Preparation method of SCR (Selective Catalytic Reduction) catalyst
Patent Information
- Application Number
- CN202510520566.5
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-04-24
- Publication Date
- 2025-08-01
AI Technical Summary
[0004](2)氨逃逸：过量氨氧化生成NOx或直接排放，造成二次污染
[0040] (1) By doping silver aluminate and lithium nitrate, the sulfur dioxide resistance performance of the catalyst is improved.
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Abstract
Description
Technical Field
[0001] The present invention relates to the technical field of flue gas denitrification, and particularly to a preparation method of an SCR catalyst. Background Art
[0002] With the development of industry and the increasing strictness of environmental protection regulations, the selective catalytic reduction (SCR) technology has become the mainstream method for flue gas denitrification. Its core is to reduce nitrogen oxides to nitrogen and water by using ammonia over a catalyst within a specific temperature window. Traditional SCR catalysts (such as vanadium-based, tungsten-based, and titanium-based) have problems such as poor low-temperature activity, susceptibility to sulfur dioxide poisoning, and ammonia slip. Zeolite-based catalysts (such as Fe / ZSM-5) have attracted much attention due to their wide-temperature activity and high hydrothermal stability, but still face the following challenges:
[0003] (1) Sulfur dioxide poisoning: Sulfur dioxide in the flue gas reacts with active metals (such as silver and iron) to form sulfates, blocking the catalyst pores or covering the active sites, resulting in catalyst deactivation.
[0004] (2) Ammonia slip: Excessive ammonia is oxidized to NO x or directly discharged, causing secondary pollution.
[0005] (3) Uneven iron dispersion: The distribution of divalent iron / trivalent iron in the zeolite pores is uneven, affecting the utilization rate of active sites.
[0006] (4) Noble metal waste: Noble metals such as platinum (Pt) are loaded inside the zeolite micropores, and the diffusion limitation reduces the reaction efficiency. Moreover, after the zeolite pores are blocked, the platinum inside the pore diameter cannot play a catalytic role, resulting in noble metal waste.
[0007] Therefore, it is of great significance to provide a low-cost SCR catalyst with reduced sulfur poisoning, prevention of ammonia slip, and relatively high catalytic efficiency. Summary of the Invention
[0008] To solve the above problems, in the first aspect of the present invention, a preparation method of an SCR catalyst is provided. Through multi-step modification (such as divalent iron high-temperature ion exchange, EDTA chelation dispersion, silver aluminate doping, etc.), the sulfur resistance and ammonia control ability of the catalyst are comprehensively improved, and it includes the following steps:
[0009] Step S1, divalent iron and zeolite ion exchange reaction: In a nitrogen atmosphere, the zeolite is dispersed in an aqueous solution of ferrous nitrate for ion exchange reaction, and then obtained zeolite A through filtration and calcination;
[0010] Step S2, impregnating zeolite A with a ferrocene benzene solution: In a nitrogen atmosphere, zeolite A is impregnated with a ferrocene benzene solution, and then obtained zeolite B through filtration, drying, and calcination;
[0011] Step S3, impregnating zeolite B with lithium nitrate solution: Zeolite B is impregnated with lithium nitrate solution, and then filtered, dried, and calcined to obtain zeolite C;
[0012] Step S4, impregnating zeolite C with tert-butanol: Zeolite C is impregnated in tert-butanol and washed to make zeolite D;
[0013] Step S5, impregnating zeolite D with chloroplatinic acid aqueous solution: Zeolite D is impregnated with chloroplatinic acid aqueous solution, and then filtered, dried, and calcined to obtain zeolite E;
[0014] Step S6, EDTA treatment: Ferric nitrate and EDTA are dissolved in water to make a chelating solution. Cerium dioxide powder is dispersed in the chelating solution, and after separation by filtration and calcination, cerium dioxide F is obtained;
[0015] Step S7, silica bonding: Cerium dioxide F, zeolite E, and silica sol are mixed and ball-milled to make slurry G;
[0016] Step S8, preparing the first oxide layer: Cordierite is impregnated in slurry G and dried and calcined to make the first oxide layer;
[0017] Step S9, silica bonding: Cerium dioxide F, zeolite C, and silica sol are mixed and ball-milled to make slurry H;
[0018] Step S10, preparing the adsorption layer: Cordierite is impregnated in slurry H and dried and calcined to make the adsorption layer;
[0019] Step S11, silver aluminate treatment: Slurry H is mixed with silver aluminate and ball-milled to make slurry I;
[0020] Step S12, preparing the second oxide layer: Cordierite is impregnated in slurry I and dried and calcined to make the second oxide layer;
[0021] Step S13, stacking and bonding: The first oxide layer, the adsorption layer, and the second oxide layer are stacked and bonded in sequence to make the SCR catalyst.
[0022] As a preferred technical solution, the mass concentration of the ferrous nitrate aqueous solution in Step S1 is 2% - 10%; the mass ratio of the zeolite to the ferrous nitrate aqueous solution is 1:(15 - 25); the ion exchange reaction time is 10 hours - 20 hours; the ion exchange reaction temperature is 80°C - 100°C; the ion exchange reaction pH is 1 - 3; the calcination temperature is 300°C - 500°C; the calcination time is 8 hours - 10 hours; it is measured that the mass concentration of iron in zeolite A is 0.2% - 1%; this step is repeated 1 - 5 times.
[0023] As a preferred technical solution, in step S2, the mass concentration of the ferrocene benzene solution is 3% - 5%; the mass ratio of zeolite A to the ferrocene benzene solution is 1:(3 - 5); the impregnation time is 10 hours - 20 hours; the impregnation temperature is 20°C - 30°C; the drying time is 4 hours - 6 hours; the drying temperature is 40°C - 60°C; the calcination temperature is 300°C - 500°C; the calcination time is 4 hours - 6 hours; the mass concentration of iron in zeolite B is 2% - 4%; this step is repeated 1 - 5 times.
[0024] As a preferred technical solution, in step S3, the mass concentration of the lithium nitrate solution is 0.2 - 0.4%; the mass ratio of zeolite B to the lithium nitrate solution is 1:(3 - 5); the impregnation time is 3 hours - 5 hours; the impregnation temperature is 40°C - 50°C; the drying temperature is 50°C - 150°C; the drying time is 2 hours - 4 hours; the calcination temperature is 400°C - 500°C; the calcination time is 3 hours - 5 hours; this step is repeated 1 - 5 times.
[0025] As a preferred technical solution, in step S4, the mass ratio of zeolite C to tert-butanol is 1:(4 - 5); the impregnation time is 3 hours - 5 hours; the impregnation temperature is 40°C - 50°C.
[0026] As a preferred technical solution, in step S5, the mass concentration of the chloroplatinic acid aqueous solution is 10% - 15%; the mass ratio of zeolite D to the chloroplatinic acid aqueous solution is 1:(2 - 4); the impregnation time is 3 hours - 5 hours; the impregnation temperature is 40°C - 50°C; the drying temperature is 50°C - 150°C; the drying time is 2 hours - 4 hours; the calcination temperature is 400°C - 500°C; the calcination time is 3 hours - 5 hours; this step is repeated 1 - 5 times.
[0027] As a preferred technical solution, in step S6, the dispersion time is 1 hour - 2 hours, the dispersion temperature is 30°C - 40°C; the pH of the chelating solution is 4 - 6; the mass concentration of EDTA in the chelating solution is 2% - 4%; the mass concentration of iron nitrate in the chelating solution is 3% - 5%; the calcination temperature is 500°C - 600°C; the calcination time is 2 hours - 4 hours; the specific surface area of cerium dioxide is 150m 2 / g - 180m 2 / g; the mass concentration of iron in cerium dioxide F is 0.5% - 1%; this step is repeated 1 - 5 times.
[0028] As a preferred technical solution, the mass ratio of cerium dioxide F, zeolite E, and silica sol in step S7 is 1:(4 - 5):(1 - 2); the mass concentration of silica in the silica sol is 20% - 30%.
[0029] As a preferred technical solution, the thickness of the first oxide layer in step S8 is 5 cm - 10 cm; the drying temperature is 50°C - 150°C; the calcination temperature is 500°C - 1000°C; the drying time is 2 hours - 4 hours; the calcination time is 3 hours - 5 hours; the dosage of slurry G is 100 g - 150 g / L cordierite.
[0030] As a preferred technical solution, the mass ratio of cerium dioxide, zeolite, and silica sol in step S9 is 1:(4 - 5):(1 - 2); the mass concentration of silica in the silica sol is 20% - 30%.
[0031] As a preferred technical solution, the thickness of the adsorption layer in step S10 is 5 cm - 10 cm; the drying temperature is 50°C - 150°C; the calcination temperature is 500°C - 1000°C; the drying time is 2 hours - 4 hours; the calcination time is 3 hours - 5 hours; the dosage of slurry H is 100 g - 150 g / L cordierite.
[0032] As a preferred technical solution, the mass ratio of slurry H to silver aluminate in step S11 is 1:(0.1 - 0.2).
[0033] As a preferred technical solution, the thickness of the second oxide layer in step S12 is 5 cm - 10 cm; the drying temperature is 50°C - 150°C; the calcination temperature is 500°C - 1000°C; the drying time is 2 hours - 4 hours; the calcination time is 3 hours - 5 hours; the dosage of slurry I is 100 g - 150 g / L cordierite.
[0034] In the second aspect of the present invention, an SCR catalyst is provided, and the SCR catalyst is made by the aforementioned preparation method.
[0035] The cerium dioxide in the present invention has unique oxygen storage capacity. Its trivalent cerium / quadrivalent cerium reversible redox cycle can quickly release or store oxygen under different atmospheres (oxidation / reduction), promoting the adsorption and activation of NO x and dynamically regulating the oxygen migration rate. The Lewis acid sites present on its surface enhance the adsorption of ammonia.
[0036] The zeolite in the present invention has abundant acid sites, can adsorb ammonia, and promotes the SCR reaction between ammonia and NO x .
[0037] When using the SCR catalyst prepared by the present invention, the first oxidation layer is the air inlet end, and the second oxidation layer is the air inlet end.
[0038] Generally, the content of nitrogen monoxide in flue gas is much higher than that of nitrogen dioxide. When using the SCR catalyst prepared by the present invention, a reducing agent ammonia can be provided in the adsorption layer. In this case, the first oxidation layer oxidizes part of the nitrogen monoxide into nitrogen dioxide, and the nitrogen monoxide, nitrogen dioxide and ammonia carry out rapid SCR reaction and standard SCR reaction in the adsorption layer to reduce the nitrogen oxides in the flue gas to nitrogen. The excessive ammonia is oxidized into nitrogen in the second oxidation layer to reduce ammonia leakage. When providing the reducing agent ammonia in the first oxidation layer, in this case, the first oxidation layer oxidizes part of the nitrogen monoxide into nitrogen dioxide, and at the same time, rapid SCR reaction and standard SCR reaction occur; the unreacted gases are mostly nitrogen monoxide and ammonia, and standard SCR reaction is carried out in the adsorption layer to reduce the nitrogen oxides in the flue gas to nitrogen. The excessive ammonia is oxidized into nitrogen in the second oxidation layer to reduce ammonia leakage.
[0039] Through the above technical solutions, the present invention has the following technical effects:
[0040] (1) By doping silver aluminate and lithium nitrate, the sulfur dioxide resistance performance of the catalyst is improved.
[0041] (2) By setting the first oxidation layer, adsorption layer and second oxidation layer, the ammonia slip amount is reduced and the NO x conversion rate is increased.
[0042] (3) By using EDTA, the uniformity of the distribution of iron on the surface of cerium dioxide is improved, and the NO x conversion rate is increased.
[0043] (4) By filling tert-butanol in the micropores of zeolite, platinum is mainly loaded on the outer surface position of zeolite, thereby improving the reaction efficiency, increasing the utilization rate of platinum and reducing the platinum dosage.
[0044] (5) By impregnating with ferrocene benzene solution, iron can be effectively introduced into the hydrophobic region of the zeolite pores, improving the uniformity and density of the distribution of iron in the zeolite pores, and increasing the NO x conversion rate.
[0045] (6) By raising the temperature to shrink the hydration layer of divalent iron, the divalent iron enters the zeolite pores to form active centers, improving the uniformity and density of the distribution of iron in the zeolite pores, and increasing the NO x conversion rate. Detailed implementation manners
[0046] To make the above objects, features and advantages of the present invention more obvious and understandable, the applicant will explain and analyze through specific examples and comparative examples.
[0047] Example 1
[0048] Step S1, divalent iron and zeolite ion exchange reaction: Under a nitrogen atmosphere, disperse zeolite in an aqueous solution of ferrous nitrate, conduct an ion exchange reaction, and then obtain zeolite A through filtration and calcination; the mass concentration of the aqueous ferrous nitrate solution is 2%; the mass ratio of the zeolite to the aqueous ferrous nitrate solution is 1:15; the ion exchange reaction time is 10 hours; the ion exchange reaction temperature is 80 °C; the pH of the ion exchange reaction is 1; the calcination temperature is 300 °C; the calcination time is 8 hours; after measurement, the mass concentration of iron in zeolite A is 0.2%; this step is repeated 5 times;
[0049] Step S2, impregnate zeolite A with a ferrocene benzene solution: Under a nitrogen atmosphere, impregnate zeolite A with a ferrocene benzene solution, and then obtain zeolite B through filtration, drying, and calcination; the mass concentration of the ferrocene benzene solution is 3%; the mass ratio of zeolite A to the ferrocene benzene solution is 1:3; the impregnation time is 10 hours; the impregnation temperature is 20 °C; the drying time is 4 hours; the drying temperature is 40 °C; the calcination temperature is 300 °C; the calcination time is 4 hours; the mass concentration of iron in zeolite B is 2%; this step is repeated 5 times;
[0050] Step S3, impregnate zeolite B with a lithium nitrate solution: Impregnate zeolite B with a lithium nitrate solution, and then obtain zeolite C through filtration, drying, and calcination; the mass concentration of the lithium nitrate solution is 0.2%; the mass ratio of zeolite B to the lithium nitrate solution is 1:3; the impregnation time is 3 hours; the impregnation temperature is 40 °C; the drying temperature is 50 °C; the drying time is 2 hours; the calcination temperature is 400 °C; the calcination time is 3 hours; this step is repeated 5 times;
[0051] Step S4, impregnate zeolite C with tert-butanol: Immerse zeolite C in tert-butanol and wash to make zeolite D; the mass ratio of zeolite C to tert-butanol is 1:4; the impregnation time is 3 hours; the impregnation temperature is 40 °C;
[0052] Step S5, impregnate zeolite D with an aqueous solution of chloroplatinic acid: Impregnate zeolite D with an aqueous solution of chloroplatinic acid, and then obtain zeolite E through filtration, drying, and calcination; the mass concentration of the aqueous chloroplatinic acid solution is 10%; the mass ratio of zeolite D to the aqueous chloroplatinic acid solution is 1:2; the impregnation time is 3 hours; the impregnation temperature is 40 °C; the drying temperature is 50 °C; the drying time is 2 hours; the calcination temperature is 400 °C; the calcination time is 3 hours; this step is repeated 5 times;
[0053] Step S6, EDTA treatment: Dissolve ferric nitrate and EDTA in water to form a chelating solution. Disperse cerium dioxide powder in the chelating solution, and obtain cerium dioxide F through separation, filtration, and calcination. The dispersion time is 1 hour, and the dispersion temperature is 30°C. The pH of the chelating solution is 4. The mass concentration of EDTA in the chelating solution is 2%. The mass concentration of ferric nitrate in the chelating solution is 3%. The calcination temperature is 500°C, and the calcination time is 2 hours. The specific surface area of the cerium dioxide is 150 m 2 / g. The mass concentration of iron in the cerium dioxide F is 0.5%. This step is repeated 5 times;
[0054] Step S7, silica bonding: Mix cerium dioxide F, zeolite E, and silica sol, and ball-mill to form slurry G. The mass ratio of cerium dioxide F, zeolite E, and silica sol is 1:4:1. The mass concentration of silica in the silica sol is 20%;
[0055] Step S8, prepare the first oxide layer: Immerse cordierite in slurry G, and obtain the first oxide layer through drying and calcination. The thickness of the first oxide layer is 5 cm. The drying temperature is 50°C, the calcination temperature is 500°C, the drying time is 2 hours, the calcination time is 3 hours, and the dosage of slurry G is 100 g / L cordierite;
[0056] Step S9, silica bonding: Mix cerium dioxide F, zeolite C, and silica sol, and ball-mill to form slurry H. The mass ratio of cerium dioxide, zeolite, and silica sol is 1:4:1. The mass concentration of silica in the silica sol is 20%;
[0057] Step S10, prepare the adsorption layer: Immerse cordierite in slurry H, and obtain the adsorption layer through drying and calcination. The thickness of the adsorption layer is 5 cm. The drying temperature is 50°C, the calcination temperature is 500°C, the drying time is 2 hours, the calcination time is 3 hours, and the dosage of slurry H is 100 g / L cordierite;
[0058] Step S11, silver aluminate treatment: Mix slurry H and silver aluminate, and ball-mill to form slurry I. The mass ratio of slurry H to silver aluminate is 1:0.1;
[0059] Step S12, prepare the second oxide layer: Immerse cordierite in slurry I, and obtain the second oxide layer through drying and calcination. The thickness of the second oxide layer is 5 cm. The drying temperature is 50°C, the calcination temperature is 500°C, the drying time is 2 hours, the calcination time is 3 hours, and the dosage of slurry I is 100 g / L cordierite;
[0060] Step S13, superposition bonding: Stack and bond the first oxide layer, the adsorption layer, and the second oxide layer in sequence to produce the SCR catalyst.
[0061] Example 2
[0062] Step S1, divalent iron and zeolite ion exchange reaction: Under a nitrogen atmosphere, disperse the zeolite in an aqueous solution of ferrous nitrate for an ion exchange reaction, and then obtain zeolite A through filtration and calcination; the mass concentration of the aqueous solution of ferrous nitrate is 5%; the mass ratio of the zeolite to the aqueous solution of ferrous nitrate is 1:20; the ion exchange reaction time is 15 hours; the ion exchange reaction temperature is 90 °C; the pH of the ion exchange reaction is 2; the calcination temperature is 400 °C; the calcination time is 9 hours; it is measured that the mass concentration of iron in the zeolite A is 0.5%; this step is repeated 3 times;
[0063] Step S2, impregnate zeolite A with a ferrocene benzene solution: Under a nitrogen atmosphere, impregnate zeolite A with a ferrocene benzene solution, and then obtain zeolite B through filtration, drying, and calcination; the mass concentration of the ferrocene benzene solution is 4%; the mass ratio of zeolite A to the ferrocene benzene solution is 1:4; the impregnation time is 15 hours; the impregnation temperature is 25 °C; the drying time is 5 hours; the drying temperature is 50 °C; the calcination temperature is 400 °C; the calcination time is 5 hours; the mass concentration of iron in the zeolite B is 3%; this step is repeated 3 times;
[0064] Step S3, impregnate zeolite B with a lithium nitrate solution: Impregnate zeolite B with a lithium nitrate solution, and then obtain zeolite C through filtration, drying, and calcination; the mass concentration of the lithium nitrate solution is 0.3%; the mass ratio of zeolite B to the lithium nitrate solution is 1:4; the impregnation time is 4 hours; the impregnation temperature is 45 °C; the drying temperature is 100 °C; the drying time is 3 hours; the calcination temperature is 450 °C; the calcination time is 4 hours; this step is repeated 3 times;
[0065] Step S4, impregnate zeolite C with tert-butanol: Impregnate zeolite C in tert-butanol and wash to make zeolite D; the mass ratio of zeolite C to tert-butanol is 1:4.5; the impregnation time is 4 hours; the impregnation temperature is 45 °C;
[0066] Step S5, impregnate zeolite D with an aqueous solution of chloroplatinic acid: Impregnate zeolite D with an aqueous solution of chloroplatinic acid, and then obtain zeolite E through filtration, drying, and calcination; the mass concentration of the aqueous solution of chloroplatinic acid is 12%; the mass ratio of zeolite D to the aqueous solution of chloroplatinic acid is 1:3; the impregnation time is 4 hours; the impregnation temperature is 45 °C; the drying temperature is 100 °C; the drying time is 3 hours; the calcination temperature is 450 °C; the calcination time is 4 hours; this step is repeated 3 times;
[0067] Step S6, EDTA treatment: Dissolve ferric nitrate and EDTA in water to form a chelating solution. Disperse the cerium dioxide powder in the chelating solution, and obtain cerium dioxide F through separation, filtration, and calcination. The dispersion time is 1.5 hours, and the dispersion temperature is 35°C. The pH of the chelating solution is 5. The mass concentration of EDTA in the chelating solution is 3%. The mass concentration of ferric nitrate in the chelating solution is 4%. The calcination temperature is 550°C. The calcination time is 3 hours. The specific surface area of the cerium dioxide is 160 m 2 / g. The mass concentration of iron in the cerium dioxide F is 0.7%. This step is repeated 3 times.
[0068] Step S7, silica bonding: Mix cerium dioxide F, zeolite E, and silica sol, and ball-mill to form slurry G. The mass ratio of cerium dioxide F, zeolite E, and silica sol is 1:4.5:1.5. The mass concentration of silica in the silica sol is 25%.
[0069] Step S8, prepare the first oxide layer: Immerse cordierite in slurry G, and obtain the first oxide layer through drying and calcination. The thickness of the first oxide layer is 7 cm. The drying temperature is 100°C. The calcination temperature is 800°C. The drying time is 3 hours. The calcination time is 4 hours. The dosage of slurry G is 120 g / L of cordierite.
[0070] Step S9, silica bonding: Mix cerium dioxide F, zeolite C, and silica sol, and ball-mill to form slurry H. The mass ratio of cerium dioxide, zeolite, and silica sol is 1:4.5:1.5. The mass concentration of silica in the silica sol is 25%.
[0071] Step S10, prepare the adsorption layer: Immerse cordierite in slurry H, and obtain the adsorption layer through drying and calcination. The thickness of the adsorption layer is 7 cm. The drying temperature is 100°C. The calcination temperature is 800°C. The drying time is 3 hours. The calcination time is 4 hours. The dosage of slurry H is 120 g / L of cordierite.
[0072] Step S11, silver aluminate treatment: Mix slurry H and silver aluminate, and ball-mill to form slurry I. The mass ratio of slurry H to silver aluminate is 1:0.15.
[0073] Step S12, prepare the second oxide layer: Immerse cordierite in slurry I, and obtain the second oxide layer through drying and calcination. The thickness of the second oxide layer is 7 cm. The drying temperature is 100°C. The calcination temperature is 800°C. The drying time is 3 hours. The calcination time is 4 hours. The dosage of slurry I is 120 g / L of cordierite.
[0074] Step S13, superposition bonding: Stack and bond the first oxide layer, the adsorption layer, and the second oxide layer in sequence to fabricate the SCR catalyst.
[0075] Example 3
[0076] Step S1, divalent iron and zeolite ion exchange reaction: Under a nitrogen atmosphere, disperse zeolite in an aqueous solution of ferrous nitrate for ion exchange reaction, and then obtain zeolite A through filtration and calcination; the mass concentration of the aqueous solution of ferrous nitrate is 10%; the mass ratio of the zeolite to the aqueous solution of ferrous nitrate is 1:25; the ion exchange reaction time is 20 hours; the ion exchange reaction temperature is 100 °C; the pH of the ion exchange reaction is 3; the calcination temperature is 500 °C; the calcination time is 10 hours; it is measured that the mass concentration of iron in the zeolite A is 1%;
[0077] Step S2, impregnate zeolite A with ferrocene benzene solution: Under a nitrogen atmosphere, impregnate zeolite A with a ferrocene benzene solution, and then obtain zeolite B through filtration, drying, and calcination; the mass concentration of the ferrocene benzene solution is 5%; the mass ratio of the zeolite A to the ferrocene benzene solution is 1:5; the impregnation time is 20 hours; the impregnation temperature is 30 °C; the drying time is 6 hours; the drying temperature is 60 °C; the calcination temperature is 500 °C; the calcination time is 6 hours; the mass concentration of iron in the zeolite B is 4%;
[0078] Step S3, impregnate zeolite B with lithium nitrate solution: Impregnate zeolite B with a lithium nitrate solution, and then obtain zeolite C through filtration, drying, and calcination; the mass concentration of the lithium nitrate solution is 0.4%; the mass ratio of the zeolite B to the lithium nitrate solution is 1:5; the impregnation time is 4 hours; the impregnation temperature is 50 °C; the drying temperature is 150 °C; the drying time is 4 hours; the calcination temperature is 500 °C; the calcination time is 5 hours;
[0079] Step S4, impregnate zeolite C with tert-butanol: Impregnate zeolite C in tert-butanol and wash to make zeolite D; the mass ratio of the zeolite C to the tert-butanol is 1:5; the impregnation time is 5 hours; the impregnation temperature is 50 °C;
[0080] Step S5, impregnate zeolite D with an aqueous solution of chloroplatinic acid: Impregnate zeolite D with an aqueous solution of chloroplatinic acid, and then obtain zeolite E through filtration, drying, and calcination; the mass concentration of the aqueous solution of chloroplatinic acid is 15%; the mass ratio of the zeolite D to the aqueous solution of chloroplatinic acid is 1:4; the impregnation time is 5 hours; the impregnation temperature is 50 °C; the drying temperature is 150 °C; the drying time is 4 hours; the calcination temperature is 500 °C; the calcination time is 5 hours;
[0081] Step S6, EDTA treatment: Dissolve ferric nitrate and EDTA in water to form a chelating solution. Disperse cerium dioxide powder in the chelating solution, and obtain cerium dioxide F through separation, filtration, and calcination. The dispersion time is 2 hours, and the dispersion temperature is 40°C. The pH of the chelating solution is 6. The mass concentration of EDTA in the chelating solution is 4%. The mass concentration of ferric nitrate in the chelating solution is 5%. The calcination temperature is 600°C, and the calcination time is 4 hours. The specific surface area of the cerium dioxide is 180m 2 / g. The mass concentration of iron in the cerium dioxide F is 1%;
[0082] Step S7, silica bonding: Mix cerium dioxide F, zeolite E, and silica sol, and ball-mill to form slurry G. The mass ratio of cerium dioxide F, zeolite E, and silica sol is 1:5:2. The mass concentration of silica in the silica sol is 30%;
[0083] Step S8, prepare the first oxide layer: Immerse cordierite in slurry G, and obtain the first oxide layer through drying and calcination. The thickness of the first oxide layer is 10 cm. The drying temperature is 150°C, and the calcination temperature is 1000°C. The drying time is 4 hours, and the calcination time is 5 hours. The dosage of slurry G is 150 g / L of cordierite;
[0084] Step S9, silica bonding: Mix cerium dioxide F, zeolite C, and silica sol, and ball-mill to form slurry H. The mass ratio of cerium dioxide, zeolite, and silica sol is 1:5:2. The mass concentration of silica in the silica sol is 30%;
[0085] Step S10, prepare the adsorption layer: Immerse cordierite in slurry H, and obtain the adsorption layer through drying and calcination. The thickness of the adsorption layer is 10 cm. The drying temperature is 150°C, and the calcination temperature is 1000°C. The drying time is 4 hours, and the calcination time is 5 hours. The dosage of slurry H is 150 g / L of cordierite;
[0086] Step S11, silver aluminate treatment: Mix slurry H and silver aluminate, and ball-mill to form slurry I. The mass ratio of slurry H to silver aluminate is 1:0.2;
[0087] Step S12, prepare the second oxide layer: Immerse cordierite in slurry I, and obtain the second oxide layer through drying and calcination. The thickness of the second oxide layer is 10 cm. The drying temperature is 150°C, and the calcination temperature is 1000°C. The drying time is 4 hours, and the calcination time is 5 hours. The dosage of slurry I is 150 g / L of cordierite;
[0088] Step S13, stacking and bonding: stacking and bonding the first oxide layer, the adsorption layer, and the second oxide layer in sequence to form an SCR catalyst.
[0089] The following is a systematic explanation of the technical effects achieved by the technical solution of the present invention through comparative examples.
[0090] Comparative Example 1
[0091] In step S11, silver nitrate is used instead of silver aluminate, and the other steps are the same as those in Example 1.
[0092] Comparative Example 2
[0093] In step S11, chloroplatinic acid is used instead of silver aluminate, and the other steps are the same as those in Example 1.
[0094] Comparative Example 3
[0095] In step S3, no lithium nitrate solution impregnation is performed, and the other steps are the same as those in Example 1.
[0096] Comparative Example 4
[0097] The SCR catalyst was prepared using the first oxidation layer and the adsorption layer, without using the second oxidation layer. Other steps were the same as those in Example 1.
[0098] Comparative Example 5
[0099] Only the first oxide layer was used to prepare the SCR catalyst, and the other steps were the same as those in Comparative Example 4.
[0100] Comparative Example 6
[0101] In step S6, EDTA was not used, and ferric nitrate was directly dissolved in water. The other steps were the same as those in Example 1.
[0102] Comparative Example 7
[0103] In step S4, tert-butanol impregnation was not performed, and chloroplatinic acid aqueous solution impregnation was performed directly, and the other steps were consistent with Comparative Example 6.
[0104] Comparative Example 8
[0105] In step S2, no ferrocenylbenzene solution impregnation was performed, and the other steps were the same as those in Comparative Example 7.
[0106] Comparative Example 9
[0107] In step S1, trivalent iron (ferric nitrate) is used for ion exchange reaction with zeolite, and the other steps are consistent with Comparative Example 8.
[0108] Comparative Example 10
[0109] In step S1, a divalent iron (ferrous nitrate) is used for an ion exchange reaction with zeolite, where the reaction temperature is 25°C, and other steps are the same as those in Comparative Example 8.
[0110] The zeolite model used in the above examples and comparative examples is ZSM-5 zeolite.
[0111] According to GB / T 38219-2019 "Technical Specification for Flue Gas Denitration Catalyst Testing", NO x conversion rate, that is, the percentage of NO x reduced; ammonia slip is measured, that is, the concentration of unreacted ammonia; the sulfur dioxide resistance performance is measured, that is, after the catalyst is treated with flue gas containing sulfur dioxide for 100 hours, compared with the initial value, the proportion of the decrease in the NO x conversion rate. NO x represents nitrogen oxides.
[0112] The test results are shown in the following table.
[0113] (1) Compared with Example 1, the sulfur dioxide resistance performance of Comparative Example 1 decreased. Compared with silver nitrate, silver ions in silver aluminate are embedded in the aluminum oxide lattice to form strong chemical bonds, making the oxidation of ammonia by Ag moderate and the selectivity relatively high, and it is not easy to form NO x , so the conversion rate is relatively high. In Comparative Example 1, silver nitrate has a strong oxidizing property and a low selectivity, resulting in over-oxidation of ammonia to form NO x , causing the conversion rate to decrease. Silver ions in silver aluminate are embedded in the aluminum oxide lattice to form strong chemical bonds, and it is difficult to form silver sulfate, so the sulfur dioxide resistance performance is relatively high. In Comparative Example 1, silver nitrate has a low sulfur dioxide resistance performance and is easy to form silver sulfate, resulting in sulfur poisoning and reducing the oxidation performance of silver, causing an increase in ammonia slip.
[0114] (2) Compared with Example 1, the sulfur dioxide resistance performance of Comparative Example 2 decreased. Compared with chloroplatinic acid, silver ions in silver aluminate are embedded in the aluminum oxide lattice to form strong chemical bonds, making the oxidation of ammonia by silver moderate and the selectivity relatively high, and it is not easy to form NO x , so the conversion rate is relatively high. In Comparative Example 2, chloroplatinic acid has a strong oxidizing property and a low selectivity, resulting in over-oxidation of ammonia to form NO x , causing the conversion rate to decrease. Silver ions in silver aluminate are embedded in the aluminum oxide lattice to form strong chemical bonds, and it is difficult to form silver sulfate, so the sulfur dioxide resistance performance is relatively high. In Comparative Example 2, chloroplatinic acid has a low sulfur dioxide resistance performance, resulting in sulfur poisoning and reducing the oxidation performance of platinum, causing an increase in ammonia slip.
[0115] (3) Compared with Example 1, the sulfur dioxide resistance of Comparative Example 3 decreased. Lithium is an alkali metal with extremely strong reducibility and is very easy to lose electrons. Lithium preferentially reacts with sulfides (such as sulfur dioxide) to form sulfates, thereby reducing the poisoning effect of sulfur on active metals (such as silver and iron) and maintaining the activity of the catalyst. Subsequently, the catalyst is regenerated by high-temperature decomposition of lithium sulfate. By impregnating with a lithium nitrate solution, lithium is doped into the SCR catalyst, improving the sulfur dioxide resistance of the SCR catalyst.
[0116] (4) Compared with Example 1, the ammonia slip of Comparative Example 4 increased. By setting the second oxide layer, the ammonia slip can be reduced. During the SCR reaction, generally ammonia is in excess. The second oxide layer can effectively prevent ammonia slip. The ammonia slip values of silver aluminate, silver nitrate, and chloroplatinic acid in the second oxide layer are all extremely low.
[0117] (5) Compared with Comparative Example 4, the NO x conversion rate decreased and the ammonia slip increased. The first oxide layer contains a strong oxidant platinum, which oxidizes nitric oxide in the gas into nitrogen dioxide, increasing the proportion of nitrogen dioxide and promoting the fast SCR reaction. The remaining nitric oxide and ammonia after the fast SCR reaction reach the adsorption layer. The acidic sites in the zeolite in the adsorption layer can adsorb ammonia and nitric oxide and continue the standard SCR reaction to further increase the NO x conversion rate. The extremely small amount of ammonia remaining after the standard SCR reaction reaches the second oxide layer and is oxidized to form nitrogen gas under the action of silver aluminate in the second oxide layer, avoiding the over-oxidation of ammonia to form nitric oxide and preventing ammonia leakage at the same time. In Comparative Example 5, the adsorption layer and the second oxide layer were not set, resulting in a decrease in the NO x conversion rate and an increase in ammonia slip.
[0118] (6) Compared with Example 1, the NO x conversion rate decreased. During the impregnation process, EDTA forms stable complexes (such as Fe-EDTA) with metal ions (such as ferric ions) to ensure the uniform dispersion of ferric ions on the surface of cerium dioxide during the impregnation process. During drying, EDTA inhibits the crystallization and agglomeration of ferric nitrate, making ferric ions uniformly cover the surface of cerium dioxide. During calcination, EDTA and ferric nitrate decompose at high temperature to form Fe-O-Ce bonds and are fixed on the surface of cerium dioxide. By using EDTA, the uniformity of the distribution of iron on the surface of cerium dioxide is improved, increasing the NO x conversion rate.
[0119] (7) Compared with Comparative Example 6, the NO xThe conversion rate decreases. By filling tert-butanol in the micropores of the zeolite, it is prevented that platinum enters the interior of the micropores of the zeolite during the loading process, thereby ensuring that platinum is mainly loaded on the outer surface position of the zeolite. If platinum is located inside the micropores of the zeolite, firstly, reactants such as nitric oxide need to diffuse into the narrow pores to contact platinum, and the diffusion resistance will reduce the reaction rate; secondly, if some pores are blocked, it will hinder the diffusion of reactants and products and reduce the catalytic efficiency. When platinum is located on the zeolite surface and directly exposed to the gas stream, the reactants do not need to experience pore diffusion limitation and can quickly reach the active sites. Even if the pore structure is blocked, it will not affect the reaction efficiency, thus improving the reaction efficiency.
[0120] (8) Compared with Comparative Example 7, in Comparative Example 8, NO x The conversion rate decreases. Restricted by the preparation process, the zeolite has non-uniformity, resulting in the possible existence of hydrophilic regions and hydrophobic regions in the micropores of the zeolite. In step S1, ferrous nitrate is used for the ion exchange reaction, which is effective for the hydrophilic regions, but the ability to bind divalent iron in the hydrophobic regions is weak. Ferrocene is an organometallic compound with a sandwich structure formed by an iron atom sandwiched between two cyclopentadienyl anions. By impregnating with a ferrocene benzene solution, iron can be effectively loaded into the hydrophobic pores of the zeolite, and the iron is fixed in the hydrophobic regions during the subsequent calcination process, further improving the uniformity and density of the distribution of iron ions in the zeolite pores, thereby significantly improving the activity of the SCR catalyst and increasing the NO x conversion rate.
[0121] (9) Compared with Comparative Example 8, in Comparative Example 9 and Comparative Example 10, NO x The conversion rate decreases. The hydrated ionic radius of divalent iron in an aqueous solution at 25 °C is about 0.6 nm - 0.7 nm, which is larger than the pore diameter of ZSM-5 zeolite of about 0.5 nm - 0.6 nm. However, at elevated temperatures and in an inert atmosphere, the hydration layer of divalent iron will shrink (from the heptahydrate to the monohydrate step by step), thereby reducing its size to be able to enter the zeolite pores. Through ion exchange, iron ions are fixed in the pores of the zeolite. During the subsequent aerobic calcination process, divalent iron is oxidized to Fe 3+ , forming the active center. While the hydrated layer of iron ions (Fe 3+ ) is larger and has a higher charge density under the same conditions, resulting in a more stable hydrated layer and being difficult to reduce the size by heating. Affected by steric hindrance, Fe 3+ is difficult to enter the deep part of the zeolite pores. Therefore, the catalytic activity after ion exchange with divalent iron at high temperature is significantly higher than that of Fe 3+ , and also higher than that at 25 °C.
[0122] Through the technical solution of the present invention, the NO x conversion rate is relatively high, all greater than 99%; the ammonia slip is extremely low, only 0.01 mg / m 3; High sulfur dioxide resistance, and the reduction ratios of NO x conversion rates are all lower than 1%.
[0123] Table 1: Detection results of examples and comparative examples
[0124]
[0125]
Claims
1. A preparation method of an SCR catalyst, characterized in that, It includes the following steps: Step S1, divalent iron and zeolite ion exchange reaction: Under a nitrogen atmosphere, disperse zeolite in an aqueous solution of ferrous nitrate for ion exchange reaction, and then obtain zeolite A through filtration and calcination; Step S2, impregnate zeolite A with a ferrocene benzene solution: Under a nitrogen atmosphere, impregnate zeolite A with a ferrocene benzene solution, and then obtain zeolite B through filtration, drying, and calcination; Step S3, impregnate zeolite B with a lithium nitrate solution: Impregnate zeolite B with a lithium nitrate solution, and then obtain zeolite C through filtration, drying, and calcination; Step S4, impregnate zeolite C with tert-butanol: Impregnate zeolite C in tert-butanol and wash to make zeolite D; Step S5, impregnate zeolite D with an aqueous solution of chloroplatinic acid: Impregnate zeolite D with an aqueous solution of chloroplatinic acid, and then obtain zeolite E through filtration, drying, and calcination; Step S6, EDTA treatment: Dissolve ferric nitrate and EDTA in water to make a chelating solution, disperse cerium dioxide powder in the chelating solution, and obtain cerium dioxide F through separation by filtration and calcination; Step S7, silica bonding: Mix cerium dioxide F, zeolite E, and silica sol, and ball mill to make slurry G; Step S8, prepare the first oxide layer: Impregnate cordierite in slurry G and make the first oxide layer through drying and calcination; Step S9, silica bonding: Mix cerium dioxide F, zeolite C, and silica sol, and ball mill to make slurry H; Step S10, prepare the adsorption layer: Impregnate cordierite in slurry H and make the adsorption layer through drying and calcination; Step S11, silver aluminate treatment: Mix slurry H with silver aluminate and ball mill to make slurry I; Step S12, prepare the second oxide layer: Impregnate cordierite in slurry I and make the second oxide layer through drying and calcination; Step S13, stack and bond: Stack and bond the first oxide layer, adsorption layer, and second oxide layer in sequence to make an SCR catalyst.
2. The preparation method according to claim 1, wherein In step S1, the mass concentration of the aqueous solution of ferrous nitrate is 2% - 10%; the mass ratio of the zeolite to the aqueous solution of ferrous nitrate is 1:(15 - 25); the ion exchange reaction time is 10 hours - 20 hours; the ion exchange reaction temperature is 80°C - 100°C; the ion exchange reaction pH is 1 - 3; the calcination temperature is 300°C - 500°C; the calcination time is 8 hours - 10 hours.
3. The preparation method according to claim 2, characterized in that, In step S2, the mass concentration of the ferrocene benzene solution is 3% - 5%; the mass ratio of zeolite A to the ferrocene benzene solution is 1:(3 - 5); the impregnation time is 10 hours - 20 hours; the impregnation temperature is 20°C - 30°C; the drying time is 4 hours - 6 hours; the drying temperature is 40°C - 60°C; the calcination temperature is 300°C - 500°C; the calcination time is 4 hours - 6 hours.
4. The preparation method according to claim 3, characterized in that, In the step S3, the mass concentration of the lithium nitrate solution is 0.2-0.4%; the mass ratio of the zeolite B to the lithium nitrate solution is 1:(3-5); the impregnation time is 3 hours to 5 hours; the impregnation temperature is 40°C to 50°C; the drying temperature is 50°C to 150°C; the drying time is 2 hours to 4 hours; the calcination temperature is 400°C to 500°C; the calcination time is 3 hours to 5 hours.
5. The preparation method according to claim 4, characterized in that, In the step S4, the mass ratio of the zeolite C to the tert-butanol is 1:(4-5); the impregnation time is 3 hours to 5 hours; the impregnation temperature is 40°C to 50°C.
6. The preparation method according to claim 5, characterized in that, In the step S5, the mass concentration of the chloroplatinic acid aqueous solution is 10%-15%; the mass ratio of the zeolite D to the chloroplatinic acid aqueous solution is 1:(2-4); the impregnation time is 3 hours to 5 hours; the impregnation temperature is 40°C to 50°C; the drying temperature is 50°C to 150°C; the drying time is 2 hours to 4 hours; the calcination temperature is 400°C to 500°C; the calcination time is 3 hours to 5 hours.
7. The preparation method according to claim 6, characterized in that In the step S6, the dispersion time is 1 hour to 2 hours, and the dispersion temperature is 30°C to 40°C; the pH of the chelating solution is 4 to 6; the mass concentration of EDTA in the chelating solution is 2% to 4%; the mass concentration of iron nitrate in the chelating solution is 3% to 5%; the calcination temperature is 500°C to 600°C; the calcination time is 2 hours to 4 hours; the specific surface area of the cerium dioxide is 150m 2 / g to 180m 2 / g; the mass concentration of iron in the cerium dioxide F is 0.5% to 1%.
8. The preparation method according to claim 7, wherein In the step S7, the mass ratio of the cerium dioxide F, the zeolite E, and the silica sol is 1:(4-5):(1-2); the mass concentration of the silica in the silica sol is 20%-30%.
9. An SCR catalyst, characterized in that, The SCR catalyst is prepared by the preparation method described in claim 1.