Preparation method of catalyst, catalyst and application of catalyst

Abstract

The invention relates to a preparation method of a catalyst, the catalyst and application of the catalyst.The preparation method comprises the steps that molecular sieve powder is added into a first solvent to be prepared into a first solution, a metal oxide precursor is added into a second solvent to be prepared into a second solution, a precipitator is added into a third solvent to be prepared into a third solution, the precipitator is an alkaline solution; heating the first solution to a preset temperature, and dropwise adding the second solution and the third solution into the first solution at the same time to obtain a precipitate which is a metal hydroxide adsorbed on a molecular sieve; the precipitate is aged, washed, dried and roasted, the catalyst is obtained, and the catalyst is a metal oxide adsorbed on a molecular sieve. Compared with the traditional mode of grinding and mixing the metal oxide and the molecular sieve powder, the preparation method disclosed by the invention has the advantages that the metal oxide is uniformly deposited on the surface of the molecular sieve, and the distance between the two active components is shortened, so that the activity of the catalyst is improved, and the repeatability is relatively high.

Description

Technical Field

[0001] The present disclosure relates to the field of catalysts, and in particular to a preparation method of a catalyst, a catalyst, and an application of the catalyst. Background Art

[0002] With the use of fossil fuels such as coal, petroleum, and natural gas in power generation, industrial production, and transportation, a large number of CO2 emission sources have been generated. As the main greenhouse gas, excessive emissions of CO2 have led to an increase in the global average temperature, which in turn has caused a series of problems such as glacier melting and sea level rise. Therefore, the utilization of CO2 has received increasing attention. In particular, using CO2 as a carbon source to produce chemicals is environmentally friendly and sustainable. It not only helps to reduce the concentration of CO2 in the atmosphere but also can replace the traditional chemical production method based on fossil fuels.

[0003] Aromatics are one of the important basic chemical raw materials in the synthesis of organic materials. Many polymer materials such as polystyrene, phenol resin, nylon, and polyethylene terephthalate resin can be synthesized using aromatics. At present, direct synthesis of hydrocarbons from CO2 hydrogenation is one of the more common routes. Compared with the indirect method, the direct method has advantages such as simple operation, fewer processes, and better efficiency. The direct method usually uses a bifunctional catalyst, that is, a catalyst system in which a metal oxide is coupled with a molecular sieve.

[0004] Numerous studies have shown that the distance between different active sites in the bifunctional catalyst significantly affects the catalytic performance, and its CO2 conversion rate, CO selectivity, and aromatics selectivity all increase with the shortening of the distance between the dual active sites. At present, metal oxides are usually prepared first, and then the metal oxide powder and the molecular sieve powder are physically mixed and granulated. However, there are uniformity problems in the powder mixing of different batches of catalysts, resulting in poor repeatability of catalyst performance. Therefore, it is necessary to develop a more effective mixing method to maximize the catalyst performance and stability. Summary of the Invention

[0005] The purpose of the present disclosure is to overcome the deficiencies of the prior art and provide a preparation method of a catalyst, a catalyst, and an application of the catalyst.

[0006] According to the first aspect of the present disclosure, a preparation method of a catalyst is provided. The preparation method of the catalyst includes the following steps: S1. Add the molecular sieve powder to a first solvent to form a first solution, add the metal oxide precursor to a second solvent to form a second solution, and add a precipitating agent to a third solvent to form a third solution. The precipitating agent is an alkaline solution; S2. Heat the first solution to a preset temperature, and simultaneously drop the second solution and the third solution into the first solution to obtain a precipitate, which is a metal hydroxide adsorbed on the molecular sieve. S3. Age, wash, dry, and calcine the precipitate to obtain the catalyst, which is a metal oxide adsorbed on the molecular sieve.

[0007] In one embodiment of the present disclosure, the molecular sieve in step S1 is a ZSM-5 molecular sieve.

[0008] In one embodiment of the present disclosure, the molar ratio of SiO2 to Al2O3 of the molecular sieve is 25 - 500.

[0009] In one embodiment of the present disclosure, the metal oxide precursor includes a first metal salt and a second metal salt; The first metal salt is at least one of a nitrate, a sulfate, and a chloride salt of Zr element; The second metal salt is at least one of a nitrate, a sulfate, and a chloride salt of Ce element, and / or at least one of a nitrate, a sulfate, and a chloride salt of Zn element, and / or at least one of a nitrate, a sulfate, and a chloride salt of Cr element, and / or at least one of a nitrate, a sulfate, and a chloride salt of In element.

[0010] In one embodiment of the present disclosure, the precipitating agent is selected from at least one of NH3·H2O, (NH4)2CO3, Na2CO3, NaHCO3, and NaOH.

[0011] In one embodiment of the present disclosure, the mass concentration of the molecular sieve in the first solution is 5 - 50 g / L.

[0012] In one embodiment of the present disclosure, the concentration of the second solution is 0.1 - 2 mol / L.

[0013] In one embodiment of the present disclosure, the concentration of the third solution is 0.1 - 3 mol / L.

[0014] In one embodiment of the present disclosure, the first solvent, the second solvent, and the third solvent in step S1 are all deionized water.

[0015] In one embodiment of the present disclosure, in step S2, the first solution is heated to the preset temperature by a water bath, and the preset temperature is 50 - 85 °C.

[0016] In one embodiment of the present disclosure, during the process of simultaneously dropping the second solution and the third solution into the first solution in step S2, the dropping rate of the third solution is controlled so that the pH value of the first solution is maintained at 7 - 9.

[0017] In one embodiment of the present disclosure, in step S3, aging, washing, drying, and calcining the precipitate include: Aging the precipitate in a water bath for 1 - 5 h, centrifuging, washing 1 - 5 times, then placing it in an oven and drying at 90 - 130 °C for 4 - 24 h, and transferring it to a muffle furnace for calcining at 400 - 600 °C for 2 - 12 h.

[0018] According to a second aspect of the present disclosure, a catalyst is provided. The catalyst is prepared by the preparation method described in any one of the above embodiments, and the catalyst is a metal oxide adsorbed on a molecular sieve; The metal oxide includes XZr oxide, where X includes at least one of Ce, Zn, Cr, and In, and the molar ratio of the metal elements of X and Zr in the metal oxide is 1:5 - 10:1.

[0019] In one embodiment of the present disclosure, the mass ratio of the metal oxide to the molecular sieve is 0.2 - 5.

[0020] According to a third aspect of the present disclosure, an application of a catalyst is provided. The catalyst is prepared by the preparation method described in any one of the above embodiments and is applied to directly prepare aromatics by hydrogenating CO2. The catalyst is pretreated, and then a mixed raw material of CO2 and H2 is introduced into a reactor filled with the catalyst for a chemical reaction to prepare aromatics.

[0021] In one embodiment of the present disclosure, the volume ratio of CO2 to H2 in the mixed raw material is 1:3 - 5, the reaction temperature is 300 - 400 °C, the reaction pressure is 2 - 6 MPa, and the reaction space velocity is 500 - 20000 h -1 .

[0022] In one embodiment of the present disclosure, the pretreatment of the catalyst includes: Loading the catalyst into a reactor and introducing a gas containing H2 into the reactor for a reduction reaction.

[0023] In one embodiment of the present disclosure, the temperature of the reduction reaction is 300 - 500 °C, and the time of the reduction reaction is 2 - 10 h.

[0024] One beneficial effect of the preparation method of the catalyst of the present disclosure is that, in this preparation method, a molecular sieve and a metal oxide precursor are configured into solutions, and the two solutions are mixed in the alkaline environment provided by a precipitant, so that metal hydroxide precipitates uniformly adheres to the molecular sieve in the solution. After subsequent treatment to remove crystal water, metal oxide adsorbed on the molecular sieve is obtained. The catalyst produced by this method solves the problem of uniformity in the mixing of different active components in the catalyst and shortens the distance between the two active components compared with the traditional mixing method of grinding and pressing a metal oxide catalyst and molecular sieve powder, thereby improving the activity of the catalyst. In addition, this preparation method is simple and has high repeatability, and has both high activity and stability, and is suitable for industrial scale-up applications.

[0025] The catalyst of the present disclosure is prepared by the above preparation method, and thus has the same technical effects as the preparation method of the catalyst, which will not be elaborated herein.

[0026] In the application of the catalyst of the present disclosure, the catalyst prepared by the above preparation method stably improves the selectivity of aromatics and reduces the generation of methane by-products. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] The drawings incorporated in and constituting a part of this specification illustrate embodiments of the present disclosure and, together with the description, serve to explain the principles of the present disclosure.

[0028] Figure 1 It is a flowchart of a preparation method of a catalyst provided in an embodiment of the present disclosure. DETAILED DESCRIPTION

[0029] Various exemplary embodiments of the present disclosure will now be described in detail with reference to the drawings. It should be noted that: Unless otherwise specifically stated, the relative arrangements of components and steps, numerical expressions and values set forth in these embodiments do not limit the scope of the present disclosure.

[0030] The following description of at least one exemplary embodiment is merely illustrative in nature and in no way limits the present disclosure, its application or use.

[0031] Techniques, methods, and devices known to those of ordinary skill in the relevant art may not be discussed in detail, but where appropriate, the techniques, methods, and devices should be considered as part of the specification.

[0032] In all examples shown and discussed herein, any specific value should be construed as merely exemplary and not as a limitation. Thus, other examples of exemplary embodiments may have different values.

[0033] It should be noted that like reference numerals and letters refer to like items in the following figures, and thus, once an item is defined in one figure, further discussion thereof in subsequent figures is not necessary.

[0034] In this document, terms such as "upper", "lower", "front", "rear", "left", "right", etc. are only used to represent the relative positional relationship between relevant parts, rather than defining the absolute positions of these relevant parts.

[0035] In this document, terms such as "first", "second", etc. are only used to distinguish each other, rather than indicating importance, order, and the prerequisite for each other's existence, etc.

[0036] In this document, terms such as "equal", "same", etc. are not strict mathematical and / or geometric restrictions, and also include errors that can be understood by those skilled in the art and are allowed in manufacturing or using, etc.

[0037] Zr: zirconium, Ce: cerium, Cr: chromium, Zn: zinc, In: indium, SiO2: silicon dioxide, Al2O3: aluminum oxide, NH3·H2O: ammonia water, (NH4)2CO3: ammonium carbonate, Na2CO3: sodium carbonate, NaHCO3: sodium bicarbonate, NaOH: sodium hydroxide.

[0038] Precursor: A precursor refers to the initial substance that can be transformed into the target product through a series of steps during a chemical reaction or physical change process. Specifically, a precursor can be an element, a compound, or a complex, and its main characteristic is that it can undergo chemical transformation to generate the required final product under specific conditions.

[0039] Space velocity: Space velocity (Gas Hourly Space Velocity, abbreviated as GHSV) is an important parameter in chemical engineering used to describe the flow rate of gas in a fixed-bed reactor. It is defined as the volume of gas passing through a unit volume of catalyst per unit time, usually expressed as the number of standard cubic meters of gas passing through each cubic meter of catalyst per hour (m 3 / (m 3 ·h) or h -1 ). Simply put, the space velocity reflects the length of time for the gas to contact the catalyst.

[0040] It should be noted that the raw materials used in the present invention are all ordinary commercially available products, and thus no specific limitation is imposed on their sources.

[0041] Conventional catalysts for the direct hydrogenation of CO2 to aromatics usually first prepare metal oxides, and then physically mix the metal oxides and molecular sieve powders and granulate them. However, there are uniformity problems in the powder mixing of different batches of catalysts, resulting in poor repeatability of catalyst performance. For this reason, the present disclosure provides a method for preparing a catalyst, a catalyst, and an application of the catalyst. For ease of understanding, the following will refer to Figure 1 and, in conjunction with examples, detail the method for preparing the catalyst, the catalyst, and the application of the catalyst of the present disclosure.

[0042] The present disclosure provides a method for preparing a catalyst, comprising the following steps: S1. Add molecular sieve powder to a first solvent to form a first solution, add a metal oxide precursor to a second solvent to form a second solution, and add a precipitating agent to a third solvent to form a third solution. The precipitating agent is an alkaline solution; S2. Heat the first solution to a preset temperature, and simultaneously drip the second solution and the third solution into the first solution to obtain a precipitate, which is a metal hydroxide adsorbed on the molecular sieve; S3. Age, wash, dry, and calcine the precipitate to obtain a catalyst, which is a metal oxide adsorbed on the molecular sieve.

[0043] Specifically, the molecular sieve is a crystalline aluminosilicate material with a regular microporous structure, which can selectively adsorb or repel molecules of different sizes and shapes. The molecular sieve powder is dispersed in the first solvent and stirred to form a uniform suspension solution, i.e., the first solution. The metal oxide precursor is a metal salt, and the precursor is added to the second solvent to form a second solution, so that the second solution contains metal cations. The precipitating agent is mainly used to adjust the pH, construct an alkaline environment, and provide hydroxide ions.

[0044] Heating the first solution helps to increase the reaction rate. The second solution and the third solution are simultaneously dripped into the first solution. The second solution provides metal cations, and the third solution provides hydroxide ions, which combine in the first solution to form a metal hydroxide precipitate and are uniformly adsorbed on the molecular sieve.

[0045] The metal hydroxide adsorbed on the molecular sieve is aged, washed, dried, and calcined to remove the crystal water therein, and finally a metal oxide adsorbed on the molecular sieve is obtained as the catalyst.

[0046] By configuring molecular sieves and metal oxide precursors into solutions and mixing the two solutions in an alkaline environment provided by a precipitating agent, metal hydroxides precipitate and uniformly adhere to the molecular sieves in the solution. After subsequent treatment to remove crystal water, metal oxides adsorbed on the molecular sieves are obtained. The catalyst produced by this method solves the problem of uniformity in the mixing of different active components in the catalyst and shortens the distance between the two active components compared with the traditional mixing method of grinding and pressing metal oxide catalysts and molecular sieve powders, thereby improving the activity of the catalyst. In addition, this preparation method is simple, has high repeatability, and has both high activity and stability, making it suitable for industrial scale-up applications.

[0047] In one embodiment of the present disclosure, the molecular sieve in step S1 is a ZSM-5 molecular sieve.

[0048] Specifically, ZSM-5 (Zeolite Socony Mobil-5) is a synthetic zeolite molecular sieve with a unique three-dimensional pore structure, which can provide uniformly distributed strong acid centers, helping to improve the selectivity of the reaction. In addition, due to its unique pore structure, the ZSM-5 molecular sieve also has the function of shape-selective catalysis, which can achieve selective catalysis of molecular size.

[0049] In one embodiment of the present disclosure, the molar ratio of SiO2 to Al2O3 in the molecular sieve is 25 - 500.

[0050] Specifically, the acidity of the molecular sieve comes from the presence of aluminum atoms in its framework. When the molar ratio of SiO2 to Al2O3 is low, it means that more aluminum atoms are embedded in the silicon-oxygen tetrahedron framework, thereby enhancing the acid catalytic activity of the catalyst.

[0051] In one embodiment of the present disclosure, the metal oxide precursor includes a first metal salt and a second metal salt; The first metal salt is at least one of nitrate, sulfate, and chloride salts of Zr element; The second metal salt is at least one of nitrate, sulfate, and chloride salts of Ce element, and / or at least one of nitrate, sulfate, and chloride salts of Zn element, and / or at least one of nitrate, sulfate, and chloride salts of Cr element, and / or at least one of nitrate, sulfate, and chloride salts of In element.

[0052] Specifically, the final product is a metal oxide attached to the molecular sieve. Therefore, two or more metal salts are used as the precursors. The first metal salt contains Zr element, such as Zr(NO3)4, Zr(SO4)2, ZrCl4. In practical applications, due to the high hygroscopicity of the metal salts of Zr element, the hydrate form is usually used, for example, Zr(NO3)4·5H2O. The second metal salt contains at least one of Ce element, Zn element, Cr element, and In element, such as Ce(NO3)3, Ce2(SO4)3, CeCl3, Zn(NO3)2, ZnSO4, ZnCl2, Cr(NO3)3, Cr2(SO4)3, CrCl3, In(NO3)3, In2(SO4)3, InCl3. Similarly, in practical applications, due to the hygroscopicity, the hydrate form is usually used, such as Ce(NO3)3·6H2O, Zn(NO3)2·6H2O, In(NO3)3·9H2O.

[0053] In an embodiment of the present disclosure, the precipitant is selected from at least one of NH3·H2O, (NH4)2CO3, Na2CO3, NaHCO3, and NaOH.

[0054] Specifically, the precipitant is an alkaline solution, which is used to be added dropwise to the first solution to adjust the pH value, so that metal cations combine with hydroxide ions to form metal hydroxide precipitates. Using at least one of NH3·H2O, (NH4)2CO3, Na2CO3, NaHCO3, and NaOH, on the one hand, these alkaline solutions are easily obtained. On the other hand, + the Na - combined with OH

[0055] In an embodiment of the present disclosure, the mass concentration of the molecular sieve in the first solution is 5 - 50 g / L.

[0056] Specifically, increasing the mass concentration of the molecular sieve usually means an increase in the number of active sites per unit volume, which can improve the activity of the catalyst. However, at the same time, the cost increases. Therefore, the mass concentration of the molecular sieve needs to be considered comprehensively in terms of the performance of the catalyst and the production cost.

[0057] In an embodiment of the present disclosure, the concentration of the second solution is 0.1 - 2 mol / L.

[0058] Specifically, the concentration of the second solution determines the number of metal cations in the solution. Increasing the concentration of the second solution, there are more metal cations in the solution, and more metal hydroxide precipitates will be formed with hydroxide ions. Preferably, the concentration of the second solution is 0.5 mol / L.

[0059] In one embodiment of the present disclosure, the concentration of the third solution is 0.1 - 3 mol / L.

[0060] Specifically, increasing the concentration of the third solution and dropping it into the first solution provides more reactants, namely hydroxide ions, for the first solution, thereby increasing the chance of contact and reaction with metal cations. According to the principle of chemical kinetics, the increase in the concentration of reactants can accelerate the reaction process. Preferably, the concentration of the third solution is 1 mol / L.

[0061] In one embodiment of the present disclosure, in step S1, the first solvent, the second solvent, and the third solvent are all deionized water.

[0062] Specifically, deionized water is treated by ion exchange resin to remove most of the dissolved minerals and salts, so it has a high purity. This helps to avoid introducing impurity ions, can minimize side reactions caused by water quality, and ensure the selectivity and yield of the main reaction.

[0063] In one embodiment of the present disclosure, in step S2, the first solution is heated to a preset temperature by a water bath, and the preset temperature is 50 - 85 °C.

[0064] Specifically, by means of water bath heating, the first solution can be heated evenly. Generally, since the higher temperature increases the energy of molecules or ions, the rate of chemical reaction increases with the increase of temperature. Therefore, water bath heating promotes the hydrolysis reaction and increases the rate of forming metal hydroxide precipitation. Preferably, the preset temperature for heating the first solution by water bath is 70 °C.

[0065] In one embodiment of the present disclosure, during the process of simultaneously dropping the second solution and the third solution into the first solution in step S2, the dropping rate of the third solution is controlled to maintain the pH value of the first solution at 7 - 9.

[0066] Specifically, the metal salt solution will undergo a hydrolysis reaction in an alkaline environment to form the corresponding metal hydroxide precipitation. For example, when adding an alkaline solution to a Zn(NO3)2 solution and adjusting the pH value of the mixed solution to make it alkaline, Zn 2+ combines with OH - to form Zn(OH)2.

[0067] Zn 2+ + 2OH − → Zn(OH)2↓ The third solution is an alkaline solution, which is added dropwise to the first solution to adjust the pH value, so that metal cations combine with hydroxide ions to form metal hydroxide precipitates. Increasing the dropping rate of the third solution increases the pH value of the first solution, and vice versa. Decreasing the dropping rate of the third solution decreases the pH value of the first solution. The pH value of the first solution is maintained at 7-9 to continuously generate metal hydroxide precipitates from metal cations.

[0068] In one embodiment of the present disclosure, in step S3, aging, washing, drying, and calcining the precipitate include: Aging the precipitate in a water bath for 1-5 h, centrifuging, washing 1-5 times, then placing it in an oven and drying at 90-130 °C for 4-24 h, and transferring it to a muffle furnace and calcining at 400-600 °C for 2-12 h.

[0069] Specifically, in the field of catalysts, the role of water bath aging is that by controlling the time and temperature of water bath aging, the surface acid site distribution and pore structure characteristics of the catalyst can be adjusted to a certain extent, thereby affecting the selectivity and activity of the catalyst. For solid catalysts such as molecular sieves, water bath aging can be used to simulate the steam environment encountered under industrial operating conditions and investigate the stability and lifespan of the catalyst under actual working conditions. Preferably, the time of water bath aging can be selected as 3 h, and the temperature of water bath aging is 70 °C.

[0070] After centrifuging and washing, the second and third solutions on the surface of the precipitate are removed, and then drying treatment is carried out to remove the physically adsorbed water and part of the chemically bound water of the precipitate. This can prevent the precipitate from bursting or structural damage during the subsequent calcination process. If the precipitate contains a large amount of water and directly enters a high-temperature environment, the water will quickly evaporate into steam. Since the space occupied by steam is much larger than that of liquid water, this will cause a sharp increase in internal pressure, which may damage the surface or internal structure of the molecular sieve and affect the catalytic performance of the catalyst. In addition, the pre-drying treatment can improve the calcination efficiency, making the energy in the calcination process used for the heat treatment of the precipitate itself rather than the evaporation of water, and improving the energy utilization efficiency of the overall process. Preferably, the number of washing times is selected as 3 times, the drying temperature is selected as 100 °C, and the drying time is selected as 12 h.

[0071] Muffle furnaces are relatively common in the field of catalyst preparation. They can not only perform high-temperature heating evenly, but also be equipped with a control system that can precisely control parameters such as the heating rate, holding time, and cooling rate, which is crucial for adjusting the physical and chemical properties of the catalyst. Transferring the precipitate to a muffle furnace for calcination can remove the crystal water of the metal hydroxide and obtain metal oxides. Preferably, the calcination temperature is selected as 500 °C, and the calcination time is selected as 3 h.

[0072] According to a second aspect of the present disclosure, a catalyst is provided. The catalyst is prepared by the preparation method of any of the above embodiments, and the catalyst is a metal oxide adsorbed on a molecular sieve; The metal oxide includes XZr oxide, X includes at least one of Ce, Zn, Cr, and In, and the molar ratio of the metal elements of X and Zr in the metal oxide is 1:5 - 10:1.

[0073] Specifically, the molar ratio of other metal elements to Zr element in the composite metal oxide affects the number and properties of active centers. When different metals combine with Zr, different active sites can be formed. By adjusting the molar ratio of these metal elements and Zr element, the number and distribution of active sites can be controlled, thereby directly affecting the activity and selectivity of the catalyst. In addition, ZrO2 itself has good thermal stability and chemical stability, but when combined with other metal oxides, its stability may be affected by the interaction between the two. Adjusting the molar ratio of other metal elements and Zr element can help optimize the microstructure of the composite material. Preferably, the molar ratio of the metal elements of X and Zr in the metal oxide is 1:5 - 10:1.

[0074] Since the metal hydroxide precipitate is uniformly attached to the molecular sieve in the solution during the preparation of the catalyst of the present disclosure, and the crystal water is removed through subsequent treatment, a metal oxide adsorbed on the molecular sieve is obtained. Compared with the traditional mixing method of grinding and pressing a metal oxide catalyst and a molecular sieve powder, the problem of uniformity in the mixing of different active components in the catalyst is solved, and the distance between the two active components is shortened, thereby improving the activity of the catalyst.

[0075] In an embodiment of the present disclosure, the mass ratio of the metal oxide to the molecular sieve is 0.2 - 5.

[0076] Specifically, by adjusting the mass ratio of the metal oxide to the molecular sieve, the number and distribution of active sites on the catalyst surface can be controlled. For example, in the acid-catalyzed process, increasing the proportion of the molecular sieve may increase the number of acidic sites; while in the case where redox activity needs to be introduced, increasing the proportion of the metal oxide may be more beneficial. In addition, a higher molecular sieve content helps to improve the thermal stability of the composite material because the molecular sieve itself has good thermal stability and mechanical strength, enabling the catalyst to remain stable during high-temperature catalytic processes.

[0077] According to a third aspect of the present disclosure, an application of a catalyst is provided. The catalyst is prepared by the preparation method of any of the above embodiments, and is applied to directly prepare aromatic hydrocarbons by hydrogenation of CO2. The catalyst is pretreated, and then a mixed raw material of CO2 and H2 is introduced into a reactor equipped with the catalyst for a chemical reaction to prepare aromatic hydrocarbons.

[0078] In one embodiment of the present disclosure, the volume ratio of CO2 to H2 in the mixed raw material is 1:3 - 5, the reaction temperature is 300 - 400 °C, the reaction pressure is 2 - 6 MPa, and the reaction space velocity is 500 - 20000 h -1 .

[0079] Specifically, by controlling the reaction raw materials, temperature, pressure, and space velocity, the product selectivity and conversion rate of the reaction can be controlled. For example, excessive H2 can promote the reverse water-gas shift reaction, but too much may lead to an increase in by-products such as methane. Conversely, if H2 is insufficient, the efficiency of the entire process may be limited. Preferably, the volume ratio of CO2 to H2 is 1:3, the reaction temperature is selected as 340 °C, the reaction pressure is selected as 3 Mpa, and the reaction space velocity is selected as 3000 h -1 .

[0080] In one embodiment of the present disclosure, the pretreatment of the catalyst includes: Loading the catalyst into the reactor and introducing a gas containing H2 into the reactor for reduction reaction.

[0081] Specifically, the pretreatment of the catalyst is usually to activate the catalyst because the active components in the catalyst exist in an oxidized state. Oxidized metals generally do not have high catalytic activity and need to be reduced to the corresponding metal form to exhibit the best performance. Hydrogen reduction can convert metal oxides into a more active metal state. In addition, the pretreatment can also remove impurities and surface adsorbates, which helps to clean the catalyst surface, ensure the effective exposure of active sites, and thus improve the catalytic efficiency.

[0082] In one embodiment of the present disclosure, the temperature of the reduction reaction is 300 - 500 °C, and the time of the reduction reaction is 2 - 10 h.

[0083] Specifically, by controlling the temperature and time of the reduction reaction, it is ensured that the catalyst is reduced to the corresponding metal form and the active sites are effectively exposed. Preferably, the temperature of the reduction reaction is selected as 400 °C, and the time of the reduction reaction is selected as 5 h The following illustrates the improvement of the aromatic selectivity of the catalyst prepared by the preparation method of the present disclosure based on some examples and comparative examples.

[0084] Example 1: Take 4.5 g of ZSM-5 molecular sieve with a molar ratio of SiO2 to Al2O3 of 100. Add 4.5 g of ZSM-5 molecular sieve to 300 mL of deionized water to prepare a suspension solution. Place a magnetic stirrer and heat it in a water bath to 70 °C. Add 2 g of Zn(NO3)2·6H2O and 23 g of Zr(NO3)4·5H2O to deionized water to prepare a 0.5 mol / L mixed solution, and carry out co-current titration with 1 mol / L (NH4)2CO3 solution at 70 °C and pH = 8 until precipitation occurs in the suspension solution. After the titration is completed, age at 70 °C for 2 h, centrifuge and wash 3 times, then place it in an oven at 100 °C and dry for 12 h. Then transfer it to a muffle furnace and program the temperature to 500 °C and calcine for 3 h to obtain catalyst A (the molar ratio of Zn to Zr is 1:8, and the mass ratio of metal oxide to molecular sieve is 1:1). Take 1 g of 40-60 mesh catalyst A and load it into a fixed-bed reactor. Pass pure H2 and reduce it at 400 °C for 5 h. Then cool down to 340 °C and pass a mixed gas of H2 and CO2 with a volume ratio of H2 to CO2 of 3:1. React under the conditions of 340 °C, 3 Mpa, and 3000 h -1 for the reaction.

[0085] Example 2: Take 4.5 g of ZSM-5 molecular sieve with a molar ratio of SiO2 to Al2O3 of 100. Add 4.5 g of ZSM-5 molecular sieve to 300 mL of deionized water to prepare a suspension solution. Place a magnetic stirrer and heat it in a water bath to 70 °C. Add 2 g of In(NO3)3·9H2O and 23 g of Zr(NO3)4·5H2O to deionized water to prepare a 0.5 mol / L mixed solution, and carry out co-current titration with 1 mol / L (NH4)2CO3 solution at 70 °C and pH = 8 until precipitation occurs in the suspension solution. After the titration is completed, age at 70 °C for 2 h, centrifuge and wash 3 times, then place it in an oven at 100 °C and dry for 12 h. Then transfer it to a muffle furnace and program the temperature to 500 °C and calcine for 3 h to obtain catalyst B (the molar ratio of In to Zr is 1:8, and the mass ratio of metal oxide to molecular sieve is 1:1). Take 1 g of 40-60 mesh catalyst B and load it into a fixed-bed reactor. Pass pure H2 and reduce it at 400 °C for 5 h. Then cool down to 340 °C and pass a mixed gas of H2 and CO2 with a volume ratio of H2 to CO2 of 3:1. React under the conditions of 340 °C, 3 Mpa, and 3000 h -1 for the reaction.

[0086] Example 3: Take 4.5 g of ZSM-5 molecular sieve with a molar ratio of SiO2 to Al2O3 of 100. Add 4.5 g of ZSM-5 molecular sieve to 300 mL of deionized water to prepare a suspension solution, place a magnetic stirrer for stirring and heat it up to 70 °C in a water bath. Add 3 g of Ce(NO3)3·6H2O and 23 g of Zr(NO3)4·5H2O to deionized water to prepare a mixed solution with a concentration of 0.5 mol / L, and carry out co-current titration with 1 mol / L (NH4)2CO3 solution at 70 °C and pH = 8 until precipitation occurs in the suspension solution. After the titration is completed, age it at 70 °C for 2 h, centrifuge and wash it 3 times, then place it in an oven at 100 °C and dry it for 12 h. Then transfer it to a muffle furnace and program the temperature to 500 °C and calcine it for 3 h to obtain catalyst C (the molar ratio of Ce to Zr is 1:8, and the mass ratio of metal oxide to molecular sieve is 1:1). Take 1 g of 40-60 mesh catalyst C and load it into a fixed-bed reactor, introduce pure H2 and reduce it at 400 °C for 5 h. Then cool it down to 340 °C and introduce a mixed gas of H2 and CO2 with a volume ratio of H2 to CO2 of 3:1. React under the conditions of 340 °C, 3 Mpa, and 3000 h -1 React under the conditions.

[0087] Example 4: Take 9 g of ZSM-5 molecular sieve with a molar ratio of SiO2 to Al2O3 of 25. Add 9 g of ZSM-5 molecular sieve to 500 mL of deionized water to prepare a suspension solution, place a magnetic stirrer for stirring and heat it up to 70 °C in a water bath. Add 2 g of Zn(NO3)2·6H2O and 11.5 g of Zr(NO3)4·5H2O to deionized water to prepare a mixed solution with a concentration of 0.5 mol / L, and carry out co-current titration with 1 mol / L (NH4)2CO3 solution at 70 °C and pH = 8 until precipitation occurs in the suspension solution. After the titration is completed, age it at 70 °C for 2 h, centrifuge and wash it 3 times, then place it in an oven at 100 °C and dry it for 12 h. Then transfer it to a muffle furnace and program the temperature to 500 °C and calcine it for 3 h to obtain catalyst D (the molar ratio of Zn to Zr is 1:4, and the mass ratio of metal oxide to molecular sieve is 1:2). Take 1 g of 40-60 mesh catalyst D and load it into a fixed-bed reactor, introduce pure H2 and reduce it at 400 °C for 5 h. Then cool it down to 340 °C and introduce a mixed gas of H2 and CO2 with a volume ratio of H2 to CO2 of 3:1. React under the conditions of 340 °C, 3 Mpa, and 3000 h -1 React under the conditions.

[0088] Example 5: Take 9 g of ZSM-5 molecular sieve with a molar ratio of SiO2 to Al2O3 of 300. Add 9 g of ZSM-5 molecular sieve to 500 mL of deionized water to prepare a suspension solution. Place a magnetic stirrer and heat it in a water bath to 70 °C. Add 2 g of Zn(NO3)2·6H2O and 5.8 g of Zr(NO3)4·5H2O to deionized water to prepare a 0.5 mol / L mixed solution, and carry out co-current titration with 1 mol / L (NH4)2CO3 solution at 70 °C and pH = 8 until precipitation occurs in the suspension solution. After the titration is completed, age it at 70 °C for 2 h, centrifuge and wash it 3 times, then place it in an oven at 100 °C and dry it for 12 h. Then transfer it to a muffle furnace and program the temperature to 500 °C and calcine it for 3 h to obtain catalyst E (the molar ratio of Zn to Zr is 1:2, and the mass ratio of metal oxide to molecular sieve is 1:2). Take 1 g of 40-60 mesh catalyst E and load it into a fixed-bed reactor. Pass pure H2 and reduce it at 400 °C for 5 h, then cool it down to 330 °C, and pass a mixed gas of H2 and CO2 with a volume ratio of H2 to CO2 of 3:1. React under the conditions of 330 °C, 3 MPa, and 3000 h -1 under the conditions.

[0089] Comparative Example 1: Add 2 g of Zn(NO3)2·6H2O and 23 g of Zr(NO3)4·5H2O to deionized water to prepare a 0.5 mol / L mixed solution, and carry out co-current titration with 1 mol / L (NH4)2CO3 solution at 70 °C and pH = 8 until precipitation occurs in the suspension solution. After the titration is completed, age it at 70 °C for 2 h, centrifuge and wash it 3 times, then place it in an oven at 100 °C and dry it for 12 h. Then transfer it to a muffle furnace and program the temperature to 500 °C and calcine it for 3 h to obtain a composite metal oxide powder. Take 1 g of ZSM-5 molecular sieve powder with a molar ratio of SiO2 to Al2O3 of 100, take 1 g of the composite metal oxide powder and grind it with 1 g of ZSM-5 molecular sieve powder, and then press and screen it to obtain 40-60 mesh catalyst C1 (the molar ratio of Zn to Zr is 1:8, and the mass ratio of metal oxide to molecular sieve is 1:1). Take 1 g of 40-60 mesh catalyst C1 and load it into a fixed-bed reactor. Pass pure H2 and reduce it at 400 °C for 5 h, then cool it down to 340 °C, and pass a mixed gas of H2 and CO2 with a volume ratio of H2 to CO2 of 3:1. React under the conditions of 340 °C, 3 MPa, and 3000 h -1 under the conditions.

[0090] Comparative Example 2: 2 g of Zn(NO3)2·6H2O and 23 g of Zr(NO3)4·5H2O were added to deionized water to prepare a 0.5 mol / L mixed solution, which was subjected to co-current titration with 1 mol / L (NH4)2CO3 solution at 70 °C and pH = 8 until precipitation occurred in the suspension solution. After the titration was completed, it was aged at 70 °C for 2 h, centrifuged, washed three times, then placed in an oven at 100 °C and dried for 12 h, and then transferred to a muffle furnace and calcined at a programmed temperature of 500 °C for 3 h to obtain the composite metal oxide powder. 1 g of ZSM-5 molecular sieve powder with a molar ratio of SiO2 to Al2O3 of 100 was taken, 1 g of the composite metal oxide powder was shaken and mixed with 1 g of ZSM-5 molecular sieve powder, and then pressed and sieved to obtain a 40-60 mesh catalyst C2 (the molar ratio of Zn to Zr was 1:8, and the mass ratio of the metal oxide to the molecular sieve was 1:1). 1 g of the 40-60 mesh catalyst C2 was loaded into a fixed-bed reactor, and pure H2 was introduced for reduction treatment at 400 °C for 5 h. After that, the temperature was lowered to 340 °C, and a mixed gas of H2 and CO2 with a volume ratio of H2 to CO2 of 3:1 was introduced. The reaction was carried out at 340 °C, 3 Mpa, and 3000 h -1 conditions.

[0091] Comparative Example 3: 2 g of Zn(NO3)2·6H2O and 23 g of Zr(NO3)4·5H2O were added to deionized water to prepare a 0.5 mol / L mixed solution, which was subjected to co-current titration with 1 mol / L (NH4)2CO3 solution at 70 °C and pH = 8 until precipitation occurred in the suspension solution. After the titration was completed, it was aged at 70 °C for 2 h, centrifuged, washed three times, then placed in an oven at 100 °C and dried for 12 h, and then transferred to a muffle furnace and calcined at a programmed temperature of 500 °C for 3 h to obtain the composite metal oxide powder. 1 g of 40-60 mesh ZSM-5 molecular sieve powder with a molar ratio of SiO2 to Al2O3 of 100 was taken, 1 g of 40-60 mesh composite metal oxide powder was shaken and mixed with 1 g of 40-60 mesh ZSM-5 molecular sieve powder to obtain catalyst C3 (the molar ratio of Zn to Zr was 1:8, and the mass ratio of the metal oxide to the molecular sieve was 1:1). 1 g of the 40-60 mesh catalyst C3 was loaded into a fixed-bed reactor, and pure H2 was introduced for reduction treatment at 400 °C for 5 h. After that, the temperature was lowered to 340 °C, and a mixed gas of H2 and CO2 with a volume ratio of H2 to CO2 of 3:1 was introduced. The reaction was carried out at 340 °C, 3 Mpa, and 3000 h -1 conditions.

[0092] Table 1:

[0093] Catalyst A was prepared by the preparation method described in Example 1, catalyst B was prepared by the preparation method described in Example 2, catalyst C was prepared by the preparation method described in Example 3, catalyst D was prepared by the preparation method described in Example 4, and catalyst E was prepared by the preparation method described in Example 5. All of them adopted the preparation method of the present disclosure. Catalyst C1 was prepared by the preparation method described in Comparative Example 1, which was obtained by grinding the composite metal oxide powder and the molecular sieve powder and then pressing, screening. Catalyst C2 was prepared by the preparation method described in Comparative Example 2, which was obtained by shaking and mixing the composite metal oxide powder and the molecular sieve powder and then pressing, screening. Catalyst C3 was prepared by the preparation method described in Comparative Example 3, which was obtained by directly selecting 40-60 mesh composite metal oxide powder and 40-60 mesh molecular sieve powder and shaking and mixing them.

[0094] As shown in Table 1, after comparison, the CO2 conversion rate of the catalysts prepared by the preparation method of the present disclosure was higher than that of the comparative examples, the CO selectivity was lower than that of the comparative examples, the selectivity of aromatics basically reached more than 70, the stability was better, and the selectivity of methane was greatly reduced.

[0095] The embodiments of the present disclosure have been described above. The above description is exemplary and not exhaustive, and is not limited to the disclosed embodiments. Many modifications and variations are obvious to those of ordinary skill in the art without departing from the scope and spirit of the described embodiments. The selection of the terms used herein is intended to best explain the principles of the embodiments, practical applications or improvements to the technology in the market, or to enable other ordinary skill in the art to understand the embodiments disclosed herein. The scope of the present disclosure is defined by the appended claims.

Claims

1. A method for preparing a catalyst, characterized in that, The preparation method of the catalyst comprises the following steps: S1. Add molecular sieve powder into a first solvent to form a first solution, add a metal oxide precursor into a second solvent to form a second solution, and add a precipitant into a third solvent to form a third solution, wherein the precipitant is an alkaline solution; S2. Heat the first solution to a preset temperature, and simultaneously drop the second solution and the third solution into the first solution to obtain a precipitate, which is a metal hydroxide adsorbed on the molecular sieve; S3. Age, wash, dry, and calcine the precipitate to obtain the catalyst, which is a metal oxide adsorbed on the molecular sieve.

2. The preparation method according to claim 1, characterized in that, The molecular sieve in step S1 is a ZSM-5 molecular sieve.

3. The preparation method according to claim 2, wherein The molar ratio of SiO2 to Al2O3 of the molecular sieve is 25 - 500.

4. The preparation method according to claim 3, wherein The metal oxide precursor includes a first metal salt and a second metal salt; The first metal salt is at least one of nitrate, sulfate, and chloride salts of Zr element; The second metal salt is at least one of nitrate, sulfate, and chloride salts of Ce element, and / or at least one of nitrate, sulfate, and chloride salts of Zn element, and / or at least one of nitrate, sulfate, and chloride salts of Cr element, and / or at least one of nitrate, sulfate, and chloride salts of In element.

5. The preparation method according to claim 4, characterized in that, The precipitant is selected from at least one of NH3·H2O, (NH4)2CO3, Na2CO3, NaHCO3, and NaOH.

6. The preparation method according to claim 5, wherein The mass concentration of the molecular sieve in the first solution is 5 - 50 g / L.

7. The preparation method according to claim 6, wherein The concentration of the second solution is 0.1 - 2 mol / L.

8. The preparation method according to claim 7, characterized in that, The concentration of the third solution is 0.1 - 3 mol / L.

9. The preparation method according to claim 1, wherein, In step S1, the first solvent, the second solvent, and the third solvent are all deionized water.

10. The preparation method according to claim 9, wherein, In step S2, the first solution is heated to the preset temperature by water bath, and the preset temperature is 50 - 85 °C.

11. The preparation method according to claim 10, characterized in that, In the process of simultaneously dropping the second solution and the third solution into the first solution in step S2, control the dropping rate of the third solution to keep the pH value of the first solution at 7 - 9.

12. The preparation method according to claim 11, wherein In step S3, aging, washing, drying, and calcining the precipitate include: Aging the precipitate by water bath for 1 - 5 h, centrifuging and washing it 1 - 5 times, then placing it in an oven to dry at 90 - 130 °C for 4 - 24 h, and transferring it to a muffle furnace to calcine at 400 - 600 °C for 2 - 12 h.

13. A catalyst, which is prepared by the preparation method according to any one of claims 1-12, characterized in that, The catalyst is a metal oxide adsorbed on the molecular sieve; The metal oxide includes an XZr oxide, where X includes at least one of Ce, Zn, Cr, and In, and the molar ratio of the metal elements of X and Zr in the metal oxide is 1:5 - 10:

1.

14. The catalyst according to claim 13, wherein, The mass ratio of the metal oxide to the molecular sieve is 0.2 - 5.

15. Application of a catalyst, wherein the catalyst is prepared by the preparation method according to any one of claims 1-12 and is applied to the direct preparation of aromatic hydrocarbons by hydrogenation of CO2, characterized in that, The catalyst is pretreated, and then a mixed raw material of CO2 and H2 is introduced into a reactor equipped with the catalyst for a chemical reaction to prepare aromatics.

16. The application of a catalyst according to claim 15, wherein, The volume ratio of CO2 to H2 in the mixed raw material is 1:3 - 5, the reaction temperature is 300 - 400 °C, the reaction pressure is 2 - 6 MPa, and the reaction space velocity is 500 - 20000 h -1 .

17. The use of a catalyst according to claim 16, characterized in that, The pretreatment of the catalyst includes: Loading the catalyst into a reactor, and introducing a gas containing H2 into the reactor for a reduction reaction.

18. Use of a catalyst according to claim 17, characterized in that, The temperature of the reduction reaction is 300 - 500 °C, and the time of the reduction reaction is 2 - 10 h.

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