Preparation method of a ZIF-8 coated supported palladium catalyst and its application in acetylene selective hydrogenation reaction

Abstract

The invention discloses a preparation method of a ZIF-8 coated supported palladium catalyst and application thereof in a selective hydrogenation reaction of acetylene. The catalyst consists of a carrier, an active component loaded on the carrier and a film selectively coating the active component, wherein the active component is metal palladium, the carrier is α-Al2O3, the film selectively coating Pd / Al2O3 is a zeolite imidazole framework ZIF-8, the regular pore structure of ZIF-8 separates Pd active sites with a molecular-level grid framework, and can significantly improve ethylene selectivity; the molecular-level network does not cover the active sites, and substantially maintains a hydrogenation activity equivalent to that of Pd / Al2O3, and can simultaneously take into account acetylene hydrogenation activity and ethylene selectivity in the selective hydrogenation reaction of acetylene. The preparation method of the invention is simple, easy to operate, and is conducive to industrial large-scale production.

Description

Technical Field

[0001] The invention belongs to the technical field of acetylene selective hydrogenation reaction catalysts, and specifically relates to a preparation method of a ZIF-8 coated supported palladium catalyst and application of the catalyst in acetylene selective hydrogenation reaction. Background Art

[0002] Ethylene is one of the important chemical raw materials. In industry, ethylene is mainly produced through the naphtha cracking process. However, in addition to the target product ethylene, the obtained raw gas also contains a small amount of acetylene impurities. Trace amounts of acetylene impurities can cause the Ziegler-Natta catalyst used in the ethylene polymerization process to be quickly poisoned and deactivated. Therefore, it is necessary to reduce the acetylene content to below 5 ppm (1×10-6) before the polymerization reaction.

[0003] The catalytic selective hydrogenation method can be used to hydrogenate acetylene to ethylene, which can simultaneously remove impurities and increase the ethylene content. The process flow is simple and the economic benefits are high. The commonly used catalyst is a Pd-based catalyst with high hydrogenation activity. However, the unmodified Pd-based catalyst has a high ethylene selectivity that is difficult to meet industrial needs due to severe over-hydrogenation. The further hydrogenation energy barrier and desorption energy barrier of the adsorbed ethylene generated by acetylene hydrogenation determine the ethylene selectivity. A lower desorption energy barrier helps to improve the selectivity. The adsorption configuration and strength of gas molecules are closely related to the catalyst surface structure. Compared with trimetallic sites and bimetallic sites, the adsorption strength of ethylene on single-atom sites is significantly reduced. Therefore, isolating Pd metal active sites has become an effective strategy to improve ethylene selectivity. At present, the specific methods for isolating metal active sites are: (1) Second metal component modification: using relatively low-activity elements (Ag, Au, Cu; Zn, In) to form alloys or intermetallic compounds with Pd. For example, the research group of Professor Zhang Tao from the Dalian Institute of Chemical Physics of the Chinese Academy of Sciences prepared a series of Pd / Ag alloys with different Pd / Ag atomic ratios and found that the catalytic performance was best when the Pd / Ag atomic ratio was 0.005 (i.e., AgPd0.005 / SiO2). At 240°C, an acetylene conversion rate of 92.6% and an ethylene selectivity of 92.3% were obtained (ACS Catalysis, 2015, 5(6):3717-3725.); (2) Single-atom catalysts: The research group of Professor Martin from Peking University used defective nanodiamond-graphene (ND@G) to prepare a single-atom dispersed metal catalyst (Pd1 / ND@G). The catalyst showed excellent performance in the selective hydrogenation of acetylene, that is, when the conversion rate of acetylene hydrogenation to ethylene was 100%, the selectivity of ethylene reached 90% (Journal of the American Chemical Society, 2018, 140(41):13142–13146.); (3) Selective coating: mainly using organic matter, carbon materials and metal oxides, etc., to improve the performance of the catalyst in the selective hydrogenation reaction of acetylene by covering and poisoning some active sites. For example, the research group of Professor Lu Junling of the University of Science and Technology of China used the atomic deposition method to in situ coat Ga2O3 coating on the Ag@Pd / SiO2 bimetallic catalyst to prepare a new catalyst (Ga-Ag@Pd / SiO2), which was applied to the selective hydrogenation reaction of acetylene. Compared with the catalyst without Ga2O3 coating, 10cGa-Ag@Pd / SiO2 catalyst can significantly improve the ethylene selectivity to 95% (Angewandte Chemie International Edition, 2021, 60 (35): 19324-19330).While the above work is accompanied by an improvement in ethylene selectivity, the hydrogenation activity of the catalyst is usually reduced to a significant extent; in addition, although the atomic deposition technology can achieve precise control of the active sites of the catalyst at the atomic layer level, this method is complex to operate and has high costs, making it difficult to industrialize.

[0004] Based on the above technical background, the present invention coats a layer of ZIF-8 film on the surface of the Pd / Al2O3 supported catalyst by a deposition precipitation method. Based on the good thermal stability, regular pore structure, high specific surface area and other characteristics of ZIF-8, the Pd active sites are separated by a molecular-level grid framework. Therefore, while significantly improving the ethylene selectivity, the hydrogenation activity is basically maintained at the same level as that of Pd / Al2O3. Summary of the invention

[0005] The invention aims at the problem that it is difficult to take both hydrogenation activity and ethylene selectivity into consideration in the current selective hydrogenation reaction of acetylene, and provides a preparation method of a ZIF-8 coated supported palladium catalyst. The method mainly adopts a simple and effective precipitation deposition method, and uses dimethylimidazole and a soluble zinc source as precursors to in-situ modify a ZIF-8 film on the surface of a Pd / Al2O3 supported catalyst to form a Pd / Al2O3@ZIF-8 (m) catalyst, wherein m represents the amount of the soluble zinc source substance of the ZIF-8 precursor, and the ZIF-8 with a regular pore structure separates the Pd active sites with a molecular-level grid, which significantly improves the ethylene selectivity; meanwhile, the molecular-level network does not cover the active sites, and the hydrogenation activity thereof is not significantly reduced, which is basically equivalent to that of the parent material Pd / Al2O3. Therefore, the catalyst can take both acetylene hydrogenation activity and ethylene selectivity into consideration in the selective hydrogenation reaction of acetylene.

[0006] The present invention adopts the following technical scheme to achieve the above object, a method for preparing a ZIF-8 coated supported palladium catalyst, characterized in that the specific steps are:

[0007] Step S1: using a soluble palladium source solution and an α-Al2O3 carrier as raw materials, an active metal palladium is loaded on the surface of the α-Al2O3 carrier by an impregnation method, and then sequentially dried in the shade for 6 to 24 hours, dried at 50 to 150° C. for 6 to 24 hours, and calcined at 200 to 400° C. for 2 to 5 hours to obtain a Pd / Al2O3 loaded catalyst;

[0008] Step S2: dissolving an organic ligand 2-methylimidazole in methanol or water to obtain a solution A, dissolving a soluble zinc source in methanol or water to obtain a solution B, and then adding the solution B to the solution A and stirring and mixing in a water bath at 20-50° C. to obtain a mixed solution;

[0009] Step S3: adding the Pd / Al2O3 supported catalyst obtained in step S1 to the mixed solution obtained in step S2 and stirring in a water bath at 20-50°C for 6-24h to obtain a suspension;

[0010] Step S4: The suspension obtained in step S3 is centrifugally washed several times and then dried at 50-150°C for 6-24h, and then ground and calcined at 200-400°C for 2-5h to obtain a ZIF-8 coated supported palladium catalyst, namely Pd / Al2O3@ZIF-8 (m), wherein m represents the amount of the soluble zinc source of the ZIF-8 precursor.

[0011] It is further defined that the soluble palladium source in step S1 is one or more of palladium nitrate, palladium chloride or palladium acetate.

[0012] It is further defined that the soluble zinc source in step S2 is one or more of zinc nitrate hexahydrate, zinc acetate or zinc chloride, and the molar ratio of the zinc source to the organic ligand is 1:5 to 1:20.

[0013] It is further defined that in step S4, the centrifugal speed is 8000-10000 rpm, the centrifugal time is 5 min, and methanol is used for washing after centrifugation.

[0014] The ZIF-8 coated supported palladium catalyst of the present invention is characterized in that the catalyst consists of a carrier, an active component loaded on the carrier and a film selectively coating the active component, wherein the active component is metal palladium, the carrier is α-Al2O3, the film selectively coating Pd / Al2O3 is a zeolite imidazole framework ZIF-8, the regular pore structure of ZIF-8 separates Pd active sites with a molecular-level grid framework, and can significantly improve ethylene selectivity; the molecular-level network does not cover the active sites, and basically maintains a hydrogenation activity equivalent to that of Pd / Al2O3, and can simultaneously take into account acetylene hydrogenation activity and ethylene selectivity in the acetylene selective hydrogenation reaction.

[0015] It is further defined that the loading amount of the metal palladium is 0.05-0.5 wt %.

[0016] The invention discloses an application of a ZIF-8 coated supported palladium catalyst in a selective hydrogenation reaction of acetylene, characterized in that: in the selective hydrogenation reaction of acetylene, the use temperature of the catalyst is 60-325° C., the raw gas composition is: 1 Vol % acetylene, 5-20 Vol % hydrogen, 20 Vol % ethylene, argon is the balance gas, and the space velocity is 36000-300000 mL / (g·h).

[0017] The application of the ZIF-8 coated supported palladium catalyst in the selective hydrogenation reaction of acetylene is characterized in that: during the selective hydrogenation reaction of acetylene, the average ethylene selectivities of the catalysts Pd / Al2O3@ZIF-8 (2.6) and Pd / Al2O3@ZIF-8 (6.5) are as high as 85.7% and 81.8%, respectively, and the catalyst Pd / Al2O3@ZIF-8 (2.6) can achieve 86% ethylene selectivity while achieving full conversion of acetylene under reaction conditions of 125°C.

[0018] The application of the ZIF-8 coated supported palladium catalyst in the selective hydrogenation reaction of acetylene is characterized in that: during the selective hydrogenation reaction of acetylene, within a wide temperature range of 150-275°C, the catalyst Pd / Al2O3@ZIF-8 (2.6) can take into account both 100% hydrogenation activity and ≥77.7% ethylene selectivity.

[0019] It is further defined that the specific preparation process of the catalyst Pd / Al2O3@ZIF-8 (2.6) is as follows: weigh 1.7089g of organic ligand dimethylimidazole, add 16mL of methanol and stir until a colorless and transparent solution is obtained, which is recorded as solution A; weigh 0.7768g of zinc nitrate hexahydrate, dissolve it in 16mL of methanol to obtain a methanol solution of zinc nitrate hexahydrate, which is recorded as solution B; add solution B to solution A to obtain a mixed solution C; add 0.4000g of Pd / Al2O3 supported catalyst to the mixed solution C and stir to mix evenly to obtain a suspension; centrifuge the obtained suspension at a centrifugal speed of 8000rpm and a centrifugal time of 5min, wash the precipitate with methanol for 3 times, discard the supernatant, and then dry the obtained precipitate at 60°C; grind the obtained solid and put it into a box-type high-temperature resistance furnace, and calcine it at 300°C for 3h in an air atmosphere to obtain the catalyst Pd / Al2O3@ZIF-8 (2.6).

[0020] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0021] 1. Aiming at the problem that severe over-hydrogenation of Pd-based catalysts leads to poor ethylene selectivity, the present invention effectively improves ethylene selectivity by isolating Pd active sites;

[0022] 2. The present invention utilizes a deposition precipitation method to in-situ modify the ZIF-8 film on the Pd / Al2O3 supported catalyst. The regular pore structure of ZIF-8 separates the Pd active sites with a molecular-level network structure, while not affecting the contact between the reactant molecules and the active sites and the timely departure of the target product, and can effectively improve the ethylene selectivity without reducing the hydrogenation activity of the catalyst;

[0023] 3. In the evaluation test of acetylene selective hydrogenation reaction of the ZIF-8 coated supported palladium catalyst prepared by the present invention, the hydrogenation performance of the catalyst Pd / Al2O3@ZIF-8 (m) is significantly better than that of the Pd / Al2O3 supported catalyst, and the ethylene selectivity of the catalyst Pd / Al2O3@ZIF-8 (2.6) is maintained above 80% in the entire test range of 75-325°C, and the hydrogenation activity is basically equivalent to that of the parent material Pd / Al2O3 supported catalyst;

[0024] 4. The preparation method of the present invention is simple, easy to operate, and is conducive to large-scale industrial production. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 XRD patterns of the catalyst Pd / Al2O3 prepared in Comparative Example 1 and the catalyst Pd / Al2O3@ZIF-8 (m) prepared in Examples 1 to 3.

[0026] Figure 2 IR graphs of the catalyst Pd / Al2O3 prepared in Comparative Example 1 and the catalyst Pd / Al2O3@ZIF-8 (m) prepared in Examples 1 to 3.

[0027] Figure 3 The SEM images of the catalyst Pd / Al2O3 prepared in Comparative Example 1 and the catalyst Pd / Al2O3@ZIF-8 (m) prepared in Examples 1 to 3. Among them, (ac) is Pd / Al2O3; (df) is Pd / Al2O3@ZIF-8 (1.3); (gi) is Pd / Al2O3@ZIF-8 (2.6); (jl) is Pd / Al2O3@ZIF-8 (6.5).

[0028] Figure 4 The graph shows the change of acetylene conversion rate (a) and ethylene selectivity (b) of the catalyst Pd / Al2O3 prepared in Comparative Example 1 and the catalyst Pd / Al2O3@ZIF-8 (m) prepared in Examples 1 to 3 for selective hydrogenation of acetylene as a function of reaction temperature. DETAILED DESCRIPTION

[0029] The above contents of the present invention are further described in detail below through embodiments. All technologies realized based on the above contents of the present invention belong to the scope of the present invention.

[0030] Comparative Example 1

[0031] (1) Preparation of Pd / Al2O3 supported catalyst

[0032] The Pd / Al2O3 supported catalyst with a theoretical loading of 0.1wt% was prepared by impregnation. First, 1.000mL of 0.001g / mL palladium nitrate solution and 0.8000mL of secondary water were respectively transferred with a pipette and stirred to obtain a metal precursor solution. Then, 1.000g of dry Al2O3 carrier was weighed using an electronic balance and added to the above metal precursor solution. After being placed at room temperature for 12h to dry naturally in the shade, it was transferred to an electric heated blast drying oven and dried at 120°C for 12h. Finally, the sample was taken out and ground, and calcined at 300°C for 3h in a box-type high-temperature resistance furnace to obtain a Pd / Al2O3 supported catalyst. The XRD, SEM, and IR characterization results are shown in Figure 2. Figure 1 , Figure 2 , Figure 3 .

[0033] (2) Evaluation of hydrogenation performance of Pd / Al2O3 catalyst

[0034] First, place a small amount of quartz wool evenly at the middle and lower end of the quartz tube (make a dent at the middle and lower part of the quartz tube), take 20 mg of Pd / Al2O3 loaded catalyst powder and 150 mg of quartz sand powder, mix them evenly and put them into the quartz tube covered with quartz sand, and use a small amount of quartz wool to fix the sample on top of the sample. Treat at 300°C for 1h in a hydrogen atmosphere with a flow rate of 30mL / min, then cool to room temperature in a hydrogen atmosphere, and then conduct an acetylene selective hydrogenation reaction test, introducing raw gas: 1Vol% acetylene, 10Vol% hydrogen, 20Vol% ethylene, argon as the balance gas, space velocity 150000mL / (g·h), the operating temperature of the catalyst is 60~325°C, and the reaction product is detected by gas chromatography. The evaluation results of the acetylene selective hydrogenation performance are shown in Figure 4 . Example

[0035] (1) Preparation of Pd / Al2O3@ZIF-8 (6.5) catalyst

[0036] 4.2753 g of dimethylimidazole was accurately weighed with an electronic balance and placed in a beaker. 40 mL of methanol was added and a magnet was placed. The mixture was stirred at 500 rpm on a magnetic stirrer until a colorless and transparent solution was obtained, which was recorded as solution A. 1.9352 g of zinc nitrate hexahydrate was weighed and dissolved in 40 mL of methanol to obtain a methanol solution of zinc nitrate hexahydrate, which was recorded as solution B. Solution B was added to solution A to obtain a mixed solution C. After 2 minutes, 0.4000 g of The Pd / Al2O3 supported catalyst was added to the mixed solution C, and stirred at 500 rpm for 12 h to obtain a suspension; the obtained suspension was centrifuged at a centrifugal rate of 8000 rpm for 5 min, and the supernatant methanol was finally poured out; the precipitate was washed 3 times with methanol, the supernatant was discarded, and the obtained precipitate was dried at 60°C overnight; the obtained solid was then ground and placed in a box-type high-temperature resistance furnace, and calcined at 300°C for 3 h in an air atmosphere to obtain the target catalyst Pd / Al2O3@ZIF-8 (6.5), and its XRD, SEM, and IR characterization results are shown in Figures 2 and 3, respectively. Figure 1 , Figure 2 , Figure 3 .

[0037] (2) Evaluation of hydrogenation performance of Pd / Al2O3@ZIF-8 (6.5) catalyst

[0038] First, place a small amount of quartz wool evenly at the middle and lower end of the quartz tube (make a dent at the middle and lower part of the quartz tube), take 20 mg of catalyst Pd / Al2O3@ZIF-8 (6.5) powder and 150 mg of quartz sand powder, mix them evenly and put them into the quartz tube covered with quartz sand, and use a small amount of quartz wool to fix the sample on top of the sample. Treat at 300 ° C for 1 hour in a hydrogen atmosphere with a flow rate of 30 mL / min, then cool to room temperature in a hydrogen atmosphere, and then conduct an acetylene selective hydrogenation reaction test, introducing raw gas: 1 Vol% acetylene, 10 Vol% hydrogen, 20 Vol% ethylene, argon as the balance gas, space velocity 150000 mL / (g·h), the catalyst operating temperature is 60~325 ° C, and the reaction product is detected by gas chromatography. The evaluation results of acetylene selective hydrogenation performance are shown in Figure 4 . Example

[0039] (1) Preparation of Pd / Al2O3@ZIF-8 (2.6) catalyst

[0040] 1.7089 g of dimethylimidazole was accurately weighed with an electronic balance and placed in a beaker. 16 mL of methanol was added and a magnet was placed. The mixture was stirred at 500 rpm on a magnetic stirrer until a colorless and transparent solution was obtained, which was recorded as solution A. 0.7768 g of zinc nitrate hexahydrate was weighed and dissolved in 16 mL of methanol to obtain a methanol solution of zinc nitrate hexahydrate, which was recorded as solution B. Solution B was added to solution A to obtain a mixed solution C. After 2 minutes, 0.4000 g of The Pd / Al2O3 supported catalyst was added to the mixed solution C, and stirred at 500 rpm for 12 h to obtain a suspension; the obtained suspension was centrifuged at a centrifugal rate of 8000 rpm for 5 min, and the supernatant methanol was finally poured out; the precipitate was washed 3 times with methanol, the supernatant was discarded, and the obtained precipitate was dried at 60°C overnight; the obtained solid was then ground and placed in a box-type high-temperature resistance furnace, and calcined at 300°C for 3 h in an air atmosphere to obtain the target catalyst Pd / Al2O3@ZIF-8 (2.6), and its XRD, SEM, and IR characterization results are shown in Figures 2 and 3, respectively. Figure 1 , Figure 2 , Figure 3 .

[0041] (2) Evaluation of hydrogenation performance of Pd / Al2O3@ZIF-8 (2.6) catalyst

[0042] First, place a small amount of quartz wool evenly at the middle and lower end of the quartz tube (make a dent in the middle and lower part of the quartz tube), take 20 mg of catalyst Pd / Al2O3@ZIF-8 (2.6) powder and 150 mg of quartz sand powder, mix them evenly and put them into the quartz tube covered with quartz sand, and use a small amount of quartz wool to fix the sample on top of the sample. Treat at 300 ° C for 1 hour in a hydrogen atmosphere with a flow rate of 30 mL / min, then cool to room temperature in a hydrogen atmosphere, and then conduct an acetylene selective hydrogenation reaction test, introducing raw gas: 1 Vol% acetylene, 10 Vol% hydrogen, 20 Vol% ethylene, argon as the balance gas, space velocity 150000 mL / (g·h), the operating temperature of the catalyst is 60~325 ° C, and the reaction product is detected by gas chromatography. The evaluation results of the acetylene selective hydrogenation performance are shown in Figure 4 . Example

[0043] (1) Preparation of Pd / Al2O3@ZIF-8 (1.3) catalyst

[0044] Use an electronic balance to accurately weigh 0.8541g of dimethylimidazole and place it in a beaker. Add 8mL of methanol and put in a magnet. Stir on a magnetic stirrer at a speed of 500rpm until a colorless and transparent solution is obtained, which is recorded as solution A. Weigh 0.3887g of zinc nitrate hexahydrate and dissolve it in 8mL of methanol to obtain a methanol solution of zinc nitrate hexahydrate, which is recorded as solution B. Add solution B to solution A to obtain a mixed solution C. After 2 minutes, add 0.4000g Pd / Al2O3 supported catalyst was added to the mixed solution C, and stirred at 500 rpm for 12 h to obtain a suspension; the obtained suspension was centrifuged at a centrifugal rate of 8000 rpm for 5 min, and the supernatant methanol was finally poured out; the precipitate was washed 3 times with methanol, the supernatant was discarded, and the obtained precipitate was dried at 60°C overnight; the obtained solid was then ground and placed in a box-type high-temperature resistance furnace, and calcined at 300°C for 3 h in an air atmosphere to obtain the target catalyst Pd / Al2O3@ZIF-8 (1.3), and its XRD, SEM and IR characterization results are shown in Figures 1 and 2. Figure 1 , Figure 2 , Figure 3 .

[0045] (2) Evaluation of hydrogenation performance of Pd / Al2O3@ZIF-8 (1.3) catalyst

[0046] First, place a small amount of quartz wool evenly at the middle and lower end of the quartz tube (make a dent at the middle and lower part of the quartz tube), take 20 mg of catalyst Pd / Al2O3@ZIF-8 (1.3) powder and 150 mg of quartz sand powder, mix them evenly and put them into the quartz tube covered with quartz sand, and use a small amount of quartz wool to fix the sample on top of the sample. Treat at 300 ° C for 1 hour in a hydrogen atmosphere with a flow rate of 30 mL / min, then cool to room temperature in a hydrogen atmosphere, and then conduct an acetylene selective hydrogenation reaction test, introducing raw gas: 1 Vol% acetylene, 10 Vol% hydrogen, 20 Vol% ethylene, argon as the balance gas, space velocity 150000 mL / (g·h), the catalyst operating temperature is 60 ~ 325 ° C, and the reaction product is detected by gas chromatography. The evaluation results of acetylene selective hydrogenation performance are shown in Figure 4 .

[0047] The above embodiments describe the basic principles, main features and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The above embodiments and descriptions are only for illustrating the principles of the present invention. Without departing from the scope of the principles of the present invention, the present invention may have various changes and improvements, and these changes and improvements all fall within the scope of protection of the present invention.

Claims

1. Application of ZIF-8 coated supported palladium catalyst in selective hydrogenation of acetylene, characterized in that: In the selective hydrogenation of acetylene, the catalyst temperature is 60~325℃, the raw gas composition is: 1Vol% acetylene, 5~20Vol% hydrogen, 20Vol% ethylene, argon is the balance gas, the space velocity is 36000~300000mL / (g·h), and in the wide temperature range of 150~275℃, the catalyst Pd / Al2O3@ZIF-8 (2.6) can take into account 100% hydrogenation activity and ≥77.7% ethylene selectivity; The ZIF-8 coated supported palladium catalyst is composed of a carrier, an active component loaded on the carrier, and a film selectively coating the active component, wherein the active component is metal palladium, the carrier is α-Al2O3, the film selectively coating Pd / Al2O3 is a zeolite imidazole framework ZIF-8, the regular pore structure of ZIF-8 separates Pd active sites with a molecular-level grid framework, and can significantly improve ethylene selectivity; the molecular-level network does not cover the active sites, and basically maintains a hydrogenation activity equivalent to that of Pd / Al2O3, and can simultaneously take into account acetylene hydrogenation activity and ethylene selectivity in an acetylene selective hydrogenation reaction; The specific preparation process of the catalyst Pd / Al2O3@ZIF-8 (2.6) is as follows: weigh 1.7089g of organic ligand dimethylimidazole, add 16mL of methanol and stir until a colorless and transparent solution is obtained, which is recorded as solution A; weigh 0.7768g of zinc nitrate hexahydrate, dissolve it in 16mL of methanol to obtain a methanol solution of zinc nitrate hexahydrate, which is recorded as solution B; add solution B to solution A to obtain a mixed solution C; add 0.4000g of Pd / Al2O3 supported catalyst to the mixed solution C and stir to mix evenly to obtain a suspension; centrifuge the obtained suspension at a centrifugal speed of 8000rpm for 5min, wash the precipitate with methanol for 3 times, discard the supernatant, and then dry the obtained precipitate at 60°C; grind the obtained solid and put it into a box-type high-temperature resistance furnace, and calcine it at 300°C for 3h in an air atmosphere to obtain the catalyst Pd / Al2O3@ZIF-8 (2.6).

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