reaction scheme:
SO.sub.2+.sub.2H.sub.2.fwdarw.S+2H.sub.2O (Equation 1)
SO.sub.2+3H.sub.2.fwdarw.H.sub.2S+2H.sub.2O (Equation 2)
[0138] The yield of H.sub.2S was calculated based on the peak area of H.sub.2S and SO.sub.2 using the following equation:
where (SO.sub.2).sub.in is the SO.sub.2 molar flow rate in the feed gas (mol/s) and (H.sub.2S).sub.out is the H.sub.2S molar flow rate in the bed effluent (mol/s).
[0139] The conversion of SO.sub.2 was calculated based on the peak area of SO.sub.2 using the following equation:
where (SO.sub.2).sub.in is the SO.sub.2 molar flow rate in the feed gas (mol/s) and (SO.sub.2).sub.out is the SO.sub.2 molar flow rate in the bed effluent (mol/s).
[0140] The selectivity to H.sub.2S was calculated based on the peak area of H.sub.2S and SO.sub.2 using the following equations:
Kinetic Studies
[0141] The average SO.sub.2 conversion rate r (mol/s.Math.g.sub.active) was calculated using the following equation:
where m.sub.active (g) is the mass of the catalyst active phase (Ni.sub.5P.sub.4/Ni.sub.2P/Ni.sub.12P.sub.5/Ni.sub.2P).
[0142] The turn over frequency (TOF, s.sup.−1) was calculated based on the average SO.sub.2 conversion rate using the following equation:
TOF=r×M.sub.active (Equation 7)
where r is the average reaction rate, M.sub.active is the molar mass of Ni.sub.5P.sub.4 (417.36 g/mol), Ni.sub.2P (148.36 g/mol), Ni.sub.12P.sub.5 (859.19 g/mol) or CoMoS (186.94 g/mol).
[0143] The average rate constant k (m.sup.3/s.Math.g) was calculated based on the average rate of reaction, using the following expression applied for a PFR (plug flow reactor) assuming r=k*concentration of SO.sub.2 (the reaction rate is assumed to be first order in SO.sub.2) as per the equation (8):
[0144] where c (SO.sub.2).sub.in is the concentration of SO.sub.2 in the feed gas.
[0145] The activation energy of reaction was calculated based on the average rate constant using the following equation derived from the Arrhenius expression (equation (9)):
where: k (m.sup.3/s.Math.g) is the average rate constant, A is the pre-exponential factors, E.sub.a is the activation energy, R is the ideal gas constant which value is 8.314 J/(K.Math.mol), T (K) is the reaction temperature. E.sub.a is derived from the slope of line plotted from ln k vs. 1/T.
Catalyst Characterization Results—Structural Characterization
[0146] Three types of pure phase Ni.sub.xP.sub.y particles (1-Ni.sub.5P.sub.4, n-Ni.sub.2P, n-Ni.sub.12P.sub.5) were synthesized using the methodologies of group “A” in
[0147]
[0148] The XRD patterns of samples m-Ni.sub.5P.sub.4, h-Ni.sub.5P.sub.4, and p-Ni.sub.5P.sub.4 are presented in
[0149] For m-Ni.sub.5P.sub.4, without OA, the TOPO served a dual role of solvent and surfactant. The high ramping rate up to 350° C., leads to a fast pass through the nucleation whereas the injection of TOP, at 350° C., leads to the rapid insertion of P into the Ni lattice. Hence the P insertion occurs simultaneously along with the Ni nucleation process, which facilitates the formation of a P-rich phase NiP.sub.2 due to the excessive phosphorization. In the case of h-Ni.sub.5P.sub.4, the nucleation process was allowed to progress at 230° C. before the TOP injection. Then, the TOP was injected after the nucleation of Ni particles. This leads to a more difficult insertion step of P into the Ni lattice, thus leading to the Ni-rich phase Ni.sub.2P. In the synthesis of p-Ni.sub.5P.sub.4, the same steps were followed as in the case of 1-Ni.sub.5P.sub.4, with the TOPO being added after the nucleation, though no alteration in the resulting crystal phase of the product was found. The pure phase of Ni.sub.5P.sub.4 was achieved for p-Ni.sub.5P.sub.4 as 1-Ni.sub.5P.sub.4. Ni.sub.2P, Ni.sub.5P.sub.4, and NiP.sub.2 phases are formed in a narrow temperature range between 300° C. to 350° C. and this demonstrates the sensitivity of the phosphorization reaction towards the temperature. Hence, to modify the morphology while preserving the crystal phase purity requires fine tuning of synthesis parameters.
[0150] The XRD patterns of sample n-Ni.sub.5P.sub.4@SiO.sub.2, u-Ni.sub.5P.sub.4@SiO.sub.2, and u-Ni.sub.5P.sub.4@SiO.sub.2-1 are shown in
[0151] For n-Ni.sub.5P.sub.4@SiO.sub.2, Ni.sub.2P nanoparticles were first coated with mesoporous SiO.sub.2 and then the phosphorization step was conducted at 350° C. The mesoporous SiO.sub.2 provided the channels for P diffusion towards the nanoparticles. Due to the inadequate contact of P to some unevenly dispersed Ni.sub.2P particles which were enclosed within SiO.sub.2, the Ni.sub.2P phase and the Ni.sub.5P.sub.4 phase are coexistent in
[0152] The loading of Ni.sub.xP.sub.y crystals compared to the SiO.sub.2 support is shown in Table 1 expressed as Ni/(Ni+Si) ratio. The atomic ratio of Ni loading to Ni+Si in 1-Ni.sub.5P.sub.4@SiO.sub.2, n-Ni.sub.2P@SiO.sub.2, and n-Ni.sub.12P.sub.5@SiO.sub.2 is about 41 at. %, 22 at. %, and 15 at. % respectively. For n-Ni.sub.5P@SiO.sub.2 it is about 28 at. % which is similar to n-Ni.sub.2P@SiO.sub.2. u-Ni.sub.5P.sub.4@SiO.sub.2 and u-Ni.sub.5P.sub.4@SiO.sub.2-1 contain about 5 at. % loading of Ni.sub.5P.sub.4 clusters confined by the mesoporous SiO.sub.2, which are much lower than the samples with SiO.sub.2 coating after treatment.
TABLE-US-00001 TABLE 1 Phase identification as derived from XRD study and compositional analysis of the catalysts conducted using SEM/EDX before and after catalytic performance testing. Atomic Ratio*.sup.a Weight Ratio*.sup.b Catalyst Phase (XRD) Ni/(Ni + Si) Ni/P*.sup.c (fresh) Ni/P*.sup.c (spent) Ni.sub.xP.sub.y (%) l-Ni.sub.5P.sub.4@SiO.sub.2 Ni.sub.5P.sub.4 41% 1.1 1.3 50 n-Ni.sub.2P@SiO.sub.2 Ni.sub.2P 22% 1.8 1.6 26 n-Ni.sub.12P.sub.5@SiO.sub.2 Ni.sub.12P.sub.5 15% 1.7 1.5 18 m-Ni.sub.5P.sub.4 Ni.sub.5P.sub.4 + NiP.sub.2 100% 0.9 0.7 100 h-Ni.sub.5P.sub.4 Ni.sub.2P + Ni.sub.5P.sub.4 100% 1.8 1.5 100 p-Ni.sub.5P.sub.4 Ni.sub.5P.sub.4 100% 1.4 0.9 100 n-Ni.sub.5P.sub.4@SiO.sub.2 Ni.sub.2P + Ni.sub.5P.sub.4 28% 1.3 1.1 35 u-Ni.sub.5P.sub.4@SiO.sub.2 Ni.sub.2P + Ni.sub.5P.sub.4 5% 0.6 0.8 9 u-Ni.sub.5P.sub.4@SiO.sub.2-l Ni.sub.5P.sub.4 5% 0.5 0.7 10 *.sup.aAverage data from 5 measurements, error = ~2%. *.sup.bNi.sub.xP.sub.y/(Ni.sub.xP.sub.y + SiO.sub.2), calculated based on the atomic ratio data of fresh catalysts. *.sup.cThe stoichiometry Ni/P atomic ratio of Ni.sub.xP.sub.y (x/y) phases were: Ni.sub.12P.sub.5 (2.4), Ni.sub.2P (2.0), Ni.sub.5P.sub.4 (1.25), NiP.sub.2 (0.5).
[0153] The EDX data reveal the Ni:P atomic ratio of each sample which is also listed in Table 1. The stoichiometry Ni:P atomic ratio of Ni.sub.xP.sub.y (x/y) phases are as follows: Ni.sub.12P.sub.5 (2.4), Ni.sub.2P (2.0), Ni.sub.5P.sub.4 (1.25), NiP.sub.2 (0.5); the experimental Ni:P atomic ratio data of 1-Ni.sub.5P.sub.4@SiO.sub.2 (Ni:P=1.1, Ni.sub.5P.sub.4phase), n-Ni.sub.2P@SiO.sub.2 (Ni:P=1.8, Ni.sub.2P phase), and p-Ni.sub.5P.sub.4 (Ni:P=1.4, Ni.sub.5P.sub.4 phase) are in agreement to the nominal Ni:P atomic ratio, which corroborates their XRD results. For the sample n-Ni.sub.12P.sub.5@SiO.sub.2 (Ni:P=1.7, Ni.sub.12P.sub.5 phase) which was synthesized at a lower temperature (250° C.) than the synthesis of 1-Ni.sub.5P.sub.4@SiO.sub.2 (350° C.) and n-Ni.sub.2P@SiO.sub.2 (300° C.), the Ni:P atomic ratio was found to be lower than the nominal ratio which is likely due to the adhesive P with excess undecomposed TOP on the nanoparticles.
[0154] For the sample m-Ni.sub.5P.sub.4 (Ni:P=0.9) with mixed phases of Ni.sub.5P.sub.4 and NiP.sub.2 (average stoichiometry Ni:P atomic ratio is 0.9), and h-Ni.sub.5P.sub.4(Ni:P=1.8) with mixed phases of Ni.sub.2P+Ni.sub.5P.sub.4 (average stoichiometry Ni:P atomic ratio is 1.6), the experimental data agree with the nominal Ni:P atomic ratio, which corroborates the XRD patterns over this catalyst as well.
[0155] The sample n-Ni.sub.5P.sub.4@SiO.sub.2 (Ni:P=1.3), u-Ni.sub.5P.sub.4@SiO.sub.2 (Ni:P=0.6), and u-Ni.sub.5P.sub.4@SiO.sub.2-1 (Ni:P=0.5) show much lower experimental Ni:P atomic ratio than their nominal ratio corresponding to their XRD phase analysis (Ni:P=1.25-1.8). This is likely due to the excess P incorporation with the SiO.sub.2 during the decomposition of TOP during the phosphorization step, as the Ni loading is much lower compared to the SiO.sub.2 matrix. A small amount of excess P can lead to the high ratio of P compare to Ni.
[0156] The Ni:P atomic ratio of the spent sample in Table 1 is described in more detail in the subsequent paragraphs of spent catalyst, and the weight ratio of Ni.sub.xP.sub.y are listed as well and are calculated as the active composition of each sample for the catalytic efficiency analysis in the subsequent section. Most of these results are consistent with the Ni/P atomic ratio results from SEM-EDX. One exception comes from the m-Ni.sub.5P.sub.4 which had non uniform particle size and phase distribution, and the other two exceptions come from the n-Ni.sub.5P.sub.4@SiO.sub.2 and u-Ni.sub.5P.sub.4@SiO.sub.2-1 which had high ratios of SiO.sub.2 that lead to the inaccurate quantification of small Ni and P peaks.
[0157]
[0158] 1-Ni.sub.5P.sub.4@SiO.sub.2 shows large clusters of nearly spherical particles possessing a diameter of ˜500 nm (Panel A,
[0159] The synthesis of small size phase-pure Ni.sub.5P.sub.4 using solution-phase approaches is challenging due to the aggregation of Ni.sub.5P.sub.4 crystal at 350° C. (compare to n-Ni.sub.2P and n-Ni.sub.12P.sub.5, 1-Ni.sub.5P.sub.4 aggregated to −500 nm clusters). The role of OA in preventing the aggregation of Ni.sub.xP.sub.y weakens at such high temperatures (350° C., exceeds the OA boiling point of 348° C.). Thus, a better suited stabilizing agent to avoid the crystal size growth and sintering at high temperature up to 350° C. is in demand.
[0160] Two approaches were applied to restrict the Ni.sub.5P.sub.4 aggregation: (i) introduction of a high boiling point solvent instead of OA and (ii) introduction of a solid frame to limit the crystal size. TOPO with a higher boiling point of 411.2° C. was introduced into the mixture as an assistant solvent to provide a more stable environment to prevent the aggregation of Ni.sub.5P.sub.4 crystals (m-Ni.sub.5P.sub.4 and p-Ni.sub.5P.sub.4). The addition of TOP or TOPO at high temperatures was also used as an effective morphology adjustment approach (m-Ni.sub.5P.sub.4, h-Ni.sub.5P.sub.4, p-Ni.sub.5P.sub.4). SiO.sub.2 is an inert and stable support, so the mesoporous SiO.sub.2 can serve as a frame for the confinement of the Ni.sub.xP.sub.y crystal growth and aggregation, thus providing an effective size control pathway (n-Ni.sub.5P.sub.4@SiO.sub.2, u-Ni.sub.5P.sub.4@SiO.sub.2, u-Ni.sub.5P.sub.4@SiO.sub.2-1).
[0161] The TEM image of m-Ni.sub.5P.sub.4 in panel G of
[0162] For n-Ni.sub.5P.sub.4@SiO.sub.2, the embedded nanoparticles maintain their size and morphology before and after the phase transformation process, owing to the protection of mesoporous SiO.sub.2 coating (Panel J,
[0163] To show the dispersion of ultrafine Ni.sub.5P.sub.4 clusters confined in mesoporous SiO.sub.2, a further characterization by HRTEM and STEM-HAADF/EDS of Ni and Si elemental mapping for the u-Ni.sub.5P.sub.4@SiO.sub.2 (
Catalyst Characterization Results—Textural Characterization
[0164] The textural properties of the samples were studied by N.sub.2 adsorption/desorption experiments at 77K. The collected isotherms along with the pore size distributions are presented in
TABLE-US-00002 TABLE 2 Summary of the treatment processes during synthesis, as well as the size and morphology characteristics derived from TEM studies and the porosity data derived from N.sub.2 adsorption-desorption at 77 K. V.sub.p S.sub.BET d.sub.BJH Catalyst Ni.sub.xP.sub.y Size/Morphology (cm.sup.3 .Math. g.sup.−1) (m.sup.2 .Math. .sup.g−1) (nm) l-Ni.sub.5P.sub.4@SiO.sub.2 >500 nm/spherical 0.07 22 1.7 n-Ni.sub.2P@SiO.sub.2 ~110 nm/particles 0.20 99 N/A n-Ni.sub.12P.sub.5@SiO.sub.2 ~12 nm/particles 0.28 178 2.2 m-Ni.sub.5P.sub.4 20~50 nm/particles N/A N/A N/A h-Ni.sub.5P.sub.4 ~50 nm/hollow particles N/A N/A N/A p-Ni.sub.5P.sub.4 50~100 nm/porous network 0.04 10 2.3 n-Ni.sub.5P.sub.4@SiO.sub.2 ~11 nm/particles 0.24 57 4.3 u-Ni.sub.5P.sub.4@SiO.sub.2 <2 nm/ultra-fine clusters 0.28 255 2.2 u-Ni.sub.5P.sub.4@SiO.sub.2-l <2 nm/ultra-fine clusters 0.09 24 4.5
[0165] 1-Ni.sub.5P.sub.4@SiO.sub.2 (
[0166] The BET surface area and the pore volume for 1-Ni.sub.5P.sub.4@SiO.sub.2 (50 wt. % Ni.sub.xP.sub.y) are 22 m.sup.2.Math.g.sup.1 and 0.07 cm.sup.3.Math.g.sup.−1 respectively; for n-Ni.sub.2P@SiO.sub.2 (26 wt. % Ni.sub.xP.sub.y) are 99 m.sup.2.Math..sup.−1 and 0.20 cm.sup.3.Math.g.sup.−1 respectively; for 1-Ni.sub.12P.sub.5@SiO.sub.2 (18 wt. % Ni.sub.xP.sub.y) are 178 m.sup.2.Math.g.sup.−1 and 0.28 cm.sup.3.Math.g.sup.−1 respectively; and for n-Ni.sub.5P.sub.4@SiO.sub.2 (35 wt. % Ni.sub.xP.sub.y) is 57 m.sup.2.Math.g.sup.−1 and 0.24 cm.sup.3.Math.g.sup.−1 respectively. These differences come from the different ratio of SiO.sub.2 in the above four samples, as the porosity is influenced by the SiO.sub.2 coating rather than the Ni.sub.xP.sub.y nanoparticles, the higher the ratio of SiO.sub.2 coating, the higher the surface area and volume of the sample. As shown in the BJH pore size distribution of the above four samples, the sharp distribution centered at around 2 nm and the broader distribution between 40-50 nm suggest that the porous structure of the sample is comprised of large widely distributed cavities interconnected with mesoporous channels (see
[0167] The BET surface area for u-Ni.sub.5P.sub.4@SiO.sub.2 is 255 m.sup.2.Math.g.sup.−1, the pore volume is 0.28 cm.sup.3.Math.g.sup.−1 and the BJH pore size distribution of u-Ni.sub.5P.sub.4@SiO.sub.2 shows a sharp distribution centered at 2.2 nm which is attributed to the hexagonal honeycomb channels of typical MCM-41 (
[0168] For all the above samples with SiO.sub.2, their porosity comes from the SiO.sub.2, while p-Ni.sub.5P.sub.4 (
Catalytic Performance—Catalyst Screening
[0169] The catalytic activity of the samples containing different phases (Ni.sub.5P.sub.4, Ni.sub.2P, Ni.sub.12P.sub.5, and CoMoS), expressed as SO.sub.2 conversion to H.sub.2S, is plotted in
[0170] For the 1-Ni.sub.5P.sub.4@SiO.sub.2 and commercial CoMoS@Al.sub.2O.sub.3 catalyst samples, the H.sub.2S selectivity increases with the temperature. The 1-Ni.sub.5P.sub.4@SiO.sub.2 sample in particular, with its predominant Ni.sub.5P.sub.4 phase, presented almost twice as high of a yield of H.sub.2S than the commercial CoMoS@Al.sub.2O.sub.3 catalyst, in the range of 91% and 94% at 305° C. and 325° C. for the 1-Ni.sub.5P.sub.4@SiO.sub.2 sample vs. 42% and 45% yield at 305° C. and 325° C. for the commercial catalyst. The H.sub.2S yield provided by the 1-Ni.sub.5P.sub.4@SiO.sub.2 sample between 265° C. and 285° C., was similar to that provided by the commercial catalyst at 50° C. higher temperature (˜45% H.sub.2S yield at 325° C.).
[0171] These results suggest that the activity and selectivity are strongly dependent upon the crystal phase of samples, as the different phases of Ni.sub.xP.sub.y can play a key role for the modulation of their catalytic properties. Compared to Ni.sub.12P.sub.5 (0.29 at. % of P) and Ni.sub.2P (0.33 at. % of P) phases, the Ni.sub.5P.sub.4 phase has a higher P atomic ratio (0.44 at. % of P) in the crystal structure. If we compare the (001) surface of Ni.sub.5P.sub.4 and Ni.sub.2P crystals, the Ni—P bond length in Ni.sub.5P.sub.4 (˜2.306 Å) is longer than in Ni.sub.2P (˜2.201 Å), while the Ni-Ni bond length of the trigonal Ni.sub.3 site in Ni.sub.5P.sub.4 (˜2.563 Å) is shorter than in Ni.sub.2P (˜2.640 Å). The overlap of the filled Ni valence orbitals and the hydrogen is orbital can increase in Ni.sub.5P.sub.4, and the covalent interaction can increase as well, thus the first electron transfer can be more favorable. This can decrease the energy barrier and accelerate the reaction to generate H.sub.2S (which demand more activated H.sub.2 compare to the generation of S).
Catalytic Performance—Morphology Impact
[0172] The SO.sub.2 conversion to H.sub.2S over Ni.sub.5P.sub.4 samples with different morphologies (20˜50 nm medium size particles, ˜50 nm hollow particles, 50˜100 nm porous network, 11 nm Ni.sub.5P.sub.4 particles, and <2 nm ultra-fine Ni.sub.5P.sub.4 clusters) was determined and the results are plotted in
[0173] For the catalysts m-Ni.sub.5P.sub.4, h-Ni.sub.5P.sub.4, p-Ni.sub.5P.sub.4, and n-Ni.sub.5P.sub.4@SiO.sub.2, the yield of H.sub.2S increased with temperature. At 320° C., h-Ni.sub.5P.sub.4 hollow particles (mixed Ni.sub.2P and Ni.sub.5P.sub.4 phase from the XRD analysis, Table 1) displayed the best performance, achieving 93% H.sub.2S yield, while p-Ni.sub.5P.sub.4 (pure Ni.sub.5P.sub.4 phase, Table 1) achieved a 70% H.sub.2S yield, n-Ni.sub.5P.sub.4@SiO.sub.2 (mixed Ni.sub.2P and Ni.sub.5P.sub.4 phase, Table 1) achieved a 65% H.sub.2S yield, and m-Ni.sub.5P.sub.4 (mixed Ni.sub.5P.sub.4 and NiP.sub.2 phase, Table 1) achieved a 63% H.sub.2S yield.
[0174] The catalyst performance tests of 1-Ni.sub.5P.sub.4@SiO.sub.2, n-Ni.sub.2P@SiO.sub.2, and n-Ni.sub.12P.sub.5@SiO.sub.2 suggest that the Ni.sub.5P.sub.4 is the active phase for SO.sub.2 conversion to H.sub.2S. Across the temperature range of 200-260° C., both m-Ni.sub.5P.sub.4 (non-uniform sized particles) which is comprised of a mixed phase of Ni.sub.5P.sub.4 and NiP.sub.2 and p-Ni.sub.5P.sub.4 (porous network) which is comprised of a Ni.sub.5P.sub.4 network achieve better performance than h-Ni.sub.5P.sub.4(hollow particles), but their high-temperature performance was not as good as h-Ni.sub.5P.sub.4. h-Ni.sub.5P.sub.4 displayed good performance, despite its mixture of Ni.sub.2P and Ni.sub.5P.sub.4 phases which is likely due to the uneven distribution of P in the hollow particles. The hollow particle surface allows for the formation of P-rich phase easily, due to the Kirkendall effect (the Ni migration outwards is faster than the P migration inward) which leads to the creation of voids. The Ni.sub.2P phase on the surface of h-Ni.sub.5P.sub.4 inhibits the formation of H.sub.2S below 260° C., while between 260-320° C., the Ni.sub.5P.sub.4 phase plays a dominant role favoring the selectivity towards H.sub.2S (>90%). Compared to the solid Ni.sub.5P.sub.4 particles, the hollowed particles have a relatively lower density for the same weight of catalyst, thus the h-Ni.sub.5P.sub.4 can provide more accessibility to the active sites to facilitate contact with the substrate.
[0175] n-Ni.sub.5P.sub.4@SiO.sub.2 is comprised of mixed Ni.sub.2P and Ni.sub.5P.sub.4 phases possessing small particle size (˜11 nm particles), however, the majority of the particles are still Ni.sub.2P phase so its relatively low selectivity towards H.sub.2S may be due to the low Ni.sub.5P.sub.4 content.
[0176] Comparing the u-Ni.sub.5P.sub.4@SiO.sub.2 and u-Ni.sub.5P.sub.4@SiO.sub.2-1, both of those samples contained very small Ni.sub.5P.sub.4 clusters confined in the mesoporous skeleton. u-Ni.sub.5P.sub.4@SiO.sub.2-1 underwent a 4 hours phosphorization process, so it is expected that its phase transfer ratio is higher than the sample of u-Ni.sub.5P.sub.4@SiO.sub.2 which only had 2 hours of phosphorization. Compared to u-Ni.sub.5P.sub.4@SiO.sub.2-1, there is still some Ni.sub.2P phase in the u-Ni.sub.5P.sub.4@SiO.sub.2 which leads to the lower selectivity towards H.sub.2S. Both of samples have high SO.sub.2 conversion, with u-Ni.sub.5P.sub.4@SiO.sub.2 providing an SO.sub.2 conversion of 65% at 200° C. and 97% at 320° C. and u-Ni.sub.5P.sub.4@SiO.sub.2-1 providing an SO.sub.2 conversion exceeding 95% in the temperature range of about 200 to about 280° C. This is likely due to the size effect because the Ni.sub.5P.sub.4 or Ni.sub.2P clusters with a size of <2 nm provide a very highly dispersed active site for the SO.sub.2 conversion. The highest H.sub.2S yield for u-Ni.sub.5P.sub.4@SiO.sub.2 was achieved at 300° C. (32% H.sub.2S yield), while the highest H.sub.2S yield for u-Ni.sub.5P.sub.4@SiO.sub.2-1 was at 240° C. (33% H.sub.2S yield).
[0177] Based on the above results, we can conclude that the Ni.sub.xP.sub.y catalyst performance for the conversion of SO.sub.2 to H.sub.2S can be influenced by two factors: a) the purity of Ni.sub.5P.sub.4 phase, and b) the Ni.sub.5P.sub.4 phase-reactants contact area/interface. The Ni.sub.5P.sub.4 phase provides high affinity to activate the H.sub.2, thus lowering the energy barrier and accelerating the production of H.sub.2S, while the high contact area of Ni.sub.5P.sub.4 with reactants can improve the catalyst's efficiency. Either by decreasing the size of the Ni.sub.5P.sub.4 crystal (m-Ni.sub.5P.sub.4, n-Ni.sub.5P.sub.4@SiO.sub.2, u-Ni.sub.5P.sub.4@SiO.sub.2, u-Ni.sub.5P.sub.4@SiO.sub.2-1) and/or by creating voids and porosity in the Ni.sub.5P.sub.4 clusters (h-Ni.sub.5P.sub.4, p-Ni.sub.5P.sub.4), the catalytic density is decreased and surface area per unit weight of catalyst is increased, thereby increasing the contact between the active sites (Ni.sub.5P.sub.4) of the catalyst and reactants.
Assessment of Reaction Kinetics
[0178] The average SO.sub.2 conversion rate (in μmols of SO.sub.2 per second per gram of active catalysts (Ni.sub.xP.sub.y)) was computed based on the Ni.sub.xP.sub.y or Ni.sub.xP.sub.y loading in SiO.sub.2. Hence the results reflect the activity per site.
[0179]
[0180] DFT computations on the mechanism of hydrogen reacting with sulfur dioxide show that the reaction can follow the H radical path for the reduction of SO.sub.2 and that the activation energy for the formation of H radical is 586.80 kJ/mol, which is much higher than the subsequent reactions steps. The Ni.sub.xP.sub.y phase offers optimal hydrogen binding and shows much higher activity than the sulfurized metal phase and the formation of H radicals on the Ni.sub.xP.sub.y phase is efficient enough to facilitate the formation of S. The Ni.sub.5P.sub.4 phase has even higher efficiency than the Ni.sub.2P and N.sub.12P.sub.5 phase, so the S can react with the excess H radical on the Ni.sub.5P.sub.4 phase to produce H.sub.2S.
Catalytic Active Sites
[0181] H.sub.2-TPR profiles of n-Ni.sub.12P.sub.5, n-Ni.sub.2P, I—Ni.sub.5P.sub.4, and u-Ni.sub.5P.sub.4@SiO.sub.2-1 are shown in
[0182] The X-ray photoelectron spectra (XPS) of the catalysts were recorded to identify chemical state information for Ni and P and changes in surface composition and are shown in
[0183] With regard to the intensities of the Ni 2p.sub.3/2 and P 2p peaks for the different nickel phosphide catalysts, the photoelectron intensity from the bulk phosphide is strongest for the m-Ni.sub.5P.sub.4, h-Ni.sub.5P.sub.4 and p-Ni.sub.5P.sub.4 catalysts, the other SiO.sub.2 coated catalysts showed very weak peaks. For these latter catalysts, the thin SiO.sub.2 layer is attenuating the signal from the underlying nickel phosphide catalyst particulates.
[0184] The experimental and calculated .sup.31P MAS ssNMR spectrum of the 1-Ni.sub.5P.sub.4 sample is shown in
TABLE-US-00003 TABLE 3 DFT calculated and Experimental 31P ssNMR data of the isotropic shift δ.sub.iso, chemical shift anisotropy CSA and asymmetry parameter η of each site. δ.sub.iso Δ(calc)/ δ.sub.iso Δ(calc)/ Site (calc)/ppm ppm η (exp)/ppm ppm η P9 1469 −217.3 0.0 1168.4 −488.8 0.0 P7 1913 −403.1 0.471 1842.3 −450.4 0.107 P5 1992 440.5 0.208 1984.4 550.1 0.265 P1 881 367.2 0.0 947.8 153.6 0.0
[0185] Four NMR shifts could be identified and were analyzed in the SOLA lineshape simulation package, as presented in Table 3. From the crystallography point of view, there are 4 unique P sites which are all distinctively coordinated. Based on the number of Ni atoms coordinated to each site, an all Ni-atom 9-coordinated octahedral site named P.sub.9 was identified, as were an all Ni-atom 7-coordinated site P.sub.7, a 5 coordinated cuboid site bonded to 4 Ni atoms and one P atom, which is the last unique site named P.sub.1 as it is a tetrahedron coordinated to 3 P atoms from the P.sub.5 site and 1 Ni atom. To assign the experimental .sup.31P NMR shifts to the different phosphorus sites, DFT calculations of the NMR Knight shifts were performed with the WIEN2K package, according to formula K=K.sub.FC+K.sub.dip+K.sub.orb. Calculated Knight shifts, anisotropies (A) and asymmetry parameters are presented in Table 3. The simulated theoretical spectrum shows that the shift at 1984.4 ppm corresponds to the P.sub.5 site, the shift at 1842.3 ppm to the P.sub.7 site, the shift at 1168.4 ppm to the P.sub.9 coordination, and the shift at 947.8 to the P.sub.1 site. This assignment is important to understand the catalytic activity of Ni.sub.5P.sub.4, as shifts towards more positive frequencies in nickel phosphides are directly correlated to higher density of states at the Fermi level, indicating enhanced catalytic activity. This was indeed the case with Ni.sub.5P.sub.4, which showed that P.sub.7 and P.sub.5 sites (i.e. Ni.sub.4P.sub.3 and Ni.sub.3P.sub.3 layers) showing the highest NMR frequency shift, are exposed on the surface of Ni.sub.5P.sub.4 microcrystals.
Spent Catalyst Characterization
[0186] To assess catalyst structural and morphological changes due to the reaction conditions, spent catalysts of the above samples were characterized using TEM imaging, XRD, EDX and XPS analysis.
[0187] The images for the particles coating with SiO.sub.2 (panels A, B, C and G) show that the particle size and shape did not change. In the m-Ni.sub.5P.sub.4 sample (panel D), the nanoparticles retained their size and morphology as well (the particles were stuck on the quartz during the sample preparation before the test). Furthermore, the size and morphology changes were absent for the h-Ni.sub.5P.sub.4 (panel E) and p-Ni.sub.5P.sub.4 (panel F), their hollowed morphology and the porous network structure were observed as clear as the fresh catalysts. In panels H and I, the mesoporous SiO.sub.2 structures of u-Ni.sub.5P.sub.4@m-SiO.sub.2 and u-Ni.sub.5P.sub.4@m-SiO.sub.2-1 remained intact. Moreover, the active phase ultra-fine Ni.sub.5P.sub.4 crystals retained their size and shape, with no aggregation of Ni.sub.5P.sub.4 crystals observed. The EDX results (shown in Table 1) of the samples after the reaction show that the Ni/P ratio remained intact.
[0188]
[0189] Comparing the XRD patterns of the post-performance testing samples to their respective “fresh” sample patterns, the XRD patterns of the used samples maintained the crystallinity except for a strong peak of quartz which was mixed with the catalysts during the performance test, suggesting the absence of any structural changes experienced by the catalysts. For the XPS of used 1-Ni.sub.5P.sub.4@SiO.sub.2 and the used u-Ni.sub.5P.sub.4@SiO.sub.2-1, no meaningful differences were observed from the spectra of the used samples compared to the spectra of the corresponding fresh samples. The Ni.sub.xP.sub.y catalysts have their active temperature zones below 320° C. There are several possible factors that may contribute to the catalyst activity deterioration at high temperature (>350° C.): (a) the sintering of active sites at high temperature; (b) possible reaction between P and SiO.sub.2; (c) the coverage of surface active sites with synthesis organic remnants (e.g. OA, TOP, or CTAB); (d) the leaching of P atoms and the subsequent stoichiometry change; (e) structural changes induced by the temperature leading to exposing a less favorable facet for reaction. For the ultrafine Ni.sub.5P.sub.4 samples, the active Ni.sub.5P.sub.4 crystal sites are even smaller and incorporated into SiO.sub.2 with high weight ratio (Table 1), so it is even more sensitive to the above-described parasitic conditions leading to deactivation at temperatures above 260° C. As previously mentioned, red phosphorus powders formed after the H.sub.2-TPR test may be indicative of phosphorus leaching at high temperatures and may be the main reason for Ni.sub.xP.sub.y catalysts deactivation at T>350° C.
Conclusions
[0190] Highly active Ni.sub.5P.sub.4@SiO.sub.2 catalysts were synthesized for the selective hydrogenation of SO.sub.2 to H.sub.2S. The liquid synthesis of Ni.sub.5P.sub.4 in N.sub.2 with OA and TOP or TOPO was modified to control Ni.sub.5P.sub.4 phase and morphology. Compared to the Ni.sub.12P.sub.5 and Ni.sub.2P phases, the active sites to convert SO.sub.2 to H.sub.2S effectively originate from the Ni.sub.5P.sub.4 phase at T>150° C. in the presence of H.sub.2. Pure phase Ni.sub.5P.sub.4 clusters with a diameter of ˜500 nm and a SiO.sub.2 coating shows the highest activity (95% H.sub.2S yield at 325° C.) among all tested catalysts. Mesoporous SiO.sub.2 confined Ni.sub.5P.sub.4 cluster (<2 nm) shows an improved low-temperature performance (33% H.sub.2S yield at 240° C.), which require lower active site loading and less energy cost. STEM-HAADF studies over the u-Ni.sub.5P.sub.4@SiO.sub.2 system proved the presence of Ni-entities of less than 2 nm size even under conditions of prolonged phosphorization (2-4 hrs at 350° C.).
[0191] With regards to morphology control, Ni.sub.5P.sub.4 of 20-50 nm nanoparticles, ˜50 nm hollowed nanoparticles, 50˜100 nm macroporous network structures, and 11 nm Ni.sub.5P.sub.4 were successfully prepared and showed promising activity for the selective hydrogenation of SO.sub.2 to H.sub.2S (>60% H.sub.2S yield at 320° C.).
[0192] XPS studies designated the presence of some Ni oxidation species such as Ni(OH).sub.2 and Ni.sub.3(PO).sub.4. Solid state NMR studies showed that Ni.sub.5P.sub.4 microcrystals contain P-sites (P.sub.7 and P.sub.5 sites in Ni.sub.4P.sub.3 and Ni.sub.3P.sub.3 layers), with the highest NMR frequency shift, the latter coinciding with high Fermi level electron density leading to high intrinsic activity. Studies over the spent catalysts confirmed the preservation of the crystallinity, the morphology, and the Ni/P ratio for all of the investigated catalysts after the SO.sub.2 hydrogenation reactions were run under the specific conditions. This suggests the stability of these systems under the aforementioned reaction conditions.
[0193] Table 4 below provides a summary of the experimental parameters applied in the catalytic performance evaluation of various known catalysts for the reduction of SO.sub.2 with H.sub.2, including two of the inventive catalysts (1-Ni.sub.5P.sub.4@SiO.sub.2 and u-Ni.sub.5P.sub.4@ SiO.sub.2-1) and various known catalysts. Table 5 below provides a summary of the catalytic performance of those same catalysts for the reduction of SO.sub.2 with H.sub.2 expressed as SO.sub.2 conversion, sulfur selectivity, H.sub.2S Selectivity, and TOF.
TABLE-US-00004 TABLE 4 summary of experimental parameters of inventive catalysts and known catalysts SO.sub.2 Flow Mass of Active Synthesis Space SO.sub.2/H.sub.2 SO.sub.2 Rate Catalyst Component Catalyst Method Velocity (mol/mol) (ppm) (mL/min) (g) (wt %) Co—Mo/Al.sub.2O.sub.3 Commercially WHSV = 1/3 10.sup.6 2.5 2 11 & presulfided 3000 mL/g/h Fe/γ-Al.sub.2O.sub.3 Impregnation & GHSV = 1/2 10.sup.6 3 2 10 presulfided 3600/h Co/γ-Al.sub.2O.sub.3 Impregnation & GHSV = 1/2 10.sup.6 3 2 10 presulfided 3600/h Ni/r-Al.sub.2O.sub.3 Impregnation & GHSV = 1/2 10.sup.6 3 2 10 presulfided 3600/h Ru@TiO.sub.2 Impregnation & WHSV = 1/2 10.sup.6 20 0.4 1.5 presulfided 9000 mL/g/h NiO/r-Al.sub.2O.sub.3 Impregnation & WHSV = 1/2 12000 14 0.5 16 presulfided 5040 mL/g/h SnO.sub.2—ZrO.sub.2 Precipitate GHSV = 1/2 20000 55 0.5 100 10000/h Fe/γ-Al.sub.2O.sub.3 Slurry method WHSV = 4/96 10.sup.6 4.8 0.2 2 & presulfided 36000 mL/g/h Fe—Si—Cr Co-precipitation WHSV = 4/96 10.sup.6 4.8 0.2 Fe/Si/Cr = & presulfided 36000 1/0.6/0.01 mL/g/h l-Ni.sub.5P.sub.4@SiO.sub.2 Phosphorization GHSV = 1/200 103 20 0.04 50 & Coating ~50000/h WHSV = 60000 mL/g/h u-Ni.sub.5P.sub.4@SiO.sub.2-l One-pot & GHSV = 1/200 103 20 0.04 10 Phosphorization ~50000/h WHSV = 60000 mL/g/h
TABLE-US-00005 TABLE 5 summary of catalytic performance of inventive catalysts and known catalysts SO.sub.2 Sulfur H.sub.2S Sulfur H2S T Conv. Select. Select Yield Yield TOF Catalyst (° C.) (%) (%) (%) (%) (%) (10.sup.−6/s) Co—Mo/Al.sub.2O.sub.3 300 84.2 95.4 4.6 80.3 3.9 573 Fe/γ-Al.sub.2O.sub.3 300 44.9 95.2 4.8 42.7 2.2 256 Co/γ-Al.sub.2O.sub.3 300 66.7 93.7 6.3 62.5 4.2 402 Ni/r-Al.sub.2O.sub.3 300 63.9 91.9 8.1 58.7 5.2 353 Ru@TiO.sub.2 300 90.2 100 0 90.2 0 206988 NiO/r-Al.sub.2O.sub.3 320 98 69 31 67.6 30.4 82 SnO.sub.2—ZrO.sub.2 550 98 55 45 53.9 44.1 208 Fe/γ-Al.sub.2O.sub.3 240 100 0 100 0 100 45682 Fe—Si—Cr 190 100 0 100 0 100 91364 l-Ni.sub.5P.sub.4@SiO.sub.2 325 96 1 99 1 95 28 u-Ni.sub.5P.sub.4@SiO.sub.2-l 240 97 66 34 64 33 143
[0194] The methodology described herein as well as the findings are foreseen to impact a wide range of catalytic and electrocatalytic applications, such as the hydrodesulfinization (HDS), hydrodenitrification (HDN), hydrogen evolution reactions (HER) where the N.sub.15P.sub.4 phase has a pivotal role as a non-noble active catalyst.
Example 3
[0195] Additional Characterization and Testing of Ni.sub.xP.sub.y Nanoparticles
[0196] Several different Ni—P nanoparticles were produced, characterized, and tested. The methodology for producing, characterizing, and testing each sample is described below in respective subsections. Unless otherwise indicated, the sample production methodology described below utilizes the same ammonia, Ni(acac).sub.2, OA, TEOS, TOP, and TOPO reagents as described above in Examples 1 and 2. Following the respective subsections are Tables 6-8, which summarize the finding from the characterization and testing of the samples.
Sample 1
[0197] Under a N.sub.2 atmosphere, 2 mmol of nickel precursor Ni(acac).sub.2 was dissolved in 10 mL of OA and 5 mL of TOP. The reaction mixture was subjected to magnetic stirring for 10 min at 80° C., followed by heating to 230° C. for 1 hour. Another 5 mL of TOP was injected into the mixture and stirred at 350° C. for another 2 hours. After cooling to room temperature, the black particles were precipitated by the addition of ethanol and subsequently centrifuged for 10 min at 4,500 rpm. The supernatant was discarded, thereby separating the nanoparticles from the solution. To remove any excess surfactants, the nanoparticles were then washed three times by dispersion in hexane followed by precipitation with ethanol and isolation by centrifugation. Finally, the resulting nanoparticles were dried at room temperature.
[0198] The particles were examined under TEM and subjected to XRD. The SO.sub.2 conversion, H.sub.2S yield, and H.sub.2S selectivity of the nanoparticles was also tested at various temperatures. A TEM image of the particles is shown in
Sample 2
[0199] Under a N.sub.2 atmosphere, 2 mmol of nickel precursor Ni(acac).sub.2 was dissolved in 10 mL of OA. The reaction mixture was subjected to magnetic stirring for 10 min at 80° C., followed by heating to 230° C. for 1 hour. Another 5 mL of TOP was then injected into the mixture and the mixture was stirred at 350° C. for another 2 hours. After cooling to room temperature, the black particles were precipitated by the addition of ethanol and subsequently centrifuged for 10 min at 4,500 rpm. The supernatant was discarded, thereby separating the nanoparticles from the solution. To remove any excess surfactants, the nanoparticles were then washed three times by dispersion in hexane followed by precipitation with ethanol and isolation by centrifugation. Finally, the resulting nanoparticles were dried at room temperature.
[0200] The particles were examined under TEM and subjected to XRD. The SO.sub.2 conversion, H.sub.2S yield, and H.sub.2S selectivity of the nanoparticles was also tested at various temperatures. A TEM image of the particles is shown in
Sample 3
[0201] Under a N.sub.2 atmosphere, 2 mmol of nickel precursor Ni(acac).sub.2 was dissolved in 10 mL of OA and 5 mL of TOP. The reaction mixture was subjected to magnetic stirring for 10 min at 80° C., and then stirred for another 2 hours at a temperature of 350° C. After cooling to room temperature, the black particles were precipitated by the addition of ethanol and subsequently centrifuged for 10 min at 4,500 rpm. The supernatant was discarded, thereby separating the nanoparticles from the solution. To remove any excess surfactants, the nanoparticles were then washed three times by dispersion in hexane followed by precipitation with ethanol and isolation by centrifugation. Finally, the resulting nanoparticles were dried at room temperature.
[0202] The particles were examined under TEM and subjected to XRD. The SO.sub.2 conversion, H.sub.2S yield, and H.sub.2S selectivity of the nanoparticles was also tested at various temperatures. A TEM image of the particles is shown in
Sample 4
[0203] Under a N.sub.2 atmosphere, 2 mmol of nickel precursor Ni(acac).sub.2 was dissolved in 10 mL of OA and 5 mL of TOP. The reaction mixture was subjected to magnetic stirring for 10 min at 80° C., and then heated to a temperature of 230° C. for 1 hour. Five grams of TOPO was added to the mixture and stirred for another 2 hours at a temperature of 350° C. After cooling to room temperature, the black particles were precipitated by the addition of ethanol and subsequently centrifuged for 10 min at 4,500 rpm. The supernatant was discarded, thereby separating the nanoparticles from the solution. To remove any excess surfactants, the nanoparticles were then washed three times by dispersion in hexane followed by precipitation with ethanol and isolation by centrifugation. Finally, the resulting nanoparticles were dried at room temperature.
[0204] The particles were examined under TEM and subjected to XRD. The SO.sub.2 conversion, H.sub.2S yield, and H.sub.2S selectivity of the nanoparticles was also tested at various temperatures. A TEM image of the particles is shown in
Sample 5
[0205] Under a N.sub.2 atmosphere, 2 mmol of nickel precursor Ni(acac).sub.2 was dissolved in 10 mL of OA and 5 mL of TOP. The reaction mixture was subjected to magnetic stirring for 10 min at 80° C., and then heated to a temperature of 230° C. for 1 hour. Five grams of TOPO was added to the mixture and stirred for another 2 hours at a temperature of 380° C. After cooling to room temperature, the black particles were precipitated by the addition of ethanol and subsequently centrifuged for 10 min at 4,500 rpm. The supernatant was discarded, thereby separating the nanoparticles from the solution. To remove any excess surfactants, the nanoparticles were then washed three times by dispersion in hexane followed by precipitation with ethanol and isolation by centrifugation. Finally, the resulting nanoparticles were dried at room temperature.
[0206] The particles were examined under TEM and subjected to XRD. The SO.sub.2 conversion, H.sub.2S yield, and H.sub.2S selectivity of the nanoparticles was also tested at various temperatures. A TEM image of the particles is shown in
Sample 6
[0207] Under a N.sub.2 atmosphere, 1 mmol of nickel precursor Ni(acac).sub.2 was dissolved in 5 mL of TOP. The reaction mixture was subjected to magnetic stirring for 10 min at 80° C., and then heated to a temperature of 230° C. for 1 hour. Five grams of TOPO was added to the mixture and stirred for another 2 hours at a temperature of 350° C. After cooling to room temperature, the black particles were precipitated by the addition of ethanol and subsequently centrifuged for 10 min at 4,500 rpm. The supernatant was discarded, thereby separating the nanoparticles from the solution. To remove any excess surfactants, the nanoparticles were then washed three times by dispersion in hexane followed by precipitation with ethanol and isolation by centrifugation. Finally, the resulting nanoparticles were dried at room temperature.
[0208] The particles were examined under TEM and subjected to XRD. The SO.sub.2 conversion, H.sub.2S yield, and H.sub.2S selectivity of the nanoparticles was also tested at various temperatures. A TEM image of the particles is shown in
Sample 7
[0209] Under a N.sub.2 atmosphere, 2 mmol of nickel precursor Ni(acac).sub.2 was dissolved in 10 mL OA. The reaction mixture was subjected to magnetic stirring for 10 min at 80° C., and then heated to a temperature of 230° C. for 1 hour. Five mL of TOP was added to the mixture and stirred for another hour at a temperature of 300° C. Five grams of TOPO was then added to the mixture and the mixture stirred at 380° C. for another 2 hours. After cooling to room temperature, the black particles were precipitated by the addition of ethanol and subsequently centrifuged for 10 min at 4,500 rpm. The supernatant was discarded, thereby separating the nanoparticles from the solution. To remove any excess surfactants, the nanoparticles were then washed three times by dispersion in hexane followed by precipitation with ethanol and isolation by centrifugation. Finally, the resulting nanoparticles were dried at room temperature.
[0210] The particles were examined under TEM and subjected to XRD. The SO.sub.2 conversion, H.sub.2S yield, and H.sub.2S selectivity of the nanoparticles was also tested at various temperatures. A TEM image of the particles is shown in
Sample 8
[0211] Under a N.sub.2 atmosphere, 2 mmol of nickel precursor Ni(acac).sub.2 was dissolved in 5 g of TOPO and 5 mL of TOP. The reaction mixture was subjected to magnetic stirring for 10 min at 80° C., and then heated to a temperature of 350° C. for 2 hours. After cooling to room temperature, the black particles were precipitated by the addition of ethanol and subsequently centrifuged for 10 min at 4,500 rpm. The supernatant was discarded, thereby separating the nanoparticles from the solution. To remove any excess surfactants, the nanoparticles were then washed three times by dispersion in hexane followed by precipitation with ethanol and isolation by centrifugation. Finally, the resulting nanoparticles were dried at room temperature.
[0212] The particles were examined under TEM and subjected to XRD. The SO.sub.2 conversion, H.sub.2S yield, and H.sub.2S selectivity of the nanoparticles was also tested at various temperatures. A TEM image of the particles is shown in
Sample 9
[0213] Under a N.sub.2 atmosphere, 2 mmol of nickel precursor Ni(acac).sub.2 was dissolved in 5 g of TOPO. The reaction mixture was subjected to magnetic stirring for 10 min at 80° C., and then 5 mL of TOP was added. The mixture was then stirred at a temperature of 350° C. for another 2 hours. After cooling to room temperature, the black particles were precipitated by the addition of ethanol and subsequently centrifuged for 10 min at 4,500 rpm. The supernatant was discarded, thereby separating the nanoparticles from the solution. To remove any excess surfactants, the nanoparticles were then washed three times by dispersion in hexane followed by precipitation with ethanol and isolation by centrifugation. Finally, the resulting nanoparticles were dried at room temperature.
[0214] The particles were examined under TEM and subjected to XRD. The SO.sub.2 conversion, H.sub.2S yield, and H.sub.2S selectivity of the nanoparticles was also tested at various temperatures. A TEM image of the particles is shown in
Sample 10
[0215] Under a N.sub.2 atmosphere, 2 mmol of nickel precursor Ni(acac).sub.2 was dissolved in 10 mL of OA. The reaction mixture was subjected to magnetic stirring for 10 min at 80° C., and then 5 mL TOP was added and the mixture stirred for another 2 hours at a temperature of 350° C. After cooling to room temperature, the black particles were precipitated by the addition of ethanol and subsequently centrifuged for 10 min at 4,500 rpm. The supernatant was discarded, thereby separating the nanoparticles from the solution. To remove any excess surfactants, the nanoparticles were then washed three times by dispersion in hexane followed by precipitation with ethanol and isolation by centrifugation. Finally, the resulting nanoparticles were dried at room temperature.
[0216] The particles were examined under TEM and subjected to XRD. The SO.sub.2 conversion, H.sub.2S yield, and H.sub.2S selectivity of the nanoparticles was also tested at various temperatures. A TEM image of the particles is shown in
Sample 11
[0217] Under a N.sub.2 atmosphere, 2 mmol of nickel precursor Ni(acac).sub.2 was dissolved in 10 mL of OA and 5 mL of TOP. The reaction mixture was subjected to magnetic stirring for 10 min at 80° C. followed by heating to 230° C. for 1 hour. Then another 5 mL TOP was added and the mixture stirred for another 2 hours at a temperature of 300° C. After cooling to room temperature, the black particles were precipitated by the addition of ethanol and subsequently centrifuged for 10 min at 4,500 rpm. The supernatant was discarded, thereby separating the nanoparticles from the solution. To remove any excess surfactants, the nanoparticles were then washed three times by dispersion in hexane followed by precipitation with ethanol and isolation by centrifugation. Finally, the resulting Ni.sub.xP.sub.y nanoparticles were dried at room temperature. 100 mg of the Ni.sub.xP.sub.y nanoparticles were dispersed in 5 mL of hexane. 50 mL of aqueous CTAB solution was added and the mixture sonicated for 30 minutes. The resulting emulsion was stirred at room temperature overnight, and then the nanoparticles were isolated from the solution via centrifugation. The resulting CTAB-coated Ni.sub.xP.sub.y nanoparticles were washed and recovered again by centrifugation. Finally, the coated nanoparticles were dispersed in 50 mL of deionized water to form a stable hydrosol. 0.5 mL of TEOS was added dropwise into 50 mL of the CTAB-coated Ni.sub.xP.sub.y nanoparticle hydrosol solution and stirred vigorously for 15 minutes. Then 70 μL of aqueous ammonia solution was added and the reaction allowed to take place at room temperature for 24 hours. The CTAB/SiO.sub.2-coated Ni.sub.xP.sub.y particles were recovered by centrifugation and washed with H.sub.2O followed by ethanol. The CTAB was removed by stirring the sample in a dilute HCl/ethanol solution (0.4 mL of 1 M HCl in 40 mL of ethanol) at room temperature for 1 hour. After 3 extractions, the final product was washed by ethanol, recovered by centrifugation, and dried at room temperature to obtain the Ni.sub.xP.sub.y@meso-SiO.sub.2 nanoparticles.
[0218] Under a N.sub.2 atmosphere, 0.1 g of the Ni.sub.xP.sub.y@meso-SiOx nanoparticles were dispersed in 10 mL of OA and 5 mL of TOP. The reaction mixture was subjected to magnetic stirring for 30 min at 100° C. and then stirred for another 2 hours at a temperature of 350° C. After cooling to room temperature, the powder was precipitated by the addition of ethanol and subsequently centrifuged for 10 min at 4,500 rpm. The supernatant was discarded, thereby separating the nanoparticles from the solution. To remove any excess surfactants, the nanoparticles were then washed three times by dispersion in hexane followed by precipitation with ethanol and isolation by centrifugation. Finally, the resulting nanoparticles were dried at room temperature.
[0219] The particles were examined under TEM and subjected to XRD. The SO.sub.2 conversion, H.sub.2S yield, and H.sub.2S selectivity of the nanoparticles was also tested at various temperatures. A TEM image of the particles is shown in
Sample 12
[0220] Under a N.sub.2 atmosphere, 2 mmol of nickel precursor Ni(acac).sub.2 was dissolved in 10 mL of OA and 5 mL of TOP. The reaction mixture was subjected to magnetic stirring for 10 min at 80° C. followed by heating to 230° C. for 1 hour. Then another 5 mL TOP was added and the mixture stirred for another 2 hours at a temperature of 300° C. After cooling to room temperature, the black particles were precipitated by the addition of ethanol and subsequently centrifuged for 10 min at 4,500 rpm. The supernatant was discarded, thereby separating the nanoparticles from the solution. To remove any excess surfactants, the nanoparticles were then washed three times by dispersion in hexane followed by precipitation with ethanol and isolation by centrifugation. Finally, the resulting Ni.sub.xP.sub.y nanoparticles were dried at room temperature.
[0221] 100 mg of the Ni.sub.xP.sub.y nanoparticles were dispersed in 5 mL of hexane and then mixed with 50 mL of aqueous CTAB solution. The mixture was sonicated for 30 minutes. The resulting emulsion was stirred at room temperature overnight and then the nanoparticles were isolated from the solution via centrifugation. The resulting CTAB-coated Ni.sub.xP.sub.y nanoparticles were washed and recovered again by centrifugation. Finally, the coated nanoparticles were dispersed in 50 mL of deionized water to form a stable hydrosol.
[0222] 0.5 mL of TEOS was added dropwise into 50 mL of the CTAB-coated Ni.sub.xP.sub.y nanoparticle hydrosol solution and stirred vigorously for 15 minutes. 70 μL of aqueous ammonia solution was then added and the reaction allowed to take place at room temperature for 24 hours. The CTAB/SiO.sub.2-coated Ni.sub.xP.sub.y particles were recovered by centrifugation and then washed with H.sub.2O followed by ethanol. The CTAB was removed by stirring the sample in a dilute HCl/ethanol solution (0.4 mL of 1 M HCl in 40 mL of ethanol) at room temperature for 1 hour. After 3 extractions, the final product was washed by ethanol, recovered by centrifugation, and then dried at room temperature to obtain the Ni.sub.xP.sub.y@meso-SiO.sub.2 nanoparticles.
[0223] Under a N.sub.2 atmosphere, 0.1 g of the Ni.sub.xP.sub.y@meso-SiOx nanoparticles were dissolved in 5 mL of TOP. 5 g of TOPO was added and the reaction mixture subjected to magnetic stirring for 30 min at 100° C. followed by another 2 hours of stirring at a temperature of 380° C. After cooling to room temperature, the powder was precipitated by the addition of ethanol and subsequently centrifuged for 10 min at 4,500 rpm. The supernatant was discarded, thereby separating the nanoparticles from the solution. To remove any excess surfactants, the nanoparticles were then washed three times by dispersion in hexane followed by precipitation with ethanol and isolation by centrifugation. Finally, the resulting nanoparticles were dried at room temperature.
[0224] The particles were examined under TEM and subjected to XRD. The SO.sub.2 conversion, H.sub.2S yield, and H.sub.2S selectivity of the nanoparticles was also tested at various temperatures. A TEM image of the particles is shown in
Sample 13
[0225] Under a N.sub.2 atmosphere, 2 mmol of nickel precursor Ni(acac).sub.2 was dissolved in 10 mL of OA and 5 mL of TOP. The reaction mixture was subjected to magnetic stirring for 10 min at 80° C. followed by heating to 230° C. for 1 hour. Then another 5 mL TOP was added and the mixture stirred for another 2 hours at a temperature of 300° C. After cooling to room temperature, the black particles were precipitated by the addition of ethanol and subsequently centrifuged for 10 min at 4,500 rpm. The supernatant was discarded, thereby separating the nanoparticles from the solution. To remove any excess surfactants, the nanoparticles were then washed three times by dispersion in hexane followed by precipitation with ethanol and isolation by centrifugation. Finally, the resulting Ni.sub.xP.sub.y nanoparticles were dried at room temperature.
[0226] 100 mg of the Ni.sub.xP.sub.y nanoparticles were dispersed in 5 mL of hexane. 50 mL of aqueous CTAB solution was added and the mixture sonicated for 30 minutes. The resulting emulsion was stirred at room temperature overnight and then the nanoparticles were isolated from the solution via centrifugation. The resulting CTAB-coated Ni.sub.xP.sub.y nanoparticles were washed and recovered again by centrifugation. Finally, the coated nanoparticles were dispersed in 50 mL of deionized water to form a stable hydrosol.
[0227] 0.5 mL of TEOS was added dropwise into 50 mL of the CTAB-coated Ni.sub.xP.sub.y nanoparticle hydrosol solution and stirred vigorously for 15 minutes. 70 μL of aqueous ammonia solution was then added and the reaction allowed to take place at room temperature for 24 hours. The CTAB/SiO.sub.2-coated Ni.sub.xP.sub.y particles were recovered by centrifugation and then washed with H.sub.2O followed by ethanol. The CTAB was removed by stirring the sample in a dilute HCl/ethanol solution (0.4 mL of 1 M HCl in 40 mL of ethanol) at room temperature for 1 hour. After 3 extractions, the final product was washed by ethanol, recovered by centrifugation, and then dried at room temperature to obtain the Ni.sub.xP.sub.y@meso-SiO.sub.2 nanoparticles.
[0228] Under a N.sub.2 atmosphere, 0.1 g of the Ni.sub.xP.sub.y@meso-SiOx nanoparticles were dissolved in 5 mL of TOP. 10 g of TOPO was added, and the reaction mixture was subjected to magnetic stirring for 30 min at 100° C. and then stirred for another 4 hours at a temperature of 380° C. After cooling to room temperature, the powder was precipitated by the addition of ethanol and subsequently centrifuged for 10 min at 4,500 rpm. The supernatant was discarded, thereby separating the nanoparticles from the solution. To remove any excess surfactants, the nanoparticles were then washed three times by dispersion in hexane followed by precipitation with ethanol and isolation by centrifugation. Finally, the resulting nanoparticles were dried at room temperature.
[0229] The particles were examined under TEM and subjected to XRD. The SO.sub.2 conversion, H.sub.2S yield, and H.sub.2S selectivity of the nanoparticles was also tested at various temperatures. A TEM image of the particles is shown in
Sample 14
[0230] To prepare a Na.sub.2SiO.sub.3 solution, 32.0 g of sodium hydroxide was first dissolved in 800 mL of deionized water. Then 187 mL Ludox™ HS-40 colloidal silica (40 wt % in H.sub.2O; available from Millipore Sigma) was added and the mixture closely stirred (i.e., stirred slowly to avoid creation of bubbles) at 40° C. overnight to produce a clear solution. This Na.sub.2SiO.sub.3 solution was stored in a sealed Teflon bottle at room temperature and can be stored as such for several weeks or until the mixture is no longer clear.
[0231] 1.0 g CTAB and 1 mmol nickel precursor Ni(acac).sub.2 were dissolved in 35 mL of deionized water and closely stirred at a temperature of 60° C. for 1 hour until the surfactant was completely dissolved to form a clear viscous solution (the undissolved precipitate was isolated by centrifugation).
[0232] 25 g of the Na.sub.2SiO.sub.3 solution was stirred at 60° C. for 1 hour and then the CTAB solution was added dropwise into the Na.sub.2SiO.sub.3 solution. The mixture was stirred vigorously at 60° C. for 1 hour and then stirred overnight at room temperature. A powder was then separated from the mixed solution by subjecting the solution to centrifugation for 10 min at 4500 rpm followed by removing the supernatant. To remove excess surfactants, the powder was washed three times by dispersion in H.sub.2O, then washed two times by dispersion in ethanol, and then isolated by centrifugation. The solid was dried in an oven at 80° C. overnight to obtain about 1.5 g of a light green powder.
[0233] Under a N.sub.2 atmosphere, 0.5 g of the light green powder was dissolved in 10 mL of OA and 5 mL of TOP. The reaction mixture was subjected to magnetic stirring for 10 min at 80° C. followed by stirring at 350° C. for 2 hours. After cooling to room temperature, a powder was precipitated by the addition of ethanol and subsequently centrifuged for 10 min at 4,500 rpm. The supernatant was discarded, thereby separating the nanoparticles from the solution. To remove any excess surfactants, the nanoparticles were then washed three times by dispersion in hexane followed by precipitation with ethanol and isolation by centrifugation. Finally, the resulting nanoparticles were dried in an 80° C. oven overnight.
[0234] The particles were examined under TEM and subjected to XRD. The SO.sub.2 conversion, H.sub.2S yield, and H.sub.2S selectivity of the nanoparticles was also tested at various temperatures. A TEM image of the particles is shown in
Sample 15
[0235] To prepare a Na.sub.2SiO.sub.3 solution, 32.0 g of sodium hydroxide was first dissolved in 800 mL of deionized water. Then 187 mL Ludox™ HS-40 colloidal silica (40 wt % in H.sub.2O) was added and the mixture closely stirred at 40° C. overnight to produce a clear solution.
[0236] 1.0 g CTAB and 1 mmol nickel precursor Ni(acac).sub.2 were dissolved in 35 mL of deionized water and closely stirred at a temperature of 60° C. for 1 hour until the surfactant was completely dissolved to form a clear viscous solution.
[0237] 25 g of the Na.sub.2SiO.sub.3 solution was stirred at 60° C. for 1 hour and then the CTAB solution was added dropwise into the Na.sub.2SiO.sub.3 solution. The mixture was stirred vigorously at 60° C. for 1 hour and then stirred overnight at room temperature. A powder was then separated from the mixed solution by subjecting the solution to centrifugation for 10 min at 4500 rpm followed by removing the supernatant. To remove excess surfactants, the powder was washed three times by dispersion in H.sub.2O, then washed two times by dispersion in ethanol, and then isolated by centrifugation. The solid was dried in an oven at 80° C. overnight to obtain about 1.5 g of a light green powder.
[0238] Under a N2 atmosphere, 0.5 g of the light green powder was dissolved in a mixture of 10 g of TOPO and 5 mL of TOP. The reaction mixture was subjected to magnetic stirring for 10 min at 80° C. followed by stirring at 400° C. for another 2 hours. After cooling to room temperature, a powder was precipitated by the addition of ethanol and subsequently centrifuged for 10 min at 4,500 rpm. The supernatant was discarded, thereby separating the nanoparticles from the solution. To remove any excess surfactants, the nanoparticles were then washed three times by dispersion in hexane followed by precipitation with ethanol and isolation by centrifugation. Finally, the resulting nanoparticles were dried in a 80° C. oven overnight.
[0239] The particles were examined under TEM and subjected to XRD. The SO.sub.2 conversion, H.sub.2S yield, and H.sub.2S selectivity of the nanoparticles was also tested at various temperatures. A TEM image of the particles is shown in
Sample 16
[0240] To prepare a Na.sub.2SiO.sub.3 solution, 32.0 g of sodium hydroxide was first dissolved in 800 mL of deionized water. Then 187 mL Ludox™ HS-40 colloidal silica (40 wt % in H.sub.2O) was added and the mixture closely stirred at 40° C. overnight to produce a clear solution.
[0241] 1.0 g CTAB and 0.3 g nickel precursor Ni(NO.sub.3).sub.2 (>97%, available from Millipore Sigma) were dissolved in 50 mL of deionized water and closely stirred at a temperature of 60° C. for 1 hour until the surfactant was completely dissolved to form a clear viscous solution.
[0242] 25 g of the Na.sub.2SiO.sub.3 solution was stirred at 60° C. for 1 hour and then the CTAB solution was added dropwise into the Na.sub.2SiO.sub.3 solution. The mixture was stirred vigorously at 60° C. for 1 hour and then stirred overnight at room temperature. A powder was then separated from the mixed solution by subjecting the solution to centrifugation for 10 min at 4500 rpm followed by removing the supernatant. To remove excess surfactants, the powder was washed three times by dispersion in H.sub.2O, then washed two times by dispersion in ethanol, and then isolated by centrifugation. The solid was dried in an oven at 80° C. overnight to obtain about 1.5 g of a light green powder.
[0243] Under a N.sub.2 atmosphere, 0.5 g of the light green powder was dissolved in a mixture of 10 mL of OA and 5 mL of TOP. The reaction mixture was subjected to magnetic stirring for 10 min at 80° C. followed by stirring at 350° C. for another 2 hours. After cooling to room temperature, a powder was precipitated by the addition of ethanol and subsequently centrifuged for 10 min at 4,500 rpm. The supernatant was discarded, thereby separating the nanoparticles from the solution. To remove any excess surfactants, the nanoparticles were then washed three times by dispersion in hexane followed by precipitation with ethanol and isolation by centrifugation. Finally, the resulting nanoparticles were dried in an 80° C. oven overnight.
[0244] The particles were examined under TEM and subjected to XRD. The SO.sub.2 conversion, H.sub.2S yield, and H.sub.2S selectivity of the nanoparticles was also tested at various temperatures. A TEM image of the particles is shown in
Sample 17
[0245] To prepare a Na.sub.2SiO.sub.3 solution, 32.0 g of sodium hydroxide was first dissolved in 800 mL of deionized water. Then 187 mL Ludox™ HS-40 colloidal silica (40 wt % in H.sub.2O) was added and the mixture closely stirred at 40° C. overnight to produce a clear solution.
[0246] 1.0 g CTAB and 1.5 g nickel precursor Ni(NO.sub.3).sub.2 were dissolved in 35 mL of deionized water and closely stirred at a temperature of 60° C. for 1 hour until the surfactant was completely dissolved to form a clear viscous solution.
[0247] 25 g of the Na.sub.2SiO.sub.3 solution was stirred at 60° C. for 1 hour and then the CTAB solution was added dropwise into the Na.sub.2SiO.sub.3 solution. The mixture was stirred vigorously at 60° C. for 1 hour and then stirred overnight at room temperature. A powder was then separated from the mixed solution by subjecting the solution to centrifugation for 10 min at 4500 rpm followed by removing the supernatant. To remove excess surfactants, the powder was washed three times by dispersion in H.sub.2O, then washed two times by dispersion in ethanol, and then isolated by centrifugation. The solid was dried in an oven at 80° C. overnight to obtain about 1.5 g of a light green powder.
[0248] Under a N2 atmosphere, 0.5 g of the light green powder was dissolved in a mixture of 10 mL of OA and 5 mL of TOP. The reaction mixture was subjected to magnetic stirring for 10 min at 80° C. followed by stirring at 350° C. for another 2 hours. After cooling to room temperature, a powder was precipitated by the addition of ethanol and subsequently centrifuged for 10 min at 4,500 rpm. The supernatant was discarded, thereby separating the nanoparticles from the solution. To remove any excess surfactants, the nanoparticles were then washed three times by dispersion in hexane followed by precipitation with ethanol and isolation by centrifugation. Finally, the resulting nanoparticles were dried in an 80° C. oven overnight.
[0249] The particles were examined under TEM and subjected to XRD. The SO.sub.2 conversion, H.sub.2S yield, and H.sub.2S selectivity of the nanoparticles was also tested at various temperatures. A TEM image of the particles is shown in
Sample 18
[0250] Under a N.sub.2 atmosphere, 2 mmol of molybdenum precursor Mo(CO).sub.6 (98%, available from Millipore Sigma) was dissolved in a mixture of 10 mL of OA and 5 mL of TOP. The reaction mixture was subjected to magnetic stirring for 10 min at 80° C. followed by stirring at 350° C. for another 2 hours. After cooling to room temperature, black particles were precipitated by the addition of ethanol and subsequently centrifuged for 10 min at 4,500 rpm. The supernatant was discarded, thereby separating the black nanoparticles from the solution. To remove any excess surfactants, the nanoparticles were then washed three times by dispersion in hexane followed by precipitation with ethanol and isolation by centrifugation. Finally, the resulting nanoparticles were dried at room temperature.
[0251] The particles were examined under TEM and subjected to XRD. The SO.sub.2 conversion, H.sub.2S yield, and H.sub.2S selectivity of the nanoparticles was also tested at various temperatures. A TEM image of the particles is shown in
Sample 19
[0252] Under a N.sub.2 atmosphere, 2 mmol of cobalt precursor Co(acac).sub.2 (97%, available from Millipore Sigma) was dissolved in a mixture of 10 mL of OA and 5 mL of TOP. The reaction mixture was subjected to magnetic stirring for 10 min at 80° C. followed by heating to 180° C. for 1 hour. An additional 5 mL of TOP was added to the mixture and the mixture was then stirred at 350° C. for another 2 hours. After cooling to room temperature, black particles were precipitated by the addition of ethanol and subsequently centrifuged for 10 min at 4,500 rpm. The supernatant was discarded, thereby separating the black nanoparticles from the solution. To remove any excess surfactants, the nanoparticles were then washed three times by dispersion in hexane followed by precipitation with ethanol and isolation by centrifugation. Finally, the resulting nanoparticles were dried at room temperature.
[0253] The particles were examined under TEM and subjected to XRD. The SO.sub.2 conversion, H.sub.2S yield, and H.sub.2S selectivity of the nanoparticles was also tested at various temperatures. A TEM image of the particles is shown in
Sample 20
[0254] Under a N.sub.2 atmosphere, 1 mmol of nickel precursor Ni(acac).sub.2 and 1 mmol cobalt precursor Co(acac).sub.2 were dissolved in a mixture of 10 mL of OA and 5 mL of TOP. The reaction mixture was subjected to magnetic stirring for 10 min at 80° C. and then stirred at a temperature of 350° C. for another 2 hours. After cooling to room temperature, black particles were precipitated by the addition of ethanol and subsequently centrifuged for 10 min at 4,500 rpm. The supernatant was discarded, thereby separating the black nanoparticles from the solution. To remove any excess surfactants, the nanoparticles were then washed three times by dispersion in hexane followed by precipitation with ethanol and isolation by centrifugation. Finally, the resulting nanoparticles were dried at room temperature.
[0255] The particles were examined under TEM and subjected to XRD. The SO.sub.2 conversion, H.sub.2S yield, and H.sub.2S selectivity of the nanoparticles was also tested at various temperatures. A TEM image of the particles is shown in
Sample 21
[0256] Under a N.sub.2 atmosphere, 1 mmol of nickel precursor Ni(acac).sub.2 and 1 mmol of molybdenum precursor (NH.sub.4).sub.6M.sub.o7O.sub.24 4H.sub.2O (99.98%, available from Millipore Sigma) were dissolved in a mixture of 10 mL of OA and 5 mL of TOP. The reaction mixture was subjected to magnetic stirring for 10 min at 80° C. and then stirred at a temperature of 350° C. for another 2 hours. After cooling to room temperature, black particles were precipitated by the addition of ethanol and subsequently centrifuged for 10 min at 4,500 rpm. The supernatant was discarded, thereby separating the black nanoparticles from the solution. To remove any excess surfactants, the nanoparticles were then washed three times by dispersion in hexane followed by precipitation with ethanol and isolation by centrifugation. Finally, the resulting nanoparticles were dried at room temperature.
[0257] The particles were examined under TEM and subjected to XRD. The SO.sub.2 conversion, H.sub.2S yield, and H.sub.2S selectivity of the nanoparticles was also tested at various temperatures. A TEM image of the particles is shown in
Sample 22
[0258] Under a N.sub.2 atmosphere, 1 mmol of nickel precursor Ni(acac).sub.2 and 1 mmol of iron precursor Fe(acac).sub.3 (≥97%, available from Millipore Sigma) were dissolved in a mixture of 10 mL of OA and 5 mL of TOP. The reaction mixture was subjected to magnetic stirring for 10 min at 80° C. and then stirred at a temperature of 350° C. for another 2 hours. After cooling to room temperature, black particles were precipitated by the addition of ethanol and subsequently centrifuged for 10 min at 4,500 rpm. The supernatant was discarded, thereby separating the black nanoparticles from the solution. To remove any excess surfactants, the nanoparticles were then washed three times by dispersion in hexane followed by precipitation with ethanol and isolation by centrifugation. Finally, the resulting nanoparticles were dried at room temperature.
[0259] The particles were examined under TEM and subjected to XRD. The SO.sub.2 conversion, H.sub.2S yield, and H.sub.2S selectivity of the nanoparticles was also tested at various temperatures. A TEM image of the particles is shown in
Sample 23
[0260] Under a N.sub.2 atmosphere, 1 mmol of nickel precursor Ni(acac).sub.2 and 1 mmol of tungsten precursor WCl.sub.4 (95%, available from Millipore Sigma) were dissolved in a mixture of 10 mL of OA and 5 mL of TOP. The reaction mixture was subjected to magnetic stirring for 10 min at 80° C. and then stirred at a temperature of 350° C. for another 2 hours. After cooling to room temperature, black particles were precipitated by the addition of ethanol and subsequently centrifuged for 10 min at 4,500 rpm. The supernatant was discarded, thereby separating the black nanoparticles from the solution. To remove any excess surfactants, the nanoparticles were then washed three times by dispersion in hexane followed by precipitation with ethanol and isolation by centrifugation. Finally, the resulting nanoparticles were dried at room temperature.
[0261] The particles were examined under TEM and subjected to XRD. The SO.sub.2 conversion, H.sub.2S yield, and H.sub.2S selectivity of the nanoparticles was also tested at various temperatures. A TEM image of the particles is shown in
Sample 24
[0262] Under a N.sub.2 atmosphere, 1 mmol of nickel precursor Ni(acac).sub.2, 1 mmol of cobalt precursor Co(acac).sub.2, and 1 mmol of molybdenum precursor ((NH.sub.4).sub.6M.sub.o7O.sub.24 4H.sub.2O) were dissolved in a mixture of 15 mL of OA and 7.5 mL of TOP. The reaction mixture was subjected to magnetic stirring for 10 min at 80° C. and then stirred at a temperature of 350° C. for another 2 hours. After cooling to room temperature, black particles were precipitated by the addition of ethanol and subsequently centrifuged for 10 min at 4,500 rpm. The supernatant was discarded, thereby separating the black nanoparticles from the solution. To remove any excess surfactants, the nanoparticles were then washed three times by dispersion in hexane followed by precipitation with ethanol and isolation by centrifugation. Finally, the resulting nanoparticles were dried at room temperature.
[0263] The particles were examined under TEM and subjected to XRD. The SO.sub.2 conversion, H.sub.2S yield, and H.sub.2S selectivity of the nanoparticles was also tested at various temperatures. A TEM image of the particles is shown in
Sample 25
[0264] Under a N.sub.2 atmosphere, 2 mmol of nickel precursor Ni(acac).sub.2 was dissolved in a mixture of 10 mL of OA and 5 mL of TOP. The reaction mixture was subjected to magnetic stirring for 10 min at 80° C. and then heated to a temperature of 230° C. for one hour. Another 5 mL of TOP was added to the mixture and the mixture stirred at 300° C. for another 2 hours. After cooling to room temperature, black particles were precipitated by the addition of ethanol and subsequently centrifuged for 10 min at 4,500 rpm. The supernatant was discarded, thereby separating the black nanoparticles from the solution. To remove any excess surfactants, the nanoparticles were then washed three times by dispersion in hexane followed by precipitation with ethanol and isolation by centrifugation. Finally, the resulting nanoparticles were dried at room temperature.
[0265] The particles were examined under TEM and subjected to XRD. The SO.sub.2 conversion, H.sub.2S yield, and H.sub.2S selectivity of the nanoparticles was also tested at various temperatures. A TEM image of the particles is shown in
Sample 26
[0266] Under a N.sub.2 atmosphere, 2 mmol of nickel precursor Ni(acac).sub.2 was dissolved in a mixture of 10 mL of OA and 5 mL of TOP. The reaction mixture was subjected to magnetic stirring for 10 min at 80° C. and then heated to a temperature of 230° C. for one hour. Another 5 mL of TOP was added to the mixture and the mixture stirred at 300° C. for another 8 hours. After cooling to room temperature, black particles were precipitated by the addition of ethanol and subsequently centrifuged for 10 min at 4,500 rpm. The supernatant was discarded, thereby separating the black nanoparticles from the solution. To remove any excess surfactants, the nanoparticles were then washed three times by dispersion in hexane followed by precipitation with ethanol and isolation by centrifugation. Finally, the resulting nanoparticles were dried at room temperature.
[0267] The particles were examined under TEM and subjected to XRD. The SO.sub.2 conversion, H.sub.2S yield, and H.sub.2S selectivity of the nanoparticles was also tested at various temperatures. A TEM image of the particles is shown in
Sample 27
[0268] Under a N.sub.2 atmosphere, 2 mmol of nickel precursor Ni(acac).sub.2 was dissolved in a mixture of 10 mL of OA and 5 mL of TOP. The reaction mixture was subjected to magnetic stirring for 10 min at 80° C. and then stirred for another 1 hour at 350° C. After cooling to room temperature, black particles were precipitated by the addition of ethanol and subsequently centrifuged for 10 min at 4,500 rpm. The supernatant was discarded, thereby separating the black nanoparticles from the solution. To remove any excess surfactants, the nanoparticles were then washed three times by dispersion in hexane followed by precipitation with ethanol and isolation by centrifugation. Finally, the resulting nanoparticles were dried at room temperature.
[0269] The particles were examined under TEM and subjected to XRD. The SO.sub.2 conversion, H.sub.2S yield, and H.sub.2S selectivity of the nanoparticles was also tested at various temperatures. A TEM image of the particles is shown in
Sample 28
[0270] Under a N.sub.2 atmosphere, 1 mmol of nickel precursor Ni(acac).sub.2 and 1 mmol of molybdenum precursor Mo(CO).sub.6 were dissolved in a mixture of 10 mL of OA and 5 mL of TOP. The reaction mixture was subjected to magnetic stirring for 10 min at 80° C. and then stirred for another 2 hours at 350° C. After cooling to room temperature, black particles were precipitated by the addition of ethanol and subsequently centrifuged for 10 min at 4,500 rpm. The supernatant was discarded, thereby separating the black nanoparticles from the solution. To remove any excess surfactants, the nanoparticles were then washed three times by dispersion in hexane followed by precipitation with ethanol and isolation by centrifugation. Finally, the resulting nanoparticles were dried at room temperature.
[0271] The particles were examined under TEM and subjected to XRD. The SO.sub.2 conversion, H.sub.2S yield, and H.sub.2S selectivity of the nanoparticles was also tested at various temperatures. A TEM image of the particles is shown in
Sample 29
[0272] To prepare a Na.sub.2SiO.sub.3 solution, 32.0 g of sodium hydroxide was first dissolved in 800 mL of deionized water. Then 187 mL Ludox™ HS-40 colloidal silica (40 wt % in H.sub.2O) was added and the mixture closely stirred at 40° C. overnight to produce a clear solution.
[0273] 1.0 g CTAB and 1 mmol nickel precursor Ni(acac).sub.2 were dissolved in 35 mL of deionized water and closely stirred at a temperature of 60° C. for 1 hour until the surfactant was completely dissolved to form a clear viscous solution (the undissolved precipitate was isolated by centrifugation).
[0274] 25 g of the Na.sub.2SiO.sub.3 solution was stirred at 60° C. for 1 hour and then the CTAB solution was added dropwise into the Na.sub.2SiO.sub.3 solution. The mixture was stirred vigorously at 60° C. for 1 hour and then stirred overnight at room temperature. A powder was then separated from the mixed solution by subjecting the solution to centrifugation for 10 min at 4500 rpm followed by removing the supernatant. To remove excess surfactants, the powder was washed three times by dispersion in H.sub.2O, then washed two times by dispersion in ethanol, and then isolated by centrifugation. The solid was dried in an oven at 80° C. overnight to obtain about 1.5 g of a light green powder.
[0275] Under a N.sub.2 atmosphere, 0.5 g of the light green powder was dissolved in a mixture of 10 mL of OA and 5 mL of TOP. The reaction mixture was subjected to magnetic stirring for 10 min at 80° C. followed by stirring at 300° C. for another 2 hours. After cooling to room temperature, a powder was precipitated by the addition of ethanol and subsequently centrifuged for 10 min at 4,500 rpm. The supernatant was discarded, thereby separating the nanoparticles from the solution. To remove any excess surfactants, the nanoparticles were then washed three times by dispersion in hexane followed by precipitation with ethanol and isolation by centrifugation. Finally, the resulting nanoparticles were dried in an 80° C. oven overnight.
[0276] The particles were examined under TEM and subjected to XRD. The SO.sub.2 conversion, H.sub.2S yield, and H.sub.2S selectivity of the nanoparticles was also tested at various temperatures. A TEM image of the particles is shown in
Sample 30
[0277] Under a N.sub.2 atmosphere, 1 mmol of nickel precursor Ni(acac).sub.2 and 1 mmol of cobalt precursor Co(acac).sub.2 were dissolved in a mixture of 10 mL of OA and 2.5 mL of TOP. The reaction mixture was subjected to magnetic stirring for 10 min at 80° C. and then heated to a temperature of 230° C. for 1 hour. The mixture was then stirred at 300° C. for another 2 hours. After cooling to room temperature, black particles were precipitated by the addition of ethanol and subsequently centrifuged for 10 min at 4,500 rpm. The supernatant was discarded, thereby separating the black nanoparticles from the solution. To remove any excess surfactants, the nanoparticles were then washed three times by dispersion in hexane followed by precipitation with ethanol and isolation by centrifugation. Finally, the resulting nanoparticles were dried at room temperature.
[0278] The particles were examined under TEM and subjected to XRD. The SO.sub.2 conversion, H.sub.2S yield, and H.sub.2S selectivity of the nanoparticles was also tested at various temperatures. A TEM image of the particles is shown in
TABLE-US-00006 TABLE 6 The phase, size, morphology, and conversion of SO.sub.2 and yield of H.sub.2S at 320° C. of various Samples described above in Example 3. Phase Size Morphology Conv. of SO.sub.2 Yield of H.sub.2S Sample (XRD) (TEM) (TEM) (@320° C.) (@320° C.) 1 Ni.sub.5P.sub.4 500-1000 mn clusters 80 78 2 Ni.sub.2P + Ni.sub.5P.sub.4 50 nm hollow particles 93 93 3 Ni.sub.5P.sub.4 200 nm particles 48 36 4 Ni.sub.5P.sub.4 100 nm particles 95 70 5 Ni.sub.5P.sub.4 200 mn particles 56 31 6 Ni.sub.5P.sub.4 50-500 mn clusters 5 3 7 Ni.sub.5P.sub.4 100 nm clusters 18 14 8 Ni.sub.2P + Ni.sub.5P.sub.4 + NiP.sub.2 700 nm clusters 71 46 9 Ni.sub.5P.sub.4 + NiP.sub.2 20-50 nm particles 87 63 10 Ni.sub.2P + Ni.sub.5P.sub.4 100 nm hollow particles 41 32 11 Ni.sub.2P + Ni.sub.5P.sub.4 + NiP.sub.2 10 nm particles@SiO.sub.2 81 65 12 Ni.sub.2P + Ni.sub.5P.sub.4 + NiP.sub.2 10 nm particles@SiO.sub.2 31 27 13 Ni.sub.5P.sub.4 + NiP.sub.2 10-100 nm particles@SiO.sub.2 9 4 14 Ni.sub.2P + Ni.sub.5P.sub.4 <2 nm invisible@SiO.sub.2 97 24 15 Ni.sub.2P + Ni.sub.5P.sub.4 <2 nm invisible@SiO.sub.2 94 35 16 Ni.sub.2P + Ni.sub.5P.sub.4 <5 mn particles@SiO.sub.2 97 4 17 Ni.sub.2P + Ni.sub.5P.sub.4 <5 mn particles@SiO.sub.2 85 3 18 N/A N/A amorphous 98 5 19 CoP 10 nm particle + rod 95 62 20 Ni.sub.2P + CoP 10 nm particles 91 56 21 Ni.sub.5P.sub.4 10-1000 nm clusters 92 43 22 Ni.sub.5P.sub.2 + FeP.sub.4 10-20 nm tadpole clove 34 12 23 Ni.sub.2P 10-50 nm rod 22 6 24 Ni.sub.2P + CoP + Co.sub.2P 10 nm particles + rod 98 14 25 Ni.sub.2P 10 nm particles 70 0 26 Ni.sub.2P 10 nm particles 93 18 27 Ni.sub.2P 10 nm particles 87 0 28 Ni.sub.2P 10 nm particles 78 24 29 Ni.sub.2P <2 nm clusters 100 3 30 Ni.sub.2P + Co.sub.2P 10-30 nm particles + rod 21 0
TABLE-US-00007 TABLE 7 The phase and atomic ratio of Ni, P, and Si from EDX analysis of various Samples described above in Example 3. Atomic Ratio Sample Phase (XRD) Ni/P Ni/(Ni + Si) 1 Ni.sub.5P.sub.4 1.5 100% 2 Ni.sub.2P + Ni.sub.5P.sub.4 1.8 100% 3 Ni.sub.5P.sub.4 1.7 100% 4 Ni.sub.5P.sub.4 1.4 100% 5 Ni.sub.5P.sub.4 1.5 100% 6 Ni.sub.5P.sub.4 1.6 100% 7 Ni.sub.5P.sub.4 1.7 100% 8 Ni.sub.2P + Ni.sub.5P.sub.4 + NiP.sub.2 1.3 100% 9 Ni.sub.5P.sub.4 + NiP.sub.2 0.9 100% 10 Ni.sub.2P + Ni.sub.5P.sub.4 1.3 100% 11 Ni.sub.2P + Ni.sub.5P.sub.4 + NiP.sub.2 1.3 28% 12 Ni.sub.2P + Ni.sub.5P.sub.4 + NiP.sub.2 1.3 84% 13 Ni.sub.5P.sub.4 + NiP.sub.2 0.5 34% 14 Ni.sub.2P + Ni.sub.5P.sub.4 0.6 5% 15 Ni.sub.2P + Ni.sub.5P.sub.4 0.5 3% 16 Ni.sub.2P + Ni.sub.5P.sub.4 0.9 6% 17 Ni.sub.2P + Ni.sub.5P.sub.4 0.8 10% 25 Ni.sub.2P 2.2 100% 26 Ni.sub.2P 2.2 100% 27 Ni.sub.2P 2 100% 29 Ni.sub.2P 0.5 7%
TABLE-US-00008 TABLE 8 The phase and atomic ratio of different elements from EDX analysis of various Samples described above in Example 3. Atomic Ratio (%) Sample Phase (XRD) P Ni Co Fe Mo W 18 N/A 55 45 19 CoP 57 43 20 Ni.sub.2P + CoP 40 32 28 21 Ni.sub.5P.sub.4 41 45 14 22 Ni.sub.5P.sub.2 + FeP.sub.4 49 26 25 23 Ni.sub.2P 52 44 4 24 Ni.sub.2P + CoP + Co.sub.2P 50 23 19 8 28 Ni.sub.2P 51 43 6 30 Ni.sub.2P + Co.sub.2P 29 38 33
Example 4
[0279] Ni.sub.2P Nanoparticles Embedded in Mesoporous SiO.sub.2
[0280] This example demonstrates the synthesis and catalytic performance of a new class of nano-engineered catalysts encapsulated in a protective mesoporous silica whereby the P insertion step occurs within the mesoporous silica matrix. The Ni precursor is incorporated into the SiO.sub.2 matrix simultaneously during the formation of the mesoporous SiO.sub.2 framework and then the phosphorization step is conducted on the resulting composite material. The presence of the silica hinders the aggregation or uneven distribution of Ni precursor on the SiO.sub.2 surface. Moreover, the mesoporous channels in SiO.sub.2 provide a limited space, which facilitates the formation of ultrafine Ni.sub.2P nano crystals while preventing crystal growth during the phase transformation from Ni to Ni.sub.2P. The mesoporous SiO.sub.2 confined ultrafine Ni.sub.2P nano clusters, demonstrate herein a superior catalytic performance, especially by the sub-2 nm particle, when compared to the 11 nm Ni.sub.2P nano particles and the commercial Ni.sub.2P catalyst, thereby achieving higher conversions and selectivity at lower temperatures.
Catalytic Synthesis
[0281]
Catalytic Synthesis—Ni Precursor Confined in Mesoporous SiO.SUB.2
[0282] 32 g sodium hydroxide was dissolved in 800 mL deionized water, then 187 mL Ludox (40 wt. %) was added into the above NaOH solution and stirred at 40° C. overnight (until clear) to prepare the Na.sub.2SiO.sub.3 solution. Following, 1.0 g CTAB and 1 mmol nickel precursor (Ni(acac).sub.2) were dissolved in 35 mL deionized water and slowly stirred at 60° C. for 1 hour until the surfactant was dissolved completely to form a clear viscous solution (the precipitate was isolated by centrifugation). At the same time, 25 g of the above Na.sub.2SiO.sub.3 solution was stirred at 60° C. for 1 hour. Then the CTAB solution was added into the Na.sub.2SiO.sub.3 solution. After 1 hour of vigorous stirring at 60° C., this mixture was stirred at room temperature overnight. The powder was precipitated by centrifugation for 10 min at 4500 rpm. To remove the excess of surfactants, the obtained powder was washed three times by dispersion in H.sub.2O, then two times by dispersion in ethanol and finally separated by centrifugation. The solid was dried at 80° C. overnight to obtain a light green powder, corresponding to Ni precursor confined in mesoporous SiO.sub.2.
Catalytic Synthesis—Phosphorization
[0283] In a N.sub.2 atmosphere, 2 mmol nickel precursor (Ni(acac).sub.2) or 0.5 g Ni confined in SiO.sub.2 was first dissolved/dispersed in 10 mL OA and 5 mL TOP in a 100 mL volume three-necked round-bottom flask (installed with a condenser for the reflux and a thermocouple for the temperature control). The reaction mixture was stirred for 10 min at 80° C., followed by stirring at 300° C. for another 2 hours. All the above operations were carried out in a fume hood to minimize the hazards arising from the chemical nature of the reactants used (e.g. the serious poisoning and damage to the skin and eyes caused by the TOP and its vapour, and the skin irritation that can be caused by OA). After cooling to room temperature, a powder was precipitated by addition of ethanol and subsequently centrifuged for 10 min at 4500 rpm. To remove the excess surfactants, the obtained solid was washed three times by dispersion in hexane, then precipitated with ethanol and isolated by centrifugation. Finally, the resulting black powder was dried overnight.
u-Ni.sub.2P@m-SiO.sub.2 (Mesoporous SiO.sub.2 Confined Ultrafine Ni.sub.2P Nano Clusters, Methodology “A” of
[0284] 1 mmol nickel precursor (Ni(acac).sub.2) was confined in mesoporous SiO.sub.2 to get about 1.5 g light green powder. Then 0.5 g of the obtained light green powder was treated using the phosphorization process shown in methodology “A” of
n-Ni.sub.2P (11 Nm Ni.sub.2P Nano Particles, Methodology “B” ofFigure 47)
[0285] In a N.sub.2 atmosphere, 2 mmol nickel precursor (Ni(acac).sub.2) was treated following the phosphorization process shown in methodology “B” of
u-Ni@m-SiO.sub.2 (Mesoporous SiO.sub.2 Confined Ultrafine Ni Precursor, Methodology “C” ofFigure 47)
[0286] 1 mmol nickel precursor (Ni(acac).sub.2) was confined in mesoporous SiO.sub.2 to get about 1.5 g light green powder. Then 0.5 g obtained green powder was calcined in air at 550° C. for 6 hours (with a 2° C./min heating rate).
c-Ni.sub.2P (Commercial Ni.sub.2P Powder)
[0287] The commercial Ni.sub.2P from Sigma-Aldrich was directly used without any further treatment.
Characterization
[0288] The XRD patterns of the fresh catalysts and the spent catalyst (in the presence of quartz) were collected with a Panalytical X′Pert PRO powder diffractometer using Cu-Ka radiation (λ=1.5406 Å) operated at 40 mA and 40 kV. The mean particle size and morphology of the fresh catalysts and the spent catalysts (with quartz) were determined using high-resolution transmission electron microscopy HR-TEM (FEI Tecnai, 200 kV), the area for image capture were selected to avoid the quartz particles. Additionally, selected HR-TEM studies were carried out over some of the herein catalysts using Titan 80-300 ST electron microscope, operated at 300 kV. The microscope was equipped with a spherical aberration (Cs) corrector for the image (CEOS CETCOR), and an energy filter (model GIF Quantum 963, Gatan, Inc.). However, nanoscale elemental mapping was carried out using scanning TEM, STEM-EELS mode. The entire TEM data acquisition and post processing was done by utilizing Gatan Microscopy Suite (GMS, version 3.2). Elemental analysis was also conducted in FEI Quanta 250 FEG scanning microscope. The electron source of this instrument is a Schottky field emission gun, possessing a spatial resolution of approximately 1 nm at 30 kV (SE) and 3.0 nm at 1 kV (SE). Elemental analysis was conducted using an equipped Apollo silicon drift detector (SDD) integrated with the EDAX Genesis software, the fresh catalysts were tested directly, and the spent catalysts were prepared with the powders where the quartz particles were removed as much as possible. Nitrogen adsorption-desorption isotherms of the fresh catalysts were carried out at 77 K using a 3Flex Micromeritics (Atlanta, USA) instrument. Samples (˜90 mg, fresh) were pretreated at 130° C. in vacuum overnight for degassing before any measurements. UV-vis diffuse reflection spectra were measured by a VARIAN CARY 5000 uv-vis-nir spectrophotometer. The photoelectron spectra of the samples were recorded using a ESCALAB Thermo Scientific Theta Probe Angle-Resolved X-ray Photoelectron Spectrometer (East Grinstead, UK). The spectrometer is equipped with a monochromatic Al Ka X-ray source (hv=1486.6 eV). A pass energy of 300 eV was used to obtain the survey spectra, whereas the high-resolution core level spectra were acquired at a pass energy of 50 eV. The binding energy scale was calibrated (charge reference) by centering the C 1 s peak at 285.0 eV for all the spectra. The static .sup.31P solid-state nuclear magnetic resonance (ssNMR) spectrum was collected at a magnetic Field of 9.4 T on a home-built broadband coherent NMR spectrometer using a home-built probe. For acquisition, a standard Hahn echo pulse sequence, with variation of frequency along the NMR line was employed, with a 90° excitation pulse of 3.5 s, corresponding to rf field of 71.4 kHz. NMR shifts were referenced to H.sub.3PO.sub.4 85 wt % at 0 ppm.
Catalytic Assessment: Reaction Metrics
[0289] SO.sub.2 hydrogenation experiments were conducted at atmospheric pressure in a fixed bed U-shaped quartz reactor. A 40 mg catalyst mixed with 180 mg of quartz particles (125 to 250 μm) were placed in a quartz reaction tube having 4 mm internal diameter. The catalyst bed was initially pretreated for 1 hour at 100° C. by introducing a stream of Ar at 40 mL/min. Then, a feed gas consisting of 103 ppm SO.sub.2 at 20 mL/min and a feed gas of 2% H.sub.2 in N.sub.2 at 20 mL/min was fed into the reactor (total feed gas at 40 ml/min, GHSV=˜50000/h, WHSV=60000 mL/g/h), the reaction was run across the temperature range of 100-320° C. The effluent gas stream (reactants and reaction products) was analyzed using a Perkin Elmer Clarus 580 Gas Chromatograph and Model Arnel 4016 PPC Sulphur Chemiluminescence Detector (SCD).
[0290] For SO.sub.2 catalytic measurements, while the experiments were done only once for each sample, the measurements of the experimental parameters were repeated as follows: [0291] a. Flow measurements were repeated five times in each experiment. [0292] b. Mass of sample measurements were repeated 3 times prior to each experiment. [0293] c. At each experimental temperature, five measurements were made to compute the conversion. [0294] d. Reference SO.sub.2 areas used to determine SO.sub.2/H.sub.2S concentrations were measured 10 times per experiment.
[0295] Following, the standard errors computed from the repeated measurements were used to compute the expected error (standard deviation) in the SO.sub.2 average rate and rate constant by the method of the propagation of uncertainty.
[0296] The conversion of SO.sub.2 was calculated based on the peak area using the following Equation 10:
where (SO.sub.2).sub.in is SO.sub.2 molar flow rate in the feed gas (mol/s), (SO.sub.2).sub.out is SO.sub.2 molar flow rate in the bed effluent (mol/s).
[0297] The selectivity to sulfur was calculated based on the peak area of H.sub.2S and SO.sub.2 using the following Equation 11:
where: (SO.sub.2).sub.in is SO.sub.2 molar flow rate in the feed gas (mol/s), (SO.sub.2).sub.out is SO.sub.2 molar flow rate in the bed effluent (mol/s), (H.sub.2 S).sub.out is H.sub.2S molar flow rate in the bed effluent (mol/s).
Catalytic Assessment: Kinetic Studies
[0298] The average reaction rate r (mol/s.Math.g.sub.active) was calculated based on the conversion of SO.sub.2 using Equation 12:
where m.sub.active (g) is the mass of the catalyst active phase (e.g. Ni.sub.2P).
[0299] The average rate constant k (m.sup.3/s.Math.g) was calculated based on the average rate of reaction, using the following Equation 13 derived for a PFR (plug flow reactor model) assuming r=k*concentration of SO.sub.2 (the reaction rate is assumed to be first order in SO.sub.2):
where c (SO.sub.2).sub.in is the concentration of SO.sub.2 in the feed gas.
[0300] The activation energy of reaction was based on the average rate constant using the following Equation 14 derived from the Arrhenius expression:
where: k (m.sup.3/s.Math.g) is the average rate constant, A is the pre-exponential factors, E.sub.a is the activation energy, R is the ideal gas constant which value is 8.314 J/(K.Math.mol), T (K) is the reaction temperature. E.sub.a is derived from the slope of the ln k vs. 1/T linear plot (Arrhenius plot).
[0301] The turn over frequency (TOF, s.sup.1) was calculated based on the average reaction rate using the following Equation 15:
TOF=r×M.sub.active(8) (Equation 15)
where r is the average reaction rate, M.sub.active is the molar mass of Ni.sub.2P (148.361 g/mol) or Ni (58.693 g/mol).
Results—Structural Characterization
[0302]
[0303] Low-angle XRD was performed to study the mesoporous silica structure, and the patterns are shown in
[0304]
[0305] UV-Vis is used to probe the ligand-to-metal charge transfer (LMCT), which is highly sensitive to the coordination environment and the extent of aggregation. The coordination environment of the Ni and Ni.sub.2P incorporated into the mesoporous SiO.sub.2 is of interest. The absorption bands between 200-300 nm are related to the mesoporous silica matrix. The absorption bands around 400 nm (Ni.sup.2+(1):.sup.3A.sub.2g.fwdarw..sup.3T.sub.1g(P)) and 740 nm (Ni.sup.2+(2): .sup.3A.sub.2g.fwdarw..sup.3T.sub.1g(F)) are related to the octahedral coordinated Ni.sup.2+ in Ni and Ni.sub.2P, whereas the bands of the O.sup.2−(2p).fwdarw.Ni.sup.2+ (3d) charge transfer in the NiO phase are in the 250˜350 nm range. The NiO species could be attributed to the surface oxidation of u-Ni.sub.2P@m-SiO.sub.2 and u-Ni@m-SiO.sub.2 after long storage in atmosphere. For the Ni phosphate, the presence of which has also been confirmed using XPS and ssNMR (as discussed further below) the 400-600 nm band as well as the band >700 nm can be assigned. These bands correspond to Ni.sup.2+ species bound in an octahedral environment (O.sub.h) in the phosphate structure. No meaningful bands for the Ni.sub.2P nano particles and commercial Ni.sub.2P in the displayed area (200-800 nm) were observed due to its narrow band gap. Also, comparing the UV-vis spectrum of the u-Ni@m-SiO.sub.2 (
[0306]
[0307] The highly dispersed ultrafine Ni.sub.2P clusters were further studied using the STEM-HAADF/EDS mapping, which are shown in
[0308] The X-ray photoelectron spectra (XPS) of the above catalysts were measured to identify the chemical states present at the surface. The high-resolution XPS spectra are shown in
[0309] With regard to the intensities of the Ni 2p.sub.3/2 and P 2p peaks for the different Ni.sub.2P catalysts, the photoelectron intensity decreases in the order n-Ni.sub.2P>c-Ni.sub.2P>u-Ni.sub.2P. The n-Ni.sub.2P particles were freshly prepared, so exhibited a thinner oxidized layer than the commercially procured c-Ni.sub.2P powder. The absence of a Ni.sub.2P bulk P 2p peak for the u-Ni.sub.2P@SiO.sub.2 catalyst suggests the formation of a thicker and more strongly oxidized layer on the Ni.sub.2P nanoparticles in the SiO.sub.2 matrix. This could be a result of their very small diameter, providing a larger surface area and more highly stressed (hence weaker, more porous oxidized layer) leading to a greater degree of Ni.sub.2P oxidation. However, the SiO.sub.2 matrix encapsulating the Ni.sub.2P nanoparticles may also have attenuated the photoelectron signal, which could explain the presence of only peaks corresponding to the surface oxide and not the bulk Ni.sub.2P.
[0310]
[0311] The textural properties of the samples containing mesoporous silica were studied employing N.sub.2 adsorption/desorption experiments. The collected isotherms along with the NLDFT pore size distributions are presented in
TABLE-US-00009 TABLE 9 Summary of synthesis parameters, size and morphology characteristics, and porosity data Treatment Process Size & V.sub.p S.sub.BET d.sub.NLDFT Sample Name SiO.sub.2 *.sup.a P Cal. Morphology (cm.sup.3 .Math. g.sup.−1) (m.sup.2 .Math. g.sup.−1) (nm) u-Ni.sub.2P@m-SiO.sub.2 Yes Yes No <2 nm Ni.sub.2P @ SiO.sub.2 0.13 53 3.3/5.1 n-Ni.sub.2P No Yes No ~11 nm Ni.sub.2P particles N/A N/A N/A u-Ni@m-SiO.sub.2 Yes No Yes <2 nm Ni @ SiO.sub.2 0.23 214 3.8/5.9 c-Ni.sub.2P N/A N/A N/A >1 μm Ni.sub.2P blocks N/A N/A N/A *.sup.a: Average data from 5 measurements; error = 2%
[0312] Sample u-Ni.sub.2P@m-SiO.sub.2 (
[0313] The possible Ni-containing phases have been evaluated using XRD, XPS, UV-vis and ssNMR. XRD studies for the n-Ni.sub.2P and the c-Ni.sub.2P samples confirmed the presence of the Ni.sub.2P phase. Also, EDX elemental composition confirmed the Ni/P ratio of 1.8, close to the nominal one (2) for those two catalysts. The XPS Ni/P signals from the underlying Ni.sub.2P bulk are of very low intensity. Hence, it is not possible to reliably calculate the Ni:P stoichiometry.
[0314] For the u-Ni@SiO.sub.2 and u-Ni.sub.2P@SiO.sub.2 samples, the XRD patterns showed a lack of XRD peaks or minor peaks (after magnification), respectively. Particularly for the u-Ni.sub.2P@SiO.sub.2 catalyst, the XRD results indicate that the grain size is clearly very similar to that expected for growth of Ni.sub.2P nano-particulates in the SiO.sub.2 matrix pores, suggesting that the particulates are purely crystalline and there is no significant amorphous phase present. After the phosphorization step, the P atoms are inserted into the lattice of Ni (either crystalline or amorphous species), thus forming the Ni.sub.2P phase, as confirmed using the XRD, XPS and NMR studies. The presence of other possible Ni—P containing phases (different stoichiometries) can be discounted, as they are typically synthesized at different phosphorization temperatures in the presence of OA; for example, the Ni.sub.12P.sub.5, Ni.sub.5P.sub.4 and NiP.sub.2 phases need a phosphorization temperature of 250° C., 350° C., and 400° C., respectively, which was not the case in the synthesis procedures used in this study. In the synthesis followed herein in OA with excess TOP, the Ni—P phase was controlled by the temperature. Based on the SEM-EDX results, the ratio of P/Ni is about 2 for the u-Ni.sub.2P@SiO.sub.2, which is an excess compared to the nominal P/Ni ratio of 0.5 for the Ni.sub.2P. The excess is likely due to the presence of compounds other than Ni.sub.2P, such as P(OH) species and PO.sub.4.sup.3−(phosphates), as indicated by the NMR and XPS studies. The amorphous Ni is unlikely to survive in OA at 300° C. in the presence of excess amounts of TOP (P-source). Though, in the sample u-Ni@m-SiO.sub.2, without phosphorization, the Ni was distributed in the SiO.sub.2 matrix and is likely present as Ni-containing phase (e.g. NiO, Ni(OH).sub.2) based on the UV-vis and XPS analysis.
Mechanistic Insights on the Phosphorization Process
[0315] The conversion of the Ni precursor to Ni.sub.2P (phosphorization) includes decomposing the Ni(acac).sub.2 precursor to Ni by raising the temperature above ˜230° C. The insertion of P resulting from the decomposition of the TOP precursor (carrier of C—P bonds) into the Ni crystal occurs at about the same temperature. The phosphorization rate increases gradually with temperature, and after 2 hours of heating to ˜300° C. the phase transformation of Ni to Ni.sub.2P occurs. The long carbon chain of OA acts as a surfactant that prevents the aggregation of Ni.sub.2P crystals. To control the size and morphology of nano particles, the type and carbon chain length of the surfactant are important. Due to the high temperature requirement to achieve the Ni.sub.2P phase, a stable “surfactant” which can withstand temperatures above 300° C. is desirable for controlling the size and morphology the Ni.sub.2P crystals. Mesoporous SiO.sub.2 which is stable at high temperature (up to −600° C.) is a suitable candidate serving as a “hard template”.
[0316] In some embodiments of this invention, mesoporous silica is used to prevent aggregation and limit growth of the crystals during the phosphorization step by introducing the Ni precursor into the mesoporous silica. With the assistance of CTAB as a surfactant, the Ni(acac).sub.2 is well dispersed in the silica matrix. When introducing Ni(acac).sub.2 into the CTAB solution, the removal of any precipitate of the precursor is desirable since the solubility of Ni(acac).sub.2 is very low. The clear solution of the liquid precursor, separated by centrifugation, ensures good dispersion of Ni(acac).sub.2 and prevents formation of aggregated nickel. To form the ultra-fine Ni.sub.2P clusters, low loading of Ni precursor is advantageous as excess Ni will tend to form aggregates of larger particles on the available surface of SiO.sub.2 support. Depending on the solubility of Ni(acac).sub.2 in water, the upper limit of well dispersed Ni incorporated into the SiO.sub.2 matrix without giving rise to Ni aggregation is a Ni/Si ratio of about 5%. Only the soluble Ni(acac).sub.2 is enclosed in MCM-41, so the Ni precursor is highly dispersed. It may be possible to change the size range of the produced nanoparticles by modifying the Ni precursor to TOP ratio, however, altering that ratio is unlikely to produce ultrafine Ni.sub.2P nanoparticles because the particles will slowly grow to around 10 nm during the 2 hours of phosphorization at 300° C. In the synthesis performed for these experiments, either for the 11 nm n-Ni.sub.2P or the ultrafine u-Ni.sub.2P@mSiO.sub.2, both the TOP and OA were in excess so the influence of the amount of precursor was not an accountable parameter here.
[0317] The resulting composite is mixed with OA and TOP in order to initiate the phosphorization. The surfactant CTAB in the silica skeleton slowly decomposes when the as the temperature exceeds 250° C., thereby exposing the Ni precursor to P insertion, and the phosphorization occurs simultaneously. Due to the confinement effect of the stable mesoporous silica matrix, the Ni.sub.2P crystals can only grow within the honeycomb channels which are less than 2 nm width. Hence, the phase transfer from Ni to Ni.sub.2P can be completed after 2 hours heating at 300° C. while also ensuring that the Ni.sub.2P nano cluster size remains in a range that is less than about 2 nm. From the EDX analysis, the atomic ratio of Ni precursor in SiO.sub.2 is about 5%, and Ni.sub.2P loading in SiO.sub.2 is about 3.5%, as shown in the following Table 10:
TABLE-US-00010 TABLE 10 Compositional analysis of catalysts before and after performance testing Atomic Ratio*.sup.a Before Performance Test After Performance Test Sample Name Ni/P Ni/(Ni + Si) S/Ni Ni/P Ni/(Ni + Si) S/Ni u-Ni.sub.2P@m-SiO.sub.2 0.5 7% 0% 0.5 10% 0% n-Ni.sub.2P 2.2 100% 0% 1.8 100% 1.7% u-Ni@m-SiO.sub.2 N/A 5% 0% N/A 6% 5.3% c-Ni.sub.2P 2.0 100% 0% 1.8 100% 0.1% *.sup.aAverage data from 5 measurements, error = 2%.
Compared to the c-Ni.sub.2P and n-Ni.sub.2P, the u-Ni.sub.2P@m-SiO.sub.2 shows a much higher P ratio. Based on the XPS and NMR analysis, it is clear that the excess P reacted with SiO.sub.2 during the phosphorization step, leading to the formation of phosphate species on the surface of SiO.sub.2.
Catalytic Performance
[0318]
[0319]
[0320]
[0321] Tables 11 and 12 below illustrate the superior performance of the u-Ni.sub.2P@m-SiO.sub.2 and n-Ni.sub.2P catalysts in reducing SO.sub.2 to sulfur with H.sub.2 as compared to various known catalysts.
TABLE-US-00011 TABLE 11 summary of experimental parameters of inventive catalysts and known catalysts SO.sub.2 Flow Mass of Active Synthesis Space SO.sub.2/H.sub.2 SO.sub.2 Rate Catalyst Component Catalyst Method Velocity (mol/mol) (ppm) (mL/min) (g) (wt %) Co—Mo/Al.sub.2O.sub.3 Commercially WHSV = 1/3 10.sup.6 2.5 2 11 & presulfided 3000 mL/g/h Fe/γ-Al.sub.2O.sub.3 Impregnation & GHSV = 1/2 10.sup.6 3 2 10 presulfided 3600/h Co/γ-Al.sub.2O.sub.3 Impregnation & GHSV = 1/2 10.sup.6 3 2 10 presulfided 3600/h Ni/r-Al.sub.2O.sub.3 Impregnation & GHSV = 1/2 10.sup.6 3 2 10 presulfided 3600/h Ru@TiO.sub.2 Impregnation & WHSV = 1/2 10.sup.6 20 0.4 1.5 presulfided 9000 mL/g/h NiO/r-Al.sub.2O.sub.3 Impregnation & WHSV = 1/2 12000 14 0.5 16 presulfided 5040 mL/g/h SnO.sub.2—ZrO.sub.2 Precipitate GHSV = 1/2 20000 55 0.5 100 10000/h u-Ni.sub.2P@m-SiO.sub.2 One-pot & GHSV = 1/200 103 20 0.04 6 Phosphorization ~5000/h WHSV = 60000 mL/g/h n-NiP Phosphorization GHSV = 1/200 103 20 0.04 100 ~50000/h WHSV = 60000 mL/g/h u-Ni@m-SiO.sub.2 One-pot GHSV = 1/200 103 20 0.04 3 ~50000/h WHSV = 60000 mL/g/h c-Ni.sub.2P Commercial GHSV = 1/200 103 20 0.04 100 ~5000/h WHSV = 60000 mL/g/h
TABLE-US-00012 TABLE 12 summary of catalytic performance of inventive catalysts and known catalysts T SO.sub.2 Conv. Sulfur Select. TOF Catalyst (° C.) (%) (%) (10.sup.−6/s) Co—Mo/Al.sub.2O.sub.3 300 84.2 95.4 573 Fe/γ-Al.sub.2O.sub.3 300 44.9 95.2 256 Co/γ-Al.sub.2O.sub.3 300 66.7 93.7 402 Ni/r-Al.sub.2O.sub.3 300 63.9 91.9 353 Ru@TiO.sub.2 300 90.2 100 206988*.sup.b NiO/r-Al.sub.2O.sub.3 320 98 69 82 SnO.sub.2—ZrO.sub.2 550 98 55 208 u-Ni.sub.2P@m-SiO.sub.2 220 93.8 98.9 81 320 99.6 96.8 87 n-Ni.sub.2P 220 43.1 100 2 320 93.8 100 5 u-Ni@m-SiO.sub.2 220 18.2 100 8 320 7.1 100 3 c-Ni.sub.2P 220 0.0 100 0 320 12.6 97.5 1 *.sup.bThis high value is caused by the feed gas of SO.sub.2 which had a high flow rate of 99.9% purity SO.sub.2 gas without dilution
[0322] The GHSV employed in this work is by far higher than known catalysts (5-20 times higher), which provides for smaller reactors and lower operating and capital costs. In addition, the performance of the CoMoS/Al.sub.2O.sub.3 commercial catalyst is given in
Spent Catalyst Characterization
[0323] To assess catalyst structural and morphological changes due to the reaction conditions, spent catalysts of the samples u-Ni.sub.2P@m-SiO.sub.2 and u-Ni@m-SiO.sub.2 were characterized using TEM imaging, TEM/EDX elemental analysis and XRD.
[0324]
[0325] The XRD patterns of the above samples are presented in
[0326] The XRD patterns for the fresh samples and the spent samples were similar, except for the strong peak of quartz which was mixed with the catalysts during the performance test. The peaks at 2θ of 20.9° (100), 26.6° (101), 36.5° (110), 40.3° (111), 42.4° (200), 45.8° (201), 50.1° (112), 54.9° (202), 60.0° (211), and 67.70 (212) corresponds to the typical quartz characteristic peaks (PDF #46-1045). This suggests the absence of any structural changes experienced by the catalysts during use. A comparison of the STEM-HAADF/EDS elemental mapping in
Assessment of Reaction Kinetics
[0327] The average reaction rate in units μmols of SO.sub.2 per second per gram of active catalysts (Ni.sub.2P or Ni) was computed based on the Ni.sub.2P loading in SiO.sub.2. Hence the results reflect the activity per site.
Conclusions
[0328] Highly active mesoporous SiO.sub.2 confined ultrafine Ni.sub.2P nano cluster was synthesized by the phase conversion method in OA and TOP at 300° C. for the enhancement of the catalytic reduction of SO.sub.2 to sulfur in the presence of H.sub.2. The Ni precursor was dispersed in the mesoporous SiO.sub.2 matrix before phosphorization. The honeycomb channels in the SiO.sub.2 matrix provide a stable confined crystal grow space, thus facilitating the formation of ultrafine Ni.sub.2P nano clusters of sizes less than 2 nm. The XRD patterns show the typical Ni.sub.2P broad peaks and the TEM images reveal the ordered fingerprint 2D hexagonal honeycomb pores of MCM-41. The NMR study indicates that this ultrafine Ni.sub.2P catalysts exhibits a higher ratio of energetically favored Ni.sub.3P.sub.2 terminations. XPS and UV-DRS studies demonstrated that phosphate species are also formed on the surface. Compared to the commercial bulk Ni.sub.2P and the 11 nm Ni.sub.2P nano particles, the mesoporous SiO.sub.2 confined ultrafine Ni.sub.2P nano clusters display a high activity for the SO.sub.2 reduction to sulfur in H.sub.2 (94% SO.sub.2 conversion at 220° C. and ˜99% at 240° C., >97% selectivity to sulfur, GHSV=˜50000/h, WHSV=60000 mL/g/h), and the ultrafine Ni.sub.2P nano clusters significantly reduces the activation energy of the SO.sub.2 hydrogenation. This mesoporous SiO.sub.2 confined nano crystal phase transfer method provides a new strategy for the high dispersion ultrafine nano crystal catalyst synthesis as well as the active site phase and size control, achieving catalysts of great potential for the other transition metal phosphide and the industry application.