Preparation method of mesoporous Fe—Cu-SSZ-13 molecular sieve

Abstract

A method of preparing a mesoporous Fe—Cu—SSZ-13 molecular sieve includes activating an aluminum source, a silicon source, an iron source and a copper source respectively; mixing the activated minerals with sodium hydroxide, water and a seed crystal at 25-90° C., while controlling feeding amounts of respective raw materials so that molar ratios of respective materials in a synthesis system are as follows: SiO.sub.2/Al.sub.2O.sub.3=10-100, SiO.sub.2/Fe.sub.2O.sub.3=30-3000, SiO.sub.2/CuO=1-100, Na.sub.2O/SiO.sub.2=0.1-0.5, H.sub.2O/SiO.sub.2=10-50, template/SiO.sub.2=0.01-0.5; adding an acid source to adjust pH of the system for first aging; and adding the acid source again to adjust the pH of the system for second aging to obtain aged gel; pouring an aged mixture into a kettle; cooling a crystallized product and filtering to remove a liquor; washing a filter cake; drying to obtain a solid; performing ion exchange; and filtering, washing and drying the solid to obtain powder; and placing the powder in a muffle furnace.

Claims

1. A method of preparing a mesoporous Fe-Cu-SSZ-13 molecular sieve, comprising the steps of: (1) activation of minerals: activating an aluminum source, a silicon source, an iron source and a copper source, respectively; (2) mixing the activated minerals with sodium hydroxide, water and a seed crystal at 25-90° C., while controlling feeding amounts of respective raw materials so that molar ratios of respective materials in a synthesis system are as follows: SiO.sub.2/Al.sub.2O.sub.3=10-100, SiO.sub.2/Fe.sub.2O.sub.3=30-3000, SiO.sub.2/CuO=1-100, Na.sub.2O/SiO.sub.2=0.1-0.5, H.sub.2O/SiO.sub.2:10-50, template/SiO.sub.2=0.01-0.5; adding an acid source after mixing to adjust pH of the system to 5-13 for first aging; and adding the acid source again to adjust the pH of the system to 5-13 for second aging to obtain aged gel; (3) pouring an aged mixture into a polytetrafluoroethylene-lined stainless-steel crystallization kettle for crystallization; after the crystallization is completed, cooling a crystallized product and filtering to remove a mother liquor; washing a filter cake with deionized water to neutrality; drying to obtain a solid; then performing ion exchange on the solid; and filtering, washing and drying the ion-exchanged solid to obtain powder, wherein the drying is performed at 80-150° C. overnight; and (4) placing the powder obtained in step (3) in a muffle furnace for roasting to obtain the Fe-Cu-SSZ-13 molecular sieve, wherein the content of Fe.sub.2O.sub.3 in the mesoporous Fe-Cu-SSZ-13 molecular sieve accounts for 0.1-10% of the total weight of the molecular sieve, in which the content of Fe in a framework accounts for more than 95% of a total iron content, and Fe is evenly distributed within the framework; the content of CuO in the molecular sieve accounts for 0.1-10% of the total weight of the molecular sieve, in which the content of Cu.sup.2+ accounts for more than 90% of a total copper content, and Cu.sup.2+ is evenly distributed on an inner surface of the molecular sieve; and the mesoporous Fe-Cu-SSZ-13 molecular sieve comprises the following raw materials: the deionized water, the aluminum source, the silicon source, the iron source, the copper source, the acid source, and the template; the aluminum source is one or a mixture of more of mica, alumite, bauxite, diatomite, rectorite, or natural zeolite; the silicon source is one or a mixture of more of bauxite, diatomite, rectorite, natural zeolite, or opal; the iron source is one or a mixture of more of bauxite, diatomite, rectorite, pyrite, mica hematite, or red mud; the copper source is one or a mixture of more of tenorite, bornite, magnetite, malachite, covellite, or chalcopyrite; the acid source is one or a mixture of more of 2-hydroxy-tricarballylic acid, sulfurous acid and nitrous acid, sulfuric acid, hydrochloric acid, nitric acid, oxalic acid, or acetic acid; and the template is one or a mixture of more of diaminomethylpyridine, diaminopropane, p-butylcyclohexanecarboxylic acid, methylediamine, tetraethylenepentamine.

2. The method according to claim 1, wherein both the first aging and the second aging in step (2) are carried out at 10-80° C. and both aging times are 2-12 h.

3. The method according to claim 2, wherein the roasting in step (3) lasts for −10 h, with a roasting temperature of 500-600° C.

4. The method according to claim 1, wherein in step (2), the molar ratios of respective materials in the synthesis system are as follows: SiO.sub.2/Al.sub.2O.sub.3=10-100, SiO.sub.2/Fe.sub.2O.sub.3=30-2550, SiO.sub.2/CuO=20˜100, Na.sub.2O/SiO.sub.2=0.1-0.5, H.sub.2O/SiO.sub.2=10˜50, and template/SiO.sub.2=0.01-0.5.

5. The method according to claim 4, wherein the roasting in step (3) lasts for −10 h, with a roasting temperature of 500-600° C.

6. The method according to claim 1, wherein the amount of the seed crystal added in step (2) is 1-15% of the total man of SiO.sub.2 in the synthesis system.

7. The method according to claim 1, wherein the crystallization in step (3) is carried out at 100-190° C., with a crystallization time of 12-120 h.

8. The method according to claim 1, wherein the ion exchange in step (3) comprises the sub-steps of performing ion exchange on the dried solid and 0.1-2M HNO.sub.3 solution at a mass ratio of 1:10 to 1:100, and heating and stirring at 10-80° C. for 3-8 h.

9. The method according to claim 1, wherein the roasting in step (3) lasts for 4-10 h, with a roasting temperature of 500-600° C.

10. An application of a Fe-Cu-SSZ-13 molecular sieve prepared by the method according to claim 1 is to selective catalytic reduction reactions of nitrogen oxides.

Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

(1) FIG. 1 is an X-ray diffraction (XRD) spectrum of a Fe—Cu—SSZ-13 molecular sieve prepared in Embodiment 1 of the invention; and

(2) FIG. 2 is a diagram showing the pore diameter distribution of the Fe—Cu—SSZ-13 molecular sieve prepared in Embodiment 1 of the invention.

DETAILED DESCRIPTION OF THE INVENTION

(3) The invention will be illustrated below in terms of implementation processes and beneficial effects in detail through specific embodiments, which is intended to help better understand the essence and characteristics of the invention and is not intended to limit the implementable scope of the invention.

Embodiment 1

(4) Preparation of Reagents

(5) Selection of minerals: the used rectorite, diatomite, bornite and tenorite are commercially available products. The rectorite includes the following main components in terms of content: 43.2 wt % of SiO.sub.2 is, 37.2 wt % of Al.sub.2O.sub.3, and 0.5 wt % of Fe.sub.2O.sub.3. The diatomite includes the following main components in terms of content: 93.2 wt % of SiO.sub.2, 3.3 wt % of Al.sub.2O.sub.3, and 1.5 wt % of Fe.sub.2O.sub.3. The bornite includes the following components in terms of content: 63.33 wt % of Cu, and 11.12 wt % of Fe. The tenorite includes 79.89 wt % of Cu in content.

(6) Activation of minerals: the commercially available diatomite was dried and crushed into powder, and 50.00 g of the diatomite powder was weighed and roasted at 800° C. for 4 hours for later use; the commercially available bornite was dried and crushed into powder, and 50.00 g of the bornite powder was weighed and roasted at 790° C. for 4 hours for later use; the commercially available tenorite was dried and crushed into powder, and 50.00 g of the tenorite powder was weighed and roasted at 850° C. for 4 hours for later use; and 60.00 g of rectorite, 72 g of sodium hydroxide, and 300 g of water were weighed, mechanically stirred at room temperature for 1 h, then activated in an oven at 255° C. for 12 h, and then crushed for later use.

(7) Preparation of the molecular sieve: 2.79 g of the activated rectorite and 4.04 g of the NaOH were weighed and dissolved in 50 g of deionized water; 6.5 g of TEPA was added dropwise; after stirring for 5 min, 6.7 g of the activated tenorite was added; after stirring for 1 h, 8.08 g of the diatomite was added; 1.2 g of sulfuric acid was added to adjust the pH to 11; then a resulting product was placed in a water bath at 70° C. for 4 h, and then cooled to room temperature; 1.3 g of sulfuric acid was added to adjust the pH to 10; and a resulting product was mixed and stirred at 35° C. for 4 h. A resulting mixture was poured into a polytetrafluoroethylene-lined stainless-steel crystallization kettle, and heated to 140° C. for static crystallization for 72 h. After the crystallization is completed, a resulting product was cooled and filtered to remove a mother liquor, then washed to neutrality, and dried at 120° C. to obtain a product of sodium-type Fe—Cu—SSZ-13 molecular sieve; the sodium-type Fe—Cu—SSZ-13 molecular sieve was exchanged with 0.2 M HNO3 at 80° C. for 6 h, and filtered to remove a mother liquor; and a filter cake was washed to neutrality with deionized water, and then dried to obtain a hydrogen-type Fe—Cu—SSZ-13 molecular sieve. The mesoporous pore diameter of the obtained sample is mainly concentrated at 40 nm; the specific surface area is 550 m.sup.2/g; the external specific surface area is 500 m.sup.2/g; and the content of Fe.sub.2O.sub.3 accounts for 1.5% of the total weight of the molecular sieve, with the iron content in the framework accounts for 95% of the total iron content. The CuO content is 4.5% of the total weight of the molecular sieve, with the content of bivalent copper ions accounting for 93% of the total copper content.

Embodiment 2

(8) This embodiment provides a Fe—Cu—SSZ-13 catalyst, and the preparation steps are the same as those in Embodiment 1, only with some parameters altered as follows:

(9) Preparation of the molecular sieve: 0.418 g of the activated rectorite and 1.11 g of the NaOH were weighed and dissolved in 50 g of deionized water; 5.255 g of TEPA was added dropwise; after stirring for 5 min, 0.34 g of Cu(NO.sub.3).sub.2 and 0.7 g of the activated tenorite was added; after stirring for 1 h, 4.3 g of the diatomite was added; 1 g of hydrochloric acid was added to adjust the pH to 13; then a resulting product was placed in a water bath at 60° C. for 4 h, and then cooled to room temperature; 2 g of hydrochloric acid was added to adjust the pH to 10; and a resulting product was mixed and stirred at 35° C. for 4 h. A resulting mixture was poured into a polytetrafluoroethylene-lined stainless-steel crystallization kettle, and heated to 140° C. for static crystallization for 72 h. After the crystallization is completed, a resulting product was cooled and filtered to remove a mother liquor, then washed to neutrality, and dried at 120° C. to obtain a product of sodium-type Fe—Cu—SSZ-13 molecular sieve; the sodium-type Fe—Cu—SSZ-13 molecular sieve was exchanged with 0.15 M HNO.sub.3 at 70° C. for 9 h, and filtered to remove a mother liquor; and a filter cake was washed to neutrality with deionized water, and then dried to obtain a hydrogen-type Fe—Cu—SSZ-13 molecular sieve. The mesoporous pore diameter of the obtained sample is mainly concentrated at 35 nm; the specific surface area is 560 m.sup.2/g; the external specific surface area is 420 m.sup.2/g; and the content of Fe.sub.2O.sub.3 accounts for 1% of the total weight of the molecular sieve, with the iron content in the framework accounts for 97% of the total iron content. The CuO content is 2% of the total weight of the molecular sieve, with the content of bivalent copper ions accounting for 90% of the total copper content.

Embodiment 3

(10) This embodiment provides a Fe—Cu—SSZ-13 catalyst, and the preparation steps are the same as those in Embodiment 1, only with some parameters altered as follows:

(11) Preparation of the molecular sieve: 2.28 g of the activated rectorite and 1 g of the NaOH were weighed and dissolved in 50 g of deionized water; 3 g of acetic acid was added to adjust the pH to 10; 5.3 g of TEPA was added dropwise; after stirring for 5 min, 0.234 g of the bornite was added; after stirring for 1 h, 2.73 g of the diatomite was added; 1.1 g of iron nitrate nonahydrate was added; then a resulting product was placed in a water bath at 70° C. for 4 h, and then cooled to room temperature; 1 g of acetic acid was added to adjust the pH to 11; and a resulting product was mixed and stirred at 35° C. for 4 h. A resulting mixture was poured into a polytetrafluoroethylene-lined stainless-steel crystallization kettle, and heated to 140° C. for static crystallization for 72 h. After the crystallization is completed, a resulting product was cooled and filtered to remove a mother liquor, then washed to neutrality, and dried at 120° C. to obtain a product of sodium-type Fe—Cu—SSZ-13 molecular sieve; the sodium-type Fe—Cu—SSZ-13 molecular sieve was exchanged with 0.15 M HNO.sub.3 at 70° C. for 9 h, and filtered to remove a mother liquor; and a filter cake was washed to neutrality with deionized water, and then dried to obtain a hydrogen-type Fe—Cu—SSZ-13 molecular sieve. The mesoporous pore diameter of the obtained sample is mainly concentrated at 35 nm; the specific surface area is 660 m.sup.2/g; the external specific surface area is 520 m.sup.2/g; and the content of Fe.sub.2O.sub.3 accounts for 6% of the total weight of the molecular sieve, with the iron content in the framework accounts for 97% of the total iron content. The CuO content is 3% of the total weight of the molecular sieve, with the content of bivalent copper ions accounting for 90% of the total copper content.

Embodiment 4

(12) In this embodiment, the catalyst prepared in Embodiment 1 was used in a fixed-bed reaction for activity testing, including the following steps:

(13) The catalyst A obtained in Embodiment 1 above was tabletted and sieved, and catalyst particles of 20-40 meshes were taken for activity evaluation. A catalyst activity evaluation device is an atmospheric-pressure micro fixed-bed reaction device, which is a reaction system composed of a gas mixing and preheating furnace and a reaction furnace, and a reactor is a quartz tube with an inner diameter of 7 mm. In the process of the experiment, the reaction was carried out in a temperature-programmed manner, with a temperature controller for controlling the temperature of the heating furnace. When reaching a data collection point, 30-minute stay was reserved for data processing and recording. Reaction conditions were as follows: 500 ppm of NO, 500 ppm of NH3, 5 v % of O.sub.2, N.sub.2 as a balance gas, the total gas flow being 600 mL/min, 200 mg of the catalyst used, and the reaction volume space velocity being 180000 h−1. The concentrations of NO, NH.sub.3 and NO.sub.2 were all qualitatively and quantitatively analyzed online by a flue gas analyzer (Testo340, Testo AG, German). The concentration of N.sub.2O was measured a Fourier transform infrared spectrometer (Nicolet iS50) equipped with a gas cell having a 2-m optical path.

Embodiment 5

(14) In this embodiment, the catalyst prepared in Embodiment 1 was used in a fixed-bed reaction for activity testing; and the steps were the same as those in Embodiment 4, with a parameter variation as follows: the catalyst was replaced by the catalyst prepared in Embodiment 2.

Embodiment 6

(15) In this embodiment, the catalyst prepared in Embodiment 1 was used in a fixed-bed reaction for activity testing; and the steps were the same as those in Embodiment 4, with a parameter variation as follows: the catalyst was replaced by the catalyst prepared in Embodiment 3.

Embodiment 7

(16) In this embodiment, the catalyst prepared in Embodiment 1 was used in a fixed-bed reaction for activity testing; and the steps were the same as those in Embodiment 4, with a parameter variation as follows: the catalyst was replaced by the catalyst prepared in Embodiment 2 and then hydrothermally treated at 700° C. for 4 h.

Comparative Example 1

(17) (1) To demonstrate the technical effect of the technical solution of the invention, the invention also provides comparative examples. In this comparative example, the hydrothermal synthesis method as the most commonly used method for synthesizing the SSZ-13 molecular sieve was used, where N,N,N-trimethyl-1-adamantyl ammonium hydroxide (TMADAOH) was used as a template; a feeding ratio is the same as that in Embodiment 3, only with the variations as follows: no iron and copper sources were added in the synthesis process, and silica sol was used to replace the diatomite.

(18) (2) 0.62 g of Cu(NO.sub.3).sub.2.3H.sub.2O, 3.22 g of Fe(NO.sub.3).sub.3.9H.sub.2O, and 5 g of deionized water were weighed, then mixed evenly, and then slowly dropped to 10 g of the molecular sieve synthesized in step (1); the molecular sieve was sonicated for 2 h, dried at room temperature, then placed in an oven and dried at 120° C. for 8 h, finally roasted in a muffle furnace at 520° C. for 5 h, and then cooled to room temperature.

Comparative Example 2

(19) In this embodiment, the catalyst prepared in Embodiment 1 was used in a fixed-bed reaction for activity testing; and the steps were the same as those in Embodiment 4, with a parameter variation as follows: the catalyst was replaced by the catalyst obtained in Comparative Example 1.

Comparative Example 3

(20) In this embodiment, the catalyst prepared in Embodiment 1 was used in a fixed-bed reaction for activity testing; and the steps were the same as those in Embodiment 4, with a parameter variation as follows: the catalyst was replaced by the catalyst prepared in Comparative Example 1 and then hydrothermally treated at 700° C. for 4 h.

(21) TABLE-US-00001 TABLE 1 Test results of all embodiments and fixed- bed reaction based activity testing Temperature window (° C.) N.sub.2 Selectivity (%) Embodiment 4 150-700 >990 Embodiment 5 175-700 >990 Embodiment 6 150-700 >99.5 Embodiment 7 130-650 >99.5 Comparative 200-350 <90.0 Example 2 Comparative 200-300 <35.0 Example 3

(22) Note: The temperature window is a temperature interval when the conversion rate of NO is more than 90%.

(23) As can be seen from Table 1, the mesoporous Fe—Cu—SSZ-13 molecular sieve provided by the invention has an ultra-wide temperature window (especially the activity at medium and high temperature), excellent N2 selectivity, good hydrothermal stability and the like. The method of the invention not only is low in cost, simple in process and easy to operate, but also has good economic and environmental benefits.

(24) Although the invention has been described above with reference to the accompanying drawings, the invention is not limited to the specific embodiments above. The specific embodiments above are only illustrative but not limiting. Those of ordinary skills in the art may also make many variations without departing from the object of the invention under the teaching of the invention, and all of these variations shall fall within the protection of the invention.