A method and application of Ce-modified Cu-SSZ-13 catalyst supported by carbon media.

Abstract

A method for modifying Cu-SSZ-13 catalyst by carbon medium assisted loading of Ce and its application, wherein NH4 + ‑SSZ‑13 or H + ‑SSZ‑13 is added to a copper acetate solution, and after a water bath loaded with copper species, a Cu‑SSZ‑13 filter cake is filtered to obtain the Cu‑SSZ‑13 filter cake. The Cu‑SSZ‑13 filter cake is washed with 0.5 to 1 times the volume of the copper acetate solution and dried. The above-mentioned molecular sieve filter cake powder is then added to the muffle furnace cavity by 10% volume, and calcined at 200 to 400°C in a closed state to obtain Cu‑SSZ‑13 powder. The Cu‑SSZ‑13 powder is immersed in a constant temperature water bath in a cerium nitrate solution, and after impregnation with loaded cerium, it is dried and calcined under an air atmosphere to prepare a Ce‑Cu‑SSZ‑13 catalyst. The inventive method can prepare a low / high temperature, high-efficiency, hydrothermally stable molecular sieve catalyst, which can be used for selective catalytic reduction of NOx in diesel exhaust and NH3‑SCR denitration catalyst. The inventive method is simple to operate and suitable for industrial production.

Description

Technical Field

[0001] This invention belongs to the field of catalyst technology, specifically relating to catalyst technology for selective catalytic reduction (NH3-SCR) of NOx in diesel engine exhaust. Background Art

[0002] NOx, a major pollutant emitted from diesel vehicle exhaust, is a primary culprit in smog and photochemical smog. Compared to vanadium-based SCR catalysts, Cu-SSZ-13 molecular sieve SCR catalysts exhibit superior low-temperature activity, a wider activity temperature window, and resistance to both low-temperature and high-temperature aging, making them a primary coating material for China VI emission standard SCR catalysts.

[0003] With the implementation of the China VI b emission regulations, the solicitation of opinions on the "Limits for Fuel Consumption of Heavy Commercial Vehicles", and the adoption of non-EGR routes by OEMs, SCR catalysts are forced to have more efficient NOx reduction performance. Studies have shown that compared with other metal elements, copper-modified SSZ-13 has the best catalytic performance, thus becoming the main active metal in SSZ-13 molecular sieves. Other active metals are used as auxiliary metal doping, and the interaction between the active metal copper and the doped metal can effectively improve the catalyst performance. Due to its excellent redox properties, Ce is widely used in the doping modification of Cu-SSZ-13 molecular sieves. Li Xiaoliang (Reaction kinetics, mechanisms and catalysis, 2019, 128(1)) conducted Ce modification research on Cu-SSZ-13 materials prepared by one-step method. The results showed that Ce modification promoted the enhanced interaction between Ce and active copper species, thereby promoting the catalyst's adsorption capacity for NH3 and NO+O2, and ultimately improving the catalyst's catalytic performance and anti-sulfur poisoning performance. Zhang Weibo et al. discovered that modified cerium with Ce 3+ CeO2 nanoparticles are located on the surface of Cu / CHA (Journal of Rare Earths 41 (2023) 1551-1561). However, some studies have shown that the introduction of Ce metal actually leads to a decrease in NH3-SCR performance (Rare Earths, 2023, 44 & Journal of Cleaner Production, 2022, 362, 132255, Journal of Rare Earths 41 (2023) 1551-1561). This is because when impregnated or ion-exchanged with strong acid-weak base metal salts such as cerium nitrate, the cerium metal salts hydrolyze to produce H2O. + This leads to the copper species in Cu-SSZ-13 being absorbed by H. +After re-exchange, the copper species precipitates and remains free on the outer surface of the molecular sieve material. After drying and calcination, some of the copper species are released as CuO. x The presence of species leads to lower low-temperature or high-temperature activity of the catalyst, which in turn affects the catalyst's anti-aging performance.

[0004] Therefore, it is necessary to develop a simple process for modifying the copper-cerium bimetallic SSZ-13 catalyst that can effectively control the effect of the cerium modification process on the active metal Cu. Summary of the Invention

[0005] The purpose of this invention is to provide a method for supporting Ce metal-modified Cu-SSZ-13 catalyst with a carbon-mediated process to prepare a low / high temperature, high-efficiency, hydrothermally stable molecular sieve catalyst. This invention also provides applications of the method.

[0006] The inventors' research shows that, due to the large radius of Ce metal ions, it is difficult for them to enter the multi-ring or CHA cage of the molecular sieve. Therefore, regardless of whether Cu-SSZ-13 is modified by ion exchange or impregnation, most of the Ce metal remains as Ce. 3+ Cerium exists in the form of metal oxides within the molecular sieve channels or on its surface. In acidic solutions, Ce ions undergo hydrolysis to produce H₂. + During the Ce modification of Cu-SSZ-13, active copper species are prone to re-exchange and transformation into inactive copper species. To avoid this, H2O is introduced during the Ce metal modification of Cu-SSZ-13. + To mitigate the impact on active copper, rapid Ce anchoring must be achieved during the modification process to suppress Ce. 3+ Hydrolysis, thereby inhibiting the absorption of active copper species by H + The cerium metal salts are re-exchanged and precipitated into the solution. Carbon, with its large specific surface area, can effectively adsorb cerium metal salts, anchoring metallic cerium, which can then be converted into variable-valence cerium oxides through calcination. Industrially, this process is often based on NH4+. 4+ -SSZ-13 or H + Cu-SSZ-13 is prepared by ion exchange using SSZ-13 molecular sieves. Copper acetate is the preferred copper metal salt for industrial preparation of Cu-SSZ-13 due to its high and rapid copper loading capacity. Furthermore, the acetate ions remaining after copper acetate exchange loading can form relatively uniform carbon in the channels or on the surface of the molecular sieve after incomplete calcination, thus enabling rapid anchoring of Ce metal.

[0007] Based on the above research results and inventive design concept, the technical solution adopted by this invention is as follows:

[0008] A method for carbon-media-assisted supported Ce-modified Cu-SSZ-13 catalyst, the method being as follows:

[0009] 1) NH 4+ -SSZ-13 or H + -SSZ-13 was added to a copper acetate solution, and after loading copper species in a water bath, Cu-SSZ-13 filter cake was obtained by filtration. The volume concentration of the copper acetate solution was 0.01 mol / L to 0.085 mol / L.

[0010] 2) Wash the Cu-SSZ-13 filter cake with 0.5 to 1 times the volume of copper acetate solution in deionized water to form acetate ions that remain in the filter cake layer, providing carbon sources for the formation of carbon species in the subsequent calcination process;

[0011] 3) Dry the washed Cu-SSZ-13 filter cake;

[0012] 4) Add Cu-SSZ-13 molecular sieve dry powder at 10% of the muffle furnace cavity volume, and calcine in a sealed environment at 200–400℃ for 1–6 hours to obtain incompletely calcined Cu-SSZ-13 powder. The incomplete calcination of acetate ions forms a carbon medium, which assists in the subsequent Ce loading and inhibits Ce. 3+ H formed by ion hydrolysis + With Cu 2+ exchange;

[0013] 5) The Cu-SSZ-13 powder was impregnated in a cerium nitrate solution in a constant temperature water bath. After impregnation and loading of cerium, it was dried and calcined in air to prepare the Ce-Cu-SSZ-13 catalyst.

[0014] Further, in step 1), the NH 4+ -SSZ-13 or H + The mass ratio of SSZ-13 to copper acetate solution is 1:15 to 1:18.

[0015] Furthermore, in step 1), when SSZ-13 is added to the copper acetate solution and copper species are loaded in a water bath, the water bath temperature is 50–85°C.

[0016] Further, in step 5), when impregnating Cu-SSZ-13 powder with cerium load, the mass ratio of cerium nitrate solution to Cu-SSZ-13 powder is 2:1 to 1:1.

[0017] Furthermore, when impregnating Cu-SSZ-13 powder with cerium load, the impregnation time is 0.5 to 5 hours.

[0018] Furthermore, in step 5), the Cu-SSZ-13 powder impregnated with cerium is dried by oven drying or spray drying.

[0019] Further, in step 5), the Cu-SSZ-13 powder impregnated with cerium is calcined at 550-650°C for 1-4 hours.

[0020] The Ce-Cu-SSZ-13 catalyst prepared by the above method can be used for selective catalytic reduction (NH3-SCR) of NOx in diesel engine exhaust.

[0021] The method of this invention can prepare Ce-Cu-SSZ-13 catalyst with good low-temperature and high-temperature high-efficiency hydrothermal stability. This catalyst can be used as a catalyst for the selective catalytic reduction of NOx in diesel engine exhaust gas into NH3-SCR denitrification.

[0022] Compared with existing Cu-SSZ-13 molecular sieves or conventional Ce metal salt impregnation and modification techniques for Cu-SSZ-13 catalysts, the Ce-modified Cu-SSZ-13 molecular sieve catalyst prepared by this invention has the following advantages:

[0023] (1) This invention uses copper acetate solution, based on NH4+. 4+ -SSZ-13 or H + -SSZ-13 was used as a copper ion exchange loading method for copper. Low-concentration copper acetate solutions (0.01 mol / L to 0.085 mol / L) were selected for modification with SSZ-13 molecular sieves to achieve rapid loading of copper species in their active valence state onto the loading sites. Other researchers in this field have also used Na... + -SSZ-13 is used for copper modification, but the residual Na pairs will cause changes in the acid sites and copper species state, resulting in a decrease in the performance of NH3-SCR.

[0024] (2) The Cu-SSZ-13 filter cake is washed with deionized water for quantitative analysis, which can ensure that acetate ions remain in the filter cake layer and provide carbon source for carbon species formation during subsequent low-temperature calcination.

[0025] (3) Based on the closed combustion of the muffle furnace, by adjusting the low-temperature calcination temperature, duration, and amount of calcined molecular sieve material, incomplete calcination of dried filter cake powder or spray-dried powder is achieved to form carbon species. When Cu-SSZ-13 powder formed after drying or spraying is calcined under high-temperature oxygen-rich or long-term conditions, acetate ions will be completely burned to form CO2 and H2O. However, under closed conditions, when the oxygen content is reduced and the calcination temperature and duration are low, acetate ions are not completely calcined to form carbon species. By adjusting the calcination temperature, calcination duration, and amount of calcined molecular sieve material, the acetate ions are not completely calcined to form carbon media, thereby assisting the loading of Ce, promoting the adsorption of cerium metal salt, and inhibiting Ce. 3+ H formed by ion hydrolysis + With Cu 2+Exchange. Furthermore, calcination temperatures that are too low (<200℃) will not achieve acetate ion calcination, preventing the formation of carbon species; calcination temperatures that are too high will result in more acetate ions forming CO2; calcination time and the amount of molecular sieve material added will further affect the residual carbon content in the molecular sieve. This invention achieves carbon formation by controlling the calcination temperature, time, and amount of molecular sieve material added under closed muffle furnace conditions. The inventors discovered in their research that if external carbon loading is used, i.e., physically mixing Cu-SSZ-13 with externally introduced carbon, the carbon will remain suspended on the water surface during the cerium metal solution modification process and cannot combine with Cu-SSZ-13, leading to the failure of subsequent cerium loading.

[0026] (4) In the cerium modification process, by introducing carbon, Ce can be rapidly anchored, which can effectively inhibit the re-exchange of active copper species, avoid the exchange of the original active copper species, maintain a large number of active copper species, and further improve the low-temperature and high-temperature performance of fresh molecular sieve catalysts through the interaction between copper species and cerium oxide species.

[0027] (5) During the cerium modification process, the transformation of active copper species into CuOx species was inhibited, and the framework collapse caused by CuOx combining with framework Al under high temperature hydrothermal conditions was reduced; furthermore, the cerium species inhibited the attack of H2O on the β acid sites of the molecular sieve framework, effectively improving the hydrothermal stability.

[0028] (6) The method for Ce-modified Cu-SSZ-13 catalyst provided by the present invention is simple, requires no special equipment, and is easy to industrialize.

[0029] In summary, the method of this invention involves ion-exchange loaded copper species onto a Cu-SSZ-13 filter cake, followed by low-to-medium temperature calcination to control the carbon content in the molecular sieve. Further, the calcined Cu-SSZ-13 is impregnated with a cerium metal solution, where cerium is primarily adsorbed onto the carbon species. After drying and calcination, a low-temperature, high-temperature, high-efficiency hydrothermal stable Ce-Cu-SSZ-13 catalyst is prepared. This catalyst effectively introduces a second active metal while avoiding the substitution of active copper species by the second metal. This ensures the activity of the copper species while enhancing low-temperature and high-temperature activity through the interaction between cerium metal and copper species. Furthermore, cerium mainly exists as cerium oxide species in the catalyst channels or covers the catalyst surface, effectively suppressing the attack of H2O on the framework at high temperatures and improving the hydrothermal stability of the catalyst. Attached Figure Description

[0030] Figure 1 The catalytic freshness of the Ce-Cu-SSZ-13 catalyst prepared by the method of the present invention (Examples 1 and 2) is compared with that of the Cu-SSZ-13 catalyst prepared by the conventional ion exchange method (Comparative Example 1) and the conventional Ce metal impregnation modified Cu-SSZ-13 catalyst (Comparative Example 2).

[0031] Figure 2 The catalytic aging performance of Ce-Cu-SSZ-13 catalysts prepared by the present invention (Examples 1 and 2), Cu-SSZ-13 catalysts prepared by conventional ion exchange method (Comparative Example 1), and conventional Ce metal impregnation modified Cu-SSZ-13 catalysts (Comparative Example 2) are compared.

[0032] Figure 3 XPS spectra of Cu 2p in Comparative Example 2 and Example 2 samples after fresh and aged conditions;

[0033] Figure 4 XPS spectra of fresh Ce 3d samples from Comparative Example 2 and Example 2;

[0034] Figure 5 The overall catalyst preparation process is shown in the comparative examples and embodiments. Detailed Implementation

[0035] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments. Obviously, the described embodiments are only a part of the embodiments of the present invention. Based on the implementation of the present invention, similar embodiments obtained by those skilled in the art without creative effort are all within the protection scope of the present invention.

[0036] Example 1

[0037] Prepare a 0.085 mol / L copper acetate solution according to the molecular sieve H... + -SSZ-13:copper acetate solution = 1:18 mass ratio, H + Cu-SSZ-13 was added to a copper acetate solution, and copper species were loaded in a water bath at 70°C for 3 hours. The mixture was then filtered to obtain a Cu-SSZ-13 filter cake. The Cu-SSZ-13 filter cake was washed with 0.5 times the volume of copper acetate solution in deionized water, dried at 120°C, and then calcined at 300°C for 4 hours to obtain Cu-SSZ-13 powder. A 0.070 mol / L cerium nitrate solution was prepared. Cu-SSZ-13 powder was added to the cerium nitrate solution at a mass ratio of Cu-SSZ-13 powder to cerium nitrate solution of 1:1 to load cerium. The mixture was impregnated in a water bath at 50°C with simultaneous stirring for 3 hours. The suspension was then placed in an oven, dried at 120°C, and calcined at 550°C for 4 hours to prepare the Ce-Cu-SSZ-13 molecular sieve catalyst (named Example Ce-HG-Cu-1).

[0038] Example 2

[0039] Prepare a 0.085 mol / L copper acetate solution according to H +-SSZ-13:copper acetate solution = 1:18 mass ratio, H + Cu-SSZ-13 was added to a copper acetate solution, and copper species were loaded in a water bath at 70°C for 3 hours. The mixture was then filtered to obtain a Cu-SSZ-13 filter cake. The Cu-SSZ-13 filter cake was washed with 0.5 times the volume of copper acetate solution in deionized water. After drying the filter cake at 120°C, Cu-SSZ-13 filter cake powder was added at 10% of the volume of the muffle furnace cavity. The mixture was calcined at 300°C for 4 hours to obtain Cu-SSZ-13 powder. A 0.070 mol / L cerium nitrate solution was prepared. Cu-SSZ-13 powder was added to the cerium nitrate solution at a mass ratio of 1:1 to load cerium. The mixture was impregnated in a water bath at 50°C with simultaneous stirring for 3 hours. The suspension was then spray-dried at a spray outlet temperature of 120°C. The resulting powder was then calcined at 550°C for 4 hours to prepare a Ce-Cu-SSZ-13 molecular sieve catalyst (named Example Ce-PW-Cu-2).

[0040] Example 3

[0041] To prepare a 0.035 mol / L copper acetate solution, follow the NH4+ formula. 4+ -SSZ-13:copper acetate solution = 1:15 mass ratio, NH 4+ Cu-SSZ-13 was added to a copper acetate solution, and copper species were loaded in a water bath at 85°C for 1 hour. The mixture was then filtered to obtain a Cu-SSZ-13 filter cake. The Cu-SSZ-13 filter cake was washed with 0.75 times the volume of copper acetate solution in deionized water, dried at 120°C, and then subjected to copper loading with copper acetate solution as described above. The Cu-SSZ-13 filter cake powder was then added to the muffle furnace cavity at 10% of its volume, and calcined at 400°C for 1 hour to obtain Cu-SSZ-13 powder. A 0.2 mol / L cerium nitrate solution was prepared. Cu-SSZ-13 powder was added to the cerium nitrate solution at a mass ratio of 1:1.5 to load cerium. The mixture was impregnated in a water bath at 70°C with simultaneous stirring for 2 hours. After the cerium loading was complete, the Cu-SSZ-13 powder was dried in an oven at 120°C and then calcined at 600°C for 1.5 hours to prepare the Ce-Cu-SSZ-13 molecular sieve catalyst.

[0042] Example 4

[0043] Prepare a 0.035 mol / L copper acetate solution according to H + -SSZ-13:copper acetate solution = 1:18 mass ratio, H +-SSZ-13 was added to a copper acetate solution, and copper species were loaded in a water bath at 50°C for 3 hours. The mixture was then filtered to obtain a Cu-SSZ-13 filter cake. The Cu-SSZ-13 filter cake was washed with 0.75 times the volume of copper acetate solution in deionized water, dried at 120°C, and then subjected to a second copper loading process using the same method. Then, Cu-SSZ-13 filter cake powder, after two copper exchange cycles, was added to 10% of the muffle furnace cavity volume, and calcined at 200°C for 6 hours to obtain Cu-SSZ-13 powder. A 0.01 mol / L cerium nitrate solution was prepared. Cu-SSZ-13 powder was added to the cerium nitrate solution at a mass ratio of 1:1 to load cerium. The mixture was impregnated in a water bath at 60°C with stirring for 5 hours. After the cerium loading was completed, the Cu-SSZ-13 powder was dried in an oven at 120°C and then calcined at 650°C for 1 hour to prepare the Ce-Cu-SSZ-13 molecular sieve catalyst.

[0044] Example 5

[0045] To prepare a 0.01 mol / L copper acetate solution, follow the NH4+ formula. 4+ -SSZ-13:copper acetate solution = 1:15 mass ratio, NH 4+ -SSZ-13 was added to a copper acetate solution, and copper species were loaded in a water bath at 70°C for 3 hours. The mixture was then filtered to obtain a Cu-SSZ-13 filter cake. The Cu-SSZ-13 filter cake was washed with 1.0 times the volume of copper acetate solution in deionized water, and the copper loading process was repeated three times using the same method. After drying the filter cake at 120°C, the Cu-SSZ-13 filter cake powder was added at 10% of the volume of the muffle furnace cavity, and calcined at 400°C for 1 hour to obtain Cu-SSZ-13 powder. A 0.03 mol / L cerium nitrate solution was prepared. Cu-SSZ-13 powder was added to the cerium nitrate solution at a mass ratio of 1:2 to load cerium. The mixture was impregnated in a water bath at 85°C with simultaneous stirring for 0.5 h. After the cerium loading was complete, the Cu-SSZ-13 powder was dried in an oven at 120°C and calcined at 550°C for 4 h to prepare the Ce-Cu-SSZ-13 molecular sieve catalyst.

[0046] Comparative Example 1

[0047] Prepare a 0.085 mol / L copper acetate solution according to H... + -SSZ-13:copper acetate solution = 1:18 mass ratio, H +-SSZ-13 was added to a copper acetate solution, and the filter cake was filtered after a 3-hour water bath at 70°C. The filter cake was then washed with deionized water until the aqueous solution was neutral (pH=7). The filter cake was dried at 120°C and then calcined at 550°C for 4 hours to prepare the Cu-SSZ-13 molecular sieve catalyst (named Comparative Example Cu-1).

[0048] Comparative Example 2

[0049] Prepare a 0.085 mol / L copper acetate solution according to H + -SSZ-13: Copper acetate solution = 1:18 (mass ratio of H added) + Cu-SSZ-13 molecular sieve was prepared by filtration in a 70℃ water bath for 3 hours, followed by washing with 0.5 times its volume of deionized water, drying at 120℃, and then calcining at 550℃ for 4 hours. A 0.070 mol / L cerium nitrate solution was prepared, and Cu-SSZ-13 molecular sieve was added to the cerium nitrate solution at a mass ratio of 1:1. The mixture was stirred in a 50℃ water bath for 3 hours, then spray-dried at 120℃, and finally calcined at 550℃ for 4 hours to prepare a Ce-PW-Cu-SSZ-13 molecular sieve catalyst (named Comparative Ce-PW-Cu-2).

[0050] The process from modified powder material preparation to monolithic catalyst sample preparation is as follows: Figure 5 As shown, the preparation of the monolithic catalyst sample is as follows.

[0051] The molecular sieve catalysts prepared in Examples 1 and 2, and Comparative Examples 1 and 2 were mixed with water and aluminum adhesive, respectively, with a mass ratio of molecular sieve catalyst to aluminum adhesive of 90:10. After grinding, the final slurry particle size was controlled to be D90=4-7μm and the solid content to be 35-45%, thus completing the slurry preparation. Using existing technology, the slurry was coated onto a cordierite support, dried, and calcined to prepare a monolithic catalyst with a loading of 140g / L. A small sample of the monolithic catalyst with a size of φ25.4mm*76.2mm was further cut.

[0052] The monolithic catalyst is subjected to hydrothermal aging as follows:

[0053] The extracted monolithic catalyst samples were placed in a non-standard monolithic water aging device and aged at a total flow rate of 19.3 L / min. The volume ratio of air and water in the aging atmosphere was 10%, with N2 as the carrier gas. The temperature was increased to 800℃ at a rate of 10℃ / min and maintained for 16 hours.

[0054] The NOx conversion performance of the monolithic catalyst sample was evaluated using the following method:

[0055] The activity of fresh and hydrothermally aged monolithic catalyst samples was evaluated in a fixed-bed reactor (non-standard). 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:

[0056] NOx conversion rate (%) = (NO inlet - NO outlet - NO2 outlet - 2 * N2O outlet) / NO inlet * 100%;

[0057] In the above formula, NO inlet represents the NO concentration (ppm) at the catalyst inlet, and NO outlet, NO2 outlet, and N2O outlet represent the corresponding atmosphere concentration (ppm) at the catalyst outlet.

[0058] Figure 1 The NOx conversion efficiencies of the Ce-Cu-SSZ-13 catalyst prepared by the method of the present invention (Examples 1 and 2), the Cu-SSZ-13 catalyst prepared by the conventional ion exchange method (Comparative Example 1), and the conventional Ce metal impregnation modified Cu-SSZ-13 catalyst (Comparative Example 2) are shown. Figure 1 It can be seen that the low-temperature performance of Cu-SSZ-13 impregnated with conventional cerium metal salts (comparative example Ce-PW-Cu-2) is lower than that of Cu-SSZ-13 modified with monometallic metals (comparative example Cu-1), while the high-temperature performance is slightly improved. However, the Ce-Cu-SSZ-13 prepared by the method of this invention (Examples Ce-HG-Cu-1 and Ce-PW-Cu-2) exhibits superior low-temperature and high-temperature performance compared to monometallic Cu-SSZ-13 (comparative example Cu-1) or conventionally cerium-modified Cu-SSZ-13 (comparative example Ce-PW-Cu-2). Furthermore, the catalyst prepared by spray drying (Example Ce-PW-Cu-2) exhibits even better low-temperature and high-temperature performance.

[0059] Figure 2 The NOx conversion efficiency at the aging stage is shown for the Ce-Cu-SSZ-13 catalyst prepared by the present invention (Examples 1 and 2), the Cu-SSZ-13 catalyst prepared by the conventional ion exchange method (Comparative Example 1), and the conventional Ce metal impregnation modified Cu-SSZ-13 catalyst (Comparative Example 2). Figure 2 It can be seen that after catalyst aging, the Ce-Cu-SSZ-13 catalyst prepared in Example 2 of this invention exhibits the best NOx conversion efficiency at low and high temperatures.

[0060] Figure 3 , Figure 4 XPS spectra of Cu2p (a) and Ce3d (b) for samples from Comparative Example 2 and Example 2, respectively. Figure 3 It can be concluded that the 931.5 eV peak belongs to Cu. + The 933 eV peak is attributed to Cu. 2+ Compared to Comparative Example 2, Example 2 of the present invention has a peak at 933 eV attributed to Cu. 2+ The peak intensity increases, and the 931.5 eV peak belongs to the category of decreased peak intensity, therefore Cu 2+ / (Cu 2+ +Cu + The increased proportion of Cu indicates that the Ce exchange process affects the active copper species in Cu-SSZ-13 catalyst prepared by the present invention. Similarly, after catalyst aging, Example 2 of the present invention exhibits a higher Cu content. 2+ Percentage content. From Figure 4 It can be seen that the preparation of Ce-Cu-SSZ-13 using Comparative Example 2 or Example 2 does not ultimately affect the valence state of Ce; Ce mainly exists as Ce. 4+ It exists in form, and there is a portion of Ce. 3 + Species.

[0061] Table 1 shows the XRF analysis results of the suspensions after cerium water bath loading modification in Comparative Example 2 and Example 2, after static separation and drying / calcination of the clear liquid. The XRF analysis results show that the Cu-SSZ-13 modification process using this invention significantly reduces the copper content precipitated from the solution.

[0062] Table 1. XRF analysis of the composition of cerium-modified clarified liquid.

[0063]

[0064] In summary, the Ce-Cu-SSZ-13 catalyst prepared by the method of this invention can effectively solve the problem of re-precipitation of active copper metal caused by conventional cerium metal salt impregnation method, effectively ensure the low and high temperature performance and hydrothermal stability of the catalyst, achieve more efficient NOx purification, and can be used as a catalyst for the selective catalytic reduction of NOx in diesel engine exhaust gas by NH3-SCR denitrification.

Claims

1. A method for supporting Ce-modified Cu-SSZ-13 catalyst with carbon media, characterized in that, The method is as follows: 1) NH4 + -SSZ-13 or H + -SSZ-13 was added to a copper acetate solution, and after loading copper species in a water bath, Cu-SSZ-13 filter cake was obtained by filtration. The volume concentration of the copper acetate solution was 0.01 mol / L to 0.085 mol / L. The NH4+... + -SSZ-13 or H + The mass ratio of SSZ-13 to copper acetate solution is 1:15 to 1:

18. 2) Wash the Cu-SSZ-13 filter cake with 0.5 to 1 times the volume of copper acetate solution in deionized water to form acetate ions that remain in the filter cake layer, providing carbon sources for the formation of carbon species in the subsequent calcination process; 3) Dry the washed Cu-SSZ-13 filter cake; 4) Add Cu-SSZ-13 molecular sieve dry powder at 10% of the muffle furnace cavity volume, and calcine in a sealed environment at 200–400℃ for 1–6 hours to obtain incompletely calcined Cu-SSZ-13 powder. The incomplete calcination of acetate ions forms a carbon medium, which assists in the subsequent Ce loading and inhibits Ce. 3+ H formed by ion hydrolysis + With Cu 2+ exchange; 5) The Cu-SSZ-13 powder was impregnated in a cerium nitrate solution in a constant temperature water bath. After impregnation and loading of cerium, it was dried and calcined in air to prepare the Ce-Cu-SSZ-13 catalyst.

2. The method for carbon-media-assisted supported Ce-modified Cu-SSZ-13 catalyst according to claim 1, characterized in that, In step 1), NH4 + -SSZ-13 or H + When adding -SSZ-13 to a copper acetate solution and loading copper species in a water bath, the water bath temperature is 50–85°C.

3. The method for carbon-media-assisted supported Ce-modified Cu-SSZ-13 catalyst according to claim 1 or 2, characterized in that, In step 5), when impregnating Cu-SSZ-13 powder with cerium load, the mass ratio of cerium nitrate solution to Cu-SSZ-13 powder is 2:1 to 1:

1.

4. The method for carbon-media-assisted supported Ce-modified Cu-SSZ-13 catalyst according to claim 3, characterized in that, When impregnating Cu-SSZ-13 powder with cerium load, the impregnation time is 0.5 to 5 hours.

5. A method for carbon-media-assisted supported Ce-modified Cu-SSZ-13 catalyst according to claim 1 or 2, characterized in that, In step 5), the Cu-SSZ-13 powder impregnated with cerium is dried by oven drying or spray drying.

6. A method for carbon-media-assisted supported Ce-modified Cu-SSZ-13 catalyst according to claim 1 or 2, characterized in that, In step 5), the Cu-SSZ-13 powder impregnated with cerium is calcined at 550-650℃ for 1-4 hours.

7. The Ce-Cu-SSZ-13 catalyst prepared by the method according to any one of claims 1 to 6 is used as a catalyst for the selective catalytic reduction of NOx in diesel engine exhaust gas by NH3-SCR denitrification.

Images