Method for in-situ packaging synthesis of confinement type PtZn coated ZSM-5 bimetallic cluster catalyst by microwave-assisted hydrothermal method

Abstract

The invention discloses a method for in-situ packaging synthesis of a confinement type PtZn-coated ZSM-5 bimetallic cluster catalyst by a microwave-assisted hydrothermal method, and belongs to the technical field of metal-molecular sieve catalyst synthesis. A complex solution of Pt and Zn is added into a raw material of a ZSM-5 molecular sieve synthesized by microwave-assisted hydrothermal crystallization by a one-pot method; after reconstruction is completed, the confinement type PtZn-coated ZSM-5 bimetallic cluster catalyst can be obtained through the processes of roasting, activation and the like, and the catalyst has high propane conversion rate and propylene selectivity. According to the catalyst, the defect that precious metal is prone to agglomeration is greatly overcome, the utilization rate and stability of precious metal atoms are greatly improved, and the synthesis strategy can be popularized to controllable synthesis of other bimetallic cluster catalysts.

Description

Technical Field

[0001] The invention relates to the technical field of metal-molecular sieve catalyst synthesis, and in particular to a method for in-situ encapsulation synthesis of confined PtZn@ZSM-5 bimetallic cluster catalysts using a microwave-assisted hydrothermal method. Background Art

[0002] As a core component of the petrochemical industry, the output of propylene has become a key indicator for evaluating the progress of a country's petrochemical industry. As the second largest member of the olefin series, propylene is a key bulk industrial raw material that is widely used in the manufacture of a variety of high-value polymers, chemical intermediates and oxygen-containing compounds (polypropylene, propylene oxide and acrylonitrile, etc.). With the accelerated advancement of the global economy and industrialization, the diversity and output of propylene downstream products continue to expand, which in turn drives a significant increase in the global market demand for propylene.

[0003] The traditional sources of propylene are mainly the cracking of naphtha or other oil products and the catalytic cracking of petroleum products. However, the traditional naphtha cracking and catalytic cracking processes are difficult to meet the increasing demand for propylene in the market, so it is particularly necessary to develop new propylene production processes. Shale gas contains abundant propane resources, and propane dehydrogenation (PDH) technology, as the most important target olefin production technology, is becoming increasingly important.

[0004] The best catalysts in the propane dehydrogenation reaction are Cr-based and Pt-based catalysts. Among them, Cr-based catalysts are highly toxic, and effective measures need to be taken in the production, use and treatment of waste catalysts to avoid harm to the human body and the environment. Pt-based catalysts have attracted much attention due to their high activity and pollution-free characteristics. However, under high temperature and low pressure reaction conditions, single metal Pt catalysts are prone to the following problems: first, the conversion rate is low, and alkanes are prone to cracking, isomerization and other side reactions under the reaction conditions, resulting in low selectivity of the target product; second, the particles are prone to agglomeration and carbon deposition, which reduces the performance of the catalyst and shortens its life. In order to improve the activity, selectivity and stability of Pt-based catalysts, it is particularly necessary to modify the catalyst. The main strategy is to adopt a controllable catalyst synthesis method, select a suitable carrier and add additives. The catalysts synthesized by traditional methods have limitations such as poor structural uniformity and random distribution of components. Therefore, it is necessary to adopt a new controllable catalyst synthesis technology to accurately construct a Pt-based bimetallic catalyst with a specific structure. Summary of the invention

[0005] The purpose of the present invention is to provide a method for in-situ encapsulation synthesis of confined PtZn@ZSM-5 bimetallic cluster catalysts by microwave-assisted hydrothermal method, so as to solve the problems of low activity and easy sintering of current Pt-based propane dehydrogenation catalysts.

[0006] To achieve the above object, the present invention provides a method for in-situ encapsulation synthesis of confined PtZn@ZSM-5 bimetallic cluster catalysts by microwave-assisted hydrothermal method, comprising the following synthesis steps:

[0007] S1, synthesizing a mixed solution of an alkali source and a template agent, dissolving the alkali source and the template agent in deionized water according to a certain molar ratio, and stirring to obtain an alkaline solution;

[0008] S2, adding ZSM-5 molecular sieve as seed crystals into the alkaline solution, and stirring evenly to form a gel;

[0009] S3, transferring the gel to a hydrothermal reactor and performing a crystallization reaction in a microwave digestion apparatus;

[0010] S4. Add a complex solution of Pt and Zn to the raw material of ZSM-5 molecular sieve synthesized by microwave-assisted hydrothermal crystallization, centrifuge, wash, dry and calcine the catalyst precursor to obtain a PtZn@ZSM-5 bimetallic cluster catalyst.

[0011] Preferably, in step S1, the base is one or more of urea, potassium hydroxide or sodium hydroxide.

[0012] Preferably, in step S1, the template is one or more of N,N,N-trimethyl-adamantyl ammonium hydroxide, choline chloride or choline hydroxide.

[0013] Preferably, in step S1, the molar ratio of the base to the template is 0.2 to 8:1, and the mass ratio of the seed crystal to the template is 0.3 to 1:1.

[0014] Preferably, in step S3, the microwave irradiation power is 100-500 W and the frequency is 2450 MHz.

[0015] Preferably, in step S3, the crystallization temperature is 140-200° C., and the crystallization time is 1-8 hours; the calcination temperature is 450-850° C., and the calcination time is 1-10 hours, and the activation time is 1-6 hours.

[0016] Preferably, in step S4, the complex solution is one or more of ethylenediamine, ethylenediaminetetraacetic acid, sodium ethylenediaminetetraacetate or ammonium citrate, and its concentration range is 0.1 to 0.6 mol / L.

[0017] Preferably, in step S4, microporous ZSM-5 is used as a carrier to synthesize a multi-level pore-confined PtZn@ZSM-5 bimetallic cluster catalyst by an in-situ encapsulation method, wherein the PtZn bimetallic is uniformly confined in the pores of the molecular sieve in the form of highly dispersed clusters.

[0018] Preferably, the Pt packaging amount of the PtZn@ZSM-5 bimetallic cluster catalyst is 0.1-1 wt%, and the Zn packaging amount is 1-10 wt%.

[0019] Preferably, the particle size of the carrier ZSM-5 molecular sieve is 100 to 800 nm.

[0020] Therefore, the method for in-situ encapsulation and synthesis of confined PtZn@ZSM-5 bimetallic cluster catalysts by the microwave-assisted hydrothermal method of the above structure has the following advantages:

[0021] The present invention adopts the strategy of encapsulation confinement to synthesize a highly active and highly stable bimetallic cluster catalyst in one pot. In the process of synthesizing the catalyst by microwave-assisted hydrothermal method, the synthesis time of PtZn@ZSM-5 catalyst is greatly shortened by introducing seed crystals and microwave treatment, and microwave treatment helps the mesopore formation of molecular sieve, and still maintains the original crystal structure. At the same time, microwave treatment helps metal dispersion, metal size clustering and bimetallic alloying, which can further improve the catalytic reaction activity. In addition, this method has certain universality. For example, we can also realize the controllable synthesis of bimetallic cluster catalysts such as IrZn@ZSM-5 and RhZn@ZSM-5.

[0022] The catalyst structure of the present invention is precisely controllable and can be synthesized in batches. The loading amount and size of the active components of the obtained catalyst are simple and controllable, and the catalyst has excellent catalytic performance. The catalyst is applied to the reaction of dehydrogenating propane to produce propylene, and high reaction activity, selectivity and stability can be obtained. The occurrence of side reactions such as cracking and carbon deposition can also be effectively inhibited, and the reaction selectivity can be improved. After the reaction is completed, the catalyst is easy to separate and recover.

[0023] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 XRD diagrams of catalysts synthesized in Example A, B, C, D and E of the method for in-situ encapsulation synthesis of confined PtZn@ZSM-5 bimetallic cluster catalysts by microwave-assisted hydrothermal method of the present invention and Comparative Examples X, Y and Z.

[0025] Figure 2 This is the HAADF-STEM image of the 0.5Pt7Zn@ZSM-5 bimetallic cluster catalyst in Example 4.

[0026] Figure 3 This is the HAADF-STEM image of the 0.5I r7Zn@ZSM-5 bimetallic cluster catalyst in Example 6.

[0027] Figure 4This is the HAADF-STEM image of the Pt@ZSM-5 catalyst in Comparative Example 2. DETAILED DESCRIPTION

[0028] In order to better understand the above technical solution, the above technical solution will be described in detail below in conjunction with the accompanying drawings and specific implementation methods. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0029] The terms used in the embodiments of the present invention are only for the purpose of describing specific embodiments, and are not intended to limit the present invention. The singular forms "a", "said" and "the" used in the embodiments of the present invention and the appended claims are also intended to include plural forms, unless the context clearly indicates other meanings, and "multiple" generally includes at least two.

[0030] It should also be noted that the term "includes", "comprising" or any other variation thereof is intended to cover non-exclusive inclusion, so that a commodity or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such commodity or device. In the absence of more restrictions, the elements defined by the sentence "comprising a ..." do not exclude the existence of other identical elements in the commodity or device including the elements.

[0031] Example 1

[0032] Catalyst synthesis: Dissolve 0.3g of sodium hydroxide in 22.5mL of deionized water according to the ratio, stir evenly to obtain an alkaline solution, heat to 48°C, and slowly drop 6.75g of the template agent N,N,N-trimethyl-adamantyl ammonium hydroxide into the solution under continuous heating and stirring. Add seed crystal ZSM-5 (SiO2 / Al2O3=300) molecular sieves, stir for 1h, then add 0.5352mL of 0.1mol / L Pt complex solution and 1.065mL of 0.3mol / L Zn complex solution, and continue stirring for 1h after adding; the solution is loaded into a hydrothermal reactor, crystallized at 160°C in a microwave digester for 4h to obtain a catalyst precursor, and the catalyst precursor is centrifuged, washed, dried at 80°C for 12h, calcined at 550°C for 10h, and activated for 2h to obtain 0.5Pt1 Zn@ZSM-5 catalyst A. Figure 1It can be seen that sample A is a 0.5Pt1 Zn@ZSM-5 catalyst, which shows characteristic diffraction peaks belonging to the MFI topological structure, which are 7.94°, 8.83°, 23.08°, 23.32° and 23.95° at 2θ, respectively. The crystalline structure of ZSM-5 is still retained, and there are no peaks of Pt and Zn crystalline phases, indicating that the metal exists in a highly dispersed form.

[0033] Example 2

[0034] Catalyst synthesis: Dissolve 0.3g of sodium hydroxide in 22.5mL of deionized water according to the ratio, stir evenly to obtain an alkaline solution, heat to 48°C, and slowly drop 6.75g of the template agent N,N,N-trimethyl-adamantyl ammonium hydroxide into the solution under continuous heating and stirring, add seed crystal ZSM-5 (SiO2 / Al2O3=300) molecular sieve, stir for 1h, then add 0.5352mL of 0.1mol / L Pt complex solution and 3.194mL of 0.3mol / L Zn complex solution, continue stirring for 1h after adding; put the solution into a hydrothermal reactor, crystallize at 160°C in a microwave digester for 4h to obtain a catalyst precursor, centrifuge the catalyst precursor, wash, dry at 80°C for 12h, calcine at 550°C for 10h and activate for 2h to obtain 0.5Pt3Zn@ZSM-5 catalyst B. Figure 1 It can be seen that sample B is a 0.5Pt3Zn@ZSM-5 catalyst, which shows characteristic diffraction peaks belonging to the MFI topological structure, which are 7.94°, 8.83°, 23.08°, 23.32° and 23.95° at 2θ, respectively. The crystalline structure of ZSM-5 is still retained, and there are no peaks of Pt and Zn crystalline phases, indicating that the metal exists in a highly dispersed form.

[0035] Example 3

[0036] Catalyst synthesis: Dissolve 0.3g of sodium hydroxide in 22.5mL of deionized water according to the ratio, stir evenly to obtain an alkaline solution, heat to 48°C, and slowly drop 6.75g of the template agent N,N,N-trimethyl-adamantyl ammonium hydroxide into the solution under continuous heating and stirring, add seed crystal ZSM-5 (SiO2 / Al2O3=300) molecular sieve, stir for 1h, then add 0.5352mL of 0.1mol / L Pt complex solution and 5.316mL of 0.3mol / L Zn complex solution, and continue stirring for 1h after adding; the solution is loaded into a hydrothermal reactor, crystallized at 160°C in a microwave digester for 4h to obtain a catalyst precursor, and the catalyst precursor is centrifuged, washed, dried at 80°C for 12h, calcined at 550°C for 10h, and activated for 2h to obtain 0.5Pt5Zn@ZSM-5 catalyst C. Figure 1It can be seen that sample C is a 0.5Pt5Zn@ZSM-5 catalyst. The crystalline structure of ZSM-5 is still retained, but the intensity of the diffraction peak decreases slightly. The main reason for the decrease in the intensity of the diffraction peak is that the ZSM-5 component is impregnated and covered by Pt and Zn species, but there are no peaks of Pt and Zn crystalline phases, indicating that the metal exists in a highly dispersed form.

[0037] Example 4

[0038] Catalyst synthesis: Dissolve 0.3g of sodium hydroxide in 22.5mL of deionized water according to the ratio, stir evenly to obtain an alkaline solution, heat to 48°C, and slowly drop 6.75g of the template agent N,N,N-trimethyl-adamantyl ammonium hydroxide into the solution under continuous heating and stirring, add seed crystal ZSM-5 (SiO2 / Al2O3=300) molecular sieve, stir for 1h, then add 0.5352mL of 0.1mol / L Pt complex solution and 7.442mL of 0.3mol / L Zn complex solution, continue stirring for 1h after adding; put the solution into a hydrothermal reactor, crystallize at 160°C in a microwave digester for 4h to obtain a catalyst precursor, centrifuge the catalyst precursor, wash, dry at 80°C for 12h, calcine at 550°C for 10h and activate for 2h to obtain 0.5Pt7Zn@ZSM-5 catalyst D. Figure 1 It can be seen that sample D is a 0.5Pt7Zn@ZSM-5 catalyst. The crystalline structure of ZSM-5 is still retained, but the intensity of the diffraction peak decreases slightly. The main reason for the decrease in the intensity of the diffraction peak is that the ZSM-5 component is impregnated and covered by Pt and Zn species, but there is no peak of Pt and Zn crystalline phase, indicating that the metal exists in a highly dispersed form. Figure 2 It can be seen that the catalyst metal particle size is 1 to 2 nm, and it is a highly dispersed bimetallic cluster.

[0039] Example 5

[0040] Catalyst synthesis: Dissolve 0.3g of sodium hydroxide in 22.5mL of deionized water according to the ratio, stir evenly to obtain an alkaline solution, heat to 48°C, and slowly drop 6.75g of the template agent N,N,N-trimethyl-adamantyl ammonium hydroxide into the solution under continuous heating and stirring, add seed crystal ZSM-5 (SiO2 / Al2O3=300) molecular sieve, stir for 1h, then add 0.5352mL of 0.1mol / L Pt complex solution and 10.632mL of 0.3mol / L Zn complex solution, and continue stirring for 1h after adding; the solution is loaded into a hydrothermal reactor, crystallized at 160°C in a microwave digester for 4h to obtain a catalyst precursor, and the catalyst precursor is centrifuged, washed, dried at 80°C for 12h, calcined at 550°C for 10h, and activated for 2h to obtain 0.5Pt10Zn@ZSM-5 catalyst E. Figure 1 It can be seen that sample E is a 0.5Pt10Zn@ZSM-5 catalyst. The crystalline structure of ZSM-5 is still retained, but the intensity of the diffraction peak decreases slightly. The main reason for the decrease in the intensity of the diffraction peak is that the ZSM-5 component is impregnated and covered by Pt and Zn species.

[0041] Example 6

[0042] Catalyst synthesis: Dissolve 0.3g of sodium hydroxide in 22.5mL of deionized water according to the ratio, stir evenly to obtain an alkaline solution, heat to 48°C, and slowly drop 6.75g of the template agent N,N,N-trimethyl-adamantyl ammonium hydroxide into the solution under continuous heating and stirring, add seed crystal ZSM-5 (SiO2 / Al2O3=300) molecular sieve, stir for 1h, then add 0.5352mL of 0.1mol / L Ir complex solution and 7.442mL of 0.3mol / L Zn complex solution, continue stirring for 1h after adding; put the solution into a hydrothermal reactor, crystallize at 160°C in a microwave digester for 4h to obtain a catalyst precursor, centrifuge the catalyst precursor, wash, dry at 80°C for 12h, calcine at 550°C for 10h and activate for 2h to obtain 0.5Ir7Zn@ZSM-5 catalyst. Figure 3 It can be seen that the average particle size of the catalyst metal is 0.86 nm, which is a highly dispersed bimetallic cluster.

[0043] Comparative Example 1

[0044] Catalyst synthesis: Dissolve 0.3g of sodium hydroxide in 22.5mL of deionized water according to the ratio, stir evenly to obtain an alkaline solution, heat to 48°C, and slowly drop 6.75g of the template agent N,N,N-trimethyl-adamantyl ammonium hydroxide into the solution under continuous heating and stirring. Add seed crystal ZSM-5 (SiO2 / Al2O3=300) molecular sieves, stir for 1h, then add 0.5352mL of 0.1mol / L Pt complex solution and 7.442mL of 0.3mol / L Zn complex solution, continue stirring for 1h after adding, load the solution into a hydrothermal reactor, crystallize at 160°C in a homogeneous reactor for 48h to obtain a catalyst precursor, centrifuge the catalyst precursor, wash, dry at 80°C for 12h, calcine at 550°C for 10h, and activate for 2h to obtain 0.5Pt7Zn@ZSM-5 catalyst X. Figure 1 It can be seen that the peak intensity of the catalyst synthesized by traditional hydrothermal synthesis is significantly higher than that of the catalyst synthesized by microwave-assisted method, but the peaks corresponding to Pt and Zn crystalline phases are not detected, indicating that the metal dispersion is good in the synthesis of the catalyst and no large metal nanoclusters are formed.

[0045] Comparative Example 2

[0046] Dissolve 0.3g of sodium hydroxide in 22.5mL of deionized water according to the ratio, stir evenly to obtain an alkaline solution, heat to 48°C, and slowly drop 6.75g of the template agent N,N,N-trimethyl-adamantyl ammonium hydroxide into the solution under continuous heating and stirring. Add seed crystal ZSM-5 (SiO2 / Al2O3=300) molecular sieves and stir for 1h, then add 0.5352mL of 0.1mol / L Pt complex solution, continue stirring for 1h after adding, and charge the solution into a hydrothermal reactor. Crystallize at 160°C in a homogeneous reactor for 48h to obtain a catalyst precursor. The catalyst precursor is centrifuged, washed, dried at 80°C for 12h, calcined at 550°C for 10h, and activated for 2h to obtain 0.5Pt@ZSM-5 catalyst Y. Figure 1 It can be seen that a characteristic diffraction peak belonging to the CHA topological structure appears at 2θ of 9.6. This may be because part of the ZSM-5 crystal structure decomposes and transforms into CHA in an alkaline medium during the synthesis of the catalyst, causing the diffraction peak intensity belonging to ZSM-5 to decrease and a mixed phase to appear. Figure 4 It can be seen that the metal clusters of 0.5Pt@ZSM-5 catalyst have larger particle size and poor metal dispersion.

[0047] Comparative Example 3

[0048] Catalyst synthesis: Dissolve 0.3g of sodium hydroxide in 22.5mL of deionized water according to the ratio, stir evenly to obtain an alkaline solution, heat to 48°C, and slowly drop 6.75g of the template agent N,N,N-trimethyl-adamantyl ammonium hydroxide into the solution under continuous heating and stirring. Add seed crystal ZSM-5 (SiO2 / Al2O3=300) molecular sieves, stir for 1h, add 7.442mL of 0.3mol / L Zn complex solution, continue stirring for 1h after adding, load the solution into a hydrothermal reactor, crystallize at 160°C in a homogeneous reactor for 48h to obtain a catalyst precursor, centrifuge the catalyst precursor, wash, dry at 80°C for 12h, calcine at 550°C for 10h, and activate for 2h to obtain 7Zn@ZSM-5 catalyst Z. Figure 1 It can be seen that the crystalline structure of ZSM-5 is still retained, but the intensity of the diffraction peak decreases slightly.

[0049] The performance of the catalyst prepared in the above embodiment was evaluated using a fixed bed reactor. After the catalyst was pressed into tablets and crushed into 40-60 mesh, the hydrogenation reaction was carried out in a 6mm inner diameter stainless steel tube reactor. Before the reaction, the catalyst was reduced with H2 containing H2 at a flow rate of 30mL / min at 550°C for 2 hours, and then switched to a C3H8:N2:H2=1:1:4 mixed gas for reaction. The reaction conditions of the above embodiment and comparative example are: reaction pressure is normal pressure, reaction temperature is 600°C, and reaction catalysis is 20h. The catalytic results are shown in Table 1.

[0050] Table 1 Catalyst evaluation results data table

[0051] catalyst Conversion rate (%) Selectivity (%) A 40.5 91.9 B 55.0 94.4 C 57.4 93.9 D 62.6 96.5 E 61.9 96.0 X 62.1 95.1 Y 10.0 71.9 Z 6.5 72.7

[0052] Therefore, the present invention adopts the method of in-situ encapsulation synthesis of confined PtZn@ZSM-5 bimetallic cluster catalyst by microwave-assisted hydrothermal method of the above structure, and adopts the strategy of encapsulation confinement to synthesize high-activity and high-stability bimetallic cluster catalyst in one pot. In the process of synthesizing catalyst by microwave-assisted hydrothermal method, by introducing crystal seeds and microwave treatment, the synthesis time of PtZn@ZSM-5 catalyst is greatly shortened, and microwave treatment contributes to the formation of mesopores of molecular sieve, and still maintains the original crystal structure, while microwave treatment contributes to metal dispersion, reduces metal particle size, and makes PtZn metal oxide easy to reduce to PtZn alloy, which can further enhance catalytic activity. In addition, the method has certain universality, for example, we can also realize the controllable synthesis of bimetallic cluster catalysts such as IrZn@ZSM-5 and RhZn@ZSM-5. The structure of the catalyst is precisely controllable and can be synthesized in batches. The loading amount and size of the active components of the obtained catalyst are simple and controllable, and it has excellent catalytic performance. The catalyst is applied to the reaction of propane dehydrogenation to propylene to obtain high reaction activity, selectivity and stability, and can also effectively inhibit the occurrence of side reactions such as cracking and carbon deposition, improve the reaction selectivity, and the catalyst is easy to separate and recover after the reaction is completed.

[0053] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that they can still modify or replace the technical solution of the present invention with equivalents, and these modifications or equivalent replacements cannot cause the modified technical solution to deviate from the spirit and scope of the technical solution of the present invention.

Claims

1. A method for in-situ encapsulation synthesis of confined PtZn@ZSM-5 bimetallic cluster catalysts by microwave-assisted hydrothermal method, characterized in that: The synthesis steps include: S1, synthesizing a mixed solution of an alkali source and a template agent, dissolving the alkali source and the template agent in deionized water according to a certain molar ratio, and stirring to obtain an alkaline solution; S2, adding ZSM-5 molecular sieve as seed crystals into the alkaline solution, and stirring evenly to form a gel; S3, transferring the gel to a hydrothermal reactor and performing a crystallization reaction in a microwave digestion apparatus; S4. Add a complex solution of Pt and Zn to the raw material of ZSM-5 molecular sieve synthesized by microwave-assisted hydrothermal crystallization, centrifuge, wash, dry and calcine the catalyst precursor to obtain a PtZn@ZSM-5 bimetallic cluster catalyst.

2. The method for in-situ encapsulation synthesis of confined PtZn@ZSM-5 bimetallic cluster catalyst by microwave-assisted hydrothermal method according to claim 1, characterized in that: In step S1, the alkali is one or more of urea, potassium hydroxide or sodium hydroxide.

3. The method for in-situ encapsulation synthesis of confined PtZn@ZSM-5 bimetallic cluster catalyst by microwave-assisted hydrothermal method according to claim 2, characterized in that: In step S1, the template agent is one or more of N,N,N-trimethyl-adamantyl ammonium hydroxide, choline chloride or choline hydroxide.

4. The method for in-situ encapsulation synthesis of confined PtZn@ZSM-5 bimetallic cluster catalyst by microwave-assisted hydrothermal method according to claim 3, characterized in that: In the step S1, the molar ratio of the base to the template is 0.2 to 8:1, and the mass ratio of the seed crystal to the template is 0.3 to 1:

1.

5. The method for in-situ encapsulation synthesis of confined PtZn@ZSM-5 bimetallic cluster catalyst by microwave-assisted hydrothermal method according to claim 4, characterized in that: In step S3, the microwave irradiation power is 100-500W and the frequency is 2450MHz.

6. The method for in-situ encapsulation synthesis of confined PtZn@ZSM-5 bimetallic cluster catalyst by microwave-assisted hydrothermal method according to claim 5, characterized in that: In the step S3, the crystallization temperature is 140-200° C., the crystallization time is 1-8 hours; the calcination temperature is 450-850° C., the calcination time is 1-10 hours, and the activation time is 1-6 hours.

7. The method for in-situ encapsulation synthesis of confined PtZn@ZSM-5 bimetallic cluster catalyst by microwave-assisted hydrothermal method according to claim 5, characterized in that: In step S4, the complex solution is one or more of ethylenediamine, ethylenediaminetetraacetic acid, sodium ethylenediaminetetraacetate or ammonium citrate, and its concentration range is 0.1-0.6 mol / L.

8. The method for in-situ encapsulation synthesis of confined PtZn@ZSM-5 bimetallic cluster catalyst by microwave-assisted hydrothermal method according to claim 5, characterized in that: In step S4, microporous ZSM-5 is used as a carrier to synthesize a multi-level pore-confined PtZn@ZSM-5 bimetallic cluster catalyst by an in-situ encapsulation method, wherein the PtZn bimetallic is uniformly confined in the molecular sieve pores in the form of highly dispersed clusters.

9. The method for in-situ encapsulation synthesis of confined PtZn@ZSM-5 bimetallic cluster catalyst by microwave-assisted hydrothermal method according to claim 5, characterized in that: The Pt packaging amount of the PtZn@ZSM-5 bimetallic cluster catalyst is 0.1-1 wt %, and the Zn packaging amount is 1-10 wt %.

10. The method for in-situ encapsulation synthesis of confined PtZn@ZSM-5 bimetallic cluster catalyst by microwave-assisted hydrothermal method according to claim 5, characterized in that: The particle size of the carrier ZSM-5 molecular sieve is 100-800 nm.

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