Preparation method of composite metal oxide catalyst and composite metal oxide catalyst prepared thereby

Abstract

The present invention discloses a preparation method of a composite metal oxide catalyst for directly decomposing nitrous oxide and the composite metal oxide catalyst prepared thereby, wherein the composite metal oxide catalyst is a metal oxide catalyst obtained after being sieved to 40 to 60 meshes. The composite metal oxide catalyst is synthesized by coprecipitation and coprecipitation-impregnation, wherein at least one of iron, sodium, potassium and manganese is modified. The composite metal oxide catalyst is evaluated for its catalytic performance of direct decomposition of N2O, and the N2O conversion rate can reach 90% at 432°C. The preparation method of the composite metal oxide catalyst of the present invention has the advantages of simplicity, low cost, excellent catalytic performance, high stability and high mechanical strength.

Description

Technical Field

[0001] The present invention belongs to the technical field of catalysts, and in particular relates to a method for preparing a composite metal oxide catalyst for decomposing nitrous oxide and the prepared composite metal oxide catalyst. Background Art

[0002] Nitrous oxide (N2O) is the third largest anthropogenic greenhouse gas and the largest stratospheric ozone depleting substance. The production of N2O can include both natural and anthropogenic sources, with human activities that lead to N2O emissions mainly including the biological conversion of fertilizer nitrogen to N2O (agriculture), biomass burning, fossil fuel combustion, industrial activities, wastewater treatment, aquaculture and solvent use.

[0003] Currently, several post-treatment technologies have been developed and adopted to control N2O emissions in the chemical and energy industries, including: (1) thermal decomposition, (2) non-selective catalytic reduction (NSCR), (3) selective catalytic reduction (SCR), and (4) direct catalytic decomposition (deN2O), among which N2O catalytic decomposition is one of the most promising methods to control N2O emissions due to its simplicity, high efficiency, and low energy consumption.

[0004] Chinese patent No. CN111359645A discloses a cobalt-based catalyst for nitrous oxide decomposition reaction. The cobalt-based catalyst is a complex of carbonate compounds of any one or several metal elements of alkaline earth metal A and / or La and Co3O4, which achieves a 5000h -1 Under the condition of a space velocity of 1000 ℃ and a nitrous oxide concentration of 10% in the raw gas, the temperature at which nitrous oxide is completely decomposed is 350° C. Although the temperature at which nitrous oxide is completely converted by the catalyst used in this patent is low, the cobalt-based cost is relatively high.

[0005] Chinese Patent No. CN112973777B discloses a molecular sieve catalyst with low Ir loading, wherein the active component of the molecular sieve catalyst is an oxide of the precious metal Ir, and the carrier is a CHA type microporous molecular sieve SSZ-13. The conversion rate of nitrous oxide is above 80% at 350°C, but the molecular sieve catalyst has poor stability at higher temperatures. Summary of the invention

[0006] The invention provides a method for preparing a composite metal oxide catalyst for efficiently decomposing nitrous oxide.

[0007] The present invention achieves the above-mentioned purpose through the following technical scheme: A method for preparing a composite metal oxide catalyst comprises the following steps:

[0008] Calcium nitrate and magnesium nitrate in a molar ratio of 10:0.1 to 10:1 are added to 100 to 200 milliliters (ml) of deionized water. After dissolution, an alkaline precipitant is slowly added thereto for co-precipitation. The whole process is carried out at a constant temperature of 70 to 80°C. When the pH reaches 10.5 to 11, the titration end point is reached and the addition of the alkaline precipitant is stopped; stirring is continued while keeping the temperature constant, and aging is performed for 0.5 to 5 hours (h). After the aging is completed, suction filtration is performed immediately. During the suction filtration process, the filter cake is washed with 0.5 to 4 liters (L) of deionized water. The filter cake obtained by suction filtration is dried at 80 to 120°C for 10 to 20 hours, and then calcined at 550 to 700°C for 3.5 to 6.5 hours to obtain a metal-modified composite metal oxide; the composite metal oxide is tableted and ground to be sieved to 40 to 60 meshes to obtain the composite metal oxide catalyst for directly decomposing nitrous oxide of the present invention.

[0009] In one embodiment, the alkaline precipitant may be at least one of aqueous ammonia, sodium hydroxide and aqueous sodium carbonate solution with a concentration of 0.01 to 5 mol / L.

[0010] The present invention also achieves the above object through the following technical scheme: A method for preparing a composite metal oxide catalyst comprises the following steps:

[0011] Calcium nitrate and magnesium nitrate are added in a molar ratio of 10:0.1 to 10:1 to 100 to 200 ml of deionized water, and after dissolution, a mixed solution is obtained, hereinafter referred to as solution A. In another beaker, sodium carbonate is added to 100 to 200 ml of deionized water to obtain a solution, hereinafter referred to as solution B; then, the solution A and the solution B are transferred to two constant pressure funnels respectively, and are simultaneously added dropwise to a four-necked flask for coprecipitation. The whole process is carried out at a constant temperature of 70 to 80°C, and the pH is maintained at 10.5 to 11. After reaching the titration endpoint, the temperature is maintained constant and stirring is continued, and aging is performed for 0.5 to 5 hours. After aging, suction filtration is performed immediately, and the obtained filter cake is washed with 0.5 to 4L of deionized water, and the alkali metal ion content in the filter cake, including sodium and potassium, is adjusted, and the pH of the filter cake is adjusted to 10.5 to 11. The filter cake is dried for 10 to 20 hours, wherein the drying temperature is controlled at 80 to 120° C., and after drying, it is calcined at 550 to 700° C. for 4 to 8 hours to obtain calcium magnesium metal oxide (bimetallic oxide).

[0012] Next, the metal auxiliary agent (through nitrate) is loaded on the calcium magnesium metal oxide by an equal volume impregnation method. The metal auxiliary agent is introduced when the catalyst is modified to improve the structure of the metal oxide, thereby improving its catalytic performance. The specific method is as follows: nitrate is added to deionized water to form a nitrate solution; the calcium magnesium metal oxide is impregnated in the nitrate solution, and after the impregnation is completed, it is allowed to stand for 24 to 36 hours, and is placed in an oven for drying for 10 to 20 hours, wherein the drying temperature is controlled at 80 to 120° C. After the drying is completed, it is calcined at a temperature of 550 to 700° C. for 3.5 to 6.5 hours to obtain a composite metal oxide; the composite metal oxide is tableted and ground to be sieved to 40 to 60 meshes to obtain the composite metal oxide catalyst for directly decomposing nitrous oxide of the present invention.

[0013] In one embodiment, the metal promoter is selected from at least one of the group consisting of iron, sodium, potassium and manganese.

[0014] In one embodiment, the content of the metal promoter is 0.5% to 8% of the total mass of the composite metal oxide catalyst.

[0015] Further, the catalytic performance of the composite metal oxide catalyst of the present invention is evaluated: the composite metal oxide catalyst is loaded in the constant temperature section of the fixed bed tubular reactor, and then the temperature is raised from room temperature to the reaction temperature at 2 to 5°C / min under a nitrogen purge environment, and then the nitrogen gas is switched to the reaction raw gas, and then the temperature is raised to 600°C at a heating rate of 2 to 5°C / min. During this period, the product is passed into the gas chromatograph every 10 to 50°C, and then the product after the reaction is analyzed by gas chromatography for component content, and the catalytic performance is evaluated. The reaction conditions are: 40% nitrous oxide is used at normal pressure, the time is 6 to 15h, the temperature is controlled at 200 to 600°C, and the raw gas flow rate is 50 to 150ml / min. The volume ratio of N2O to N2 to O2 in the reaction raw gas is 2:2:1, the reaction temperature is controlled at 200 to 600°C, the reaction pressure is controlled at 0.1MPa, and the space velocity is controlled at 3000 to 7000h. -1 , the reaction time is 12 to 36 hours.

[0016] The composite metal oxide catalyst obtained by the preparation method of the composite metal oxide catalyst of the present invention has the following advantages: the preparation method is simple and easy to operate, the required raw materials are cheap and easy to obtain, the catalytic performance is excellent, the catalytic life is long, the mechanical strength is high, and it has extremely high industrial application value and prospects. Further, the composite metal oxide catalyst of the present invention can be used for the treatment of high-concentration N2O tail gas in the adipic acid and nitric acid production industries that produce a large amount of nitrous oxide during the production process. The composite metal oxide catalyst of the present invention can directly decompose nitrous oxide into nitrogen and oxygen, and has higher performance at a lower temperature, avoiding the conversion of nitrous oxide into various nitrogen oxides, thereby reducing environmental pollution. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For those skilled in the art, other drawings can be obtained based on these drawings without creative work.

[0018] Figure 1 It is a schematic diagram of the catalytic performance of composite metal oxide catalysts with different calcium-magnesium metal ratios and composite metal oxide catalysts modified by sodium and potassium for catalytic decomposition of nitrous oxide;

[0019] Figure 2 A composite metal oxide catalyst modified simultaneously by sodium and potassium is shown; and

[0020] Figure 3 A composite metal oxide catalyst modified simultaneously by sodium and potassium is shown. Specific implementation plan

[0021] The present invention will be further described below in conjunction with specific examples. The experimental methods used in the following examples are conventional methods unless otherwise specified. The materials, reagents, etc. used in the following examples, unless otherwise specified, can all be obtained from commercial sources. It should be understood that these examples are only used to illustrate the present invention and are not intended to limit the scope of the present invention.

[0022] A method for preparing a composite metal oxide catalyst according to one embodiment of the present invention comprises the following steps:

[0023] (a) dissolving calcium nitrate and magnesium nitrate in water to form a mixed solution, wherein the molar ratio of calcium nitrate to magnesium nitrate is 10:0.1 to 10:1, for example, 10:0.1, 10:0.2, 10:0.3, 10:0.4, 10:0.5, 10:0.6, 10:0.7, 10:0.8, 10:0.9, 10:1. (b) adding an alkaline precipitant to the mixed solution at 70 to 80°C (for example, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 80°C) to perform coprecipitation, and stopping the addition of the alkaline precipitant when the pH reaches 10.5 to 11. (c) maintaining the temperature of step (b), continuing to stir the mixed solution to which the alkaline precipitant has been added, and aging for 0.5 to 5 hours (e.g., 0.5, 0.6, 0.7, 0.8, 0.9, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5 hours). (d) filtering after aging. (e) drying the filter cake obtained by suction filtration at 80 to 120° C. (e.g., 80, 85, 90, 95, 100, 105, 110, 115, 120° C.) for 10 to 20 hours (e.g., 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20 hours), and calcining at 550 to 700° C. (e.g., 550, 600, 650, 700° C.) for 3.5 to 6.5 hours (e.g., 3.5, 4, 4.5, 5, 5.5, 6, 6.5 hours) to obtain a composite metal oxide; and (f) sieving the composite metal oxide to obtain a composite metal oxide catalyst.

[0024] In one embodiment, the composite metal oxide is tableted, ground, and sieved into particles of 40 to 60 mesh (eg, 40, 45, 50, 55, 60 mesh) to obtain the composite metal oxide catalyst.

[0025] In one embodiment, the alkaline precipitant can be selected from one or more of the group consisting of aqueous ammonia, sodium hydroxide and aqueous sodium carbonate, and the concentration can be 0.01 to 5 mol / L, for example, 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 1, 2, 3, 4, 5 mol / L.

[0026] According to another embodiment of the present invention, a method for preparing a composite metal oxide catalyst comprises the following steps: (a) dissolving calcium nitrate and magnesium nitrate in water to form a first mixed solution, wherein the molar ratio of the calcium nitrate to the magnesium nitrate is 10:0.1 to 10:1, for example, 10:0.1, 10:0.2, 10:0.3, 10:0.4, 10:0.5, 10:0.6, 10:0.7, 10:0.8, 10:0.9, 10:1. (b) dissolving sodium carbonate in water to form a second solution. (c) adding the first solution and the second solution to a container at 70 to 80° C. (for example, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 80° C.) to perform coprecipitation, and maintaining the pH at 10.5 to 11. (d) After reaching the titration endpoint, keep the temperature constant and continue stirring to age for 0.5 to 5 hours (for example: 0.5, 0.6, 0.7, 0.8, 0.9, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5 hours). (e) After the aging is completed, filter and wash the obtained filter cake, adjust the alkali metal ion content in the filter cake, including sodium and potassium, and adjust the pH to 10.5 to 11. (f) Dry the filter cake at 80 to 120°C (for example: 80, 85, 90, 95, 100, 105, 110, 115, 120°C) for 10 to 20 hours. (g) calcining the dried filter cake at 550 to 700° C. (e.g., 550, 600, 650, 700° C.) for 4 to 8 hours (e.g., 4, 5, 6, 7, 8 hours) to obtain calcium magnesium metal oxide. (h) impregnating the calcium magnesium metal oxide in a nitrate solution, wherein the nitrate solution can be selected from the group consisting of iron nitrate solution, sodium nitrate solution, potassium nitrate solution and manganese nitrate solution. (I) the impregnated calcium magnesium metal oxide is allowed to stand for 24 to 36 hours (e.g., 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36 hours), and dried at 80 to 120° C. (e.g., 80, 85, 90, 95, 100, 105, 110, 115, 120° C.) for 10 to 20 hours (e.g., 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20 hours), and finally calcined at 550 to 700° C. (e.g., 550, 600, 650, 700° C.) for 3.5 to 6.5 hours (e.g., 3.5, 4, 4.5, 5, 5.5, 6, 6.5 hours) to obtain a composite metal oxide. and (J) sieving the composite metal oxide to obtain a composite metal oxide catalyst.

[0027] In one embodiment, the composite metal oxide is tableted, ground, and sieved into particles of 40 to 60 mesh (eg, 40, 45, 50, 55, 60 mesh) to obtain the composite metal oxide catalyst.

[0028] In one embodiment, the metal content in the nitrate solution is 0.5% to 8% (for example: 0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, 5.5, 6, 6.5, 7, 7.5, 8%) of the total mass of the composite metal oxide catalyst. In another embodiment, the metal content in the nitrate solution is 0.5% to 5% of the total mass of the composite metal oxide catalyst.

[0029] Further, the obtained composite metal oxide catalyst is evaluated for catalytic performance in the following manner: the composite metal oxide catalyst is loaded into the constant temperature section of the fixed bed tubular reactor, the temperature is raised from room temperature to the reaction temperature at 2 to 5°C / min under a nitrogen purge environment, the nitrogen gas is switched to the reaction raw gas, and the temperature is raised to 600°C at a heating rate of 2 to 5°C / min, during which the product is passed into the gas chromatograph every 10 to 50°C. Then, the product after the reaction is analyzed for component content by gas chromatography to evaluate the catalytic performance. The reaction conditions are: 40% nitrous oxide is used at normal pressure, the time is 6 to 15h, the temperature is controlled at 200 to 600°C, and the raw gas flow rate is 50 to 150ml / min; the volume ratio of N2O to N2 to O2 in the reaction raw gas is 2:2:1, the reaction temperature is controlled at 200 to 600°C, the reaction pressure is controlled at 0.1MPa, and the space velocity is controlled at 3000 to 7000h. -1 , the reaction time is 12 to 36 hours.

[0030] Throughout the text, various embodiments of the present invention can be presented in a range format. It should be understood that the description of the range format is only for convenience and brevity, and should not be construed as a rigid limitation on the scope of the invention. Therefore, the description of the range should be considered to have specifically disclosed all possible sub-ranges and each numerical value in the range. For example, the description of a range such as 1 to 6 should be considered to have specifically disclosed sub-ranges, such as 1 to 3, 1 to 4, 1 to 5, 2 to 4, 2 to 6, 3 to 6, etc., and single digits in the range, such as 1, 2, 3, 4, 5 and 6. No matter how wide the range is, it is applicable.

[0031] During the patent validity period of this application, it is expected that many related processes for the preparation of copper-zinc catalysts will be developed, and the scope of this application is intended to include all such new technologies a priori.

[0032] The terms "comprises," "comprising," "includes," "including," "having" and their variations mean "including but not limited to."

[0033] It should be understood that, for the sake of clarity, certain features of the invention described in the context of separate embodiments may also be provided in combination in a single embodiment. Conversely, for the sake of brevity, various features of the invention described in the context of a single embodiment may also be provided individually, or in any suitable sub-combination, or as appropriate in any other described embodiment of the invention. Certain features described in the context of various embodiments should not be considered essential features of those embodiments, unless the embodiments are inoperative without these elements.

[0034] In order to clearly illustrate the preparation method of the composite metal oxide catalyst of the present invention, the preparation method of the catalyst is described below using relevant examples. Relevant practitioners should be aware that the case described below is illustrative rather than restrictive, and the scope of protection of the present invention should not be limited by the following illustrative examples.

[0035] The reagents used in the embodiments of the present invention are shown in Table 1:

[0036] Table 1

[0037]

[0038] Example 1: Calcium-magnesium metal oxide (the molar ratio of calcium to magnesium is 10:1)

[0039] 200 ml of deionized water was added to a beaker and placed in a 70°C constant temperature water bath, 23.615 g of calcium nitrate hexahydrate and 2.564 g of magnesium nitrate hexahydrate solids were poured into the beaker, and magnetic stirring was turned on to completely dissolve the solids to obtain a metal nitrate precursor solution, hereinafter referred to as solution A. 200 ml of 0.1 mol / L sodium carbonate and sodium hydroxide solution was prepared as a precipitant, hereinafter referred to as solution B. Pour solution A and solution B into two constant pressure funnels respectively, take a three-necked flask under a constant temperature condition of 70°C, add 150 ml of deionized water to the three-necked flask, slowly drop solution A and solution B in the constant pressure funnel into the three-necked flask respectively (drop at a rate of 1 drop per second), and keep stirring, monitor the pH of the solution in real time by a pH meter, adjust the dropping speed of the alkali, and control the pH between 10.5 and 11. After the solution A and solution B in the constant pressure funnel are added, continue stirring at a constant temperature to age the generated suspension for 60 minutes.

[0040] The suspension is washed and filtered until the filtrate is neutral, the filter cake is dried at 110°C, and calcined at 550°C for 5 hours to obtain calcium magnesium metal oxide, wherein the molar ratio of calcium to magnesium is 10: 1. The calcium magnesium metal oxide is sieved to 40 to 60 meshes to obtain a composite metal oxide catalyst.

[0041] Determination of catalyst structure: The size and morphology of the prepared composite metal oxide catalyst were determined by scanning electron microscopy and transmission electron microscopy.

[0042] Evaluation of the catalytic performance of the composite metal oxide catalyst:

[0043] The performance evaluation of the composite metal oxide catalyst is carried out in a fixed bed tubular reactor. 0.5 g of the composite metal oxide catalyst is placed in the constant temperature section of the reaction tube of the fixed bed tubular reactor, and then the temperature is raised from room temperature to the reaction temperature at 2 to 5 ° C / min in a nitrogen environment. The reaction gas flow rate is 100 ml / min. After the temperature rises to the target temperature, the reaction raw gas is switched. The volume ratio of N2O to N2 to O2 in the reaction raw gas is 2:2:1, the reaction temperature is controlled at 200 to 600 ° C, the reaction pressure is controlled at 0.1 MPa, and the space velocity is controlled at 3000 to 7000 h -1 The reaction time is 12 to 36 hours. The reaction results are shown in Table 2 below.

[0044] Example 2: Calcium-magnesium metal oxide (the molar ratio of calcium to magnesium is 5:1)

[0045] 200 ml of deionized water was added to a beaker and placed in a 70°C constant temperature water bath, 23.615 g of calcium nitrate hexahydrate and 5.128 g of magnesium nitrate hexahydrate solids were poured into the beaker, and magnetic stirring was turned on to completely dissolve the solids to obtain a metal nitrate precursor solution, hereinafter referred to as solution A. 200 ml of 0.1 mol / L sodium carbonate and sodium hydroxide solution were prepared as precipitants, hereinafter referred to as solution B. Pour solution A and solution B into two constant pressure funnels respectively, take a three-necked flask under a constant temperature condition of 70°C, add 150 ml of deionized water into the three-necked flask, slowly drop solution A and solution B in the constant pressure funnel into the three-necked flask respectively (drop at a rate of 1 drop per second), and keep stirring, monitor the pH of the solution in real time by a pH meter, adjust the dropping speed of the alkali, and control the pH between 10.5 and 11. After the solution A and solution B in the constant pressure funnel are added, continue stirring at a constant temperature to age the generated suspension for 60 minutes.

[0046] The suspension is washed and filtered until the filtrate is neutral, the filter cake is dried at 110°C, and calcined at 550°C for 5 hours to obtain calcium magnesium metal oxide, wherein the molar ratio of calcium to magnesium is 5: 1. The calcium magnesium metal oxide is sieved to 40 to 60 meshes to obtain a composite metal oxide catalyst.

[0047] Determination of catalyst structure: The size and morphology of the prepared composite metal oxide catalyst were determined by scanning electron microscopy and transmission electron microscopy.

[0048] Evaluation of the catalytic performance of the composite metal oxide catalyst:

[0049] The performance evaluation of the composite catalyst is carried out in a fixed bed tubular reactor. 0.5 g of the composite catalyst is placed in the constant temperature section of the reaction tube of the fixed bed tubular reactor, and then the temperature is raised from room temperature to the reaction temperature at 2 to 5 ° C / min in a nitrogen environment. The reaction gas flow rate is 100 ml / min. After the temperature rises to the target temperature, the reaction raw gas is switched. The volume ratio of N2O to N2 to O2 in the reaction raw gas is 2:2:1, the reaction temperature is controlled at 200 to 600 ° C, the reaction pressure is controlled at 0.1 MPa, and the space velocity is controlled at 3000 to 7000 h -1 The reaction time is 12 to 36 hours. The reaction results are shown in Table 2 below.

[0050] Example 3: Calcium-magnesium metal oxide (the molar ratio of calcium to magnesium is 2:1)

[0051] 200 ml of deionized water was added to a beaker and placed in a 70°C constant temperature water bath, 23.615 g of calcium nitrate hexahydrate and 12.82 g of magnesium nitrate hexahydrate solids were poured into the beaker, and magnetic stirring was turned on to completely dissolve the solids to obtain a metal nitrate precursor solution, hereinafter referred to as solution A. 200 ml of 0.1 mol / L sodium carbonate and sodium hydroxide solution were prepared as precipitants, hereinafter referred to as solution B. Pour solution A and solution B into two constant pressure funnels respectively, take a three-necked flask under a constant temperature condition of 70°C, add 150 ml of deionized water to the three-necked flask, slowly drop solution A and solution B in the constant pressure funnel into the three-necked flask respectively (drop at a rate of 1 drop per second), and keep stirring, monitor the pH of the solution in real time by a pH meter, adjust the dropping speed of the alkali, and control the pH between 10.5 and 11. After the solution A and solution B in the constant pressure funnel are added, continue stirring at a constant temperature to age the generated suspension for 60 minutes.

[0052] The suspension is washed and filtered until the filtrate is neutral, the filter cake is dried at 110°C, and calcined at 550°C for 5 hours to obtain calcium magnesium metal oxide, wherein the molar ratio of calcium to magnesium is 2: 1. The calcium magnesium metal oxide is sieved to 40 to 60 meshes to obtain a composite metal oxide catalyst.

[0053] Determination of catalyst structure: The size and morphology of the prepared catalyst were determined by scanning electron microscopy and transmission electron microscopy.

[0054] Evaluation of the catalytic performance of the composite metal oxide catalyst:

[0055] The performance evaluation of the composite metal oxide catalyst is carried out in a fixed bed tubular reactor. 0.5 g of the composite metal oxide catalyst is placed in the constant temperature section of the reaction tube of the fixed bed tubular reactor, and then the temperature is raised from room temperature to the reaction temperature at 2 to 5 ° C / min in a nitrogen environment. The reaction gas flow rate is 100 ml / min. After the temperature rises to the target temperature, the reaction raw gas is switched. The volume ratio of N2O to N2 to O2 in the reaction raw gas is 2:2:1, the reaction temperature is controlled at 200 to 600 ° C, the reaction pressure is controlled at 0.1 MPa, and the space velocity is controlled at 3000 to 7000 h -1 The reaction time is 12 to 36 hours. The reaction results are shown in Table 2 below.

[0056] Example 4: Sodium-modified calcium-magnesium metal oxide (molar ratio of calcium to magnesium is 10:1)

[0057] 200 ml of deionized water was added to a beaker and placed in a 70°C constant temperature water bath, 23.615 g of calcium nitrate hexahydrate and 2.564 g of magnesium nitrate hexahydrate solids were poured into the beaker, and magnetic stirring was turned on to completely dissolve the solids to obtain a metal nitrate precursor solution, hereinafter referred to as solution A. 200 ml of 0.1 mol / L sodium carbonate and sodium hydroxide solution were prepared as precipitants, hereinafter referred to as solution B. Pour solution A and solution B into two constant pressure funnels respectively, take a three-necked flask under a constant temperature condition of 70°C, add 150 ml of deionized water into the three-necked flask, slowly drop solution A and solution B in the constant pressure funnel into the three-necked flask respectively (drop at a rate of 1 drop per second), and keep stirring, monitor the pH of the solution in real time by a pH meter, adjust the dropping speed of the alkali, and control the pH between 10.5 and 11. After the solution A and solution B in the constant pressure funnel are added, continue stirring while keeping the temperature constant, and age the generated suspension for 60 minutes.

[0058] The suspension is washed and filtered until the filtrate is neutral, the filter cake is dried at 110°C, and calcined at 550°C for 5 hours to obtain calcium magnesium metal oxide, wherein the molar ratio of calcium to magnesium is 10:1. The obtained calcium magnesium metal oxide is ball-milled to less than 1000 mesh for subsequent impregnation. 4g of sodium carbonate is weighed and prepared into a sodium carbonate solution with 40ml of deionized water, and the calcium magnesium metal oxide is impregnated in the sodium carbonate solution. After impregnation, it is allowed to stand for 24 hours, dried at 110°C for 12 hours, and the obtained solid is ground into powder and calcined at 550°C for 5 hours to obtain sodium-modified calcium magnesium metal oxide.

[0059] The sodium-modified calcium-magnesium metal oxide is in the form of an amorphous powder with a particle size of less than 15 μm. The pore volume of the sodium-modified calcium-magnesium metal oxide is 0.2326 cm 3 / g, specific surface area is 18.2561m 2 / g, and the average pore size is 12.7409nm. The sodium-modified calcium magnesium metal oxide is sieved to 40 to 60 meshes to obtain the composite metal oxide catalyst of the present invention.

[0060] Determination of catalyst structure:

[0061] The size and morphology of the prepared composite metal oxide catalyst were determined by scanning electron microscopy and transmission electron microscopy.

[0062] Evaluation of the catalytic performance of the composite metal oxide catalyst:

[0063] The performance evaluation of the composite metal oxide catalyst is carried out in a fixed bed tubular reactor. 0.5 g of the composite metal oxide catalyst is placed in the constant temperature section of the reaction tube of the fixed bed tubular reactor, and then the temperature is raised from room temperature to the reaction temperature at 2 to 5 ° C / min in a nitrogen environment. The reaction gas flow rate is 100 ml / min. After the temperature rises to the target temperature, the reaction raw gas is switched. The volume ratio of N2O to N2 to O2 in the reaction raw gas is 2:2:1, the reaction temperature is controlled at 200 to 600 ° C, the reaction pressure is controlled at 0.1 MPa, and the space velocity is controlled at 3000 to 7000 h -1 The reaction time is 12 to 36 hours. The reaction results are shown in Table 2 below.

[0064] Example 5: Potassium-modified calcium-magnesium metal oxide (molar ratio of calcium to magnesium is 10:1)

[0065] 200 ml of deionized water was added to a beaker and placed in a 70°C constant temperature water bath, 23.615 g of calcium nitrate hexahydrate and 2.564 g of magnesium nitrate hexahydrate solids were poured into the beaker, and magnetic stirring was turned on to completely dissolve the solids to obtain a metal nitrate precursor solution, hereinafter referred to as solution A. 200 ml of 0.1 mol / L sodium carbonate and sodium hydroxide solution was prepared as a precipitant, hereinafter referred to as solution B. Pour solution A and solution B into two constant pressure funnels respectively, take a three-necked flask under a constant temperature condition of 70°C, add 150 ml of deionized water to the three-necked flask, slowly drop solution A and solution B in the constant pressure funnel into the three-necked flask respectively (drop at a rate of 1 drop per second), and keep stirring, monitor the pH of the solution in real time by a pH meter, adjust the dropping speed of the alkali, and control the pH between 10.5 and 11. After the solution A and solution B in the constant pressure funnel are added, continue stirring while keeping the temperature constant, and age the generated suspension for 60 minutes.

[0066] The suspension is washed and filtered until the filtrate is neutral, the filter cake is dried at 110°C, and calcined at 550°C for 5 hours to obtain calcium magnesium metal oxide, wherein the molar ratio of calcium to magnesium is 10: 1. The obtained calcium magnesium metal oxide is ball-milled to less than 1000 mesh for subsequent impregnation process.

[0067] Weigh 4g of potassium carbonate and prepare a potassium carbonate solution with 40ml of deionized water. Immerse the calcium magnesium metal oxide in the potassium carbonate solution. After immersion, let it stand for 24 hours, dry it at 110°C for 12 hours, grind the obtained solid into powder and roast it at 550°C for 5 hours to obtain potassium-modified calcium magnesium metal oxide. The potassium-modified calcium magnesium metal oxide has a regular layered structure and a particle size of less than 15um. The pore volume of the sodium-modified calcium magnesium oxide is 0.2694cm 3 / g, specific surface area is 17.6249m 2 / g, and the average pore size is 15.2851nm. The potassium-modified calcium magnesium metal oxide is sieved to 40 to 60 meshes to obtain a composite metal oxide catalyst.

[0068] Determination of catalyst structure:

[0069] The size and morphology of the prepared composite metal oxide catalyst were determined by scanning electron microscopy and transmission electron microscopy.

[0070] Evaluation of the catalytic performance of the composite metal oxide catalyst:

[0071] The performance evaluation of the composite metal oxide catalyst is carried out in a fixed bed tubular reactor. 0.5 g of the composite metal oxide catalyst is placed in the constant temperature section of the reaction tube of the fixed bed tubular reactor, and then the temperature is raised from room temperature to the reaction temperature at 2 to 5 ° C / min in a nitrogen environment. The reaction gas flow rate is 100 ml / min. After the temperature rises to the target temperature, the reaction raw gas is switched. The volume ratio of N2O to N2 to O2 in the reaction raw gas is 2:2:1, the reaction temperature is controlled at 200 to 600 ° C, the reaction pressure is controlled at 0.1 MPa, and the space velocity is controlled at 3000 to 7000 h -1 The reaction time is 12 to 36 hours. The reaction results are shown in Table 2 below.

[0072] Example 6: Potassium-modified calcium-magnesium metal oxide (molar ratio of calcium to magnesium is 10:1)

[0073] 200 ml of deionized water was added to a beaker and placed in a 70°C constant temperature water bath, 23.615 g of calcium nitrate hexahydrate and 2.564 g of magnesium nitrate hexahydrate solids were poured into the beaker, and magnetic stirring was turned on to completely dissolve the solids to obtain a metal nitrate precursor solution, hereinafter referred to as solution A. 200 ml of 0.1 mol / L sodium carbonate and sodium hydroxide solution was prepared as a precipitant, hereinafter referred to as solution B. Pour solution A and solution B into two constant pressure funnels respectively, take a three-necked flask at a constant temperature of 70°C, add 150 ml of deionized water to the three-necked flask, slowly drop solution A and solution B in the constant pressure funnel into the three-necked flask respectively (drop at a rate of 1 drop per second), and keep stirring, monitor the pH of the solution in real time by a pH meter, adjust the dropping speed of the alkali, and control the pH between 10.5 and 11. After the solution A and solution B in the constant pressure funnel are added, continue stirring while keeping the temperature constant, and age the generated suspension for 60 minutes.

[0074] The suspension is washed and filtered until the filtrate is neutral, the filter cake is dried at 110°C, and calcined at 550°C for 5 hours to obtain calcium magnesium metal oxide, wherein the molar ratio of calcium to magnesium is 10: 1. The obtained calcium magnesium metal oxide is ball-milled to less than 1000 mesh for subsequent impregnation process.

[0075] Weigh 4g of potassium carbonate and 4g of sodium carbonate, and prepare a sodium carbonate potassium carbonate mixed solution with 40ml of deionized water. Immerse the above calcium magnesium metal oxide in the sodium carbonate potassium carbonate mixed solution. After the immersion is completed, let it stand for 24 hours, dry it at 110°C for 12 hours, grind the obtained solid into powder and roast it at 550°C for 5 hours to obtain sodium-potassium modified calcium magnesium metal oxide. The sodium-potassium modified calcium magnesium metal oxide is an amorphous powder with a particle size of less than 15um. The pore volume of the sodium-modified calcium magnesium metal oxide is 0.2857cm 3 / g, specific surface area is 20.4941m 2 / g, and the average pore size is 13.9406nm. The sodium-potassium modified calcium-magnesium metal oxide is sieved to 40 to 60 meshes to obtain the composite metal oxide catalyst of the present invention.

[0076] Determination of catalyst structure:

[0077] The size and morphology of the prepared composite metal oxide catalyst are determined by scanning electron microscopy and transmission electron microscopy;

[0078] Evaluation of the catalytic performance of the composite metal oxide catalyst:

[0079] The performance evaluation of the composite metal oxide catalyst is carried out in a fixed bed tubular reactor. 0.5 g of the composite metal oxide catalyst is placed in the constant temperature section of the reaction tube of the fixed bed tubular reactor, and then the temperature is raised from room temperature to the reaction temperature at 2 to 5 ° C / min in a nitrogen environment. The reaction gas flow rate is 100 ml / min. After the temperature rises to the target temperature, the reaction raw gas is switched. The volume ratio of N2O to N2 to O2 in the reaction raw gas is 2:2:1, the reaction temperature is controlled at 200 to 600 ° C, the reaction pressure is controlled at 0.1 MPa, and the space velocity is controlled at 3000 to 7000 h -1 The reaction time is 12 to 36 hours. The reaction results are shown in Table 2 below.

[0080] Table 2

[0081]

[0082]

[0083] The numbers following Examples 1 to 6 in Table 2 represent the conversion rates of N2O. Figure 1 is a schematic diagram of the catalytic performance of calcium-magnesium metal oxide catalysts with different calcium-magnesium metal ratios and sodium- and potassium-modified calcium-magnesium metal oxide catalysts for the catalytic decomposition of nitrous oxide; and Figure 2 and Figure 3It is the structure of the calcium-magnesium catalyst modified by sodium and potassium at the same time. It can be seen that it is a regular layered structure, which is also a characteristic that a calcium catalyst should have. Referring to Table 2, first, according to Example 1, Example 2 and Example 3, it can be concluded that the performance is best when the ratio of calcium to magnesium in the calcium-magnesium metal catalyst is 10:1. Furthermore, compared with Example 3, Example 4, Example 5 and Example 6, the introduction of the metal auxiliary sodium into the calcium-magnesium metal oxide can greatly reduce the temperature at which the nitrous oxide conversion rate reaches 10%, 50% and 90%, especially after adding the sodium-potassium auxiliary at the same time, the activation temperature can be reduced, and t90 (the temperature at which the conversion rate reaches 90%) reaches 432°C. It can be seen that the catalytic performance of the composite metal oxide catalyst of the present invention is better than that of the traditional calcium-based catalyst, and because the main component is calcium, the cost is greatly reduced compared with the precious metal catalyst and the cobalt-based catalyst.

[0084] The above is only a preferred embodiment of the present invention. It should be pointed out that ordinary technicians in this technical field can make several improvements and modifications without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. An application of a composite metal oxide catalyst for directly decomposing nitrous oxide, characterized in that: The preparation method of the composite metal oxide catalyst comprises the following steps: (a) dissolving calcium nitrate and magnesium nitrate in water to form a first mixed solution, wherein the molar ratio of the calcium nitrate to the magnesium nitrate is 10:0.1 to 10:1; (b) dissolving sodium carbonate in water to form a second solution; (c) adding the first solution and the second solution simultaneously into a container at 70 to 80° C. to perform co-precipitation, and maintaining the pH at 10.5 to 11; (d) After reaching the titration endpoint, keep the temperature constant and continue stirring to age for 0.5 to 5 hours; (e) After aging, filtering is performed, washing the obtained filter cake, and adjusting the alkali metal ion content and pH in the filter cake; (f) drying the filter cake at 80 to 120° C. for 10 to 20 hours; (g) calcining the dried filter cake at 550 to 700° C. for 4 to 8 hours to obtain calcium magnesium metal oxide; (h) impregnating the calcium magnesium metal oxide in a carbonate solution, the carbonate comprising potassium carbonate and sodium carbonate; (I) allowing the impregnated calcium magnesium metal oxide to stand for 24 to 36 hours, drying at 80 to 120° C. for 10 to 20 hours, and finally calcining at 550 to 700° C. for 3.5 to 6.5 hours to obtain a composite metal oxide; and (J) Sieving the composite metal oxide to obtain a composite metal oxide catalyst.

2. The use according to claim 1, characterized in that: The composite metal oxide is sieved to 40 to 60 meshes to obtain the composite metal oxide catalyst.

3. The use according to claim 1, characterized in that: The content of metal in the carbonate solution accounts for 0.5% to 8% of the total mass of the composite metal oxide catalyst.

4. The use according to claim 1, characterized in that: The composite metal oxide catalyst is amorphous solid particles with a particle size of 10 to 740 microns.

Images