Core-shell series ammonia selective catalytic oxidation catalyst and preparation and application thereof

Abstract

The application discloses a core-shell structure series ammonia selective catalytic oxidation catalyst and a preparation method and application thereof in NH3-SCO treatment of ammonia-containing tail gas. The catalyst takes Cu-ZSM-5 as an inner core, takes a cobalt-cerium composite oxide rich in oxygen vacancies etched by hydrogen peroxide as an outer shell, and forms an SCO-quick SCR series reaction system between the inner core and the outer shell. The preparation method comprises the following steps: dissolving cobalt salt and cerium salt in a citric acid solution, adding HZSM-5 molecular sieve after uniform dissolution, uniformly stirring, and then performing evaporation drying, drying and calcination to obtain a core-shell type precursor; performing hydrogen peroxide etching treatment on the core-shell type precursor, and performing drying and calcination to obtain an etching precursor; performing saturated copper ion exchange treatment on the etching precursor, and performing drying and calcination to obtain the core-shell structure series ammonia selective catalytic oxidation catalyst.

Description

Technical Field

[0001] This invention relates to the field of air pollution control and environmental catalysis technology, specifically to a core-shell structured tandem ammonia selective oxidation (NH3-SCO) catalyst, its preparation method, and its application. Background Technology

[0002] Ammonia (NH3), as a zero-carbon fuel and a highly efficient hydrogen carrier, has broad application prospects in internal combustion engines, gas turbines, and fuel cells. However, the utilization of ammonia fuel produces unburned NH3, with concentrations reaching 1000–10,000 ppm. Direct release into the atmosphere not only leads to eutrophication of water bodies through nitrogen deposition but also reacts with acidic gases to generate secondary aerosols, exacerbating PM2.5 pollution. 2.5 Pollution causes serious harm to the ecological environment and human health. NH3-SCO is an ideal technical route for the selective oxidation of NH3 to N2 and H2O (4NH3 + 3O2 → 2N2 + 6H2O), offering advantages such as simple process, high treatment efficiency, and low energy consumption compared to absorption, adsorption, and catalytic decomposition methods. However, the NH3-SCO process is accompanied by competing side reactions, generating NO and NO2 (collectively referred to as NO). x The core challenge lies in achieving both high NH3 conversion rate and high N2 selectivity.

[0003] Currently, NH3-SCO catalysts are mainly divided into two categories: noble metal-based and transition metal-based. Noble metal-based catalysts (such as Pt, Ru, and Ag-based catalysts) exhibit excellent low-temperature NH3 oxidation activity. Platinum-based catalysts, represented by Pt / Al2O3, can achieve complete NH3 conversion around 200℃, but they are prone to over-oxidation during the reaction, producing large amounts of N2O and NO. x Furthermore, Pt is expensive. While Ru-based catalysts exhibit a lower intrinsic N2O formation tendency, their low-temperature activity is significantly inhibited by water vapor, and they still require a high content of precious metals. Ag-based catalysts are relatively inexpensive, but their N2 selectivity is extremely sensitive to Ag particle size and support properties, and NO2 production at high temperatures is also affected. x The yield increased significantly. Overall, noble metal-based catalysts are limited by high cost and difficulty in controlling N2 selectivity, making it difficult to balance activity and selectivity across a wide temperature window. Transition metal-based catalysts are less expensive, among which Cu-based molecular sieve catalysts (such as Cu-ZSM-5 and Cu-SSZ-13) have isolated Cu atoms within their framework. 2+ / Cu +These species exhibit excellent SCR (selective catalytic reduction) activity, displaying superior N2 selectivity in NH3-SCO, but their ability to oxidize NH3 is insufficient, with complete conversion temperatures typically exceeding 300℃. Co-based oxides (such as Co3O4) possess low-temperature oxidation activity comparable to noble metals, but when used alone, their N2 selectivity is extremely poor, generating large amounts of N2O and NO during the reaction. x By combining Co3O4 with CeO2 and MnO x Combining these elements to construct Co-O-Ce or Co-O-Mn interfaces can further enhance redox capabilities, but it still cannot fundamentally solve the problem of the sharp decline in N2 selectivity with increasing temperature. A single transition metal component is unlikely to simultaneously meet the requirements of high activity and high selectivity.

[0004] To overcome the aforementioned problems, tandem catalyst design strategies have attracted widespread attention. The core idea is to spatially separate oxidation and reduction functional sites to construct a "SCO-SCR" tandem reaction system. The inner and outer layers are anchored to oxidation and reduction sites respectively, enabling the low-temperature oxidation of NH3 and the SCR reaction, thus achieving a balance between high activity and high selectivity.

[0005] Chinese patent document CN118558318B discloses a photodeposition method for preparing Pt / TiO2 catalysts, reducing the amount of noble metals from approximately 2 wt.% to 1 wt.%, achieving complete oxidation of NH3 up to 200℃. However, the N2 selectivity is below 80%, resulting in the production of relatively large amounts of N2O and NO. x The byproducts pose a risk of secondary pollution in practical applications.

[0006] Chinese patent document CN111068764A discloses a catalyst with cobalt and copper co-supported on Beta molecular sieve, which achieves complete oxidation of NH3 at around 250℃ and maintains more than 80% N2 selectivity in the range of 250-350℃. However, the simulated exhaust gas in the application example does not contain moisture, making it difficult to reflect the performance in actual application scenarios, and there is still room for further improvement in N2 selectivity.

[0007] Chinese patent document CN118217995A discloses an NH3-SCO core-shell catalyst and its synthesis and application. By adjusting the dosage ratio of the core and shell materials and the thickness of the shell, the catalytic efficiency and selectivity of the catalyst can be improved. The optimized CuCr@TiO2 core-shell catalyst achieves efficient removal of ammonia-containing waste gas, demonstrating the advantages of the core-shell structure. However, in specific application examples, the N2 selectivity is still less than 90%.

[0008] In summary, existing NH3-SCO catalysts still lag significantly behind in achieving high activity, high N2 selectivity, wide temperature window, low cost, and ease of preparation. In particular, controlling multiple byproducts, including N2O, NO, and NO2, within a wide temperature window using metal-free tandem catalysts remains a challenging technical problem to be solved. Therefore, developing an NH3-SCO catalyst that combines high activity, high N2 selectivity, wide temperature window, low cost, and simple preparation process has significant practical value and broad application prospects. Summary of the Invention

[0009] To address the aforementioned technical problems and shortcomings in the field, this invention provides a core-shell structured tandem NH3-SCO catalyst, using hydrogen peroxide to etch a cobalt-cerium mixed metal oxide (e-CoCeO). x A core-shell tandem Cu-ZSM-5@e-CoCeO3 membrane is constructed with a ZSM-5 molecular sieve (Cu ion exchange type) as the outer shell to perform NH3 oxidation and a Cu ion-exchange ZSM-5 molecular sieve as the core to perform SCR (Selective Catalytic Reduction) function. x The catalyst enables a highly efficient tandem catalytic system without precious metals.

[0010] The specific technical solution is as follows: In a first aspect, the present invention provides a core-shell structured tandem ammonia-selective catalytic oxidation catalyst, with a Cu ion-exchanged ZSM-5 molecular sieve (Cu-ZSM-5) as the core and a hydrogen peroxide-etched cobalt-cerium composite oxide (e-CoCeO) rich in oxygen vacancies. x The core (Cu-ZSM-5) forms the outer shell, and the core and the outer shell form an SCO-fast SCR tandem reaction system; the molar ratio of cobalt to cerium in the outer shell is (0.5~1.5):1, preferably 1:1. Under these preferred conditions, the catalyst exhibits better NH3 conversion and N2 selectivity in the NH3-SCO reaction; the core (Cu-ZSM-5) and the outer shell (e-CoCeO) form a tandem reaction system. x The mass ratio of the outer shell (based on the total mass of CeO2 and Co3O4) is (0.25~3):1, for example 0.5:1, 0.6:1, 1:1, 1.1:1, 1.5:1, 2:1, 2.5:1, etc., preferably (0.5~0.6):1. Under these preferred conditions, the catalyst exhibits better NH3 conversion and N2 selectivity in the NH3-SCO reaction. x It includes a mixed phase of CeO2 and Co3O4, with a Co-O-Ce interface structure formed between CeO2 and Co3O4, which is rich in oxygen vacancies.

[0011] Furthermore, in the core-shell structured tandem ammonia selective catalytic oxidation catalyst, the Cu species in the core Cu-ZSM-5 exists in the ionic state (Cu... δ+δ can be in the form of 1 or 2) anchored to the Brønsted acid site of the ZSM-5 framework.

[0012] This invention employs a core-shell structure to achieve spatial separation of oxidation and reduction functional sites: after etching with hydrogen peroxide, the outer shell e-CoCeO x The Co-O-Ce interface structure is rich in oxygen vacancies, exhibiting excellent redox properties, enabling low-temperature and efficient oxidation of NH3 while simultaneously producing N2O and NO. x (Contains a large amount of NO2) byproducts; the core ZSM-5 molecular sieve inhibits N2O formation through enhanced acidic sites, while Cu δ+ The site simultaneously removes NO and NO2 migrating from the shell via the SCR pathway, constructing an SCO-fast SCR tandem reaction system, thereby maintaining high N2 selectivity over a wide temperature window.

[0013] In some preferred embodiments, the Cu species in the core-shell structured tandem ammonia selective oxidation catalyst Cu-ZSM-5 is obtained by saturated copper ion exchange.

[0014] In some preferred embodiments, the core-shell structured tandem ammonia selective catalytic oxidation catalyst, Cu-ZSM-5, has a Cu species loading of 0.5% to 4% by mass, for example, 3.5%.

[0015] In a second aspect, the present invention provides a method for preparing the core-shell structured tandem ammonia selective catalytic oxidation catalyst described in the first aspect, comprising the steps of: (1) Dissolve cobalt salt and cerium salt in citric acid (CA) solution. After dissolving evenly, add HZSM-5 (H-type ZSM-5) molecular sieve, stir evenly, and then evaporate to dryness (to form a gel), dry and calcined to obtain a core-shell precursor. (2) The core-shell precursor was subjected to hydrogen peroxide etching, and then dried and calcined to obtain the etched precursor; (3) The etching precursor was subjected to saturated copper ion exchange treatment, and after drying and calcination, a core-shell structured tandem ammonia selective oxidation catalyst was obtained.

[0016] In some preferred embodiments, in step (1), the cobalt salt includes at least one of cobalt nitrate and cobalt acetate.

[0017] In some preferred embodiments, in step (1), the cerium salt includes at least one of cerium nitrate and cerium ammonium nitrate.

[0018] In some preferred embodiments, in step (1), the ratio of the molar amount of citric acid to the total molar amount of cobalt in the cobalt salt and cerium in the cerium salt is (1.1:1) to (1.5:1), for example, 1.3:1, etc.

[0019] In some preferred embodiments, in step (1), the HZSM-5 molecular sieve is added in powder form.

[0020] In some preferred embodiments, in step (1), the silica-alumina ratio of the HZSM-5 molecular sieve is 20~30, for example 25.

[0021] In some preferred embodiments, in step (1), the evaporation is carried out by water bath evaporation.

[0022] In some preferred embodiments, in step (1), the temperature of the evaporation is 70~90°C, for example 80°C.

[0023] In some preferred embodiments, in step (1), the drying temperature is 100~130°C (e.g., 120°C, etc.) and the time is 10~24 h (e.g., 20 h, etc.).

[0024] In some preferred embodiments, in step (1), the calcination temperature is 450~600℃ (e.g., 500℃, etc.), the time is 3~6 h (e.g., 4 h, etc.), and the heating rate is 2~10℃ / min (e.g., 5℃ / min, etc.).

[0025] In some preferred embodiments, in step (2), the concentration of H2O2 in the hydrogen peroxide used is 0.1~0.2 mol / L.

[0026] In some preferred embodiments, in step (2), the ratio of the volume of hydrogen peroxide used to the mass of the core-shell precursor is (10~15) mL:1 g.

[0027] In some preferred embodiments, in step (2), the etching process is performed at room temperature for 24 to 36 hours.

[0028] In some preferred embodiments, in step (2), the drying temperature is 100~130℃ and the time is 10~24 h.

[0029] In some preferred embodiments, in step (2), the calcination temperature is 450~600℃ (e.g., 500℃, etc.), the time is 3~6 h (e.g., 4 h, etc.), and the heating rate is 2~10℃ / min (e.g., 5℃ / min, etc.).

[0030] In some preferred embodiments, in step (3), the saturated copper ion exchange treatment uses a copper acetate solution.

[0031] In some preferred embodiments, in step (3), the concentration of the copper acetate solution is 0.01~0.5 mol / L, for example 0.02 mol / L.

[0032] In some preferred embodiments, in step (3), the temperature of the saturated copper ion exchange treatment is 60~90℃, for example 80℃.

[0033] In some preferred embodiments, in step (3), the number of exchanges in the saturated copper ion exchange treatment is 2 to 4 times (e.g., 3 times), and the time for each exchange is 1 to 4 hours (e.g., 2 hours).

[0034] In some preferred embodiments, in step (3), the calcination temperature is 400~600℃ (e.g., 500℃, etc.) and the time is 3~6 h (e.g., 4 h, etc.).

[0035] Thirdly, the present invention provides the application of the core-shell structured tandem ammonia selective catalytic oxidation catalyst described in the first aspect in the treatment of ammonia-containing tail gas using NH3-SCO.

[0036] In some preferred embodiments, the ammonia-containing tail gas has an NH3 volume concentration of 1,000 to 10,000 ppm, an O2 volume fraction of 1% to 10%, and a water vapor volume fraction of 0 to 5%.

[0037] In some preferred embodiments, the NH3-SCO treatment temperature is 150~500℃, such as 175℃, 200℃, 225℃, 250℃, 275℃, 300℃, 325℃, 350℃, 375℃, 400℃, 425℃, 450℃, 475℃, etc.

[0038] In some preferred embodiments, the catalyst volume space velocity (GHSV) during NH3-SCO treatment is 40,000 to 100,000 h⁻¹. -1 .

[0039] Compared with the prior art, the present invention has the following advantages: 1) This invention, through core-shell structure design, incorporates e-CoCeO x The oxide shell and the Cu-ZSM-5 reducing core are spatially separated, realizing the SCO-fast SCR tandem reaction system, achieving an NH3 conversion rate of over 90% and an N2 selectivity of over 94% in the range of 250~400℃.

[0040] 2) This invention uses all transition metal components (Co, Ce, Cu), which are completely free of precious metals, significantly reducing catalyst costs. At the same time, it reduces the amount of molecular sieve used, and the preparation process is relatively simple, which is conducive to large-scale industrial application.

[0041] 3) This invention uses hydrogen peroxide to treat the outer shell CoCeO x The composition underwent further etching to obtain e-CoCeO with a higher oxygen vacancy content. x The components enhance the oxidation capacity of the catalyst.

[0042] 4) The catalyst shell e-CoCeO prepared in this invention x It produces a large amount of NO2 byproducts, which react with the Cu core. δ+ The rapid SCR pathway (co-reduction of NO and NO2) at the site forms a natural match, enabling comprehensive control over N2O, NO, and NO2 byproducts. Detailed Implementation

[0043] The present invention will be further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Operating methods not specifically specified in the following embodiments are generally performed under conventional conditions or as recommended by the manufacturer.

[0044] Example 1: A core-shell structured tandem ammonia selective oxidation catalyst comprises a Cu-ZSM-5 core and a cobalt-cerium composite oxide rich in oxygen vacancies etched by hydrogen peroxide as the outer shell, forming an SCO-fast SCR tandem reaction system between the core and the shell; the molar ratio of cobalt to cerium in the shell is 1:1; the core Cu-ZSM-5 and the shell e-CoCeO x The mass ratio is approximately 0.5:1. In Cu-ZSM-5, Cu species are anchored in ionic form at Brønsted acid sites on the ZSM-5 framework, and the Cu species are obtained through saturated copper ion exchange.

[0045] Step (1): Dissolve 8.73 g of cobalt nitrate (Co(NO3)2·6H2O, 0.03 mol) and 13.03 g of cerium nitrate (Ce(NO3)2·6H2O, 0.03 mol) in 100 mL of deionized water containing 15 g of citric acid (0.078 mol), stir until clear, add 4 g of HZSM-5 powder (silicon-to-aluminum ratio 25), transfer to an 80℃ water bath and stir until the solvent evaporates to form a gel, dry at 120℃ for 20 h, grind and calcine at 500℃ for 4 h (heating rate 5℃ / min) to obtain HZSM-5@CoCeO x -0.5 precursor; Step (2): The precursor obtained in step (1) was etched in a hydrogen peroxide solution (H2O2 concentration of 0.1 mol / L) at room temperature. The volume ratio of the hydrogen peroxide solution to the mass of the precursor obtained in step (1) was 10 mL:1 g. The etching time was 24 h. After filtration, washing, and drying, it was calcined in a muffle furnace at 500℃ for 4 h to obtain HZ@e-CoCeO x -0.5 precursor; Step (3): The precursor obtained in step (2) was placed in a copper acetate solution (concentration 0.02 mol / L) at 80℃ for ion exchange, each exchange lasting 2 h, repeated 3 times. After filtration, washing, and drying, it was calcined at 500℃ for 4 h to obtain the core-shell structured tandem ammonia selective catalytic oxidation catalyst Cu-ZSM-5@e-CoCeO x -0.5. In the core Cu-ZSM-5, the Cu species loading mass is 3.5%.

[0046] Example 2: The difference from Example 1 is that 2 g of HZSM-5 powder was added in step (1), while the rest were the same, to obtain Cu-ZSM-5@e-CoCeO x -0.25 catalyst.

[0047] Example 3 The difference from Example 1 is that 8 g of HZSM-5 powder was added in step (1), while the rest were the same, to obtain Cu-ZSM-5@e-CoCeO x -1 catalyst.

[0048] Example 4: The difference from Example 1 is that 16 g of HZSM-5 powder was added in step (1), while the rest were the same, to obtain Cu-ZSM-5@e-CoCeO x -2 catalyst.

[0049] Example 5: The difference from Example 1 is that 17.46 g of cobalt nitrate was added in step (1), but cerium nitrate was not added. The rest were the same, and Cu-ZSM-5@e-Co3O4-0.5 catalyst was obtained.

[0050] Example 6: The difference from Example 1 is that 26.06 g of cerium nitrate was added in step (1), but cobalt nitrate was not added. The rest were the same, and Cu-ZSM-5@e-CeO2-0.5 catalyst was obtained.

[0051] Comparative Example 1: The difference from Example 1 is that the hydrogen peroxide etching process in step (2) and the copper ion exchange process in step (3) are not performed, resulting in HZSM-5@CoCeO. x -0.5 catalyst.

[0052] Comparative Example 2: The difference from Example 1 is that the copper ion exchange treatment in step (3) is not performed, resulting in HZSM-5@e-CoCeO. x -0.5 catalyst.

[0053] Comparative Example 3: The difference from Example 1 is that HZSM-5 powder is not added in step (1), and step (3) is omitted, and e-CoCeO is prepared directly. x Oxide catalysts.

[0054] Comparative Example 4: HZSM-5 powder (silicon-to-aluminum ratio 25) was placed in a copper acetate solution (concentration 0.02 mol / L) at 80℃ for ion exchange. Each exchange lasted 2 h and was repeated 3 times. After filtration, washing, and drying, the product was calcined at 500℃ for 4 h to obtain Cu-ZSM-5 catalyst.

[0055] The e-CoCeO from Comparative Example 3 x The oxide catalyst and Cu-ZSM-5 catalyst were physically mixed at a mass ratio of approximately 2:1, as described in Example 1, to obtain Cu-ZSM-5 & e-CoCeO x catalyst.

[0056] Application Example 1: The catalysts prepared in Examples 1-6 and Comparative Examples 1-4 were subjected to NH3-SCO activity testing. The test conditions were: 1000 ppm NH3 (volume ratio), 10 vol% O2, 5 vol% H2O, N2 as carrier gas, GHSV = 40,000 h⁻¹. -1 The catalyst loading was 2.3 mL, with a particle size of 40-60 mesh. The NH3 conversion and N2 selectivity were calculated using the following formula: The test results are shown in Tables 1, 2, 3, 4 and 5.

[0057] Table 1 Catalytic oxidation efficiency of catalysts for NH3 Table 2. N2 selectivity of catalysts for NH3 oxidation As shown in Tables 1 and 2, the catalyst in Example 1 achieved an NH3 conversion rate of over 95% within the temperature range of 225-400℃, while maintaining an N2 selectivity of over 94%, demonstrating the best overall performance. The catalyst in Example 2 exhibited higher activity than that in Example 1, but its N2 selectivity decreased significantly at high temperatures. The catalysts in Examples 3 and 4 showed the highest selectivity but slightly lower activity. Therefore, a core-shell mass ratio of (0.5~0.6):1 was determined to be the optimal ratio.

[0058] The shell of Example 5 is a single Co3O4 oxide, which has less activity than Example 1; the shell of Example 6 is a single CeO2 oxide, which has far less activity than Example 1. This indicates that the shell of Example 1 is e-CoCeO x The component exhibits the strongest NH3 oxidation activity, which is related to the highly active Co-O-Ce structure at the interface. Therefore, co-loading of Co and Ce was determined to be the optimal formulation.

[0059] Comparative Example 1 (without hydrogen peroxide etching and copper ion exchange) showed lower activity than Comparative Example 2, indicating that hydrogen peroxide etching can significantly enhance the NH3 oxidation capacity of the oxidizing component at low temperatures. This is attributed to the generation of more oxygen vacancies after etching. Comparative Example 2 (without copper ion exchange) showed slightly better activity than Example 1, but its N2 selectivity decreased significantly at high temperatures. Comparative Example 3 (containing only e-CoCeO) showed lower activity. x The activity of Cu is the best, but the N2 selectivity is the worst, which proves the effectiveness of the core-shell tandem structure and Cu. δ+ The site plays a crucial role in maintaining high N2 selectivity. Comparative Example 4 (physically mixed sample) showed comparable activity to Example 1, but significantly lower N2 selectivity. Therefore, it is clear that the tandem core-shell structure exhibits the best NH3-SCO performance.

[0060] Table 3. Selectivity of catalysts for N2O oxidation of NH3 Table 4. NO selectivity of catalysts for NH3 oxidation Table 5. Selectivity of catalysts for NO2 oxidation of NH3 Data from Tables 3, 4, and 5 show that the catalyst in Comparative Example 3 produced a large amount of N2O, NO, and NO2 byproducts during the NH3-SCO process. When the reaction temperature exceeded 250℃, NO2 gradually became the main byproduct. The catalyst in Comparative Example 2 has a core-shell structure, exhibiting a tandem reaction of outer shell oxidation and core reduction. Compared to Comparative Example 3, the byproducts were significantly suppressed, but the problem of NO2 overflow at high temperatures still existed. The catalyst in Example 1 further suppressed the formation of byproducts, especially at 200-400℃ where almost no NO2 was produced. This is the result of the synergistic catalytic reduction of NO and NO2, corresponding to the rapid SCR function of Cu species.

[0061] Application Example 2: The NH3-SCR activity of the catalysts prepared in Example 1 and Comparative Examples 2-3 was tested. The test conditions were: 550 ppmv NH3, 500 ppmv NO, 10 vol% O2, 5 vol% H2O, N2 as carrier gas, GHSV = 40,000 h. -1 The catalyst loading was 2.3 mL, with a particle size of 40-60 mesh. NO conversion and N2 selectivity were calculated using the following formula: The test results are shown in Tables 6 and 7.

[0062] Table 6 Catalytic reduction efficiency of catalysts for NO Table 7. N2 selectivity for NO reduction catalyzed by the catalyst As shown in Tables 6 and 7, the catalyst in Example 1 achieved a NO conversion rate of over 90% in the temperature range of 175–400°C and maintained an N2 selectivity of over 95% in the temperature range of 150–400°C, indicating its excellent SCR performance. The catalyst in Comparative Example 2 also exhibited certain SCR performance, achieving a NO conversion rate of over 90% in the temperature range of 200–300°C and maintaining an N2 selectivity of over 95% in the temperature range of 150–300°C, indicating that the copper ion exchange process is key to the SCR function. Meanwhile, the catalyst in Comparative Example 3 lacked a temperature window with a NO conversion rate exceeding 90% and exhibited low N2 selectivity, indicating that the shell-e-CoCeO… x It does not have SCR function; the core Cu-ZSM-5 is the main region of the SCR sub-reaction, which is the key to the SCO-fast SCR tandem reaction system.

[0063] Application Example 3: The catalyst prepared in Example 1 was subjected to periodic stability testing. The test conditions were the same as in Application Example 1, with continuous operation at 250°C. The results showed that the catalyst maintained a stable NH3 conversion of over 90% and an N2 selectivity of over 94% during a long-term operation of 1000 min, demonstrating that the catalyst of the present invention has good catalytic stability.

[0064] In summary, this invention provides a core-shell structured tandem ammonia selective catalytic oxidation catalyst, its preparation method, and its applications. This catalyst uses a Cu ion-exchanged ZSM-5 molecular sieve as its core and a hydrogen peroxide-etched cobalt-cerium composite oxide (e-CoCeO₂) as its outer shell. x The outer shell consists of a Co-O-Ce interface structure that provides NH3 oxidation activity, while the core contains Cu. δ+ The site synergistically removes NO and NO2 byproducts via a rapid SCR pathway, constructing an SCO-rapid SCR tandem reaction system. The preparation method includes: dissolving cobalt and cerium salts in citric acid solution, adding HZSM-5 powder, evaporating to dryness in a water bath, and calcining to obtain a core-shell precursor. After etching with hydrogen peroxide and saturated copper ion exchange treatment, the target catalyst is obtained. This catalyst is completely free of precious metals, achieves over 90% NH3 conversion within the range of 225–400℃, and maintains over 94% N2 selectivity, making it suitable for the purification of ammonia-containing waste gases such as ammonia fuel tail gas.

[0065] The advantages of the non-precious metal core-shell tandem NH3-SCO catalyst of the present invention are: 1. Wide active temperature window, exhibiting excellent low-temperature NH3 oxidation activity and N2 selectivity; 2. Simple preparation process, low catalyst cost, and certain water resistance and good cycle operation stability.

[0066] Furthermore, it should be understood that after reading the above description of the present invention, those skilled in the art can make various alterations or modifications to the present invention, and these equivalent forms also fall within the scope defined by the appended claims.

Claims

1. A core-shell structured tandem ammonia selective catalytic oxidation catalyst, characterized in that, The core is Cu-ZSM-5, and the shell is a cobalt-cerium composite oxide rich in oxygen vacancies etched by hydrogen peroxide. An SCO-fast SCR tandem reaction system is formed between the core and the shell. The molar ratio of cobalt to cerium in the shell is (0.5~1.5):1, preferably 1:

1. The mass ratio of the core to the shell is (0.25~3):1, preferably (0.5~0.6):

1.

2. The core-shell structured tandem ammonia selective catalytic oxidation catalyst according to claim 1, characterized in that, In the core Cu-ZSM-5, Cu species are anchored in ionic form to the Brønsted acid sites of the ZSM-5 framework. The Cu species are obtained by saturated copper ion exchange, with a loading mass of 0.5%-4%.

3. The method for preparing the core-shell structured tandem ammonia selective catalytic oxidation catalyst according to claim 1 or 2, characterized in that, Including the following steps: (1) Dissolve cobalt salt and cerium salt in citric acid solution. After dissolving evenly, add HZSM-5 molecular sieve, stir evenly, and then evaporate, dry and calcine to obtain core-shell precursor; (2) The core-shell precursor was subjected to hydrogen peroxide etching, and then dried and calcined to obtain the etched precursor; (3) The etching precursor was subjected to saturated copper ion exchange treatment, and after drying and calcination, a core-shell structured tandem ammonia selective oxidation catalyst was obtained.

4. The preparation method according to claim 3, characterized in that, In step (1): The cobalt salt includes at least one of cobalt nitrate and cobalt acetate; The cerium salt includes at least one of cerium nitrate and cerium ammonium nitrate; The ratio of the molar amount of citric acid to the total molar amount of cobalt in the cobalt salt and cerium in the cerium salt is (1.1:1) to (1.5:1); HZSM-5 molecular sieve was added in powder form; The silica-alumina ratio of HZSM-5 molecular sieve is 20~30; The evaporation is performed using a water bath. The temperature for evaporation is 70~90℃; The drying temperature is 100~130℃, and the time is 10~24 h; The calcination temperature is 450~600℃, the time is 3~6 h, and the heating rate is 2~10℃ / min.

5. The preparation method according to claim 3, characterized in that, In step (2): The concentration of H2O2 in the hydrogen peroxide used is 0.1~0.2 mol / L; The ratio of hydrogen peroxide volume to core-shell precursor mass used is (10~15) mL:1 g; The etching process is performed at room temperature for 24-36 hours. The drying temperature is 100~130℃, and the time is 10~24 h; The calcination temperature is 450~600℃, the time is 3~6 h, and the heating rate is 2~10℃ / min.

6. The preparation method according to claim 3, characterized in that, In step (3): The saturated copper ion exchange treatment uses a copper acetate solution. The concentration of copper acetate solution is 0.01~0.5 mol / L; The temperature for the saturated copper ion exchange treatment is 60~90℃; The saturated copper ion exchange treatment is performed 2 to 4 times, with each exchange lasting 1 to 4 hours. The calcination temperature is 400~600℃, and the time is 3~6 h.

7. The application of the core-shell structured tandem ammonia selective catalytic oxidation catalyst according to claim 1 or 2 in the treatment of ammonia-containing tail gas using NH3-SCO.

8. The application according to claim 7, characterized in that, The ammonia-containing tail gas has an NH3 volume concentration of 1000~10,000 ppm, an O2 volume fraction of 1%~10%, and a water vapor volume fraction of 0~5%. The NH3-SCO treatment temperature is 150~500℃; The catalyst volume hourly space velocity (VHSV) during the NH3-SCO treatment process is 40,000–100,000 h⁻¹. -1 .

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