Catalyst for low-temperature catalytic decomposition of N2O, preparation method and use thereof

Abstract

The present invention relates to a catalyst for the low-temperature catalytic decomposition of N2O, as well as a preparation method and use. The present invention utilizes a two-step process, coprecipitation followed by hydrothermal reaction, to prepare the Co3O4 catalyst. By adjusting the amount of precipitant added, the addition rate, and the N2O pressure applied to the catalyst to control the micromorphology and exposed active crystal faces, the catalyst's low-temperature catalytic decomposition of N2O is significantly improved. Using the Co3O4 catalyst at low temperatures, the present invention can catalytically decompose N2O in adipic acid industrial tail gas into harmless N2 and O2. The catalyst exhibits a high N2O removal rate, high selectivity, high stability, and environmental friendliness. This significantly reduces the catalyst reaction temperature and the cost of tail gas catalytic treatment, resulting in significant practical significance and engineering application value.

Description

Technical Field

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

[0002] N2O is a colorless, odorless, chemically stable greenhouse gas with a global warming potential (GWP) 310 times that of CO2. It also severely damages the ozone layer, endangering human health and the ecological environment. Currently, N2O emissions are increasing annually at an annual rate of 0.2%-0.3%. Every doubling of N2O emissions will cause a global temperature rise of 0.3°C. Industrial N2O production accounts for approximately 15% of total anthropogenic emissions, primarily from the production of adipic acid and nitric acid. Therefore, controlling N2O emissions from industrial exhaust has received widespread attention.

[0003] Currently, processes for controlling N2O emissions from industrial exhaust gases include thermal decomposition, direct catalytic decomposition, and selective reduction. Direct catalytic decomposition is the most widely used, using a catalyst within a temperature window of 450-550°C to decompose N2O into N2 and O2. The core of this process is the catalyst, but currently available catalysts suffer from high reaction temperatures, narrow temperature windows, low selectivity, and susceptibility to deactivation. Transition metal Co oxides, due to their unique crystal structure and strong redox properties, exhibit excellent catalytic activity in N2O decomposition reactions and have been widely studied.

[0004] For example, CN115739090A discloses a method for preparing a transition metal oxide catalyst using a surfactant-assisted sol-gel method, which includes processes such as the addition of a surfactant and an inorganic acid, the shaping of a precipitate, and catalyst activation, wherein the catalyst is one or more of Co, Ni, and Cu as active components. The method specifically dissolves 3.0g of a surfactant in deionized water, adds 2.4g of an inorganic acid, is stirred at room temperature until dissolved, then adds a transition metal nitrate, is stirred in a water bath to form a gel that is difficult to stir, and then the resulting mixture is dried and calcined to obtain the target catalyst. However, the method has the drawback that it involves the addition of an activator and an inorganic acid, and the preparation cost is high; the catalyst activation process needs to be calcined at different temperatures for different times, and the preparation process is cumbersome.

[0005] CN 115430453A discloses a method for preparing a transition metal oxide Co3O4 catalyst for low-temperature decomposition of N2O. The method employs acid treatment to modify the micromorphology, resulting in a uniform distribution of Co crystals and an increase in active sites on the catalyst surface. This transition metal oxide catalyst for low-temperature catalytic decomposition of N2O comprises the following steps: dispersing a transition metal oxide matrix in an acid solution, subjecting it to acid treatment, separating it, and drying and calcining the resulting precipitate to obtain the target product. However, this method requires the addition of nitric acid to the previously prepared Co3O4 catalyst, followed by ultrasonic treatment, and further high-temperature calcination to obtain the final Co metal oxide catalyst. This complex preparation process can easily generate difficult-to-treat acidic wastewater.

[0006] CN 112138725A discloses a method for preparing a cobalt-based metal-organic framework-derived catalyst for catalytically decomposing N₂O. The method involves dissolving 2-methylimidazole and a proton-removing agent in deionized water, adding a Co(NO₃)₂·6H₂O solution with thorough stirring, and then allowing the mixture to stand at room temperature for 10 minutes. The solid precipitate is then centrifuged and washed, and then dried to prepare a precursor of a zeolitic imidazolate framework structure. The catalyst is then calcined at high temperature to obtain the cobalt-based metal-organic framework-derived catalyst. However, this method involves a coordination control agent and a proton-removing agent, and requires high-temperature calcination in a nitrogen atmosphere, placing high demands on the preparation process.

[0007] CN 113996305A discloses a method for preparing a composite oxide catalyst for catalytic decomposition of N2O at medium and low temperatures. The catalyst's active components include one or more of Co3O4, NiO, and CuO, and a promoter is either a rare earth metal Gd or an alkali metal K, thereby enhancing the catalyst's low-temperature activity. However, this preparation method requires the additional addition of two promoters, alkali metal K and rare earth metal Gd, which is costly.

[0008] For example, Xiong et al. (Environment Science & Technology. 2021, 55, 13335-13344) found that the particle size of pure Co3O4 metal oxide catalyst is 27.9 nm, and the main exposed crystal planes are (111) and (311). After doping with Gd, the catalyst particle size is reduced to 4.9 nm, and more crystal planes are exposed, including crystal plane (400), crystal plane (440) and crystal plane (511), and the activity is further improved. Zasada et al. (The Journal of Physical Chemistry. 2011, 115, 6423-6432) studied the surface energy of the (100), (111) and (110) crystal planes on Co3O4 catalysts through density functional calculation (DFT), and the results follow the following order: 1.38 J m -2 (100)<1.48J m-2 (111)<1.65J m -2 (110), (110) crystal plane has the highest surface energy and is more conducive to the decomposition of N2O. Differently, Klegova et al. (Applied Catalysis B:Environment.2019,255,117745) found that in the process of N2O catalytic decomposition, the activity of crystal plane (100) was better than that of crystal plane (111), and by doping Mn and Al, the exposure ratio of crystal plane (100) was increased, thereby promoting the N2O decomposition activity of Co catalyst. Gudyka et al. (Applied Catalysis B:Environmental.2017,201,339-347) used glycerol to assist in the preparation of Co3O4 / α-Al2O3 catalyst, which promoted the dispersion of Co nanocrystals and increased the exposure area of ​​active crystal plane (100).

[0009] In summary, current research on Co₃O₄ catalysts, including complex preparation methods and inconsistent results regarding active crystal faces, leads to significant discrepancies in activity. Consequently, overcoming the shortcomings of existing catalysts and enabling them to achieve high activity at low temperatures, low cost, environmentally friendly production, and suitability for treating high-concentration N₂O exhaust, has become a pressing challenge in current technological development. Summary of the Invention

[0010] To address the aforementioned technical problems, the present invention provides a catalyst, preparation method, and use for the low-temperature catalytic decomposition of N2O. The catalyst is prepared via a two-step process of coprecipitation and hydrothermal reaction without the addition of additives. The catalyst's exposed active crystal faces are primarily (040), resulting in an N2O decomposition efficiency of 80% at 250°C and above 98% between 300°C and 550°C. This overcomes the drawbacks of the prior art, such as the complex preparation process and high cost.

[0011] The present invention provides a catalyst for low-temperature catalytic decomposition of N2O. The catalyst is Co3O4, and the exposed active crystal faces include at least one of (040), (110), (111), (440), (311) and (220).

[0012] Furthermore, the active crystal face exposed by the catalyst is a single crystal face (040).

[0013] The present invention also provides a method for preparing the aforementioned catalyst, the preparation method comprising the following steps:

[0014] Step 1: Dissolve Co salt in deionized water, stir at room temperature for 15-30 minutes, and prepare a Co salt solution with a Co ion concentration of 2-3 mol / L; dissolve soluble carbonate or bicarbonate in deionized water, stir at room temperature for 30-45 minutes, and prepare a carbonate or bicarbonate solution with a concentration of 0.4-0.6 mol / L as a precipitant;

[0015] Step 2: Place the Co salt solution obtained in step 1 in a constant temperature water bath at 30-50°C and continue stirring, and add the carbonate or bicarbonate solution dropwise, first slowly adding the carbonate or bicarbonate solution at a rate of 50-75 mL / h for 1±0.5h, then quickly adding the carbonate or bicarbonate solution at a rate of 95-145 mL / h, and finally adjusting the pH value of the reaction solution to 9-11;

[0016] Step 3: Transfer the reaction solution obtained in step 2 to a sealed high-temperature and high-pressure reactor for hydrothermal reaction synthesis, control the temperature of the reactor to 180-220° C., stir at a speed of 350-450 r / min, and stir for 2-4 h;

[0017] Step 4: The reaction solution obtained in step 3 is washed with deionized water until neutral, and then placed in an oven at 100-120° C. for 4-6 hours;

[0018] Step 5: Grind the sample obtained in step 4 into powder and spread it flat on a magnetic boat. Then place it in a muffle furnace and calcine it at 480-520°C for 2-4h. Then cool it naturally to room temperature to obtain a Co3O4 catalyst.

[0019] Furthermore, in step 1, the Co salt comprises an inorganic Co salt or an organic Co salt.

[0020] Furthermore, in step 1, the inorganic Co salt includes at least one of Co(OH)2, CoCO3, Co(NO3)2·6H2O, CoSO4·6H2O and CoCl2·6H2O.

[0021] Furthermore, in step 1, the organic Co salt includes at least one of cobalt naphthenate, cobalt stearate and cobalt neodecanoate.

[0022] Furthermore, in step 1, the soluble carbonate or bicarbonate includes at least one of Na2CO3, K2CO3, NaHCO3 and KHCO3.

[0023] Furthermore, in step 2, the stirring speed of the constant temperature water bath is 15-30 r / min.

[0024] Furthermore, in step 2, the time for rapidly adding the carbonate or bicarbonate solution is 30 to 40 minutes.

[0025] Furthermore, in step 3, N2O with a purity of 100% is introduced into the sealed high-temperature and high-pressure reactor, so that the reactor is pressurized to 0.5-1 MPa.

[0026] Furthermore, in step 5, the sample in step 4 is heated from room temperature to 480-520° C. at a heating rate of 5° C. / min.

[0027] The present invention also provides a use of the above-mentioned catalyst for catalyzing N2O at low temperature, wherein the catalyst is placed in a quartz tube fixed bed reactor, the input flue gas contains 5-10% N2O, 3-10% O2, 0-3% CO2, 0-2% H2O, He is the balance gas, and the gas flow rate of the flue gas is 25-200 mL / min; the catalytic reaction temperature is controlled to be 150-550°C, each temperature interval is stabilized for 30-60 minutes, and the space velocity of the flue gas is 5000-20000 h -1 .

[0028] The beneficial effects of the present invention are:

[0029] 1. The catalyst Co3O4 of the present invention was characterized by SEM. The microstructure at 100 nm showed strip-shaped particles and the active sites were further increased, indicating that the Co3O4 catalyst prepared by combining coprecipitation and hydrothermal reaction promoted crystal growth. The exposed active crystal faces included (040), especially the single crystal face (040).

[0030] 2. Conventional Co3O4 prepared in the prior art achieves a 100% N2O decomposition efficiency at 450-550°C, with the active crystal faces of the catalyst primarily being (100), (111), and (110). The Co3O4 catalyst prepared in the present invention, without the need for additives, has the primary exposed active crystal face being (040). The N2O decomposition efficiency can reach 80% at 250°C and maintain over 98% between 300-550°C.

[0031] 3. The enhanced activity of the Co₃O₄ catalyst stems from changes in the micromorphology and exposed active crystal faces of the Co₃O₄ catalyst. In the reaction 2N₂O → 2N₂ + O₂, gaseous N₂O adsorbs onto active sites on the catalyst surface, breaking the NO bond to form N₂ and O. The dissociation of O at the active sites is the rate-limiting step in the reaction and is closely related to the exposed active crystal faces of the catalyst. The higher the surface energy of the exposed active crystal faces, the easier it is for O to dissociate, resulting in higher activity.

[0032] 4. The exposed active crystal face of the catalyst of the present invention is a single crystal face (040), which is prepared by a two-step method of coprecipitation and hydrothermal reaction. It is found that the Co3O4 catalyst prepared by the catalyst has outstanding performance in catalytic decomposition of N2O, which is superior to the synthesis preparation methods of single coprecipitation and single hydrothermal reaction. Especially at low temperatures, the N2O decomposition efficiency can reach 98% at 350°C. The micromorphology of the catalyst at the same scale of 100nm was observed by SEM characterization. It was found that the Co3O4 catalyst prepared by single coprecipitation showed a relatively dense micromorphology and a small particle area; while the Co3O4 catalyst prepared by single hydrothermal reaction had a dispersed micromorphology, an increase in active sites, and a larger particle area. The Co3O4 catalyst prepared by combining coprecipitation and hydrothermal reaction showed strip-shaped particles and a further increase in active sites, indicating that hydrothermal reaction promoted crystal growth. Furthermore, combined with TEM characterization analysis, it was found that the main exposed active crystal face of the Co3O4 catalyst prepared by co-precipitation alone was (111), the active crystal face exposed by the catalyst prepared by hydrothermal alone was (110), and the active crystal face exposed by the catalyst prepared by co-precipitation and hydrothermal combination was a single crystal face (040).

[0033] 5. The present invention unexpectedly discovered that the dripping speed can significantly affect the microscopic morphology of the Co3O4 catalyst surface, especially the exposure of different active crystal faces. The present invention adopts a dripping speed of 50-75mL / h first and then 95-145mL / h, and adjusts the pH value to the optimal 9-11, which can significantly improve the low-temperature performance of the catalyst. The prepared Co3O4 catalyst can reach 80% at 250°C. Through SEM characterization and observation of the microscopic morphology of the catalyst at the same scale of 100nm, it was found that the Co3O4 catalyst prepared by variable speed dripping precipitant has more strip-shaped particles, which are denser and more regular, indicating that the active sites are increased and the growth of crystals is promoted. The active crystal face exposed by the catalyst of the present invention is (040), which is more single and has a higher proportion, indicating that the crystal face (040) is a highly active crystal face and is a key factor in promoting the improvement of the catalyst's performance in decomposing N2O.

[0034] 6. The present invention discovered that introducing N2O into the reactor during pressurization can regulate the crystallization reaction of the precursor and form N2O-friendly crystal faces, thereby further improving the performance of the Co3O4 catalyst. The decomposition efficiency can reach 60% at 200°C and more than 80% at 250°C, with outstanding low-temperature performance.

[0035] 7. The present invention provides a method for preparing a catalyst for low-temperature catalytic decomposition of N2O. Compared with existing catalysts, the preparation method of the present invention can achieve low-temperature and high-performance catalysts, can continuously solve the problem of tail gas emissions from the adipic acid industry, make it meet industrial emission standards, and reduce the cost of tail gas treatment for enterprises. It has important practical significance and engineering application value. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 The figure is a flow chart of the preparation process of the catalyst of the present invention.

[0037] Figure 2 1 and 2 and comparative examples 1-3 show the efficiency curves of the catalysts for decomposing N2O.

[0038] Figure 3 These are SEM images of the catalysts obtained in Example 1 of the present invention and Comparative Examples 1-3.

[0039] Figure 4 TEM images of the catalysts obtained in Example 1 and Comparative Examples 1-3 of the present invention. DETAILED DESCRIPTION

[0040] The present invention will be further described below with reference to the examples, but the present invention is not limited to the following examples.

[0041] Example 1

[0042] like Figure 1 and Figure 4 As shown, this embodiment 1 provides a catalyst Co3O4 for catalytic decomposition of N2O at low temperature, wherein the exposed active crystal face is a single crystal face (040). The specific steps of the preparation method are as follows:

[0043] Step 1: Dissolve 10g of cobalt nitrate hexahydrate (Co(NO3)2.6H2O) in 50mL of deionized water and stir at room temperature for 30min to prepare a Co(NO3)2 solution with a Co ion concentration of 2.5mol / L; dissolve 26.5g of sodium carbonate (Na2CO3) in 500mL of deionized water and stir at room temperature for 45min to prepare a precipitant Na2CO3 solution with a concentration of 0.5mol / L;

[0044] Step 2: Place the Co(NO3)2 solution obtained in step 1 in a constant temperature water bath at 40°C and continue stirring at a stirring speed of 20 r / min, and add the precipitant Na2CO3 solution dropwise, first slowly adding it for 1 hour at a speed of 60 mL / h, then quickly adding it at a speed of 120 mL / h until the pH of the reaction solution reaches 9.5-10.5;

[0045] Step 3: The reaction solution with a pH of 9.5-10.5 obtained in step 2 was transferred to a sealed high-temperature and high-pressure reactor for hydrothermal reaction. The temperature of the reactor was controlled at 200° C., the stirring speed was 400 r / min, and the stirring time was 3 h.

[0046] Step 4: The reaction solution after the hydrothermal reaction in step 3 was washed with deionized water until neutral, and then dried in an oven at 105°C for 5 hours;

[0047] Step 5: Grind the sample obtained in step 4 into powder and spread it flat on a magnetic boat. Then place it in a muffle furnace, raise the temperature from room temperature to 500°C at a heating rate of 5°C / min, and calcine at a constant temperature of 500°C for 3 hours. After naturally cooling to room temperature, press the tablets and sieve them to 25-40 mesh to finally obtain the Co3O4 catalyst sample.

[0048] The catalytic activity of the above-mentioned Co3O4 catalyst was tested: the Co3O4 catalyst prepared in Example 1 was placed in a quartz tube fixed bed reactor for activity testing, wherein the input simulated flue gas contained 7% N2O, He was used as the balance gas, and the gas flow rate was 50 mL / min; the catalytic reaction temperature was controlled to be 150-550°C, each temperature was stabilized for 30 minutes, and the space velocity was 10000 h -1 .

[0049] The catalytic decomposition efficiency of the Co3O4 catalyst prepared in Example 1 at different temperatures (150°C, 200°C, 250°C, 300°C, 350°C, 400°C, 450°C, 500°C, 550°C) is shown in Table 1. Figure 2 It can be seen that the N2O decomposition efficiency can reach 80% at 250℃ and can maintain more than 98% decomposition efficiency between 300-550℃. The content of by-products NO and NO2 in the tail gas is less than 25ppm, and the catalyst selectivity is higher than 99.99%. x , lower than the NO specified in GB 31571-2015 "Petrochemical Industry Pollutant Emission Standard" x Emission limit 180mg / m 3 In accordance with the requirements of Example 1, the tail gas can be directly discharged into the atmosphere. The main reaction formula involved in the decomposition of N2O is:

[0050] 2N2O=2N2+O2,

[0051] Example 1 reduces the reaction temperature for catalytic decomposition of N2O, broadens the temperature window, saves the heat required for heating the exhaust gas, and achieves a 100% N2O conversion rate. This can accelerate the treatment of adipic acid exhaust gas and can be used with upstream enterprises that continuously produce adipic acid on a large scale, continuously and quickly performing harmless treatment of adipic acid industrial exhaust gas to meet environmental protection requirements.

[0052] Table 1 Decomposition efficiency of N2O catalyzed by the catalysts prepared in Examples and Comparative Examples

[0053]

[0054] Example 2

[0055] like Figure 1As shown, this embodiment 2 provides a catalyst Co3O4 for catalytic decomposition of N2O at low temperature, wherein the exposed active crystal face is a single crystal face (040). The specific steps of the preparation method are as follows:

[0056] Step 1: Dissolve 10g of cobalt nitrate hexahydrate (Co(NO3)2.6H2O) in 50mL of deionized water and stir at room temperature for 30min to prepare a Co(NO3)2 solution with a Co ion concentration of 2.5mol / L; dissolve 26.5g of sodium carbonate (Na2CO3) in 500mL of deionized water and stir at room temperature for 45min to prepare a precipitant Na2CO3 solution with a concentration of 0.5mol / L;

[0057] Step 2: Place the Co(NO3)2 solution obtained in step 1 in a constant temperature water bath at 40°C and continue stirring at a stirring speed of 20 r / min, and add the precipitant Na2CO3 solution dropwise, first slowly adding it for 1 hour at a speed of 60 mL / h, then quickly adding it at a speed of 120 mL / h until the pH of the reaction solution reaches 9.5-10.5;

[0058] Step 3: The reaction solution with a pH of 9.5-10.5 obtained in step 2 was transferred to a sealed high-temperature and high-pressure reactor for hydrothermal reaction, and 100% pure N2O was introduced for pressurization to 0.6 MPa;

[0059] The pressurized reaction solution was transferred to a sealed high-temperature and high-pressure reactor for hydrothermal reaction. The temperature of the reactor was controlled at 200°C, the stirring speed was 400 r / min, and the stirring time was 3 h.

[0060] Step 4: The reaction solution after the hydrothermal reaction in step 3 was washed with deionized water until neutral, and then dried in an oven at 105°C for 5 hours;

[0061] Step 5: Grind the sample obtained in step 4 into powder and spread it flat on a magnetic boat. Then place it in a muffle furnace, raise the temperature from room temperature to 500°C at a heating rate of 5°C / min, and calcine at a constant temperature of 500°C for 3 hours. After naturally cooling to room temperature, press the tablets and sieve them to 25-40 mesh to finally obtain the Co3O4 catalyst sample.

[0062] The catalytic activity of the Co3O4 catalyst was tested by placing the Co3O4 catalyst prepared in Example 2 into a quartz tube fixed bed reactor for activity testing. The simulated flue gas input contained 7% N2O, with He as the balance gas and a gas flow rate of 50 mL / min. The reaction temperature was 150-550°C, and each temperature was stabilized for 30 minutes. The space velocity was 10,000 h / min. -1 .

[0063] The catalytic decomposition efficiency of the Co3O4 catalyst prepared in Example 2 at different temperatures (150°C, 200°C, 250°C, 300°C, 350°C, 400°C, 450°C, 500°C, 550°C) is shown in Table 1. Figure 2 As can be seen in the figure, the performance of the Co3O4 catalyst is further improved after N2O pressure regulation, with the N2O decomposition efficiency reaching 93% at 250°C and maintaining over 99.9% between 300-550°C. N2O pressure regulation exposes more active crystal faces in the Co3O4 catalyst.

[0064] Comparative Example 1

[0065] like Figure 4 As shown, this comparative example 1 provides a catalyst Co3O4 for catalytic decomposition of N2O at low temperature, and the exposed active crystal face is (110).

[0066] Step 1: Dissolve 10g of cobalt nitrate hexahydrate (Co(NO3)2.6H2O) in 50mL of deionized water and stir at room temperature for 30min to prepare a Co(NO3)2 solution with a Co ion concentration of 2.5mol / L; dissolve 26.5g of sodium carbonate (Na2CO3) in 500mL of deionized water and stir at room temperature for 45min to prepare a precipitant Na2CO3 solution with a concentration of 0.5mol / L;

[0067] Step 2: Place the Co(NO3)2 solution obtained in step 1 in a constant temperature water bath at 40°C and continue stirring at a stirring speed of 20 r / min, and add the precipitant Na2CO3 solution dropwise at a dropping speed of 60 mL / h until the pH of the reaction solution reaches 9.5-10.5;

[0068] Step 3: The reaction solution with a pH of 9.5-10.5 obtained in step 2 was transferred to a sealed high-temperature and high-pressure reactor for hydrothermal reaction at a temperature of 200° C., a stirring speed of 400 r / min, and a stirring time of 3 h;

[0069] Step 4: The reaction solution after the hydrothermal reaction in step 3 was washed with deionized water until neutral, and dried in an oven at 105°C for 5 hours;

[0070] Step 5: Grind the sample obtained in step 4 into powder and spread it flat on a magnetic boat. Then place it in a muffle furnace, raise the temperature from room temperature to 500°C at a heating rate of 5°C / min, and calcine at a constant temperature of 500°C for 3 hours. After naturally cooling to room temperature, press the tablets and sieve them to 25-40 mesh to finally obtain the Co3O4 catalyst sample.

[0071] The catalytic activity of the above-mentioned Co3O4 catalyst was tested by placing the prepared Co3O4 catalyst into a quartz tube fixed-bed reactor for activity testing. The input simulated flue gas contained 7% N2O, He was used as the balance gas, and the gas flow rate was 50 mL / min. The reaction temperature was 150-550°C, and each temperature was stabilized for 30 minutes. The space velocity was 10000 h-1. -1 .

[0072] The catalytic decomposition efficiency of the Co3O4 catalyst prepared in Comparative Example 1 at different temperatures (150°C, 200°C, 250°C, 300°C, 350°C, 400°C, 450°C, 500°C, 550°C) is shown in Table 1. Figure 2 It can be seen that the N2O decomposition efficiency is only 55% at 350℃. The catalyst has a high activation temperature and poor low-temperature activity. Its activity is mainly manifested at high temperatures of 400-550℃.

[0073] Comparative Example 2

[0074] like Figure 4 As shown, this comparative example 2 provides a catalyst Co3O4 for catalytic decomposition of N2O at low temperature, wherein the exposed active crystal faces are (111), (311) and (440). The catalyst is prepared by a co-precipitation method, which comprises the following steps:

[0075] Step 1: Dissolve 10g of cobalt nitrate hexahydrate (Co(NO3)2.6H2O) in 50mL of deionized water and stir at room temperature for 30min to prepare a Co(NO3)2 solution with a Co ion concentration of 2.5mol / L; dissolve 26.5g of sodium carbonate (Na2CO3) in 500mL of deionized water and stir at room temperature for 45min to prepare a precipitant Na2CO3 solution with a concentration of 0.5mol / L;

[0076] Step 2: Place the Co(NO3)2 solution obtained in step 1 in a constant temperature water bath at 40°C and continue stirring at a speed of 20 r / min, and add the precipitant Na2CO3 solution dropwise at a speed of 60 mL / h until the pH of the Co(NO3)2 solution reaches 9.5-10.5, and continue stirring for 3 hours;

[0077] Step 3: The Co(NO3)2 solution with a pH of 9.5-10.5 obtained in step 2 was washed with deionized water until neutral and dried in an oven at 105°C for 5 hours;

[0078] Step 4: Grind the sample obtained in step 3 into powder and spread it flat on a magnetic boat. Then place it in a muffle furnace, raise the temperature from room temperature to 500°C at a heating rate of 5°C / min, and calcine at a constant temperature of 500°C for 3 hours. After naturally cooling to room temperature, press the tablets and sieve them to 25-40 mesh to finally obtain the Co3O4 catalyst sample.

[0079] The catalytic activity of the above-mentioned Co3O4 catalyst was tested by placing the prepared Co3O4 catalyst into a quartz tube fixed-bed reactor for activity testing. The input simulated flue gas concentration contained 7% N2O, He was used as the balance gas, and the gas flow rate was 50 mL / min. The reaction temperature was 150-550°C, and each temperature range was stabilized for 30 minutes. The space velocity was 10,000 h-1. -1 .

[0080] The catalytic decomposition efficiency of Co3O4 catalyst prepared in Comparative Example 2 at different temperatures (150℃, 200℃, 250℃, 300℃, 350℃, 400℃, 450℃, 500℃, 550℃) is shown in Table 1. Figure 2 It can be seen that the N2O decomposition efficiency is only 85% at 400℃. The catalyst has a high activation temperature and poor low-temperature activity, and its activity range is 400-550℃.

[0081] Comparative Example 3

[0082] like Figure 4 As shown, this comparative example 3 provides a catalyst Co3O4 for catalytic decomposition of N2O at low temperature, wherein the exposed active crystal faces are (110) and (220). The catalyst is prepared by a one-step hydrothermal synthesis method, which comprises the following steps:

[0083] Step 1: Dissolve 10g of cobalt nitrate hexahydrate (Co(NO3)2.6H2O) in 50mL of deionized water and stir at room temperature for 30min to prepare a Co(NO3)2 solution with a Co ion concentration of 2.5mol / L; dissolve 26.5g of sodium carbonate (Na2CO3) in 500mL of deionized water and stir at room temperature for 45min to prepare a precipitant Na2CO3 solution with a concentration of 0.5mol / L;

[0084] Step 2: directly mix the Co(NO3)2 solution and the Na2CO3 solution obtained in step 1, and then transfer them to a sealed high-temperature and high-pressure reactor for hydrothermal reaction. The reactor temperature is 200°C, the stirring speed is 400 r / min, and the stirring time is 3 hours;

[0085] Step 3: The reaction solution after the hydrothermal reaction in step 2 was washed with deionized water until neutral, and then dried in an oven at 105°C for 5 hours;

[0086] Step 4: Grind the sample obtained in step 3 into powder and spread it flat on a magnetic boat. Then place it in a muffle furnace, raise the temperature from room temperature to 500°C at a heating rate of 5°C / min, and calcine at a constant temperature of 500°C for 3 hours. After naturally cooling to room temperature, press the tablets and sieve them to 25-40 mesh to finally obtain the Co3O4 catalyst sample.

[0087] The catalytic activity of the above-mentioned Co3O4 catalyst was tested by placing the prepared Co3O4 catalyst into a quartz tube fixed-bed reactor for activity testing. The input simulated flue gas contained 7% N2O, He was used as the balance gas, and the gas flow rate was 50 mL / min. The reaction temperature was 150-550°C, and each temperature was stabilized for 30 minutes. The space velocity was 10000 h-1. -1 .

[0088] The catalytic decomposition efficiency of Co3O4 catalyst prepared in Comparative Example 2 at different temperatures (150℃, 200℃, 250℃, 300℃, 350℃, 400℃, 450℃, 500℃, 550℃) is shown in Table 1. Figure 2 It can be seen that the decomposition efficiency of N2O can reach 87% at 400℃. The catalyst has a high activation temperature and poor low-temperature activity. Its activity is mainly manifested at high temperatures of 400-550℃.

[0089] Figure 3 The following are SEM images of the catalysts obtained in Example 1 and Comparative Examples 1-3 of the present invention. Example 1 is a Co3O4 catalyst prepared by variable-speed coprecipitation and hydrothermal treatment. The hydrothermal process promotes the growth of crystal faces, increases the particle size, and mainly presents an elongated shape. The particles are evenly dispersed, exposing more active sites. Comparative Example 1 is a Co3O4 catalyst prepared by uniform-speed coprecipitation and hydrothermal treatment. The hydrothermal process promotes the growth of crystal faces, increases the particle size, and mainly presents an elongated shape. However, the dispersion is uneven, with gaps and overlaps, and the active sites are not fully exposed. Comparative Example 2 is a Co3O4 catalyst prepared by uniform-speed coprecipitation, which exhibits a dense microscopic morphology of small particles with a single shape and dense distribution. Comparative Example 3 is a Co3O4 catalyst prepared by hydrothermal treatment. The crystal faces grow, but the shapes are diverse, the surface gaps are large, and the dispersion is uneven.

[0090] In summary, the performance of the Co3O4 catalyst prepared by the two-step method of coprecipitation followed by hydrothermal reaction is better than that of the single coprecipitation and hydrothermal reaction preparation methods. Adjusting the amount of precipitant Na2CO3 added can affect the N2O decomposition performance of the catalyst. Changing the drop rate of the precipitant Na2CO3 and the N2O pressure regulation can further significantly regulate the micromorphology and exposed active crystal faces of the catalyst, and significantly improve the low-temperature performance of the catalyst. The catalyst preparation method of the embodiment of the present invention produces a Co3O4 catalyst with low-temperature high activity by controlling the preparation parameters, catalytically decomposing N2O into harmless N2 and O2, achieving the purpose of treating N2O in adipic acid tail gas. The N2O removal rate is high, the selectivity is high, and it is environmentally friendly. It can significantly reduce the cost of tail gas catalytic treatment and has important practical significance and engineering application value.

[0091] The above description is merely a preferred embodiment of the present invention and does not constitute any other form of limitation to the present invention. Any modification or equivalent variation based on the technical essence of the present invention shall still fall within the scope of protection claimed by the present invention.

Claims

1. A catalyst for low-temperature catalytic decomposition of N2O, characterized in that: The catalyst is Co3O4, and the exposed active crystal face is (040); The preparation method comprises the following steps: Step 1: Dissolve Co salt in deionized water and stir at room temperature for 15-30 minutes to prepare a Co salt solution with a Co ion concentration of 2-3 mol / L; dissolve soluble carbonate or bicarbonate in deionized water and stir at room temperature for 30-45 minutes to prepare a carbonate or bicarbonate solution with a concentration of 0.4-0.6 mol / L as a precipitant; Step 2: Place the Co salt solution obtained in step 1 in a constant temperature water bath at 30-50°C and continue stirring, and add the carbonate or bicarbonate solution dropwise, first slowly adding the carbonate or bicarbonate solution at a rate of 50-75 mL / h for 1±0.5 h, then quickly adding the carbonate or bicarbonate solution at a rate of 95-145 mL / h, and finally adjusting the pH value of the reaction solution to 9-11; Step 3: Transfer the reaction solution obtained in step 2 to a sealed high-temperature and high-pressure reactor for hydrothermal reaction synthesis, control the temperature of the reactor to 180-220° C., stir at a speed of 350-450 r / min, and stir for 2-4 h; Step 4: The reaction solution obtained in step 3 was washed with deionized water until neutral, and then dried 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 flat on a magnetic boat. Then place it in a muffle furnace and calcine it at 480-520°C for 2-4 h. Then cool it naturally to room temperature to obtain a Co3O4 catalyst.

2. The catalyst according to claim 1, characterized in that The catalyst has a decomposition efficiency of N2O exceeding 80% at 250°C and a decomposition efficiency exceeding 98% at temperatures between 300°C and 550°C.

3. A method for preparing the catalyst according to any one of claims 1 to 2, characterized in that: The preparation method comprises the following steps: Step 1: Dissolve Co salt in deionized water and stir at room temperature for 15-30 minutes to prepare a Co salt solution with a Co ion concentration of 2-3 mol / L; dissolve soluble carbonate or bicarbonate in deionized water and stir at room temperature for 30-45 minutes to prepare a carbonate or bicarbonate solution with a concentration of 0.4-0.6 mol / L as a precipitant; Step 2: Place the Co salt solution obtained in step 1 in a constant temperature water bath at 30-50°C and continue stirring, and add the carbonate or bicarbonate solution dropwise, first slowly adding the carbonate or bicarbonate solution at a rate of 50-75 mL / h for 1±0.5 h, then quickly adding the carbonate or bicarbonate solution at a rate of 95-145 mL / h, and finally adjusting the pH value of the reaction solution to 9-11; Step 3: Transfer the reaction solution obtained in step 2 to a sealed high-temperature and high-pressure reactor for hydrothermal reaction synthesis, control the temperature of the reactor to 180-220° C., stir at a speed of 350-450 r / min, and stir for 2-4 h; Step 4: The reaction solution obtained in step 3 was washed with deionized water until neutral, and then dried 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 flat on a magnetic boat. Then place it in a muffle furnace and calcine it at 480-520°C for 2-4 h. Then cool it naturally to room temperature to obtain a Co3O4 catalyst.

4. The preparation method according to claim 3, characterized in that In step 1, the Co salt comprises an inorganic Co salt or an organic Co salt.

5. The preparation method according to claim 4, characterized in that In step 1, the inorganic Co salt includes at least one of Co(OH)2, CoCO3, Co(NO3)2·6H2O, CoSO4·6H2O and CoCl2·6H2O.

6. The preparation method according to claim 4, characterized in that In step 1, the organic Co salt includes at least one of cobalt naphthenate, cobalt stearate and cobalt neodecanoate.

7. The preparation method according to claim 3, characterized in that In step 3, N2O with a purity of 100% is introduced into the sealed high-temperature and high-pressure reactor to pressurize the reactor to 0.5-1 MPa.

8. The preparation method according to claim 3, characterized in that In step 5, the sample in step 4 is heated from room temperature to 480-520° C. at a heating rate of 5° C. / min.

9. Use of the catalyst according to any one of claims 1-2 for low-temperature catalytic production of N2O, characterized in that: The catalyst is placed in a quartz tube fixed bed reactor, the input flue gas contains 5-10% N2O, 3-10% O2, 0-3% CO2, 0-2% H2O, He is the balance gas, and the gas flow rate of the flue gas is 25-200 mL / min; the catalytic reaction temperature is controlled to be 150-550°C, each temperature interval is stable for 30-60 minutes, and the space velocity of the flue gas is 5000-20000 h -1 .

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