Metal oxide catalyst for low-temperature catalytic decomposition of N2O as well as preparation method and application of metal oxide catalyst

Abstract

The invention relates to a metal oxide catalyst for low-temperature catalytic decomposition of N2O and a preparation method and application thereof. The GdxCo3O4 catalyst is prepared by adopting a coprecipitation and hydrothermal reaction synthesis two-step method, the active crystal face and active sites of the catalyst are regulated and controlled by changing the Gd / Co molar ratio x, and the low-temperature N2O catalytic decomposition performance of the catalyst is remarkably improved. The method is simple in process and environment-friendly, the prepared catalyst can be used for removing high-concentration N2O in waste gas of chemical industries such as adipic acid and caprolactam production at low temperature, the reaction temperature is low, the N2O conversion rate is high, selectivity is high, heat stability is good, environment friendliness is achieved, an important breakthrough in the field of N2O low-temperature direct catalytic decomposition is achieved, and wide engineering application prospects are achieved.

Description

Technical Field

[0001] The present invention relates to the field of industrial tail gas N2O removal, and specifically relates to a metal oxide catalyst for low-temperature catalytic decomposition of N2O, a preparation method thereof, and an application thereof. Background Art

[0002] Nitrous oxide (N2O), as the third largest greenhouse gas, has a global warming potential (GWP) 310 times that of carbon dioxide (CO2) and 24 times that of methane (CH4). During the production processes of adipic acid and caprolactam, a large amount of N2O is generated and directly emitted into the atmosphere. Due to the highly stable physical and chemical properties of N2O, its survival time in the atmosphere can be as long as 150 years, thus significantly intensifying the global greenhouse effect. In addition, N2O has a destructive effect on the ozone layer, which may lead to the formation of ozone holes, and thus pose a potential threat to human health and the ecological environment. Therefore, effectively controlling the emission of N2O in industrial tail gas has become an important problem to be solved urgently.

[0003] Currently, the common technologies for N2O emission reduction in industrial tail gas mainly include high-temperature thermal decomposition, direct catalytic decomposition, and selective catalytic reduction technologies. Among them, the direct catalytic decomposition of N2O technology has attracted much attention due to its high conversion rate and wide applicability, and is considered to be one of the most promising N2O emission reduction technologies. The key to this technology lies in the selection of the catalyst. Among them, the metal oxide Co3O4 catalyst has become a research hotspot due to its excellent redox performance and abundant surface oxygen species. However, unmodified pure Co3O4 is difficult to meet the requirements of N2O direct catalytic decomposition in terms of cost and performance. Therefore, by introducing promoters to construct a unique microstructure of the Co3O4 catalyst and increase the number of active sites, the low-temperature activity and resistance can be further improved, thus effectively solving the technical problem that pure Co3O4 in the prior art cannot meet the requirements of N2O catalytic decomposition.

[0004] For example, CN116786147A discloses a preparation method of a composite catalyst composed of Co3O4 and alkaline earth metal carbonate. The catalyst is prepared by a molar ratio of the alkaline earth metal element to the cobalt element of 0.1-1. Specifically, this method reacts a soluble cobalt salt, a soluble precursor salt of alkaline earth metal carbonate, and a precipitant to generate a solid-liquid mixture, collects, washes, and dries the precipitate in the solid-liquid mixture, and calcines the precipitate in the air to obtain the target catalyst. However, the defect of this method is that it involves alkaline earth metal carbonate, such as SrCO3, which is not a common carrier and has a high cost.

[0005] CN117282434A discloses a preparation method of a rare earth-doped cobalt-based catalyst for catalytic decomposition of N2O. The catalyst comprises Co3O4 and TmCo3O4. The doping of Tm can, to a certain extent, increase the number of surface active oxygen sites and charge distribution of the catalyst. The molar ratio of cobalt ions to thulium ions is 1:(0.025 - 0.075). The preparation method specifically includes the following steps: obtaining an aqueous solution of soluble cobalt salt, soluble thulium salt, urea, and citric acid; performing heat treatment on the aqueous solution until a sol is formed; performing drying treatment on the sol; and performing calcination treatment on the dried sol to obtain the target catalyst. However, when this catalyst is applied to the direct catalytic decomposition of N2O, it does not exhibit good low-temperature catalytic activity. For example, at 350 °C, the conversion rate of Tm 0.05 Co to N2O is about 20%.

[0006] CN117943092A discloses a preparation method of a catalyst for catalytic decomposition of N2O derived from Co-MOFs. This method uses Co-MOFs as a precursor and derivatively synthesizes a stable cobalt oxide catalyst by regulating the types of precursors, the gas atmosphere, temperature, heating rate, time, and number of calcination. However, this preparation method requires multiple calcinations and changes in the calcination gas atmosphere, and the preparation process is cumbersome.

[0007] CN118594548A discloses a preparation method of a catalyst for decomposing N2O. The catalyst composition includes: active component Co3O4, promoter alkaline earth metal oxide, and carrier ZrO2. The preparation method includes the following steps: dissolving soluble salts of cobalt, soluble salts of alkaline earth metals, soluble salts of zirconium, and a surfactant in deionized water, adding a precipitant, stirring, aging, mixing the obtained mixed precipitate with deionized water and stirring, pouring it into a heating device, washing and filtering, drying and calcining to obtain the target catalyst. However, the defect of this method is that the manufacturing process involves strict temperature control, is time-consuming, and has high requirements for the preparation process.

[0008] For example, Xue et al. (Applied Catalysis B: Environmental. 2007, 75, 167-174) found that adding CeO2 to Co3O4 can increase the specific surface area of ​​Co3O4, promote the decomposition of adsorbed oxygen, and further improve the catalytic activity of N2O. Zhao et al. (Journal of Environmental Chemical Engineering. 2024, 12, 113907) found that Cs doping can significantly enhance the low temperature performance and antioxidant properties of Co3O4 catalysts, mainly attributed to the presence of Cs inhibiting the growth of Co3O4 grains, increasing the specific surface area, and significantly increasing the number of exposed oxygen vacancies. Xiong et al. (Environmental Science&Technology. 2021, 55, 13335-13344) prepared Gd-promoted Co3O4 catalysts and found that during the catalytic decomposition of N2O, the addition of Gd weakened the strength of the Co-O bond, reduced the grain size and produced abundant active sites Co. 3+ Differently, Gong et al. (Environmental Science & Technology. 2023, 58, 906-914) believed that Co 2+ It is the main active site for the decomposition of N2O. Doping metals can 3+ Donate electrons and generate more Co 2+ .

[0009] In summary, a lot of research has been done on the catalytic decomposition of N2O by different metal-doped Co3O4 catalysts, but the decomposition temperature is still high and the activity of different catalysts varies greatly. Therefore, the development of new catalysts with high activity at low temperature, green production and suitability for high-concentration N2O tail gas treatment has become a key technical issue that needs to be solved in this field. Summary of the invention

[0010] In order to solve the above-mentioned technical problems, the present invention provides a metal oxide catalyst for low-temperature catalytic decomposition of N2O and its preparation method and application. The catalyst is prepared by a two-step method of coprecipitation + hydrothermal reaction synthesis to obtain GdCo3O4, exposing high-index interface and more active sites Co 3+ At 200℃, the N2O conversion rate can reach 79.4%, and N2O can be completely converted at 250-550℃, which effectively overcomes the problem of low conversion efficiency of high-concentration N2O at low temperature in current technology.

[0011] The invention provides a metal oxide for catalytically decomposing N2O at low temperature, wherein the catalyst is GdCo3O4.

[0012] Furthermore, the catalyst exposes high-index boundary crystal planes (040-040) and more active sites are Co 3+ .

[0013] The present invention also provides a preparation method for adding an auxiliary agent Gd and changing the doping ratio of the aforementioned catalyst. The preparation method includes the following steps:

[0014] Step 1: First, dissolve cobalt salt (Co salt) and gadolinium salt (Gd salt) in deionized water and stir for 10-15 min at room temperature. Prepare according to the molar ratio of Gd / Co of 0.05-0.15 to ensure that the concentration of cobalt ions in the mixed solution is maintained within the range of 0.5-1.5 mol / L. At the same time, dissolve soluble carbonate, bicarbonate or hydroxide in deionized water and also stir for 10-15 min at room temperature to prepare a precipitant solution with a concentration of 0.4-0.6 mol / L;

[0015] Step 2: Place the mixed metal salt solution prepared in Step 1 in a constant temperature water bath environment at 30-50 °C and continue stirring, and slowly drop the above-mentioned precipitant solution at a rate of 40-80 mL / h for a duration of 2±0.1 h. Adjust the pH value of the reaction solution through this process to finally reach the range of 8-10;

[0016] Step 3: Transfer the reaction solution obtained in Step 2 to a sealed high-temperature and high-pressure reaction kettle for hydrothermal reaction synthesis. During this process, control the temperature in the reaction kettle to be 160-220 °C, set the stirring speed to 300-500 r / min, and keep the stirring time at 2-4 h;

[0017] Step 4: After washing the reaction solution obtained in Step 3 with deionized water until it is neutral, place it in an oven at 100-120 °C and dry for 4-6 h;

[0018] Step 5: Grind the sample obtained in Step 4 into powder and evenly spread it on a magnetic boat, then put it into a muffle furnace and calcine it at a temperature of 400-600 °C for 3-5 h, and then naturally cool it to room temperature to obtain the GdxCo3O4 catalyst.

[0019] Furthermore, in Step 1, the Co salt includes inorganic Co salt or organic Co salt. The inorganic Co salt includes at least one of Co(OH)2, CoCO3, Co(NO3)2·6H2O, CoSO4·6H2O and CoCl2·6H2O; the organic Co salt includes at least one of cobalt acetate, cobalt naphthenate, cobalt stearate and cobalt neodecanoate.

[0020] Further, in Step 1, the Gd salt includes at least one of Gd(NO3)3·6H2O, GdCl3·6H2O, and C3Gd2O9.

[0021] Further, in Step 1, the molar ratio of Gd / Co is at least one of 0.05, 0.06, 0.07, 0.08, 0.09, 0.10, 0.11, 0.12, 0.13, 0.14, and 0.15.

[0022] Further, in Step 1, the soluble carbonate, bicarbonate, or hydroxide includes at least one of Na2CO3, K2CO3, NaHCO3, KHCO3, NaOH, and KOH.

[0023] The present invention also provides an application of the aforementioned catalyst. The catalyst is placed in a quartz tube fixed-bed reactor, and the flue gas composition introduced includes 5 vol.% - 30 vol.% of N2O, 0 - 21 vol.% of O2, 0 - 3 vol.% of CO2, and 0 - 2 vol.% of H2O, with He as the balance gas. The gas flow rate of the flue gas is set to 25 - 200 mL / min. The catalytic reaction temperature is controlled within the range of 150 °C, 200 °C, 250 °C, 300 °C, 350 °C, 400 °C, 450 °C, 500 °C, and 550 °C, and a stable time of 30 - 60 minutes is maintained in each temperature segment. The space velocity range of the flue gas is 5000 - 20000 h -1 。

[0024] The beneficial effects of the present invention are as follows:

[0025] 1. For the catalyst of the present invention, through HAADF-STEM characterization and analysis, it is found that the doping of the promoter Gd successfully induces the formation of a new high-index boundary crystal plane (040-040) on GdCo3O4, and Gd is mainly dispersed at the interface of the (040) and (040) crystal planes at the nanoscale.

[0026] 2. Conventional Co3O4 prepared by common synthesis methods at present can achieve complete decomposition of N2O in the range of 450 - 550 °C, and its main active crystal planes include (100), (111), and (110). However, for the GdCo3O4 catalyst prepared by the present invention, the exposed active crystal plane is the high-index boundary crystal plane (040-040). This catalyst can reach a N2O decomposition efficiency of 79.4% at 200 °C and can maintain a high decomposition performance of 100% in the temperature range of 250 - 550 °C.

[0027] 3. The improvement in the activity of the GdCo3O4 catalyst is fundamentally due to changes in its microstructure and the exposure of the active crystal faces. In the reaction 2N2O→2N2+O2, the gaseous N2O molecules need to first adsorb to the active sites on the catalyst surface, and then break the NO bonds to generate N2 and O. Among them, the dissociation process of O at the active sites is the rate-controlling step of the entire reaction, and this process is closely related to the exposed active crystal faces of the catalyst. Generally speaking, the higher the surface energy of the exposed crystal face, the easier it is for O to dissociate, making the catalyst more active.

[0028] 4. The active sites exposed by the GdCo3O4 catalyst of the present invention are Co 3+ Mainly, through coprecipitation +

[0029] It was prepared by a two-step hydrothermal reaction. It was found that after adding the additive Gd, the performance of the Co3O4 catalyst in catalyzing the decomposition of N2O was outstanding, which was better than the Co3O4 prepared by the two-step coprecipitation + hydrothermal synthesis without adding additives. Especially at low temperatures, the decomposition efficiency of N2O at 200°C can reach 79.40%. The Co in the catalyst was analyzed by H2-TPR. 3+

[0030] Compared with the Co3O4 catalyst prepared by the two-step method of coprecipitation + hydrothermal synthesis, the Co 3+ The reduction peak temperature decreases, indicating that it has stronger reducing ability and active Co-O bonds, which is beneficial to the reduction of N2O to N2 and O2. 3+ The content of Co in Gd0.1Co3O4 is significantly increased. 3+

[0031] The active site content is the highest, reaching 55.9%. 3+ The higher proportion indicates that Co 3+ It is the key factor to improve the performance of catalyst in decomposing N2O.

[0032] 5. The present invention provides a method for preparing a metal oxide catalyst for low-temperature catalytic decomposition of N2O. Compared with existing catalysts, the catalyst can be used for low-temperature removal of high-concentration N2O in waste gas from chemical industries such as adipic acid and caprolactam production. The catalyst has low reaction temperature, high N2O conversion rate, high selectivity, good thermal stability and environmental friendliness, achieving an important breakthrough in the field of low-temperature direct catalytic decomposition of N2O and having broad prospects for engineering application. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 The present invention is a process flow chart for preparing the catalyst.

[0034] Figure 2Efficiency curve of the catalyst for decomposing N2O obtained in Examples 1-3 and Comparative Examples 1-2 of the present invention.

[0035] Figure 3 H2-TPR diagram of the catalyst obtained in Examples 1-3 and Comparative Examples 1-2 of the present invention.

[0036] Figure 4 Efficiency curve of the catalyst for decomposing N2O obtained in Example 2 and Comparative Examples 3-7 of the present invention.

[0037] Figure 5 HAADF-STEM diagram of the catalyst obtained in Example 2 of the present invention. Detailed implementation mode

[0038] The present invention will be further described below in conjunction with embodiments, but the present invention is not limited to the following embodiments.

[0039] Example 1

[0040] Example 1

[0041] As Figure 1 shown, Example 1 of the present invention provides a catalyst Gd0.05Co3O4 for low-temperature catalytic decomposition of N2O, and the specific steps of the preparation method are as follows:

[0042] Step 1: Dissolve 10 g of cobalt nitrate hexahydrate (Co(NO3)2·6H2O) and 0.76 g of gadolinium nitrate (Gd(NO3)2·6H2O) in 50 mL of deionized water, and stir for 15 min at room temperature to prepare a mixed metal salt solution with a Co ion concentration of 0.8 mol / L. At the same time, take 26.5 g of sodium carbonate (Na2CO3) and dissolve it in 500 mL of deionized water, and also stir for 15 min at room temperature to prepare a precipitant Na2CO3 solution with a concentration of 0.5 mol / L.

[0043] Step 2: Place the mixed metal salt solution prepared in Step 1 in a 40°C constant temperature water bath environment and continue stirring at a stirring rate of 15 r / min, and slowly add the precipitant Na2CO3 solution at a rate of 60 mL / h for a dropping time of 2 ± 0.1 hours until the pH value of the reaction solution reaches 9.5.

[0044] Step 3: Transfer the reaction solution adjusted to a pH value of 9.5 in Step 2 to a sealed high-temperature and high-pressure reaction kettle for hydrothermal reaction. Set the reaction kettle temperature to 200°C, the stirring speed to 400 r / min, and the stirring duration to 3 h.

[0045] Step 4: Wash the reaction solution after the hydrothermal reaction in Step 3 with deionized water until it is neutral, and then place it in an oven at 105°C and dry it for 3 h.

[0046] Step 5: Grind the sample obtained in Step 4 into powder and evenly spread it in a magnetic boat, then place it in a muffle furnace. Heat it from room temperature to 500 °C at a heating rate of 5 °C / min and keep it calcined at a constant temperature of 500 °C for 3 h. After naturally cooling to room temperature, press the sample and screen it through a 40-60 mesh sieve to finally obtain the Gd0.05Co3O4 catalyst sample.

[0047] Perform activity tests on the above Gd0.05Co3O4 catalyst: Place the Gd0.05Co3O4 catalyst prepared in Example 1 in a quartz tube fixed-bed reactor. Use simulated flue gas containing 7 vol.% N2O as the input gas and He as the balance gas. The gas flow rate is 50 mL / min and the space velocity is 10000 h -1 , and the reaction temperature range is 150 - 550 °C, and stabilize for 30 min at each temperature point.

[0048] According to the data in Table 1, this catalyst shows excellent N2O decomposition efficiency at different temperatures. When the temperature reaches 250 °C, the N2O conversion rate is 79.05%. In the range of 300 - 550 °C, the conversion rate exceeds 95% and the selectivity exceeds 99.99%. By optimizing the formula, Example 1 significantly reduces the starting temperature of N2O catalytic decomposition, broadens the effective temperature window, reduces energy consumption, achieves a conversion rate close to 100%, improves the treatment efficiency of adipic acid tail gas, meets the environmental protection requirements of large enterprises, and promotes the sustainable development of related industries.

[0049] Table 1 Decomposition efficiency of the catalysts prepared in the examples and comparative examples for catalytic decomposition of N2O

[0050]

[0051] Example 2

[0052] Example 2

[0053] As Figure 1 shown, this Example 2 provides a composite catalyst Gd0.1Co3O4 for low-temperature catalytic decomposition of N2O. The specific steps of the preparation method are as follows:

[0054] Step 1: Take 10 g of cobalt nitrate hexahydrate (Co(NO3)2·6H2O) and 1.55 g of gadolinium nitrate hexahydrate (Gd(NO3)3·6H2O) and dissolve them in 50 mL of deionized water. Stir at room temperature for 15 min to prepare a mixed metal salt solution with a Co ion concentration of 0.8 mol / L according to the molar ratio Gd / Co = 0.1; take 26.5 g of sodium carbonate (Na2CO3) and dissolve it in 500 mL of deionized water. Stir at room temperature for 15 min to prepare a precipitant Na2CO3 solution with a concentration of 0.5 mol / L;

[0055] Step 2: Place the mixed metal salt solution obtained in Step 1 in a 40°C constant temperature water bath and continue stirring at a stirring speed of 15 r / min. Then, add the precipitant Na2CO3 solution at a rate of 60 mL / h for 2 h ± 0.1 h until the pH of the reaction solution reaches 9.5.

[0056] Step 3: Transfer the reaction solution with a pH of 9.5 obtained in Step 2 to a sealed high-temperature and high-pressure reactor for hydrothermal reaction. Control the temperature of the reactor at 200°C, the stirring speed at 400 r / min, and the stirring time at 3 h.

[0057] Step 4: Wash the reaction solution after hydrothermal reaction in Step 3 with deionized water until it is neutral, and then place it in an oven at 105°C for drying for 3 h.

[0058] Step 5: Grind the sample obtained in Step 4 into powder, spread it evenly in a magnetic boat, and then place it in a muffle furnace. Heat it from room temperature to 500°C at a heating rate of 5°C / min and calcine it at 500°C for 3 h. After natural cooling to room temperature, press and sieve it to 40 - 60 mesh to finally obtain the Gd0.1Co3O4 catalyst sample.

[0059] Test the catalytic activity of the above Gd0.1Co3O4 catalyst: Put the Gd0.1Co3O4 catalyst prepared in Example 2 into a quartz tube fixed-bed reactor for activity testing. Among them, the input simulated flue gas is: containing 7 vol.% of N2O, with He as the balance gas, and the gas flow rate is 50 mL / min; control the catalytic reaction temperature at 150 - 550°C, keep each temperature stable for 30 min, and the space velocity is 10000 h -1 。

[0060] According to the data in Table 1, with a molar ratio of Gd / Co = 0.1, the performance of the Gd0.1Co3O4 catalyst is further improved, showing excellent N2O decomposition efficiency at different temperatures, reaching 79.4% at 200°C and achieving complete conversion of N2O between 250 - 550°C. An appropriate amount of the promoter Gd and Co co-catalyze the decomposition of N2O, and regulate the Gd0.1Co3O4 catalyst to expose more active sites Co 3 + 。

[0061] Example 3

[0062] Example 3

[0063] As Figure 1 shown, this Example 3 provides a composite catalyst Gd0.15Co3O4 for low-temperature catalytic decomposition of N2O, and the specific steps of the preparation method are as follows:

[0064] Step 1: Take 10 g of cobalt(II) nitrate hexahydrate (Co(NO3)2·6H2O) and 2.28 g of gadolinium(III) nitrate hexahydrate (Gd(NO3)3·6H2O), dissolve them in 50 mL of deionized water, stir for 15 min at room temperature, and prepare a mixed metal salt solution with a Co ion concentration of 0.8 mol / L according to the molar ratio Gd / Co = 0.15; take 26.5 g of sodium carbonate (Na2CO3), dissolve it in 500 mL of deionized water, stir for 15 min at room temperature, and prepare a precipitant Na2CO3 solution with a concentration of 0.5 mol / L.

[0065] Step 2: Place the mixed metal salt solution obtained in Step 1 in a 40 °C constant temperature water bath and continue stirring at a stirring speed of 15 r / min, and dropwise add the precipitant Na2CO3 solution at a rate of 60 mL / h for 2 h ± 0.1 h until the pH of the reaction solution reaches 9.5.

[0066] Step 3: Transfer the reaction solution with a pH of 9.5 obtained in Step 2 to a sealed high-temperature and high-pressure reactor for hydrothermal reaction, control the temperature of the reactor to 200 °C, the stirring speed to 400 r / min, and the stirring time to 3 h.

[0067] Step 4: Wash the reaction solution after the hydrothermal reaction in Step 3 with deionized water until it is neutral, and place it in an oven at 105 °C to dry for 3 h.

[0068] Step 5: Grind the sample obtained in Step 4 into powder, spread it evenly in a porcelain boat, then place it in a muffle furnace, heat it from room temperature to 500 °C at a heating rate of 5 °C / min, and calcine it at 500 °C for 3 h. After natural cooling to room temperature, press and sieve it to 40 - 60 mesh to finally obtain the Gd0.15Co3O4 catalyst sample.

[0069] Test the catalytic activity of the above Gd0.15Co3O4 catalyst: Put the Gd0.15Co3O4 catalyst prepared in Example 3 into a quartz tube fixed-bed reactor for activity testing. Among them, the input simulated flue gas is: containing 7 vol.% of N2O, with He as the balance gas, and the gas flow rate is 50 mL / min; control the catalytic reaction temperature to 150 - 550 °C, stabilize for 30 min at each temperature, and the space velocity is 10000 h -1 。

[0070] According to the data in Table 1, with the molar ratio Gd / Co = 0.15, the performance of the adjusted Gd0.15Co3O4 catalyst has not been improved, but has instead decreased. The N2O decomposition efficiency is 93.07% at 250 °C, and complete conversion of N2O can be achieved between 300 - 550 °C. Excessive Gd doping will cover the active sites, thereby reducing the activity.

[0071] Comparative Example 1

[0072] As Figure 1 shown, Comparative Example 1 provides a catalyst Co3O4 for catalytic decomposition of N2O at low temperature. The specific steps of the preparation method are as follows:

[0073] Step 1: Dissolve 10 g of cobalt nitrate hexahydrate (Co(NO3)2·6H2O) in 50 mL of deionized water, stir at room temperature for 15 min to prepare a mixed metal salt solution with a Co ion concentration of 0.8 mol / L; dissolve 26.5 g of sodium carbonate (Na2CO3) in 500 mL of deionized water, stir at room temperature for 15 min to prepare a precipitant Na2CO3 solution with a concentration of 0.5 mol / L;

[0074] Step 2: Place the mixed metal salt solution obtained in Step 1 in a constant temperature water bath at 40 °C and continue stirring at a stirring speed of 15 r / min, and dropwise add the precipitant Na2CO3 solution at a speed of 60 mL / h for 2 h ± 0.1 h until the pH of the reaction solution reaches 9.5;

[0075] Step 3: Transfer the reaction solution with a pH of 9.5 obtained in Step 2 to a sealed high-temperature and high-pressure reactor for hydrothermal reaction, control the temperature of the reactor to 200 °C, the stirring speed to 400 r / min, and the stirring time to 3 h;

[0076] Step 4: Wash the reaction solution after hydrothermal reaction in Step 3 with deionized water until neutral, and place it in an oven at 105 °C for drying for 3 h;

[0077] Step 5: Grind the sample obtained in Step 4 into powder, spread it evenly on a magnetic boat, then place it in a muffle furnace, heat it from room temperature to 500 °C at a heating rate of 5 °C / min, and calcine it at 500 °C for 3 h. After natural cooling to room temperature, press and screen it to 40 - 60 mesh to finally obtain the Co3O4 catalyst sample.

[0078] Test the catalytic activity of the above Co3O4 catalyst: Put the Co3O4 catalyst prepared in Comparative Example 1 into a quartz tube fixed-bed reactor for activity testing. Among them, the input simulated flue gas is: containing 7% of N2O, He as the balance gas, and the gas flow rate is 50 mL / min; the reaction temperatures are 150 °C, 200 °C, 250 °C, 300 °C, 350 °C, 400 °C, 450 °C, 500 °C, and 550 °C. Each temperature point is stabilized for 30 min, and the space velocity is 10000 h -1 .

[0079] According to the data in Table 1, the Co3O4 catalyst can achieve an N2O conversion rate of 85.7% at 300 °C. The catalyst has a high activation temperature and poor low-temperature activity, and the activity is mainly manifested at high temperatures of 350 - 550 °C.

[0080] Comparative Example 2

[0081] As Figure 1 shown, this Comparative Example 2 provides a composite catalyst Gd0.2Co3O4 for catalytic decomposition of N2O at low temperature. The specific steps of the preparation method are as follows:

[0082] Step 1: Take 10 g of cobalt nitrate hexahydrate (Co(NO3)2·6H2O) and 3.04 g of gadolinium nitrate hexahydrate (Gd(NO3)3·6H2O), dissolve them in 50 mL of deionized water, stir at room temperature for 15 min, and prepare a mixed metal salt solution with a Co ion concentration of 0.8 mol / L according to the molar ratio Gd / Co = 0.2; take 26.5 g of sodium carbonate (Na2CO3), dissolve it in 500 mL of deionized water, stir at room temperature for 15 min, and prepare a precipitant Na2CO3 solution with a concentration of 0.5 mol / L;

[0083] Step 2: Place the mixed metal salt solution obtained in Step 1 in a constant temperature water bath at 40 °C and continue stirring at a stirring speed of 15 r / min, and dropwise add the precipitant Na2CO3 solution at a speed of 60 mL / h for 2 h ± 0.1 h until the pH of the reaction solution reaches 9.5;

[0084] Step 3: Transfer the reaction solution with a pH of 9.5 obtained in Step 2 to a sealed high-temperature and high-pressure reaction kettle for hydrothermal reaction, control the temperature of the reaction kettle at 200 °C, the stirring speed at 400 r / min, and the stirring time at 3 h;

[0085] Step 4: Wash the reaction solution after hydrothermal reaction in Step 3 with deionized water until it is neutral, and place it in an oven at 105 °C to dry for 3 h;

[0086] Step 5: Grind the sample obtained in Step 4 into powder, spread it flat in a boat, then place it in a muffle furnace, heat it from room temperature to 500 °C at a heating rate of 5 °C / min, and calcine it at 500 °C for 3 h. After natural cooling to room temperature, press and sieve it to 40 - 60 mesh to finally obtain the Gd0.2Co3O4 catalyst sample.

[0087] Test the catalytic activity of the above Gd0.2Co3O4 catalyst: Put the Gd0.2Co3O4 catalyst prepared in Comparative Example 2 into a quartz tube fixed-bed reactor for activity testing. Among them, the input simulated flue gas is: containing 7% of N2O, with He as the balance gas, and the gas flow rate is 50 mL / min; the reaction temperatures are 150 °C, 200 °C, 250 °C, 300 °C, 350 °C, 400 °C, 450 °C, 500 °C, and 550 °C, and each temperature point is stabilized for 30 min, and the space velocity is 10000 h -1 .

[0088] According to the data in Table 1, the molar ratio Gd / Co = 0.2. After regulation, the performance of the Gd0.2Co3O4 catalyst decreased significantly. The N2O decomposition efficiency was only 20.16% at 250 °C, and the conversion rate of N2O was above 80% between 300 - 550 °C. Excessive Gd doping would cover the active sites, thus reducing the activity.

[0089] Comparative Example 3

[0090] This Comparative Example 3 provides a composite catalyst Li0.1Co3O4 for low-temperature catalytic decomposition of N2O. The preparation method of the catalyst includes the following steps:

[0091] Step 1: Take 10 g of cobalt nitrate hexahydrate (Co(NO3)2·6H2O) and 0.24 g of lithium nitrate (LiNO3) and dissolve them in 50 mL of deionized water. Stir at room temperature for 15 min, and prepare a mixed metal salt solution with a Co ion concentration of 0.8 mol / L according to the molar ratio Li / Co = 0.1; Take 26.5 g of sodium carbonate (Na2CO3) and dissolve it in 500 mL of deionized water. Stir at room temperature for 15 min to prepare a precipitant Na2CO3 solution with a concentration of 0.5 mol / L;

[0092] Step 2: Place the mixed metal salt solution obtained in Step 1 in a 40 °C constant temperature water bath and continue stirring at a stirring speed of 15 r / min, and dropwise add the precipitant Na2CO3 solution at a speed of 60 mL / h for 2 h ± 0.1 h until the pH of the reaction solution = 9.5;

[0093] Step 3: Transfer the reaction solution with pH = 9.5 obtained in Step 2 to a sealed high-temperature and high-pressure reaction kettle for hydrothermal reaction, control the temperature of the reaction kettle at 200 °C, the stirring speed at 400 r / min, and the stirring time at 3 h;

[0094] Step 4: Wash the reaction solution after hydrothermal reaction in Step 3 with deionized water until it is neutral, and place it in an oven at 105 °C for drying for 3 h;

[0095] Step 5: Grind the sample obtained in Step 4 into powder, spread it flat in a porcelain boat, then place it in a muffle furnace, heat it from room temperature to 500 °C at a heating rate of 5 °C / min, and calcine it at 500 °C for 3 h. After natural cooling to room temperature, press and sieve it to 40 - 60 mesh to finally obtain the Li0.1Co3O4 catalyst sample.

[0096] Testing the catalytic activity of the above Li0.1Co3O4 catalyst: The prepared Li0.1Co3O4 catalyst in Comparative Example 3 was placed in a quartz tube fixed-bed reactor for activity testing. Among them, the input simulated flue gas was: containing 7 vol.% of N2O, with He as the balance gas, and the gas flow rate was 50 mL / min; the reaction temperatures were 150 °C, 200 °C, 250 °C, 300 °C, 350 °C, 400 °C, 450 °C, 500 °C and 550 °C. Each temperature point was stabilized for 30 min, and the space velocity was 10,000 h -1 .

[0097] According to the data in Table 1, with the molar ratio Li / Co = 0.1, the N2O decomposition efficiency of the regulated Li0.1Co3O4 catalyst can only reach 18.9% at 300 °C. The catalyst has a high activation temperature and poor low-temperature activity, and its activity is mainly manifested at high temperatures of 450 - 550 °C.

[0098] Comparative Example 4

[0099] This Comparative Example 4 provides a composite catalyst K0.1Co3O4 for low-temperature catalytic decomposition of N2O. The preparation method of the catalyst includes the following steps:

[0100] Step 1: Take 10 g of cobalt nitrate hexahydrate (Co(NO3)2·6H2O) and 0.34 g of potassium nitrate (KNO3) and dissolve them in 50 mL of deionized water. Stir at room temperature for 15 min, and prepare a mixed metal salt solution with a Co ion concentration of 0.8 mol / L according to the molar ratio K / Co = 0.1; take 26.5 g of sodium carbonate (Na2CO3) and dissolve it in 500 mL of deionized water. Stir at room temperature for 15 min to prepare a precipitant Na2CO3 solution with a concentration of 0.5 mol / L.

[0101] Step 2: Place the mixed metal salt solution obtained in Step 1 in a 40 °C constant temperature water bath and continue stirring at a stirring speed of 15 r / min. Dropwise add the precipitant Na2CO3 solution at a speed of 60 mL / h for 2 h ± 0.1 h until the pH of the reaction solution reaches 9.5.

[0102] Step 3: Transfer the reaction solution with a pH of 9.5 obtained in Step 2 to a sealed high-temperature and high-pressure reaction kettle for hydrothermal reaction. Control the temperature of the reaction kettle to 200 °C, the stirring speed to 400 r / min, and the stirring time to 3 h.

[0103] Step 4: Wash the reaction solution after hydrothermal reaction in Step 3 with deionized water until it is neutral, and place it in an oven at 105 °C for drying for 3 h.

[0104] Step 5: Grind the sample obtained in Step 4 into powder, spread it evenly in a magnetic boat, and then place it in a muffle furnace. Heat it from room temperature to 500 °C at a heating rate of 5 °C / min, and calcine it isothermally at 500 °C for 3 h. After natural cooling to room temperature, press the sample into tablets and sieve it to 40-60 mesh to finally obtain the K0.1Co3O4 catalyst sample.

[0105] Test the catalytic activity of the above K0.1Co3O4 catalyst: Put the K0.1Co3O4 catalyst prepared in Comparative Example 4 into a quartz tube fixed-bed reactor for activity testing. Among them, the input simulated flue gas is: containing 7 vol.% of N2O, with He as the balance gas, and the gas flow rate is 50 mL / min; the reaction temperatures are 150 °C, 200 °C, 250 °C, 300 °C, 350 °C, 400 °C, 450 °C, 500 °C and 550 °C. Each temperature point is stabilized for 30 min, and the space velocity is 10000 h -1 。

[0106] According to the data in Table 1, with a molar ratio of K / Co = 0.1, the regulated K0.1Co3O4 catalyst can only achieve an N2O decomposition efficiency of 33.46% at 350 °C. The catalyst has a high activation temperature and poor low-temperature activity, and its activity is mainly manifested at high temperatures of 450-550 °C.

[0107] Comparative Example 5

[0108] This Comparative Example 5 provides a composite catalyst Mn0.1Co3O4 for low-temperature catalytic decomposition of N2O. The preparation method of the catalyst includes the following steps:

[0109] Step 1: Take 10 g of cobalt nitrate hexahydrate (Co(NO3)2·6H2O) and 0.85 g of manganese nitrate tetrahydrate (Mn(NO3)2·4H2O) and dissolve them in 50 mL of deionized water. Stir at room temperature for 15 min to prepare a mixed metal salt solution with a Co ion concentration of 0.8 mol / L according to a molar ratio of Mn / Co = 0.1; take 26.5 g of sodium carbonate (Na2CO3) and dissolve it in 500 mL of deionized water. Stir at room temperature for 15 min to prepare a precipitant Na2CO3 solution with a concentration of 0.5 mol / L;

[0110] Step 2: Place the mixed metal salt solution obtained in Step 1 in a 40 °C constant temperature water bath and continue stirring at a stirring speed of 15 r / min, and dropwise add the precipitant Na2CO3 solution at a speed of 60 mL / h for 2 h ± 0.1 h until the pH of the reaction solution reaches 9.5;

[0111] Step 3: Transfer the reaction solution with a pH of 9.5 obtained in Step 2 to a sealed high-temperature and high-pressure reaction kettle for hydrothermal reaction, control the temperature of the reaction kettle to 200 °C, the stirring speed to 400 r / min, and the stirring time to 3 h;

[0112] Step 4: Wash the reaction solution after the hydrothermal reaction in Step 3 with deionized water until it is neutral, and place it in an oven at 105 °C for drying for 3 h;

[0113] Step 5: Grind the sample obtained in Step 4 into powder, spread it evenly in a magnetic boat, then place it in a muffle furnace, heat it from room temperature to 500 °C at a heating rate of 5 °C / min, and calcine it at 500 °C for 3 h. After natural cooling to room temperature, press and sieve it to 40 - 60 mesh, and finally obtain the Mn0.1Co3O4 catalyst sample.

[0114] Test the catalytic activity of the above Mn0.1Co3O4 catalyst: Put the Mn0.1Co3O4 catalyst prepared in Comparative Example 5 into a quartz tube fixed-bed reactor for activity testing. Among them, the input simulated flue gas is: containing 7% N2O, with He as the balance gas, and the gas flow rate is 50 mL / min; the reaction temperatures are 150 °C, 200 °C, 250 °C, 300 °C, 350 °C, 400 °C, 450 °C, 500 °C and 550 °C. Each temperature point is stabilized for 30 min, and the space velocity is 10000 h -1 .

[0115] According to the data in Table 1, with a molar ratio of Mn / Co = 0.1, the Mn0.1Co3O4 catalyst after regulation can only achieve an N2O decomposition efficiency of 49.6% at 350 °C. The catalyst has a high activation temperature and poor low-temperature activity, and the active range is at a high temperature of 400 - 550 °C.

[0116] Comparative Example 6

[0117] This Comparative Example 6 provides a composite catalyst Cu0.1Co3O4 for low-temperature catalytic decomposition of N2O. The preparation method of the catalyst includes the following steps:

[0118] Step 1: Take 10 g of cobalt nitrate hexahydrate (Co(NO3)2·6H2O) and 0.83 g of copper nitrate trihydrate (Cu(NO3)2·3H2O), dissolve them in 50 mL of deionized water, stir at room temperature for 15 min, and prepare a mixed metal salt solution with a Co ion concentration of 0.8 mol / L according to a molar ratio of Cu / Co = 0.1; take 26.5 g of sodium carbonate (Na2CO3), dissolve it in 500 mL of deionized water, and stir at room temperature for 15 min to prepare a precipitant Na2CO3 solution with a concentration of 0.5 mol / L;

[0119] Step 2: Place the mixed metal salt solution obtained in Step 1 in a constant temperature water bath at 40 °C and continue to stir at a stirring speed of 15 r / min, and dropwise add the precipitant Na2CO3 solution at a speed of 60 mL / h for 2 h ± 0.1 h until the pH of the reaction solution is 9.5;

[0120] Step 3: Transfer the reaction solution with pH = 9.5 obtained in Step 2 to a sealed high-temperature and high-pressure reactor for hydrothermal reaction. Control the temperature of the reactor at 200 °C, the stirring speed at 400 r / min, and the stirring time at 3 h;

[0121] Step 4: Wash the reaction solution after hydrothermal reaction in Step 3 with deionized water until it is neutral, and place it in an oven at 105 °C for drying for 3 h;

[0122] Step 5: Grind the sample obtained in Step 4 into powder, spread it evenly in a magnetic boat, and then place it in a muffle furnace. Heat it from room temperature to 500 °C at a heating rate of 5 °C / min, and calcine it at 500 °C for 3 h. After natural cooling to room temperature, press and screen it to 40 - 60 mesh to finally obtain the Cu0.1Co3O4 catalyst sample.

[0123] Test the catalytic activity of the above Cu0.1Co3O4 catalyst: Put the Cu0.1Co3O4 catalyst prepared in Comparative Example 6 into a quartz tube fixed-bed reactor for activity testing. Among them, the input simulated flue gas is: containing 7% of N2O, with He as the balance gas, and the gas flow rate is 50 mL / min; the reaction temperatures are 150 °C, 200 °C, 250 °C, 300 °C, 350 °C, 400 °C, 450 °C, 500 °C and 550 °C. Each temperature point is stabilized for 30 min, and the space velocity is 10000 h -1 。

[0124] According to the data in Table 1, with a molar ratio of Cu / Co = 0.1, the decomposition efficiency of N2O of the regulated Cu0.1Co3O4 catalyst can only reach 22.43% at 350 °C. The catalyst has a high activation temperature and poor low-temperature activity, and the active range is at a high temperature of 450 - 550 °C.

[0125] Comparative Example 7

[0126] This Comparative Example 7 provides a composite catalyst Ce0.1Co3O4 for low-temperature catalytic decomposition of N2O. The catalyst preparation method includes the following steps:

[0127] Step 1: Take 10 g of cobalt nitrate hexahydrate (Co(NO3)2·6H2O) and 1.46 g of cerium nitrate hexahydrate (Ce(NO3)3·6H2O) and dissolve them in 50 mL of deionized water. Stir at room temperature for 15 min to prepare a mixed metal salt solution with a Co ion concentration of 0.8 mol / L according to a molar ratio of Ce / Co = 0.1; take 26.5 g of sodium carbonate (Na2CO3) and dissolve it in 500 mL of deionized water. Stir at room temperature for 15 min to prepare a precipitant Na2CO3 solution with a concentration of 0.5 mol / L;

[0128] Step 2: Place the mixed metal salt solution obtained in Step 1 in a constant temperature water bath at 40 °C and continue stirring at a stirring speed of 15 r / min. Then, add the precipitant Na2CO3 solution at a rate of 60 mL / h for 2 h ± 0.1 h until the pH of the reaction solution reaches 9.5.

[0129] Step 3: Transfer the reaction solution with a pH of 9.5 obtained in Step 2 to a sealed high-temperature and high-pressure autoclave for hydrothermal reaction. Control the temperature of the autoclave at 200 °C, the stirring speed at 400 r / min, and the stirring time at 3 h.

[0130] Step 4: Wash the reaction solution after hydrothermal reaction in Step 3 with deionized water until it is neutral, and then place it in an oven at 105 °C for drying for 3 h.

[0131] Step 5: Grind the sample obtained in Step 4 into powder, spread it evenly in a porcelain boat, and then place it in a muffle furnace. Heat it from room temperature to 500 °C at a heating rate of 5 °C / min, and calcine it at 500 °C for 3 h. After natural cooling to room temperature, press and sieve it to 40 - 60 mesh to finally obtain the Ce0.1Co3O4 catalyst sample.

[0132] Test the catalytic activity of the above Ce0.1Co3O4 catalyst: Put the Ce0.1Co3O4 catalyst prepared in Comparative Example 7 into a quartz tube fixed-bed reactor for activity testing. Among them, the input simulated flue gas is: containing 7% N2O, with He as the balance gas, and the gas flow rate is 50 mL / min; the reaction temperatures are 150 °C, 200 °C, 250 °C, 300 °C, 350 °C, 400 °C, 450 °C, 500 °C, and 550 °C. Each temperature point is stabilized for 30 min, and the space velocity is 10000 h -1 。

[0133] According to the data in Table 1, with a molar ratio of Ce / Co = 0.1, the Ce0.1Co3O4 catalyst after regulation can achieve an N2O decomposition efficiency of up to 92.9% at 350 °C. The catalyst has a high activation temperature and poor low-temperature activity, and its activity is mainly manifested at high temperatures of 400 - 550 °C.

[0134] In summary, the performance of the Gd0.1Co3O4 catalyst prepared by the two-step synthesis method of coprecipitation + hydrothermal reaction is significantly better than that of Co3O4 without doping additives, and is also better than that of Co3O4 doped with K, Li, Mn, Cu, and Ce additives. By adjusting the Gd / Co molar ratio, the microscopic morphology and exposed active sites of the catalyst are regulated, which significantly improves the low-temperature performance of the catalyst. In this invention, the GdxCo3O4 catalyst is prepared by the two-step method of coprecipitation + hydrothermal reaction. By changing the Gd / Co molar ratio x, the active crystal plane and active sites of the catalyst are regulated, significantly improving the low-temperature catalytic decomposition performance of N2O of the catalyst. The process of this invention is simple and environmentally friendly. The prepared catalyst can be used to remove high-concentration N2O in the waste gas of the chemical industry such as adipic acid and caprolactam production at low temperature. The reaction temperature is low, the N2O conversion rate is high, the selectivity is high, the thermal stability is good, and it is environmentally friendly, achieving an important breakthrough in the field of low-temperature direct catalytic decomposition of N2O, and having broad engineering application prospects.

[0135] The above description is only a preferred embodiment of the present invention, and does not impose any other form of limitation on the present invention. Any modification or equivalent change made based on the technical essence of the present invention still falls within the scope claimed by the present invention.

Claims

1. A metal oxide catalyst for low temperature catalytic decomposition of N2O, characterized in that: The metal oxide catalyst is GdxCo3O4, wherein x represents a molar ratio of Gd to Co of 0.05-0.15:

1.

2. The catalyst according to claim 1, characterized in that The catalyst has a molar ratio of Gd / Co of 0.

1.

3. A method for preparing a catalyst as claimed in claim 1 or 2, characterized in that: The steps include: Step 1: First, dissolve a cobalt salt, i.e., Co salt, and a gadolinium salt, i.e., Gd salt, in deionized water, and stir for 10-15 minutes at room temperature; prepare the solution according to a molar ratio of Gd / Co of 0.05-0.15, and ensure that the concentration of cobalt ions in the mixed solution is maintained in the range of 0.5-1.5 mol / L; at the same time, dissolve a soluble carbonate, bicarbonate, or hydroxide in deionized water, and stir for 10-15 minutes at room temperature to prepare a precipitant solution with a concentration of 0.4-0.6 mol / L; Step 2: Place the mixed metal salt solution prepared in step 1 in a constant temperature water bath at 30-50°C and continue stirring, and dropwise add the above precipitant solution at a rate of 40-80 mL / h for a duration of 2±0.1 h; adjust the pH value of the reaction solution through this process to eventually reach a range of 8-10; Step 3: The reaction solution obtained in step 2 is transferred to a sealed reactor for hydrothermal reaction synthesis; during this process, the temperature in the reactor is controlled to be 160-220° C., the stirring speed is set to 300-500 r / min, and the stirring time is maintained at 2-4 h; Step 4: The reaction solution obtained in step 3 is washed with deionized water until it is neutral, and then placed in an oven at 100-120° C. for 4-6 hours; Step 5: Grind the sample obtained in step 4 into powder and spread it evenly in a magnetic boat, then put it into a muffle furnace, calcine it at 400-600°C for 3-5h, and then naturally cool it to room temperature to obtain a GdxCo3O4 catalyst.

4. The method according to claim 3, characterized in that The cobalt salt in step 1 is an inorganic cobalt salt or an organic cobalt salt. The inorganic Co salt includes at least one of Co(OH)2, CoCO3, Co(NO3)2·6H2O, CoSO4·6H2O and CoCl2·6H2O; the organic Co includes at least one of cobalt acetate, cobalt cyclohexaneate, cobalt stearate and cobalt neodecanoate.

5. The method according to claim 3, characterized in that: The Gd salt in step 1 includes at least one of Gd(NO3)3·6H2O, GdCl3·6H2O and C3Gd2O9.

6. The method according to claim 3, characterized in that The Gd / Co molar ratio in step 1 is at least one of 0.05, 0.06, 0.07, 0.08, 0.09, 0.10, 0.11, 0.12, 0.13, 0.14 and 0.

15.

7. Use of the catalyst according to claim 1 or 2, characterized in that: The catalyst is placed in a quartz tube fixed bed reactor, and the flue gas composition includes 5vol.%-30vol.% N2O, 0-21vol.% O2, 0-3vol.% CO2 and 0-2vol.% H2O, with He as the balance gas. The gas flow rate of the flue gas is set to 25-200mL / min. The catalytic reaction temperature is controlled in the range of 150℃-550℃, and the stabilization time is maintained at each temperature for 30-60 minutes. The temperatures are 150℃, 200℃, 250℃, 300℃, 350℃, 400℃, 450℃, and 500℃ respectively; the space velocity range of the flue gas is 5000-20000h -1 .

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