Preparation method and application of high-efficiency low-N2O-selectivity monolithic CeOx-Cu / SSZ-13 catalyst

Abstract

The invention relates to a preparation method and application of a high-efficiency low-N2O selective monolithic CeOx-Cu / SSZ-13 catalyst, and the method comprises the following steps: adding cupric acetate monohydrate into an ethylene glycol aqueous solution to obtain a cupric acetate solution; adding the H / SSZ-13 molecular sieve into a cupric acetate solution for ion exchange to obtain a molecular sieve mixed solution, filtering the obtained molecular sieve mixed solution to obtain a filter cake, and performing high-temperature calcination to prepare the Cu / SSZ-13 molecular sieve material; the preparation method comprises the following steps: calcining cerium nitrate hexahydrate at different temperatures, adding the obtained CeOx into deionized water, grinding to obtain slurry, mixing the obtained slurry with alumina gel and Cu / SSZ-13 powder, further grinding, and adding xanthan gum to obtain coating slurry; and coating a cordierite carrier with the coating slurry, and then drying and calcining the cordierite carrier to prepare the integral CeOx-Cu / SSZ-13 catalyst. The monolithic CeOx-Cu / SSZ-13 catalyst prepared by the method provided by the invention can solve the problem of high N2O selectivity caused by high species of ZCuOH and CuOx in the existing Cu / SSZ-13 catalyst and the problem of insufficient low-temperature activity under low species of ZCuOH, and realizes that the SCR catalyst has efficient NOx reduction performance and low N2O selectivity.

Description

Technical Field

[0001] This invention belongs to the field of catalyst technology, specifically relating to an integral CeOx-Cu / SSZ-13 catalyst for NOx reduction in new fuel engines that meets non-road T4 / T5 and China VI / China VII regulations for NOx reduction in diesel engines. Background Technology

[0002] Cu / SSZ-13 possesses excellent low-temperature and hydrothermal aging resistance, making it the preferred catalytic coating material for non-road T4 and China VI NOx reduction (SCR) in diesel engines. However, with the implementation of Phase IV regulations for commercial vehicles and the application of non-EGR engine technology, new challenges have been posed to the control of high-concentration NOx and low-temperature NOx emissions. The greenhouse effect of N2O from motor vehicles is nearly 300 times that of CO2. During the SCR catalytic reaction, N2O is non-selectively generated, and the China VII emission regulations are expected to further tighten controls on N2O emissions. Therefore, current SCR catalysts need to possess more efficient NOx reduction performance and lower N2O selectivity.

[0003] NOx reduction efficiency and N2O selectivity are significantly correlated with the active copper species state of the catalyst. Industry research indicates that isolated Cu species... 2+ It is the active site of NH3-SCR, Cu 2+ The copper-based molecular sieve catalyst primarily exists in the ZCuOH and Z2Cu states. Using an ion exchange method to load copper species, Z2Cu is preferentially formed. Once Z2Cu exchange is saturated, ZCuOH species begin to form, and higher ion exchange temperatures can increase the saturation limit of Z2Cu species. ZCuOH is beneficial for improving NOx reduction performance at low temperatures. Compared to ZCuOH, Z2Cu is associated with high-temperature performance and exhibits better hydrothermal stability. In the NH3-SCR reaction, N2O formation in the copper-based molecular sieve catalyst exhibits two temperature ranges: N2O formation in the 180-350℃ range mainly originates from the decomposition of NH4NO3 intermediate species, while in the 400-550℃ range it mainly originates from NH3 oxidation. Compared to Z2Cu species, ZCuOH is more favorable for N2O formation in the mid-to-low temperature range. Mid-to-high temperature N2O formation is mainly related to CuOx. A high Cu / Al ratio more readily forms ZCuOH and CuOx species, resulting in a significant increase in N2O formation across the entire activity temperature window.

[0004] Therefore, improving NOx conversion efficiency at low temperatures depends on the ZCuOH species content, while high ZCuOH content also leads to high N2O selectivity. Balancing NOx reduction performance and N2O reduction remains the main technical challenge.

[0005] Ce, with its variable valence, is widely used in the optimization of Cu-SSZ-13. Chinese patent CN 11203269A discloses a method for preparing a multi-metal-CHA type molecular sieve catalyst, in which a first active Cu salt and a second active Ce salt are simultaneously dissolved in an aqueous solution, followed by thermal loading of the active metal onto the CHA molecular sieve. This catalyst exhibits excellent NOx conversion efficiency and hydrothermal stability. Chinese patent CN 118904388A discloses a Cu-SSZ-13 molecular sieve-supported CeO2 catalyst and its preparation method. It is prepared by uniformly loading the rare earth element Ce onto a Cu-SSZ-13 molecular sieve support according to stoichiometric ratio using an equal-volume impregnation method. This catalyst can be used in catalytic reactions that simultaneously eliminate particulate matter and nitrogen oxides in diesel engines. Chinese patent CN 116532151 A discloses a method for preparing a supported CeO2 / Cu-SSZ-13 composite catalyst. This method uses Cu-SSZ-13 molecular sieve as a support, and sequentially mixes and calcines the support with a Ce source (cerium nitrate) to obtain the supported CeO2 / Cu-SSZ-13 composite catalyst. By supporting CeO2, the low-temperature activity, hydrothermal stability, and sulfur resistance of the Cu-SSZ-13 molecular sieve catalyst for NH3-SCR are comprehensively improved. All of the above techniques use Ce metal salts for modification, and the prepared catalysts show good technical effects on NOx conversion efficiency, hydrothermal stability, sulfur resistance, and soot particulate combustion. However, the method for N2O generation is not clearly described.

[0006] The inventors discovered that Ce modification of Cu-SSZ-13, utilizing Ce's oxygen storage and release properties, helps improve the catalyst's low-temperature performance. Furthermore, the interaction between Ce and active copper species and acidic sites inhibits N2O formation. Conventional techniques for modifying Cu-SSZ-13 molecular sieves often rely on acidic cerium salts (such as nitrates), which can lead to the degradation of the already loaded Cu. 2+ CuOx precipitates, thus affecting the performance of the NH3-SCR catalyst. During the simultaneous modification of SSZ-13 with Ce and Cu bimetals, on the one hand, Ce... 3+ The ion diameter (approximately 0.2 nm) is smaller than the CHA cage diameter in CHA molecular sieves (approximately 0.38 nm), and can interact with Cu. 2+ Competing molecular sieve sites. On the other hand, Ce... 3+ It forms hydrated Ce³⁺ with H₂O (e.g., [Ce(H₂O]). n ]³⁺), forming a steric hindrance, which will also affect Cu 2+ Supported on molecular sieve sites. Therefore, it is necessary to develop an SCR catalyst with simple process and to avoid the influence of Ce-supported modification on copper species, so as to achieve low N2O selectivity and high NOx conversion efficiency. Summary of the Invention

[0007] The purpose of this invention is to fill the gap in the prior art and provide a method for preparing a highly efficient, low-N2O selective monolithic CeOx-Cu / SSZ-13 catalyst. This invention also provides applications of the catalyst prepared by the said method.

[0008] The inventors discovered that N2O control can be achieved by modulating the Cu species type. Specifically, by combining various methods such as increasing ion exchange temperature, raising calcination temperature, and developing new process routes, the formation of Z2Cu can be promoted while inhibiting the formation of ZCuOH and CuOx species. Simultaneously, addressing the issue of insufficient ZCuOH species leading to low-temperature NH3-SCR performance, oxygen-storing CeO2 species can be introduced to oxidize NO to NO2, promoting rapid SCR reactions and compensating for low-temperature performance deficiencies. This results in improved low-temperature NOx efficiency while simultaneously reducing N2O.

[0009] Based on the above research, this invention proposes using a mixed solution of ethylene glycol and water as a solvent to raise the boiling point of the solution, thereby increasing the ion exchange temperature. This, combined with high-temperature calcination, promotes the presence of Cu primarily in the Z₂Cu form. Given that modification with metal salts such as cerium nitrate affects Cu… 2+ To mitigate the effects of precipitation, this invention modifies CeOx oxide obtained by calcining cerium nitrate metal salts using Cu-SSZ-13. Specifically, calcination at different temperatures achieves varying mass ratios of Ce₂O₃ to CeO₂ in CeOx, thereby facilitating the precipitation process during NO oxidation. 3+ ↔Ce 4+ Continuous circulation ensures continuous oxygen release during the reaction process, enhancing the sustainability of the NOx reaction process during transient reactions.

[0010] Based on the above research foundation and the purpose of the invention, the technical solution adopted by the present invention is as follows: A method for preparing a highly efficient, low-N2O selective monolithic CeOx-Cu / SSZ-13 catalyst is as follows: (1) Preparation of Cu / SSZ-13: 1) Preparation of copper acetate solution: Mix ethylene glycol with deionized water to form an ethylene glycol aqueous solution, with ethylene glycol accounting for 30-40 wt.% in the ethylene glycol aqueous solution; then add copper acetate to the ethylene glycol aqueous solution to obtain a copper acetate solution with a concentration of 0.05-0.20 mol / L; 2) Ion exchange: Copper acetate solution in an oil bath at 90-100℃, stirred until the copper acetate is completely dissolved, then add H / SSZ-13 molecular sieve, stir and mix, and maintain at the oil bath temperature for 30 min-1 h to obtain a molecular sieve mixture; the proportion of molecular sieve in the molecular sieve mixture is 40-50 wt.%, and the molar ratio of SiO2 to Al2O3 in H / SSZ-13 molecular sieve is 10-40; 3) Filtration and washing: Filter the molecular sieve mixture to obtain a filter cake, and wash the filter cake with 1 to 2 times the mass of deionized water in copper acetate solution. 4) Drying and calcining filter cake: Dry the washed filter cake at 110-130℃ and then calcine it at 600-700℃ for 1-5 hours to prepare Cu / SSZ-13 molecular sieve material; (2) Preparation of CeOx: 1) Preparation of CeOx oxide: Cerium nitrate hexahydrate is calcined at 450-800℃ for 1 hour in air atmosphere to form CeOx; 2) Preparation of CeOx abrasive: CeOx is added to deionized water and mixed and circulated for grinding to obtain CeOx abrasive. The D90 of CeOx abrasive is controlled to be 0.5-1.5μm; the mass ratio of CeOx to deionized water is 1:8-10. (3) Preparation of monolithic CeOx-Cu / SSZ-13 catalyst: 1) Weigh the CeOx abrasive, add deionized water, add the binder aluminum colloid, stir and disperse, then add Cu / SSZ-13 molecular sieve material, stir evenly, and obtain a slurry with a solid content of 30-50 wt.%; wherein, CeOx accounts for 0.5-15% of the dry weight of oxides in the slurry, Cu / SSZ-13 accounts for 70-94.5% of the dry weight of oxides in the slurry, and the Al2O3 corresponding to the aluminum colloid accounts for 5-15% of the dry weight of oxides in the slurry; the oxides in the slurry are CeOx, Al2O3 corresponding to the aluminum colloid, and Cu / SSZ-13 molecular sieve; 2) Grind the slurry to control the final slurry particle size D90 = 4.5-6.0 μm; 3) Add xanthan gum to the ground slurry to thicken it, and control the slurry viscosity to 1000-2500cp to obtain a coating slurry. Coat the coating slurry onto a straight cordierite carrier, dry it, and then perform a second coating. The slurry loading is 90-180g / L. After coating, dry it at 100-150℃ and calcine it at 450-550℃ for 1h to prepare the monolithic CeOx-Cu / SSZ-13 catalyst.

[0011] The highly efficient, low-N2O selective monolithic CeOx-Cu / SSZ-13 catalyst prepared by the above method can be used in non-road T4 / T5 and China VI / China VII diesel engines and new fuel engines for NO x reduction.

[0012] Furthermore, for catalysts used in non-road T4 / China VI emission standards, a Cu / Al atomic ratio of less than or equal to 0.25 and a CeOx addition of 0.5-15% are preferred.

[0013] Furthermore, in response to the NOx reduction requirements of diesel / new fuel engines under the China VII emission standard, a Cu / Al atomic ratio greater than or equal to 0.20 and a CeOx addition amount of 0.5-15% are preferred.

[0014] Compared with commercial Cu-SSZ-13 catalysts, the monolithic CeOx-Cu / SSZ-13 catalytic coating material prepared by this invention has the following advantages: (1) Using ethylene glycol mixed aqueous solution and increasing the temperature of the exchange solution can increase the loading content of Z2Cu, reduce the formation of ZCuOH and CuOx, and inhibit the generation of N2O.

[0015] (2) Cu / SSZ-13 is prepared by high-temperature calcination, which promotes the reaction of a small amount of ZCuOH formed during the ion exchange process with the acidic sites of the framework B to form Z2Cu species. At the same time, it promotes the formation of a small amount of CuOx species during the ion exchange, and solid-state ion exchange occurs under high-temperature heat treatment to form Z2Cu, thereby reducing the content of ZCuOH and CuOx and synergistically reducing the generation of N2O.

[0016] (3) By adjusting the calcination temperature, CeOx can have different Ce2O3 / CeO2 ratios. By utilizing the oxygen storage and release characteristics of Ce2O3-CeO2, low-temperature NO can be continuously oxidized into NO2, promoting the continuous occurrence of rapid SCR reaction and significantly enhancing the low-temperature NOx conversion efficiency.

[0017] (4) The method of the present invention is simple to operate and suitable for industrial production. Attached Figure Description

[0018] Figure 1 The images show the H2-TPR diagrams of the Cu / SSZ-13 molecular sieve prepared in Example 1 and the Cu / SSZ-13 molecular sieve prepared in Comparative Example 1.

[0019] Figure 2 NOx conversion efficiency curves of Cu / SSZ-13 molecular sieve prepared in Example 1, fresh monolithic CeOx-Cu / SSZ-13 catalyst prepared in Examples 1-3, fresh monolithic Cu / SSZ-13 catalyst prepared in Comparative Example 1, and fresh monolithic CeO2-Cu / SSZ-13 catalyst prepared in Comparative Example 2.

[0020] Figure 3 The NOx conversion efficiency curves of the Cu / SSZ-13 molecular sieve prepared in Example 1, the monolithic CeOx-Cu / SSZ-13 catalyst prepared in Examples 1-3, the monolithic Cu / SSZ-13 catalyst prepared in Comparative Example 1, and the monolithic CeO2-Cu / SSZ-13 catalyst prepared in Comparative Example 2 after hydrothermal aging treatment.

[0021] Figure 4 N2O generation curves of Cu / SSZ-13 molecular sieve prepared in Example 1, fresh monolithic CeOx-Cu / SSZ-13 catalyst prepared in Examples 1-3, fresh monolithic Cu / SSZ-13 catalyst prepared in Comparative Example 1, and fresh monolithic CeO2-Cu / SSZ-13 catalyst prepared in Comparative Example 2.

[0022] Figure 5 The N2O generation efficiency curves of Cu / SSZ-13 molecular sieve prepared in Example 1, monolithic CeOx-Cu / SSZ-13 catalyst prepared in Examples 1-3, monolithic Cu / SSZ-13 catalyst prepared in Comparative Example 1, and monolithic CeO2-Cu / SSZ-13 catalyst prepared in Comparative Example 2 after hydrothermal aging treatment are shown.

[0023] Figure 6 NOx conversion efficiency curves for the fresh catalysts prepared in Example 6 and Comparative Example 3 and the catalysts subjected to hydrothermal aging treatment.

[0024] Figure 7 The N2O generation concentration curves are for the fresh catalysts prepared in Example 6 and Comparative Example 3 and the catalysts treated with hydrothermal aging. Detailed Implementation

[0025] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments. The described embodiments are only some embodiments of the present invention and are not intended to limit the scope of protection of the present invention. Based on the scope of the claims of the present invention, similar embodiments obtained by those skilled in the art without inventive effort are all within the scope of protection of the present invention. Example 1

[0026] A method for preparing a highly efficient, low-N2O selective monolithic CeOx-Cu / SSZ-13 catalyst involves mixing ethylene glycol and deionized water at a mass ratio of 4:6 to form an ethylene glycol aqueous solution. Copper acetate is then added and stirred to obtain a 0.2 mol / L copper acetate solution. The copper acetate solution is heated in an oil bath at 100°C until completely dissolved. H / SSZ-13 molecular sieves with a SiO2 / Al2O3 ratio of 15 are then added to the completely dissolved copper acetate solution, and the mixture is stirred and maintained at the oil bath temperature for 30 minutes to obtain a molecular sieve mixture (a suspension). The molecular sieves constitute 45 wt.% of the mixture. The mixture is filtered to obtain a filter cake, which is washed with 1.5 times the mass of deionized water containing the copper acetate solution. After washing, the cake is dried at 130°C and then calcined at 600°C for 5 hours to obtain the Cu / SSZ-13 molecular sieve material. A certain amount of cerium nitrate hexahydrate was weighed and placed in a calcining pan, then calcined at 600℃ for 1 hour to obtain CeOx powder. The CeOx powder was added to deionized water to obtain a solid-liquid mixture with a solid content of 10%. The solid-liquid mixture was circulated and ground to control the CeOx D90 = 0.5 μm, resulting in a CeOx grinding slurry. A certain amount of the CeOx grinding slurry was weighed, and a certain amount of deionized water was added. Aluminum glue was added according to the ratio of Al2O3 to the dry weight of the slurry oxides, and after stirring and dispersing, Cu / SSZ-13 molecular sieve was added and stirred evenly to obtain a slurry with a solid content of 35 wt.%. CeOx accounted for 6% of the dry weight of the slurry oxides, and Cu / SSZ-13 accounted for 84% of the dry weight of the slurry oxides. The above slurry was circulated and ground to control the final slurry particle size D90 = 4.5 μm. Finally, xanthan gum was added to the slurry for thickening, controlling the slurry viscosity to 2500 cp, resulting in a coating slurry. The coating slurry was coated at a rate of 70 g / L onto a straight-through cordierite support. After drying, a second coating was performed. The catalyst was then dried and calcined at 500°C for 1 hour to prepare the monolithic CeOx-Cu / SSZ-13 catalyst. Example 2

[0027] A method for preparing a highly efficient, low-N2O selective monolithic CeOx-Cu / SSZ-13 catalyst involves mixing ethylene glycol and deionized water at a mass ratio of 3:7 to form an ethylene glycol aqueous solution. Copper acetate is then added and stirred to obtain a 0.1 mol / L copper acetate solution. The copper acetate solution is heated in an oil bath at 90°C until completely dissolved. H / SSZ-13 molecular sieves with a SiO2 / Al2O3 ratio of 15 are then added to the completely dissolved copper acetate solution, and the mixture is stirred and maintained at the oil bath temperature for 1 hour to obtain a molecular sieve mixture. The molecular sieves constitute 40 wt.% of the mixture. The mixture is filtered to obtain a filter cake, which is washed with deionized water at a concentration equal to the mass of the copper acetate solution. After washing, the cake is dried at 110°C and then calcined at 700°C for 1 hour to obtain the Cu / SSZ-13 molecular sieve material. A certain amount of cerium nitrate hexahydrate was weighed and placed in a calcining pan, then calcined at 600℃ for 1 hour to obtain CeOx powder. The CeOx powder was added to deionized water to obtain a solid-liquid mixture with a solid content of 10%. The solid-liquid mixture was circulated and ground to control the CeOx D90 = 1.5 μm, resulting in a CeOx grinding slurry. A certain amount of the CeOx grinding slurry was weighed, and a certain amount of deionized water was added. Aluminum glue was added according to the ratio of Al2O3 to the dry weight of the slurry oxides, and after stirring and dispersing, Cu / SSZ-13 molecular sieve was added and stirred evenly to obtain a slurry with a solid content of 40 wt.%. CeOx accounted for 3% of the dry weight of the slurry oxides, and Cu / SSZ-13 accounted for 87% of the dry weight of the slurry oxides. The above slurry was circulated and ground to control the final slurry particle size D90 = 6.0 μm. Finally, xanthan gum was added to the slurry for thickening, controlling the slurry viscosity to 1500 cp, resulting in a coating slurry. The coating slurry was coated at a rate of 70 g / L onto a straight-through cordierite support. After drying, a second coating was performed. The catalyst was then dried and calcined at 500°C for 1 hour to prepare the monolithic CeOx-Cu / SSZ-13 catalyst. Example 3

[0028] A method for preparing a highly efficient, low-N2O selective monolithic CeOx-Cu / SSZ-13 catalyst involves mixing ethylene glycol and deionized water at a mass ratio of 3:7 to form an ethylene glycol aqueous solution. Copper acetate is then added and stirred to obtain a 0.15 mol / L copper acetate solution. The copper acetate solution is heated in an oil bath at 90°C until completely dissolved. H / SSZ-13 molecular sieves with a SiO2 / Al2O3 ratio of 15 are then added to the completely dissolved copper acetate solution, stirred, and maintained at the oil bath temperature for 1 hour to obtain a molecular sieve mixture. The molecular sieves constitute 50 wt.% of the mixture. The mixture is filtered to obtain a filter cake, which is washed with deionized water at a concentration equal to the mass of the copper acetate solution. After washing, the cake is dried at 120°C and then calcined at 600°C for 5 hours to obtain the Cu / SSZ-13 molecular sieve material. A certain amount of cerium nitrate hexahydrate was weighed and placed in a calcining pan, then calcined at 700℃ for 1 hour to obtain CeOx powder. The CeOx powder was added to deionized water to obtain a solid-liquid mixture with a solid content of 10%. The solid-liquid mixture was circulated and ground to control the CeOx D90 = 1.0 μm, resulting in a CeOx grinding slurry. A certain amount of the CeOx grinding slurry was weighed, and a certain amount of deionized water was added. Aluminum glue was added according to the ratio of Al2O3 to the dry weight of the slurry oxides, and the mixture was stirred and dispersed. Then, Cu / SSZ-13 molecular sieve was added and stirred evenly to obtain a slurry with a solid content of 50 wt.%. CeOx accounted for 9% of the dry weight of the slurry oxides, and Cu / SSZ-13 accounted for 81% of the dry weight of the slurry oxides. The above slurry was circulated and ground to control the final slurry particle size D90 = 5.0 μm. Finally, xanthan gum was added to the slurry for thickening, controlling the slurry viscosity to 2000 cp, resulting in a coating slurry. The coating slurry was coated at a rate of 70 g / L onto a straight-through cordierite support. After drying, a second coating was performed. The catalyst was then dried and calcined at 500°C for 1 hour to prepare the monolithic CeOx-Cu / SSZ-13 catalyst. Example 4

[0029] A method for preparing a highly efficient, low-N2O selective monolithic CeOx-Cu / SSZ-13 catalyst involves mixing ethylene glycol and deionized water at a mass ratio of 4:6 to form an ethylene glycol aqueous solution. Copper acetate is then added and stirred to obtain a 0.15 mol / L copper acetate solution. The copper acetate solution is heated in an oil bath at 95°C until completely dissolved. H / SSZ-13 molecular sieves with a SiO2 / Al2O3 ratio of 10 are then added to the completely dissolved copper acetate solution, and the mixture is stirred and maintained at the oil bath temperature for 30 minutes to obtain a molecular sieve mixture. The molecular sieves constitute 45 wt.% of the mixture. The mixture is filtered to obtain a filter cake, which is washed with deionized water at a concentration equal to the mass of the copper acetate solution. After washing, the cake is dried at 120°C and then calcined at 650°C for 2 hours to obtain the Cu / SSZ-13 molecular sieve material. A certain amount of cerium nitrate hexahydrate was weighed and placed in a calcining pan, then calcined at 450℃ for 1 hour to obtain CeOx powder. The CeOx powder was added to deionized water to obtain a solid-liquid mixture with a solid content of 9.50%. The solid-liquid mixture was circulated and ground to control the CeOx D90 = 1.5 μm, resulting in a CeOx grinding slurry. A certain amount of the CeOx grinding slurry was weighed, and a certain amount of deionized water was added. Aluminum glue was added according to the ratio of Al2O3 to the dry weight of the slurry oxides, and after stirring and dispersing, Cu / SSZ-13 molecular sieve was added and stirred evenly to obtain a slurry with a solid content of 30 wt.%. CeOx accounted for 0.5% of the dry weight of the slurry oxides, and Cu / SSZ-13 accounted for 94.5% of the dry weight of the slurry oxides. The above slurry was circulated and ground to control the final slurry particle size D90 = 6.0 μm. Finally, xanthan gum was added to the slurry for thickening, controlling the slurry viscosity to 1000 cp, resulting in a coating slurry. The coating slurry was coated at a rate of 70 g / L onto a straight-through cordierite support. After drying, a second coating was performed. The catalyst was then dried and calcined at 500°C for 1 hour to prepare the monolithic CeOx-Cu / SSZ-13 catalyst. Example 5

[0030] A method for preparing a highly efficient, low-N2O selective monolithic CeOx-Cu / SSZ-13 catalyst involves mixing ethylene glycol and deionized water at a mass ratio of 4:6 to form an ethylene glycol aqueous solution. Copper acetate is then added and stirred to obtain a 0.1 mol / L copper acetate solution. The copper acetate solution is heated in an oil bath at 95°C until completely dissolved. H / SSZ-13 molecular sieves with a SiO2 / Al2O3 ratio of 40 are then added to the completely dissolved copper acetate solution, and the mixture is stirred and maintained at the oil bath temperature for 30 min to obtain a molecular sieve mixture. The molecular sieves constitute 40 wt.% of the mixture. The mixture is filtered to obtain a filter cake, which is washed with twice the mass of deionized water containing the copper acetate solution. After washing, the cake is dried at 120°C and then calcined at 650°C for 2 h to obtain the Cu / SSZ-13 molecular sieve material. A certain amount of cerium nitrate hexahydrate was weighed and placed in a calcining pan, then calcined at 600℃ for 1 hour to obtain CeOx powder. The CeOx powder was added to deionized water to obtain a solid-liquid mixture with a solid content of 10%. The solid-liquid mixture was circulated and ground to control the CeOx D90 = 0.5 μm, resulting in a CeOx grinding slurry. A certain amount of the CeOx grinding slurry was weighed, and a certain amount of deionized water was added. Aluminum glue was added according to the ratio of Al2O3 to the dry weight of the slurry oxides, and after stirring and dispersing, Cu / SSZ-13 molecular sieve was added and stirred evenly to obtain a slurry with a solid content of 40 wt.%. CeOx accounted for 15% of the dry weight of the slurry oxides, and Cu / SSZ-13 accounted for 70% of the dry weight of the slurry oxides. The above slurry was circulated and ground to control the final slurry particle size D90 = 4.5 μm. Finally, xanthan gum was added to the slurry to thicken it, and the slurry viscosity was controlled at 1500 cp. It was then coated onto a straight cordierite support at a rate of 70 g / L. After drying, a second coating was performed. After coating, the catalyst was dried and calcined at 450℃ for 1 h to prepare the monolithic CeOx-Cu / SSZ-13 catalyst. Example 6

[0031] A method for preparing a highly efficient, low-N2O selective monolithic CeOx-Cu / SSZ-13 catalyst involves mixing ethylene glycol and deionized water at a mass ratio of 4:6 to form an ethylene glycol aqueous solution. Copper acetate is then added and stirred to obtain a 0.05 mol / L copper acetate solution. The copper acetate solution is heated in an oil bath at 95°C until completely dissolved. H / SSZ-13 molecular sieves with a SiO2 / Al2O3 ratio of 22 are then added to the completely dissolved copper acetate solution, stirred, and maintained at the oil bath temperature for 30 minutes to obtain a molecular sieve mixture. The molecular sieves constitute 48 wt.% of the mixture. The mixture is filtered to obtain a filter cake, which is washed with deionized water at a concentration equal to the mass of the copper acetate solution. After washing, the cake is dried at 120°C and then calcined at 650°C for 2 hours to obtain the Cu / SSZ-13 molecular sieve material. A certain amount of cerium nitrate hexahydrate was weighed and placed in a calcining pan, then calcined at 8000℃ for 1 hour to obtain CeOx powder. The CeOx powder was added to deionized water to obtain a solid-liquid mixture with a solid content of 10%. The solid-liquid mixture was circulated and ground to control the CeOx D90 = 0.5 μm, resulting in a CeOx grinding slurry. A certain amount of the CeOx grinding slurry was weighed, and a certain amount of deionized water was added. Aluminum glue was added according to the ratio of Al2O3 to the dry weight of the slurry oxides, and the mixture was stirred and dispersed. Then, Cu / SSZ-13 molecular sieves were added and stirred evenly to obtain a slurry with a solid content of 45 wt.%. CeOx accounted for 3% of the dry weight of the slurry oxides, and Cu / SSZ-13 accounted for 92% of the dry weight of the slurry oxides. The above slurry was circulated and ground to control the final slurry particle size D90 = 4.5 μm. Finally, xanthan gum was added to the slurry for thickening, controlling the slurry viscosity to 1500 cp, resulting in a coating slurry. The coating slurry was coated at a rate of 140 g / L onto a straight-through cordierite support. After drying, a second coating was performed. The catalyst was then dried and calcined at 450 °C for 1 h to prepare the monolithic CeOx-Cu / SSZ-13 catalyst.

[0032] A 0.05 mol / L copper acetate solution was prepared. H / SSZ-13 (SiO2 / Al2O3 molar ratio = 15) was added to the copper acetate solution at a mass ratio of H / SSZ-13:copper acetate solution = 1:4. After a 3-hour water bath at 70°C, the filter cake was filtered. The filter cake was washed with deionized water until the aqueous solution was neutral (pH = 7). The filter cake was then dried at 120°C, and a second ion exchange was performed using the same method. After the second ion exchange, the filter cake was calcined at 550°C for 2 hours to obtain Cu / SSZ-13 molecular sieve powder. The Cu / SSZ-13 molecular sieve powder was added to deionized water and ground to control the D90 particle size at 4.5 μm. The resulting slurry was mixed with aluminum glue, stirred and dispersed, and thickened with xanthan gum, controlling the solid content of the slurry to 30-35%. The mass ratio of molecular sieve to binder oxide (Al2O3) was 9:1. The prepared slurry was coated onto a cordierite support, dried at 120°C, and calcined at 500°C to prepare a monolithic Cu / SSZ-13 catalyst with a loading of 140 g / L. Comparative Example 2

[0033] The Cu / SSZ-13 molecular sieve powder prepared in Comparative Example 1 was added to deionized water and ground to control the D90 particle size at 4.5 μm, resulting in a grinding slurry. CeO2 (D90 = 17 μm) was added to the above grinding slurry, followed by the addition of aluminum glue, and the mixture was stirred and dispersed. The dry weight ratio of CeO2:molecular sieve:binder oxide (Al2O3) was 6:84:10. Xanthan gum was added to thicken the slurry, controlling the final solid content to 30-35%. The final slurry was coated onto a cordierite support, dried at 120℃, and calcined at 500℃ to prepare a monolithic CeO2-Cu / SSZ-13 catalyst with a loading of 140 g / L. Comparative Example 3

[0034] A 0.05 mol / L copper acetate solution was prepared. H / SSZ-13 (SiO2 / Al2O3 molar ratio = 22) was added to the copper acetate solution at a mass ratio of H / SSZ-13:copper acetate solution = 1:4. After a 3-hour water bath at 70°C, the filter cake was filtered. The filter cake was washed with deionized water until the aqueous solution was neutral (pH = 7). The filter cake was then dried at 120°C. The resulting filter cake underwent a second ion exchange using the same method. After the second exchange, the filter cake was calcined at 550°C for 2 hours to prepare Cu / SSZ-13 molecular sieve powder. The Cu / SSZ-13 molecular sieve powder was then added to deionized water and ground to control the D90 particle size at 4.5 μm, resulting in a grinding slurry. This slurry was mixed with aluminum glue and stirred until homogeneous. Xanthan gum was then added to thicken the slurry, controlling the solid content to 30-35%, thus completing the slurry preparation. The mass ratio of molecular sieve to binder oxide was 9:1. The prepared slurry was coated onto a cordierite support, dried at 120°C, and calcined at 500°C to prepare an integral Cu / SSZ-13 catalyst with a loading of 140 g / L.

[0035] A small, monolithic catalyst sample with dimensions of φ25.4mm*76.2mm was further cut and subjected to hydrothermal aging, as follows: The extracted monolithic catalyst samples were placed on fixed-bed reactors for aging. The reactor setup was as described in the literature "Study on NH3-SCR Performance and Ammonia Storage Characteristics Based on Different Cu-CHA Catalyst Schemes" (Inorganic Salt Industry 56.12(2024):159-166). Aging was carried out at a total flow rate of 19.3 L / min, with water comprising 10% of the aging atmosphere. Air was used as the carrier gas, and the temperature was increased to 650°C at a rate of 10°C / min and maintained for 100 h. The aged catalyst was named Example XA or Comparative Example XA, where X represents the corresponding example or comparative example number.

[0036] The NOx conversion performance of the monolithic catalyst sample was evaluated using the following method: Fresh and hydrothermally aged monolithic catalyst samples were evaluated for activity in the aforementioned fixed-bed reactor. The test atmosphere consisted of 500 ppm NH3, 500 ppm NO, 10% H2O, and 10% O2, with a reaction space velocity of 80,000 / h. The NOx conversion rate was calculated using the following formula: NOx conversion rate (%) = (NOx conversion rate) 入口 -NO 出口 -NO 2出口 -2×N2O 出口 ) / NO 入口 ×100%; In the above formula, NO 入口 These represent the NO concentration (ppm) at the catalyst inlet, and NO... 出口NO concentration at catalyst outlet (ppm) 2出口 The concentration of NO2 (ppm) at the catalyst outlet, and N2O 出口 The concentration of N2O at the catalyst outlet (ppm) is given.

[0037] Table 1 shows the results of ICP-OES testing of Cu / Al ratio and CeO2 mass content in Examples 1-3, 6 and Comparative Examples 1-3.

[0038] Table 2 shows the specific surface area and pore size test results for Examples 1-3, 6 and Comparative Examples 1-3.

[0039] Figure 1 The images show the H2-TPR diagrams of the Cu / SSZ-13 molecular sieve prepared in Example 1 and the Cu / SSZ-13 molecular sieve prepared in Comparative Example 1.

[0040] Figure 2 NOx conversion efficiency curves of Cu / SSZ-13 molecular sieve prepared in Example 1, fresh monolithic CeOx-Cu / SSZ-13 catalyst prepared in Examples 1-3, fresh monolithic Cu / SSZ-13 catalyst prepared in Comparative Example 1, and fresh monolithic CeO2-Cu / SSZ-13 catalyst prepared in Comparative Example 2.

[0041] Figure 3 The NOx conversion efficiency curves of the Cu / SSZ-13 molecular sieve prepared in Example 1, the monolithic CeOx-Cu / SSZ-13 catalyst prepared in Examples 1-3, the monolithic Cu / SSZ-13 catalyst prepared in Comparative Example 1, and the monolithic CeO2-Cu / SSZ-13 catalyst prepared in Comparative Example 2 after hydrothermal aging treatment.

[0042] Figure 4 N2O generation curves of Cu / SSZ-13 molecular sieve prepared in Example 1, fresh monolithic CeOx-Cu / SSZ-13 catalyst prepared in Examples 1-3, fresh monolithic Cu / SSZ-13 catalyst prepared in Comparative Example 1, and fresh monolithic CeO2-Cu / SSZ-13 catalyst prepared in Comparative Example 2.

[0043] Figure 5 The N2O generation efficiency curves of Cu / SSZ-13 molecular sieve prepared in Example 1, monolithic CeOx-Cu / SSZ-13 catalyst prepared in Examples 1-3, monolithic Cu / SSZ-13 catalyst prepared in Comparative Example 1, and monolithic CeO2-Cu / SSZ-13 catalyst prepared in Comparative Example 2 after hydrothermal aging treatment are shown.

[0044] Figure 6NOx conversion efficiency curves for the fresh catalysts prepared for Example 6 and Comparative Example 3 and the catalysts subjected to hydrothermal aging treatment (Example 6-A, Comparative Example 3-A).

[0045] Figure 7 N2O generation concentration curves for the fresh catalysts prepared for Example 6 and Comparative Example 3 and the catalysts subjected to hydrothermal aging treatment (Example 6-A, Comparative Example 3-A).

[0046] Table 1 and Figure 1 This indicates that, under the same copper content (equivalent Cu / Al), compared to conventional techniques (Comparative Example 1), the Cu-SSZ-13 (Example 1) prepared by this invention can reduce CuOx and ZCuOH species and increase Z2Cu content. Compared to conventional techniques (Comparative Example 1), or similar CeO2 doping techniques of this invention (Comparative Example 2), the catalyst prepared by this invention exhibits superior NOx conversion efficiency both fresh and aged, see [reference needed]. Figure 2 and Figure 3 Table 2 shows that, compared with the conventional technical solution (Comparative Example 1), the CeOx-Cu / CHA catalyst prepared by the present invention exhibits further modification in terms of specific surface area and pore size, resulting in lower specific surface area and pore size. Similar to the CeO2 doping technique of the present invention (Comparative Example 2), although the specific surface area and pore size are reduced, the difference is not significant. This indicates that Comparative Example 2 cannot achieve cerium oxide species dispersion and loading on the Cu-SSZ-13 surface, and the Ce species, copper sites, and Brønsted acid sites cannot form an effective interaction, thereby inhibiting N2O formation. (See Table 2 for details.) Figure 4 , Figure 5 .

[0047] Furthermore, the catalyst prepared based on this invention (Example 6) can achieve NOx conversion performance comparable to that of commercial solutions (Comparative Example 3) at a lower Cu / Al ratio (Example 6 and Comparative Example 3 in Table 1), see... Figure 6 Simultaneously achieving lower N2O generation, see... Figure 7 .

[0048] Table 1

[0049] Table 2

[0050] The highly efficient, low-N2O selective monolithic CeOx-Cu / SSZ-13 catalyst prepared by the method of this invention can be used for NOx reduction in diesel engines and new fuel engines compliant with non-road T4 / T5 and China VI / China VII regulations. Specifically, for the catalyst used in non-road T4 / China VI applications, a Cu / Al atomic ratio of less than or equal to 0.25 and a CeOx addition of 0.5-15% are preferred. For NOx reduction in diesel engines and new fuel engines compliant with China VII regulations, a Cu / Al atomic ratio of greater than or equal to 0.20 and a CeOx addition of 0.5-15% are preferred.

Claims

1. A method for preparing a highly efficient, low-N2O selective monolithic CeOx-Cu / SSZ-13 catalyst, characterized in that, The method is as follows: (1) Preparation of Cu / SSZ-13: 1) Preparation of copper acetate solution: Mix ethylene glycol with deionized water to form an ethylene glycol aqueous solution, with ethylene glycol accounting for 30-40 wt.% in the ethylene glycol aqueous solution; then add copper acetate to the ethylene glycol aqueous solution to obtain a copper acetate solution with a concentration of 0.05-0.20 mol / L; 2) Ion exchange: 90-100℃ oil bath copper acetate solution, stir, and after the copper acetate is completely dissolved, add H / SSZ-13 molecular sieve, stir and mix, and keep at the oil bath temperature for 30 min-1 h to obtain molecular sieve mixture; The proportion of molecular sieve in the molecular sieve mixture is 40-50 wt.%, and the molar ratio of SiO2 to Al2O3 in H / SSZ-13 molecular sieve is 10-40; 3) Filtration and washing: Filter the molecular sieve mixture to obtain a filter cake, and wash the filter cake with 1 to 2 times the mass of deionized water in copper acetate solution. 4) Drying and calcining filter cake: Dry the washed filter cake at 110-130℃ and then calcine it at 600-700℃ for 1-5 hours to prepare Cu / SSZ-13 molecular sieve material; (2) Preparation of CeOx: 1) Preparation of CeOx oxide: Cerium nitrate hexahydrate is calcined at 450-800℃ for 1 hour in air atmosphere to form CeOx; 2) Preparation of CeOx abrasive: CeOx is added to deionized water and mixed and circulated for grinding to obtain CeOx abrasive. The D90 of CeOx abrasive is controlled to be 0.5-1.5μm; the mass ratio of CeOx to deionized water is 1:8-10. (3) Preparation of monolithic CeOx-Cu / SSZ-13 catalyst: 1) Weigh the CeOx abrasive, add deionized water, add the binder aluminum colloid, stir and disperse, then add Cu / SSZ-13 molecular sieve material, stir evenly, and obtain a slurry with a solid content of 30-50 wt.%; wherein, CeOx accounts for 0.5-15% of the dry weight of oxides in the slurry, Cu / SSZ-13 accounts for 70-94.5% of the dry weight of oxides in the slurry, and the Al2O3 corresponding to the aluminum colloid accounts for 5-15% of the dry weight of oxides in the slurry; the oxides in the slurry are CeOx, Al2O3 corresponding to the aluminum colloid, and Cu / SSZ-13 molecular sieve; 2) Grind the slurry to control the final slurry particle size D90 = 4.5-6.0 μm; 3) Add xanthan gum to the ground slurry to thicken it, and control the slurry viscosity to 1000-2500cp to obtain a coating slurry. Coat the coating slurry onto a straight cordierite carrier, dry it, and then perform a second coating. The slurry loading is 90-180g / L. After coating, dry it at 100-150℃ and calcine it at 450-550℃ for 1h to prepare the monolithic CeOx-Cu / SSZ-13 catalyst.

2. The highly efficient, low-N2O selective monolithic CeOx-Cu / SSZ-13 catalyst prepared by the method of claim 1 is used for NO removal in diesel engines and new fuel engines. x reduction.

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