Preparation method of low-temperature sulfur-tolerant Cu-CHA denitration catalyst without Cu sites on surface
By selectively removing copper sites on the surface of Cu-CHA catalyst and constructing an inert protective layer using macromolecular complexing agents, combined with the microporous sieving effect of CHA molecular sieves, the problem of easy deactivation of Cu-CHA catalyst in low-temperature SO2-containing waste gas was solved, achieving high efficiency, sulfur resistance, stability, and high denitrification activity.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- QINGYUAN INNOVATION LABORATORY
- Filing Date
- 2026-03-03
- Publication Date
- 2026-06-02
AI Technical Summary
Existing Cu-CHA catalysts are prone to deactivation in low-temperature SO2-containing waste gas, mainly because SO2 oxidizes at copper sites on the catalyst surface to form sulfates, leading to a decrease in catalyst activity. Current technologies have failed to effectively address the precise control and removal of copper sites on the surface.
By selectively complexing the Cu sites on the surface of the Cu-CHA catalyst with a macromolecular complexing agent, the surface copper sites are removed and an inert protective layer is constructed. At the same time, the microporous sieving effect of CHA molecular sieve is utilized to block SO2 from entering the interior and contacting the active Cu sites.
This study achieved high sulfur resistance and stability of the catalyst under low temperature and high sulfur environment, maintained high denitrification activity for a long time, avoided sulfate formation, and improved the catalyst's sulfur resistance performance.
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Figure CN121755262B_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of environmental catalysis and air pollution control technology, specifically relating to a method for preparing a low-temperature sulfur-resistant Cu-CHA denitrification catalyst with no Cu sites on its surface. Background Technology
[0002] Nitrogen oxides (NO) x NOx is one of the major air pollutants. Its large-scale emissions lead to a series of environmental problems, including photochemical smog, acid rain, fine particulate matter formation, and ozone layer depletion, and seriously endanger human health. Therefore, developing efficient NOx emission control technologies is crucial. x Purification technology has urgent practical significance. Among numerous denitrification technologies, ammonia selective catalytic reduction (NH3-SCR) technology is widely used for NO removal from both stationary and mobile sources due to its high efficiency and selectivity. x The core technology for emission control lies in the development of high-performance catalysts.
[0003] Currently, one of the main challenges faced by low-temperature NH3-SCR catalysts in practical applications is SO2 poisoning. Especially in low-temperature exhaust gas environments (typically below 250 °C), SO2 is easily oxidized to SO4 at the redox active sites of the catalyst. 2- This leads to a reaction with NH3 to form NH4HSO4 or (NH4)2SO4. These sulfate species can both coat the surface of the active sites and physically block the reaction pathways. - SO2 can also form thermally stable surface sulfates with active metal components, disrupting the redox cycle required for the NH3-SCR reaction, leading to a significant decrease in catalyst activity or even deactivation. Therefore, the essence of low-temperature SO2 poisoning can be attributed to the catalytic oxidation of SO2 at active sites. If the oxidation process of SO2 at active sites can be inhibited or avoided, it is hoped that the sulfur resistance of the catalyst can be improved from the root.
[0004] Among numerous low-temperature NH3-SCR catalysts, copper-based molecular sieve catalysts, especially Cu-SSZ-13 and Cu-SAPO-34 with chalcogenide (CHA) structures, have become mainstream commercial catalysts for denitrification of exhaust gases from mobile sources such as diesel vehicles due to their excellent low-temperature activity, wide temperature window, good hydrothermal stability, and nitrogen selectivity. The active centers of these catalysts are copper ions distributed in the pores of the CHA framework, mainly located at six-membered and eight-membered ring positions. Their structural characteristics determine that copper sites exist simultaneously on the molecular sieve surface and in the internal pores. While the copper sites exposed on the surface participate in the catalytic reaction, they also become the main sites for SO2 oxidation and sulfate formation, leading to pore inlet blockage and active site coverage. On the other hand, the microporous structure (approximately 0.38 nm) of the CHA framework itself possesses a certain molecular sieving effect, theoretically restricting the free entry of larger SO2 molecules (molecular dynamic diameter approximately 0.41 nm) into the pores, thereby protecting the internal copper sites from SO2 erosion.
[0005] Based on the above analysis, if copper species on the surface of Cu-CHA catalysts can be selectively removed or passivated, retaining only the copper active sites inside the pores, it is possible to prevent SO2 oxidation on the catalyst surface by eliminating surface copper sites, thereby blocking the surface formation and deposition of substances such as NH4HSO4. Simultaneously, due to the size effect of CHA pores, SO2 has difficulty penetrating deep into the pores and contacting the internal copper sites, thus improving the overall sulfur resistance of the catalyst. However, existing research on improving the sulfur resistance of Cu-CHA catalysts mainly focuses on introducing protective components (Chinese patent applications CN115739171A, CN105478161A), optimizing the preparation process, or performing post-treatment modifications (Chinese patent applications CN115920957A, CN108355707A). There are no reports on constructing a "surface inert, internally active" structure by precisely controlling the spatial distribution of copper sites and selectively removing surface copper. Summary of the Invention
[0006] The purpose of this invention is to overcome the technical defect of existing Cu-CHA catalysts being easily deactivated in low-temperature SO2-containing waste gas, and to provide a method for preparing a low-temperature sulfur-resistant Cu-CHA denitrification catalyst with no Cu sites on its surface.
[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows:
[0008] A method for preparing a low-temperature sulfur-resistant Cu-CHA denitration catalyst with no Cu sites on its surface includes the following steps:
[0009] (1) Add silicon source, aluminum source, alkali source, template agent and deionized water to a beaker and age at 35~90 °C for 1~16 h to form a gel. Then transfer the gel to a reaction vessel with a polytetrafluoroethylene liner and crystallize at 140~200 °C for 1~10 days. After crystallization, filter, wash and dry the product and calcine at 500~650 °C for 5~8 h to obtain a solid product.
[0010] (2) Add the above solid product to an ammonium salt solution, stir at 45~90 °C for 3~24 h to carry out ammonium exchange, then filter, wash, dry, and calcine at 400~650 °C for 2~18 h to obtain hydrogen-form CHA molecular sieve.
[0011] (3) Add hydrogen-type CHA molecular sieve to copper salt solution, stir at 30~80 °C for 3~12 h to exchange copper, then filter, wash and dry, and calcine at 450~700 °C for 1~12 h to obtain Cu-CHA denitration catalyst.
[0012] (4) Add the Cu-CHA denitrification catalyst to the macromolecular complexing agent solution, stir at 25~60 °C for 1~36 h, then filter, wash and dry to obtain a low-temperature sulfur-resistant Cu-CHA denitrification catalyst with no Cu sites on the surface.
[0013] In step (1), the molar ratio of the silicon source, aluminum source, alkali source, template agent and deionized water is 1:0.005~0.98:0.001~3.6:0.01~10:10~1000.
[0014] In step (1), the silicon source is at least one of fumed silica, ethyl silicate, water glass, silica sol, silica fume, and sodium silicate.
[0015] In step (1), the aluminum source is at least one of boehmite, aluminum nitrate, aluminum hydroxide, aluminum isopropoxide, aluminum oxide, and sodium aluminate.
[0016] In step (1), the alkali source is at least one of sodium hydroxide, potassium hydroxide, and cesium hydroxide.
[0017] In step (1), the template agent is at least one of N,N,N-trimethyl-1-adamantyl ammonium hydroxide and N,N-dimethylethylcyclohexylamine.
[0018] In step (2), the ammonium salt solution is at least one of ammonium sulfate solution, ammonium nitrate solution, and ammonium chloride solution.
[0019] In step (2), the concentration of the ammonium salt solution is 0.01~2 mol / L, and the ratio of the amount of solid product to the amount of ammonium salt solution is 1g:50~300mL.
[0020] In step (3), the copper salt solution is at least one of copper sulfate solution, copper chloride solution, and copper acetate solution.
[0021] In step (3), the concentration of the copper salt solution is 0.001~1 mol / L, and the ratio of hydrogen-form CHA molecular sieve to copper salt solution is 1g:10~150mL.
[0022] In step (4), the macromolecular complexing agent is at least one of grafted iminodiacetic acid, grafted triethylenetetramine, polystyrene, polyacrylic acid microspheres, and polyamide-amine dendritic polymer.
[0023] In step (4), the ratio of Cu-CHA denitrification catalyst to macromolecular complexing agent solution is 1g:1~200mL, and the mass volume fraction of macromolecular complexing agent in macromolecular complexing agent solution is 10~80%.
[0024] This invention employs the above technical solution to provide a method for NO control in waste gas pollution prevention and control. x A catalyst for the selective catalytic reduction of ammonia is provided, which is a Cu-CHA denitrification catalyst with a Cu-free surface and excellent resistance to sulfur poisoning. Compared with existing technologies, the advantages of this invention are:
[0025] 1. This invention utilizes the steric hindrance effect of macromolecular complexing agents to achieve precise differentiation and selective removal of copper sites on the surface and inside of Cu-CHA catalysts, thereby improving their low-temperature sulfur resistance. The principle lies in the selective complexation of macromolecular complexing agents with Cu sites on the surface of the Cu-CHA denitrification catalyst. Without entering the internal pores of the catalyst, Cu species are specifically removed from the surface, thus constructing a "Cu-free" protective layer on the catalyst surface while completely preserving the internal active Cu sites. The formation of this surface structure completely blocks the oxidation reaction of SO2 at the Cu sites on the catalyst surface, fundamentally avoiding the formation of toxic byproducts such as ammonium bisulfate and copper sulfate during low-temperature denitrification. Simultaneously, the inherent microporous sieving effect of the Cu-CHA molecular sieve (its pore size is smaller than the dynamic diameter of SO2 molecules) effectively prevents SO2 molecules from diffusing into the pores and contacting the active Cu sites. The synergistic effect of these two mechanisms enables the prepared catalyst to exhibit excellent sulfur resistance stability in harsh low-temperature, sulfur-containing flue gas environments. Experiments show that the catalyst can maintain high denitrification activity for a long time under simulated low temperature and high sulfur conditions in actual industry.
[0026] 2. This invention constructs a novel gradient functionalized sulfur-resistant structure with an inert outer surface and active inner pores. This structure physically isolates and functionally integrates the catalytically active region (internal pores) and the anti-poisoning protection region (inert surface) in space, forming a dual synergistic protection mechanism that actively eliminates surface reactivity and passively utilizes size sieving.
[0027] 3. This invention develops a method for preparing a sulfur-resistant high-performance denitrification catalyst that is mild, simple, and easy to scale up. This method provides an efficient and low-cost technical path for upgrading the performance of existing commercial Cu-CHA catalysts. It can meet the urgent needs of many non-power industries and other low-temperature flue gas denitrification scenarios for efficient and stable catalysts and has good prospects for industrial application. Attached Figure Description
[0028] Figure 1 The images show the XRD patterns of the catalysts obtained in Example 1 and Comparative Example 1 of this invention.
[0029] Figure 2 The graphs show the low-temperature sulfur resistance performance evaluation of the catalysts obtained in Examples 1-5 and Comparative Example 1 of this invention. Detailed Implementation
[0030] Example 1
[0031] A method for preparing a low-temperature sulfur-resistant Cu-CHA denitration catalyst with no Cu sites on its surface includes the following steps:
[0032] (1) Weigh 16.8 g of silica sol, 1.63 g of alumina, 0.32 g of sodium hydroxide, 10.3 g of N,N,N-trimethyl-1-adamantyl ammonium hydroxide, and 35 g of deionized water and add them sequentially to a beaker. The mixture is aged at 60 °C for 3 h to form a gel. Then, it is transferred to a high-pressure reactor with a polytetrafluoroethylene liner and crystallized at 160 °C for 6 d. After crystallization, the mixture is filtered, washed, and dried to obtain a solid product. The solid product is then calcined at 600 °C for 6 h to obtain Na-SSZ-13.
[0033] (2) Weigh 3 g of Na-SSZ-13 and add it to 300 ml of 1 mol / L ammonium chloride solution. Stir at 80 °C for 6 h, filter, wash, dry and calcine at 500 °C for 5 h to obtain H-SSZ-13.
[0034] (3) Weigh 2 g of H-SSZ-13 and add it to 100 ml of 0.2 mol / L copper nitrate solution. Stir at 60 °C for 3 h, filter, wash, dry and calcine at 550 °C for 6 h to obtain Cu-SSZ-13.
[0035] (4) Weigh 2 g of Cu-SSZ-13 and add it to 150 ml of grafted iminodiacetic acid solution with a mass volume fraction of 30%. Stir at 25 °C for 6 h, filter, wash and dry to obtain low-temperature sulfur-resistant Cu-SSZ-13 with no Cu sites on the surface.
[0036] Example 2
[0037] A method for preparing a low-temperature sulfur-resistant Cu-CHA denitration catalyst with no Cu sites on its surface includes the following steps:
[0038] (1) Weigh 4.6 g of fumed silica, 1.12 g of aluminum hydroxide, 0.42 g of potassium hydroxide, 6.8 g of N,N,N-trimethyl-1-adamantyl ammonium hydroxide, and 45 g of deionized water and add them sequentially to a beaker. The mixture is aged at 70 °C for 5 h to form a gel. It is then transferred to a high-pressure reactor with a polytetrafluoroethylene liner and crystallized at 170 °C for 5 days. After crystallization, the product is filtered, washed, and dried to obtain a solid product. The solid product is then calcined at 650 °C for 5 h to obtain Na-SSZ-13.
[0039] (2) Weigh 3.5 g Na-SSZ-13 and add it to 360 ml of 1.25 mol / L ammonium sulfate solution. Stir at 70 °C for 8 h, filter, wash and dry, and then calcine at 600 °C for 6 h to obtain H-SSZ-13.
[0040] (3) Weigh 2.5 g of H-SSZ-13 and add it to 125 ml of 0.3 mol / L copper acetate solution. Stir at 70 °C for 2 h, filter, wash and dry, and then calcine at 500 °C for 5 h to obtain Cu-SSZ-13.
[0041] (4) Weigh 2.5 g of Cu-SSZ-13 and add it to 200 ml of a 45% (w / v) grafted triethylenetetramine solution. Stir at 30 °C for 4 h. After filtration, washing and drying, obtain low-temperature sulfur-resistant Cu-SSZ-13 with no Cu sites on the surface.
[0042] Example 3
[0043] A method for preparing a low-temperature sulfur-resistant Cu-CHA denitration catalyst with no Cu sites on its surface includes the following steps:
[0044] (1) Weigh 17.6 g of water glass, 0.92 g of aluminum nitrate, 0.32 g of cesium hydroxide, 11.7 g of N,N,N-trimethyl-1-adamantyl ammonium hydroxide, and 30 g of deionized water and add them sequentially to a beaker. The mixture is aged at 80 °C for 5 h to form a gel. Then, it is transferred to a high-pressure reactor with a polytetrafluoroethylene liner and crystallized at 150 °C for 7 days. After crystallization, the product is filtered, washed, and dried to obtain a solid product. The solid product is then calcined at 500 °C for 8 h to obtain Na-SSZ-13.
[0045] (2) Weigh 4 g of Na-SSZ-13 and add it to 450 ml of 1.5 mol / L ammonium nitrate solution. Stir at 70 °C for 8 h, filter, wash, dry and calcine at 550 °C for 4 h to obtain H-SSZ-13.
[0046] (3) Weigh 3 g of H-SSZ-13 and add it to 160 ml of 0.27 mol / L copper chloride solution. Stir at 65 °C for 3.5 h, filter, wash, dry and calcine at 500 °C for 5 h to obtain Cu-SSZ-13.
[0047] (4) Weigh 3 g of Cu-SSZ-13 and add it to 120 ml of polystyrene solution with a mass volume fraction of 45%. Stir at 25 °C for 5 h, filter, wash and dry to obtain low-temperature sulfur-resistant Cu-SSZ-13 with no Cu sites on the surface.
[0048] Example 4
[0049] A method for preparing a low-temperature sulfur-resistant Cu-CHA denitration catalyst with no Cu sites on its surface includes the following steps:
[0050] (1) Weigh 5.6 g sodium silicate, 0.61 g aluminum isopropoxide, 0.43 g sodium hydroxide, 13.8 g N,N,N-trimethyl-1-adamantyl ammonium hydroxide, and 43 g deionized water and add them sequentially to a beaker. The mixture is aged at 75 °C for 5 h to form a gel. Then, it is transferred to a high-pressure reactor with a polytetrafluoroethylene liner and crystallized at 165 °C for 5 days. After crystallization, the product is filtered, washed, and dried to obtain a solid product. The solid product is then calcined at 600 °C for 5 h to obtain Na-SSZ-13.
[0051] (2) Weigh 2 g of Na-SSZ-13 and add it to 120 ml of 1.5 mol / L ammonium chloride solution. Stir at 70 °C for 5 h, filter, wash, dry and calcine at 550 °C for 6 h to obtain H-SSZ-13.
[0052] (3) Weigh 1 g of H-SSZ-13 and add it to 60 ml of 0.16 mol / L copper nitrate solution. Stir at 65 °C for 3.5 h, filter, wash and dry, and then calcine at 600 °C for 5 h to obtain Cu-SSZ-13.
[0053] (4) Weigh 1 g of Cu-SSZ-13 and add it to 75 ml of grafted iminodiacetic acid solution with a mass volume fraction of 35%. Stir at 25 °C for 4 h. After filtration, washing and drying, obtain low-temperature sulfur-resistant Cu-SSZ-13 with no Cu sites on the surface.
[0054] Example 5
[0055] A method for preparing a low-temperature sulfur-resistant Cu-CHA denitration catalyst with no Cu sites on its surface includes the following steps:
[0056] (1) Weigh 18.5 g of silica sol, 0.51 g of aluminum hydroxide, 0.64 g of sodium hydroxide, 13.8 g of N,N,N-trimethyl-1-adamantyl ammonium hydroxide, and 30 g of deionized water and add them sequentially to a beaker. The mixture is aged at 75 °C for 8 h to form a gel. Then, it is transferred to a high-pressure reactor with a polytetrafluoroethylene liner and crystallized at 175 °C for 4 days. After crystallization, the product is filtered, washed, and dried to obtain a solid product. The solid product is then calcined at 650 °C for 7 h to obtain Na-SSZ-13.
[0057] (2) Weigh 3.5 g Na-SSZ-13 and add it to 450 ml of 1.5 mol / L ammonium sulfate solution. Stir at 70 °C for 7 h, filter, wash, dry and calcine at 600 °C for 6 h to obtain H-SSZ-13.
[0058] (3) Weigh 3 g of H-SSZ-13 and add it to 175 ml of 0.37 mol / L copper sulfate solution. Stir at 75 °C for 4 h, filter, wash, dry and calcine at 600 °C for 6.5 h to obtain Cu-SSZ-13.
[0059] (4) Weigh 3 g of Cu-SSZ-13 and add it to 215 ml of 50% polyacrylic acid microsphere solution. Stir at 35 °C for 8 h, filter, wash and dry to obtain low-temperature sulfur-resistant Cu-SSZ-13 with no Cu sites on the surface.
[0060] Comparative Example 1
[0061] Except for step (4), the other processes are the same as those in Example 1.
[0062] Catalyst XRD determination
[0063] Example 1 and Comparative Example 1 were tested using a Rigaku D / max Ultima X-ray diffractometer. The results are as follows: Figure 1 As shown, the XRD characteristic peaks of the two samples are consistent, and their relative crystallinity is basically the same, indicating that the macromolecular complexing agent has no effect on the crystal structure of the Cu-CHA catalyst.
[0064] Catalyst sulfur resistance test
[0065] The catalysts prepared in Examples 1-5 and Comparative Example 1 were evaluated for their long-term sulfur and nitrogen denitrification performance in an SCR fixed-bed reactor. The catalysts were granulated through a 20-40 mesh sieve, and 0.25 g of catalyst was charged into the SCR reactor. The simulated gas composition was 500 ppm NO, 500 ppm NH3, 5 vol% O2, 500 ppm SO2, with N2 as the balance gas. The total gas flow rate was 600 mL / min, corresponding to a space velocity of approximately 160,000 h⁻¹. -1 The reaction was evaluated at a temperature range of 140 °C. The chemical composition of the fixed-bed outlet flue gas was determined using an Antaris™ IGS infrared gas analyzer manufactured by Thermo Fisher Scientific.
[0066] NO x Conversion rate calculation formula:
[0067] NO x conversion (%)=
[0068] The results are as follows Figure 2 As shown, the catalysts in Examples 1-5 were evaluated under the above-mentioned simulated flue gas for 400 hours, and the NO content was... x The conversion rates of all catalysts exceeded 95.2%, while the conversion rate of catalyst 1 in Comparative Example 1 was significantly lower than that of NO within 25 hours. x The conversion rate was less than 15%. These results indicate that the Cu-CHA catalyst with no copper sites on its surface, prepared based on the method of this invention, exhibits excellent low-temperature sulfur resistance.
Claims
1. A method for preparing a low-temperature sulfur-resistant Cu-CHA denitration catalyst with no Cu sites on its surface, characterized in that, Includes the following steps: (1) A silicon source, aluminum source, alkali source, template agent and water are aged at 35~90 °C for 1~16 h to form a gel. The gel is then transferred to a reaction vessel with a polytetrafluoroethylene liner and crystallized at 140~200 °C for 1~10 days. After crystallization, the product is filtered, washed, dried and calcined to obtain a solid product. (2) Add the above solid product to an ammonium salt solution and stir at 45~90 °C for 3~24 h to carry out ammonium exchange. Then filter, wash, dry and calcine to obtain hydrogen-type CHA molecular sieve. (3) Add hydrogen-type CHA molecular sieve to copper salt solution, stir at 30~80 °C for 3~12 h to exchange copper, then filter, wash, dry and calcine to obtain Cu-CHA denitrification catalyst; (4) Add Cu-CHA denitrification catalyst to macromolecular complexing agent solution, stir at 25~60 °C for 1~36 h, then filter, wash and dry to obtain low-temperature sulfur-resistant Cu-CHA denitrification catalyst with no Cu sites on the surface. The macromolecular complexing agent is at least one of grafted iminodiacetic acid, grafted triethylenetetramine, polyacrylic acid microspheres, and polyamide-amine dendritic polymer.
2. The preparation method of a low-temperature sulfur-resistant Cu-CHA denitrification catalyst with no Cu sites on its surface according to claim 1, characterized in that, In step (1), the silicon source is at least one of fumed silica, ethyl silicate, water glass, silica sol, silica fume, and sodium silicate; the aluminum source is at least one of boehmite, aluminum nitrate, aluminum hydroxide, aluminum isopropoxide, aluminum oxide, and sodium aluminate; the alkali source is at least one of sodium hydroxide, potassium hydroxide, and cesium hydroxide; the template agent is at least one of N,N,N-trimethyl-1-adamantyl ammonium hydroxide and N,N-dimethylethylcyclohexylamine; and the molar ratio of the silicon source, aluminum source, alkali source, template agent, and water is 1:0.005~0.98:0.001~3.6:0.01~10:10~1000.
3. The preparation method of a low-temperature sulfur-resistant Cu-CHA denitrification catalyst with no Cu sites on its surface according to claim 1, characterized in that, In step (2), the ammonium salt solution is at least one of ammonium sulfate solution, ammonium nitrate solution, and ammonium chloride solution.
4. The preparation method of a low-temperature sulfur-resistant Cu-CHA denitrification catalyst with no Cu sites on its surface according to claim 1, characterized in that, In step (2), the concentration of the ammonium salt solution is 0.01~2 mol / L, and the ratio of the amount of solid product to the amount of ammonium salt solution is 1g:50~300mL.
5. The preparation method of a low-temperature sulfur-resistant Cu-CHA denitrification catalyst with no Cu sites on its surface according to claim 1, characterized in that, In step (3), the copper salt solution is at least one of copper sulfate solution, copper chloride solution, and copper acetate solution.
6. The preparation method of a low-temperature sulfur-resistant Cu-CHA denitrification catalyst with no Cu sites on its surface according to claim 1, characterized in that, In step (3), the concentration of the copper salt solution is 0.001~1 mol / L, and the ratio of hydrogen-form CHA molecular sieve to copper salt solution is 1g:10~150mL.
7. The preparation method of a low-temperature sulfur-resistant Cu-CHA denitrification catalyst with no Cu sites on its surface according to claim 1, characterized in that, In step (4), the ratio of Cu-CHA denitrification catalyst to macromolecular complexing agent solution is 1g:1~200mL, and the mass volume fraction of macromolecular complexing agent in macromolecular complexing agent solution is 10~80%.
8. The preparation method of a low-temperature sulfur-resistant Cu-CHA denitrification catalyst with no Cu sites on its surface according to claim 1, characterized in that, The roasting in step (1) is at 500~650 °C for 5~8 h, the roasting in step (2) is at 400~650 °C for 2~18 h, and the roasting in step (3) is at 450~700 °C for 1~12 h.
9. A low-temperature sulfur-resistant Cu-CHA denitrification catalyst with no Cu sites on its surface, prepared by the method according to any one of claims 1 to 8.