Metal oxide catalyst as well as preparation method and application method thereof

Abstract

The invention relates to a metal oxide catalyst and a preparation method and an application method thereof, and belongs to the technical field of catalyst synthesis, the preparation method comprises the following steps: preparing a metal nitrate solution, metal nitrate in the metal nitrate solution comprising nitrate of an active component, and the active component comprising cobalt; a metal nitrate solution is loaded on a carrier, ultrasonic treatment, drying and roasting are carried out, the metal oxide catalyst is obtained, the metal oxide catalyst comprises the carrier and an active component loaded on the carrier, and therefore the metal oxide catalyst suitable for preparing nitric acid through selective decomposition of nitrous oxide is provided and is simple in preparation method, low in cost and suitable for industrial production. In the nitrous oxide decomposition process, the catalyst has high selectivity on nitric oxide and high conversion rate on nitrous oxide, nitric acid can be prepared while nitrous oxide is treated, the secondary utilization rate of nitrous oxide in the industry is improved, and therefore higher economic benefits can be brought while the aim of reducing emission of nitrous oxide can be achieved.

Description

Technical Field

[0001] This application relates to the technical field of catalyst synthesis, and specifically relates to a metal oxide catalyst, a preparation method thereof, and an application method thereof. Background Art

[0002] Nitrous oxide (N2O) is the third largest greenhouse gas and can exist stably in the atmosphere for a long time. Research shows that N2O not only has a strong greenhouse effect, but also causes damage to the ozone layer, and it is a pollutant that cannot be ignored in the atmosphere. The main methods for N2O decomposition include high-temperature thermal decomposition method, (non)selective catalytic reduction method, direct catalytic decomposition method, etc. Commonly used catalysts mainly include molecular sieve catalysts, semiconductor photocatalysts, and metal oxide catalysts, among which metal oxide catalysts have the characteristics of low cost and good thermal stability.

[0003] However, the metal oxide catalysts in the prior art mainly achieve the emission reduction goal by directly catalytically decomposing nitrous oxide into nitrogen and oxygen, but the development of the secondary utilization technology of nitrous oxide in industry is still insufficient. Therefore, it is particularly important to explore how to improve the secondary utilization rate of nitrous oxide in industry while achieving the nitrous oxide emission reduction goal. Summary of the Invention

[0004] The purpose of this application is to provide a metal oxide catalyst, a preparation method thereof, and an application method thereof, so as to prepare a metal oxide catalyst applicable to the selective decomposition of nitrous oxide to prepare nitric acid, thereby improving the secondary utilization rate of nitrous oxide in industry while achieving the nitrous oxide emission reduction goal.

[0005] The embodiment of this application provides a preparation method of a metal oxide catalyst. The preparation method of the metal oxide catalyst includes: preparing a metal nitrate solution, where the metal nitrate in the metal nitrate solution includes the nitrate of the active component, and the active component includes cobalt; loading the metal nitrate solution onto a support, and performing ultrasonic treatment, drying, and calcination to obtain a metal oxide catalyst. The metal oxide catalyst includes a support and an active component loaded on the support.

[0006] Wherein, the metal nitrate further includes the nitrate of the modifying component, and the modifying component includes sodium and / or potassium; and, the metal oxide catalyst further includes a modifying component loaded on the support, and in the metal oxide catalyst, the mass ratio of the active component to the mass of the support is 3-7%, and the mass ratio of the modifying component to the mass of the support is 1-7%.

[0007] Wherein, the support is an activated alumina support.

[0008] Wherein, loading the metal nitrate solution onto the support includes: loading the metal nitrate solution onto the support by the equal-volume impregnation method.

[0009] Among them, loading the metal nitrate solution onto the carrier includes: adding the carrier into a container filled with the metal nitrate solution.

[0010] Among them, loading the metal nitrate solution onto the carrier, followed by ultrasonic treatment, drying, and calcination to obtain the metal oxide catalyst, includes: loading the metal nitrate solution onto the carrier, performing ultrasonic treatment at room temperature for 1 to 5 h, drying overnight, and then calcining in an air atmosphere at 900 to 1000 °C for 150 to 250 min to obtain the metal oxide catalyst.

[0011] Among them, preparing the metal nitrate solution includes: weighing the metal nitrate and dissolving the weighed metal nitrate in deionized water under a constant temperature condition of 20 to 30 °C to obtain the metal nitrate solution.

[0012] The embodiment of the present application also provides a metal oxide catalyst, which is prepared by using the preparation method of the metal oxide catalyst in any one of the above.

[0013] The embodiment of the present application also provides an application method of the metal oxide catalyst. The application method of the metal oxide catalyst includes: using the above metal oxide catalyst to catalytically decompose nitrous oxide into nitric oxide, and oxidizing and absorbing the nitric oxide to obtain nitric acid.

[0014] Among them, using the above metal oxide catalyst to catalytically decompose nitrous oxide into nitric oxide, and oxidizing and absorbing the nitric oxide to obtain nitric acid includes: filling the above metal oxide catalyst into the reaction tube of a fixed-bed tubular reactor, and making the metal oxide catalyst located within the constant-temperature section interval of the reactor. Then, nitrogen is introduced into the reactor, and the temperature of the reactor is raised from room temperature to the target temperature at a rate of 2 to 5 °C / min. The target temperature is 600 to 900 °C. After reaching the target temperature, the gas introduced into the reactor is switched from nitrogen to the reaction raw material gas, so that the reaction raw material gas reacts under the action of the metal oxide catalyst. The reaction raw material gas includes nitrous oxide and oxygen. The gas product at the outlet of the reactor is cooled by a condenser and then transported through a pipeline to a washing bottle filled with deionized water, where it is absorbed and converted into nitric acid.

[0015] The metal oxide catalyst provided by the present application, its preparation method and application method. By preparing a metal nitrate solution, the metal nitrate in the metal nitrate solution includes the nitrate of the active component, and the active component includes cobalt. Then, the metal nitrate solution is loaded onto a carrier, and ultrasonic treatment, drying and calcination are carried out to obtain the metal oxide catalyst. The metal oxide catalyst includes a carrier and an active component loaded on the carrier, thereby providing a metal oxide catalyst applicable to the selective decomposition of nitrous oxide to prepare nitric acid. The preparation method of this metal oxide catalyst is simple, with low cost. Moreover, during the decomposition of nitrous oxide, this metal oxide catalyst has a high selectivity for nitric oxide, a high conversion rate for nitrous oxide, and can produce nitric acid while treating nitrous oxide, improving the secondary utilization rate of nitrous oxide in industry. Therefore, it can bring higher economic benefits while achieving the nitrous oxide emission reduction target. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] The following will combine the drawings and describe in detail the specific embodiments of the present application, making the technical solutions and other beneficial effects of the present application obvious.

[0017] Figure 1 is a schematic flow chart of the preparation method of the metal oxide catalyst provided by the embodiment of the present application;

[0018] Figure 2 is a schematic diagram of the conversion rate of the metal oxide catalyst prepared by the preparation method of the metal oxide catalyst provided by Embodiments 1 to 7 of the present application to nitrous oxide;

[0019] Figure 3 is a schematic diagram of the selectivity of the metal oxide catalyst prepared by the preparation method of the metal oxide catalyst provided by Embodiments 1 to 7 of the present application to nitric oxide. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0020] The following will further describe the present application in detail in combination with the drawings and embodiments. It should be specifically noted that the following embodiments are only used to illustrate the present application, but do not limit the scope of the present application. Similarly, the following embodiments are only some embodiments of the present application rather than all embodiments. All other embodiments obtained by those of ordinary skill in the art without creative efforts fall within the scope of protection of the present application.

[0021] In the following description of the present application, reference is made to "some embodiments", which describe a subset of all possible embodiments. However, it can be understood that "some embodiments" can be the same subset or different subsets of all possible embodiments and can be combined with each other without conflict.

[0022] In the following description of the present application, the terms "first", "second", and "third" are only used to distinguish similar objects and do not represent a specific order for the objects. It can be understood that, where permitted, "first", "second", and "third" can be interchanged in a specific order or sequence so that the embodiments of the present application described herein can be implemented in an order other than that illustrated or described herein.

[0023] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the technical field to which this application belongs. The terms used herein are only for the purpose of describing embodiments of the present application and are not intended to limit the present application.

[0024] The following is a detailed description with reference to specific embodiments. It should be noted that the serial numbers of the following embodiments do not limit the preferred order of the embodiments.

[0025] Please refer to Figure 1 , Figure 1 which is a schematic flowchart of a method for preparing a metal oxide catalyst provided by an embodiment of the present application. The specific process of the method for preparing the metal oxide catalyst can be as follows:

[0026] Step S11. Prepare a metal nitrate solution, where the metal nitrate in the metal nitrate solution includes nitrates of active components, and the active components include cobalt.

[0027] Among them, the solvent in the metal nitrate solution can be water, for example, it can specifically be deionized water.

[0028] In some examples, the nitrate of the active component can specifically be cobalt nitrate hexahydrate.

[0029] In some embodiments, the metal nitrate in the metal nitrate solution can further include nitrates of modifying components, and the modifying components can include sodium and / or potassium. In some examples, the nitrates of the modifying components can specifically be potassium nitrate or sodium nitrate.

[0030] In some embodiments, the above step S11 can include: weighing the metal nitrate and dissolving the weighed metal nitrate in deionized water under a constant temperature condition of 20 - 30 °C to obtain a metal nitrate solution.

[0031] In some specific embodiments, the metal nitrate in the above metal nitrate solution can specifically be cobalt nitrate hexahydrate. Moreover, the process of preparing the metal nitrate solution may include: weighing a certain mass (for example, 0.3626 g) of cobalt nitrate hexahydrate with an electronic balance, pouring the weighed cobalt nitrate hexahydrate into a beaker containing a certain mass (for example, 1.9931 g) of deionized water, then placing the beaker in a constant temperature water bath at 20 - 30 °C, and continuously stirring until the cobalt nitrate hexahydrate is completely dissolved to obtain the metal nitrate solution.

[0032] In some other specific embodiments, the metal nitrate in the above metal nitrate solution can specifically be cobalt nitrate hexahydrate and sodium nitrate. Moreover, the process of preparing the metal nitrate solution may include: weighing a certain mass (for example, 0.3626 g) of cobalt nitrate hexahydrate and a certain mass (for example, 0.0548 g, 0.1644 g, or 0.274 g) of sodium nitrate respectively with an electronic balance, pouring the weighed cobalt nitrate hexahydrate and sodium nitrate into a beaker containing a certain mass (for example, 1.9931 g) of deionized water, then placing the beaker in a constant temperature water bath at 20 - 30 °C, and continuously stirring until the cobalt nitrate hexahydrate and sodium nitrate are completely dissolved to obtain the metal nitrate solution.

[0033] In some other specific embodiments, the metal nitrate in the above metal nitrate solution can specifically be cobalt nitrate hexahydrate and potassium nitrate. Moreover, the process of preparing the metal nitrate solution may include: weighing a certain mass (for example, 0.3626 g) of cobalt nitrate hexahydrate and a certain mass (for example, 0.04293 g, 0.1288 g, or 0.2147 g) of potassium nitrate respectively with an electronic balance, pouring the weighed cobalt nitrate hexahydrate and potassium nitrate into a beaker containing a certain mass (for example, 1.9931 g) of deionized water, then placing the beaker in a constant temperature water bath at 20 - 30 °C, and continuously stirring until the cobalt nitrate hexahydrate and potassium nitrate are completely dissolved to obtain the metal nitrate solution.

[0034] Step S12. Load the metal nitrate solution onto a carrier, perform ultrasonic treatment, drying, and calcination to obtain a metal oxide catalyst, where the metal oxide catalyst includes a carrier and an active component supported on the carrier.

[0035] In this embodiment, the metal oxide catalyst obtained after completing the above step S12 can be a cobalt-based metal oxide, and its mesh number can be 40 - 60 mesh so that it can be used as a catalyst in the decomposition reaction of nitrous oxide.

[0036] Among them, the carrier can be an activated alumina carrier. For example, it can specifically be an activated alumina carrier with a mesh size of 40 to 60. Due to the porous structure of the activated alumina carrier, it ensures that the metal oxide catalyst obtained after the completion of the above step S12 can have a large specific surface area, thus being beneficial to improving the catalytic performance of the metal oxide catalyst.

[0037] Specifically, in the above step S12, the ultrasonic time can be 1 to 5 h. For example, it can specifically be 1 h, 2 h, 3 h, 4 h, or 5 h, etc. The drying temperature can be 105 to 115 °C. For example, it can specifically be 105 °C, 106 °C, 107 °C, 108 °C, 109 °C, 110 °C, 111 °C, 112 °C, 113 °C, 114 °C, or 115 °C, etc. The calcination temperature can be 900 to 1000 °C. For example, it can specifically be 900 °C, 910 °C, 920 °C, 930 °C, 940 °C, 950 °C, 960 °C, 970 °C, 980 °C, 990 °C, or 1000 °C, etc. The calcination time can be 150 to 250 min. For example, it can specifically be 150 min, 160 min, 170 min, 180 min, 190 min, 200 min, 210 min, 220 min, 230 min, 240 min, or 250 min, etc.

[0038] Moreover, in specific implementation, the above step S12 can specifically include: loading the metal nitrate solution onto the carrier, ultrasonically treating it at room temperature for 1 to 5 h (for example, 3 h), drying it at 105 to 115 °C (for example, 110 °C), and after drying overnight, calcining it in an air atmosphere at 900 to 1000 °C (for example, 950 °C) for 150 to 250 min (for example, 180 min) to obtain the metal oxide catalyst.

[0039] In this embodiment, in the metal oxide catalyst obtained after the completion of the above step S12, the loading amount of the active component (that is, the mass ratio of the active component to the mass of the carrier) can be 3 to 7%. For example, it can specifically be 3%, 4%, 5%, 6%, or 7%, etc. And in specific implementation, by controlling the mass ratio of the active component included in the metal nitrate solution in the above step S11 to the mass of the carrier used in the above step S12 to be 3 to 7%, the mass ratio of the active component to the mass of the carrier in the metal oxide catalyst obtained after the completion of the above step S12 can be made 3 to 7%.

[0040] Specifically, in the above embodiments where the metal nitrate in the metal nitrate solution further includes the nitrate of the modifying component, the metal oxide catalyst obtained after the completion of the above step S12 may further include the modifying component supported on the carrier. Moreover, in this metal oxide catalyst, the loading amount of the modifying component (i.e., the mass ratio of the modifying component to the mass of the carrier) may be 1 to 7%, for example, it may specifically be 1%, 2%, 3%, 4%, 5%, 6% or 7%, etc. And specifically in implementation, by controlling the mass ratio of the modifying component included in the metal nitrate solution in the above step S11 to the mass of the carrier used in the above step S12 to be 1 to 7%, the mass ratio of the active component to the mass of the carrier in the metal oxide catalyst obtained after the completion of the above step S12 can be made 1 to 7%.

[0041] In some embodiments, the above loading of the metal nitrate solution onto the carrier may include: loading the metal nitrate solution onto the carrier by the equal-volume impregnation method. Specifically, the volume of the carrier used in the above step S12 may be equal to the volume of the metal nitrate solution.

[0042] In some embodiments, the above loading of the metal nitrate solution onto the carrier may include: adding the carrier to a container filled with the metal nitrate solution. Specifically, the carrier (such as an activated alumina carrier) can be dried and then added to a beaker filled with the metal nitrate solution, thereby realizing the loading of the metal nitrate solution onto the carrier, and during the loading process, the loss of the metal nitrate solution during transfer can be avoided.

[0043] In some specific embodiments, the above step S12 may include: weighing a certain mass (such as 2 g) of the dried activated alumina carrier with an electronic balance, and slowly and evenly pouring the weighed activated alumina carrier into a beaker filled with the metal nitrate solution. After the activated alumina carrier is fully loaded with the metal nitrate solution, cover the beaker mouth with plastic wrap and fix it with a rubber band. Then, place the beaker in an ultrasonic instrument and ultrasonicate for 3 h. After the ultrasonication is completed, place the beaker in an oven at 110°C for drying. After drying overnight, transfer it to a muffle furnace and calcine at 950°C for 180 min, and then cool it naturally to obtain a cobalt-based metal oxide. After that, grind and screen the obtained cobalt-based metal oxide to 40 - 60 mesh, and a metal oxide catalyst that can be used for the selective decomposition of nitrous oxide to prepare nitric acid can be obtained.

[0044] It should be noted that in the related prior art of using a metal oxide catalyst to catalytically decompose nitrous oxide:

[0045] 1) Chinese patent document (CN118287088A)

[0046] Disclosed are a nitrous oxide catalytic decomposition catalyst, a preparation method thereof and an application thereof. The catalyst mainly consists of a carrier CeO2 nanorod and an active component NiO. First, the CeO2 nanorod was prepared, and the NiO / CeO2 catalyst was prepared by a wet impregnation method. Subsequently, different proportions of NiO / CeO2 catalysts were obtained by adjusting the Ni / CeO2 mass ratio. Through experiments in a N2O decomposition experimental device, the invention found that as the Ni addition amount increased, the decomposition efficiency of the NiO / CeO2 catalyst for N2O gradually increased and then decreased. The catalyst with the best nitrous oxide catalytic decomposition activity was the NiO / CeO2 catalyst with a Ni / CeO2 mass ratio of 3.6%, indicating that when the dispersion degree of the active site NiO was higher, the activity of the catalyst per active site was poorer, and the activity of the agglomerated NiO per active site was better instead. The catalyst in the invention has good catalytic activity, relatively stable performance, simple preparation process and low cost.

[0047] 2) Chinese Patent CN116371413A

[0048] Disclosed are a modified cobalt-based catalyst for low-temperature and high-efficiency decomposition of nitrous oxide, a preparation method thereof and an application thereof. The invention uses Co3O4 nanoparticles as a carrier and modifies Co3O4 with cesium-containing nitrate. Judging from the results, the N2O conversion rate of the modified cobalt-based catalyst after treatment was higher than 50% at 300 °C and as high as 91% at 350 °C. The catalyst performance in the medium and low temperature range was significantly better than that of pure Co3O4. While constructing basic sites to promote the redox characteristics of the catalyst, the catalyst of the invention greatly improves the water and oxygen resistance of the catalyst, and the selected materials are inexpensive and environmentally friendly.

[0049] The catalysts in the above patent documents mainly achieve the purpose of emission reduction by directly catalytically decomposing nitrous oxide into nitrogen and oxygen. However, the development of the secondary utilization technology of nitrous oxide in industry is not sufficient. Therefore, compared with the related technologies of catalytically decomposing nitrous oxide using metal oxide catalysts in the prior art, the metal oxide catalyst provided in the embodiments of the present application can selectively decompose nitrous oxide to generate nitric acid, thereby improving the secondary utilization rate of nitrous oxide in industry and bringing higher economic benefits while achieving the nitrous oxide emission reduction target. In addition, the metal oxide catalyst provided in the embodiments of the present application has low cost and simple production method, and has good application value.

[0050] For the convenience of understanding, the present application will be further described in detail below through seven specific examples (i.e., Examples 1 to 7).

[0051] Example 1

[0052] In Example 1, the specific process of the preparation method of the metal oxide catalyst can be as follows:

[0053] Step S21. Weigh 0.3626 g of cobalt nitrate hexahydrate with an electronic balance, pour it into a beaker containing 1.9931 g of deionized water, and then place the beaker in a constant temperature water bath at 20 - 30 °C. Continuously stir to completely dissolve the solid to obtain a metal nitrate solution.

[0054] Step S22. Weigh 2 g of the dried activated alumina support with an electronic balance, and slowly and evenly pour the weighed activated alumina support into the beaker containing the metal nitrate solution in Step S21. After the activated alumina support is fully loaded with the metal nitrate solution, cover the beaker mouth with plastic wrap and fix it with a rubber band. Then place the beaker in an ultrasonic instrument and ultrasonicate for 3 h. After ultrasonication is completed, place the beaker in an oven at 110 °C for drying. After drying overnight, transfer it to a muffle furnace and calcine at 950 °C for 180 min, and then naturally cool to obtain a cobalt-based metal oxide. The loading amount of the active component (i.e., cobalt element) in this cobalt-based metal oxide is 5%. After grinding and sieving the obtained cobalt-based metal oxide to 40 - 60 mesh, a metal oxide catalyst that can be used for the selective decomposition of nitrous oxide to prepare nitric acid can be obtained, denoted as metal oxide catalyst 5% Co.

[0055] Example 2

[0056] In Example 2, the specific process for preparing the metal oxide catalyst can be as follows:

[0057] Step S31. Weigh 0.3626 g of cobalt nitrate hexahydrate and 0.0548 g of sodium nitrate with an electronic balance respectively, pour them into a beaker containing 1.9931 g of deionized water, and then place the beaker in a constant temperature water bath at 20 - 30 °C. Continuously stir to completely dissolve the solid to obtain a metal nitrate solution.

[0058] Step S32. Weigh 2 g of the dried activated alumina support with an electronic balance, and slowly and evenly pour the weighed activated alumina support into the beaker containing the metal nitrate solution in Step S31. After the activated alumina support is fully loaded with the metal nitrate solution, cover the beaker mouth with plastic wrap and fix it with a rubber band. Then place the beaker in an ultrasonic instrument and ultrasonicate for 3 h. After ultrasonication is completed, place the beaker in an oven at 110 °C for drying. After drying overnight, transfer it to a muffle furnace and calcine at 950 °C for 180 min, and then naturally cool to obtain a cobalt-based metal oxide. The loading amount of the active component (i.e., cobalt element) in this cobalt-based metal oxide is 5%, and the loading amount of the modified component (i.e., sodium element) is 1%. After grinding and sieving the obtained cobalt-based metal oxide to 40 - 60 mesh, a metal oxide catalyst that can be used for the selective decomposition of nitrous oxide to prepare nitric acid can be obtained, denoted as metal oxide catalyst 5% Co - 1% Na.

[0059] Example 3

[0060] In Example 3, the specific process for preparing the metal oxide catalyst can be as follows:

[0061] Step S41. Weigh 0.3626 g of cobalt nitrate hexahydrate and 0.1644 g of sodium nitrate respectively with an electronic balance, pour them into a beaker containing 1.9931 g of deionized water, and then place the beaker in a constant temperature water bath at 20 - 30 °C. Stir continuously to completely dissolve the solids to obtain a metal nitrate solution.

[0062] Step S42. Weigh 2 g of the dried activated alumina support with an electronic balance, and slowly and evenly pour the weighed activated alumina support into the beaker containing the metal nitrate solution in Step S41. After the activated alumina support is fully loaded with the metal nitrate solution, cover the beaker mouth with plastic wrap and fix it with a rubber band. Then place the beaker in an ultrasonic instrument for ultrasonic treatment for 3 h. After the ultrasonic treatment is completed, place the beaker in an oven at 110 °C for drying. After drying overnight, transfer it to a muffle furnace and calcine it at 950 °C for 180 min, and then cool it naturally to obtain a cobalt-based metal oxide. The loading amount of the active component (i.e., cobalt element) in this cobalt-based metal oxide is 5%, and the loading amount of the modified component (i.e., sodium element) is 3%. After grinding and screening the obtained cobalt-based metal oxide to 40 - 60 mesh, a metal oxide catalyst that can be used for the selective decomposition of nitrous oxide to prepare nitric acid can be obtained, denoted as metal oxide catalyst 5% Co - 3% Na.

[0063] Example 4

[0064] In Example 4, the specific process for preparing the metal oxide catalyst can be as follows:

[0065] Step S51. Weigh 0.3626 g of cobalt nitrate hexahydrate and 0.274 g of sodium nitrate respectively with an electronic balance, pour them into a beaker containing 1.9931 g of deionized water, and then place the beaker in a constant temperature water bath at 20 - 30 °C. Stir continuously to completely dissolve the solids to obtain a metal nitrate solution.

[0066] Step S52. Weigh 2 g of the dried activated alumina support with an electronic balance, and slowly and evenly pour the weighed activated alumina support into the beaker containing the metal nitrate solution in Step S51. After the activated alumina support is fully loaded with the metal nitrate solution, cover the beaker mouth with plastic wrap and fix it with a rubber band. Then, place the beaker in an ultrasonic instrument and ultrasonicate for 3 h. After ultrasonication is completed, place the beaker in an oven at 110 °C for drying. After drying overnight, transfer it to a muffle furnace and calcine at 950 °C for 180 min, and then cool it naturally to obtain the cobalt-based metal oxide. The loading amount of the active component (i.e., cobalt element) in the cobalt-based metal oxide is 5%, and the loading amount of the modified component (i.e., sodium element) is 5%. After the obtained cobalt-based metal oxide is ground and sieved to 40-60 mesh, the metal oxide catalyst that can be used for the selective decomposition of nitrous oxide to prepare nitric acid can be obtained, denoted as metal oxide catalyst 5%Co-5%Na.

[0067] Example 5

[0068] In Example 5, the specific process flow of the preparation method of the metal oxide catalyst can be as follows:

[0069] Step S61. Weigh 0.3626 g of cobalt nitrate hexahydrate and 0.04293 g of potassium nitrate with an electronic balance, pour them into a beaker containing 1.9931 g of deionized water, and then place the beaker in a constant temperature water bath at 20-30 °C and stir continuously to completely dissolve the solid to obtain a metal nitrate solution.

[0070] Step S62. Weigh 2 g of the dried activated alumina support with an electronic balance, and slowly and evenly pour the weighed activated alumina support into the beaker containing the metal nitrate solution in Step S61. After the activated alumina support is fully loaded with the metal nitrate solution, cover the beaker mouth with plastic wrap and fix it with a rubber band. Then, place the beaker in an ultrasonic instrument and ultrasonicate for 3 h. After ultrasonication is completed, place the beaker in an oven at 110 °C for drying. After drying overnight, transfer it to a muffle furnace and calcine at 950 °C for 180 min, and then cool it naturally to obtain the cobalt-based metal oxide. The loading amount of the active component (i.e., cobalt element) in the cobalt-based metal oxide is 5%, and the loading amount of the modified component (i.e., potassium element) is 1%. After the obtained cobalt-based metal oxide is ground and sieved to 40-60 mesh, the metal oxide catalyst that can be used for the selective decomposition of nitrous oxide to prepare nitric acid can be obtained, denoted as metal oxide catalyst 5%Co-1%K.

[0071] Example 6

[0072] In Example 6, the specific process flow of the preparation method of the metal oxide catalyst can be as follows:

[0073] Step S71. Weigh 0.3626 g of cobalt nitrate hexahydrate and 0.1288 g of potassium nitrate respectively with an electronic balance, pour them into a beaker containing 1.9931 g of deionized water, then place the beaker in a constant temperature water bath at 20 - 30 °C, and continuously stir to completely dissolve the solids to obtain a metal nitrate solution.

[0074] Step S72. Weigh 2 g of the dried activated alumina support with an electronic balance, and slowly and evenly pour the weighed activated alumina support into the beaker containing the metal nitrate solution in Step S71. After the activated alumina support is fully loaded with the metal nitrate solution, cover the beaker mouth with plastic wrap and fix it with a rubber band. Then place the beaker in an ultrasonic instrument for ultrasonic treatment for 3 h. After the ultrasonic treatment is completed, place the beaker in an oven at 110 °C for drying. After drying overnight, transfer it to a muffle furnace and calcine it at 950 °C for 180 min, and then let it cool naturally to obtain a cobalt-based metal oxide. The loading amount of the active component (i.e., cobalt element) in the cobalt-based metal oxide is 5%, and the loading amount of the modified component (i.e., potassium element) is 3%. After the obtained cobalt-based metal oxide is ground and sieved to 40 - 60 mesh, a metal oxide catalyst that can be used for selectively decomposing nitrous oxide to prepare nitric acid can be obtained, denoted as metal oxide catalyst 5% Co - 3% K.

[0075] Example 7

[0076] In Example 7, the specific process for preparing the metal oxide catalyst can be as follows:

[0077] Step S81. Weigh 0.3626 g of cobalt nitrate hexahydrate and 0.2147 g of potassium nitrate respectively with an electronic balance, pour them into a beaker containing 1.9931 g of deionized water, then place the beaker in a constant temperature water bath at 20 - 30 °C, and continuously stir to completely dissolve the solids to obtain a metal nitrate solution.

[0078] Step S82. Weigh 2 g of the dried activated alumina support using an electronic balance, and slowly and evenly pour the weighed activated alumina support into the beaker containing the metal nitrate solution in Step S81. After the activated alumina support is fully loaded with the metal nitrate solution, cover the beaker mouth with plastic wrap and fix it with a rubber band. Then, place the beaker in an ultrasonic instrument and ultrasonicate for 3 h. After the ultrasonication is completed, place the beaker in an oven at 110 °C for drying. After drying overnight, transfer it to a muffle furnace and calcine at 950 °C for 180 min, and then cool it naturally to obtain cobalt-based metal oxide. The loading amount of the active component (i.e., cobalt element) in this cobalt-based metal oxide is 5%, and the loading amount of the modified component (i.e., potassium element) is 5%. After that, grind and screen the obtained cobalt-based metal oxide to 40 - 60 mesh to obtain a metal oxide catalyst that can be used for the selective decomposition of nitrous oxide to prepare nitric acid, denoted as metal oxide catalyst 5%Co - 5%K.

[0079] It should be noted that cobalt nitrate hexahydrate, potassium nitrate, sodium nitrate, and activated alumina used in the above embodiments (including Embodiment 1, Embodiment 2, Embodiment 3, Embodiment 4, Embodiment 5, Embodiment 6, and Embodiment 7) are all of analytical grade and can be directly purchased from a reagent company (such as Sinopharm Chemical Reagent Co., Ltd.).

[0080] Moreover, by respectively testing the N2O conversion rate and NO selectivity of the metal oxide catalysts 5%Co, 5%Co - 1%Na, 5%Co - 3%Na, 5%Co - 5%Na, 5%Co - 1%K, 5%Co - 3%K, and 5%Co - 5%K prepared in the above Embodiment 1 to the above Embodiment 7 at different reaction temperatures, the N2O conversion rates of each metal oxide catalyst at different reaction temperatures are as Figure 2 and shown in Table 1 below, and the NO selectivities of each metal oxide catalyst at different reaction temperatures are as Figure 3 and shown in Table 2 below.

[0081] Among them, the process of testing the N2O conversion rate and NO selectivity of the metal oxide catalyst at different reaction temperatures may include: loading 0.5 g of the metal oxide catalyst into the reaction tube of a fixed-bed tubular reactor, and placing the metal oxide catalyst within the constant-temperature section of the reactor. Then, nitrogen is introduced into the reactor, and the temperature of the reactor is raised from room temperature to 600 °C at a rate of 3 °C / min. After reaching 600 °C, the gas introduced into the reactor is switched from nitrogen to the reaction feed gas, so that the reaction feed gas reacts under the action of the metal oxide catalyst. The volume ratio of each gas component in the reaction feed gas is: nitrous oxide / nitrogen / oxygen = 2 / 2 / 1, the reaction pressure is atmospheric pressure, and the gas flow rate is 100 mL / min. After stabilizing for a period of time, the gas product at the outlet of the reactor is cooled by a condenser and then transported through a pipeline to a washing bottle containing 100 mL of ionized water for absorption to obtain nitric acid. The ventilation time is set to 30 minutes. After completion, the pH value of the solution in the washing bottle is measured using a pH meter to calculate the selectivity of the catalyst for nitric oxide during the decomposition of nitrous oxide. At the same time, a gas chromatograph is used to analyze the tail gas at the outlet of the reactor, and by comparing the content of nitrous oxide remaining in the reaction with the content of nitrous oxide in the feed gas, the N2O conversion rate of the metal oxide catalyst at 600 °C is obtained. Subsequently, the reaction temperature (i.e., the target temperature) is raised to 700 °C, 800 °C, and 900 °C, and the above steps are repeated to obtain the N2O conversion rate and NO selectivity at each temperature.

[0082] Table 1

[0083] Temperature 600℃ 700℃ 800℃ 900℃ Example 1 79.82％ 99.81％ 100％ 100％ Example 2 20.28％ 79.57％ 99.42％ 100％ Example 3 19.00％ 85.41％ 99.93％ 100％ Example 4 17.71％ 81.39％ 99.82％ 100％ Example 5 25.31％ 93.11％ 100％ 100％ Example 6 26.19％ 89.62％ 99.31％ 100％ Example 7 22.87％ 93.58％ 100％ 100％

[0084] As can be seen from Table 1 and Figure 2 it can be known that for the metal oxide catalysts prepared from Example 1 to Example 7 (i.e., metal oxide catalyst 5% Co, metal oxide catalyst 5% Co - 1% Na, metal oxide catalyst 5% Co - 3% Na, metal oxide catalyst 5% Co - 5% Na, metal oxide catalyst 5% Co - 1% K, metal oxide catalyst 5% Co - 3% K, and metal oxide catalyst 5% Co - 5% K), when the reaction temperature is higher than 700 °C, the conversion rate of N2O can be close to 100%, and it has good catalytic performance and high heat resistance.

[0085] Table 2

[0086] Temperature 600℃ 700℃ 800℃ 900℃ Example 1 0.18％ 0.087％ 0.49％ 3.10％ Example 2 0.24％ 1.03％ 2.46％ 4.28％ Example 3 0.06％ 1.10％ 2.46％ 3.73％ Example 4 0.25％ 1.07％ 2.89％ 2.58％ Example 5 0.21％ 0.96％ 1.70％ 3.32％ Example 6 0.07％ 0.91％ 2.00％ 3.81％ Example 7 0.54％ 1.74％ 2.05％ 4.08％

[0087] As can be seen from Table 2 and Figure 3It can be seen that the metal oxide catalysts prepared in Examples 1 to 7 (i.e., metal oxide catalyst 5% Co, metal oxide catalyst 5% Co - 1% Na, metal oxide catalyst 5% Co - 3% Na, metal oxide catalyst 5% Co - 5% Na, metal oxide catalyst 5% Co - 1% K, metal oxide catalyst 5% Co - 3% K, and metal oxide catalyst 5% Co - 5% K) can selectively decompose N2O into NO under high-temperature conditions. At the same time, the selectivity of this metal oxide catalyst for NO increases with the increase of temperature after 600 °C and can reach 4.276% at 900 °C.

[0088] Furthermore, from Table 2 and Figure 3 It can be seen that under the condition that the reaction temperature is 600 °C, the metal oxide catalysts prepared in Examples 1 to 7 (i.e., metal oxide catalyst 5% Co, metal oxide catalyst 5% Co - 1% Na, metal oxide catalyst 5% Co - 3% Na, metal oxide catalyst 5% Co - 5% Na, metal oxide catalyst 5% Co - 1% K, metal oxide catalyst 5% Co - 3% K, and metal oxide catalyst 5% Co - 5% K) can decompose N2O into NO to produce nitric acid. However, the selectivity of NO at this time is relatively small, and the metal oxide catalyst 5% Co - 5% K prepared in Example 7 has the highest selectivity for NO.

[0089] Under the condition that the reaction temperature is 700 °C, the metal oxide catalysts prepared in Examples 1 to 7 (i.e., metal oxide catalyst 5% Co, metal oxide catalyst 5% Co - 1% Na, metal oxide catalyst 5% Co - 3% Na, metal oxide catalyst 5% Co - 5% Na, metal oxide catalyst 5% Co - 1% K, metal oxide catalyst 5% Co - 3% K, and metal oxide catalyst 5% Co - 5% K) still have selectivity for NO, but there are differences in selectivity. Among them, the metal oxide catalyst 5% Co - 5% K prepared in Example 7 has the highest selectivity for NO.

[0090] Under the condition that the reaction temperature is 800 °C, the metal oxide catalysts prepared in Examples 1 to 7 (i.e., metal oxide catalyst 5% Co, metal oxide catalyst 5% Co - 1% Na, metal oxide catalyst 5% Co - 3% Na, metal oxide catalyst 5% Co - 5% Na, metal oxide catalyst 5% Co - 1% K, metal oxide catalyst 5% Co - 3% K, and metal oxide catalyst 5% Co - 5% K) can decompose N2O into NO, and the metal oxide catalyst 5% Co - 5% Na prepared in Example 4 has the highest selectivity for NO.

[0091] Under the condition that the reaction temperature is 900 °C, the metal oxide catalysts prepared in Examples 1 to 7 (i.e., metal oxide catalyst 5% Co, metal oxide catalyst 5% Co - 1% Na, metal oxide catalyst 5% Co - 3% Na, metal oxide catalyst 5% Co - 5% Na, metal oxide catalyst 5% Co - 1% K, metal oxide catalyst 5% Co - 3% K, and metal oxide catalyst 5% Co - 5% K) can decompose N2O into NO, and among them, the metal oxide catalyst 5% Co - 1% Na prepared in Example 2 has the highest selectivity for NO.

[0092] From the above analysis, it can be seen that during the decomposition of nitrous oxide, the loadings of the active component and the modified component in the metal oxide catalyst provided in the embodiments of the present application have a great influence on the NO selectivity of the metal oxide catalyst, and the reaction temperature also has a great influence on the NO selectivity of the metal oxide catalyst.

[0093] As can be seen from the above, the preparation method of the metal oxide catalyst provided in this embodiment, by preparing a metal nitrate solution, the metal nitrate in the metal nitrate solution includes the nitrate of the active component, the active component includes cobalt, and then loading the metal nitrate solution onto the carrier, performing ultrasonic treatment, drying, and calcination to obtain the metal oxide catalyst, the metal oxide catalyst includes the carrier and the active component loaded on the carrier, thereby providing a metal oxide catalyst applicable to the selective decomposition of nitrous oxide to prepare nitric acid. The preparation method of this metal oxide catalyst is simple, low in cost, and during the decomposition of nitrous oxide, this metal oxide catalyst has high selectivity for nitric oxide, high conversion rate for nitrous oxide, and can produce nitric acid while treating nitrous oxide, improving the secondary utilization rate of nitrous oxide in industry. Therefore, it can bring higher economic benefits while achieving the goal of nitrous oxide emission reduction.

[0094] In order to better implement the preparation method of the metal oxide catalyst provided in the embodiments of the present application, the embodiments of the present application also provide a metal oxide catalyst, which is prepared by using the preparation method of the metal oxide catalyst provided in any of the above embodiments.

[0095] Specifically, this metal oxide catalyst is a cobalt-based metal oxide, and its mesh number can be 40 - 60 meshes so that it can be used as a catalyst in the decomposition reaction of nitrous oxide.

[0096] Specifically, the metal oxide catalyst may include a carrier and an active component supported on the carrier. Among them, the carrier may be an activated alumina carrier. For example, it may specifically be an activated alumina carrier with a mesh size of 40 to 60. The active component may include cobalt. For example, it may specifically be cobalt. And, in this metal oxide catalyst, the loading amount of the active component (i.e., the mass ratio of the active component to the mass of the carrier) may be 3 to 7%, for example, it may specifically be 3%, 4%, 5%, 6% or 7%, etc.

[0097] In some embodiments, the metal oxide catalyst may further include a modifying component supported on the carrier. Among them, the modifying component may include sodium and / or potassium. For example, it may specifically be sodium or potassium. And, in this metal oxide catalyst, the loading amount of the modifying component (i.e., the mass ratio of the modifying component to the mass of the carrier) is 1 to 7%, for example, it may specifically be 1%, 2%, 3%, 4%, 5%, 6% or 7%, etc.

[0098] And it should be noted that the metal oxide catalyst in the embodiments of the present application, since it is prepared by using the preparation method of the metal oxide catalyst provided in any of the above embodiments, thus has all the same beneficial effects, which will not be elaborated herein in this embodiment.

[0099] Based on the metal oxide catalyst described in the above embodiments, this embodiment will be further described from the perspective of the application method of the metal oxide catalyst.

[0100] The application method of the metal oxide catalyst provided in the embodiments of the present application can be applied to the scenario of selectively decomposing nitrous oxide to prepare nitric acid. The specific process of the application method of this metal oxide catalyst can be as follows:

[0101] Use the metal oxide catalyst to catalytically decompose nitrous oxide into nitric oxide, and oxidize and absorb the nitric oxide to obtain nitric acid.

[0102] Specifically, the metal oxide catalyst described in any of the above embodiments of the present application can be used to catalytically decompose nitrous oxide into nitric oxide. And, oxygen can be used to oxidize the nitric oxide, and water (such as deionized water) can be used to absorb the obtained oxidation product to obtain nitric acid.

[0103] Moreover, in specific implementation, the metal oxide catalyst described in any of the above embodiments of the present application can be loaded into the reaction tube of a fixed-bed tubular reactor, and the metal oxide catalyst is located within the constant-temperature section interval of the reactor. Then, nitrogen is introduced into the reactor, and the temperature of the reactor is raised from room temperature to the target temperature at a rate of 2-5 °C / min. The target temperature is 600-900 °C. After reaching the target temperature, the gas introduced into the reactor is switched from nitrogen to the reaction raw material gas, so that the reaction raw material gas reacts under the action of the metal oxide catalyst. The reaction raw material gas includes nitrous oxide and oxygen. The gas product at the outlet of the reactor is cooled by a condenser and then transported through a pipeline to a washing bottle filled with deionized water, where it is absorbed and converted into nitric acid.

[0104] Among them, the process of loading the metal oxide catalyst described in any of the above embodiments of the present application into the reaction tube of a fixed-bed tubular reactor and making the metal oxide catalyst located within the constant-temperature section interval of the reactor can specifically include: loading 0.5 g of the metal oxide catalyst described in any of the above embodiments of the present application into the reaction tube of a fixed-bed tubular reactor, making the metal oxide catalyst located within the constant-temperature section interval of the reactor, sandwiching the metal oxide catalyst between quartz wool, and compacting the quartz wool with 1.5 g of quartz sand with a mesh number of 8-16 above it.

[0105] Among them, the reaction raw material gas introduced into the reactor can include nitrous oxide, nitrogen, and oxygen. Moreover, the volume ratio of each gas component in the reaction raw material gas introduced into the reactor can be: nitrous oxide / nitrogen / oxygen = 2 / 2 / 1.

[0106] Among them, the reaction temperature (i.e., the above target temperature) can specifically be 600 °C, 700 °C, 800 °C, or 900 °C. The reaction pressure can be atmospheric pressure, the reaction time can be 8-40 h, and the gas flow rate in the reactor can be controlled at 100 mL / min.

[0107] In the above embodiments, the descriptions of each embodiment have their own emphases. For the parts not detailed in a certain embodiment, reference can be made to the relevant descriptions of other embodiments.

[0108] The above are only the preferred embodiments of the present application and are not intended to limit the present application. Any modifications, equivalent replacements, and improvements made within the spirit and principle of the present application shall be included within the protection scope of the present application. The above are only the preferred embodiments of the present application and are not intended to limit the present application. Any modifications, equivalent replacements, and improvements made within the spirit and principle of the present application shall be included within the protection scope of the present application.

Claims

1. A method for preparing a metal oxide catalyst, characterized in that, Comprising: Preparing a metal nitrate solution, wherein the metal nitrate in the metal nitrate solution includes the nitrate of the active component, and the active component includes cobalt; Loading the metal nitrate solution onto a support, followed by ultrasonic treatment, drying, and calcination to obtain a metal oxide catalyst, which includes the support and the active component loaded on the support.

2. The preparation method of the metal oxide catalyst according to claim 1, characterized in that, The metal nitrate further includes the nitrate of the modifying component, and the modifying component includes sodium and / or potassium; moreover, the metal oxide catalyst further includes the modifying component loaded on the support, and in the metal oxide catalyst, the mass ratio of the active component to the mass of the support is 3-7%, and the mass ratio of the modifying component to the mass of the support is 1-7%.

3. The preparation method of the metal oxide catalyst according to claim 1, wherein, The support is an activated alumina support.

4. The preparation method of the metal oxide catalyst according to claim 1, wherein, The step of loading the metal nitrate solution onto the support includes: Loading the metal nitrate solution onto the support by the equal-volume impregnation method.

5. The preparation method of the metal oxide catalyst according to claim 1, characterized in that, The step of loading the metal nitrate solution onto the support includes: Adding the support into a container filled with the metal nitrate solution.

6. The preparation method of the metal oxide catalyst according to claim 1, wherein The step of loading the metal nitrate solution onto the support, followed by ultrasonic treatment, drying, and calcination to obtain a metal oxide catalyst includes: Loading the metal nitrate solution onto the support, performing ultrasonic treatment at room temperature for 1-5 h, drying overnight, and then calcining in an air atmosphere at 900-1000 °C for 150-250 min to obtain a metal oxide catalyst.

7. The method for preparing a metal oxide catalyst according to claim 1, wherein The step of preparing the metal nitrate solution includes: Weighing the metal nitrate and dissolving the weighed metal nitrate in deionized water under a constant temperature condition of 20-30 °C to obtain a metal nitrate solution.

8. A metal oxide catalyst, characterized in that, Prepared by the method for preparing a metal oxide catalyst according to any one of claims 1-7.

9. A method for applying a metal oxide catalyst, characterized in that, Comprising: Using the metal oxide catalyst according to claim 8 to catalytically decompose nitrous oxide into nitric oxide, and oxidizing and absorbing the nitric oxide to obtain nitric acid.

10. The application method of the metal oxide catalyst according to claim 9, characterized in that, The step of using the metal oxide catalyst according to claim 8 to catalytically decompose nitrous oxide into nitric oxide, and oxidizing and absorbing the nitric oxide to obtain nitric acid includes: Loading the metal oxide catalyst according to claim 8 into the reaction tube of a fixed-bed tubular reactor, and making the metal oxide catalyst located in the constant-temperature section interval of the reactor. Then, introducing nitrogen into the reactor and heating the reactor from room temperature to the target temperature at a rate of 2-5 °C / min, where the target temperature is 600-900 °C. After reaching the target temperature, switching the gas introduced into the reactor from nitrogen to the reaction raw material gas, so that the reaction raw material gas reacts under the action of the metal oxide catalyst. The reaction raw material gas includes nitrous oxide and oxygen. The gas product at the outlet of the reactor is cooled by a condenser and then transported through a pipeline to a washing bottle filled with deionized water, where it is absorbed and converted into nitric acid.

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