Core-shell type molecular sieve catalyst as well as preparation method and application thereof

Abstract

The invention relates to the technical field of NH3-SCR catalysts, in particular to a core-shell type molecular sieve catalyst and a preparation method and application thereof. The core-shell type molecular sieve catalyst is a core-shell type molecular sieve catalyst which takes a CeCu-SSZ-13 molecular sieve as a core and CeO2 as a shell; the CeCu-SSZ-13 molecular sieve is characterized in that an H-SSZ-13 molecular sieve is used as a carrier and is respectively subjected to ion exchange with Cu < 2 + > and Ce < 4 + > to form the CeCu-SSZ-13 molecular sieve taking Cu and Ce as active components; in the CeCu-SSZ-13 molecular sieve, on the basis of the mass of the carrier, the doping amount of Cu is 0.9%-3%; and the doping amount of Ce is 0.2%-0.8%. The Cu-SSZ-13 molecular sieve is modified by doping Ce in two dimensions of an inner core and a shell, so that the low-temperature activity of the Cu-SSZ-13 molecular sieve is effectively improved, the reaction window is widened, and the sulfur-resistant activity and the thermal stability are also improved.

Description

Technical Field

[0001] The present invention relates to the technical field of NH3-SCR catalysts, and particularly relates to a core-shell zeolite catalyst, a preparation method thereof, and an application thereof. Background Art

[0002] The chemical formula of nitrogen oxides is NO x , as a common air pollutant, NO x is one of the main substances causing environmental problems such as acid rain, smog, and photochemical smog. NO x has a wide range of sources, including diesel vehicle exhaust emissions, waste incineration plants, coal-fired power plants, and various industrial exhaust emissions. Ammonia selective catalytic reduction, abbreviated as NH3-SCR, is currently one of the most effective means to control NO x . Its principle is to use NH3 as a reducing agent, and under appropriate temperature and the action of a catalyst, convert NO x into non-toxic and harmless N2 and H2O. According to the reaction temperature, the SCR process can be divided into high-temperature SCR and low-temperature SCR. The reaction temperature range of low-temperature SCR is 150°C to 300°C. The exhaust temperatures of many industrial tail gases such as nitric acid, caprolactam, and ethylene cracking gas are usually lower than 300°C, and it is suitable to use low-temperature SCR technology to treat NO x in the tail gas.

[0003] Among the many catalysts used in NH3-SCR technology, small-pore zeolite catalysts represented by copper-based chabazite zeolites, such as Cu-SSZ-13 catalysts, have been commercially applied to the purification of NO x in vehicle exhaust due to their many advantages. The advantages of Cu-SSZ-13 catalysts are mainly reflected in two aspects: on the one hand, they have excellent NH3-SCR performance. In a relatively wide temperature window of 200°C to 500°C, Cu-SSZ-13 catalysts can exhibit good catalytic performance, enabling the removal efficiency of NO x to reach more than 90%, and having good N2 selectivity; on the other hand, they have excellent hydrothermal stability. Compared with some traditional catalysts, such as the V2O5-WO3 / TiO2 system and Cu / Fe-ZSM-5, Cu / Fe-beta, etc., Cu-SSZ-13 catalysts are more stable in structure and performance in the face of a hydrothermal environment and are not easily severely degraded or deactivated due to hydrothermal conditions, which enables them to maintain more persistent catalytic activity in practical applications, especially in some complex working conditions.

[0004] However, the Cu-SSZ-13 catalyst still has deficiencies in applications. At lower temperatures below 200 °C, such as during the cold start phase of diesel vehicles, its activity is poor and it cannot meet the actual usage conditions. Under high temperature conditions, especially when the diesel particulate filter in front of the catalyst is regenerated periodically and is frequently exposed to high temperatures above 700 °C, the Cu-SSZ-13 catalyst is prone to deactivation, resulting in the need to improve its high temperature activity and stability. At the same time, the sulfur resistance of the Cu-SSZ-13 catalyst is not ideal enough. Sulfur oxides in the flue gas will affect its activity, leading to catalyst poisoning, which also limits its wide application in sulfur-containing environments. Summary of the Invention

[0005] In order to solve the problems of insufficient low temperature resistance, high temperature resistance, and sulfur resistance of the existing Cu-SSZ-13 catalyst, the purpose of the present invention is to provide a core-shell type molecular sieve catalyst, its preparation method, and application.

[0006] The present invention mainly provides a core-shell structure molecular sieve SCR catalyst with CeCu-SSZ-13 as the core and CeO2 as the shell. Through the synergistic effect of the active components Cu and Ce in the SSZ-13 molecular sieve framework, the present invention can significantly improve the denitrification reaction performance of the catalyst, and constructing the CeO2 shell through a self-assembly method can effectively improve the sulfur poisoning resistance of the catalyst. The Cu-SSZ-13 molecular sieve catalyst prepared by the present invention is tested for denitrification performance under simulated flue gas conditions, showing good denitrification efficiency, a wider temperature window, and excellent water and sulfur resistance activity, so it has good practical application prospects.

[0007] To achieve the above object, the technical solution of the present invention is as follows.

[0008] The first aspect of the present invention provides a core-shell type molecular sieve catalyst, and the core-shell type molecular sieve catalyst is a core-shell type molecular sieve catalyst with CeCu-SSZ-13 molecular sieve as the core and CeO2 as the shell; the CeCu-SSZ-13 molecular sieve uses H-SSZ-13 molecular sieve as a carrier, and is respectively 2+ ion-exchanged with Cu 4+ and Ce to form a CeCu-SSZ-13 molecular sieve with Cu and Ce as active components; in the CeCu-SSZ-13 molecular sieve, based on the mass of the carrier, the doping amount of Cu is 0.9% - 3%; the doping amount of Ce is 0.2% - 0.8%.

[0009] The second aspect of the present invention provides a preparation method of the core-shell type molecular sieve catalyst described in the first aspect, including the following steps:

[0010] Using H-SSZ-13 molecular sieve as a carrier, the H-SSZ-13 molecular sieve is respectively mixed with NH4+ solution, a solution containing Cu 2+ solution, and a solution containing Ce 4+ solution are subjected to an ion exchange reaction to obtain CeCu-SSZ-13 zeolite; the CeCu-SSZ-13 zeolite is dispersed in a solvent, polyvinylpyrrolidone, a cerium source, hexamethylenetetramine, and cetyltrimethylammonium bromide are added, and a reflux reaction is carried out under stirring conditions. After standing and aging, a calcination treatment is carried out to obtain a core-shell zeolite catalyst with CeCu-SSZ-13 zeolite as the core and CeO2 as the shell.

[0011] Preferably, the specific preparation method of CeCu-SSZ-13 zeolite is as follows:

[0012] H-SSZ-13 zeolite is subjected to an ion exchange reaction with a solution containing NH 4+ to obtain NH4-SSZ-13 zeolite; the NH4-SSZ-13 zeolite is subjected to an ion exchange reaction with a solution containing Cu 2+ and, after a calcination treatment, Cu-SSZ-13 zeolite is obtained; the Cu-SSZ-13 zeolite is subjected to an ion exchange reaction with a solution containing Ce 4+ and, after a calcination treatment, CeCu-SSZ-13 zeolite is obtained.

[0013] Preferably, the temperature of the ion exchange reaction is 50°C to 90°C; the number of times of the ion exchange reaction with the solution containing NH 4+ is 1 time; the number of times of the ion exchange reaction with the solution containing Cu 2+ is 1 to 3 times; the number of times of the ion exchange reaction with the solution containing Ce 4+ is 1 to 3 times.

[0014] Preferably, the solution containing NH 4+ is ammonium sulfate solution, the solution containing Cu 2+ is copper nitrate solution, and the solution containing Ce 4+ is cerium nitrate solution; the concentration of the solution containing NH 4+ is 0.01M to 0.04M, the concentration of the solution containing Cu 2+ is 0.01M to 0.05M, and the concentration of the solution containing Ce 4+ is 0.05M to 0.2M.

[0015] Preferably, the conditions of the calcination treatment for preparing Cu-SSZ-13 zeolite, preparing CeCu-SSZ-13 zeolite, and preparing the core-shell zeolite catalyst are the same, specifically: the temperature of the calcination treatment is 500°C to 600°C, and the time is 3h to 5h.

[0016] Preferably, the mass ratio of the CeCu-SSZ-13 molecular sieve to polyvinylpyrrolidone, cerium source, hexamethylenetetramine, and cetyltrimethylammonium bromide is 0.5:0.15-0.45:0.1-0.25:0.1-0.2:0.05-0.125; the molecular weight of polyvinylpyrrolidone is 100,000-130,000.

[0017] More preferably, the mass ratio of the CeCu-SSZ-13 molecular sieve to polyvinylpyrrolidone, cerium source, hexamethylenetetramine, and cetyltrimethylammonium bromide is 0.5:0.25:0.15:0.15:0.075.

[0018] Preferably, the temperature of the reflux reaction is 50°C-80°C, the time of the reflux reaction is 2 h-4 h; the time of static aging is 2 h-4 h.

[0019] The third aspect of the present invention provides an application of the core-shell molecular sieve catalyst described in the first aspect 1 as an NH3-SCR denitration catalyst.

[0020] Preferably, the core-shell molecular sieve catalyst as an NH3-SCR denitration catalyst can be used to purify NO in fixed source flue gas x or NO in vehicle exhaust x ; in the temperature range of 175°C-550°C, the NO x removal rate of the core-shell molecular sieve catalyst is 100%.

[0021] The specific application method is as follows:

[0022] Load the core-shell molecular sieve catalyst into a micro fixed-bed reactor, and control the reaction temperature between 100°C and 550°C. Use ammonia as the reducing gas, control the gas flow rate at 600 mL / min, and control the space velocity at 50,000 h -1 , and the reaction conditions are: 500 ppm NO, 500 ppm NH3, 5% O2, 10% H2O, balanced with N2. The test results show that the core-shell molecular sieve catalyst of the present invention has a NO x removal rate of 100% in the temperature range of 175°C-550°C and has a wider temperature window.

[0023] During the water and sulfur resistance experiment, 50 ppm SO2 is added. Use ammonia as the reducing gas, control the gas flow rate at 600 mL / min, and control the space velocity at 50,000 h -1, The specific reaction conditions are: 50 ppm SO2, 500 ppm NO, 500 ppm NH3, 5% O2, 10% H2O, balanced with N2. The test results show that when 50 ppm SO2 is added to the simulated vehicle exhaust, in the temperature range of 175 °C to 550 °C, the core-shell molecular sieve catalyst of the present invention has a removal efficiency of NO x still above 95%.

[0024] When conducting the hydrothermal aging treatment experiment, first hydrothermally age the core-shell molecular sieve catalyst, and then use the hydrothermally aged core-shell molecular sieve catalyst to eliminate NO x , The treatment conditions are: hydrothermal aging for 12 h in air containing 10% water vapor at 750 °C. The test results show that after the core-shell molecular sieve catalyst of the present invention is hydrothermally aged at 750 °C for 12 h, in the temperature range of 175 °C to 550 °C, the removal efficiency of NO x is above 90%.

[0025] The beneficial effects of the present invention:

[0026] 1. The present invention mainly modifies the Cu-SSZ-13 molecular sieve by doping Ce in both the inner core and the outer shell dimensions simultaneously, which not only effectively improves the low-temperature activity of the molecular sieve catalyst, broadens the reaction window of the catalyst, but also improves the sulfur resistance activity and thermal stability, and solves the problems of insufficient low-temperature resistance, high-temperature resistance, and sulfur resistance performance of the existing Cu-SSZ-13 catalyst.

[0027] 2. Compared with the prior art, the CeCu-SSZ-13@CeO2 core-shell catalyst prepared by the present invention, compared with the single Cu-SSZ-13 catalyst, due to the synergistic effect of the two active components of Cu and Ce in the inner core, effectively reduces the denitrification reaction temperature of the catalyst, and the CeO2 shell layer can effectively improve the sulfur poisoning resistance performance of the catalyst.

[0028] 3. The core-shell molecular sieve catalyst of the present invention can be used as an NH3-SCR denitrification catalyst to purify NO in fixed-source flue gas x or NO in vehicle exhaust x ; When conducting the denitrification performance test under simulated flue gas conditions, it shows good denitrification efficiency, a wider temperature window, and excellent water and sulfur resistance activity, so it has good practical application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1Scanning electron microscope images of the Cu-SSZ-13 molecular sieve catalyst prepared in Comparative Example 1 and the CeCu-SSZ-13@CeO2 core-shell catalyst prepared in Example 1. Among them, (a) is the scanning electron microscope image of the Cu-SSZ-13 molecular sieve catalyst prepared in Comparative Example 1; (b) is the scanning electron microscope image of the CeCu-SSZ-13@CeO2 core-shell catalyst prepared in Example 1.

[0030] Figure 2 Conversion curves of NO for Cu-SSZ-13 catalysts with different Cu doping amounts x as a function of reaction temperature.

[0031] Figure 3 Conversion curves of NO for CeCu-SSZ-13 catalysts with different Ce doping amounts x as a function of reaction temperature.

[0032] Figure 4 Comparison diagrams of the conversion curves of NO for the Cu-SSZ-13 molecular sieve catalyst prepared in Comparative Example 1 and the CeCu-SSZ-13@CeO2 core-shell catalyst prepared in Example 1 x as a function of reaction temperature.

[0033] Figure 5 Conversion curves of NO for the Cu-SSZ-13 molecular sieve catalyst prepared in Comparative Example 1 and the CeCu-SSZ-13@CeO2 core-shell catalyst prepared in Example 1 after hydrothermal aging at 750 °C x as a function of reaction temperature.

[0034] Figure 6 Conversion curves of NO for the Cu-SSZ-13 molecular sieve catalyst prepared in Comparative Example 1 and the CeCu-SSZ-13@CeO2 core-shell catalyst prepared in Example 1 after adding 50 ppm SO2 to the reaction atmosphere x as a function of reaction temperature.

[0035] Figure 7 Conversion curves of NO for the molecular sieve catalysts of Comparative Example 1, Comparative Example 4 and Comparative Example 7 and the CeCu-SSZ-13@CeO2 core-shell catalyst prepared in Example 1 x as a function of reaction temperature. Detailed implementation manners

[0036] In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0037] Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts fall within the scope of protection of the present invention.

[0038] Among many preparation techniques, introducing additional metal cations into the zeolite framework to modify Cu-SSZ-13 is an effective method to improve the NH3-SCR ability of the catalyst. This method can optimize the active sites, provide more active centers, and increase the interaction sites with the reactants; it can also change the electron cloud density and chemical environment of the active sites. For example, introducing Ce 4+ , can adjust the electronic properties of the Cu sites through the Ce 4+ / Ce 3+ redox pair, enhance the adsorption and activation of NO x , make the adsorption and activation ability of the catalyst for the reactants better, thereby optimizing the redox cycle, accelerating electron transfer, and improving the catalytic reaction efficiency; it even improves the thermal stability and stabilizes the zeolite structure. The metal cations can interact with the zeolite framework, enhance the stability of the framework, and inhibit the sintering of Cu species, thus effectively improving the low-temperature reaction activity of the catalyst. However, the existing preparation methods are relatively weak in improving the anti-poisoning performance of the catalyst and cannot effectively solve the problem of easy poisoning of the catalyst.

[0039] For example, in the prior art 1: CN116532151, it is disclosed that an impregnation method is used to prepare a supported CeO2 / Cu-SSZ-13 composite catalyst. Although the activity of the Cu-SSZ-13 zeolite modified by CeO2 impregnation has a certain improvement in the low-temperature range of <200 °C, it has no obvious effect on broadening its activity window, and its activity window is between 200 °C and 500 °C. Therefore, there is still room for further improvement in the performance of this catalyst.

[0040] Meanwhile, constructing a core-shell structure in the Cu-SSZ-13 zeolite catalyst also has important significance in many aspects. On the one hand, it can improve the catalytic performance. The core-shell structure can place substances with different catalytic activities in the core and shell layers respectively, enabling them to play a synergistic role. On the other hand, it also helps to improve selectivity. By reasonably designing the composition and properties of the core-shell structure, the reaction path can be regulated to make the reaction more inclined to produce the target product. In addition, it can enhance the stability and sulfur resistance. In practical applications, the Cu-SSZ-13 zeolite catalyst often faces a hydrothermal environment. The shell layer of the core-shell structure can serve as a physical barrier to prevent direct contact between water molecules and other impurities and the core layer of Cu-SSZ-13, reducing structural damage phenomena such as dealumination of the zeolite framework under hydrothermal conditions, thereby improving the hydrothermal stability of the catalyst and extending its service life. At the same time, the shell layer can preferentially adsorb sulfides, preventing them from binding to the active centers of the core layer, playing a role in protecting the core layer catalyst, enhancing the sulfur resistance of the catalyst, and maintaining its long-term stable catalytic performance.

[0041] Prior art 2: CN105944753A discloses a core-shell structured Cu-SSZ-13 zeolite catalyst. By self-assembling a mesoporous aluminosilicate shell on the surface of the Cu-SSZ-13 zeolite and finally using the ion exchange method to prepare the corresponding core-shell structured catalyst. The prepared core-shell structured catalyst has excellent denitrification efficiency and thermal stability, but does not involve the evaluation of sulfur resistance performance, and the low-temperature denitrification efficiency below 200 °C is not ideal enough.

[0042] The present invention mainly modifies the Cu-SSZ-13 zeolite by doping Ce in both the inner core and outer shell dimensions simultaneously, which not only effectively improves the low-temperature activity of the zeolite catalyst, broadens the reaction window of the catalyst, but also improves the sulfur resistance activity and thermal stability.

[0043] Compared with the prior art, the CeCu-SSZ-13@CeO2 core-shell catalyst prepared by the present invention, compared with the single Cu-SSZ-13 catalyst, due to the synergistic effect of the two active components of Cu and Ce in the inner core, effectively reduces the denitrification reaction temperature of the catalyst, and the CeO2 shell layer can effectively improve the sulfur resistance performance of the catalyst. The prepared catalyst is tested for denitrification performance in a fixed-bed reactor under simulated flue gas conditions, and it is found that the catalyst has good denitrification efficiency, sulfur resistance performance, and a wide temperature window.

[0044] In the experiment simulating the composition of motor vehicle exhaust, when the space velocity is 50000h -1, under the evaluation conditions of NO concentration of 500 ppm, NH3 concentration of 500 ppm, and H2O of 10%, the CeCu-SSZ-13@CeO2 core-shell catalyst prepared by the present invention has a NO x removal rate of 100% in the temperature range of 175 °C to 550 °C, and has a wider temperature window.

[0045] In addition, after the CeCu-SSZ-13@CeO2 core-shell catalyst prepared by the present invention is hydrothermally aged at 750 °C for 12 h, in the temperature range of 175 °C to 550 °C, NO x The removal efficiency is above 90%. When 50 ppm SO2 is added to the simulated vehicle exhaust gas, in the temperature range of 175 °C to 550 °C, the CeCu-SSZ-13@CeO2 core-shell catalyst prepared by the present invention has a NO x removal efficiency still above 95%.

[0046] In summary, the CeCu-SSZ-13@CeO2 core-shell catalyst prepared by the present invention can be used as an NH3-SCR denitration catalyst, and its denitration performance is tested under simulated flue gas conditions, showing good denitration efficiency, a wider temperature window, and excellent water and sulfur resistance activities. Therefore, it has good practical application prospects.

[0047] The technical solutions of the present invention will be further described below through specific examples.

[0048] In the following examples, unless otherwise specified, the methods are all conventional methods; the reagents and materials, unless otherwise specified, can all be purchased on the market.

[0049] In the following examples, the molecular weight of polyvinylpyrrolidone is about 130,000.

[0050] Example 1

[0051] A preparation method of a core-shell molecular sieve catalyst, comprising the following steps:

[0052] Step 1, raw material pretreatment:

[0053] The chabazite structure molecular sieve, denoted as H-SSZ-13. Weigh 1 g of the original powder of the chabazite structure molecular sieve, put it into a crucible, and place it in a forced-air drying oven at 110 °C for drying overnight, and reserve it to obtain the dried H-SSZ-13 powder.

[0054] Step 2, preparation of Cu-SSZ-13 molecular sieve:

[0055] 1 g of dry H-SSZ-13 powder was slowly added to 80 mL of 0.02 M ammonium sulfate solution, and the temperature of the mixture was increased to 80 °C, and stirring was continued for 75 min. After centrifugation and washing, it was placed in a forced-air drying oven at 90 °C and dried overnight to obtain NH4-SSZ-13 molecular sieve.

[0056] Next, the NH4-SSZ-13 molecular sieve was subjected to 3 times of Cu ion exchange to obtain Cu-SSZ-13 with a Cu content of 2.4 wt%. The specific operation was as follows: 1 g of the dried NH4-SSZ-13 molecular sieve was added to 40 mL of 0.02 M copper nitrate solution, and the mixture was stirred in a water bath at 80 °C for 4 hours, centrifuged and washed, and then dried. The powder dried after the first Cu ion exchange was added to 40 mL of 0.02 M copper nitrate solution, and the second and third ion exchanges were carried out respectively by repeating the above experimental process. After that, it was dried, ground into powder, and calcined at 550 °C to obtain a powdery Cu-SSZ-13 molecular sieve with a Cu content of 2.4 wt%.

[0057] Step 3, preparation of CeCu-SSZ-13 molecular sieve:

[0058] Two times of Ce ion exchange were carried out to obtain CeCu-SSZ-13 with a Ce content of 0.5 wt%. The specific operation was as follows: 0.5 g of the Cu-SSZ-13 molecular sieve that had undergone 3 times of copper ion exchange was added to 50 mL of 0.1 M cerium nitrate solution, and the mixture was stirred and refluxed at 80 °C for 4 hours, centrifuged and washed. The powder dried after the first Ce ion exchange was added to 50 mL of 0.1 M cerium nitrate solution, and the second ion exchange was carried out by repeating the above experimental process. After that, it was centrifuged and washed, dried overnight at 100 °C, and calcined at 550 °C for 4 hours to obtain a powdery CeCu-SSZ-13 molecular sieve with a Ce content of 0.5 wt%.

[0059] Step 4, preparation of CeCu-SSZ-13@CeO2 core-shell catalyst:

[0060] First, ethanol and water are mixed evenly according to a volume ratio of 1:1 to obtain an ethanol aqueous solution. Then, 0.5 g of CeCu-SSZ-13 zeolite after 2 times of Ce ion exchange is added to 500 mL of the ethanol aqueous solution, and stirring is continued for 1.0 hour to ensure the uniform dispersion of the CeCu-SSZ-13 zeolite. Then, 0.25 g of polyvinylpyrrolidone with a molecular weight of about 130,000 is added. First, it is ultrasonicated for 10 minutes until completely dissolved, and then stirring is continued for 1.0 hour. Next, 0.15 g of cerium nitrate, 0.15 g of hexamethylenetetramine, and 0.075 g of cetyltrimethylammonium bromide are added in sequence, and the mixed solution is stirred continuously for 0.5 hour. Then, the prepared solution is transferred to a 500 mL round-bottom flask, refluxed at 60 °C for 3 hours, and aged by standing for 3 h. Finally, after centrifugation, the centrifuged product is dried at 110 °C for 12 hours, and then calcined at 550 °C for 4 hours to obtain the final product CeCu-SSZ-13@CeO2 core-shell catalyst.

[0061] Example 2

[0062] A preparation method of a core-shell zeolite catalyst, comprising the following steps:

[0063] Step 1, raw material pretreatment:

[0064] The chabazite structure zeolite is denoted as H-SSZ-13. Weigh 1 g of the original powder of the chabazite structure zeolite, put it into a crucible, place it in a forced-air drying oven at 110 °C and dry it overnight for standby to obtain the dried H-SSZ-13 powder.

[0065] Step 2, preparation of Cu-SSZ-13 zeolite:

[0066] Slowly add 1 g of the dried H-SSZ-13 powder to 80 mL of 0.02 M ammonium sulfate solution, increase the temperature of the mixture to 90 °C, and continuously stir for 75 min. After centrifugal washing, place it in a forced-air drying oven at 90 °C and dry it overnight to obtain NH4-SSZ-13 zeolite.

[0067] Next, the NH4-SSZ-13 molecular sieve was subjected to three Cu ion exchanges to obtain Cu-SSZ-13 with a Cu content of 3 wt%. The specific operation was as follows: 1 g of the dried NH4-SSZ-13 molecular sieve was added to 40 mL of 0.02 M copper nitrate solution, and the mixture was stirred in a water bath at 90 °C for 4 hours, centrifuged, washed, and then dried. If two or three Cu ion exchanges were carried out, the powder dried after the first Cu ion exchange was added to 40 mL of 0.02 M copper nitrate solution, and the second and third ion exchanges were respectively repeated according to the above experimental process. After that, it was dried, ground into powder, and calcined at 500 °C to obtain a powdery Cu-SSZ-13 molecular sieve with a Cu content of 3 wt%.

[0068] Step 3, preparation of CeCu-SSZ-13 molecular sieve:

[0069] Two Ce ion exchanges were carried out to obtain CeCu-SSZ-13 with a Ce content of 0.6 wt%. The specific operation was as follows: 0.5 g of the Cu-SSZ-13 molecular sieve that had undergone three copper ion exchanges was added to 50 mL of 0.1 M cerium nitrate solution, and the mixture was stirred and refluxed at 90 °C for 4 hours, centrifuged, and washed. The powder dried after the first Ce ion exchange was added to 50 mL of 0.1 M cerium nitrate solution, and the second ion exchange was repeated according to the above experimental process. After that, it was centrifuged, washed, dried overnight at 100 °C, and calcined at 500 °C for 5 hours to obtain a powdery CeCu-SSZ-13 molecular sieve with a Ce content of 0.6 wt%.

[0070] Step 4, preparation of CeCu-SSZ-13@CeO2 core-shell catalyst:

[0071] First, ethanol and water were mixed evenly according to a volume ratio of 1:1 to obtain an ethanol aqueous solution. Then, 0.5 g of the CeCu-SSZ-13 molecular sieve that had undergone two Ce ion exchanges was added to 500 mL of the ethanol aqueous solution, and the mixture was continuously stirred for 1.0 hour to ensure the uniform dispersion of the CeCu-SSZ-13 molecular sieve. Then, 0.45 g of polyvinylpyrrolidone with a molecular weight of about 130000 was added, ultrasonically treated for 10 minutes until completely dissolved, and then continuously stirred for 1.0 hour. Next, 0.25 g of cerium nitrate, 0.2 g of hexamethylenetetramine, and 0.125 g of cetyltrimethylammonium bromide were added in sequence, and the mixed solution was continuously stirred for 0.5 hour. Then, the prepared solution was transferred to a 500 mL round-bottom flask, refluxed at 80 °C for 4 hours, and allowed to age for 4 h. Finally, after centrifugation, the centrifuged product was dried at 110 °C for 12 hours, and then calcined at 500 °C for 5 hours to obtain the final product CeCu-SSZ-13@CeO2 core-shell catalyst.

[0072] Example 3

[0073] A preparation method of a core-shell type molecular sieve catalyst, comprising the following steps:

[0074] Step 1, raw material pretreatment:

[0075] The chabazite structure molecular sieve, denoted as H-SSZ-13. Weigh 1 g of the original powder of the chabazite structure molecular sieve, put it into a crucible, and place it in a forced-air drying oven at 110 °C for drying overnight, and reserve it to obtain the dried H-SSZ-13 powder.

[0076] Step 2, preparation of Cu-SSZ-13 molecular sieve:

[0077] Slowly add 1 g of the dried H-SSZ-13 powder to 80 mL of 0.02 M ammonium sulfate solution, increase the temperature of the mixture to 60 °C, and continuously stir for 75 min. After centrifugal washing, place it in a forced-air drying oven at 90 °C for drying overnight to obtain the NH4-SSZ-13 molecular sieve.

[0078] Then perform 3 times of Cu ion exchange on the NH4-SSZ-13 molecular sieve to obtain Cu-SSZ-13 with a Cu content of 3 wt%. The specific operation is as follows: Take 1 g of the dried NH4-SSZ-13 molecular sieve and add it to 40 mL of 0.02 M copper nitrate solution, and stir in a water bath at 60 °C for 4 hours, then centrifugally wash and dry. If 2 times and 3 times of Cu ion exchange are carried out, then add the powder dried after the first Cu ion exchange to 40 mL of 0.02 M copper nitrate solution and repeat the above experimental process to carry out the second and third ion exchanges respectively, and then dry, grind into powder, and complete calcination at 600 °C to obtain the powdered Cu-SSZ-13 molecular sieve with a Cu content of 3 wt%.

[0079] Step 3, preparation of CeCu-SSZ-13 molecular sieve:

[0080] Perform 2 times of Ce ion exchange to obtain CeCu-SSZ-13 with a Ce content of 0.6 wt%. The specific operation is as follows: Add 0.5 g of the Cu-SSZ-13 molecular sieve after 3 times of copper ion exchange to 50 mL of 0.1 M cerium nitrate solution, stir and reflux at 60 °C for 4 hours, and then centrifugally wash. Then add the powder dried after the first Ce ion exchange to 50 mL of 0.1 M cerium nitrate solution and repeat the above experimental process to carry out the second ion exchange, then centrifugally wash, dry overnight at 100 °C, and calcine at 600 °C for 3 hours to obtain the powdered CeCu-SSZ-13 molecular sieve with a Ce content of 0.6 wt%.

[0081] Step 4, preparation of CeCu-SSZ-13@CeO2 core-shell type catalyst:

[0082] First, ethanol and water were mixed evenly at a volume ratio of 1:1 to obtain an ethanol aqueous solution. Then, 0.5 g of CeCu-SSZ-13 molecular sieve after 2 times of Ce ion exchange was added to 500 mL of the ethanol aqueous solution, and stirring was continued for 1.0 hour to ensure the uniform dispersion of the CeCu-SSZ-13 molecular sieve. Then, 0.15 g of polyvinylpyrrolidone with a molecular weight of about 130,000 was added. It was first ultrasonicated for 10 minutes until completely dissolved, and then stirring was continued for 1.0 hour. Next, 0.1 g of cerium nitrate, 0.1 g of hexamethylenetetramine, and 0.05 g of cetyltrimethylammonium bromide were added in sequence, and the mixed solution was stirred continuously for 0.5 hour. Then, the prepared solution was transferred to a 500 mL round-bottom flask, refluxed at 70 °C for 2 hours, and aged by standing for 2 h. Finally, after centrifugation, the centrifuged product was dried at 110 °C for 12 hours, and then calcined at 600 °C for 3 hours to obtain the final product, the CeCu-SSZ-13@CeO2 core-shell catalyst.

[0083] Test 1: Microscopic morphology characterization.

[0084] The Cu-SSZ-13 molecular sieve catalyst prepared in Comparative Example 1 and the CeCu-SSZ-13@CeO2 core-shell catalyst prepared in Example 1 were subjected to microscopic morphology characterization, and the results are as Figure 1 shown.

[0085] Figure 1 are the scanning electron microscope images of the Cu-SSZ-13 molecular sieve catalyst prepared in Comparative Example 1 and the CeCu-SSZ-13@CeO2 core-shell catalyst prepared in Example 1. Among them, (a) is the scanning electron microscope image of the Cu-SSZ-13 molecular sieve catalyst prepared in Comparative Example 1; (b) is the scanning electron microscope image of the CeCu-SSZ-13@CeO2 core-shell catalyst prepared in Example 1.

[0086] It can be seen from the microscopic morphology characterization that the Cu-SSZ-13 molecular sieve catalyst prepared in Comparative Example 1 presents a regular cubic particle morphology with a smooth surface. While the CeCu-SSZ-13@CeO2 core-shell catalyst prepared in Example 1 of the present invention also presents a regular cubic particle morphology, and a layer of CeO2 shell layer is attached to the surface.

[0087] Next, the NO removal x reaction performance of Cu-SSZ-13 molecular sieve catalysts with different Cu contents was evaluated to explore the influence of Cu content on the denitrification performance.

[0088] Comparative Example 1

[0089] A preparation method of a molecular sieve catalyst includes the following steps:

[0090] Step 1, raw material pretreatment:

[0091] The zeolite chabazite structure molecular sieve is denoted as H-SSZ-13. Weigh 1 g of the original zeolite chabazite structure molecular sieve powder, put it into a crucible, place it in a forced-air drying oven at 110 °C and dry it overnight for standby, obtaining the dried H-SSZ-13 powder.

[0092] Step 2, prepare the Cu-SSZ-13 molecular sieve catalyst:

[0093] Slowly add 1 g of the dried H-SSZ-13 powder to 80 mL of 0.02 M ammonium sulfate solution, increase the temperature of the mixture to 80 °C, and continuously stir for 75 min. After centrifugal washing, place it in a forced-air drying oven at 90 °C and dry it overnight to obtain the NH4-SSZ-13 molecular sieve.

[0094] Then perform ion exchange on the NH4-SSZ-13 molecular sieve to obtain a Cu-SSZ-13 molecular sieve with a Cu content of 2.4 wt%. The specific operation is as follows: Add 1 g of the obtained NH4-SSZ-13 molecular sieve to 40 mL of 0.02 M copper nitrate solution, and stir it in a water bath at 80 °C for 4 hours, followed by centrifugal washing. Add the powder dried after the first ion exchange to 40 mL of 0.02 M copper nitrate solution and repeat the above experimental process for the second and third ion exchanges. After that, dry and grind it into powder, and complete the calcination at 550 °C to obtain a powdered Cu-SSZ-13 molecular sieve catalyst with a Cu content of 2.4 wt%.

[0095] Comparative Example 2

[0096] A preparation method of a molecular sieve catalyst, which is different from Comparative Example 1 in that a Cu-SSZ-13 molecular sieve with a Cu content of 1.8 wt% is obtained. The specific method includes the following steps:

[0097] Step 1, perform according to the method of Comparative Example 1 to obtain the dried H-SSZ-13 powder.

[0098] Step 2, prepare the Cu-SSZ-13 molecular sieve catalyst:

[0099] Slowly add 1 g of the dried H-SSZ-13 powder to 80 mL of 0.02 M ammonium sulfate solution, increase the temperature of the mixture to 80 °C, and continuously stir for 75 min. After centrifugal washing, place it in a forced-air drying oven at 90 °C and dry it overnight to obtain the NH4-SSZ-13 molecular sieve.

[0100] Next, the NH4-SSZ-13 molecular sieve was subjected to ion exchange to obtain an NH4-SSZ-13 molecular sieve with a Cu content of 1.8 wt%. The specific operation was as follows: 1 g of the obtained NH4-SSZ-13 molecular sieve was added to 40 mL of 0.02 M copper nitrate solution, and the mixture was stirred in a water bath at 80 °C for 4 hours, followed by centrifugation and washing. The powder dried after the first ion exchange was added to 40 mL of 0.02 M copper nitrate solution, and the second ion exchange was carried out by repeating the above experimental process. After that, it was dried and ground into powder, and calcined at 550 °C to obtain a powdered Cu-SSZ-13 molecular sieve catalyst with a Cu content of 1.8 wt%.

[0101] Comparative Example 3

[0102] A method for preparing a molecular sieve catalyst, which is different from Comparative Example 1 in that an NH4-SSZ-13 molecular sieve with a Cu content of 0.9 wt% is obtained. It includes the following steps:

[0103] Step 1, carried out according to the method of Comparative Example 1 to obtain dry H-SSZ-13 powder.

[0104] Step 2, preparing a Cu-SSZ-13 molecular sieve catalyst:

[0105] 1 g of the dry H-SSZ-13 powder was slowly added to 80 mL of 0.02 M ammonium sulfate solution, and the temperature of the mixture was increased to 80 °C and continuously stirred for 75 min. After centrifugation and washing, it was placed in a forced-air drying oven at 90 °C and dried overnight to obtain an NH4-SSZ-13 molecular sieve.

[0106] Next, the NH4-SSZ-13 molecular sieve was subjected to ion exchange to obtain an NH4-SSZ-13 molecular sieve with a Cu content of 0.9 wt%. The specific operation was as follows: 1 g of the obtained NH4-SSZ-13 molecular sieve was added to 40 mL of 0.02 M copper nitrate solution, and the mixture was stirred in a water bath at 80 °C for 4 hours, followed by centrifugation and washing. After the first ion exchange, it was dried and ground into powder, and calcined at 550 °C to obtain a powdered Cu-SSZ-13 molecular sieve catalyst with a Cu content of 0.9 wt%.

[0107] Table 1 Cu-SSZ-13 molecular sieve catalysts prepared with different Cu contents

[0108] Comparative example Cu content Catalyst number of Cu-SSZ-13 molecular sieve Comparative example 1 2.4wt% Cu(2.4)-SSZ-13 Comparative example 2 1.8wt% Cu(1.8)-SSZ-13 Comparative example 3 0.9wt% Cu(0.9)-SSZ-13

[0109] Test 2: Removal of NO x Reaction performance evaluation.

[0110] Removal of NO xThe reaction performance was evaluated using a laboratory reaction apparatus. The specific evaluation conditions were as follows: in the experiment simulating the composition of motor vehicle exhaust, ammonia was used as the reducing gas, the gas flow rate was controlled at 600 mL / min, and the space velocity was controlled at 50000 h -1 , the NO concentration was 500 ppm, the NH3 concentration was 500 ppm, O2 was 5%, H2O was 10%, and N2 was the balance gas.

[0111] The conversion rate of NO over Cu-SSZ-13 zeolite catalysts with different Cu doping amounts x as a function of reaction temperature is shown as Figure 2 follows.

[0112] It can be seen from Figure 2 that the higher the Cu content incorporated in the Cu-SSZ-13 zeolite catalyst, the better its denitrification activity. The results show that after three Cu ion exchanges, the denitrification performance of the Cu-SSZ-13 zeolite catalyst in Comparative Example 1 is relatively better.

[0113] Next, the reaction performance of CeCu-SSZ-13 zeolite catalysts with different Ce contents for NO x removal was evaluated to explore the effect of Ce content on denitrification performance.

[0114] Comparative Example 4

[0115] A preparation method of a zeolite catalyst includes the following steps:

[0116] Step 1, raw material pretreatment:

[0117] The chabazite structure zeolite, denoted as H-SSZ-13. Weigh 1 g of the original powder of the chabazite structure zeolite, put it into a crucible, place it in a forced-air drying oven at 110 °C and dry it overnight for standby to obtain the dried H-SSZ-13 powder.

[0118] Step 2, preparation of Cu-SSZ-13 zeolite:

[0119] Slowly add 1 g of the dried H-SSZ-13 powder to 80 mL of 0.02 M ammonium sulfate solution, increase the temperature of the mixture to 80 °C, and continuously stir for 75 min. After centrifugal washing, place it in a forced-air drying oven at 90 °C and dry it overnight to obtain NH4-SSZ-13 zeolite.

[0120] Next, the NH4-SSZ-13 molecular sieve was subjected to three Cu ion exchanges to obtain a Cu-SSZ-13 molecular sieve with a Cu content of 2.4%. The specific operation was as follows: 1 g of the dried NH4-SSZ-13 molecular sieve was added to 40 mL of 0.02 M copper nitrate solution, and the mixture was stirred in a water bath at 80 °C for 4 hours, centrifuged, washed, and then dried. The powder dried after the first Cu ion exchange was added to 40 mL of 0.02 M copper nitrate solution, and the second and third ion exchanges were repeated according to the above experimental procedure. After that, it was dried, ground into powder, and calcined at 550 °C to obtain a Cu-SSZ-13 molecular sieve with a Cu content of 2.4 wt%.

[0121] Step 3, preparing the CeCu-SSZ-13 molecular sieve catalyst:

[0122] Two Ce ion exchanges were carried out to obtain CeCu-SSZ-13 with a Ce content of 0.5%. The specific operation was as follows: 0.5 g of the Cu-SSZ-13 molecular sieve was added to 50 mL of 0.1 M cerium nitrate solution, stirred and refluxed at 80 °C for 4 hours, centrifuged, and washed. The powder dried after the first Ce ion exchange was added to 50 mL of 0.1 M cerium nitrate solution for the second ion exchange, then centrifuged, washed, filtered, dried at 100 °C overnight, and calcined at 550 °C for 4 hours to obtain a powdery CeCu-SSZ-13 molecular sieve catalyst with a Ce content of 0.5 wt%.

[0123] Comparative Example 5

[0124] A preparation method of a molecular sieve catalyst, which is different from Comparative Example 4 in that a CeCu-SSZ-13 molecular sieve catalyst with a Ce content of 0.8 wt% is obtained. The specific method includes the following steps:

[0125] Steps 1 and 2 were carried out according to the method of Comparative Example 4 to obtain a Cu-SSZ-13 molecular sieve with a Cu content of 2.4 wt%.

[0126] Step 3, preparing the CeCu-SSZ-13 molecular sieve catalyst:

[0127] Three Ce ion exchanges were carried out to obtain a CeCu-SSZ-13 molecular sieve catalyst with a Ce content of 0.8 wt%. The specific operation was as follows: 0.5 g of the Cu-SSZ-13 molecular sieve was added to 50 mL of 0.1 M cerium nitrate solution, stirred and refluxed at 80 °C for 4 hours, centrifuged, and washed. The powder dried after the first Ce ion exchange was added to 50 mL of 0.1 M cerium nitrate solution for the second and third ion exchanges, then centrifuged, washed, filtered, dried at 100 °C overnight, and calcined at 550 °C for 4 hours to obtain a powdery CeCu-SSZ-13 molecular sieve catalyst with a Ce content of 0.8 wt%.

[0128] Comparative Example 6

[0129] A preparation method of a molecular sieve catalyst, which is different from Comparative Example 4 in that a CeCu-SSZ-13 molecular sieve catalyst with a Ce content of 0.2 wt% is obtained. The specific method includes the following steps:

[0130] Steps 1 and 2 are carried out according to the method of Comparative Example 4 to obtain a Cu-SSZ-13 molecular sieve with a Cu content of 2.4 wt%.

[0131] Step 3, prepare a CeCu-SSZ-13 molecular sieve catalyst:

[0132] Perform 1 time of Ce ion exchange to obtain a CeCu-SSZ-13 molecular sieve catalyst with a Ce content of 0.2 wt%. The specific operation is as follows: Add 0.5 g of the Cu-SSZ-13 molecular sieve to 50 mL of 0.1 M cerium nitrate solution, stir and reflux at 80 °C for 4 hours, and centrifuge and wash. After the first ion exchange, centrifuge and wash, filter and dry, dry overnight at 100 °C, and calcine at 550 °C for 4 hours to obtain a powdery CeCu-SSZ-13 molecular sieve catalyst with a Ce content of 0.2 wt%.

[0133] Table 2 CeCu-SSZ-13 molecular sieve catalysts prepared with different Ce contents

[0134] Comparative example Ce content Catalyst number of CeCu-SSZ-13 molecular sieve Comparative example 4 0.5wt% Ce(0.5)Cu-SSZ-13 Comparative example 5 0.8wt% Ce(0.8)Cu-SSZ-13 Comparative example 6 0.2wt% Ce(0.2)Cu-SSZ-13

[0135] Test 3: Removal of NO x Reaction performance evaluation.

[0136] Removal of NO x The reaction performance was evaluated using a laboratory reaction device. The specific evaluation conditions were as follows: In an experiment simulating the composition of vehicle exhaust, ammonia was used as the reducing gas, the gas flow rate was controlled at 600 mL / min, and the space velocity was controlled at 50000 h -1 , the NO concentration was 500 ppm, the NH3 concentration was 500 ppm, O2 was 5%, H2O was 10%, and N2 was the balance gas.

[0137] The NO x conversion rate of CeCu-SSZ-13 molecular sieve catalysts with different Ce doping amounts changes with the reaction temperature as shown Figure 3 below.

[0138] From Figure 3It can be seen that due to the increase in the number of Ce ion exchanges, the denitrification activity of the CeCu-SSZ-13 molecular sieve catalyst first increases and then decreases, indicating that after two Ce ion exchanges, the denitrification performance of the CeCu-SSZ-13 molecular sieve catalyst in Comparative Example 4 is relatively better.

[0139] Comparative Example 7

[0140] A preparation method of a core-shell molecular sieve catalyst, which is different from that of Example 1 in that the Ce ion exchange step is not carried out on the Cu-SSZ-13 molecular sieve with a Cu content of 2.4 wt%. The specific method includes the following steps:

[0141] Steps 1 and 2 are carried out according to the method of Example 14 to obtain a Cu-SSZ-13 molecular sieve with a Cu content of 2.4 wt%.

[0142] Step 3, prepare a Cu-SSZ-13@CeO2 core-shell catalyst:

[0143] First, ethanol and water are mixed evenly according to a volume ratio of 1:1 to obtain an ethanol aqueous solution. Then, 0.5 g of the Cu-SSZ-13 molecular sieve is added to 500 mL of the ethanol aqueous solution, and stirred continuously for 1.0 hour to ensure the uniform dispersion of the Cu-SSZ-13 molecular sieve. Then, 0.25 g of polyvinylpyrrolidone with a molecular weight of about 130,000 is added, ultrasonicated for 10 minutes until completely dissolved, and then stirred continuously for 1.0 hour. Next, 0.15 g of cerium nitrate, 0.15 g of hexamethylenetetramine, and 0.075 g of cetyltrimethylammonium bromide are added in sequence, and the mixed solution is stirred continuously for 0.5 hour. Then, the prepared solution is transferred to a 500 mL round-bottom flask, refluxed at 60 °C for 3 hours, and left to age for 3 h. Finally, after centrifugation, the centrifuged product is dried at 110 °C for 12 hours, and then calcined at 550 °C for 4 hours to obtain the final product Cu-SSZ-13@CeO2 core-shell catalyst.

[0144] Test 4: Removal of NO x Reaction performance evaluation.

[0145] Removal of NO x The reaction performance is evaluated using a laboratory reaction device. The specific evaluation conditions are as follows: in an experiment simulating the composition of motor vehicle exhaust, ammonia is used as the reducing gas, the gas flow rate is controlled at 600 mL / min, and the space velocity is controlled at 50000 h -1 , the NO concentration is 500 ppm, the NH3 concentration is 500 ppm, O2 is 5%, H2O is 10%, and N2 is the balance gas.

[0146] The conversion rate curves of the Cu-SSZ-13 molecular sieve catalyst prepared in Comparative Example 1 and the CeCu-SSZ-13@CeO2 core-shell catalyst prepared in Example 1 for NO x are as shown in Figure 4 the figure.

[0147] It can be seen from Figure 4 that the CeCu-SSZ-13@CeO2 core-shell catalyst prepared in Example 1 of the present invention has better low-temperature activity. In the temperature range of 175 °C to 550 °C, the removal rate of NO x is 100%, and it has a wider temperature window. Compared with Example 2 and Example 3, the CeCu-SSZ-13@CeO2 core-shell catalyst prepared in Example 1 of the present invention is superior to Example 2 and Example 3 both in terms of low-temperature activity and activity window.

[0148] The Cu-SSZ-13 molecular sieve catalyst prepared in Comparative Example 1 and the CeCu-SSZ-13@CeO2 core-shell catalyst prepared in Example 1 were hydrothermally aged in air containing 10% water vapor at 750 °C for 12 h, and then the reaction performance evaluation for NO x removal was carried out. The results are as shown in Figure 5 the figure.

[0149] Figure 5 are the conversion rate curves of NO x after the Cu-SSZ-13 molecular sieve catalyst prepared in Comparative Example 1 and the CeCu-SSZ-13@CeO2 core-shell catalyst prepared in Example 1 were hydrothermally aged at 750 °C, varying with the reaction temperature.

[0150] It can be seen from Figure 5 that even after hydrothermal aging at 750 °C for 12 h, in the temperature range of 175 °C to 500 °C, the removal rate of NO x by the CeCu-SSZ-13@CeO2 core-shell catalyst prepared in Example 1 is still above 90%. Compared with the Cu-SSZ-13 molecular sieve catalyst prepared in Comparative Example 1, it shows better hydrothermal stability.

[0151] In the experiment simulating the composition of motor vehicle exhaust, when 50 ppm SO2 was added to the simulated motor vehicle exhaust, the reaction performance evaluation for NO x removal was carried out. The results are as shown in Figure 6 the figure.

[0152] Figure 6 are the NOx The conversion rate change curve with the reaction temperature.

[0153] From Figure 6 it can be seen that when 50 ppm SO2 is added to the simulated vehicle exhaust gas, in the temperature range of 175 °C to 500 °C, the CeCu-SSZ-13@CeO2 core-shell catalyst prepared in Example 1 has a removal efficiency of NO x still above 95%. This shows that compared with the Cu-SSZ-13 molecular sieve catalyst prepared in Comparative Example 1, the CeCu-SSZ-13@CeO2 core-shell catalyst prepared in Example 1 of the present invention has better water and sulfur resistance activity.

[0154] For the catalysts prepared in Comparative Example 1, Comparative Example 4 and Comparative Example 7 and the CeCu-SSZ-13@CeO2 core-shell catalyst prepared in Example 1, the NO x reaction performance evaluation was carried out, and the results are shown in Table 3 and Figure 7 as shown.

[0155] Figure 7 It is the change curve of the conversion rate of NO x with the reaction temperature for the molecular sieve catalysts of Comparative Example 1, Comparative Example 4 and Comparative Example 7 and the CeCu-SSZ-13@CeO2 core-shell catalyst prepared in Example 1.

[0156] Table 3 NO x Reaction performance evaluation results

[0157] Example Catalyst Temperature range Example 1 <![CDATA[CeCu-SSZ-13@CeO2 core-shell catalyst]]> 175℃～550℃ Comparative example 1 Cu-SSZ-13 molecular sieve catalyst 200℃～500℃ Comparative example 2 CeCu-SSZ-13 molecular sieve catalyst 175℃～550℃ Comparative example 3 <![CDATA[Cu-SSZ-13@CeO2 core-shell catalyst]]> 200℃～500℃

[0158] Note: The temperature range is the temperature range when the removal efficiency of NO x during the reaction performance evaluation process is 100%. x The temperature range when the removal efficiency of NO

[0159] From Figure 7 it can be seen that compared with Comparative Example 1, the molecular sieve catalyst in Comparative Example 4 played a major role in broadening the reaction activity window, while in Comparative Example 7, it only played a role in improving the low-temperature activity part, but had little impact on broadening the activity window. Therefore, Example 1 combined the structural advantages of the molecular sieve catalysts in Comparative Example 4 and Comparative Example 7, not only broadened the temperature range, but also improved the low-temperature activity, and the presence of the surface CeO2 shell was also beneficial to improving the sulfur resistance performance of the catalyst.

[0160] In summary, in the examples of the present invention, by doping Ce in two dimensions of the inner core and the outer shell of the Cu-SSZ-13 molecular sieve, the low-temperature activity of the molecular sieve catalyst was effectively improved, the reaction window of the catalyst was broadened, and the sulfur resistance activity and thermal stability were also improved.

[0161] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included within the protection scope of the present invention.

Claims

1. A core-shell type molecular sieve catalyst, characterized in that, The core-shell zeolite catalyst is a core-shell zeolite catalyst with CeCu-SSZ-13 zeolite as the core and CeO2 as the shell; The CeCu-SSZ-13 molecular sieve uses the H-SSZ-13 molecular sieve as a carrier and is ion-exchanged with Cu 2+ and Ce 4+ respectively to form a CeCu-SSZ-13 molecular sieve with Cu and Ce as active components; In the CeCu-SSZ-13 zeolite, based on the mass of the carrier, the doping amount of Cu is 0.9% to 3%; the doping amount of Ce is 0.2% to 0.8%.

2. The preparation method of the core-shell molecular sieve catalyst according to claim 1, characterized in that, It includes the following steps: Using H-SSZ-13 molecular sieve as a carrier, the H-SSZ-13 molecular sieve was subjected to ion exchange reactions with solutions containing NH 4+ , solutions containing Cu 2+ , and solutions containing Ce 4+ respectively, and the CeCu-SSZ-13 molecular sieve was obtained after calcination treatment; Disperse the CeCu-SSZ-13 zeolite in a solvent, add polyvinylpyrrolidone, cerium source, hexamethylenetetramine and cetyltrimethylammonium bromide, carry out a reflux reaction under stirring conditions, carry out calcination treatment after standing and aging, and obtain a core-shell zeolite catalyst with CeCu-SSZ-13 zeolite as the core and CeO2 as the shell.

3. The preparation method of the core-shell molecular sieve catalyst according to claim 2, characterized in that, The specific preparation method of the CeCu-SSZ-13 zeolite is as follows: The H-SSZ-13 molecular sieve is subjected to an ion exchange reaction with a solution containing NH 4+ to obtain the NH4-SSZ-13 molecular sieve; the NH4-SSZ-13 molecular sieve is subjected to an ion exchange reaction with a solution containing Cu 2+ and is calcined to obtain the Cu-SSZ-13 molecular sieve; Ion exchange reaction is carried out between Cu-SSZ-13 molecular sieve and a solution containing Ce 4+ , and after calcination treatment, CeCu-SSZ-13 molecular sieve is obtained.

4. The preparation method of the core-shell molecular sieve catalyst according to claim 3, characterized in that, The temperature of the ion exchange reaction is 50°C to 90°C; The number of ion exchange reactions with the solution containing NH 4+ is 1 time; with a solution containing Cu 2+ The number of ion exchange reactions with the solution is 1 to 3 times; The number of ion exchange reactions with the solution containing Ce 4+ is 1 to 3 times.

5. The preparation method of the core-shell molecular sieve catalyst according to claim 3, wherein, The solution containing NH 4+ is ammonium sulfate solution, the solution containing Cu 2+ is copper nitrate solution, and the solution containing Ce 4+ is cerium nitrate solution; The concentration of the solution containing NH 4+ is 0.01 M to 0.04 M, the concentration of the solution containing Cu 2+ is 0.01 M to 0.05 M, and the concentration of the solution containing Ce 4+ is 0.05 M to 0.2 M.

6. The preparation method of the core-shell molecular sieve catalyst according to claim 3, characterized in that, The calcination treatment conditions for preparing the Cu-SSZ-13 zeolite, the CeCu-SSZ-13 zeolite and the core-shell zeolite catalyst are the same, specifically: The calcination treatment temperature is 500°C to 600°C, and the time is 3h to 5h.

7. The preparation method of the core-shell type molecular sieve catalyst according to claim 2, characterized in that, The mass ratio of the CeCu-SSZ-13 zeolite to polyvinylpyrrolidone, cerium source, hexamethylenetetramine and cetyltrimethylammonium bromide is 0.5:0.15 to 0.45:0.1 to 0.25:0.1 to 0.2:0.05 to 0.125; The molecular weight of polyvinylpyrrolidone is 100000 to 130000.

8. The preparation method of the core-shell molecular sieve catalyst according to claim 2, wherein The temperature of the reflux reaction is 50°C to 80°C, the time of the reflux reaction is 2h to 4h; the time of standing and aging is 2h to 4h.

9. Application of the core-shell zeolite catalyst according to claim 1 as an NH3-SCR denitration catalyst.

10. Use of the core-shell molecular sieve catalyst according to claim 9 as an NH3-SCR denitration catalyst, characterized in that, The core-shell molecular sieve catalyst can be used as an NH3-SCR denitration catalyst to purify NO in the flue gas of fixed sources x or NO in vehicle exhaust x ; In the temperature range of 175 °C to 550 °C, the NO removal rate of the core-shell molecular sieve catalyst is 100%. x ​

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