Process for the preparation of a catalyst for the aerobic oxidation of methane to methanol and its use

Abstract

This invention discloses a method for preparing a catalyst for the oxygen-free aromatization reaction of methane and its application, belonging to the field of chemical catalysis. The preparation method includes: reducing the prepared Mo / HZS catalyst, wherein the reduction treatment includes: placing the Mo / HZS catalyst in a fixed-bed reactor under N2 protection and heating it to 400℃~550℃, then switching to a reducing gas of hydrogen or carbon monoxide to reduce the molybdenum trioxide component of the Mo / HZS catalyst to molybdenum dioxide, obtaining a Mo / HZS-R catalyst. When applied to the oxygen-free aromatization reaction of methane, it can yield products such as benzene, toluene, and naphthalene. This preparation method is simple to operate, cost-effective, and significantly improves the performance and lifespan of the catalyst, and can be widely used in catalytic cracking, oil refining, and other industries.

Description

Technical Field

[0001] This invention belongs to the field of energy and chemical catalysts, specifically relating to the preparation method and application of a catalyst for the oxygen-free aromatization reaction of methane. Background Technology

[0002] The increasing reserves of natural gas both domestically and internationally have made the development and utilization of natural gas resources extremely urgent. Fully utilizing and converting the methane resources abundant in natural gas can bring enormous economic value. Among these methods, converting methane into high-value-added aromatic compounds has broad application prospects. Anaerobic aromatization (MDA) is an important reaction in the direct catalytic conversion of methane. Due to its high product selectivity, ease of separation, high added value, and safe and pollution-free process, it has become one of the methods for the direct conversion and utilization of natural gas. It is of great significance for the direct utilization of natural gas and for a deeper understanding of the activation nature of the CH bond in the methane molecule. Designing a reasonable and effective catalyst is one of the important conditions for improving the performance of the methane anaerobic aromatization reaction. Due to thermodynamic equilibrium limitations, the single-pass conversion rate of the methane anaerobic aromatization reaction is low, and the products contain large-molecule polycyclic aromatic hydrocarbons such as naphthalene, which are prone to carbon deposition, thereby clogging the molecular sieve channels and covering the active sites, leading to severe catalyst deactivation. Therefore, reducing reaction carbon deposition and improving catalyst lifetime have become the research focus of methane anaerobic aromatization catalysts. Summary of the Invention

[0003] To overcome the drawback of rapid deactivation of Mo active sites on conventional nanoscale molecular sieves, the catalyst preparation method provided in this invention reduces the easily migratable molybdenum trioxide in the Mo / HZS catalyst to non-migratable molybdenum dioxide located within the molecular sieve channels. This non-migratable molybdenum dioxide is in situ converted into molybdenum carbide within the molecular sieve channels during the induction stage of the methane anaerobic aromatization reaction. This molybdenum carbide serves as the active site for the methane anaerobic aromatization reaction. Since the technical solution provided in this invention allows the molybdenum carbide, which serves as the active site for the methane anaerobic aromatization reaction, to remain within the molecular sieve channels, the active component is less prone to agglomeration and sintering. Therefore, the catalyst obtained based on the preparation method provided in this invention exhibits better catalytic performance and stability in the methane anaerobic aromatization reaction.

[0004] Based on this, in a first aspect, embodiments of the present invention provide a method for preparing a catalyst for the oxygen-free aromatization reaction of methane, the preparation method comprising the following steps:

[0005] Step 01: Mix 0.3g to 0.4g of ZSM-5 type zeolite molecular sieve with a dilute solution of tetrapropylammonium hydroxide (TPAOH solution);

[0006] Step 02: Stir and heat the mixture in an autoclave at 170℃~190℃ for 9~11 hours; collect the solid by centrifugation and wash the collected solid with distilled water to obtain hollow molecular sieve HZSM-5;

[0007] Step 03: Add the solid obtained in Step 02 to 25 mL to 30 mL of TPAOH solution containing 1.0 g to 2.0 g of tetraethyl orthosilicate (TEOS), wherein the concentration of TPAOH solution is 0.01 to 0.02 M, and stir the mixture at room temperature for 12 to 24 hours;

[0008] Step 04: Place the mixture obtained in Step 03 into an autoclave and crystallize it at 80℃~100℃ for 12~36 hours, and epitaxially grow a layer of silica zeolite-1 on it;

[0009] Step 05: Dry the product obtained from the crystallization in step 04 in an oven at 100℃~120℃ for 12~24 hours without calcination to obtain the catalyst support HZS and the hollow molecular sieve HZSM-5 wrapped with a layer of silicatlite-1.

[0010] Step 06: Add HZS to a solution containing 0.03g to 0.04g of ammonium molybdate tetrahydrate ((NH4)6Mo7O) 24 In an aqueous solution of 4H2O, wherein the Mo loading is 2-3 wt%, the mixture is stirred at room temperature for 8-10 hours, and then dried in an oven at 100℃-120℃ for 12-24 hours.

[0011] Step 07: Place the powder obtained in step 06 into a fixed-bed reactor and further dry it in flowing air at a temperature of 350℃~400℃ for 12~24 hours to disperse Mo.

[0012] Step 08: Based on Step 07, increase the reactor temperature to 650℃~750℃ and calcine the sample for 2~24 hours to obtain the Mo / HZS sample.

[0013] Step 09: The Mo / HZS sample obtained in Step 08 is subjected to a one-step reduction treatment to obtain the Mo / HZS-R catalyst.

[0014] Most importantly, the restoration process includes:

[0015] Step A1: Under N2 protection, place the Mo / HZS catalyst in the reactor and gradually heat the reactor;

[0016] Step B1: Adjust the temperature of the reactor to 400℃~550℃, switch the N2 to a reducing gas atmosphere to treat the catalyst for 1~2 hours, and obtain the Mo / HZS-R catalyst.

[0017] Optionally,

[0018] The reduction treatment of the Mo / HZS sample involves reducing gases such as H2 or CO.

[0019] Secondly, embodiments of the present invention provide an application of a catalyst for the oxygen-free aromatization reaction of methane, including:

[0020] Step A2: Place the 0.3-0.5g Mo / HZS-R catalyst and 0.3-0.5g quartz wool into a fixed-bed reactor;

[0021] Step B2: Heat the catalyst in the reactor to 600℃~800℃ under N2 atmosphere and treat for 20~30 minutes. Then, under atmospheric pressure, introduce CH4 / N2 of any volume ratio at a rate of 8~15mL / min to carry out the oxygen-free aromatization reaction of methane.

[0022] Optionally,

[0023] The applications of the Mo / HZS-R catalyst include laboratory-scale and industrial applications of oxygen-free aromatization of methane.

[0024] The technical solution of the first aspect of the above invention has the following advantages or beneficial effects:

[0025] The catalyst preparation method provided in this invention reduces molybdenum trioxide, which migrates throughout the Mo / HZS catalyst, to molybdenum dioxide, which is less prone to migration, located within the molecular sieve channels. This less-migrating molybdenum dioxide is then converted in situ into molybdenum carbide within the molecular sieve channels during the induction phase of the methane anaerobic aromatization reaction. This molybdenum carbide serves as the active site for the methane anaerobic aromatization reaction. Because the technical solution provided in this invention allows the molybdenum carbide, serving as the active site for the methane anaerobic aromatization reaction, to remain within the molecular sieve channels, the active site is less prone to agglomeration and sintering. This ensures that both the acidic sites of the molecular sieve and the Mo active sites are fully utilized, significantly improving reaction efficiency and catalyst lifetime. Compared to traditional Mo / ZSM-5 catalysts, the lifetime is increased by approximately five times, and the preparation process is simpler and more cost-effective than the latest literature research, making it more conducive to industrial application. Therefore, the catalyst prepared based on the method provided in this invention exhibits better catalytic performance and stability in the methane anaerobic aromatization reaction. Attached Figure Description

[0026] Figure 1 Schematic diagram of the reaction performance of Mo / ZSM-5 catalysts of different sizes in examples of this invention;

[0027] Figure 2High-angle annular dark-field scanning transmission electron microscope image of the Mo / HZS(60) catalyst after deactivation used in this invention example;

[0028] Figure 3 Temperature-programmed reduction diagram of the Mo / HZS(60) catalyst used in this invention example;

[0029] Figure 4 High-angle annular dark-field scanning transmission electron microscope image of the Mo / HZS(60)-R catalyst in the example of this invention;

[0030] Figure 5 : Energy dispersive spectroscopy (EDS-Mapping) diagrams of each element of the Mo / HZS(60)-R catalyst in the example of this invention;

[0031] Figure 6 : Methane conversion diagram of the Mo / HZS(60)-R catalyst applied to the oxygen-free aromatization reaction of methane in the example of this invention.

[0032] Figure 7 : Graph showing the benzene yield of the Mo / HZS(60)-R catalyst applied to the oxygen-free aromatization reaction of methane in the examples of this invention. Detailed Implementation

[0033] Research has revealed that Mo-based catalysts supported on ZSM-5 zeolite molecular sieves are among the most suitable catalysts for the oxygen-free aromatization of methane. Their catalytic behavior is synergistically driven by the Brønsted acid sites of the molecular sieve and the active Mo component, making them bifunctional dehydrogenation-acid catalysis catalysts. The activation of the CH bonds in methane and the initial formation of the C-C bonds both occur in the MoC phase. x Further polymerization and cyclization occur at the Brønsted acid sites of the zeolite. The specific reaction process includes three steps: First, CH4 carbonizes the atomically dispersed MoO3 in the zeolite into MoC. x Then CH4 in MoC x C2 species are formed at the active sites; these C2 species then form benzene at the Brønsted acid sites of the zeolite. Although conventional supported Mo / ZSM-5 catalysts are the most widely studied in the oxygen-free aromatization of methane, the reactive aromatic products are prone to polymerization and carbon deposition during the reaction, leading to rapid catalyst deactivation and severely hindering its industrial development. Therefore, it is crucial to study the mechanism by which conventional Mo / ZSM-5 catalysts affect catalyst deactivation and improve catalyst lifetime based on this understanding. By studying the methane conversion rate on Mo-based catalysts supported on ZSM-5 zeolite zeolite sieves with different Brønsted acid axis sizes, the influence of different pore sizes on reaction stability can be observed, yielding... Figure 1 The diagram shows the reaction performance of Mo / ZSM-5 catalysts of different sizes. From... Figure 1It can be seen that the methane conversion rate of Mo-based catalysts supported on ZSM-5 (microsize) with a b-axis length of less than 2 nm and ZSM-5 (400) with a b-axis length of 400 nm shows the slowest decreasing trend over time, indicating better catalyst stability. Reducing the pore size of the molecular sieve can increase the outer surface area of ​​the molecular sieve, thereby reducing the coverage of active sites caused by carbon on the catalyst surface, which can alleviate catalyst deactivation and improve catalyst lifetime.

[0034] However, the study found that Mo / ZSM-5(2) with a b-axis length of 2 nm and Mo / ZSM-5(60) with a b-axis length of 60 nm have small pore sizes, but also relatively short lifetimes. Therefore, other unfavorable factors must lead to carbon deposition and deactivation on the catalyst surface, and their adverse effects outweigh the advantages brought by increasing the specific surface area of ​​the catalyst. Similarly, the catalyst structure and reaction conditions can be further improved based on the Mo / ZSM-5(60) catalyst to mitigate catalyst deactivation. Based on the research results of the previous article published by N. Wang et al. in Cell Reports Physical Science, Mo / ZSM-5(60) was induced to generate MoC. x Subsequently, hollow molecular sieve HZSM-5 coated with a layer of silicate-1 was used as MoC. x The carrier, namely MoC x The / HZS(60) catalyst showed a 10-fold increase in catalyst lifetime compared to the traditional Mo / ZSM-5(60), demonstrating that MoC x It is the active component of the catalyst.

[0035] Furthermore, scanning transmission electron microscopy analysis was performed on the Mo / HZS(60) catalyst after deactivation by the anaerobic aromatization reaction to obtain... Figure 2 The diagram shown is from... Figure 2 It can be further inferred that the catalyst rapidly deactivates due to the agglomeration and sintering of Mo species on the outer surface of the molecular sieve during the reaction process.

[0036] Based on our experimental results, the rapid deactivation of nanoscale molecular sieves is due to the fact that MoO3 species in the micropores of the molecular sieve readily migrate to the outer surface of the catalyst during the reaction, thereby leading to the deactivation of MoC. x Rapid agglomeration and sintering deactivate the catalyst. Therefore, the key to improving catalyst lifetime lies in further inhibiting the reaction of MoO3 and activated MoC. xMigration and aggregation. Studies have shown that adding a reduction step after the Mo / HZS catalyst preparation process can reduce the easily migrating MoO3 component of the catalyst to the less migrating MoO2 component. Methane undergoes CH bond activation and C / C bond formation in the micropores, at which point the in-situ generated MoC... x Active sites can stably exist within the micropores of molecular sieves, thereby delaying catalyst deactivation and improving catalyst lifetime. This preparation method is simpler and easier to implement, eliminating an induction reaction step compared to the latest research results, and its effects are significant, making it highly practical. Based on this, embodiments of the present invention provide a novel method for preparing a catalyst for the oxygen-free aromatization reaction of methane and its application.

[0037] The preparation method of the catalyst for the oxygen-free aromatization reaction of methane provided in this invention may include the following steps:

[0038] Step 01: Mix 0.3g to 0.4g of ZSM-5 type zeolite molecular sieve with an axial length of 60nm with 3mL of 0.33M tetrapropylammonium hydroxide dilute solution (TPAOH solution), and heat the mixture in an autoclave at 170℃ to 190℃ for 9 to 11 hours; collect the solid by centrifugation and wash the collected solid with distilled water;

[0039] Step 02: Add the solid obtained in Step 01 to 25-30 mL of a TPAOH solution containing 1.0 g-2.0 g of tetraethyl orthosilicate, wherein the concentration of the TPAOH solution is 0.01-0.02 M. Stir the mixture at room temperature for 12-24 hours. Then place it in an autoclave and crystallize at 80-100°C for 12-36 hours to grow a layer of silica zeolite-1 epitaxially on it.

[0040] Step 03: Dry the product obtained from the crystallization in step 02 in an oven at 100℃~120℃ for 12~24 hours without calcination to obtain the catalyst support HZS, which is a hollow molecular sieve wrapped with a layer of silica zeolite.

[0041] Step 04: Add the carrier HZS to a mixture containing 0.03g to 0.04g of ammonium molybdate tetrahydrate ((NH4)6Mo7O) 24 The sample was stirred in an aqueous solution of 4H2O at room temperature for 8–10 hours with a Mo loading of 2–3 wt%, and then dried in an oven at 100–120°C for 12–24 hours. The resulting powder was then placed in a fixed-bed reactor and further dried in flowing air at 350–400°C for 12–24 hours to disperse the Mo. Based on this, the reactor temperature was increased to 650–750°C at a rate of 8–12°C / min to calcine the sample for 2–24 hours to obtain the Mo / H2O sample.

[0042] Step 05: Place the Mo / HZS sample and quartz wool obtained in Step 04 into a fixed-bed reactor. Under N2 protection, place the Mo / HZS catalyst in the reactor and gradually heat the reactor to 400℃~550℃. Then switch N2 to reducing gas hydrogen (H2) or carbon monoxide (CO) to treat the catalyst for 1~2 hours to obtain the Mo / HZS-R catalyst.

[0043] This invention modifies the support structure based on the traditional Mo / ZSM-5 catalyst preparation, transforming it into a hollow molecular sieve encapsulated by a layer of silica zeolite. Furthermore, a reduction treatment is added, resulting in a more valuable Mo / HZS-R catalyst. Figure 3 The results of the temperature-programmed reduction experiment of Mo / HZS(60) shown demonstrate that MoO3(Mo 6+ ) to MoO2(Mo 4+ The catalyst undergoes a transformation, with the MoO3 component reduced to MoO2 at 400–550 °C. Because MoO2 is not easily migrated, it can stably exist within the micropores of the molecular sieve, thus the resulting MoC... x It can also exist stably on catalysts and is not prone to migration or aggregation. For example... Figure 4 The high-angle annular dark-field scanning transmission electron microscopy image shown reveals the structure of the Mo / HZS(60)-R catalyst, exhibiting no obvious molecular aggregation, and... Figure 5 The energy dispersive spectroscopy (EDS) analysis shown in the diagram indicates that the Mo component of the Mo / HZS(60)-R catalyst is entirely located within the micropores of the molecular sieve. Therefore, the MoC formed in situ during the aromatization reaction is entirely within the molecular sieve micropores. x It can exist stably in molecular sieves. Further comparative studies were conducted on the activities of uncoated Silicalite-1 Mo / ZSM-5, unreduced Mo / HZS(60), and reduced Mo / HZS(60)-R catalysts in the oxygen-free aromatization reaction of methane, yielding... Figure 6 and Figure 7 The diagram shows the reaction performance of the Mo / HZS(60)-R catalyst. Figure 6 and Figure 7 As shown, the reduction treatment of the Mo / HZS(60)-R catalyst resulted in the smallest slowdown in the changes of methane conversion and benzene yield over time, demonstrating that the reduction treatment can weaken the degradation of MoC. xThe migration of active components fully utilizes the acidic sites and Mo active sites on the molecular sieve, thereby reducing carbon deposition in the reaction. Compared with the unreduced Mo / HZS(60) catalyst, the deactivation time of the Mo / HZS(60)-R catalyst is extended from 400 minutes to 1000 minutes, and the lifetime is increased by about two times; while compared with the traditional Mo / ZSM-5(60) catalyst, the deactivation time of the Mo / HZS(60)-R catalyst is extended from 200 minutes to 1000 minutes, and the lifetime is increased by about five times.

[0044] Applications of Mo-HZS-R catalysts include:

[0045] Oxygen-free aromatization of methane: Mo / HZS-R(60) catalyst and quartz wool are placed in a fixed-bed reactor, and the reactor is heated to 600℃~800℃ under N2 atmosphere. After the impurities in the reactor are purified, CH4 / N2 of any volume ratio is introduced under atmospheric pressure to carry out the oxygen-free aromatization of methane. The main components of the obtained products are benzene, toluene and naphthalene.

[0046] Compared to the conventional Mo / HZSM-5 catalyst used in the oxygen-free aromatization of methane, this catalyst preparation method involves coating the catalyst with a layer of silica zeolite and adding a reduction step, resulting in a longer catalyst lifetime. Furthermore, this preparation method is simpler and easier to operate than the latest research findings, eliminating an induction reaction step, thus saving costs while maintaining significant performance. It is suitable for widespread application in industrial catalyst production.

[0047] The preparation method and application of the Mo / HZS-R catalyst for the oxygen-free aromatization of methane are described in detail below with several specific examples.

[0048] Example 1: Using ZSM-5 zeolite molecular sieve with a b-axis length of 60 nm as a support, 0.3 g of ZSM-5 zeolite molecular sieve with a silica-to-alumina ratio of 20 was mixed with 3 mL of 0.33 M tetrapropylammonium hydroxide dilute solution. The mixture was then stirred and heated in an autoclave at 170 °C for 10 hours. The resulting solid was collected by centrifugation, washed with distilled water, and then added to 26 mL of 0.01 M tetrapropylammonium hydroxide dilute solution containing 1.37 g tetraethyl orthosilicate. The mixture was stirred at room temperature for 12 hours, and then placed in an autoclave for crystallization at 100 °C for 24 hours to epitaxially grow a layer of silica zeolite-1. The obtained powder was dried in an oven at 110 °C for 12 hours without calcination to obtain the catalyst support HZS. Ammonium molybdate tetrahydrate ((NH4)6Mo7O 24 Using (NH4)4H2O as a raw material and Mo precursor, 1g of HZS was impregnated in a solution containing 0.0368g (NH4)6Mo7O. 24The catalyst was stirred in an aqueous solution of 4H2O at room temperature for 8 hours, with a Mo loading of 2wt%. It was then dried in an oven at 110℃ for 10 hours. The resulting powder was further dried in flowing air at 350℃ for 24 hours to disperse the Mo. The catalyst temperature was then increased to 700℃ at 10℃ / min and calcined for 2 hours to stabilize the Mo component at the Brønsted acid sites of the molecular sieve, yielding a Mo / HZS(60) catalyst sample. 0.3g of Mo / HZS catalyst and 0.3g of quartz wool were placed in a fixed-bed reactor with an inner diameter of 6mm and a height of 400mm. The temperature was raised to 500℃ under N2 protection, and the catalyst was then treated with H2 reduction for one hour to reduce MoO3 to MoO2, yielding the Mo / HZS(60)-R catalyst. Then, the gas was switched to N2 and heated to 700℃ at a rate of 10℃ / min for 30 minutes. Then, a CH4 / N2 mixed gas with a volume ratio of 90:10 was introduced at a rate of 10mL / min to carry out the methane oxygen-free aromatization reaction. Long-term experiments were conducted, and the methane conversion rate and benzene yield were recorded in real time. The catalyst was deactivated after 1000 minutes.

[0049] Example 2: Using ZSM-5 zeolite molecular sieve with a b-axis length of 60 nm as a support, 0.3 g of ZSM-5 zeolite molecular sieve with a silica-to-alumina ratio of 20 was mixed with 3 mL of 0.33 M tetrapropylammonium hydroxide dilute solution. The mixture was then stirred and heated in an autoclave at 170 °C for 10 hours. The resulting solid was collected by centrifugation, washed with distilled water, and then added to 26 mL of 0.01 M tetrapropylammonium hydroxide dilute solution containing 1.37 g tetraethyl orthosilicate. The mixture was stirred at room temperature for 12 hours, and then placed in an autoclave for crystallization at 100 °C for 24 hours to epitaxially grow a layer of silica zeolite-1. The obtained powder was dried in an oven at 110 °C for 12 hours without calcination to obtain the catalyst support HZS. Ammonium molybdate tetrahydrate ((NH4)6Mo7O) was used. 24 Using (NH4)4H2O as a raw material and Mo precursor, 1g of HZS was impregnated in a solution containing 0.0368g (NH4)6Mo7O. 24The catalyst was stirred in an aqueous solution of 4H2O at room temperature for 8 hours, with a Mo loading of 2wt%. It was then dried in an oven at 110℃ for 10 hours, and the resulting powder was further dried in flowing air at 350℃ for 24 hours. The catalyst temperature was then increased to 700℃ at a rate of 10℃ / min and calcined for 2 hours to obtain a Mo / HZS(60) catalyst sample. 0.3g of Mo / HZS catalyst and 0.3g of quartz wool were placed in a fixed-bed reactor with an inner diameter of 6mm and a height of 400mm. The temperature was raised to 500℃ under N2 protection, and the catalyst was treated with CO reduction for one hour to reduce MoO3 to MoO2, obtaining the Mo / HZS(60)-R catalyst. Then, the gas was switched to N2 and heated to 700℃ at a rate of 10℃ / min for 30 minutes. Then, a CH4 / N2 mixed gas with a volume ratio of 90:10 was introduced at a rate of 10mL / min to carry out the methane oxygen-free aromatization reaction. Long-term experiments were conducted, and the methane conversion rate and benzene yield were recorded in real time. The catalyst was deactivated after 950 minutes.

[0050] Example 3: Using ZSM-5 type zeolite molecular sieve with a b-axis length of 60 nm as a support, 0.3 g of ZSM-5 type zeolite molecular sieve with a silicon-to-aluminum ratio of 20 was mixed with 3 mL of 0.33 M tetrapropylammonium hydroxide dilute solution. The mixture was then stirred and heated in an autoclave at 170 °C for 10 hours. The resulting solid was collected by centrifugation, washed with distilled water, and then added to 26 mL of tetrapropylammonium hydroxide dilute solution (0.01 M) containing 1.37 g tetraethyl orthosilicate. The mixture was stirred at room temperature for 12 hours, and then placed in an autoclave for crystallization at 100 °C for 24 hours to epitaxially grow a layer of silicatlite-1. The obtained powder was dried in an oven at 110 °C for 12 hours without calcination to obtain the catalyst support HZS. Ammonium molybdate tetrahydrate ((NH4)6Mo7O 24 Using (NH4)4H2O as a raw material and Mo precursor, 1g of HZS was impregnated in a solution containing 0.0368g (NH4)6Mo7O. 24The catalyst was stirred in an aqueous solution of 4H2O at room temperature for 8 hours, with a Mo loading of 2wt%. It was then dried in an oven at 110℃ for 10 hours, and the resulting powder was further dried in flowing air at 350℃ for 24 hours. The temperature was then increased to 700℃ at 10℃ / min and calcined for 2 hours to obtain a Mo / HZS(60) catalyst sample. 0.3g of Mo / HZS catalyst and 0.3g of quartz wool were placed in a fixed-bed reactor with an inner diameter of 6mm and a height of 400mm. The temperature was raised to 450℃ under N2 protection, and the catalyst was treated with CO reduction for one hour to reduce MoO3 to MoO2, obtaining the Mo / HZS(60)-R catalyst. Then, the gas was switched to N2 and heated to 700℃ at a rate of 10℃ / min for 30 minutes. Then, a CH4 / N2 mixed gas with a volume ratio of 90:10 was introduced at a rate of 10mL / min to carry out the methane oxygen-free aromatization reaction. Long-term experiments were conducted, and the methane conversion rate and benzene yield were recorded in real time. The catalyst was deactivated after 950 minutes.

Claims

1. A method for preparing a catalyst for the oxygen-free aromatization reaction of methane, characterized in that, Includes the following steps: Step 01: Mix 0.3 g ~ 0.4 g of ZSM-5 type zeolite molecular sieve with 2 mL ~ 4 mL of 0.3 ~ 0.4 M tetrapropylammonium hydroxide solution; Step 02: Stir and heat the mixture in an autoclave at 170 ℃ ~ 190 ℃ for 9 ~ 11 hours, collect the solid by centrifugation, and wash the collected solid with distilled water to obtain hollow molecular sieve HZSM-5; Step 03: Add the solid obtained in Step 02 to 25 mL ~ 30 mL of a dilute solution of tetrapropylammonium hydroxide containing 1.0 g ~ 2.0 g of tetraethyl orthosilicate, wherein the concentration of the dilute solution of tetrapropylammonium hydroxide is 0.01 M ~ 0.02 M, and stir the mixture at room temperature for 12 ~ 24 hours; Step 04: Place the mixture obtained in Step 03 into an autoclave and crystallize at 80 ℃~100 ℃ for 12~36 hours to grow a layer of silicate-1 epitaxially on it; Step 05: Dry the product obtained from the crystallization in step 04 in an oven at 100 ℃ ~ 120 ℃ for 12 ~ 24 hours without calcination to obtain the catalyst support HZS, namely the hollow molecular sieve HZSM-5 coated with a layer of silicate-1. Step 06: Add HZS to an aqueous solution containing 0.03 g ~ 0.04 g ammonium molybdate tetrahydrate, with a Mo loading of 2 ~ 3 wt%, stir at room temperature for 8 ~ 10 hours, and then at 100 o C ~ 120 o Dry in an oven at temperature C for 12-24 hours; Step 07: Place the powder obtained in Step 06 into a fixed-bed reactor and further dry it in flowing air at a temperature of 350℃ ~ 400℃ for 12 ~ 24 hours to disperse Mo. Step 08: Based on step 07, increase the reactor temperature to 650~750°C. o The sample was calcined at C for 2 to 24 hours to obtain the Mo / HZS sample, which is a Mo-based catalyst consisting of a hollow molecular sieve HZSM-5 coated with a layer of silicate-1. Step 09: Place the Mo / HZS sample obtained in Step 08 into the reactor, and gradually heat the reactor to 400 ℃ ~ 550 ℃ under N2 protection. Switch the N2 to reducing gas hydrogen or carbon monoxide to treat the catalyst for 1 ~ 2 hours to obtain the Mo / HZS-R catalyst.

2. The application of a catalyst prepared by the method described in claim 1 for the oxygen-free aromatization reaction of methane, characterized in that, Includes the following steps: Step A2: Place 0.3 ~ 0.5 g of the Mo / HZS-R catalyst and 0.3 ~ 0.5 g of quartz wool in a fixed-bed reactor; Step B2: Heat the catalyst in the reactor to 600°C under a nitrogen atmosphere. o C ~ 800 o At C, treat for 20 to 30 minutes, then introduce CH4 / N2 of any volume ratio at a rate of 8 to 15 mL / min under atmospheric pressure to carry out the anaerobic aromatization reaction of methane.

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