A copper-based SCR catalyst and its preparation method

Abstract

The present invention belongs to the field of catalytic technology, and in particular relates to a copper-based SCR catalyst and a preparation method thereof. The copper-based SCR catalyst of the present invention uses cordierite as a carrier, and a first coating and a second coating are sequentially provided on the carrier, wherein the first coating is Cu-SSZ-39 and the second coating is Cu-SSZ-13; the silicon-aluminum ratio of Cu-SSZ-39 is (10-18):1; the copper content of Cu-SSZ-39 is 2.0-3.0%wt; the silicon-aluminum ratio of Cu-SSZ-13 is (15-25):1; and the copper content of Cu-SSZ-13 is 0.5-1.5%wt. The copper-based SCR catalyst of the present invention exhibits excellent NO reduction in a wide temperature range of 200-600°C. x Conversion efficiency, taking into account both cold start and high load conditions, with good thermal stability and anti-sintering performance, suitable for the complex environment of high temperature fluctuations in gasoline engine lean burn exhaust.

Description

Technical Field

[0001] The present invention relates to the field of catalysis technology, and in particular to a copper-based SCR catalyst and a preparation method thereof. Background Art

[0002] Faced with increasingly stringent automotive emissions regulations, gasoline engines must not only control pollutant emissions but also meet additional fuel efficiency standards. Traditional stoichiometric combustion methods struggle to achieve both these goals. Lean-burn technology, with its advantages in reducing fuel consumption and pollutant emissions, is considered a promising technology. However, controlling NOx emissions remains a key challenge in its application.

[0003] Under lean-burn conditions, traditional three-way catalysts (TWCs) are unable to effectively treat NOx due to excess oxygen. Furthermore, passenger cars are limited by space constraints and cannot accommodate urea storage equipment, making conventional NH3-SCR technology difficult to apply. Therefore, passive SCR technology has become a viable solution: during the rich-burn phase, an ammonia generation catalyst promotes ammonia generation and storage. During the lean-burn phase, ammonia stored in the SCR catalyst participates in the NH3-SCR reaction, achieving efficient NOx removal.

[0004] NOx aftertreatment significantly limits the development of lean-burn technology for gasoline engines. NH3 selective catalytic reduction (SCR) technology has been successfully applied to NOx conversion in diesel engines. "Copper-based SCR catalysts" refer to selective catalytic reduction (SCR) catalysts with copper (Cu) as the active component. They are primarily used to reduce nitrogen oxides (NOx) in automotive or industrial exhaust to harmless nitrogen (N2) and water (H2O) in the presence of ammonia (NH3) or urea. For gasoline engines, SCR catalysts must maintain high activity within a higher temperature window. Currently, mainstream diesel SCR catalysts use Cu molecular sieves as the active component, but NOx conversion rates are low in the high-temperature range. Furthermore, Cu molecular sieves are primarily prepared by ion exchange, which is complex to process and requires multiple washes to remove excess copper in the exchange solution, generating significant amounts of copper-containing wastewater.

[0005] However, compared to conventional SCR catalysts for diesel engines, lean-burn gasoline passive SCR technology faces the following two challenges: (1) Higher high-temperature tolerance requirements: Conventional diesel SCR catalysts generally operate at temperatures of 400-500°C, while lean-burn gasoline SCR catalysts must withstand higher exhaust temperatures (500-600°C) while still maintaining low-temperature activity. (2) Higher ammonia storage capacity requirements: In diesel SCR systems, the ammonia supply system directly provides the reducing agent, while passive SCR relies on ammonia stored inside the catalyst for reaction. Therefore, it is necessary to optimize the ammonia storage material and catalyst design to ensure NOx removal efficiency under lean-burn conditions.

[0006] In summary, passive SCR technology solves the ammonia supply problem of lean-burn gasoline engines through ammonia storage and utilization strategies, but further optimization of the catalyst's heat resistance and ammonia storage capacity is still needed to meet the requirements of future emission regulations. Summary of the Invention

[0007] The purpose of the present invention is to provide a copper-based SCR catalyst and a preparation method thereof, which are used to solve the problems faced by the prior art in promoting lean burn applications of gasoline engines, such as high-temperature catalyst deactivation, insufficient ammonia generation and storage capacity, complex system integration, and poor environmental friendliness of the preparation process.

[0008] A first aspect of the present invention provides a copper-based SCR catalyst, wherein the copper-based SCR catalyst uses cordierite as a carrier, and a first coating layer and a second coating layer are sequentially provided on the carrier from the inside to the outside, wherein the first coating layer is Cu-SSZ-39 and the second coating layer is Cu-SSZ-13;

[0009] The silicon-aluminum ratio of the Cu-SSZ-39 is (10-18):1; the copper content of the Cu-SSZ-39 is 2.0-3.0%wt; the copper-aluminum ratio of the Cu-SSZ-39 is (0.110-0.277):1;

[0010] The Cu-SSZ-39 is prepared by adding H-SSZ-39 molecular sieve to a copper precursor solution for ion exchange; the copper precursor in the copper precursor solution is copper acetate monohydrate;

[0011] The silicon-aluminum ratio of the Cu-SSZ-13 is (15-25): 1; the copper content of the Cu-SSZ-13 is 0.5-1.5%wt; the copper-aluminum ratio of the Cu-SSZ-13 is (0.039-0.188): 1;

[0012] The Cu-SSZ-13 is prepared by adding H-SSZ-13 molecular sieve to a copper precursor solution for ion exchange; the copper precursor in the copper precursor solution is copper acetate monohydrate;

[0013] The copper in the Cu-SSZ-39 and Cu-SSZ-13 exists in the form of copper ions.

[0014] In some embodiments of the present invention, the cordierite is honeycomb cordierite; the inner wall thickness of the cordierite is 2-4 mil; the pore density is 400-750 mesh; and the water absorption rate is 15%-35%.

[0015] In some embodiments of the present invention, the loading capacity of Cu-SSZ-39 is 50-80 g / L; the loading capacity of Cu-SSZ-13 is 50-80 g / L.

[0016] A second aspect of the present invention provides a method for preparing a copper-based SCR catalyst, comprising the following steps:

[0017] S1, adding H-SSZ-39 molecular sieve to a copper precursor solution for ion exchange to obtain Cu-SSZ-39, and adding a binder and a viscosity modifier after grinding to obtain a Cu-SSZ-39 slurry;

[0018] S2, adding H-SSZ-13 molecular sieve to the copper precursor solution for ion exchange to obtain Cu-SSZ-13, and adding a binder and a viscosity modifier after grinding to obtain a Cu-SSZ-13 slurry;

[0019] S3. Coating the Cu-SSZ-39 slurry obtained in step S1 on the cordierite, drying and calcining it, and then coating the Cu-SSZ-13 slurry obtained in step S2, drying and calcining it to obtain a copper-based SCR catalyst.

[0020] In some embodiments of the present invention, in the copper precursor solution in step S1 and step S2, the copper precursor is copper acetate monohydrate; and the solvent is deionized water.

[0021] In some embodiments of the present invention, the amount of copper precursor added to the copper precursor solution satisfies the following relationship:

[0022] ;

[0023] Among them, M CU is the amount of copper precursor added, in g;

[0024] M Z is the mass of H-SSZ-39 molecular sieve or H-SSZ-13 molecular sieve required for exchange, in g;

[0025] W is the Cu content in the copper-based SCR catalyst, in %.

[0026] In some embodiments of the present invention, the volume of the deionized water satisfies the following relationship:

[0027] ;

[0028] Among them, V H2O is the volume of deionized water, in L;

[0029] M CU is the amount of copper precursor added, in g;

[0030] C is the molar concentration of Cu in the copper precursor solution, in mol / L.

[0031] In some embodiments of the present invention, in step S1 and step S2, the ion exchange temperature is 65-85° C. and the time is 2-4 hours.

[0032] In some embodiments of the present invention, in step S1 and step S2, the binder is selected from one or more of pseudo-boehmite, liquid silica gel, and aluminum hydroxide sol.

[0033] In some embodiments of the present invention, in step S1 and step S2, the viscosity modifier is tartaric acid and / or modified styrene maleic acid copolymer solution.

[0034] In some embodiments of the present invention, in step S1, the amount of the binder added is 0.5%-3% of the mass of the H-SSZ-39 molecular sieve.

[0035] In some embodiments of the present invention, in step S1, the viscosity modifier is added in an amount of 0.5% to 3% of the mass of the H-SSZ-39 molecular sieve.

[0036] In some embodiments of the present invention, in step S1, the viscosity of the Cu-SSZ-39 slurry is 300-1000 Pa·s.

[0037] In some embodiments of the present invention, in step S2, the amount of the binder added is 0.5%-3% of the mass of the H-SSZ-13 molecular sieve.

[0038] In some embodiments of the present invention, in step S2, the viscosity modifier is added in an amount of 0.5% to 3% of the mass of the H-SSZ-13 molecular sieve.

[0039] In some embodiments of the present invention, in step S2, the viscosity of the Cu-SSZ-13 slurry is 300-1000 Pa·s.

[0040] In some embodiments of the present invention, in step S3, the loading ratio of the Cu-SSZ-39 slurry and the Cu-SSZ-13 slurry is (0.8-1.2):1.

[0041] In some embodiments of the present invention, in step S3, the drying is low-temperature slow drying followed by high-temperature rapid drying; the low-temperature slow drying is performed at a temperature of 50-70°C for 8-12 hours, and the high-temperature rapid drying is performed at a temperature of 100-150°C for 1-3 hours.

[0042] In some embodiments of the present invention, in step S3, the calcination temperature is 600-650° C. and the calcination time is 2-4 hours.

[0043] The present invention also provides the use of the copper-based SCR catalyst as described above and the copper-based SCR catalyst prepared by the preparation method as described above in NOx post-treatment.

[0044] The present invention has the following beneficial effects:

[0045] By optimizing the combination of molecular sieve types and the copper loading configuration, the present invention significantly improves the catalyst's ammonia storage capacity, thereby achieving efficient catalytic conversion of NOx over a wide temperature range of 200–600°C. This takes into account complex operating conditions such as cold start and high load, meets the application requirements of gasoline engines with lean burn and drastic temperature fluctuations, and adapts to the implementation needs of passive SCR technology in the gasoline engine field. Furthermore, the copper-based SCR catalyst of the present invention can still maintain good structural stability and uniform distribution of active sites under high temperature conditions of ≥600°C, overcoming the drawbacks of traditional Cu molecular sieve catalysts that are prone to sintering and deactivation at high temperatures. It exhibits excellent thermal stability and long-lasting catalytic performance, making it particularly suitable for the high thermal load operating environment of gasoline engines. DETAILED DESCRIPTION

[0046] Hereinafter, a copper-based SCR catalyst and a preparation method thereof will be described in detail.

[0047] The present invention connects the process of preparing copper molecular sieves by the traditional ion exchange method with the process of preparing SCR catalysts by the coating method. By using easily decomposable organic acid anions as the copper source and regulating the concentration of free Cu ions, the liquid after the ion exchange process can be directly used as part of the slurry required for preparing the catalyst by the coating method, thereby omitting the traditional filtering, washing, drying and calcining steps in the preparation process of copper molecular sieves, avoiding the treatment of residual free copper in the copper precursor solution, as well as the drying, calcining and catalyst slurry preparation processes of the molecular sieves after exchange, thereby greatly saving time and cost. At the same time, combined with the effects of different types of molecular sieves and their copper content on NO conversion performance, Cu-SSZ-13 with excellent low-temperature catalytic performance and Cu-SSZ-39 with good high-temperature stability were selected, and the copper content ranges suitable for each were further determined, and finally a copper-based SCR catalyst suitable for the lean burn technology route of gasoline engines was obtained. On this basis, the present invention was completed.

[0048] In a first aspect, the present invention provides a copper-based SCR catalyst. The copper-based SCR catalyst uses cordierite as a carrier, and a first coating and a second coating are sequentially provided on the carrier from the inside to the outside. The first coating is Cu-SSZ-39, and the second coating is Cu-SSZ-13. The silicon-aluminum ratio of Cu-SSZ-39 is (10-18):1, and can be optionally (10-13):1, (13-15):1, (15-18):1, or (10-15):1. , preferably 15:1; the copper content of Cu-SSZ-39 is 2.0-3.0%wt, optionally 2-2.5%wt, 2.5-2.8%wt, 2.8-3%wt, 2-2.5%wt or 2.5-3%wt, preferably 3%wt; the copper-aluminum ratio of Cu-SSZ-39 is (0.110-0.277):1, optionally (0.110-0.2):1 or (0.2-0.277):1;

[0049] Cu-SSZ-39 is prepared by adding H-SSZ-39 molecular sieve to a copper precursor solution for ion exchange; the copper precursor in the copper precursor solution is copper acetate monohydrate;

[0050] The silicon-aluminum ratio of Cu-SSZ-13 is (15-25):1, optionally (15-20):1, (20-25):1, preferably 20:1; the copper content of Cu-SSZ-13 is 0.5-1.5%wt, optionally 0.5-1%wt, 1-1.3%wt, 1.3-1.5%wt or 0-1.3%wt, preferably 1.3%wt; the copper-aluminum ratio of Cu-SSZ-13 is (0.039-0.188):1, optionally (0.039-0.1):1 or (0.1-0.188):1;

[0051] Cu-SSZ-13 is prepared by adding H-SSZ-13 molecular sieve to a copper precursor solution for ion exchange; the copper precursor in the copper precursor solution is copper acetate monohydrate;

[0052] The copper in Cu-SSZ-39 and Cu-SSZ-13 exists in the form of copper ions.

[0053] The silicon-aluminum ratio significantly affects the thermal stability and ammonia storage capacity of molecular sieves. While a low silicon-aluminum ratio provides more ion exchange sites, enhancing ammonia storage capacity, the high aluminum content in the framework makes the structure less stable under high-temperature hydrothermal conditions, which can easily lead to a decrease in catalytic performance after aging. Furthermore, the upper limit of copper content is limited by the maximum exchange capacity of the molecular sieve during a single exchange, meaning the added copper must be completely anchored within the molecular sieve structure. If the copper content is too low, it will be difficult to provide sufficient active centers, thus affecting the catalyst's NOx conversion efficiency in low-temperature regions.

[0054] In the copper-based SCR catalyst provided by the present invention, the cordierite is honeycomb cordierite; the inner wall thickness of the cordierite is 2-4 mil, which can be optionally 2-3 mil or 3-4 mil; the pore density is 400-750 mesh, which can be optionally 400-500 mesh, 500-600 mesh, 600-700 mesh or 700-750 mesh; the water absorption rate is 15%-35%, which can be optionally 15-20%, 20-25%, 25-30% or 30-35%.

[0055] In the copper-based SCR catalyst provided by the present invention, the loading amount of Cu-SSZ-39 is 50-80g / L, which can be 50-60g / L, 60-70g / L or 70-80g / L; the loading amount of Cu-SSZ-13 is 50-80g / L, which can be 50-60g / L, 60-70g / L or 70-80g / L. Under normal circumstances, a low coating amount will result in insufficient active components of the catalyst, affecting its NO x conversion efficiency; while too high a coating amount may result in poor slurry coating uniformity and decreased operability, while significantly increasing system pressure drop, which is not conducive to engineering applications.

[0056] A second aspect of the present invention provides a method for preparing a copper-based SCR catalyst, comprising the following steps:

[0057] S1, adding H-SSZ-39 molecular sieve to a copper precursor solution for ion exchange to obtain Cu-SSZ-39, and adding a binder and a viscosity modifier after grinding to obtain a Cu-SSZ-39 slurry;

[0058] S2, adding H-SSZ-13 molecular sieve to the copper precursor solution for ion exchange to obtain Cu-SSZ-13, and adding a binder and a viscosity modifier after grinding to obtain a Cu-SSZ-13 slurry;

[0059] S3. Coating the Cu-SSZ-39 slurry obtained in step S1 on the cordierite, drying and calcining it, and then coating the Cu-SSZ-13 slurry obtained in step S2, drying and calcining it to obtain a copper-based SCR catalyst.

[0060] In the preparation method of the copper-based SCR catalyst provided by the present invention, step S1 is to add H-SSZ-39 molecular sieve to a copper precursor solution for ion exchange to obtain Cu-SSZ-39, and then grind and add a binder and a viscosity modifier to obtain a Cu-SSZ-39 slurry. Step S2 is to add H-SSZ-13 molecular sieve to a copper precursor solution for ion exchange to obtain Cu-SSZ-13, and then grind and add a binder and a viscosity modifier to obtain a Cu-SSZ-13 slurry.

[0061] During the preparation of conventional copper-based SCR catalysts, ion exchange typically uses an excess copper ion solution to ensure sufficient copper is incorporated into the molecular sieve structure. However, this process produces unexchanged copper ions. If not adequately washed, these copper ions can easily form copper oxide during calcination, thereby affecting catalyst performance.

[0062] Through research, the applicants discovered that when the target copper loading of the catalyst is low, sufficient copper ion exchange can be achieved using a copper solution with an exchange capacity equal to that of the molecular sieve, resulting in extremely low residual unexchanged copper, thus omitting the traditional filtration and washing steps. The resulting product is in a slurry state. The applicants further adjust the solids content by regulating the concentration of the copper precursor in the exchange solution, achieving direct slurry preparation. This eliminates the need for powder drying, calcination, and subsequent slurry preparation, simplifying the process and reducing energy consumption and manufacturing costs.

[0063] In practice, different types of molecular sieves have certain tolerances for copper exchange concentrations. Above a certain concentration, copper ions cannot be fully exchanged into the framework. The applicant selected two molecular sieve materials, H-SSZ-39 and H-SSZ-13 (purchased from Tianjin Paison). Through cleaning experiments, they clearly defined the maximum copper loading achievable by these two molecular sieves during the ion exchange process, thereby determining the applicable copper content limits for each.

[0064] Because this process omits the washing step, the anions accompanying the copper solution will be retained. Therefore, the precursor needs to be a copper salt that is easily decomposed during subsequent processing and does not introduce impurity residues. Based on this, the applicant preferred copper acetate as the copper source, avoiding the use of copper sulfate and copper nitrate, which are prone to introducing sulfate and nitrate anions that are difficult to remove.

[0065] In the copper precursor solution in steps S1 and S2 of the present invention, the copper precursor is copper acetate monohydrate; the solvent is deionized water. The mass of the copper precursor in the copper precursor solution satisfies the following relationship:

[0066] ;

[0067] Among them, M CU is the amount of copper precursor added, in g;

[0068] M Z is the mass of H-SSZ-39 molecular sieve or H-SSZ-13 molecular sieve required for exchange, in g;

[0069] W is the Cu content in the copper-based SCR catalyst, in %; the volume of deionized water satisfies the following relationship:

[0070] ;

[0071] Among them, VH2O is the volume of deionized water, in L;

[0072] M CU is the amount of copper precursor added, in g;

[0073] C is the molar concentration of Cu in the copper precursor solution, in mol / L.

[0074] In step S1 and step S2 of the present invention, the ion exchange temperature is 65-85°C, optionally 65-70°C, 70-75°C, 75-80°C or 80-85°C; and the time is 2-4h, optionally 2-3h or 3-4h.

[0075] In step S1 and step S2 of the present invention, the binder is selected from one or more of pseudo-boehmite, liquid silica gel, and aluminum hydroxide sol.

[0076] In steps S1 and S2 of the present invention, the viscosity modifier is tartaric acid and / or a modified styrene-maleic acid copolymer solution. In a preferred embodiment, the modified styrene-maleic acid copolymer solution is manufactured by BYK-Chemie GmbH and is available as DISPERBYK-190. Modifications include alkaline hydrolysis: treating the styrene-maleic anhydride copolymer with sodium hydroxide or ammonia to produce its sodium or ammonium salt, improving its water solubility and stability; amidation or esterification: introducing hydrophobic segments through reaction with amines (such as laurylamine) or alcohols to improve its dispersibility in organic / inorganic systems; sulfonation: introducing sulfonic acid groups onto benzene rings to enhance its dispersion stability in polar media; and graft polymerization: grafting PEG segments, for example, to form a comb-like structure, improving its viscosity retention in high-salt or high-shear environments.

[0077] In step S1 of the present invention, the amount of binder added is 0.5%-3% of the mass of the H-SSZ-39 molecular sieve, and can be optionally 0.5-1%, 1-1.5%, 1.5-2%, 2-2.5%, 2.5-3%, 0.5-1.5% or 1.5-3%.

[0078] In step S1 of the present invention, the added amount of the viscosity modifier is 0.5%-3% of the mass of the H-SSZ-39 molecular sieve, and can be optionally 0.5-1%, 1-1.5%, 1.5-2%, 2-2.5%, 2.5-3%, 0.5-1.5% or 1.5-3%.

[0079] In step S1 of the present invention, the viscosity of the Cu-SSZ-39 slurry is 300-1000 Pa·s, and can be optionally 300-500 Pa·s, 500-800 Pa·s, or 800-1000 Pa·s.

[0080] In step S2 of the present invention, the amount of the binder added is 0.5%-3% of the mass of the H-SSZ-13 molecular sieve, and can be optionally 0.5-1%, 1-1.5%, 1.5-2%, 2-2.5%, 2.5-3%, 0.5-1.5% or 1.5-3%.

[0081] In step S2 of the present invention, the viscosity modifier is added in an amount of 0.5%-3% of the mass of the H-SSZ-13 molecular sieve, and can be optionally 0.5-1%, 1-1.5%, 1.5-2%, 2-2.5%, 2.5-3%, 0.5-1.5% or 1.5-3%.

[0082] In step S2 of the present invention, the viscosity of the Cu-SSZ-13 slurry is 300-1000 Pa·s, and can be optionally 300-500 Pa·s, 500-800 Pa·s, or 800-1000 Pa·s.

[0083] In the preparation method of the copper-based SCR catalyst provided by the present invention, step S3 is to coat the Cu-SSZ-39 slurry obtained in step S1 on the cordierite, dry and calcine it, and then coat the Cu-SSZ-13 slurry obtained in step S2, and dry and calcine it to obtain the copper-based SCR catalyst.

[0084] In step S3 of the present invention, the loading ratio of Cu-SSZ-39 slurry and Cu-SSZ-13 slurry is (0.8-1.2):1, which can be (0.8-1):1 or (1-1.2):1, and is preferably 1:1.

[0085] In step S3 of the present invention, drying is carried out after low-temperature slow drying and high-temperature rapid drying; The temperature of low-temperature slow drying is 50-70 ℃, which can be optionally 50-60 ℃ or 60-70 ℃, and the time is 8-12h, which can be optionally 8-10 h or 10-12 h. The temperature of high-temperature rapid drying is 100-150 ℃, which can be optionally 100-120 ℃ or 120-150 ℃, and the time is 1-3h, which can be optionally 1-2 h or 2-3h. Conventional processes usually treat molecular sieves by direct calcination after rapid drying, but the present invention introduces a low-temperature slow drying step on this basis, which is intended to gradually release free moisture during the heating process, reduce the migration risk of exchanged copper ions, thereby avoiding redistribution or surface enrichment before high temperature, resulting in the problem of uneven distribution of copper species in the catalyst, and further improving the uniformity and stability of the catalyst active components.

[0086] In step S3 of the present invention, the calcination temperature is 600-650° C., and may be 600-630° C. or 630-650° C.; the calcination time is 2-4 h, and may be 2-3 h or 3-4 h.

[0087] The present invention also provides the above copper-based SCR catalyst and the use of the copper-based SCR catalyst prepared by the above preparation method in NOx post-treatment.

[0088] In order to make the technical means, creative features, objectives and effects achieved by the present invention easier to understand, the present invention is described in detail below with reference to the embodiments.

[0089] In the following examples, unless otherwise specified, all reaction raw materials are commercially available products.

[0090] Unless otherwise specified, the purity of each product in each embodiment of the present invention exceeds 98%.

[0091] Example 1

[0092] Dissolve 39.27g of copper acetate monohydrate in 1229g of deionized water (the concentration of the copper precursor solution is 0.16mol / L, the H-SSZ is 500g, the designed copper content is 2.5%, the amount of copper acetate monohydrate added is: 500*2.5 / 100 / 63.55*199.65=39.27g; the amount of deionized water added is: 39.27 / 199.65 / 0.16=1.229L=1229g), and place it in a water bath after it is completely dissolved. Heat to 70°C and keep warm with continuous stirring; weigh 500g of H-SSZ-39 molecular sieve with a silicon-aluminum ratio of 15 and add it to the copper precursor solution for ion exchange at 70°C for 3h; after cooling to room temperature, grind the resulting slurry to a D50 of 2.5μm; add 10g of pseudo-boehmite and adjust the slurry viscosity to 900Pa·s using a viscosity modifier; perform coating, using a 600 / 4 cordierite carrier with a loading of 75g / L (dry After slow drying at low temperature (60℃ for 10h), high temperature rapid drying (120℃ for 1h) was performed, and coating 1 was obtained by calcining at 600℃ for 2h. 20.42g of copper acetate monohydrate was dissolved in 1023g of deionized water. After complete dissolution, the mixture was heated to 70℃ in a water bath and kept warm with continuous stirring. 500g of H-SSZ-13 molecular sieve with a silicon-aluminum ratio of 20 was weighed and added to the copper precursor solution for ion exchange at 70℃ for 3h. The mixture was cooled to After room temperature, the resulting slurry was ground to a D50 of 2.5 μm; 10 g of pseudo-boehmite was added, and the slurry viscosity was adjusted to 500 Pa·s using a viscosity modifier; coating was performed using a catalyst having coating 1 as a carrier with a loading amount of 75 g / L (dry weight); slow drying at low temperature (60°C for 10 h) was followed by rapid drying at high temperature (120°C for 2 h), and calcination was performed at 300°C for 4 h and 600°C for 2 h at a heating rate of 5°C / min with air flowing to obtain the final product.

[0093] The corresponding active component contents of the samples were: first coating, Cu-SSZ-39: 2.5% Cu (mass ratio of copper to added H-SSZ-39 molecular sieve); second coating, Cu-SSZ-13: 1.3% Cu (mass ratio of copper to added H-SSZ-13 molecular sieve). As shown in the cleaning test results in Table 1, the copper content of Cu-SSZ-13 was 1.5% without cleaning, and 1.3% after cleaning, indicating that 1.5% exceeded the limit of a single exchange under the current conditions. Therefore, 1.3% was selected as the limit for Cu-SSZ-13 copper content. For Cu-SSZ-39, the maximum value of 2.5%, the maximum concentration before and after cleaning, was selected as the limit for Cu-SSZ-39 copper content.

[0094]

[0095] The copper concentration in the cleaning solution was tested using ICP, and a mass conservation calculation was performed. The exchange rate = (total added Cu mass - total Cu in the cleaning solution) / total added Cu mass. The results are shown in Table 2 below:

[0096] Table 2

[0097]

[0098] As shown in Table 2, when the Cu exchange rate is around 99%, the difference in the measured copper concentration after calculation is too small (already lower than the deviation of the molecular sieve copper content test). For example, the actual molecular sieve copper content is 1.3%, while the content calculated by conservation of material is 1.27-1.33%. To avoid ambiguity, the test data provided only retains one decimal place, i.e. 1.3%. In addition, the cleaning solution of this application is colorless, and when the concentration of free copper ions is high, the solution is blue.

[0099] This study primarily focused on SSZ-13 molecular sieves for silicon-to-aluminum ratio (SAR) screening. Results showed that SSZ-13 with a SAR of 10 exhibited severe deactivation after aging, indicating insufficient thermal stability. SSZ-13 with a SAR of 15 exhibited slightly inferior performance to that of SAR of 20. The optimal overall performance was achieved by combining SSZ-13 with a SAR of 20 and SSZ-39 with a SAR of 15. The NO conversion rates of these catalyst combinations at different temperatures are shown in Table 3 below (temperature in °C; NO conversion rate in %):

[0100]

[0101] The results showed that the combination of SAR20-13 and SAR15-39 had the best NO conversion performance across the entire temperature range, especially exhibiting excellent activity and stability within the wide temperature window of 200-600°C, verifying the scientific nature and practicality of the catalyst ratio strategy of the present invention.

[0102] Comparative Example 1:

[0103] Compared with Example 1, the difference is that monohydrate and copper acetate are replaced by copper nitrate in equimolar amounts.

[0104] Comparative Example 2:

[0105] Compared with Example 1, the difference is that conventional drying at 120° C. for 2 h is directly performed without low-temperature drying.

[0106] Comparative Example 3:

[0107] Compared with Example 1, the difference is that the calcination heating rate is 10°C / min.

[0108] Comparative Example 4:

[0109] Compared with Example 1, the difference is that the maximum calcination temperature is 550°C.

[0110] Comparative Example 5:

[0111] Compared with Example 1, the difference is that in step 4, the slurry viscosity is adjusted to 2000 Pa·s, and the loading amount is 150 g / L, that is, it only contains the bottom coating.

[0112] Comparative Example 6:

[0113] Compared with Example 1, the difference is that starting from step 7, the slurry viscosity in step 10 is adjusted to 2000 Pa·s, and the carrier used is a cordierite blank carrier with a loading capacity of 150 g / L, that is, it only contains the outer coating Cu-SSZ-13.

[0114] Comparative Example 7:

[0115] Compared with Comparative Example 3, the difference is that the copper content of the coating is 3.5%.

[0116] Comparative Example 8:

[0117] Compared with Comparative Example 4, the difference is that the copper content of the coating is 2%.

[0118] Comparative Example 9:

[0119] Commercial Cu-SSZ-13, with a copper content of 2.8% and a silicon-aluminum ratio (SAR) of 20, is from the same manufacturer as the H-SSZ used in the experiment, Tianjin Paison.

[0120] Using a customized catalyst performance evaluation device, the system was first purged with nitrogen for 20 minutes at 500°C to remove residual gas. The temperature was then lowered to the target starting temperature. The steady-state NO conversion rates of Example 1 and Comparative Examples 1-9 were tested sequentially from low temperature to high temperature.

[0121] The analytical equipment used is a Fourier infrared flue gas analyzer (FTIR), which is used to continuously monitor the changes in NO concentration.

[0122] All samples to be tested were subjected to hydrothermal aging treatment (water content 10%) at 800°C for 16 hours in air atmosphere before testing to simulate the changes in catalyst stability under operating conditions.

[0123] The specific test conditions are as follows: CO2 concentration: 8%; H2O content: 8%; NO concentration: 500ppm; NH3 concentration: 550ppm; volume space velocity (SV): 60,000h -1 .

[0124] The NO conversion efficiencies of Example 1 and Comparative Examples 1-9 are shown in Table 4:

[0125]

[0126] The NO conversion efficiencies of Example 1 and Comparative Examples 10 and 11 are shown in Table 5:

[0127]

[0128] Ammonia storage test at a volume space velocity of 60,000 h -1 The test was conducted under conditions of 8% H₂O and 1000 ppm NH₃. Before testing, the sample was directly loaded into the reactor without pretreatment. The test gas was introduced, and the catalyst adsorbed ammonia at a constant temperature. Changes in the NH₃ concentration in the outlet gas were monitored in real time using a Fourier transform infrared (FTIR) analyzer. The ammonia storage test data for Example 1 and Comparative Example 9 are shown in Table 6:

[0129]

[0130] The above embodiments are preferred examples of the present invention and are not intended to limit the scope of protection of the present invention. However, the present invention is not limited to the specific details of the above embodiments. Within the scope of the technical concept of the present invention, various simple variations of the technical solution of the present invention can be made, and these simple variations all fall within the scope of protection of the present invention.

[0131] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any appropriate manner without contradiction. In order to avoid unnecessary repetition, the present invention will not further describe various possible combinations.

Claims

1. A copper-based SCR catalyst, characterized in that: The copper-based SCR catalyst uses cordierite as a carrier, and a first coating layer and a second coating layer are sequentially provided on the carrier from the inside to the outside, wherein the first coating layer is Cu-SSZ-39 and the second coating layer is Cu-SSZ-13; The silicon-aluminum ratio of the Cu-SSZ-39 is (10-18):1; the copper content of the Cu-SSZ-39 is 2.0-3.0%wt, calculated based on the mass of the Cu-SSZ-39; the copper-aluminum ratio of the Cu-SSZ-39 is (0.110-0.277):1; The Cu-SSZ-39 is prepared by adding H-SSZ-39 molecular sieve to a copper precursor solution for ion exchange; the copper precursor in the copper precursor solution is copper acetate monohydrate; The silicon-aluminum ratio of the Cu-SSZ-13 is (15-25):1; the copper content of the Cu-SSZ-13 is 0.5-1.5%wt, calculated based on the mass of the Cu-SSZ-13; the copper-aluminum ratio of the Cu-SSZ-13 is (0.039-0.188):1; The Cu-SSZ-13 is prepared by adding H-SSZ-13 molecular sieve to a copper precursor solution for ion exchange; the copper precursor in the copper precursor solution is copper acetate monohydrate; The copper in the Cu-SSZ-39 and Cu-SSZ-13 exists in the form of copper ions.

2. The copper-based SCR catalyst according to claim 1, characterized in that Includes any one or more of the following characteristics: A1) The cordierite is honeycomb cordierite; A2) The inner wall thickness of the cordierite is 2-4 mils; the pore density is 400-750 mesh; and the water absorption rate is 15%-35%.

3. The copper-based SCR catalyst according to claim 1, characterized in that Includes any one or more of the following characteristics: A3) the loading amount of Cu-SSZ-39 is 50-80 g / L; A4) The loading amount of Cu-SSZ-13 is 50-80 g / L.

4. The method for preparing a copper-based SCR catalyst according to any one of claims 1 to 3, characterized in that: The steps include: S1, adding H-SSZ-39 molecular sieve to a copper precursor solution for ion exchange to obtain Cu-SSZ-39, and adding a binder and a viscosity modifier after grinding to obtain a Cu-SSZ-39 slurry; S2, adding H-SSZ-13 molecular sieve to the copper precursor solution for ion exchange to obtain Cu-SSZ-13, and adding a binder and a viscosity modifier after grinding to obtain a Cu-SSZ-13 slurry; S3. Coating the Cu-SSZ-39 slurry obtained in step S1 on the cordierite, drying and calcining it, and then coating the Cu-SSZ-13 slurry obtained in step S2, drying and calcining it to obtain a copper-based SCR catalyst.

5. The method for preparing a copper-based SCR catalyst according to claim 4, characterized in that: In the copper precursor solution in step S1 and step S2, the copper precursor is copper acetate monohydrate; and the solvent is deionized water.

6. The method for preparing a copper-based SCR catalyst according to claim 5, characterized in that: Includes any one or more of the following characteristics: B1) The amount of copper precursor added to the copper precursor solution satisfies the following relationship: ； in, M Cu is the amount of copper precursor added, in g; M Z is the mass of H-SSZ-39 molecular sieve or H-SSZ-13 molecular sieve required for exchange, in g; w is the Cu content in the copper-based SCR catalyst, unit is %; B2) The volume of the deionized water satisfies the following relationship: ； in, V H2O is the volume of deionized water, in L; M Cu is the amount of copper precursor added, in g; C is the molar concentration of Cu in the copper precursor solution, in mol / L; The unit of 199.65 is g / mol.

7. The method for preparing a copper-based SCR catalyst according to claim 4, characterized in that: Includes any one or more of the following characteristics: B3) In step S1 and step S2, the ion exchange temperature is 65-85° C. and the time is 2-4 hours; B4) In step S1 and step S2, the binder is selected from one or more of pseudo-boehmite, liquid silica gel, and aluminum hydroxide sol; B5) in step S1 and step S2, the viscosity modifier is tartaric acid and / or modified styrene maleic acid copolymer solution; B6) In step S1, the amount of the binder added is 0.5%-3% of the mass of the H-SSZ-39 molecular sieve; B7) in step S1, the viscosity modifier is added in an amount of 0.5% to 3% of the mass of the H-SSZ-39 molecular sieve; B8) In step S1, the viscosity of the Cu-SSZ-39 slurry is 300-1000 Pa·s; B9) in step S2, the amount of the binder added is 0.5%-3% of the mass of the H-SSZ-13 molecular sieve; B10) in step S2, the viscosity modifier is added in an amount of 0.5% to 3% of the mass of the H-SSZ-13 molecular sieve; B11) In step S2, the viscosity of the Cu-SSZ-13 slurry is 300-1000 Pa·s.

8. The method for preparing a copper-based SCR catalyst according to claim 4, characterized in that: Includes any one or more of the following characteristics: B12) In step S3, the loading ratio of the Cu-SSZ-39 slurry and the Cu-SSZ-13 slurry is (0.8-1.2):1; B13) in step S3, the drying is performed by low-temperature slow drying followed by high-temperature rapid drying; B14) In step S3, the calcination temperature is 600-650° C. and the calcination time is 2-4 hours.

9. The method for preparing a copper-based SCR catalyst according to claim 8, characterized in that: Also includes any one or more of the following features: B131) the low-temperature slow drying is performed at a temperature of 50-70° C. for 8-12 hours; B132) The high temperature rapid drying is carried out at a temperature of 100-150° C. and for a time of 1-3 hours.

10. Use of the copper-based SCR catalyst according to any one of claims 1 to 3 and the copper-based SCR catalyst prepared by the preparation method according to any one of claims 4 to 9 in NOx post-treatment.

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