Cobalt-based supported hollow coralline structure metal oxide catalyst and preparation method and application thereof

Abstract

The invention discloses a cobalt-based supported hollow coralline structure metal oxide catalyst as well as a preparation method and application thereof. Belongs to the technical field of catalyst synthesis and application. The cobalt-based supported hollow coralline structure metal oxide catalyst is a catalyst Co / MCM-41 (IMD) obtained by loading an active component Co3O4 onto an MCM-41 carrier with a hollow coralline structure through at least two times of impregnation. The conversion rate of the S (3) 30% Co / MCM-41 (IMD) prepared by the method for catalytically decomposing N2O at 450 DEG C is almost consistent with the activity of a pure Co3O4 catalyst. At 500 DEG C, after 100 ppmv of NO, 5 vol.% of O2 and 2 vol.% of H2O are introduced, the catalytic activity is stabilized at about 38% within 12 h. The preparation method is low in preparation cost, simple in process, high in stability and good in catalyst activity.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of catalyst synthesis and application, and particularly relates to a cobalt-based supported hollow coral-shaped structure metal oxide catalyst for catalytic decomposition of N2O and a preparation method and application thereof. BACKGROUND

[0002] N2O is not only the third largest greenhouse gas after carbon dioxide and methane, but also an ozone layer depleter in the stratosphere. Its global warming potential (GWP) is 310 times that of carbon dioxide (CO2) and 21 times that of methane (CH4). N2O emitted during the industrial production of nitric acid and adipic acid is one of the main reasons for the increase in the concentration of N2O pollution in the atmosphere.

[0003] At present, the direct catalytic decomposition method has become the most promising method for N2O elimination due to its simple operation, high efficiency and no secondary pollution. However, most existing catalysts cannot solve the problems faced by actual industrial applications due to high cost or low catalyst utilization. Therefore, it is urgent to develop a low-cost N2O purification catalyst that is efficient at low temperatures and has good resistance to impurity gases.

[0004] Among the reported literature on catalytic decomposition of N2O, the catalysts used are divided into three types: noble metal type, molecular sieve type and transition metal oxide type. The noble metal catalyst was studied earlier and has high catalytic activity and good catalytic stability (Chemical Physics 264 (2001) 413-418). Subsequently, by virtue of the high specific surface area of molecular sieve materials, higher reaction activity was achieved by embedding or modifying active centers inside them. There is a reversible exchange reaction between the cations in the molecular sieve and the transition metal cations, which can adjust the type and distribution of cations and further improve the catalytic activity and selectivity of the catalyst. The most widely used catalyst is the ZSM-5 molecular sieve series catalyst. Transition metal oxide catalysts have broad research prospects due to their low cost, excellent catalytic performance and good adjustability.

[0005] Co-based metal catalysts exhibit good catalytic activity and thermal stability, low raw material cost and excellent Co 3+ / Co 2+Co-based catalysts are widely considered as one of the most promising catalyst systems in the field of direct catalytic decomposition of N2O due to their redox properties. According to the composition and structural characteristics, Co-based oxide catalysts are divided into three typical categories: spinel type, perovskite type and hydrotalcite-like type. Co3O4 and its derivative materials with spinel structure have become a research hotspot due to their low-temperature activity and structural stability. Compared with other metal oxide catalysts, Co-based catalysts have more flexible electronic structure adjustability, oxygen vacancy dynamic regulation and greater potential for doping modification. Kang et al. (Energy Fuels 2023, 37, 18019-18029) obtained Co-loaded catalysts by loading Co on microporous zeolite molecular sieves with different pore sizes. Taking the Co / Beta catalyst with the best activity as an example, its N2O conversion rate at 450℃ reached 99.6%. The results of activity test showed that the molecular sieve matrix with large pore size and three-dimensional structure was beneficial to the diffusion of Co and N2O during the preparation and catalytic process, so better catalytic activity and selectivity could be obtained.

[0006] Therefore, it is of great significance and very broad application prospect to develop a Co-based metal oxide supported catalyst with low cost, high specific surface area and fully utilized active sites of the catalyst. SUMMARY

[0007] In order to solve the above-mentioned technical problems, the purpose of the present application is to provide a cobalt-based supported hollow coral-like structure metal oxide catalyst with improved utilization of active sites of Co-based catalyst, reduced catalyst production cost, low cost, simple preparation, good stability and high activity, as well as a preparation method and application thereof.

[0008] To achieve the above-mentioned purpose of the application, the technical scheme adopted by the present application is: a cobalt-based supported hollow coral-like structure metal oxide catalyst is obtained by loading active component Co3O4 onto MCM-41 carrier with hollow coral-like structure through at least twice impregnation to obtain catalyst Co / MCM-41 (IMD); the catalyst Co / MCM-41 (IMD) is calculated by Co atoms, and the mass percentage of Co atoms in the MCM-41 carrier is 20%-35%.

[0009] Further, the cobalt-based supported hollow coral-like structure metal oxide catalyst is obtained by loading active component Co3O4 onto MCM-41 carrier with hollow coral-like structure through twice impregnation to obtain catalyst Co / MCM-41 (IMD).

[0010] The application discloses a preparation method of a cobalt-based supported hollow corallike structure metal oxide catalyst.

[0011] Further, the cobalt salt precursor is one or more of cobalt nitrate, cobalt acetate and cobalt oxalate.

[0012] Further, in the cobalt impregnation solution, the mass percentage of Co atoms in the MCM-41 carrier is 1%-10% in terms of Co atoms in the first impregnation.

[0013] Further, the standing time is 24h-48h.

[0014] Further, the drying temperature is 60℃-110℃.

[0015] Further, the heating rate is 3℃·min -1 -5℃·min -1 , the calcination temperature is 500℃-600℃, and the calcination time is 2h-4h.

[0016] The application provides an application of the cobalt-based supported hollow corallike structure metal oxide catalyst in direct catalytic decomposition of N2O.

[0017] The application has the following beneficial effects:

[0018] 1. The catalyst Co / MCM-41 (IMD) is prepared by loading active component Co3O4 on the MCM-41 carrier with a hollow corallike structure through at least twice impregnation. 2 ·g -1 -644m 2 ·g -1 The MCM-41 carrier with the hollow corallike structure has a specific surface area of 881m 2 ·g -1 -644m 2 ·g -1 and a mesopore diameter of 2.6nm-2.7nm, the active species Co is loaded on the corallike special morphology, which helps to improve the utilization rate of Co atoms and reduce the production cost of the catalyst.

[0019] 2、The preparation method provided by the application is a secondary impregnation method, and a catalyst Co / MCM-41 (IMD) is obtained by using 20%-35% of Co in mass fraction of MCM-41 carrier for secondary impregnation, and the activity of the catalyst is very close to that of original Co3O4 prepared by a deposition precipitation method. The specific surface area of the prepared catalyst Co / MCM-41 (IMD) is reduced compared with that of the hollow coralline structure MCM-41, but reaches 620.502 m 2 ·g -1 The active component Co3O4 spinel crystal is uniformly dispersed on the hollow coralline structure MCM-41 carrier, and tends to expose a high-index crystal plane with higher catalytic activity.

[0020] 3、The catalyst Co / MCM-41 (IMD) prepared by the application has good resistance to impurity gases, and shows a stable catalytic conversion rate (about 38%, GHSV=20000 h -1 ) without attenuation for more than 12 hours in a simulated nitric acid plant exhaust gas atmosphere at 500 DEG C, and the activity of the catalyst Co / MCM-41 (IMD) can still return to 100% after cutting off all impurity gases. BRIEF DESCRIPTION OF DRAWINGS

[0021] Figure 1 is a catalyst activity diagram of N2O catalytic decomposition of the catalysts obtained in Example 1 and Comparative Examples 1-5.

[0022] Figure 2 is a catalyst activity diagram of N2O catalytic decomposition of the catalysts obtained in Example 1-4 and Comparative Example 3.

[0023] Figure 3 is a catalyst activity diagram of N2O catalytic decomposition of the catalysts obtained in Example 1-4 and Comparative Example 3.

[0024] Figure 4 is a catalyst activity diagram of N2O catalytic decomposition of the catalysts obtained in Example 1-4 and Comparative Example 3.

[0025] Figure 5 is a catalyst activity diagram of N2O catalytic decomposition of the catalysts obtained in Example 1-4 and Comparative Example 3.

[0026] Figure 6 is a catalyst activity diagram of N2O catalytic decomposition of the catalysts obtained in Example 1-4 and Comparative Example 3. DETAILED DESCRIPTION

[0027] In order for those skilled in the art to have a more comprehensive understanding of the application, the application is described in more detail through the following non-limiting examples and comparative examples, but the examples and comparative examples do not limit the application in any way.

[0028] Example 1 Secondary impregnation method for preparing S(1) 20% Co / MCM-41 (IMD) catalyst

[0029] The preparation method is as follows:

[0030] 1. Preparation of MCM-41 carrier with hollow coral structure:

[0031] At 40°C, 39 g of ethanol was added to 120 mL of deionized water and stirred until the solid was completely dissolved. The solution was adjusted to pH = 11.5 with 25% NH3·H2O by mass, and kept constant. 3.4 g of TEOS (tetraethyl orthosilicate) was added to the CTAB aqueous solution, and stirring was continued for 2 h in a 40°C water bath. The white gel was transferred to a polytetrafluoroethylene stainless steel reactor, and the reaction was continued at 100°C for 48 h. Finally, the obtained solid product was washed with ethanol and deionized water. The obtained solid was dried at 60°C overnight, and finally calcined at 550°C for 6 h to obtain the MCM-41 carrier with hollow coral structure.

[0032] 2. Primary impregnation:

[0033] 0.2464 g of Co(NO3)2·6H2O was weighed into a 20 mL ceramic crucible, dissolved in 2.3 mL of deionized water, and stirred until homogeneous to obtain a primary cobalt impregnation solution. In the primary cobalt impregnation solution, the mass percentage of Co atoms in the MCM-41 carrier was 10% based on Co atoms.

[0034] 0.5 g of MCM-41 carrier was added to the primary cobalt impregnation solution, and a glass rod was used to mix the primary cobalt impregnation solution and the MCM-41 carrier thoroughly. The ceramic crucible was sealed and allowed to stand for 24 h for the first impregnation. The obtained product was dried by a constant temperature heating magnetic stirrer, and then dried at 110°C for 3 h. The dried product was placed in a muffle furnace, and heated to 500°C at a heating rate of 5°C·min -1 , and calcined for 3 h to obtain a primary impregnated catalyst, named 10%Co / MCM-41(IM) (wherein 10% represents that the mass percentage of Co atoms in the MCM-41 carrier is 10%, and IM represents primary impregnation, the same below).

[0035] 3. Secondary impregnation:

[0036] 0.2464 g of Co(NO3)2·6H2O was weighed into a 20 mL ceramic crucible, dissolved in 2.3 mL of deionized water, and stirred until homogeneous to obtain a secondary cobalt impregnation solution. In the secondary cobalt impregnation solution, the mass percentage of Co atoms in the MCM-41 carrier was 10% based on Co atoms.

[0037] Add catalyst 10%Co / MCM-41(IM) to the secondary cobalt impregnation solution, and mix the secondary cobalt impregnation solution and catalyst 10%Co / MCM-41(IM) thoroughly with a glass rod. Seal the ceramic crucible and let it stand for 24 hours for the second impregnation. Evaporate the moisture in the resulting product using a magnetic stirrer under constant temperature heating, and then dry it at 110℃ for 3 hours. Place the dried product in a pit furnace and heat it at 5℃·min. -1 The temperature was increased to 500℃ and calcined for 3 hours to obtain a secondary impregnated catalyst, named S(1)20%Co / MCM-41(IMD) (where 20% means that the mass percentage of Co atoms in the MCM-41 support is 20%, and IMD represents secondary impregnation, the same below).

[0038] Example 2 Preparation of S(2) 25%Co / MCM-41(IMD) catalyst by two-stage impregnation method

[0039] The preparation method is as follows:

[0040] 1. Preparation of MCM-41 carrier with hollow coral-like structure: Same as in Example 1.

[0041] 2. Single impregnation: Same as in Example 1.

[0042] 3. Secondary impregnation:

[0043] Weigh 0.3696 g of Co(NO3)2·6H2O into a 20 mL ceramic crucible, add 2.3 mL of deionized water to dissolve it, and stir until homogeneous to obtain a secondary cobalt impregnation solution. In the secondary cobalt impregnation solution, the mass percentage of Co atoms in the MCM-41 carrier is 15%.

[0044] Add catalyst 10%Co / MCM-41(IM) to the secondary cobalt impregnation solution, and mix the secondary cobalt impregnation solution and catalyst 10%Co / MCM-41(IM) thoroughly with a glass rod. Seal the ceramic crucible and let it stand for 24 hours for the second impregnation. Evaporate the moisture in the resulting product using a magnetic stirrer under constant temperature heating, and then dry it at 110℃ for 3 hours. Place the dried product in a pit furnace and heat it at 5℃·min. -1 The temperature was increased to 500℃ and calcined for 3 hours to obtain a secondary impregnated catalyst, named S(2)25%Co / MCM-41(IMD).

[0045] Example 3 Preparation of S(3) 30%Co / MCM-41(IMD) catalyst by two-stage impregnation method

[0046] The preparation method is as follows:

[0047] 1. Preparation of MCM-41 carrier with hollow coral-like structure: Same as in Example 1.

[0048] 2. First impregnation: same as Example 1.

[0049] 3. Second impregnation:

[0050] Take 0.4928 g of Co(N03)2-6H20 in a 20 mL ceramic crucible, add 2.3 mL of deionized water to dissolve, stir evenly, and obtain a second cobalt impregnation solution. In the second cobalt impregnation solution, the mass percentage of Co atoms in the MCM-41 carrier is 20% in terms of Co atoms.

[0051] Add the catalyst 10%Co / MCM-41(IM) to the second cobalt impregnation solution, and mix the second cobalt impregnation solution and the catalyst 10%Co / MCM-41(IM) evenly with a glass rod. Seal the ceramic crucible and let it stand for 24 h for the second impregnation. Dry the obtained product with a constant temperature heating magnetic stirrer, and then dry it at 110°C for 3 h. Put the dried product into a muffle furnace, heat it to 500°C at a heating rate of 5°C / min -1 , and calcine it for 3 h to obtain the second impregnated catalyst, named S(3)30%Co / MCM-41(IMD).

[0052] Example 4 Preparation of S(4) 35%Co / MCM-41(IMD) catalyst by second impregnation method

[0053] The preparation method is as follows:

[0054] 1. Preparation of MCM-41 carrier with hollow coral structure: same as Example 1.

[0055] 2. First impregnation: same as Example 1.

[0056] 3. Second impregnation:

[0057] Take 0.4928 g of Co(N03)2-6H20 in a 20 mL ceramic crucible, add 2.3 mL of deionized water to dissolve, stir evenly, and obtain a second cobalt impregnation solution. In the second cobalt impregnation solution, the mass percentage of Co atoms in the MCM-41 carrier is 20% in terms of Co atoms.

[0058] Add the catalyst 10%Co / MCM-41(IM) to the second cobalt impregnation solution, and mix the second cobalt impregnation solution and the catalyst 10%Co / MCM-41(IM) evenly with a glass rod. Seal the ceramic crucible and let it stand for 24 h for the second impregnation. Dry the obtained product with a constant temperature heating magnetic stirrer, and then dry it at 110°C for 3 h. Put the dried product into a muffle furnace, heat it to 500°C at a heating rate of 5°C / min -1The temperature was increased to 500℃ and calcined for 3 hours to obtain a secondary impregnated catalyst, named S(4)35%Co / MCM-41(IMD).

[0059] Comparative Example 1: Preparation of B(1) 20%Co / MCM-41(IM) catalyst by equal volume impregnation method

[0060] The preparation method is as follows:

[0061] 1. Preparation of MCM-41 carrier with hollow coral-like structure: Same as in Example 1.

[0062] 2. Equal volume impregnation:

[0063] 0.4928 g of Co(NO3)2·6H2O was weighed into a 20 mL ceramic crucible, dissolved in 2.3 mL of deionized water, and stirred until homogeneous to obtain a cobalt impregnation solution. In the cobalt impregnation solution, the mass percentage of Co atoms in the MCM-41 carrier was 20%.

[0064] Add 0.5 g of MCM-41 support to the cobalt impregnation solution and mix thoroughly with a glass rod. Seal the ceramic crucible and allow it to stand for 24 hours for impregnation. Evaporate the moisture from the resulting product using a magnetic stirrer under constant temperature heating, then dry it at 110°C for 3 hours. Place the dried product in a pit furnace and heat at 5°C / min. -1 The temperature was increased to 500℃ and calcined for 3 hours to obtain the catalyst, which was named B(1) 20%Co / MCM-41(IM).

[0065] Comparative Example 2: Preparation of B(2) 20%Co / MCM-41(IM-EGv) catalyst by ethylene glycol isovolumetric impregnation method

[0066] The preparation method is as follows:

[0067] 1. Preparation of MCM-41 carrier with hollow coral-like structure: Same as in Example 1.

[0068] 2. Equal volume impregnation with ethylene glycol:

[0069] Weigh 0.4928 g of Co(NO3)2·6H2O into a 20 mL ceramic crucible, add 2.3 mL of a mixed solvent of ethylene glycol and water (volume ratio 1:1) to dissolve it, and stir until homogeneous to obtain a cobalt impregnation solution. In the cobalt impregnation solution, the mass percentage of Co atoms in the MCM-41 carrier is 20%.

[0070] Add 0.5 g of MCM-41 support to the cobalt impregnation solution and mix thoroughly with a glass rod. Seal the ceramic crucible and allow it to stand for 24 hours for impregnation. Evaporate the moisture from the resulting product using a magnetic stirrer under constant temperature heating, then dry it at 110°C for 3 hours. Place the dried product in a pit furnace and heat at 5°C / min. -1 The temperature was increased to 500℃ and calcined for 3 hours to obtain the catalyst, which was named B(2) 20%Co / MCM-41(IM-EGv).

[0071] Comparative Example 3: Preparation of B(3)Co3O4(P) original catalyst by deposition-precipitation method

[0072] The preparation method is as follows:

[0073] 1. Weigh out a fixed amount of Co(NO3)2·6H2O and dissolve it in deionized water to prepare a solution with a concentration of 0.2 mol·L⁻¹. -1 The precursor solution.

[0074] 2. The concentration is 0.5 mol·L⁻¹ -1 Na₂CO₃ was added dropwise to the precursor solution, and the mixture was stirred at 40°C until homogeneous and a purple precipitate was completely formed and the pH of the supernatant was 9-10. The mixture was then aged at the same temperature for 2 hours, followed by washing with deionized water until the filtrate pH was neutral. The collected filter cake was then transferred to an oven and dried at 110°C for 3 hours. The dried product was then placed in a pit furnace and heated at 5°C / min. -1 The temperature was increased to 500℃ and calcined for 3 hours to obtain the original catalyst, which was named B(3)Co3O4(P).

[0075] Comparative Example 4: Preparation of B(4) 20%Co / MCM-41(SG) catalyst by solid-state grinding method

[0076] The preparation method is as follows:

[0077] 1. Preparation of MCM-41 carrier with hollow coral-like structure: Same as in Example 1.

[0078] 2. Preparation of original catalyst B(3) Co3O4(P): same as comparative example 3.

[0079] 3. Take 0.1360g of the original catalyst B(3)Co3O4(P) and 0.5g of MCM-41 support and place them in a large crucible. Add a small amount of deionized water to just wet the solid. After thorough grinding, transfer it to an oven and dry at 110℃ for 3h. Place the dried product in a pit furnace and heat at 5℃·min -1The temperature was increased to 500℃ and calcined for 3 hours to obtain catalyst B(4) 20%Co / MCM-41(SG).

[0080] Comparative Example 5: Preparation of B(5) 20%Co / MCM-41(P) catalyst by deposition-precipitation method

[0081] The preparation method is as follows:

[0082] 1. Weigh a certain amount of Na₂CO₃ and dissolve it in deionized water to prepare a solution with a concentration of 0.5 mol·L⁻¹. -1 Solution A.

[0083] 2. Weigh a certain amount of Co(NO3)2·6H2O and dissolve it in deionized water to prepare a solution with a concentration of 0.2 mol·L⁻¹. -1 Solution B.

[0084] 3. Weigh 0.5 g of MCM-41 carrier and 50 mL of solution A into a 250 mL beaker and stir thoroughly in a 40 °C water bath. Add 8.5 mL of solution B dropwise to the mixture of MCM-41 and solution A using a separatory funnel. After the addition of solution B is complete, age the mixture for 2 hours at the same temperature, then wash with deionized water until the pH of the filtrate is neutral. Transfer the collected filter cake to an oven and dry at 110 °C for 3 hours. Place the resulting product in a pit furnace and heat at 5 °C / min. -1 The temperature was increased to 500℃ at a heating rate and calcined for 3 hours to obtain catalyst B(5) 20%Co / MCM-41(P).

[0085] Example 5: Catalyst Performance Testing

[0086] 1. Performance testing of 20% Co / MCM-41 catalyst samples obtained by different preparation methods

[0087] General activity tests were performed on the catalyst samples obtained in Example 1 and Comparative Examples 1-5 using an atmospheric pressure integral fixed bed reactor: 100 mg of 40-60 mesh catalyst was added to a quartz tube reactor (inner diameter 4 mm). Feed gas N2O / Ar (GHSV = 20000 h⁻¹) was introduced. -1 The feed gas contains 2000 ppmv of N₂O, and Ar is used as the carrier gas. The flow rate of the feed gas is 50 mL / min. -1 The residual concentration of N2O was determined online using a Varian CP-3800 gas chromatograph (equipped with a phase-fixed Porapak Q and a thermal conductivity detector, with high-purity Ar as the carrier gas). The results are as follows: Figure 1 .

[0088] like Figure 1As shown, the effects of different preparation methods on the activity of the 20%Co / MCM-41 catalyst were tested. At a test temperature of 500℃, S(1) 20%Co / MCM-41(IMD) exhibited catalytic performance almost identical to that of B(3)Co3O4(P) at several temperature points, with activities of 89%, 58.5%, 35%, 12.5%, and 4.5% at 500℃-300℃, respectively. The above experimental results indicate that secondary impregnation of Co into the hollow coral-like MCM-41 support can significantly reduce the amount of Co used while obtaining catalytic activity almost identical to that of the original catalyst B(3)Co3O4(P), and compared with other preparation methods, the catalyst S(1) 20%Co / MCM-41(IMD) prepared by the secondary impregnation method of this invention exhibits the best catalytic efficiency.

[0089] 2. Performance testing of catalyst samples with different cobalt percentages.

[0090] General activity tests were performed on the catalyst samples obtained in Examples 1-4 using an atmospheric pressure integral fixed bed reactor: 100 mg of 40-60 mesh catalyst was added to a quartz tube reactor (inner diameter 4 mm). Feed gas N2O / Ar (GHSV = 20000 h⁻¹) was introduced. -1 The feed gas contains 2000 ppmv of N₂O, and Ar is used as the carrier gas. The flow rate of the feed gas is 50 mL / min. -1 The residual concentration of N2O was determined online using a Varian CP-3800 gas chromatograph (equipped with a phase-fixed Porapak Q and a thermal conductivity detector, with high-purity Ar as the carrier gas). The results are as follows: Figure 2 .

[0091] like Figure 2 As shown, the x%Co / MCM-41(IMD) series catalysts (x=20, 25, 30, 35) were compared under conditions of 2000 ppmv N2O / Ar (GHSV=20000 h⁻¹). -1 The catalytic activity of the feed gas was measured. As the Co loading in the x%Co / MCM-41(IMD) series catalysts increased from 20% to 35%, the catalytic activity of the catalysts showed a "volcano-like" trend of first increasing and then decreasing. Among them, the S(3) 30%Co / MCM-41(IMD) catalyst had the best performance, and its catalytic efficiency reached 90% at the temperature (T). 90The reaction temperature was 475℃. Under the same reaction conditions, the catalytic activities of S(3) 30%Co / MCM-41(IMD) and S(4) 35%Co / MCM-41(IMD) catalysts were slightly higher than those of pure B(3) Co3O4(P) catalyst. Since the catalytic activities of S(3) 30%Co / MCM-41(IMD) and S(4) 35%Co / MCM-41(IMD) catalysts were almost the same, S(3) 30%Co / MCM-41(IMD) was the best active catalyst based on the consideration of catalyst preparation cost.

[0092] Example 6: Test of the tolerance and stability of catalyst Co / MCM-41 (IMD) to impurity gases

[0093] The exhaust gases emitted from actual industrial plants often contain a variety of impurity gases, such as NO, O2, and H2O. These impurities can interfere with the decomposition process of N2O by the catalyst, thereby reducing the catalyst's activity and stability. Therefore, clarifying the degree of influence of different impurity gases on the catalytic decomposition efficiency of N2O is of great significance for evaluating catalyst performance.

[0094] Method: 100 mg of 40-60 mesh catalyst S(3) 30%Co / MCM-41(IMD) was added to a quartz tube reactor (4 mm inner diameter). The mixed reaction gas contained 2000 ppmv N2O, with Ar as the carrier gas. To investigate the effect of impurity gases on catalyst activity, impurity gases (5 vol.% O2, 2 vol.% H2O, or 100 ppmv NO) were introduced. One or more of these impurity gases were introduced depending on the specific circumstances, see [link to relevant documentation]. Figure 3 and Figure 4 The total flow rate of the mixed gas is 50 mL / min. -1 The residual concentration of N2O was determined online using a Varian CP-3800 gas chromatograph (equipped with a phase-fixed Porapak Q and a thermal conductivity detector, with high-purity Ar as the carrier gas). The results are as follows: Figure 3 and Figure 4 .

[0095] like Figure 3 As shown, the N2O conversion rate of S(3) 30%Co / MCM-41(IMD) catalyst under different temperature conditions is compared with the feed gas conditions of 5 vol.% O2, 2 vol.% H2O, 100 ppmv NO and 5 vol.% O2 + 2 vol.% H2O + 100 ppmv NO and 2000 ppmv N2O / Ar. Clearly, different impurity gases have different degrees of inhibitory effect on the catalyst. The Tf of the S(3) 30%Co / MCM-41(IMD) catalyst reacting in a feed gas of 2000 ppmv N2O / Ar is also shown.90 The temperature is 475℃, but when 100 ppmv NO, 5 vol% O2, 2 vol.% H2O and 5 vol.% O2 + 2 vol.% H2O + 100 ppmv NO are introduced into the feed gas respectively, T 90 The temperatures were increased to 491℃, 491℃, 488℃, and 492℃ respectively. This indicates that the presence of NO, O2, or H2O in the feed gas significantly inhibits the activity of the N2O decomposition catalyst. This phenomenon is likely caused by impurity gases competing with N2O for adsorption at the catalyst's active sites in the reaction atmosphere, thus hindering the catalytic decomposition reaction of N2O.

[0096] Figure 4 The figure shows the stability test results of the S(3) 30%Co / MCM-41(IMD) catalyst under the condition of impurity gas presence at 500℃. As can be seen from the figure, when 5 vol.% O2, 100 ppmv NO, and 2 vol.% H2O are sequentially introduced into the feed gas of 2000 ppmv N2O, the N2O conversion rate exhibits a stepwise decrease. Even after all impurity gases have been introduced, the catalyst activity remains stable at around 38% within 12 hours, indicating that the S(3) 30%Co / MCM-41(IMD) catalyst can achieve good catalytic stability with only a small amount of active component. After the 12-hour stability test, the catalyst activity recovers to 100% when the impurity gases are sequentially cut off, which sufficiently demonstrates that the inhibitory effect of impurity gases on the catalyst is reversible.

[0097] Example 7 XRD analysis of catalysts with different cobalt percentages

[0098] To further investigate the microstructure and crystal phase composition of the x%Co / MCM-41(IMD) series catalysts, the crystal structures of x%Co / MCM-41(IMD), MCM-41, and B(3)Co3O4(P) were determined by XRD. The results are as follows: Figure 5As shown in the figure, for the x%Co / MCM-41(IMD) series catalysts, diffraction peaks of amorphous silicon can be clearly observed between 20° and 30°. Diffraction peaks belonging to the cobalt spinel structure (JCPDS No. 43-1003) are only observed in the catalysts with 30% and 35% Co loading ratios. This is because the low Co loading ratio on MCM-41 results in highly uniform dispersion of Co3O4 spinel crystals on the surface of the MCM-41, which has a large specific surface area. The grain size of the active component Co3O4 in the catalyst was calculated using the Scherrer equation and the full width at half maximum (FWHM) of the maximum intensity peak in XRD, and the results are shown in Table 1. Compared to the crystallite size of B(3)Co3O4(P) (28 nm), the crystallite sizes of S(3) 30%Co / MCM-41(IMD) catalyst (crystal size = 9.7 nm) and 35%S(4)Co / MCM-41(IMD) catalyst (crystal size = 10.1 nm) were significantly reduced. This is attributed to the large specific surface area of ​​the MCM-41 support, which allows the active components to be more dispersed on the surface of the MCM-41 support. During calcination, the aggregation process of Co3O4 crystals is hindered to some extent, resulting in a smaller final crystallite size for the catalyst.

[0099] Table 1

[0100]

[0101] Example 8 TEM image analysis of the catalyst

[0102] The morphology and particle size distribution of MCM-41 and S(3) 30%Co / MCM-41(IMD) catalysts were studied by TEM characterization. Figure 6 As shown in Figures A and B, TEM analysis clearly shows that the synthesized hollow coral-like MCM-41 support has relatively regular edges and a hollow coral-like macroporous structure inside the molecular sieve. Tightly packed, ordered mesoporous structures (pore size ~2.8 nm) were also found inside MCM-41. Figure 6 As shown in Figure C, Co3O4 is uniformly dispersed on the S(3) 30%Co / MCM-41(IMD) catalyst. Co3O4 spinel particles are not only successfully supported on the catalyst surface, but also exist in small quantities within the hollow channels of MCM-41. The Co3O4 spinel particles on the catalyst surface have an uneven particle size distribution, with a grain size distribution of approximately 10.5 nm. HR-TEM images of the S(3) 30%Co / MCM-41(IMD) catalyst are shown below. Figure 6In the middle (D), not only were the (422) and (400) crystal planes belonging to Co3O4 observed, but also the (331) and (511) crystal planes. This may be an important reason why the catalyst maintains high efficiency in catalytic decomposition of N2O.

[0103] In summary, in the S(3) 30%Co / MCM-41(IMD) catalyst prepared by the secondary impregnation method, the spinel phase Co3O4 is uniformly dispersed on the catalyst surface, and the exposed different lattices work together to catalyze the decomposition of N2O.

Claims

1. A cobalt-based supported hollow coral-like structure metal oxide catalyst, characterized in that, The cobalt-based supported hollow coral-like metal oxide catalyst is obtained by loading the active component Co3O4 onto an MCM-41 support with a hollow coral-like structure through at least two impregnation methods, resulting in catalyst Co / MCM-41(IMD); the catalyst Co / MCM-41(IMD) has a Co atom content of 20%-35% by mass of the MCM-41 support.

2. The cobalt-based supported hollow coral-like structure metal oxide catalyst according to claim 1, characterized in that, The cobalt-based supported hollow coral-like metal oxide catalyst is obtained by loading the active component Co3O4 onto the MCM-41 support with a hollow coral-like structure through a two-stage impregnation method, resulting in the catalyst Co / MCM-41(IMD).

3. The method for preparing a cobalt-based supported hollow coral-like structure metal oxide catalyst according to claim 1 or 2, characterized in that, The preparation method includes the following steps: dissolving the cobalt salt precursor in deionized water and stirring until homogeneous to obtain a cobalt impregnation solution; mixing the MCM-41 support with a hollow coral-like structure with the cobalt impregnation solution until homogeneous, sealing and allowing it to stand for impregnation, evaporating the solvent, drying, and calcining; repeating the impregnation and calcination process at least twice to obtain the catalyst Co / MCM-41(IMD).

4. The preparation method according to claim 3, characterized in that, The cobalt salt precursor is one or more of cobalt nitrate, cobalt acetate, and cobalt oxalate.

5. The preparation method according to claim 3, characterized in that, During the first impregnation, the Co atoms in the cobalt impregnation solution account for 1%-10% of the mass of the MCM-41 carrier.

6. The preparation method according to claim 3, characterized in that, The settling time is 24-48 hours.

7. The preparation method according to claim 3, characterized in that, The drying process takes place at a temperature of 60℃-110℃.

8. The preparation method according to claim 3, characterized in that, The calcination process involves a heating rate of 3°C·min. -1 -5℃·min -1 The calcination temperature is 500℃-600℃, and the calcination time is 2h-4h.

9. The application of the cobalt-based supported hollow coral-like structure metal oxide catalyst according to claim 1 or 2 in the direct catalytic decomposition of N2O.

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