Alkali metal-modified catalyst for decomposition of nitrous oxide and method of making and use

Abstract

The application belongs to the field of catalysts, and provides an alkali metal modified catalyst for decomposing nitrous oxide and a preparation method and application thereof. The catalysts Co / x%K / ZrO2 and Co / y%K / z%Cs / ZrO2 provided by the application both have high activity, good tolerance to impurity gases (NO x , H2O, O2), and excellent catalytic decomposition capacity of N2O under low temperature conditions, and the latter has better comprehensive performance. It is proved that the method of the application is an important strategy for designing an efficient and high-selectivity catalyst system, and solves the problem that there is no cobalt-based catalyst with high efficiency for decomposing N2O while having good tolerance to impurity gases.

Description

Technical Field

[0001] The invention belongs to the field of catalysts and relates to an alkali metal-modified catalyst for decomposing nitrous oxide, a preparation method and an application thereof. Background Art

[0002] The information disclosed in this background technology section is only intended to enhance understanding of the overall background of the invention and should not necessarily be regarded as an admission or any form of suggestion that the information constitutes the prior art already known to those skilled in the art.

[0003] As the world's third-largest greenhouse gas, N2O (nitrous oxide) not only significantly contributes to the global warming effect but also depletes the ozone layer, increasing human exposure to harmful radiation. Direct catalytic decomposition of N2O into N2 (nitrogen) and O2 (oxygen) is currently the most effective technology for reducing N2O emissions from industrial and mobile sources. Due to its simplicity, high efficiency, zero secondary pollution, and minimal equipment requirements, it has been widely adopted. The core of this technology lies in the research and development of highly efficient and stable catalysts.

[0004] Researchers have conducted extensive research on catalysts for catalytic N2O decomposition and have found that transition metal oxides (e.g., spinel-structured cobalt oxide) have excellent low-temperature catalytic performance and are simple to prepare, making them excellent catalytic materials that have been widely used in industry. However, pure Co3O4 (cobalt oxide) cannot meet the needs of industrial applications in terms of both cost and catalytic performance. Since the catalytic process mainly occurs on the surface of the catalyst, the cobalt atoms in the bulk phase cannot be well utilized, resulting in a low specific activity of the catalyst. In actual working conditions, impurity gases, such as NO, are inevitably generated. x (nitrogen oxides), H2O (water), O2 (oxygen), the catalyst's tolerance to impurity gases is not particularly ideal.

[0005] To this end, some studies have reported an unsupported alkali-metal-containing cobalt-cerium composite oxide catalyst for the direct decomposition of N₂O; others have reported a molecular sieve-supported cobalt-based composite oxide catalyst; and others have introduced lithium and potassium ions, either singly or in combination, into Co₃O₄ to prepare catalysts. The low-temperature catalytic activity of these catalysts still needs to be improved, and their tolerance to impurity gases has not been examined, making it impossible to verify their catalytic performance under actual operating conditions.

[0006] In summary, the industry has not yet found a cobalt-based catalyst that can efficiently decompose N2O while having good tolerance to impurity gases. Summary of the Invention

[0007] To solve the above technical problems, the application provides an alkali metal modified catalyst for decomposing nitrous oxide and a preparation method and application thereof. The application jointly regulates the performance of the catalyst by alkali metal modification and introduction of a ZrO2 (zirconium dioxide) carrier, and the obtained catalyst Co (cobalt) / x%K (potassium) / ZrO2 and Co / y%K / z%Cs / ZrO2 (percentage is mass percentage) has high activity, good tolerance to impurity gases (NO x , H2O, O2), and excellent catalytic decomposition N2O capacity under low temperature conditions.

[0008] To achieve the above purpose, the application adopts the following technical solutions:

[0009] In a first aspect of the application, an alkali metal modified catalyst for decomposing nitrous oxide is provided, taking ZrO2 as a carrier, and the active component is composed of Co3O4 and alkali metal, and the alkali metal is selected from at least one of K and Cs;

[0010] In the application, the loading amount of Co3O4 is 10%-15%, and the loading amount of the alkali metal is 0.2%-2%, and the percentage is mass percentage.

[0011] The introduction of the doped cations will affect the activity of Co3O4, complex interactions between the density of states (DOS) of the catalyst surface and the molecular orbital structure of the reactants will occur, and the catalytic activity will change. Therefore, the application systematically studies the influence of different cation doping on the catalytic activity of the Co3O4 / ZrO2 system, and preferably, the alkali metal is K and Cs, wherein the loading amount of K is 0.2%-1%, and the loading amount of Cs is 0.2-1%, so as to obtain better catalytic performance.

[0012] Through the interaction between the carrier and the active component, the active surface may change, and the performance of the catalyst can be improved. Therefore, the application studies and selects the types of the carrier, and preferably, the ZrO2 is monoclinic ZrO2, which can effectively improve the utilization rate of active species, reduce the amount of transition metal used, and reduce the cost; secondly, the carrier helps the active component to resist sintering or agglomeration, prolongs the service life of the catalyst; thirdly, ZrO2 itself has high mechanical strength, which can enhance the overall structure of the catalyst and prevent it from breaking during the reaction.

[0013] The preparation process of the catalyst will affect its catalytic performance and tolerance to impurity gases, therefore, the application studies and selects the preparation process of the catalyst, and preferably, a solid-phase impregnation method is adopted, which does not need to use solvents and precipitants, simplifies the process flow, reduces the solvent treatment and recovery cost. At the same time, the active component will not be lost due to solution loss, ensuring that the theoretical loading amount is consistent with the actual loading amount, and reducing human error.

[0014] Therefore, the second aspect of the present application provides a preparation method of an alkali metal modified catalyst for decomposing nitrous oxide, comprising:

[0015] mixing the oxide of alkali metal with ZrO2, grinding, first calcining to obtain an alkali metal / ZrO2 composite;

[0016] mixing the alkali metal / ZrO2 composite with a cobalt salt, grinding, and second calcining to obtain the catalyst.

[0017] Research shows that the alkali metal can control the Fermi level and surface potential of the catalyst, and the present application finds that for Co / x%K / ZrO2 and Co / y%K / z%Cs / ZrO2, another important role of the alkali metal is to greatly improve the adsorption of N2O molecules, thereby capturing more N2O molecules to participate in the reaction. Preferably, the oxide of alkali metal is selected from at least one of potassium carbonate and cesium carbonate.

[0018] The type of cobalt salt will affect the activity of the catalyst and the tolerance to impurity gas, and for this reason, the present application has researched and screened the type of cobalt salt, and preferably, the cobalt salt is cobalt acetate tetrahydrate, so as to obtain a more optimal catalyst activity and tolerance to impurity gas.

[0019] The temperature and time of calcination will affect the activity of the catalyst and the tolerance to impurity gas, and for this reason, the present application has researched and screened the type of calcination condition, and preferably, the first calcination condition is calcination at 500-550℃ for 3-4h.

[0020] Preferably, the second calcination condition is calcination at 550-600℃ for 1.5-2h, so as to obtain a more optimal catalyst activity and tolerance to impurity gas.

[0021] Since the performance of the molecular sieve is greatly affected by the skeleton stability, the pore structure thereof is easily destroyed under the condition of water vapor, which leads to the change of active sites and specific surface area with the destruction of the structure, reduces the catalytic activity, and the water vapor inevitably limits the application of the catalyst in the actual application process. For this reason, the present application selects ZrO2 as the carrier, and preferably, the preparation method of ZrO2 comprises: uniformly mixing a zirconium salt and urea in a solvent, hydrothermally reacting, collecting the product, and washing, drying, grinding and calcining to obtain ZrO2. Compared with the molecular sieve, ZrO2 can better improve the low-temperature activity of the catalyst.

[0022] The third aspect of the present application provides the use of the above-mentioned catalyst in catalyzing the decomposition of N2O, and the catalytic decomposition is carried out at 250-500℃ and / or in the presence of impurity gas selected from O2, NOx at least one of H2O.

[0023] Advantages of the present application

[0024] (1) The transition metal oxide has excellent low-temperature catalytic performance and simple preparation method, and especially the spinel structure Co3O4 has weak Co-O bond energy and excellent redox performance, and exhibits good medium and low temperature activity. The present application solves the problems of high cost of noble metal, high production and use cost of catalyst by using Co3O4.

[0025] (2) The present application uses ZrO2 as a carrier to synthesize catalyst materials. ZrO2 has a large specific surface area, which provides suitable attachment sites for active components, and can make active species Co3O4 and electronic additives K + (potassium ions), Cs + (cesium ions) uniformly dispersed on the carrier; the excellent thermal stability of ZrO2 makes Co3O4 stable during high-temperature reaction, and can solve the problem of easy sintering of Co3O4 during use; high mechanical strength, selecting it as a carrier can enhance the durability of the catalyst and prolong the service life of the catalyst; and high melting point, corrosion resistance, which is an ideal material as a catalyst carrier.

[0026] (3) The addition of K, Cs and other alkali promoters in the present application on the one hand improves the adsorption of the catalyst to N2O molecules, which can capture more N2O molecules to participate in the reaction, thus greatly improving the probability of reaction; on the other hand, the alkali metal effectively regulates the electronic structure and electron density of the active species Co, promotes the N2O molecules to realize bond breaking under the action of Co, and promotes the catalytic reaction process. It is this "double functional effect" of alkali metal that strengthens the adsorption and bond breaking process of the reactant molecules, which has very excellent low-temperature activity, and this method is an important strategy for designing efficient and high-selectivity catalytic systems.

[0027] (4) The preferred Co / 0.8K / ZrO2 and Co / 0.4K / 0.4Cs / ZrO2 catalysts of the present application, for Co / 0.8K / ZrO2, T 90 (N2O decomposition efficiency is 90% when the temperature is 310℃; at 375℃, after the introduction of O2, the decomposition rate decreases from 88% to 78%, after the introduction of NO x , the decomposition rate remains at about 64%, and after the introduction of H2O, the decomposition rate stabilizes at 56%. After stopping the introduction of the above-mentioned impurity gas, the decomposition rate rapidly increases to the initial state. For Co / 0.4K / 0.4Cs / ZrO2, T 90 is only 300℃; at 375℃, after the introduction of O2, the decomposition rate decreases from 89% to 79%, after the introduction of NO xAfterwards, the decomposition rate is maintained at about 63%, and after the H2O is introduced, the decomposition rate is stabilized at 55%. After the introduction of the above-mentioned impurity gas is stopped, the decomposition rate is rapidly increased to the initial state. And without K + Modified Co / ZrO2 catalyst, T 90 is 405℃; at 375℃, after the O2 is introduced, the decomposition rate is decreased from 80% to 55%, after the NO x is introduced, the decomposition rate is maintained at 50%, and after the H2O is introduced, the decomposition rate is stabilized at 20%. After the introduction of the above-mentioned impurity gas is stopped, the decomposition rate is rapidly increased to the initial state.

[0028] Therefore, the preferred Co / 0.8K / ZrO2 and Co / 0.4K / 0.4Cs / ZrO2 catalysts of the present application both have more excellent low-temperature catalytic decomposition N2O performance and impurity gas resistance, and the comprehensive performance of the Co / 0.4K / 0.4Cs / ZrO2 catalyst is better. BRIEF DESCRIPTION OF DRAWINGS

[0029] The accompanying drawings, which form a part of this specification, are included to provide a further understanding of the application and are incorporated in and constitute a part of this specification. The embodiments of these drawings are set forth to explain the present application and do not limit the present application in any manner.

[0030] Figure 1 are XRD (a), Raman spectrum (b) and 650~720cm -1 Raman spectrum amplification spectrum (c).

[0031] Figure 2 are activity curves of the catalysts prepared in Examples 1-6 and Comparative Examples 1-2 in catalytic decomposition of N2O.

[0032] Figure 3 are the test results of the impurity gas resistance of the catalysts prepared in Examples 2, 5 and Comparative Example 2. DETAILED DESCRIPTION

[0033] It should be noted that the following detailed description is exemplary in nature and is intended to provide further description of the application. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs.

[0034] The present application will be described in further detail below with specific embodiments. It should be noted that the specific embodiments are intended to explain the present application, not to limit the present application.

[0035] Example 1

[0036] 0.024 mol of zirconium nitrate pentahydrate (Zr(NO₃)₄·5H₂O) and 0.24 mol of urea (CH₄N₂O) were dissolved in 60 mL of deionized water. After stirring for 30 minutes, the solution was placed in a 100 mL autoclave and reacted at 140°C for 14 hours. After the reaction, the resulting solution was centrifuged to remove the mother liquor, washed with deionized water and ethanol, and the resulting precipitate was dried overnight in a forced-air drying oven at 110°C. Finally, the sample was ground into a powder and calcined in a muffle furnace at 550°C for 4 hours to obtain the supported ZrO₂.

[0037] The prepared 2 g ZrO2 was mixed with 0.0071 g anhydrous potassium carbonate (K2CO3) and ground, and calcined at 500 °C for 4 h to obtain 0.2K / ZrO2.

[0038] The prepared 2g 0.2K / ZrO2 was mixed with 0.6206g cobalt acetate tetrahydrate ((CH3COO)2Co·4H2O) and ground, and calcined at 550°C for 2h to obtain the catalyst Co / 0.2K / ZrO2.

[0039] Example 2

[0040] 0.024 mol of zirconium nitrate pentahydrate (Zr(NO₃)₄·5H₂O) and 0.24 mol of urea (CH₄N₂O) were dissolved in 60 mL of deionized water. After stirring for 30 minutes, the solution was placed in a 100 mL autoclave and reacted at 140°C for 14 hours. After the reaction, the resulting solution was centrifuged to remove the mother liquor, washed with deionized water and ethanol, and the resulting precipitate was dried overnight in a forced-air drying oven at 110°C. Finally, the sample was ground into a powder and calcined in a muffle furnace at 550°C for 4 hours to obtain the supported ZrO₂.

[0041] The prepared 2 g ZrO2 was mixed with 0.0283 g anhydrous potassium carbonate (K2CO3) and ground, and calcined at 500 °C for 4 h to obtain 0.8K / ZrO2.

[0042] The prepared 2g 0.8K / ZrO2 was mixed with 0.6206g cobalt acetate tetrahydrate ((CH3COO)2Co·4H2O) and ground, and calcined at 550℃ for 2h to obtain the catalyst Co / 0.8K / ZrO2.

[0043] Example 3

[0044] 0.024 mol of zirconium nitrate pentahydrate (Zr(NO₃)₄·5H₂O) and 0.24 mol of urea (CH₄N₂O) were dissolved in 60 mL of deionized water. After stirring for 30 minutes, the solution was placed in a 100 mL autoclave and reacted at 140°C for 14 hours. After the reaction, the resulting solution was centrifuged to remove the mother liquor, washed with deionized water and ethanol, and the resulting precipitate was dried overnight in a forced-air drying oven at 110°C. Finally, the sample was ground into a powder and calcined in a muffle furnace at 550°C for 4 hours to obtain the supported ZrO₂.

[0045] The prepared 2 g ZrO2 was mixed with 0.0708 g anhydrous potassium carbonate (K2CO3) and ground, and calcined at 500 °C for 4 h to obtain 2.0K / ZrO2.

[0046] The prepared 2.0K / ZrO2 was mixed with 0.6206g of cobalt acetate tetrahydrate ((CH3COO)2Co·4H2O) and ground, and calcined at 550°C for 2h to obtain the catalyst Co / 2.0K / ZrO2.

[0047] Example 4

[0048] 0.024 mol of zirconium nitrate pentahydrate (Zr(NO₃)₄·5H₂O) and 0.24 mol of urea (CH₄N₂O) were dissolved in 60 mL of deionized water. After stirring for 30 minutes, the solution was placed in a 100 mL autoclave and reacted at 140°C for 14 hours. After the reaction, the resulting solution was centrifuged to remove the mother liquor, washed with deionized water and ethanol, and the resulting precipitate was dried overnight in a forced-air drying oven at 110°C. Finally, the sample was ground into a powder and calcined in a muffle furnace at 550°C for 4 hours to obtain the supported ZrO₂.

[0049] The prepared 2g ZrO2 was mixed with 0.0071 anhydrous potassium carbonate (K2CO3) and 0.0049g cesium carbonate (Cs2CO3) and ground, and calcined at 500℃ for 4h to obtain 0.2K / 0.2Cs / ZrO2.

[0050] The prepared 2g 0.2K / 0.2Cs / ZrO2 was mixed with 0.6206g cobalt acetate tetrahydrate ((CH3COO)2Co·4H2O) and ground, and calcined at 550℃ for 2h to obtain the catalyst Co / 0.2K / 0.2Cs / ZrO2.

[0051] Example 5

[0052] 0.024 mol of zirconium nitrate pentahydrate (Zr(NO₃)₄·5H₂O) and 0.24 mol of urea (CH₄N₂O) were dissolved in 60 mL of deionized water. After stirring for 30 minutes, the solution was placed in a 100 mL autoclave and reacted at 140°C for 14 hours. After the reaction, the resulting solution was centrifuged to remove the mother liquor, washed with deionized water and ethanol, and the resulting precipitate was dried overnight in a forced-air drying oven at 110°C. Finally, the sample was ground into a powder and calcined in a muffle furnace at 550°C for 4 hours to obtain the supported ZrO₂.

[0053] The prepared 2g ZrO2 was mixed with 0.0141 anhydrous potassium carbonate (K2CO3) and 0.0098g cesium carbonate (Cs2CO3) and ground, and calcined at 500℃ for 4h to obtain 0.4K / 0.4Cs / ZrO2.

[0054] The prepared 0.4K / 0.4Cs / ZrO2 (2 g) was mixed with 0.6206 g of acetic acid tetrahydrate ((CH3COO)2Co·4H2O), ground, and calcined at 550°C for 2 h to obtain the catalyst Co / 0.4K / 0.4Cs / ZrO2.

[0055] Example 6

[0056] 0.024 mol of zirconium nitrate pentahydrate (Zr(NO₃)₄·5H₂O) and 0.24 mol of urea (CH₄N₂O) were dissolved in 60 mL of deionized water. After stirring for 30 minutes, the solution was placed in a 100 mL autoclave and reacted at 140°C for 14 hours. After the reaction, the resulting solution was centrifuged to remove the mother liquor, washed with deionized water and ethanol, and the resulting precipitate was dried overnight in a forced-air drying oven at 110°C. Finally, the sample was ground into a powder and calcined in a muffle furnace at 550°C for 4 hours to obtain the supported ZrO₂.

[0057] The prepared 2 g ZrO2 was mixed with 0.0353 g anhydrous potassium carbonate (K2CO3) and 0.0245 g cesium carbonate (Cs2CO3) and ground, and calcined at 500 °C for 4 h to obtain 1.0K / 1.0Cs / ZrO2.

[0058] The prepared 2 g 1.0K / 1.0Cs / ZrO2 was mixed with 0.6206 g cobalt acetate tetrahydrate ((CH3COO)2Co·4H2O) and ground, and calcined at 550 °C for 2 h to obtain the catalyst Co / 1.0K / 1.0Cs / ZrO2.

[0059] Comparative Example 1

[0060] 0.024 mol of zirconium nitrate pentahydrate (Zr(NO₃)₄·5H₂O) and 0.24 mol of urea (CH₄N₂O) were dissolved in 60 mL of deionized water. After stirring for 30 minutes, the solution was placed in a 100 mL autoclave and reacted at 140°C for 14 hours. After the reaction, the resulting solution was centrifuged to remove the mother liquor, washed with deionized water and ethanol, and the resulting precipitate was dried overnight in a forced-air drying oven at 110°C. Finally, the sample was ground into a powder and calcined in a muffle furnace at 550°C for 4 hours to obtain the supported ZrO₂.

[0061] Comparative Example 2

[0062] 0.024 mol of zirconium nitrate pentahydrate (Zr(NO₃)₄·5H₂O) and 0.24 mol of urea (CH₄N₂O) were dissolved in 60 mL of deionized water. After stirring for 30 minutes, the solution was placed in a 100 mL autoclave and reacted at 140°C for 14 hours. After the reaction, the resulting solution was centrifuged to remove the mother liquor, washed with deionized water and ethanol, and the resulting precipitate was dried overnight in a forced-air drying oven at 110°C. Finally, the sample was ground into a powder and calcined in a muffle furnace at 550°C for 4 hours to obtain the supported ZrO₂.

[0063] The prepared 2g ZrO2 was mixed with 0.6206g cobalt acetate tetrahydrate ((CH3COO)2Co·4H2O) and ground, and calcined at 550℃ for 2h to obtain the catalyst Co / ZrO2.

[0064] The XRD spectra of the catalysts prepared in Examples 1-6 and Comparative Examples 1-2 are as follows: Figure 1 As shown in (a), all samples exhibit diffraction peaks of monoclinic ZrO2 at 2θ=24.3°(011), 28.2°(-111), 31.5°(111), 50.6°(-221), 34.5°(020), 40.8°(-112), and 55.6°(-311). The corresponding PDF card number is 37-1484, indicating that the prepared support is monoclinic ZrO2 (m-ZrO2). For the catalyst loaded with 10% Co3O4, the diffraction peak at 2θ=36.8° corresponds to the (311) crystal plane of Co3O4, and the introduction of cobalt does not cause changes in the position and half-peak width of the ZrO2 diffraction peak, indicating that the cobalt species is loaded on the catalyst surface in the form of Co3O4 and does not enter the ZrO2 lattice.

[0065] The Raman spectra of the catalysts prepared in Examples 1-6 and Comparative Examples 1-2 are as follows: Figure 1 As shown in (b), all six catalysts maintain the spinel structure of Co3O4, and no Raman peaks related to alkali metals are detected, which means that the spinel structure is +、Cs + There is no obvious effect after the addition. The A1g and F2g(3) modes are the characteristic vibration modes of the octahedral (CoO6) and tetrahedral (CoO4) sites, respectively, and the other three are not clearly identified. Figure 1 As shown in (c), the red shift of A1g is related to K + 、Cs + The residual stress caused by the incorporation of K is related to the lattice distortion, indicating that + 、Cs + It has a certain regulatory effect on the octahedral sites of Co3O4.

[0066] The catalysts prepared in Examples 1-6 and Comparative Examples 1-2 were tableted and granulated to a size of 30-45 mesh. These were then placed on top of a quartz sand core (in a fixed-bed reactor). A small amount of quartz wool was then placed on top of the catalysts. A 2000 ppm concentration of N2O reaction gas was introduced, with the remainder being supplemented with N2. The total gas flow rate was maintained at 100 mL / min, and the mass space velocity (WHSV) was 30,000 mL·g. -1 ·h -1 Finally, the temperature control program was set to increase the temperature, maintaining the heating rate at 5°C / min, keeping each point warm for 0.5h, and using infrared to monitor the N2O concentration in the exhaust gas at the outlet in real time.

[0067] The activity curves of the catalysts prepared in Examples 1-6 and Comparative Examples 1-2 for catalytic decomposition of N2O are shown in FIG. Figure 2 As shown in Figure 2, the carrier m-ZrO2 is almost inactive in catalyzing the decomposition of N2O in the temperature range of 250-500℃. The decomposition performance of Co / ZrO2 on N2O is poor, T 90 Reaching about 405℃. When 0.2wt%K is gradually introduced into the catalyst + , the activity begins to improve significantly. When it increases to 0.8wt%, the catalytic performance is the best. 90 Only 310℃, compared with no K + For the modified Co / ZrO2 catalyst, the temperature dropped by 95℃. + The higher the content, the better the effect on promoting catalytic activity. Figure 2 It can be seen that when K + Excessive, i.e., introduction of 2.0wt%K + , its N2O decomposition performance decreased instead, and its activity showed a volcanic change trend. + When the content of alkali metals reaches 0.8wt% (i.e. Co / 0.8K / ZrO2), the catalytic performance is the best, that is, when the total content of alkali metals is 0.8wt%, the catalyst activity is the best. Based on this, the K in the Co / K / Cs / ZrO2 series catalyst is designed. + and Cs +The addition ratio is as shown in Examples 4-6.

[0068] For Examples 4-6, when 0.2 wt% K was gradually introduced into the catalyst, + and 0.2wt%Cs + (i.e. the total amount of alkali metal is 0.4wt%), the decomposition performance of the catalyst for N2O is significantly improved compared with the control; when 0.4wt% K + and 0.4wt%Cs + (i.e. the total amount of alkali metal is 0.8wt%), the performance is the best, at this time T 90 The catalyst temperature was 300°C, a decrease of 105°C compared to the Co / ZrO2 catalyst and 10°C compared to the Co / 0.8K / ZrO2 catalyst. Furthermore, as the total alkali metal content increased to 2.0wt%, the catalyst performance declined, also exhibiting a volcano-like performance trend. Therefore, the Co / 0.4K / 0.4Cs / ZrO2 catalyst (i.e., a total alkali metal content of 0.8wt%) exhibited optimal N2O decomposition performance.

[0069] The catalysts prepared in Examples 2, 5 and Comparative Example 2 were tested for their tolerance to impurity gases. The results were as follows: Figure 3 Take the above catalyst and compress it into tablets and granules with a size of 30-45 mesh, then fill it on top of the quartz sand core (in the fixed bed reactor), and then take a small amount of quartz wool and fill it on top of the catalyst. Adjust the reaction gas composition NO x The concentrations of O2, NO and H2O were 5vol%, 500ppm and 5vol% respectively. The reaction temperature was 375℃. x The reaction times for , and H2O were 5 h, 17.5 h, and 29 h, respectively. Finally, the impurity gas was removed at 65 h. Before testing, the reaction gas was switched to flow directly into the detection system without passing through the sample tube to ensure that the configured gas concentration reached the set value. The reaction gas was then switched back to flow into the fixed-bed reactor over the catalyst to be tested.

[0070] For no K + The modified Co / ZrO2 catalyst (Comparative Example 2) was heated at a temperature of 375°C and a space velocity of 15000 mL·g -1 ·h -1 Under the conditions of , the decomposition efficiency of N2O reached 80%. When 5 vol% O2 was introduced into the reaction pool, the decomposition efficiency dropped significantly, from 80% to 55%, a decrease of about 25%. Subsequently, 500ppm NO was introduced into the reaction pool. x, the decomposition efficiency of N2O decreased from 55% to 50%, with a small decrease. When 5vol% H2O was introduced, the decomposition efficiency dropped significantly again, from 50% to 20%, a decrease of about 30%. x With the introduction of O2, NO x After the addition of H2O, the decomposition efficiency of N2O dropped from the initial 80% to 20%. Therefore, the catalyst has poor tolerance.

[0071] For the Co / 0.8K / ZrO2 catalyst (Example 2), at a temperature of 375°C and a space velocity of 75000 mL·g -1 ·h -1 Under the condition of , the decomposition efficiency of N2O reached 88%. When 5 vol% O2 was introduced into the reaction tank, the decomposition efficiency only decreased slightly by 10%. x , the N2O decomposition efficiency dropped from 78% to 64%. Finally, 5 vol% H2O was introduced, and the decomposition efficiency dropped slightly, but the amplitude was very small, from 64% to 56%, a decrease of only 8%. x , H2O, the decomposition efficiency can be restored to the initial state. x After adding 2% H2O, its decomposition efficiency of N2O dropped from 88% to 56%, a decrease of 32%, which is much smaller than the 60% of Co / ZrO2. The catalyst's tolerance to impurity gases is much higher than that of Co / ZrO2.

[0072] For the Co / 0.4K / 0.4Cs / ZrO2 catalyst (Example 5), the temperature was 375 ° C and the space velocity was 75000 mL g -1 ·h -1 Under the condition of , the decomposition efficiency of N2O is about 89%. When 5 vol% O2 is introduced into the reaction tank, the decomposition efficiency is reduced to 79%. When 500ppm NO is introduced into the reaction tank, the decomposition efficiency is reduced to 79%. x , the N2O decomposition efficiency continued to decrease to 63%. Finally, 5 vol% H2O was continued to be introduced, and the decomposition efficiency decreased slightly, from 63% to 55%, a decrease of 8%. x , H2O, the decomposition efficiency is restored to the initial state. O2, NO x After adding HO, its N2O decomposition efficiency dropped from 89% to 55%, a decrease of 34%, which is much smaller than the 60% of Co / ZrO2 and comparable to the Co / 0.8K / ZrO2 catalyst (Example 2). Therefore, this catalyst has good tolerance to impurity gases.

[0073] It can be seen from this that the preferred Co / 0.8K / ZrO2 and Co / 0.4K / 0.4Cs / ZrO2 catalysts of the present invention both have excellent low-temperature catalytic decomposition of N2O performance and impurity gas tolerance, but the comprehensive performance of the Co / 0.4K / 0.4Cs / ZrO2 catalyst is better.

[0074] The foregoing description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention are intended to be within the scope of protection of the present invention.

Claims

1. An alkali metal-modified catalyst for decomposing nitrous oxide, characterized in that: ZrO2 is used as the carrier, and the active ingredients are composed of Co3O4 and alkali metals; Among them, the loading amount of Co3O4 is 10%-15%, and the percentage is mass percentage; The alkali metals are K and Cs, wherein the loading amount of K is 0.4% and the loading amount of Cs is 0.4%; Alkali metal oxides are mixed with ZrO2, ground, and calcined once to obtain an alkali metal / ZrO2 composite; The alkali metal / ZrO2 complex is mixed with cobalt salt, ground, and calcined twice to obtain a catalyst.

2. The alkali metal-modified catalyst for decomposing nitrous oxide according to claim 1, wherein The ZrO2 is monoclinic ZrO2.

3. The alkali metal-modified catalyst for decomposing nitrous oxide according to claim 1, wherein The alkali metal oxide is selected from at least one of potassium carbonate and cesium carbonate.

4. The alkali metal-modified catalyst for decomposing nitrous oxide according to claim 1, wherein The cobalt salt is cobalt acetate tetrahydrate.

5. The alkali metal-modified catalyst for decomposing nitrous oxide according to claim 1, wherein The primary calcination condition is calcination at 500° C.-550° C. for 3 h-4 h.

6. The alkali metal-modified catalyst for decomposing nitrous oxide according to claim 1, wherein The secondary calcination is carried out at 550° C. to 600° C. for 1.5 h to 2 h.

7. The alkali metal-modified catalyst for decomposing nitrous oxide according to claim 1, wherein The preparation method of ZrO2 comprises: uniformly mixing zirconium salt and urea in a solvent, carrying out hydrothermal reaction, collecting the product, washing, drying, grinding and calcining to obtain ZrO2.

8. Use of the catalyst according to any one of claims 1 to 7 in catalytic decomposition of N2O, characterized in that: The catalytic decomposition is carried out at 250°C-500°C and / or in the presence of impurity gases, wherein the impurity gases are selected from O2, NO x , H2O or at least one of the following.

Images