Method for preparing gallium-doped hollow ZSM-5 molecular sieve by microwave and application thereof

Abstract

The application discloses a method for preparing gallium-doped hollow ZSM-5 molecular sieves by microwave and application thereof, and relates to the technical field of molecular sieve catalyst preparation. A precursor is prepared by mixing a silicon source, a template agent and deionized water, stirring and transferring into a digestion tank, and then the precursor is subjected to microwave hydrothermal treatment and is placed in a muffle furnace for calcination to remove the template agent, so as to obtain a pure silicon molecular sieve; the pure silicon molecular sieve is taken, an aluminum source, a template agent and deionized water are added, ultrasonic treatment is performed, and then the mixture is transferred into the digestion tank, and then the mixture is subjected to microwave hydrothermal treatment and dissolution-recrystallization, so as to obtain a product which is placed in the muffle furnace for calcination to remove the template agent, so as to obtain a hollow ZSM-5 molecular sieve; the hollow ZSM-5 molecular sieve is taken, gallium nitrate and deionized water are added, ultrasonic treatment is performed, and then the mixture is transferred into the digestion tank, and then gallium doping is performed under microwave irradiation; and the dried product is placed in a tube furnace, and is kept at 200-300 DEG C under argon atmosphere, so as to obtain the gallium-doped hollow ZSM-5 molecular sieve. The microwave hydrothermal treatment and dissolution-recrystallization process are combined, so that the preparation time of the hollow ZSM-5 molecular sieve is effectively shortened, and the energy consumption is reduced.

Description

Technical Field

[0001] This invention relates to the field of molecular sieve catalyst preparation technology, specifically to a method for preparing gallium-doped hollow ZSM-5 molecular sieves using microwave and its application. Background Technology

[0002] With the continuous development of catalysis technology, ZSM-5 molecular sieves have been widely used in the petrochemical and fine chemical industries due to their unique acidity, excellent thermal stability, and good shape selectivity, especially in the methanol aromatization to aromatics (MTA reaction), where they have demonstrated excellent catalytic performance. However, the application of traditional ZSM-5 molecular sieves in the MTA reaction still faces many limitations. Pore blockage and carbon buildup lead to low mass transfer efficiency of reactants or intermediates, and rapid catalyst deactivation, thus severely affecting the product selectivity and yield of the methanol-to-aromatics reaction.

[0003] To address the aforementioned issues, molecular sieves have undergone structural optimization in recent years through methods such as hierarchical pore modification and hollow structure design. Commonly used structural control methods include acid dissolution, alkali dissolution, and dissolution-recrystallization techniques. Among these, dissolution-recrystallization has attracted attention due to its ability to construct relatively complete hollow structures. However, traditional dissolution-recrystallization techniques employ external heating methods, such as conventional hydrothermal heating, where heat must be transferred from the heat source to the reaction medium and gradually conducted into the reaction system. This heating mode is prone to localized overheating or uneven temperature distribution, especially in complex reaction systems, resulting in uneven distribution of the prepared molecular sieve pore structure and leading to unsatisfactory catalytic effects and poor selectivity. These traditional heating methods also suffer from drawbacks such as long preparation times and high energy consumption. Summary of the Invention

[0004] The purpose of this invention is to provide a method for preparing gallium-doped hollow ZSM-5 molecular sieves using microwaves and its application, thereby solving the problems of cumbersome processes and unsatisfactory catalytic effects of the prepared molecular sieves in the prior art.

[0005] To solve the above-mentioned technical problems, the present invention adopts the following technical solution: a method for preparing gallium-doped hollow ZSM-5 molecular sieves using microwaves, characterized by comprising the following steps:

[0006] S1. Mix silicon source, template agent and deionized water, and stir for 1 to 6 hours to obtain precursor a;

[0007] S2. The precursor a is transferred to a digestion vessel and subjected to microwave hydrothermal treatment to obtain product a;

[0008] S3. Place product a in a muffle furnace and calcine to remove the template agent, thereby obtaining pure silicon molecular sieve;

[0009] S4. Take pure silicon molecular sieve, add aluminum source, template agent and deionized water, and sonicate for 1 to 3 hours to obtain precursor b;

[0010] S5. Transfer precursor b to a digestion vessel and perform microwave hydrothermal treatment and dissolution-recrystallization to obtain product b;

[0011] S6. Product b is placed in a muffle furnace and calcined to remove the template agent, yielding hollow ZSM-5 molecular sieve;

[0012] S7. Take hollow ZSM-5 molecular sieve, add gallium nitrate and deionized water, and sonicate for 1-3 hours to obtain mixture c;

[0013] S8. Transfer the mixture c to a digestion vessel, perform gallium doping under microwave irradiation, and dry the product after filtration, washing, and drying.

[0014] S9. Place the dried product in a tube furnace and heat it at 200-300℃ in an argon atmosphere for 2-4 hours to obtain gallium-doped hollow ZSM-5 molecular sieve, named Ga@Hol-ZSM-5.

[0015] A further technical solution is that in step S1, the silicon source is tetraethyl orthosilicate (TEOS), the template agent is tetrapropylammonium hydroxide (TPAOH), the amount of tetrapropylammonium hydroxide is 0.36-0.375 g / ml, and the amount of tetraethyl orthosilicate is 0.36-0.37 g / ml.

[0016] A further technical solution is that in step S2, the microwave hydrothermal treatment involves holding the product at 150–180°C for 1–4 hours under microwave irradiation, with a microwave power of 1000–2000W.

[0017] A further technical solution is that in step S3, the calcination temperature is increased to 500-700°C at a heating rate of 5-20°C / min, and held for 3-6 hours.

[0018] A further technical solution is that the average pore size of the pure silicon molecular sieve in step S3 is 1–40 nanometers, and the specific surface area is 500–800 m². 2 / g, with a particle size of 0.5–2 micrometers.

[0019] A further technical solution is that in step S4, the aluminum source is aluminum isopropoxide, the template agent is tetrapropylammonium hydroxide (TPAOH), the amount of pure silicon molecular sieve is 0.05-0.06 g / ml, the amount of tetrapropylammonium hydroxide is 0.19-0.20 g / ml, and the amount of aluminum isopropoxide is 0.001-0.003 g / ml.

[0020] A further technical solution is that in step S5, the microwave hydrothermal and dissolution-recrystallization process involves holding the solution at 150-180°C for 1-4 hours under microwave irradiation, with a microwave power of 1000-2000W.

[0021] A further technical solution is that in step S6, the calcination temperature is increased to 500-700°C at a rate of 5-20°C / min, and then held for 3-6 hours.

[0022] A further technical solution is that in step S7, the amount of hollow ZSM-5 molecular sieve used is 0.1-0.2 g / ml, and the amount of gallium nitrate used is 0.004-0.006 g / ml; in step S8, the microwave impregnation power is 1200-1500 W, the heat preservation temperature is 60-100℃, and the heat preservation time is 2-4 hours.

[0023] A further technical solution is to use the gallium-doped hollow ZSM-5 molecular sieve as a catalyst for the aromatization of methanol to produce aromatics. Specifically, the gallium-doped hollow ZSM-5 molecular sieve is pressed into a thin sheet and placed vertically in the reactor for methanol gas to pass through.

[0024] Reaction mechanism:

[0025] Construction process of hollow structure of ZSM-5 molecular sieve: Under alkaline conditions, the Si-OH groups on the surface and inside of ZSM-5 molecular sieve easily lose protons to form Si-O. - and TPA in the template agent + Ions combine via electrostatic interactions to form a Si-O-TPA intermediate, effectively protecting the surface structure of the molecular sieve. Due to the spatial confinement of the pores, TPA... + Ions have difficulty directly entering the interior of the molecular sieve, while OH- - Ions can diffuse into the interior of the molecular sieve and dissolve its internal structure. The dissolved Si groups migrate to the outer surface of the molecular sieve through diffusion and interact with the TPA on the outer surface. + A new Si-O-TPA intermediate is formed, and the template agent is removed during subsequent calcination to form a ZSM-5 molecular sieve with a hollow structure. Microwaves play a crucial role in this process; their uniform heating characteristics not only accelerate the dissociation of Si-OH groups and the dissolution of the internal structure but also significantly promote the formation and uniform distribution of the Si-O-TPA intermediate. Simultaneously, under the influence of the microwave field, TPA… + The high-speed vibration, rotation, and dipole reversal of ions enhance their diffusion efficiency on the molecular sieve surface, accelerating the migration and recrystallization of internal dissolved products. This precise process control not only shortens the reaction time but also improves the regularity of the hollow structure and the stability of the molecular sieve, giving the prepared hollow ZSM-5 molecular sieve excellent structural properties and application potential.

[0026] Gallium-doped ZSM-5 molecular sieves can regulate the acidity distribution of the sieve, enhance the selectivity of acidic active sites, promote the aromatization process of reactants, and effectively inhibit the formation of coke. Microwave impregnation, applied directly to the interior of the material, significantly improves the efficiency and uniformity of gallium loading on the molecular sieve, and also ensures a stable bond between the metal and the molecular sieve, improving the thermal stability and lifespan of the catalyst, thereby significantly enhancing the catalytic activity and product selectivity of the catalytic reaction.

[0027] In application, the methanol-to-aromatics (MTA) reaction can be divided into three main stages. First, in the methanol dehydration stage (as shown in the attached...) Figure 6 As shown in the figure, methanol dehydrates to dimethyl ether (DME) under the action of acidic sites on the catalyst. DME further cracks to generate active intermediates such as methyl cations and carbocations, providing a basis for subsequent reactions. Gallium doping optimizes the acidity distribution of the ZSM-5 zeolite, enhances the activity of weakly acidic sites, promotes efficient methanol dehydration, and provides active species for subsequent reactions. Secondly, in the low-carbon olefin formation and polymerization stage (as shown in the figure)... Figure 7 As shown in the diagram, the methyl cation reacts with intermediates to form low-carbon olefins, which further polymerize to form high-carbon olefins or chain alkanes. Gallium, through its excellent dehydrogenation ability, effectively regulates the reaction pathway of intermediates, suppresses byproduct formation, and accumulates precursors for cyclization reactions. Finally, in the cyclization and dehydrogenation aromatization stages (as shown in the attached diagram), Figure 8 As shown, high-carbon olefins and chain alkanes undergo cyclization to form cycloalkanes under the action of an acidic catalyst, which are then converted into aromatics (such as benzene, toluene, and xylene) through dehydrogenation. Gallium plays a crucial dehydrogenation role in this stage, accelerating the conversion of cycloalkanes to aromatics while inhibiting the formation of coke, thereby improving the stability of the catalyst and the yield of aromatic products.

[0028] Compared with the prior art, the beneficial effects of the present invention are:

[0029] 1. This invention provides an efficient heating and crystallization method by combining microwave hydrothermal technology with a dissolution-recrystallization process, which effectively shortens the preparation time of hollow ZSM-5 molecular sieves and reduces energy consumption.

[0030] 2. This invention utilizes microwaves to directly act on TPA in the template agent. + Ions are subjected to high-speed vibration, rotation, and dipole reversal in the reaction medium, thereby increasing their Si-O reactivity with the ZSM-5 molecular sieve surface. - This improved contact efficiency, thereby enabling the uniform and efficient preparation of hollow ZSM-5 molecular sieves.

[0031] 3. This invention employs microwave impregnation technology to ensure that gallium atoms are uniformly distributed within the ZSM-5 molecular sieve framework, resulting in high crystallinity. This allows the catalyst to maintain excellent catalytic performance during high-temperature reactions, thus extending its service life.

[0032] 4. The hollow ZSM-5 molecular sieve prepared by this invention has a large specific surface area and a unique pore structure, which effectively reduces the coking phenomenon in the catalytic process, improves the mass transfer efficiency, and enhances the anti-coking performance of the catalyst.

[0033] 5. The preparation method of the present invention is simple and quick, suitable for large-scale production, and can be widely used in industrial catalytic reactions such as methanol to aromatics, achieving high-efficiency catalysis and improving the practicality and economy of the overall process. Attached Figure Description

[0034] Figure 1 This is a process flow diagram of the present invention.

[0035] Figure 2 The X-ray powder diffraction spectra of Si-1, hollow ZSM-5 molecular sieve and gallium-doped hollow ZSM-5 molecular sieve in Example 1 of this invention are shown.

[0036] Figure 3 The images are scanning electron microscope images of Si-1, hollow ZSM-5 molecular sieves and gallium-doped hollow ZSM-5 molecular sieves in Example 1 of the present invention.

[0037] Figure 4 The images show transmission electron microscope (TEM) images and EDS elemental distribution maps of Si-1, hollow ZSM-5 molecular sieves, and gallium-doped hollow ZSM-5 molecular sieves in Example 1 of this invention.

[0038] Figure 5 This is a product distribution diagram of the MTA reaction of each ZSM-5 molecular sieve in Example 1 and the comparative example of the present invention.

[0039] Appendix Figure 6 This is a schematic diagram illustrating the reaction principle of a stage of the MTA reaction process of the present invention.

[0040] Appendix Figure 7 This is a schematic diagram of the reaction principle of the two-stage MTA reaction process of the present invention.

[0041] Appendix Figure 8 This is a schematic diagram of the three-stage MTA reaction process of the present invention.

[0042] Appendix Figure 9 This is a diagram illustrating the formation mechanism of the hollow structure of ZSM-5 molecular sieve in this invention. Detailed Implementation

[0043] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

[0044] Example 1

[0045] A gallium-doped hollow ZSM-5 molecular sieve preparation method includes the following steps:

[0046] 1. Weigh 7.4g of tetrapropylammonium hydroxide and 7.3g of tetraethyl orthosilicate, add 20mL of deionized water, and stir at room temperature for 4 hours to obtain mixture a;

[0047] 2. Transfer mixture a to a polytetrafluoroethylene digestion vessel and keep it at 170°C for 2 hours under microwave irradiation with a power of 1200W. The product is hydrothermal product a. After filtration and washing, hydrothermal product a is dried overnight.

[0048] 3. Place the hydrothermal product a in a muffle furnace and heat it to 550°C at a rate of 10°C / min. Hold it at that temperature for 5 hours to remove the template agent. The product is pure silicon ZSM-5 molecular sieve, named Si-1.

[0049] 4. Weigh 1.2g Si-1, 0.04g aluminum isopropoxide and 3.9g tetrapropylammonium hydroxide, add 20mL deionized water, and sonicate for 1 hour to obtain mixture b.

[0050] 5. Transfer mixture b to a polytetrafluoroethylene digestion vessel and keep it at 170°C for 2 hours under microwave irradiation with a power of 1200W. The product is hydrothermal product b. After filtration and washing, hydrothermal product b is dried overnight.

[0051] 6. Place the hydrothermal product b in a muffle furnace and heat it to 550°C at a rate of 10°C / min. Hold it at that temperature for 5 hours to remove the template agent. The product is a hollow ZSM-5 molecular sieve, named Hollow-ZSM-5.

[0052] 7. Weigh 0.1g of gallium nitrate, add 20ml of deionized water, and stir to form a homogeneous solution.

[0053] 8. Weigh 2g of Hollow-ZSM-5, add it to the solution, and sonicate for 1 hour to obtain mixture a.

[0054] 9. Transfer mixture a to a polytetrafluoroethylene digestion vessel and heat it at 80°C for 2 hours under microwave irradiation at a power of 1200W to obtain product a. After filtration and washing, product a is dried overnight at 60°C.

[0055] 10. The dried product a was transferred to a tube furnace and heated to 200°C at a heating rate of 2°C / min under an argon atmosphere. The temperature was held for 2 hours to obtain a gallium-doped hollow ZSM-5 molecular sieve catalyst, named Ga@Hol-ZSM-5.

[0056] Figure 2 The X-ray diffraction patterns of the ZSM-5 series samples are shown. The diffraction peaks are consistent with the data in standard PDF#44-0003, indicating that the prepared ZSM-5 series samples all formed typical MFI structures, which are characteristic structures of ZSM-5 molecular sieves. (Attached) Figure 3 The microstructure of the ZSM-5 series samples is shown, and the results indicate that the samples have a uniform morphology, with no significant changes in grain morphology observed. (See attached image.) Figure 4 The structural characteristics of the ZSM-5 series samples are shown, with Hollow-ZSM-5 and Ga@Hol-ZSM-5 samples clearly exhibiting a hollow structure, demonstrating the stability and feasibility of the process described in this invention. Additionally, [the following text is missing]. Figure 4 The elemental distribution of the Ga@Hol-ZSM-5 sample was also shown, indicating that Ga is uniformly distributed in the molecular sieve, further verifying the effectiveness of the doping process.

[0057] Example 2

[0058] The reaction process of methanol to aromatics catalyzed by gallium-doped hollow ZSM-5 molecular sieve Ga@Hol-ZSM-5 includes the following steps:

[0059] Weigh 0.4g of the Ga@Hol-ZSM-5 catalyst prepared in Example 1, press it into a catalyst sheet with a diameter of 0.8cm (matching the inner diameter of the fixed bed reactor), and place it vertically in the fixed bed reactor.

[0060] The methanol space velocity was set to 0.8 h⁻¹, the carrier gas to argon, and the reaction temperature to 450 °C. A fixed-bed reactor was connected to a gas chromatograph for qualitative and quantitative analysis of product distribution.

[0061] Comparative Example 1

[0062] This comparative example differs from Example 2 in that the catalyst used in this reaction is Si-1, which has already formed the ZSM-5 molecular sieve MFI structure in Example 1. The specific steps are as follows:

[0063] Weigh 0.4g of Si-1 catalyst, press it into a catalyst sheet with a diameter of 0.8cm, and place it vertically in a fixed-bed reactor.

[0064] The methanol space velocity was set to 0.8 h⁻¹, the carrier gas to argon, and the reaction temperature to 450 °C. A fixed-bed reactor was connected to a gas chromatograph for qualitative and quantitative analysis of product distribution.

[0065] Comparative Example 2

[0066] This comparative example differs from Example 2 in that the catalyst used in this reaction is Hollow-ZSM-5 with a hollow structure prepared in Example 1. The specific steps are as follows:

[0067] Weigh 0.4g of Hollow-ZSM-5 catalyst, press it into a catalyst sheet with a diameter of 0.8cm, and place it vertically in a fixed-bed reactor.

[0068] The methanol space velocity was set to 0.8 h⁻¹, the carrier gas to argon, and the reaction temperature to 450 °C. A fixed-bed reactor was connected to a gas chromatograph for qualitative and quantitative analysis of product distribution.

[0069] Comparative Example 3

[0070] This comparative example differs from Example 2 in that the catalyst used in this reaction is ZSM-5 prepared by a conventional hydrothermal method (purchased from Tianjin Nanhua Catalyst Co., Ltd.). The specific steps are as follows:

[0071] Weigh 0.4g of ZSM-5 catalyst, press it into a catalyst sheet with a diameter of 0.8cm, and place it vertically in a fixed-bed reactor.

[0072] The methanol space velocity was set to 0.8 h⁻¹, the carrier gas to argon, and the reaction temperature to 450 °C. A fixed-bed reactor was connected to a gas chromatograph for qualitative and quantitative analysis of product distribution.

[0073] The product distributions of Example 2 and Comparative Examples 1, 2, and 3 are shown in the attached figures. Figure 5 As shown in the figure, this figure illustrates the product distribution of different types of ZSM-5 molecular sieves (including Si-1, Hollow-ZSM-5, Ga@Hol-ZSM-5, and ZSM-5). The main comparison focuses on the ratio of aromatic products to other products. The gallium-doped Ga@Hol-ZSM-5 sample exhibits excellent selectivity for aromatic products, reaching 37%, significantly higher than other samples. In contrast, undoped samples (such as Hollow-ZSM-5 and ZSM-5) show lower aromatic yields, while Si-1 lacks catalytic activity due to the absence of reactive sites. This indicates that gallium doping and hollow structure modification significantly enhance the catalytic advantage of ZSM-5 molecular sieves in terms of aromatic selectivity.

[0074] Example 3

[0075] A gallium-doped hollow ZSM-5 molecular sieve preparation method includes the following steps:

[0076] 1. Weigh 7.4g of tetrapropylammonium hydroxide and 7.3g of tetraethyl orthosilicate, add 20mL of deionized water, and stir at room temperature for 4 hours to obtain mixture a;

[0077] 2. Transfer mixture a to a polytetrafluoroethylene digestion vessel and keep it at 180°C for 2 hours under microwave irradiation with a power of 1200W. The product is hydrothermal product a. After filtration and washing, hydrothermal product a is dried overnight.

[0078] 3. Place the hydrothermal product a in a muffle furnace and heat it to 560°C at a rate of 10°C / min. Hold it at that temperature for 5 hours to remove the template agent. The product is pure silicon ZSM-5 molecular sieve, named Si-2.

[0079] 4. Weigh 1.2g Si-2, 0.04g aluminum isopropoxide and 3.9g tetrapropylammonium hydroxide, add 20mL deionized water, and sonicate for 1 hour to obtain mixture b.

[0080] 5. Transfer mixture b to a polytetrafluoroethylene digestion vessel and keep it at 150°C for 4 hours under microwave irradiation with a power of 1200W. The product is hydrothermal product b. After filtration and washing, hydrothermal product b is dried overnight.

[0081] 6. Place the hydrothermal product b in a muffle furnace and heat it to 600°C at a rate of 10°C / min. Hold it at this temperature for 4 hours to remove the template agent. The product is a hollow ZSM-5 molecular sieve, named Hollow-ZSM-5.

[0082] 7. Weigh 0.1g of gallium nitrate, add 20ml of deionized water, and stir to form a homogeneous solution.

[0083] 8. Weigh 2g of Hollow-ZSM-5, add it to the solution, and sonicate for 1 hour to obtain mixture a.

[0084] 9. Transfer mixture a to a polytetrafluoroethylene digestion vessel and heat it at 80°C for 2 hours under microwave irradiation at a power of 1200W to obtain product a. After filtration and washing, product a is dried overnight at 60°C.

[0085] 10. The dried product a was transferred to a tube furnace and heated to 250°C at a heating rate of 2°C / min under an argon atmosphere. The temperature was held for 2 hours to obtain a gallium-doped hollow ZSM-5 molecular sieve catalyst, named Ga@Hol-ZSM-5.

[0086] Example 4

[0087] A gallium-doped hollow ZSM-5 molecular sieve preparation method includes the following steps:

[0088] 1. Weigh 7.4g of tetrapropylammonium hydroxide and 7.3g of tetraethyl orthosilicate, add 20mL of deionized water, and stir at room temperature for 4 hours to obtain mixture a;

[0089] 2. Transfer mixture a to a polytetrafluoroethylene digestion vessel and keep it at 170°C for 2 hours under microwave irradiation with a power of 1200W. The product is hydrothermal product a. After filtration and washing, hydrothermal product a is dried overnight.

[0090] 3. Place the hydrothermal product a in a muffle furnace and heat it to 550°C at a rate of 10°C / min. Hold it at that temperature for 5 hours to remove the template agent. The product is pure silicon ZSM-5 molecular sieve, named Si-1.

[0091] 4. Weigh 1.2g Si-1, 0.04g aluminum isopropoxide and 3.9g tetrapropylammonium hydroxide, add 20mL deionized water, and sonicate for 1 hour to obtain mixture b.

[0092] 5. Transfer mixture b to a polytetrafluoroethylene digestion vessel and keep it at 160°C for 2 hours under microwave irradiation with a power of 1200W. The product is hydrothermal product b. After filtration and washing, hydrothermal product b is dried overnight.

[0093] 6. Place the hydrothermal product b in a muffle furnace and heat it to 600°C at a rate of 10°C / min. Hold it at this temperature for 4 hours to remove the template agent. The product is a hollow ZSM-5 molecular sieve, named Hollow-ZSM-5.

[0094] 7. Weigh 0.1g of gallium nitrate, add 20ml of deionized water, and stir to form a homogeneous solution.

[0095] 8. Weigh 2g of Hollow-ZSM-5, add it to the solution, and sonicate for 1 hour to obtain mixture a.

[0096] 9. Transfer mixture a to a polytetrafluoroethylene digestion vessel and heat it at 80°C for 2 hours under microwave irradiation at a power of 1200W to obtain product a. After filtration and washing, product a is dried overnight at 60°C.

[0097] 10. The dried product a was transferred to a tube furnace and heated to 300°C at a heating rate of 2°C / min under an argon atmosphere. The temperature was held for 2 hours to obtain a gallium-doped hollow ZSM-5 molecular sieve catalyst, named Ga@Hol-ZSM-5.

[0098] Although the invention has been described herein with reference to several illustrative embodiments, it should be understood that many other modifications and implementations can be devised by those skilled in the art, which will fall within the scope of this disclosure. More specifically, various modifications and improvements can be made to the components or layouts within the scope of this disclosure, the drawings, and the claims. Besides modifications and improvements to the components or layouts, other uses will be apparent to those skilled in the art.

Claims

1. A method for microwave preparation of gallium-doped hollow ZSM-5 molecular sieves, characterized in that... Includes the following steps: S1. Mix silicon source, template agent and deionized water, and stir for 1 to 6 hours to obtain precursor a; S2. The precursor a is transferred to a digestion vessel and subjected to microwave hydrothermal treatment to obtain product a; S3. Place product a in a muffle furnace and calcine to remove the template agent to obtain pure silicon molecular sieve; S4. Take pure silicon molecular sieve, add aluminum source, template agent and deionized water, and sonicate for 1 to 3 hours to obtain precursor b; S5. Transfer precursor b to a digestion vessel and perform microwave hydrothermal treatment and dissolution-recrystallization to obtain product b; S6. Product b is placed in a muffle furnace and calcined to remove the template agent, yielding hollow ZSM-5 molecular sieve; S7. Take hollow ZSM-5 molecular sieve, add gallium nitrate and deionized water, and sonicate for 1 to 3 hours to obtain mixture c; S8. Transfer the mixture c to a digestion vessel, perform gallium doping under microwave irradiation, and dry the product after filtration and washing. S9. Place the dried product in a tube furnace and heat it at 200-300℃ in an argon atmosphere for 2-4 hours to obtain gallium-doped hollow ZSM-5 molecular sieve. In step S1, the silicon source is tetraethyl orthosilicate, the template agent is tetrapropylammonium hydroxide, the amount of tetrapropylammonium hydroxide is 0.36-0.375 g / ml, and the amount of tetraethyl orthosilicate is 0.36-0.37 g / ml. In step S4, the aluminum source is aluminum isopropoxide, the template agent is tetrapropylammonium hydroxide, the amount of pure silicon molecular sieve is 0.05-0.06 g / ml, the amount of tetrapropylammonium hydroxide is 0.19-0.20 g / ml, and the amount of aluminum isopropoxide is 0.001-0.003 g / ml.

2. The method according to claim 1, characterized in that: In step S2, microwave hydrothermal treatment involves holding the product at 150–180°C for 1–4 hours under microwave irradiation, with a microwave power of 1000–2000W.

3. The method according to claim 1, characterized in that: In step S3, the calcination temperature is increased to 500-700°C at a rate of 5-20°C / min, and held for 3-6 hours.

4. The method according to claim 1, characterized in that: In step S3, the pure silicon molecular sieve has an average pore size of 1–40 nanometers and a specific surface area of ​​500–800 m². 2 / g, with a particle size of 0.5–2 micrometers.

5. The method according to claim 1, characterized in that: In step S5, microwave hydrothermal treatment and dissolution-recrystallization involve holding the solution at 150–180°C for 1–4 hours under microwave irradiation with a microwave power of 1000–2000W.

6. The method according to claim 1, characterized in that: In step S6, the calcination temperature is increased to 500-700°C at a rate of 5-20°C / min, and held for 3-6 hours.

7. The method according to claim 1, characterized in that: In step S7, the amount of hollow ZSM-5 molecular sieve used is 0.1-0.2 g / ml, and the amount of gallium nitrate used is 0.004-0.006 g / ml; in step S8, the microwave impregnation power is 1200-1500 W, the heat preservation temperature is 60-100℃, and the heat preservation time is 2-4 hours.

8. The method according to claim 1, characterized in that: The gallium-doped hollow ZSM-5 molecular sieve is used as a catalyst for the aromatization of methanol to produce aromatics. Specifically, the gallium-doped hollow ZSM-5 molecular sieve is pressed into a thin sheet and placed vertically in the reactor for methanol gas to pass through.

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