MOLECULAR SIEVE SCR CATALYST AND PREPARATION METHOD

Abstract

The invention discloses a molecular sieve SCR catalyst and a preparation method, the preparation method comprising the steps of: (1) heating deionized water to 60-90? C., and adding a soluble copper salt and an additive to stir and dissolve the same to prepare a copper solution; (2) heating the deionized water to 20-90? ? C., adding a soluble yttrium salt to dissolve the same, and when maintaining the temperature, adding a molecular sieve with a silicon-aluminum ratio of ?24 and stirring the same; when maintaining the temperature, adding a copper solution and stirring to perform ion exchange; (3) cooling the solution after the ion exchange in step (2), adding an adhesive, stirring and ball-milling the mixture, and standing to obtain a slurry; (4) coating the slurry onto a support, drying and then calcining to obtain a molecular sieve SCR catalyst. The catalyst prepared according to the present invention by using a small pore molecular sieve material with a lower silicon-aluminum ratio and adding yttrium as a second active component exhibits excellent catalytic activity for NO.sub.x at low and high temperatures, and has a wide active temperature window, high hydrothermal stability and good hydrocarbon resistance.

Claims

1. A preparation method for a molecular sieve SCR catalyst, comprising the steps of: (1) copper solution blending: heating deionized water to 60-90? ? C., and adding a soluble copper salt and an additive to stir and dissolve the same to prepare a copper solution; (2) ion exchange: heating the deionized water to 60-90? ? C., adding a soluble yttrium salt to stir and dissolve the same, maintaining the temperature at 60-90? C., adding a molecular sieve with a silicon-aluminum ratio of ?24 and continuously stirring for 0.5-5 h; maintaining the temperature at 60-90? C., adding the copper solution prepared in step (1) and continuously stirring the mixture for 1-10 h; (3) slurrying: cooling the solution prepared in step (2), adding an adhesive, stirring and ball-milling the mixture, and standing for 0.5-5 h to obtain a slurry; and (4) coating and calcinating: coating the slurry prepared in step (3) onto a catalyst support, drying and then calcining in air at 300-600? ? C. for 1-6 h to obtain a molecular sieve SCR catalyst.

2. The preparation method for the molecular sieve SCR catalyst according to claim 1, wherein the molecular sieve is one of H-SSZ-13, H-SSZ-39 or a mixture of the two; and the silicon-aluminum ratio in the molecular sieve is 6-22:1.

3. The preparation method for the molecular sieve SCR catalyst according to claim 1, wherein the soluble copper salt comprises one or more of copper sulfate, copper nitrate, copper acetate and copper chloride; the additive is one of citric acid, glycine, humic acid and gluconolactone; and the soluble yttrium salt comprises yttrium nitrate.

4. The preparation method for the molecular sieve SCR catalyst according to claim 3, wherein in the catalyst, a first active component is calculated by a copper element, and the mass ratio of the copper element to the molecular sieve is <5.5 wt %; and a second active component is calculated by a yttrium element, and the mass ratio of the yttrium element to the molecular sieve is <2.5 wt %.

5. The preparation method for the molecular sieve SCR catalyst according to claim 3, wherein in step (1), the mass ratio of the additive to the copper element is 0.2-2.5:1.

6. The preparation method for the molecular sieve SCR catalyst according to claim 1, wherein in step (2), the time for performing yttrium ion exchange after adding the molecular sieve is 1-3 h; and the time for performing copper ion exchange after adding the copper solution prepared in step (1) is 2-4 h.

7. The preparation method for the molecular sieve SCR catalyst according to claim 1, wherein the adhesive is one or more of a silica sol, an aluminum sol and a zirconium sol, and the mass of the adhesive after being calcined to an oxide is 2-20 wt % of the mass of the molecular sieve

8. The preparation method for the molecular sieve SCR catalyst according to claim 1, wherein a catalyst support is one of a cordierite support, a silicon carbide support and a metal support.

9. The preparation method for the molecular sieve SCR catalyst according to claim 1, wherein in step (3), the solid content of the slurry is 30-60%, and the coating amount of the slurry is 50-200 g/L.

10. A molecular sieve SCR catalyst, wherein the catalyst is prepared by the preparation method as claimed in claim 1.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0033] FIG. 1 is a graph of NO.sub.x conversion ratios by a catalyst in examples of the invention and comparative examples;

[0034] FIG. 2 is a graph of HC conversion ratios by a catalyst in examples of the invention and comparative examples;

[0035] FIG. 3 is a graph of NO.sub.x conversion ratios after hydrothermal aging at 750? ? C.@50 h.

DETAILED DESCRIPTION

[0036] Hereinafter, the present invention will be described in further detail with reference to experimental examples and detailed description. However, it should not be understood that the scope of the above-described subject matter of the present invention is limited to the following examples. All the technologies achieved on the basis of the invention fall within the scope of the invention.

Example 1

[0037] (1) Preparation of copper solution: 50 g of deionized water was heated to 60? C., and 19.03 g of copper nitrate trihydrate and 6.05 g of citric acid were added and dissolved with stirring to prepare a copper solution.

[0038] (2) Ion exchange: 200 g of deionized water was heated to 80? ? C., 6.03 g of yttrium nitrate hexahydrate was added, stirred and dissolved completely, 140 g of H-SSZ-13 with a silicon-aluminum ratio of 13 was added while maintaining the temperature at 80? C. and continuously stirred for 3 h to perform ion exchange, and the copper solution prepared in step (1) was added while maintaining the temperature at 80? C. and continuously stirred for 4 h.

[0039] (3) Slurrying: the solution after ion exchange in step (2) was cooled to room temperature, 28 g of a silicon solution with a concentration of 30% was added, stirred and ball-milled, and stood for 1 h to obtain a slurry.

[0040] (4) Coating and calcinating: the slurry prepared in step (3) was coated on a cordierite support in a coating amount of 140 g/L, dried rapidly at 130? C. using a dryer, and then calcined in air at 500? C. for 3 h to obtain a molecular sieve SCR catalyst S1.

[0041] The cordierite supports used in the present invention were all cylindrical permeable supports with q 25.4 mm*50.8 mm and a 400 cpsi mesh.

Example 2

[0042] (1) Preparation of copper solution: 100 g of deionized water was heated to 80? C., and 20.30 g of copper acetate, 8.60 g of citric acid and water were added and dissolved at 80? ? C. with stirring to prepare a copper solution.

[0043] (2) Ion exchange: 220 g of deionized water was heated to 80? C., 3.88 g of yttrium nitrate hexahydrate was added, stirred and dissolved completely, 180 g of H-SSZ-13 was added while maintaining the temperature at 80? C. and stirred continuously for 1 h to perform ion exchange, and the copper solution prepared in step (1) was added while maintaining the temperature at 70? C. and stirred continuously for 3 h.

[0044] (3) Slurrying: the solution after ion exchange in step (2) was cooled to room temperature, 36 g of a silicon solution with a concentration of 30% was added, stirred and ball-milled, and stood for 1 h to obtain a slurry.

[0045] (4) Coating and calcinating: the slurry prepared in step (3) was coated on a cordierite support in a coating amount of 140 g/L, dried rapidly at 130? C. using a dryer, and then calcined in air at 450? ? C. for 2 h to obtain a molecular sieve SCR S2.

Example 3

[0046] (1) Preparation of copper solution: 55 g of deionized water was heated to 70? C., and 21.88 g of copper sulfate pentahydrate and 7.88 g of glycine were added and dissolved with stirring to prepare a copper solution.

[0047] (2) Ion exchange: 300 g of deionized water was heated to 70? C., 8.62 g of yttrium nitrate hexahydrate was added to stir and dissolve completely, 200 g of H-SSZ-13 with a silicon-aluminum ratio of 20 was added while maintaining the temperature at 70? C. and continuously stirring for 6 h to perform ion exchange, and the copper solution prepared in step (1) was continuously stirred and added while maintaining the temperature at 80? C., and continuously stirred for 4 h.

[0048] (3) Slurrying: the solution after ion exchange in step (2) was cooled to room temperature, 57 g of a zirconium solution with a concentration of 21% was added, stirred and ball-milled, and stood for 2 h to obtain a slurry.

[0049] (4) Coating and calcinating: the slurry prepared in step (3) was coated on a cordierite support in a coating amount of 140 g/L, dried rapidly at 120? C. using a dryer, and then calcined in air at 500? C. for 3 h to obtain a molecular sieve SCR catalyst S3.

Example 4

[0050] (1) Preparation of copper solution: 50 g of deionized water was heated to 60? C., and 30.80 g of copper nitrate trihydrate and 9.79 g of citric acid were added and dissolved with stirring to prepare a copper solution.

[0051] (2) Ion exchange: 200 g of deionized water was heated to 80? ? C., 10.34 g of yttrium nitrate hexahydrate was added, stirred and dissolved completely, 160 g of H-SSZ-13 with a silicon-aluminum ratio of 8.5 was added while maintaining the temperature at 80? C. and continuously stirring for 4 h to perform ion exchange, and the copper solution prepared in step (1) was continuously stirred and added while maintaining the temperature at 80? C., and continuously stirred for 2 h.

[0052] (3) Slurrying: the solution after ion exchange in step (2) was cooled to room temperature, 32 g of a silicon solution with a concentration of 30% was added, stirred and ball-milled, and stood for 1 h to obtain a slurry.

[0053] (4) Coating and calcinating: the slurry prepared in step (3) was coated on a cordierite support in a coating amount of 140 g/L, dried rapidly at 130? C. using a dryer, and then calcined in air at 500? ? C. for 3 h to obtain a molecular sieve SCR catalyst S4.

Example 5

[0054] (1) Preparation of copper solution: 70 g of deionized water was heated to 80? C., and 16 g of copper acetate and 6.14 g of citric acid were added and dissolved with stirring to prepare a copper solution.

[0055] (2) Ion exchange: 240 g of deionized water was heated to 80? C., 0.62 g of yttrium nitrate hexahydrate was added, stirred and dissolved completely, 160 g of H-SSZ-39 with a silicon-aluminum ratio of 17 was added while maintaining the temperature at 80? C. and continuously stirring for 1 h to perform ion exchange, and the copper solution prepared in step (1) was continuously stirred and added while maintaining the temperature at 80? C., and continuously stirred for 4 h.

[0056] (3) Slurrying: the solution after ion exchange in step (2) was cooled to room temperature, 32 g of a silicon solution with a concentration of 30% was added, stirred and ball-milled, and stood for 1 h to obtain a slurry.

[0057] (4) Coating and calcinating: the slurry prepared in step (3) was coated on a cordierite support in a coating amount of 140 g/L, dried rapidly at 130? C. using a dryer, and then calcined in air at 500? C. for 3 h to obtain a molecular sieve SCR catalyst S5.

Comparative Example 1

[0058] (1) Ion exchange: 250 g of deionized water was heated to 80? C. with continuous stirring, 140 g of H-SSZ-13 with a silicon-aluminum ratio of 13 was added with continuous stirring, and 19.03 g of copper nitrate trihydrate was added for ion exchange for 4 h.

[0059] The other preparation steps were the same as steps (3) and (4) of Example 1 to obtain a molecular sieve SCR catalyst B1.

Comparative Example 2

[0060] (1) Preparation of copper solution: 50 g of deionized water was heated to 60? C., and 19.03 g of copper nitrate trihydrate and 6.05 g of citric acid were added and dissolved with stirring to prepare a copper solution.

[0061] (2) Ion exchange: 200 g of deionized water was heated to 80? ? C. with continuous stirring, 140 g of H-SSZ-13 with a silicon-aluminum ratio of 13 was added, and the copper solution prepared in step (1) was added with continuous stirring and stirred for 4 h.

[0062] The other preparation steps were the same as steps (3) and (4) of Example 1 to obtain a molecular sieve SCR catalyst B2.

Comparative Example 3

[0063] (1) Preparation of copper solution: 55 g of deionized water was heated to 80? C., and 21.88 g of copper sulfate pentahydrate and 7.88 g of glycine were added and dissolved with stirring to prepare a copper solution.

[0064] (2) Ion exchange: 305 g of deionized water was heated to 80? C., 200 g of H-SSZ-13 with a silicon-aluminum ratio of 20 was added with constant stirring, and the copper solution prepared in step (1) was added and stirred for 4 h.

[0065] The other preparation steps were the same as steps (3) and (4) of Example 3 to obtain a molecular sieve SCR catalyst B3.

Comparative Example 4

[0066] (1) Preparation of copper solution: 50 g of deionized water was heated to 60? C., and 30.80 g of copper nitrate trihydrate and 9.79 g of citric acid were added and dissolved with stirring to prepare a copper solution.

[0067] (2) Ion exchange: 250 g deionized water was heated to 80? C., 160 g of H-SSZ-13 with a silicon-aluminum ratio of 8.5 was added, and 30.80 g of copper nitrate trihydrate was added and stirred for 2 h.

[0068] The other preparation steps were the same as steps (3) and (4) of Example 5 to obtain a molecular sieve SCR catalyst B4.

Comparative Example 5

[0069] (1) Ion exchange milling: 210 g of deionized water was heated to 80? ? C., 140 g of H-SSZ-13 with a silicon-aluminum ratio of 13 and 19.03 g of copper nitrate trihydrate were added and continuously stirred for 6 h, then filtered, washed and dried to a powder, the Cu content in the resulting product being 3.6 wt %.

[0070] (2) slurrying: 120 g of the powder after ion exchange in step (1), 180 g of water, 6.03 g of yttrium nitrate, and 28 g of a silicon solution with a concentration of 30% were subjected to stirring and ball-milling, standing for 1 h to obtain a slurry;

[0071] The other preparation steps were the same as steps (3) and (4) of Example 5 to obtain a molecular sieve SCR catalyst B5.

Comparative Example 6

[0072] (1) Preparation of copper solution: 50 g of deionized water was heated to 60? C., and 19.03 g of copper nitrate trihydrate and 6.05 g of citric acid were added and dissolved with stirring to prepare a copper solution.

[0073] (2) Ion exchange: 200 g of deionized water was heated to 80? C., 6.03 g of yttrium nitrate hexahydrate was added, stirred and dissolved completely, 140 g of H-SSZ-13 with a silicon-aluminum ratio of 27 was added while maintaining the temperature at 80? C. and continuously stirred for 3 h to perform ion exchange, and the copper solution prepared in step (1) was added while maintaining the temperature at 80? C. and continuously stirred for 4 h.

[0074] The other preparation steps were the same as steps (3) and (4) of Example 1 to obtain a molecular sieve SCR catalyst B6.

[0075] The molecular sieve SCR catalysts S1-S5 prepared in Examples 1-5 and the molecular sieve SCR catalysts B1-B6 prepared in Comparative Examples 1-6 were subjected to NO.sub.x conversion tests and HC conversion tests on a fixed bed reactor. The simulated gas composition for testing NO.sub.x conversion was [NO][NH.sub.3]=250 ppm, [O.sub.2]=10%, [H.sub.2O]=8%, and N.sub.2 as a balance gas. The simulated gas composition for testing HC conversion was [NO][NH.sub.3]=250 ppm, [C.sub.3H.sub.3]=250 ppm, [O.sub.2]=10%, [H.sub.2O]=8%, and N.sub.2 as a balance gas. The space velocity was 60000 h.sup.?1, and the reaction temperature was 175-550? C. during the test of NO.sub.x conversion and HC conversion. The gas components used were all subjected to infrared detection. The NO.sub.x conversion test results are summarized in Table 1 and the HC conversion test results are summarized in Table 2 in conversion units of %. The catalysts prepared in Example 1, Example 3, Comparative Examples 1-2, and Comparative Examples 5-6 were hydrothermally aged at 750? C. for 50 h. After the aging was completed, the NO.sub.x conversion was tested under the above-mentioned test conditions. The test results are statistically shown in Table 3. Tables 1, 2 and 3 are prepared into FIGS. 1, 2 and 3, respectively.

TABLE-US-00001 TABLE 1 Conversion ratio of molecular sieve SCR catalysts S1-S5, B1-B6 on NO.sub.x Sequence 175? 200? number C. C. 250? C. 350? C. 450? C. 500? C. 550? C. S1 82 96 99 99 99 98 95 S2 76 94 99 99 98 96 91 S3 77 92 99 99 99 95 88 S4 86 98 99 99 99 99 98 S5 74 92 99 99 99 96 87 B1 73 92 99 99 98 93 83 B2 76 94 99 99 98 94 86 B3 71 90 98 99 98 92 82 B4 64 89 99 99 98 90 75 B5 68 90 99 99 98 94 81 B6 62 90 99 99 98 89 78

TABLE-US-00002 TABLE 2 Conversion ratio of molecular sieve SCR catalysts S1-S5, B1-B6 on HC Sequence 175? 200? number C. C. 250? C. 350? C. 450? C. 500? C. 550? C. S1 75 93 98 97 98 96 92 S2 76 94 99 99 98 96 91 S3 67 90 98 97 98 94 84 S4 66 88 96 96 96 95 92 S5 63 90 98 96 99 94 85 B1 68 90 96 95 96 91 81 B2 70 92 96 95 96 92 83 B3 65 88 96 94 96 90 80 B4 52 86 97 95 96 87 74 B5 61 87 96 94 96 92 80 B6 54 87 97 97 97 87 78

TABLE-US-00003 TABLE 3 Conversion ratio of molecular sieve SCR catalysts S1, S3, B1-B2 and B5-B6 on NO.sub.x after aging at 750? C. @50 h Sequence 175? 200? number C. C. 250? C. 350? C. 450? C. 500? C. 550? C. S1 62 87 98 99 98 95 85 S3 70 94 97 99 97 91 87 B1 53 82 97 99 97 89 73 B2 57 85 97 99 97 91 74 B5 58 84 98 99 98 93 80 B6 54 80 90 98 86 75 65

[0076] It can be seen from FIG. 1 that at a low temperature of 175? C., the conversion rate of the molecular sieve SCR catalysts S1-S6 on NO.sub.x is 74-86%. At a high temperature of 550? C., the conversion rate of the molecular sieve SCR catalysts S1-S6 on NO.sub.x is 87-98%. At 175? C., the activity of Example 1 was increased by 6-20% compared with Comparative Examples 1-2. At 550? C., the activity of Example 1 was increased by 9-17% compared with Comparative Examples 1-2, indicating that the catalyst has good catalytic activity for NO.sub.x at both low temperature and high temperature. In Comparative Example 1, no additive was added. In Comparative Examples 2-4, no second active component Y was added. In Comparative Example 5, Y was not added by ion exchange. In Comparative Example 6, the conversion rate on NO.sub.x was lower with the molecular sieve having a silicon-aluminum ratio of 27. In FIG. 2, the catalyst is tested under an atmosphere of 250 ppm C.sub.3H.sub.6. The conversion rate of the molecular sieve SCR catalysts S1-S6 on HC is 63-76% at a low temperature of 175? C., and the conversion of the molecular sieve SCR catalysts S1-S6 on HC is 84-92% at a high temperature of 550? ? C. Example 1 shows a 5-21% increase in activity compared to Comparative Examples 1-2 at 175? C. Example 1 shows a 9-14% increase in activity compared to Comparative Examples 1-2 at 550? C., indicating that the catalyst of the present invention has good resistance to hydrocarbon poisoning.

[0077] As can be seen from FIG. 3, the NO.sub.x conversion performance and the reaction temperature window after hydrothermal aging of the catalyst at 750? ? C. for 50 h are significantly better than those of Comparative Examples 1 and 2, Comparative Examples 5 and 6, Example 1 and Example 3, indicating that the molecular sieve SCR catalyst prepared according to the present invention has good hydrothermal stability.

[0078] In the present invention, a small-pore molecular sieve material with a relatively low silicon-aluminum ratio is used. The dispersion of the first active component Cu on the surface of the molecular sieve and the acid density of the catalyst may be adjusted by the additive when adding the second active component yttrium, so as to improve the catalytic activity and hydrocarbon resistance of the catalyst, thereby achieving that the catalyst has an excellent catalytic activity for NO.sub.x at a relatively low silicon-aluminum ratio and at a low temperature and a high temperature, and has a wide active temperature window, a high hydrothermal stability and a relatively good hydrocarbon resistance.

[0079] The above mentioned are only preferred embodiments of the invention and is not intended to limit the invention. Any modification, equivalent substitution and improvement made within the spirit and principles of the invention shall be covered by the protection of the invention.