Alkaline earth metal/metal oxide supported catalysts

Abstract

Disclosed is a hydrocarbon gas reforming supported catalyst, and methods for its use, that includes a catalytic material capable of catalyzing the production of a gaseous mixture comprising hydrogen and carbon monoxide from a hydrocarbon gas, and a support material comprising an alkaline earth metal/metal oxide compound having a structure of D-E, wherein D is a M.sub.1 or M.sub.1M.sub.2, M.sub.1 and M.sub.2 each individually being an alkaline earth metal selected from the group consisting of Mg, Ca, Ba, and Sr, E is a metal oxide selected from the group consisting of Al.sub.2O.sub.4, SiO.sub.2, ZrO.sub.2, TiO.sub.2, and CeO.sub.2, wherein the catalytic material is attached to the support material.

Claims

1. A hydrocarbon gas reforming supported catalyst comprising: (a) a catalytic material capable of catalyzing the production of a gaseous mixture comprising hydrogen and carbon monoxide from a hydrocarbon gas; and (b) a support material comprising an alkaline earth metal/metal oxide compound having a structure of D-E, wherein D is a M.sub.1 or M.sub.1M.sub.2, M.sub.1 and M.sub.2 each individually being an alkaline earth metal selected from the group consisting of Mg, Ca, Ba, and Sr, and E is a metal oxide selected from the group consisting of Al.sub.2O.sub.4, SiO.sub.2, ZrO.sub.2, TiO.sub.2, and CeO.sub.2, wherein the catalytic material is chemically bonded to the support material, and wherein the chemical bond is a M1-O bond, where M1 is a metal from the catalyst and oxygen (O) is from the alkaline earth metal/metal oxide compound from the support material.

2. The hydrocarbon gas reforming supported catalyst of claim 1, wherein D is M.sub.1 and E is Al.sub.2O.sub.4.

3. The hydrocarbon gas reforming supported catalyst of claim 2, wherein the compound is MgAl.sub.2O.sub.4, CaAl.sub.2O.sub.4, BaAl.sub.2O.sub.4, or SrAl.sub.2O.sub.4.

4. The hydrocarbon gas reforming supported catalyst of claim 3, wherein the compound is MgAl.sub.2O.sub.4.

5. The hydrocarbon gas reforming supported catalyst of claim 1, wherein D is M.sub.1M.sub.2 and E is Al.sub.2O.sub.4.

6. The hydrocarbon gas reforming supported catalyst of claim 5, wherein M.sub.1M.sub.2 is MgCa, MgBa, MgSr, BaCa, BaSr, or CaSr.

7. The hydrocarbon gas reforming supported catalyst of claim 1, wherein the supported catalyst comprises at least 1% or more by weight of the catalytic material.

8. The hydrocarbon gas reforming supported catalyst of claim 7, wherein the supported catalyst comprises at least 80% or more by weight of the support material.

9. The hydrocarbon gas reforming supported catalyst of claim 8, wherein the supported catalyst comprises 5% to 50% by weight of the catalytic material and 95% to 50% by weight of the support material.

10. The hydrocarbon gas reforming supported catalyst of claim 1, wherein the support material is in particulate or powdered form.

11. The hydrocarbon gas reforming supported catalyst of claim 10, wherein the particle size of the support material ranges from 5 to 300 m.

12. The hydrocarbon gas reforming supported catalyst of claim 1, wherein the support material is in non-powdered form or has a fabricated geometry.

13. The hydrocarbon gas reforming supported catalyst of claim 12, wherein the fabricated geometry is a pellet, foam, honeycomb, or monolith.

14. The hydrocarbon gas reforming supported catalyst of claim 1, wherein the catalytic material is a metal catalyst or a metal oxide catalyst.

15. The hydrocarbon gas reforming supported catalyst of claim 14, wherein the metal catalyst or metal oxide catalyst comprises Pt, Pd, Au, Ag, Ir, Ni, Co, Rh, Ru, La, Mg, Ca, Sr, Ba, Li, Na, K, Fe, Sn, Cu, Zn, Zr, Mo, Nb, Bi, or Mn, or any combination thereof.

16. The hydrocarbon gas reforming supported catalyst of claim 15, wherein the metal catalyst comprises Ni, Pt, Rh, or Ru or any combination thereof.

17. The hydrocarbon gas reforming supported catalyst of claim 15, wherein the catalyst comprises Ni and Pt and the catalyst has the following formula: 7.5 wt. % Ni/2.5 wt. % Pt/MgAl.sub.2O.sub.4.

18. The hydrocarbon gas reforming supported catalyst of claim 15, wherein the catalyst comprises Ni and Rh and the catalyst has the following formula: 7.5 wt. % Ni/2.5 wt. % Rh/MgAl.sub.2O.sub.4.

19. The hydrocarbon gas reforming supported catalyst of claim 1, wherein the catalytic material comprises La and Ni and the support material comprises MgAl.sub.2O.sub.4.

20. The hydrocarbon gas reforming supported catalyst of claim 19, wherein the catalyst has the following formula: 11.5 wt. % La/4.8 wt. % Ni/MgAl.sub.2O.sub.4.

21. The hydrocarbon gas reforming supported catalyst of claim 1, wherein the catalytic material is dispersed on the surface of the support material.

22. The hydrocarbon gas reforming supported catalyst of claim 1, wherein the supported catalyst is capable of reducing carbon formation on the surface of said supported catalyst when subjected to temperatures at a range of greater than 700 C. to 1100 C.

23. The hydrocarbon gas reforming supported catalyst of claim 1, wherein the supported catalyst is capable of reducing sintering of the catalytic material or of the support material when subjected to temperatures at a range of greater than 700 C. to 1100 C.

24. The hydrocarbon gas reforming supported catalyst of claim 1, wherein the catalytic material comprises a pyrochlore of:
A.sub.xB.sub.y-zC.sub.zO.sub.7 wherein, A is a trivalent ion of an element of La, Ce, Nd, Bi, Sc, or Y, where 0x2, B is a tetravalent ion of an element of Zr, Pt, Pd, Ni, Mo, Rh, Ru, or Ir, where 0y-z2, C is a bivalent, trivalent or tetravalent ion of Ba, Ca, Cu, Mg, Ru, Rh, Pt, Pd, Ni, Co, or Mo, where 0z2.

25. The hydrocarbon gas reforming supported catalyst of claim 1, wherein the catalytic material comprises La.sub.2Ni.sub.0.11Zr.sub.1.89O.sub.7 and the support material comprises MgAl.sub.2O.sub.4.

26. The hydrocarbon gas reforming supported catalyst of claim 1, wherein the hydrocarbon gas is methane.

27. The hydrocarbon gas reforming supported catalyst of claim 1, wherein the catalyst is not Ni/MgAl.sub.2O.sub.4.

28. A method of producing the hydrocarbon gas reforming supported catalyst of claim 1 comprising: obtaining a compositions comprising (a) a continuous phase comprising a solvent and a catalytic material capable of catalyzing the production of a gaseous mixture comprising hydrogen and carbon monoxide from a hydrocarbon gas, wherein the catalytic material is solubilized in the solvent; and (b) a dispersed phase comprising an alkaline earth metal/metal oxide compound in powdered or particulate form, said compound having a structure of D-E, wherein D is a M.sub.1 or M.sub.1M.sub.2, M.sub.1 and M.sub.2 each individually being an alkaline earth metal selected from the group consisting of Mg, Ca, Ba, and Sr, and E is a metal oxide selected from the group consisting of Al.sub.2O.sub.4, SiO.sub.2, ZrO.sub.2, TiO.sub.2, and CeO.sub.2; and evaporating the solvent from said composition, wherein the hydrocarbon gas reforming supported catalyst is produced, and wherein the catalytic material is chemically bonded to the support material, and wherein the chemical bond is a M1-O bond, where M1 is a metal from the catalyst and oxygen (O) is from the alkaline earth metal/metal oxide compound from the support material.

29. A method of catalytically reforming a reactant gas mixture comprising: (a) providing a reactant gas mixture comprising a hydrocarbon and an oxidant; (b) providing the hydrocarbon gas reforming supported catalyst of claim 1; and (c) contacting the reactant gas mixture with the hydrocarbon gas reforming supported catalyst under conditions sufficient to produce a gaseous mixture comprising carbon monoxide and hydrogen.

30. The method of claim 29, wherein the hydrocarbon comprises methane and the oxidant comprises carbon dioxide or a mixture of carbon dioxide and oxygen.

31. The method of claim 30, wherein the ratio of carbon monoxide to hydrogen in the produced gaseous mixture is approximately 1.

32. The method of claim 31, wherein the hydrocarbon comprises methane and the oxidant comprises water.

33. The method of claim 32, wherein the water is water vapor.

34. The method of claim 33, wherein the ratio of carbon monoxide to hydrogen in the produced gaseous mixture is approximately 0.33.

35. The method of claim 29, further comprising contacting the reactant gas mixture with the hydrocarbon gas reforming supported catalyst at a temperature ranging from 700 C. to 1100 C., at a pressure ranging from 1 bara to 30 bara, and at a gas hourly space velocity (GHSV) ranging from 500 to 10000 h.sup.1.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1: Illustration of various products that can be produced from syngas.

(2) FIG. 2: X-ray diffractogram of (A) 20 wt % La.sub.2Ni.sub.0.11Zr.sub.1.89O.sub.7 on MgAl.sub.2O.sub.4 and (B) 11.5 wt % La and 4.8 wt % Ni on MgAl.sub.2O.sub.4.

(3) FIG. 3: CO.sub.2 reforming of methane 11.5 wt % La and 4.8 wt % Ni on MgAl.sub.2O.sub.4 catalysts at 900 C. and 1 bara, GHSV=5000 h.sup.1.

(4) FIG. 4: Performance of 10% Ni/MgAl.sub.2O.sub.4 catalyst: CH.sub.4 and CO.sub.2 conversion; and H.sub.2/CO ratio obtained at 800 C., 1 bara and GHSV=73,000 h.sup.1. Gas mixture containing 45% CH.sub.4+45% CO.sub.2+10% Ar was used as feed.

(5) FIG. 5: Performance of 7.5% Ni+2.5% Pt/MgAl.sub.2O.sub.4 catalyst: CH.sub.4 and CO.sub.2 conversion; and H.sub.2/CO ratio obtained at 800 C., 1 bara and GHSV=73,000 h.sup.1. Gas mixture containing 45% CH.sub.4+45% CO.sub.2+10% Ar was used as feed.

(6) FIG. 6: Performance of 7.5% Ni+2.5% Rh/MgAl.sub.2O.sub.4 catalyst: CH.sub.4 and CO.sub.2 conversion; and H.sub.2/CO ratio obtained at 800 C., 1 bara and GHSV=73,000 h.sup.1. Gas mixture containing 45% CH.sub.4+45% CO.sub.2+10% Ar was used as feed.

DETAILED DESCRIPTION OF THE INVENTION

(7) The currently available catalysts used to reform hydrocarbons into syngas are prone to coking and sintering, both of which can lead to inefficient catalyst performance and ultimately failure of the catalyst after relatively short periods of use. This can lead to inefficient syngas production as well increased costs associated with its production.

(8) A discovery has been made that avoids the coking and sintering issues described above. The discovery is based on the use of the alkaline earth metal/metal oxide compounds as a support for the catalytic material. Without wishing to be bound by theory, it is believed that the basicity of these compounds allow for the efficient adsorption of carbon dioxide while also suppressing carbon deposition on the surface of the catalysts of the present invention, thereby reducing the incidence of coking and sintering when the catalysts of the present invention are used to produce syngas.

(9) These and other non-limiting aspects of the present invention are discussed in further detail in the following sections.

(10) A. Alkaline Earth Metal/Metal Oxide Support

(11) The support material of the present invention can include an alkaline earth metal/metal oxide such as one having the following general structure: D-E, where D is a M.sub.1 or M.sub.1M.sub.2, and M.sub.1 and M.sub.2 are each individually an alkaline earth metal selected from the group consisting of Mg, Ca, Ba, and Sr, and E is a metal oxide selected from the group consisting of Al.sub.2O.sub.4, SiO.sub.2, ZrO.sub.2, TiO.sub.2, and CeO.sub.2. Specific compounds are disclosed above and throughout this specification. These compounds are commercially available from a wide range of sources (e.g., Sigma-Aldrich Co. LLC (St. Louis, Mo., USA); Alfa Aesar GmbH & Co KG, A Johnson Matthey Company (Germany)).

(12) Alternatively, the support materials can be made by the process used in the examples section of this specification or by processes known to those of ordinary skill in the art (e.g., precipitation/co-precipitation, sol-gel, templates/surface derivatized metal oxides synthesis, solid-state synthesis, of mixed metal oxides, microemulsion technique, solvothermal, sonochemical, combustion synthesis, etc.).

(13) B. Catalytic Materials

(14) It is contemplated that any of the known catalytic materials that are currently used in producing syngas from hydrocarbons can be used in the context of the present invention. Such catalytic materials can be supported by the clay minerals discussed above and throughout this specification, thereby resulting in a hydrocarbon gas reforming clay mineral supported catalyst of the present invention. Non-limiting examples of such catalysts can include metal catalysts (e.g., Pt, Pd, Au, Ag, Ir, Ni, Co, Rh, Ru, La, Mg, Ca, Sr, Ba, Li, Na, K, Fe, Sn, Cu, Zn, Zr, Mo, Nb, Bi, or Mn, or any combination thereof), metal oxide catalysts (e.g., La.sub.2O.sub.3, Ru.sub.2O.sub.3, CeO.sub.2, ZrO.sub.2, ZnO, MoO.sub.3, WO.sub.3, Nb.sub.2O.sub.5, and/or Ta.sub.2O), pyrochlore catalysts, and other known catalysts used in the production of syngas from hydrocarbons (e.g., perovskites type solid solutions, various metals like Pt, Pd, Ir, Ni, Co, Rh, Ru, La, Mg, Ca, Sr, Ba, Fe, Sn, Cu, or Zn supported on various metal oxides such as Al.sub.2O.sub.3, SiO.sub.2, SBA-15, MCM-40, TiO.sub.2, ZrO.sub.2, CeO.sub.2, etc.). Non-limiting examples of pyrochlore catalysts include those having the following structure:
A.sub.xB.sub.y-zC.sub.zO.sub.7
wherein, A is a trivalent ion of an element of La, Ce, Nd, Bi, Sc, or Y, where 0x2, B is a tetravalent ion of an element of Zr, Pt, Pd, Ni, Mo, Rh, Ru, or Ir, where 0y-z2, C is a bivalent, trivalent or tetravalent ion of Ba, Ca, Cu, Mg, Ru, Rh, Pt, Pd, Ni, Co, or Mo, where 0z2.
C. Methods of Making and Using the Alkaline Earth Metal/Metal Oxide Supported Catalysts

(15) The alkaline earth metal/metal oxide supported catalysts of the present invention can be made by processes known in the art that provide attachment of the catalytic material to the surface of the alkaline earth metal/metal oxide compounds. The attachment can be through chemical bonds or physical bonds or both. In particular instances, the bonds can be M1-M2 bonds (where M1 is a metal from the catalyst and M2 is a metal from the alkaline earth metal/metal oxide compound) or M1-O bonds (where M1 is a metal from the catalyst and O is oxygen from alkaline earth metal/metal oxide compound).

(16) In addition to known methods, it has been discovered that the following process could be used to prepare the alkaline earth metal supported catalysts of the present invention: 1. Preparation of a dispersion: (a) Obtain a solution that includes a solvent (e.g., any solvent that can solubilize the catalytic materialnon-limiting examples include water, methanol, ethanol, propanol, isopropanol, butanol, or mixtures thereof) and a catalytic material dissolved in said solvent. (b) Obtain an alkaline earth metal/metal oxide compound, such as one described above. It can be in particulate or powdered form. (c) Mix the compound with the solvent to create a dispersion, where the continuous phase includes the solution and the discontinuous/dispersed phase includes the compound. Mixing can occur for a period of time to create the dispersion and to contact the alkaline earth metal/metal oxide compound with the catalytic material. In one non-limiting aspect, the mixing time can occur for 5, 10, 15, 20, 25, 30, 40, 50, 60, or more minutes. In particular instances, the mixing can occur for about 10 to about 20 minutes or about 15 minutes. Any type of mixing apparatus can be used. (d) Optionally, additional materials or ingredients or other alkaline earth metal/metal oxide compounds can be added to stabilize the dispersion, modify the resulting catalyst or clay mineral, etc. For instance, a chelating agent (e.g., citric acid, EDTA, disodium EDTA, trisodium EDTA, EGTA, phosphoric acid, succinic acid, etc.) can be added to keep the metal ions apart during the initial stages of synthesis, which leads to the formation of smaller particles in catalysts. Smaller particles can result in higher surface area and pore volume which can have a positive effect on the activity of the catalysts of the present invention. 2. Processing of the dispersion to create a catalyst: (a) Subject the dispersion to a drying step such that the solvent is removed. An evaporation apparatus such as a rotary evaporator can be used. The resulting sample is dried and in powdered or particulate form. (b) The sample from (a) can then be subjected to a calcination step. Such a step can include placing the sample in a ceramic crucible and subjecting it to heat (e.g., from a muffle furnace). The sample can first be subjected to a temperature of 150 C. for 2 hours followed by 900 C. for 8 hours, with the temperature increasing at a rate of 10 C./minutes.

(17) The obtained material can then be used as a catalyst to produce syngas. It is believed that no coking or sintering will be observed when the catalyst is used at temperatures of at least 800 C., whereas coking may be observed at temperatures of 700 C. Therefore, the reaction temperature for syngas production using the catalysts of the present invention can be a range of greater than 700 C. to 1100 C. or a range from 725 C., 750 C., 775 C., or 800 C. to 900 C., 1000 C., or 1100 C. In particular instances, the range can be from 800 C. to 1000 C. or from 800 C. to 1100 C. In addition to temperature, a pressure range from 1 bara to 30 bara, and/or at a gas hourly space velocity (GHSV) range from 500 to 10000 h.sup.1 can be used as the reaction conditions for producing syngas from a hydrocarbon material and the catalysts of the present invention.

(18) A benefit of this process of making and using the catalyst is its simplicity and ease of scalability for industrial/large scale applications.

(19) The carbon dioxide in the gaseous feed mixture used in the process of the invention can be obtained from various sources. In one non-limiting instance, the carbon dioxide can be obtained from a waste or recycle gas stream (e.g. from a plant on the same site, like for example from ammonia synthesis) or after recovering the carbon dioxide from a gas stream. A benefit of recycling such carbon dioxide as starting material in the process of the invention is that it can reduce the amount of carbon dioxide emitted to the atmosphere (e.g., from a chemical production site). The hydrogen in the feed may also originate from various sources, including streams coming from other chemical processes, like ethane cracking, methanol synthesis, or conversion of methane to aromatics. The gaseous feed mixture comprising carbon dioxide and hydrogen used in the process of the invention may further contain other gases, provided that these do not negatively affect the reaction. Examples of such other gases include steam or oxygen. The hydrocarbon material used in the reaction can be methane.

(20) The resulting syngas can then be used in additional downstream reaction schemes to create additional products. FIG. 1 is an illustration of various products that can be produced from syngas. Such examples include chemical products such as methanol production, olefin synthesis (e.g. via Fischer-Tropsch reaction), aromatics production, carbonylation of methanol, carbonylation of olefins, the reduction of iron oxide in steel production, etc.

EXAMPLES

(21) The present invention will be described in greater detail by way of specific examples. The following examples are offered for illustrative purposes only, and are not intended to limit the invention in any manner. Those of skill in the art will readily recognize a variety of noncritical parameters which can be changed or modified to yield essentially the same results.

Example 1

Synthesis of MgAl2O4Supported Catalysts

(22) The following procedure was used to synthesize 10 wt. % of La.sub.2Ni.sub.0.11Zr.sub.1.89O.sub.7 pyrochlore catalysts grafted on a MgAl.sub.2O.sub.4 support: 0.8 g of La (NO.sub.3).sub.3.6H.sub.2O, 0.4 g of ZrCl.sub.4, 0.02 g of NiCl.sub.2.6H.sub.2O was dissolved in 7.5 ml of de-ionized water to form a clear solution. 0.4 g of citric acid was added to the above solution. To this 5.1 g of MgAl.sub.2O.sub.4 powder was added and transferred the flask to the Rota evaporator. The material was allowed to mix in the Rota evaporator for 15 minutes and then evaporated the solvent under vacuum until the sample got dried completely. The MgAl.sub.2O.sub.4 powder was prepared as follows: equimolar solutions of an alkaline earth metal salt (12.81 g Mg(NO.sub.3).sub.2.6H.sub.20 in 50 ml of H.sub.2O) and aluminium nitrate (37.51 g Al(NO.sub.3).sub.3.9H.sub.2O in 50 mL of H.sub.2O) were mixed in a 500 mL beaker. To this solution, 27% v/v ammonium hydroxide solution was added drop wise under vigorous stirring until the pH of the slurry reached 9.8-10. After complete precipitation, stirring was continued for 1 hour. Thereafter, the precipitated slurry was digested in a water bath for 12 hours at 80 C. The residue was separated by centrifugation, washed six times with 200 mL portions of water to eliminate any residual ions. The residue was dried at 120 C. for 12 hours followed by calcination at 800 C. for 8 hours. The produced 10 wt. % of La.sub.2Ni.sub.0.11Zr.sub.1.89O.sub.7 pyrochlore catalyst supported on MgAl.sub.2O.sub.4 was determined to have a surface area of 42.8 m.sup.2/g.

(23) A 20 wt. % of La.sub.2Ni.sub.0.11Zr.sub.1.89O.sub.7 on MgAl.sub.2O.sub.4 supported catalyst and a 11.5 wt. % La and 4.8 wt. % Ni on MgAl.sub.2O.sub.4 supported catalyst were each prepared by using the above procedure as well. The presence of diffraction peaks at 2 equal to 29.64, 31.9 and 59.84 in FIG. 2 A confirms the presence of pyrochlore phase, and peaks at 2 equal to 37.42, 45.38 and 65.78 confirms the MgAl.sub.2O.sub.4 phase in the catalyst (FIGS. 2A and B). The other peaks in (A) are because of La and Ni bimetallic phases in oxidized state.

(24) The following procedure was used to synthesize 10 wt. % CeO.sub.2/2 wt. % Pt catalyst supported on a MgAl.sub.2O.sub.4 support. The catalyst was synthesized by a two-step incipient wetness impregnation technique. First, the 10 wt. % CeO.sub.2/2 wt. % Pt catalytic material was synthesized in a two-step process. In the first step 0.17 g of tetrammine platinum chloride hydrate salt was dissolved in pore volume equivalent of water and impregnated with dried 4.9 g of MgAl.sub.2O.sub.4. The resultant product was first dried at 125 C. for 2 hours followed by calcination at 200 C. for 4 hours. In a second step, a required amount of 0.5 g of cerium ammonium nitrate salt was dissolved in pore volume equivalent of water and impregnated with Pt/MgAl.sub.2O.sub.4 sample. The resultant mixture was first dried at 150 C. for 2 hours followed by calcination at 900 C. for 8 hours. Notably, greater than 10 wt. % of CeO.sub.2 loaded catalysts can be prepared by changing the amount of cerium precursor. Also, the noble metal Pt can be replaced with Pd, Ni, Co, Fe, Cu, Zn, Mo, Rh, Ru, and Ir, with weight loading ranging from 0.1 to 30%.

(25) The above procedures can be used to create the various alkaline earth metal/metal oxide supported catalysts of the present invention by modifying the ingredients and amounts of said ingredients. For instance, 10 wt. % Ni/MgAl.sub.2O.sub.4, 7.5 wt. % Ni+2.5 wt. % Rh/MgAl.sub.2O.sub.4, and 7.5 wt. % Ni+2.5% Pt/MgAl.sub.2O.sub.4 catalysts were prepared in these manner (Example 3).

Example 2

Catalytic Activity of 11.5% La+4.8% Ni/MgAl2O4

(26) The ability of the 11.5 wt. % La and 4.8 wt. % Ni on MgAl.sub.2O.sub.4 supported catalyst for use in a CO.sub.2 reforming of methane reaction was tested according to the following procedure. A sufficient amount of catalyst was loaded into the quartz reactor. The temperature was raised to 900 C. in the presence of nitrogen atmosphere. After reaching isothermal conditions a gas mixture of 10% CH.sub.4+10% CO.sub.2+80% N.sub.2 was fed into the reactor. The outlet gas composition was measured using gas chromatograph over the duration of the reaction. The reaction pressure was 1 bara and the GHSV used was 5000 h.sup.1.

(27) The 11.5 wt. % La and 4.8 wt. % Ni supported on MgAl.sub.2O.sub.4. catalyst was found to be very active for more than 40 hours of operation without any coke formation (FIG. 3). The absence of coke was confirmed by using Transmission electron spectroscopy and Temperature programmed oxidation experiments.

Example 3

Catalytic Activity of 10% Ni/MgAl2O4, 7.5% Ni+2.5% Rh/MgAl2O4, and 7.5% Ni+2.5% Pt/MgAl2O4

(28) The ability of three catalysts (10 wt. % Ni/MgAl.sub.2O.sub.4), (7.5 wt. % Ni+2.5% Rh/MgAl.sub.2O.sub.4), and (7.5 wt. % Ni+2.5% Pt/MgAl.sub.2O.sub.4) were tested for CO.sub.2 reforming of methane at 800 C. and 1 bara pressure according to the following procedures.

(29) Catalysts testing were performed in a highthroughput reactor system supplied by HTE, Germany. Reactors were of plug flow type and made up of steel SS316, with an inner ceramic liner. Ceramic liner with 5 mm in diameter and 55 cm in length was used to avoid coking due to methane cracking on steel surface. The gas between the inner steel surface and outer ceramic liner wall was sealed with the help of leak proof graphite ferrule, which ensures 100% feed gas passes through ceramic liner containing catalyst and inert material. Catalyst pellets were crushed and sieved between 100-300 m. Catalyst sieve fraction was placed on top of inert material inside the ceramic liner. A mixture of (45% CO.sub.2+45% CH.sub.4+10% Ar) was used as feed. Argon was used as an internal standard for GC analysis. The catalyst in oxidized state was heated to 800 C. in the presence of (90% N.sub.2+10% Ar). The (CH.sub.4+CO.sub.2) mixture was dosed in 4 steps with 5 minutes intervals replacing equivalent amount of nitrogen in each step. All catalysts were tested at 800 C., 1 bar pressure and approximately gas hourly space velocity (GHSV)=25,000 h.sup.1. After reaching feed composition of (45% CO.sub.2+45% CH.sub.4+10% Ar), gas analysis was started after 1 hour of equilibration time. Agillent GC 7867 was used for gas analysis. Methane and CO.sub.2 conversion was calculated as follows:

(30) $\mathrm{Methane}\mathrm{conversion}=\frac{\mathrm{mol}\mathrm{of}\mathrm{methane}\mathrm{converted}}{\mathrm{mol}\mathrm{of}\mathrm{methane}\mathrm{in}\mathrm{feed}}100$$\mathrm{Carbon}\mathrm{dioxide}\mathrm{conversion}=\frac{\mathrm{mol}\mathrm{of}\mathrm{carbon}\mathrm{dioxide}\mathrm{converted}}{\mathrm{mol}\mathrm{of}\mathrm{carbon}\mathrm{dioxide}\mathrm{in}\mathrm{feed}}100$

(31) The ratio of hydrogen to carbon monoxide is calculated as follows,

(32) $H2\text{/}\mathrm{CO}=\frac{\mathrm{mol}\mathrm{of}\mathrm{Hydrogen}\mathrm{in}\mathrm{product}}{\mathrm{mol}\mathrm{of}\mathrm{carbon}\mathrm{monoxide}\mathrm{in}\mathrm{product}}.$

(33) All three catalysts showed very good activity over a period of 150 hours (see FIGS. 4, 5, and 6). In the case of 10% Ni/MgAl.sub.2O.sub.4 (FIG. 4) and 7.5% Ni+2.5% Pt/MgAl.sub.2O.sub.4 (FIG. 5) the H.sub.2/CO ratio obtained was 0.75, whilst in the case of 7.5% Ni+2.5%16/MgAl.sub.2O.sub.4 (FIG. 6) it was 0.94. This is because of reverse water gas shift reaction (CO.sub.2+H.sub.2CO+H.sub.2O). The reverse water gas shift reaction is dependent on methane and CO.sub.2 conversion, at higher conversion shift reaction reaches equilibrium giving higher H.sub.2/CO ratio. So, H.sub.2/CO ratio is not catalyst specific. The H.sub.2/CO ratio near to 1 can be obtained by increasing the CH.sub.4 and CO.sub.2 conversion by decreasing the GHSV, h.sup.1 of the catalytic reaction.