Preparation method and application of palladium-cerium-doped ZSM-5 molecular sieve catalyst
Through the preparation of palladium-cerium-doped ZSM-5 molecular sieve catalyst, combined with microwave hydrothermal and microwave impregnation technology, the problem of poor selectivity and low yield of target products during catalytic conversion is solved, and efficient and economical catalytic reaction is achieved, improving Product selectivity and catalyst service life.
Patent Information
- Application Number
- CN202411722249.3
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-11-28
- Publication Date
- 2025-02-18
AI Technical Summary
The prior art has poor selectivity and low yield of target products during catalytic conversion, resulting in excessive by-products and poor selectivity, requiring a large number of separation processes and low production efficiency.
The catalyst is prepared by combining microwave hydrothermal heat and microwave impregnation with palladium-cerium doped ZSM-5 molecular sieve catalyst, which improves the thermal stability and service life of the catalyst, and enhances the catalytic activity and product selectivity of the catalytic reaction.
The catalytic activity and product selectivity of the catalytic reaction are significantly improved, the generation of by-products is reduced, the economics of the catalytic reaction is optimized, and the catalytic conversion efficiency and resource utilization efficiency of low-value organic matter are improved.
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Figure CN119456020A_ABST
Abstract
Description
Technical Field
[0001] The invention relates to the technical field of ZSM-5 molecular sieve catalytic cracking, and in particular to a preparation method of a palladium-cerium doped ZSM-5 molecular sieve catalyst and application thereof. Background Art
[0002] With the widespread use of organic products, organic waste has become an important source of global environmental pollution. Food packaging, plastic bags, films and other organic products are difficult to degrade. Traditional landfill and incineration methods have brought serious ecological problems, not only wasting resources, but also releasing harmful substances to pollute the soil, water and air. Therefore, the effective recycling and treatment of organic waste has become an urgent problem to be solved.
[0003] At present, thermal cracking technology is considered to be one of the effective ways to treat organic waste. Through high-temperature cracking, the polymer chains in organic matter can be decomposed into short-chain hydrocarbon products, such as olefins and aromatics. However, the traditional thermal cracking process needs to be carried out at high temperatures of 500°C to 900°C, with high energy consumption and long reaction time. In addition, uneven heating leads to poor selectivity of cracking products, many by-products, and low yield of target products. These limitations have prompted researchers to seek more efficient and environmentally friendly cracking methods.
[0004] Microwave heating technology has been widely used in chemical reactions in recent years due to its fast and uniform heating effect, and has gradually become an ideal means to replace traditional heating methods. Microwave heating directly acts on molecules to quickly convert energy into heat, reaching the reaction temperature in a short time, with low energy consumption, and can greatly improve the cracking efficiency of low-value organic matter. However, there are still too many by-products and poor selectivity, resulting in low yields of target products. In order to obtain the target product, a large number of separation processes are required for the cracking products, resulting in low production efficiency. Summary of the invention
[0005] The purpose of the present invention is to provide a method for preparing a palladium-cerium doped ZSM-5 molecular sieve catalyst and its application, so as to solve the problems of poor selectivity and low yield of target products in the catalytic conversion process of the prior art.
[0006] In order to solve the above technical problems, the present invention adopts the following technical solution: a method for preparing a palladium-cerium doped ZSM-5 molecular sieve catalyst, characterized in that it comprises the following steps:
[0007] S1. Take tetrapropylammonium hydroxide and tetraethyl orthosilicate and add them to deionized water, and stir at room temperature to obtain a mixture a;
[0008] S2. The mixture a is transferred to a digestion tank and kept at 150-180°C for 2-4 hours under microwave irradiation to obtain a hydrothermal product a. The hydrothermal product a is filtered, washed and dried;
[0009] S3. The dried hydrothermal product a is placed in a muffle furnace and kept at 500 to 600 ° C for 4 to 5 hours to remove the template agent to obtain a pure silicon ZSM-5 molecular sieve;
[0010] S4. Add pure silicon ZSM-5 molecular sieve and aluminum isopropoxide into deionized water and mix them ultrasonically for 1 to 1.5 hours to obtain a mixture b;
[0011] S5. The mixture b is transferred to a digestion tank, and kept at 150-180° C. for 2-4 hours under microwave irradiation to obtain a hydrothermal product b, and the hydrothermal product b is filtered, washed, and then dried;
[0012] S6. The dried hydrothermal product b is placed in a tube furnace and kept at 180 to 200 ° C in an argon atmosphere for 2 to 2.5 h to obtain a ZSM-5 molecular sieve;
[0013] S7. Take ZSM-5 molecular sieve, palladium nitrate and cerium nitrate, add them into deionized water, and mix them ultrasonically for 1 to 1.5 hours to obtain a mixture c;
[0014] S8. The mixture c is transferred to a digestion tank, and kept at 60-100°C for 1-3 hours under microwave irradiation for microwave hydrothermal impregnation, and the product is filtered, washed, and dried;
[0015] S9. The dried product is placed in a tubular furnace and kept warm at 200-220° C. in an argon atmosphere for 2-2.5 hours to obtain a palladium-cerium doped ZSM-5 molecular sieve catalyst.
[0016] A further technical solution is that in step S1, 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.
[0017] A further technical solution is that the molar ratio of Al2O3 in the aluminum isopropoxide to SiO2 in the pure silicon ZSM-5 molecular sieve in step S4 is 0.05-0.15:1, and the amount of pure silicon ZSM-5 molecular sieve used is 0.05-0.08 g / ml.
[0018] A further technical solution is that the mass ratio of metal palladium to metal cerium in the palladium nitrate and cerium nitrate in step S7 is 1:1-10; the loading amount of palladium nitrate and cerium nitrate is 1-10% of the mass of the ZSM-5 molecular sieve.
[0019] A further technical solution is that the palladium-cerium doped ZSM-5 molecular sieve catalyst is used in the catalytic conversion process of low-value products.
[0020] A further technical solution is that the specific steps of the catalytic conversion process of the low-value product are as follows:
[0021] 1) impregnating a palladium-cerium doped ZSM-5 molecular sieve catalyst on a quartz wool sheet and placing silicon carbide porous sheets on both sides of the quartz wool sheet to obtain a catalyst layer plate, and placing it vertically on one side of a quartz tube;
[0022] 2) Lay the silicon carbide sheet on the bottom of the quartz crucible, place the low-value organic matter in the quartz crucible, and place it on the air inlet side of the catalyst layer plate;
[0023] 3) placing the quartz tube in a microwave tube furnace and irradiating the tube with microwaves for 10 to 60 minutes under a protective atmosphere, with the temperature maintained at 400 to 800° C.;
[0024] 4) After the cracking is completed, argon gas is introduced to collect the gas phase product, and the oil phase product is directly collected in a quartz tube.
[0025] A further technical solution is that the catalyst impregnation step is: take 0.5g of quartz wool, and use a pressing process to prepare a quartz wool sheet with a thickness of 2mm and a diameter that matches the inner diameter of the quartz tube; evenly spread 0.2g of palladium-cerium-doped ZSM-5 molecular sieve catalyst on the surface of the quartz wool sheet, and add 10ml of anhydrous ethanol to make the catalyst firmly adhere to the quartz wool sheet; after the prepared quartz wool sheet is allowed to stand at room temperature for 30 minutes, the quartz wool sheet is placed in an oven and dried at a constant temperature of 60°C for 3 hours for use.
[0026] A further technical solution is that the outer diameter of the catalyst layer plate is matched with the inner diameter of the quartz tube.
[0027] A further technical solution is that the low-value product is at least one of low-density polyethylene, high-density polyethylene, polypropylene, and epoxy resin.
[0028] A further technical solution is that the content of methane in the gas phase product is above 50%.
[0029] Compared with the prior art, the present invention has the following beneficial effects:
[0030] 1. In the present invention, molecular sieves are prepared quickly and efficiently through two microwave hydrothermal processes, which greatly shortens the preparation time of molecular sieves. Microwave impregnation is then used to directly act on the inside of the material, which greatly improves the efficiency and uniformity of palladium and cerium loading on the molecular sieves, and also makes the metal and the molecular sieve firmly combined, thereby improving the thermal stability and service life of the catalyst, thereby significantly enhancing the catalytic activity and product selectivity of the catalytic reaction.
[0031] 2. In the present invention, the palladium-cerium doped ZSM-5 molecular sieve is impregnated into a quartz wool sheet, and silicon carbide-assisted microwave heating is used to quickly crack low-value organic matter. The catalysis and selectivity of the palladium-cerium doped molecular sieve are utilized to obtain high value-added and high-yield methane and hydrogen. The product is easily collected, purified and reused through a condensation system, which greatly improves the catalytic conversion efficiency of low-value products and improves the resource utilization efficiency of low-value products.
[0032] 3. The present invention combines microwave hydrothermal with microwave impregnation to achieve rapid and efficient molecular sieve preparation and metal loading, greatly shortening the molecular sieve preparation time, reducing energy consumption, and improving impregnation efficiency. The use of ZSM-5 molecular sieve catalysts loaded with palladium and cerium effectively improves the selectivity and yield of catalytic products, on the one hand increasing the generation of high value-added chemicals such as methane; on the other hand reducing the generation of by-products and optimizing the economy of the catalytic reaction. The system of the present invention is simple in design and easy to operate. It is suitable for the catalytic treatment of large-scale low-value organic matter, and can achieve efficient resource utilization, thereby improving the practicality and economy of the overall process. BRIEF DESCRIPTION OF THE DRAWINGS
[0033] Figure 1 The invention discloses a preparation process of the palladium-cerium doped ZSM-5 molecular sieve catalyst.
[0034] Figure 2 This is the X-ray powder diffraction spectrum of the palladium-cerium doped ZSM-5 molecular sieve catalyst in Example 1.
[0035] Figure 3 This is a scanning electron microscope image of the palladium-cerium doped ZSM-5 molecular sieve catalyst in Example 1.
[0036] Figure 4 This is the pore size distribution diagram of the palladium-cerium doped ZSM-5 molecular sieve catalyst in Example 1.
[0037] Figure 5 This is the distribution diagram of the catalytic cracking products of low-density polyethylene in Example 4.
[0038] Figure 6 This is the distribution diagram of the catalytic cracking products of polypropylene in Example 5.
[0039] Figure 7 It is a schematic diagram of the catalytic reaction process of low-value organic matter in the present invention.
[0040] Figure 8 This is a scanning electron microscope image of the ZSM-5 molecular sieve prepared by conventional hydrothermal method in Comparative Example 1.
[0041] Fig. 9 Schematic diagram of the catalytic cracking principle of organic matter in Example 4.
[0042] Fig.10 This is a graph showing the gas yield of low-density polyethylene cracking catalyzed by ZSM-5 molecular sieve catalysts with different palladium-cerium loadings in Examples 1, 2, and 3. DETAILED DESCRIPTION
[0043] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.
[0044] Example 1
[0045] Preparation of palladium-cerium doped ZSM-5 molecular sieve catalyst:
[0046] 1. Weigh 7.4 g of tetrapropylammonium hydroxide and 7.3 g of tetraethyl orthosilicate, add 20 mL of deionized water, and stir at room temperature for 4 hours to obtain a mixture a;
[0047] 2. Transfer the mixture a to a polytetrafluoroethylene digestion tank, keep it at 170°C for 2 hours under microwave irradiation with a power of 1200 W, and the product is a hydrothermal product a. The hydrothermal product a is filtered, washed, and dried overnight;
[0048] 3. Place the hydrothermal product a in a muffle furnace, heat it to 550°C at a heating rate of 10°C / min, and keep it warm for 5 hours to remove the template agent. The product is pure silicon ZSM-5 molecular sieve, named Si-1;
[0049] 4. Weigh 1.2 g of Si-1 and 0.12 g of aluminum isopropoxide, add 20 mL of deionized water, and ultrasonicate for 1 hour to obtain a mixture b.
[0050] 5. Transfer the mixture b to a polytetrafluoroethylene digestion tank, keep it at 170°C for 2 hours under microwave irradiation with a power of 1200 W, and the product is a hydrothermal product b. The hydrothermal product b is filtered, washed, and dried overnight;
[0051] 6. The hydrothermal product b was transferred to a tubular furnace, heated to 200°C at a heating rate of 2°C / min, and kept warm for 2 hours under an argon atmosphere to obtain a ZSM-5 molecular sieve.
[0052] 7. Weigh 1 g of ZSM-5 molecular sieve and 0.01 g of palladium nitrate and cerium nitrate, add 20 ml of deionized water, and ultrasonicate for 1 hour to obtain a mixture c; the mass ratio of metal palladium to metal cerium in the palladium nitrate and cerium nitrate is 1:1;
[0053] 8. Transfer the mixture c to a polytetrafluoroethylene digestion tank, keep it warm at 80°C for 2 hours under microwave irradiation with a power of 1200 W, perform microwave hydrothermal impregnation, filter the product, wash it, and dry it overnight;
[0054] 9. The dried product was transferred to a tube furnace, heated to 200°C at a heating rate of 2°C / min, and kept warm for 2 hours under an argon atmosphere to obtain Pd-Ce@ZSM-5 with a loading of 1 wt%.
[0055] like Figure 2-4 As shown in the figure, the 1wt% Pd-Ce@ZSM-5 catalyst has uniform particle size and consistent morphology. XRD analysis confirmed that the loaded molecular sieve catalyst still maintains the MFI structural characteristics of the ZSM-5 molecular sieve. Pore size distribution analysis shows that its pore size is mainly concentrated at about 3nm, which is suitable for the selective generation of small molecules. This pore size characteristic combined with the synergistic catalytic effect of Pd and Ce can significantly improve the selectivity of the catalyst for high value-added small molecule products such as hydrogen and methane.
[0056] Example 2
[0057] Preparation of palladium-cerium doped ZSM-5 molecular sieve catalyst:
[0058] 1. Weigh 7.4 g of tetrapropylammonium hydroxide and 7.3 g of tetraethyl orthosilicate, add 20 mL of deionized water, and stir at room temperature for 4 hours to obtain a mixture a;
[0059] 2. Transfer the mixture a to a polytetrafluoroethylene digestion tank, keep it at 170°C for 2 hours under microwave irradiation with a power of 1200 W, and the product is a hydrothermal product a. The hydrothermal product a is filtered, washed, and dried overnight;
[0060] 3. Place the hydrothermal product a in a muffle furnace, heat it to 550°C at a heating rate of 10°C / min, and keep it warm for 5 hours to remove the template agent. The product is pure silicon ZSM-5 molecular sieve, named Si-1;
[0061] 4. Weigh 1.2 g of Si-1 and 0.12 g of aluminum isopropoxide, add 20 mL of deionized water, and ultrasonicate for 1 hour to obtain a mixture b.
[0062] 5. Transfer the mixture b to a polytetrafluoroethylene digestion tank, keep it at 170°C for 2 hours under microwave irradiation with a power of 1200 W, and the product is a hydrothermal product b. The hydrothermal product b is filtered, washed, and dried overnight;
[0063] 6. The hydrothermal product b was transferred to a tubular furnace, heated to 200°C at a heating rate of 2°C / min, and kept warm for 2 hours under an argon atmosphere to obtain a ZSM-5 molecular sieve.
[0064] 7. Weigh 1 g of ZSM-5 molecular sieve and 0.05 g of palladium nitrate and cerium nitrate, add 20 ml of deionized water, and ultrasonicate for 1 hour to obtain a mixture c; the mass ratio of metal palladium to metal cerium in the palladium nitrate and cerium nitrate is 1:1;
[0065] 8. Transfer the mixture c to a polytetrafluoroethylene digestion tank, keep it at 80°C for 2 hours under microwave irradiation with a power of 1200 W, perform microwave hydrothermal impregnation, filter the product, wash it, and dry it overnight;
[0066] 9. The dried product was transferred to a tube furnace, heated to 200°C at a heating rate of 2°C / min, and kept warm for 2 hours under an argon atmosphere to obtain Pd-Ce@ZSM-5 with a loading of 5 wt%.
[0067] Example 3
[0068] Preparation of palladium-cerium doped ZSM-5 molecular sieve catalyst:
[0069] 1. Weigh 7.4 g of tetrapropylammonium hydroxide and 7.3 g of tetraethyl orthosilicate, add 20 mL of deionized water, and stir at room temperature for 4 hours to obtain a mixture a;
[0070] 2. Transfer the mixture a to a polytetrafluoroethylene digestion tank, keep it at 180°C for 2 hours under microwave irradiation with a power of 1200 W, and the product is a hydrothermal product a. Filter and wash the hydrothermal product a, and then dry it overnight;
[0071] 3. Place the hydrothermal product a in a muffle furnace, heat it to 550°C at a heating rate of 10°C / min, and keep it warm for 5 hours to remove the template agent. The product is pure silicon ZSM-5 molecular sieve, named Si-2;
[0072] 4. Weigh 1.2 g of Si-2 and 0.12 g of aluminum isopropoxide, add 20 mL of deionized water, and ultrasonicate for 1 hour to obtain a mixture b.
[0073] 5. Transfer the mixture b to a polytetrafluoroethylene digestion tank, keep it at 180°C for 2 hours under microwave irradiation with a power of 1200 W, and the product is a hydrothermal product b. The hydrothermal product b is filtered, washed, and dried overnight;
[0074] 6. The hydrothermal product b was transferred to a tubular furnace, heated to 200°C at a heating rate of 2°C / min, and kept warm for 2 hours under an argon atmosphere to obtain a ZSM-5 molecular sieve.
[0075] 7. Weigh 1 g of ZSM-5 molecular sieve and 0.1 g of palladium nitrate and cerium nitrate, add 20 ml of deionized water, and ultrasonicate for 1 hour to obtain a mixture c; the mass ratio of metal palladium to metal cerium in the palladium nitrate and cerium nitrate is 1:1;
[0076] 8. Transfer the mixture c to a polytetrafluoroethylene digestion tank, keep it at 90°C for 2 hours under microwave irradiation with a power of 1200 W, perform microwave hydrothermal impregnation, filter the product, wash it, and dry it overnight;
[0077] 9. The dried product was transferred to a tube furnace, heated to 200°C at a heating rate of 2°C / min, and kept warm for 2 hours under an argon atmosphere to obtain Pd-Ce@ZSM-5 with a loading of 10 wt%.
[0078] As attached Fig.10 As shown, the gas yields of 5wt% Pd-Ce@ZSM-5 in Example 2 and 10wt% Pd-Ce@ZSM-5 in Example 3 are reduced to varying degrees compared with 5wt% Pd-Ce@ZSM-5 in Example 1. The excessive surface loading may cover the acidic active sites on the surface of the molecular sieve, weakening its catalytic performance, and may also cause the agglomeration effect of palladium and cerium particles, reducing the effective active surface area. In addition, high metal loading may block the pores of the molecular sieve, restrict the diffusion of reactants and products, and even lead to an increase in side reactions (such as carbon deposition), further reducing the catalytic cracking efficiency.
[0079] Example 4
[0080] Weigh 10 g of low-density polyethylene and place it in a quartz crucible, the bottom of which is filled with silicon carbide to assist heating;
[0081] 0.2 g of a ZSM-5 molecular sieve catalyst with a loading of 1 wt% of palladium and cerium is weighed and impregnated on a quartz wool sheet, silicon carbide porous sheets are added on both sides of the quartz wool sheet to prepare a catalyst layer plate, and the catalyst layer plate is vertically placed in a quartz tube; the catalyst impregnation steps are as follows: 0.5 g of quartz wool is taken and prepared into a quartz wool sheet with a thickness of 2 mm and a diameter of 40 mm by a pressing process; 0.2 g of a palladium-cerium doped ZSM-5 molecular sieve catalyst is evenly spread on the surface of the quartz wool sheet, and 10 ml of anhydrous ethanol is evenly added to make the catalyst firmly adhere to the quartz wool sheet; the prepared quartz wool sheet is allowed to stand at room temperature for 30 minutes, and then the quartz wool sheet is placed in an oven and dried at a constant temperature of 60°C for 3 hours for use.
[0082] The prepared quartz crucible is placed on the gas inlet side of the catalyst layer plate in the quartz tube;
[0083] The quartz tube was placed in a microwave tube furnace and subjected to microwave irradiation in an argon atmosphere with a microwave power of 1400 W, a catalytic cracking temperature of 450°C, and an action time of 30 minutes.
[0084] After the catalytic cracking was completed, argon was introduced to collect the gas phase products, and the oil phase products were directly collected in a quartz tube.
[0085] The gas phase products produced after microwave irradiation catalytic cracking were collected for analysis. Figure 5 The results show that in the catalytic cracking reaction of low-density polyethylene, the main products are hydrogen and methane, with a production ratio of 23.78% and 51.86%, respectively, indicating that the catalytic system has significant selectivity for small molecule gas products. In addition, ethane and propane account for 16.00% and 3.47% of the product distribution, respectively, while other small amounts of by-products account for 2.66%. The overall results show that the Pd-Ce@ZSM-5 catalyst can efficiently crack polyethylene and preferentially generate high-value-added small molecule products such as methane and hydrogen, reflecting good catalytic performance and product distribution regulation capabilities.
[0086] Taking the catalytic cracking of low-density polyethylene as an example, the reaction mechanism of other types of organic matter is similar: first, low-density polyethylene undergoes preliminary cracking near the surface of the molecular sieve catalyst through thermal cracking or the action of the catalyst active site to generate small molecular hydrocarbons; secondly, these small molecular fragments diffuse into the pores of the molecular sieve, and are further cracked, isomerized or dehydrogenated under the action of strong acidity or redox active centers, and finally generate high value-added products such as hydrogen and methane. Among them, the catalysts loaded with palladium and cerium on the molecular sieve significantly improve the selectivity of polyethylene cracking to generate methane and hydrogen through synergistic effects. The hydrogenation-dehydrogenation activity of palladium promotes the breakage of polyethylene molecular chains and releases hydrogen atoms to generate hydrogen; cerium effectively regulates the reaction environment in the catalytic process through its redox characteristics, further promoting the highly selective generation of methane. The pore structure of the molecular sieve provides a precise reaction space, which not only enhances the synergistic effect of palladium and cerium, but also inhibits the generation of by-products, ensuring the efficient output of methane and hydrogen as the main products, while extending the service life of the catalyst. The reaction process is shown in the attached Fig. 9 .
[0087] Example 5
[0088] Weigh 10 g of polypropylene and place it in a quartz crucible, the bottom of which is filled with silicon carbide to assist heating;
[0089] Weigh 0.2 g of a ZSM-5 molecular sieve catalyst with a loading of 1 wt.% palladium and cerium and impregnate it on a quartz wool sheet, add silicon carbide porous sheets on both sides of the quartz wool sheet to prepare a catalyst layer plate, and place it vertically in a quartz tube;
[0090] The prepared quartz crucible is placed on the gas inlet side of the silicon carbide porous sheet in the quartz tube;
[0091] The quartz tube was placed in a microwave tube furnace and subjected to microwave irradiation in an argon atmosphere with a microwave power of 1400 W, a catalytic cracking temperature of 450°C, and an action time of 30 minutes.
[0092] After the catalytic cracking was completed, argon was introduced to collect the gas phase products, and the oil phase products were directly collected in a quartz tube.
[0093] The gas phase products produced after microwave irradiation cracking were collected for analysis. Figure 6 The results show that in the process of catalytic cracking of polypropylene, methane is the main product, accounting for 69.83%, which is significantly higher than other products, indicating that the catalyst has extremely high selectivity for methane production. At the same time, the production ratio of hydrogen is 16.34%, showing a strong dehydrogenation ability. Other by-products include ethane (6.74%), ethylene (3.21%), propane (1.20%) and a small amount of other components (2.48%). The results show that the unique pore structure and metal loading design of the Pd-Ce@ZSM-5 catalyst can effectively promote the generation of small molecule high value-added products, especially the efficient production of methane and hydrogen.
[0094] Comparative Example 1
[0095] This comparative example prepares ZSM-5 molecular sieve according to a conventional hydrothermal method, and is compared with Example 1. The preparation method includes the following steps:
[0096] 1. Aluminum source and silicon source According to Example 1, aluminum isopropoxide and tetraethyl orthosilicate are weighed according to a molar ratio of SiO2:Al2O3:TPAOH:H2O=1:0.1:0.25:20 to obtain a mixture a;
[0097] 2. The mixture a was stirred at room temperature for 6 hours to perform an aging process to obtain a precursor a;
[0098] 3. Transfer the precursor a to a hydrothermal reactor and crystallize at 170°C for 72 hours to obtain a hydrothermal product a;
[0099] 4. Place the hydrothermal product a in a muffle furnace, heat the temperature to 550°C at a heating rate of 10°C / min, and keep it warm for 5 hours to remove the template agent. The product is ZSM-5 molecular sieve.
[0100] The morphology of the ZSM-5 molecular sieve prepared in this comparative example is shown in the attached Figure 8As shown, there is a problem of uneven morphology and particle size. In comparison, the ZSM-5 molecular sieve prepared by the microwave hydrothermal method used in Example 1 has a smaller particle size, a more uniform crystal morphology and a higher pore distribution uniformity. This is because the microwave hydrothermal method significantly shortens the crystallization time through rapid heating and uniform energy transfer, and improves the efficiency and quality of crystal formation. In the cracking reaction of waste plastics, the ZSM-5 prepared by the microwave hydrothermal method can provide more active sites due to its higher specific surface area and better pore characteristics, thereby significantly enhancing the efficiency of the cracking reaction and the selectivity for small molecule high value-added products such as methane and hydrogen.
[0101] Although the present invention is described herein with reference to a number of illustrative embodiments of the present invention, it will be appreciated that those skilled in the art may devise numerous other modifications and implementations that fall within the scope of the present disclosure. More specifically, within the scope of the present disclosure, drawings, and claims, a variety of variations and modifications may be made to the components or layout. In addition to variations and modifications to the components or layout, other uses will be apparent to those skilled in the art.
Claims
1. A method for preparing a palladium-cerium doped ZSM-5 molecular sieve catalyst, characterized in that The steps include: S1. Take tetrapropylammonium hydroxide and tetraethyl orthosilicate and add them to deionized water, and stir at room temperature to obtain a mixture a; S2. The mixture a is transferred to a digestion tank and kept at 150-180°C for 2-4 hours under microwave irradiation to obtain a hydrothermal product a. The hydrothermal product a is filtered, washed and dried; S3. The dried hydrothermal product a is placed in a muffle furnace and kept at 500 to 600 ° C for 4 to 5 hours to remove the template agent to obtain a pure silicon ZSM-5 molecular sieve; S4. Add pure silicon ZSM-5 molecular sieve and aluminum isopropoxide into deionized water and mix them ultrasonically for 1 to 1.5 hours to obtain a mixture b; S5. The mixture b is transferred to a digestion tank, and kept at 150-180° C. for 2-4 hours under microwave irradiation to obtain a hydrothermal product b, and the hydrothermal product b is filtered, washed, and then dried; S6. The dried hydrothermal product b is placed in a tube furnace and kept at 180 to 200 ° C in an argon atmosphere for 2 to 2.5 h to obtain a ZSM-5 molecular sieve; S7. Take ZSM-5 molecular sieve, palladium nitrate and cerium nitrate, add them into deionized water, and mix them ultrasonically for 1 to 1.5 hours to obtain a mixture c; S8. The mixture c is transferred to a digestion tank, and kept at 60-100°C for 1-3 hours under microwave irradiation for microwave hydrothermal impregnation, and the product is filtered, washed, and dried; S9. The dried product is placed in a tubular furnace and kept warm at 200-220° C. in an argon atmosphere for 2-2.5 hours to obtain a palladium-cerium doped ZSM-5 molecular sieve catalyst.
2. The method for preparing a palladium-cerium doped ZSM-5 molecular sieve catalyst according to claim 1, characterized in that: In step S1, the amount of tetrapropylammonium hydroxide used is 0.36-0.375 g / ml, and the amount of tetraethyl orthosilicate used is 0.36-0.37 g / ml.
3. The method for preparing a palladium-cerium doped ZSM-5 molecular sieve catalyst according to claim 1, characterized in that: The molar ratio of Al2O3 in the aluminum isopropoxide to SiO2 in the pure silicon ZSM-5 molecular sieve in step S4 is 0.05-0.15:1, and the amount of pure silicon ZSM-5 molecular sieve used is 0.05-0.08 g / ml.
4. The method for preparing a palladium-cerium doped ZSM-5 molecular sieve catalyst according to claim 1, characterized in that: In step S7, the mass ratio of metal palladium to metal cerium in the palladium nitrate and cerium nitrate is 1:1-10; the loading amount of palladium nitrate and cerium nitrate is 1-10% of the mass of the ZSM-5 molecular sieve.
5. The method for preparing a palladium-cerium doped ZSM-5 molecular sieve catalyst according to claim 1, characterized in that: The palladium-cerium doped ZSM-5 molecular sieve catalyst is used in the catalytic conversion process of low-value products.
6. The method for preparing a palladium-cerium doped ZSM-5 molecular sieve catalyst according to claim 5, characterized in that: The specific steps of the low-value product catalytic conversion process are as follows: 1) impregnating a palladium-cerium doped ZSM-5 molecular sieve catalyst on a quartz wool sheet, and placing silicon carbide porous sheets on both sides of the quartz wool sheet to obtain a catalyst layer plate, and placing it vertically on one side of a quartz tube; 2) Laying a silicon carbide sheet on the bottom of a quartz crucible, placing organic matter in the quartz crucible, and placing it on the air inlet side of the catalyst layer plate; 3) placing the quartz tube in a microwave tube furnace and irradiating the tube with microwaves for 10 to 60 minutes under a protective atmosphere, with the temperature maintained at 400 to 800° C.; 4) After the cracking is completed, argon gas is introduced to collect the gas phase product, and the oil phase product is directly collected in a quartz tube.
7. The method for preparing a palladium-cerium doped ZSM-5 molecular sieve catalyst according to claim 6, characterized in that: The outer diameter of the catalyst layer plate is matched with the inner diameter of the quartz tube.
8. The method for preparing a palladium-cerium doped ZSM-5 molecular sieve catalyst according to claim 5, characterized in that: The low-value product is at least one of low-density polyethylene, high-density polyethylene, polypropylene, and epoxy resin.
9. The method for preparing a palladium-cerium doped ZSM-5 molecular sieve catalyst according to claim 6, characterized in that: The content of methane in the gas phase product is above 50%.