A high-temperature stable PtZn@molecular sieve catalyst for propane dehydrogenation to propylene and its preparation method

Abstract

This invention discloses a high-temperature stable PtZn@molecular sieve catalyst for propane dehydrogenation to propylene and its preparation method. The catalyst primarily consists of a large single-crystal molecular sieve support and an active component, PtZn clusters. The large single-crystal molecular sieve support has a c-axis length of 12.0 to 60.0 μm, and the active component, PtZn clusters, has a particle size of 0.40 to 0.60 nm. Based on the total mass of the catalyst, the Pt loading is 0.01 to 2.00 wt%, and the Zn loading is 0.01 to 2.00 wt%. The catalyst utilizes an in-situ hydrothermal crystallization process, during which an appropriate amount of a phenolic compound is added to regulate the c-axis size of the molecular sieve crystals. The prepared PtZn@molecular sieve catalyst exhibits exceptionally high resistance to sintering and carbon deposition in propane dehydrogenation reactions, and the catalyst remains active for 180 days without deactivation.

Description

Technical Field

[0001] The present invention relates to the field of industrial catalyst preparation, and in particular to a propane dehydrogenation PtZn@molecular sieve catalyst suitable for a fixed bed reactor and a preparation method thereof. Background Art

[0002] In the modern chemical industry, propylene is second only to ethylene in importance. Its downstream products, including polypropylene, acrylonitrile, and propylene oxide, are widely used in daily life, including food, clothing, housing, and transportation. Currently, propylene is primarily produced through naphtha cracking and catalytic cracking. With the increasing demand for propylene, traditional production methods are unable to meet market demand, necessitating the development of new pathways for propylene production. In recent years, direct propane dehydrogenation to propylene has garnered significant attention. With its low propane feedstock cost, high propylene yield, and dedicated production of propylene, direct propane dehydrogenation to propylene has become a highly competitive propylene production route.

[0003] Currently, Pt / Al2O3, used in the moving bed process, is the mainstream catalyst for industrial propane dehydrogenation. Under high-temperature reaction conditions, not only does carbon deposit form on the Al2O3 carrier, but the Pt particles also migrate on the alumina surface, leading to sintering. Therefore, Pt / Al2O3 slowly deactivates during the propane dehydrogenation process, requiring frequent regeneration through oxygen-chlorine treatment. The reaction-regeneration of the Pt / Al2O3 catalyst in the propane dehydrogenation process is achieved through a moving bed process. The moving bed process consists of four reactors and a regenerator. The Pt / Al2O3 catalyst slowly moves through the four reactors. The deactivated catalyst enters the regenerator, where it is carbonized by high-temperature oxygen, treated with chlorine, and then dispersed, restoring the catalyst's activity. Although this process has been industrialized, it has the following disadvantages in actual operation: (1) The moving bed process not only has high investment costs, but also has complex operations and high operating costs; (2) The catalyst moves dynamically in the reactor, and collisions and friction between them can easily lead to catalyst breakage, which not only affects the long-term operation of the device, but also requires regular replenishment of the catalyst; (3) The high-temperature regeneration process consumes a lot of energy and emits a large amount of corrosive and harmful HCl and Cl2 gases, which not only corrodes the equipment but also harms the environment. Therefore, it is urgent to develop a high-efficiency, long-term stable propane dehydrogenation catalyst to produce propylene. A highly stable catalyst is fully suitable for the fixed bed reactor process and can solve the problems existing in the current moving bed process.

[0004] The high thermal stability and ordered pore structure of molecular sieves are considered to be ideal carriers for propane dehydrogenation. Encapsulating Pt particles in the pores of molecular sieves can improve their thermal stability. 201110283358.6 discloses a catalyst composed of metals Pt and Sn impregnated with mesoporous molecular sieve MCM-41 as a carrier; 201711068985.1 discloses a catalyst composed of Pt components, Sn components and Na components impregnated with spherical double mesoporous molecular sieves as a carrier; Patent application number 201510847986.0 discloses a molecular sieve catalyst obtained by impregnating Pt metal compounds, Group IIB metal compounds and alkaline earth metal compounds with nanosheet MFI structure molecular sieves as a carrier, and then drying and calcining them; CN 110479353 A, Angew. Chem. Int. Ed., 2020, 59, 19450-19459, J Catal., 2020, 385, 61-69 reported the in situ synthesis of sub-nanometer PtZn clusters in pure silicon MFI molecular sieves and the synthesis of MFI molecular sieve-encapsulated PtZn catalysts. The above-prepared catalysts were all prepared using molecular sieves with a c-axis size of about 0.20 μm. o C) Unstable catalytic activity. Furthermore, while the stability of these catalysts has been significantly improved compared to industrial Pt / Al2O3 catalysts, the stability of most catalysts can only be maintained for a few days, which does not yet meet the catalyst performance requirements of fixed-bed processes.

[0005] The present invention provides a PtZn@molecular sieve catalyst suitable for a fixed-bed propane dehydrogenation process. The catalyst is notably characterized in that PtZn nanoclusters are encapsulated using molecular sieve carriers with crystal grains having a c-axis size of 12.0 to 60.0 μm. Under high temperature conditions, the PtZn nanoclusters have a slow migration rate and a long diffusion path in the large-grain molecular sieve, so the catalyst has strong thermal stability. The present invention adds an appropriate amount of phenolic compounds to the crystallization of the molecular sieve to regulate the size of the molecular sieve catalyst crystal grains, especially the size of the molecular sieve in the c-axis direction, by chelating with silicon species. The PtZn@molecular sieve catalyst prepared by this method exhibits ultra-high stability in the propane dehydrogenation reaction, does not deactivate during the six-month reaction process, and meets the performance requirements of the fixed-bed process for the catalyst. Summary of the Invention

[0006] The present invention aims to address the problem that, under prolonged high-temperature conditions, Pt nanoparticles in existing Pt-based catalysts for propane dehydrogenation to propylene are susceptible to migration sintering and Oswald ripening, forming larger Pt nanoparticles and causing permanent deactivation of the Pt-based catalyst. The present invention provides a high-temperature stable PtZn@molecular sieve catalyst for propane dehydrogenation to propylene and a preparation method thereof. The catalyst encapsulates ultrasmall PtZn sub-nanoparticles within the micropores of a larger-grained molecular sieve catalyst, exhibits high propane conversion and propylene yield, and exhibits excellent catalytic stability for high-temperature, ultra-long-term reactions, meeting the performance requirements of fixed-bed processes for catalysts.

[0007] To achieve the above object, the present invention adopts the following technical solutions:

[0008] A high-temperature stable PtZn@molecular sieve catalyst for propane dehydrogenation to propylene and a preparation method thereof. The catalyst comprises a large single-crystal molecular sieve support and an active component, PtZn clusters. The molecular sieve support grains have a c-axis size of 12.0 to 60.0 μm, and the active component PtZn clusters have a particle size of 0.40 to 0.60 nm. Based on the total weight of the catalyst, the carrier is an MFI-type pure silicon molecular sieve with a loading of 90-99.5 wt%; the loading of the main active component Pt is 0.01-2.00 wt%; and the loading of the secondary active component Zn is 0.01-2.00 wt%. According to the in-situ static crystallization preparation method, an appropriate amount of phenolic compound is added to change the size of the molecular sieve catalyst grains, and ultrasmall PtZn sub-nanoclusters are encapsulated in the micropores of the MFI pure silicon molecular sieve with long c-axis grains. Experiments show that the PtZn@molecular sieve catalyst with larger grain size exhibits excellent comprehensive catalytic performance for the dehydrogenation of light alkanes.

[0009] The method for preparing a high-temperature stable PtZn@ molecular sieve catalyst for propane dehydrogenation to propylene specifically comprises the following steps:

[0010] (1) The silicon source, alkali source, template, organic complex, water, Pt metal compound and Zn metal compound are fully mixed and stirred to obtain a uniform mixed solution; wherein, the silicon source is calculated based on the content of SiO2, and the molar ratio of the feed amount of various raw materials in the system is: silicon source / alkali source = 1: 0.10-5.00; silicon source / template = 1: 0.10-10.0; silicon source / organic complex = 1: 0.10-10.0; silicon source / water = 1: 1.00-50.0;

[0011] (2) Slowly adding the homogeneous mixed solution obtained above into the polytetrafluoroethylene lining of a stainless steel crystallization kettle, then adding a certain amount of phenolic compound to adjust the length of the molecular sieve c axis, and continuing to stir thoroughly to obtain a homogeneous gel-like mixture; wherein the silicon source is calculated as the content of SiO2, and the molar ratio of the feeding amount of the phenolic compound is: silicon source / phenolic compound = 1:0.01~1.00;

[0012] (3) The stainless steel crystallization kettle was placed in a high-temperature oven and the static hydrothermal reaction crystallization was maintained for a certain period of time to obtain a crystallized solid product, which was filtered, washed multiple times, and dried, and finally directly reduced in a H2 atmosphere to obtain a PtZn@molecular sieve catalyst.

[0013] The silicon source in step (1) is any one of white carbon black, solid silica gel, ethyl orthosilicate, silica sol, and water glass, or a mixture of several thereof;

[0014] The alkaline source in step (1) is any one of NaOH, NaHCO3, Na2CO3 or a mixture of several thereof;

[0015] The template agent in step (1) is any one of tetramethylammonium bromide, tetraethylammonium bromide, tetrapropylammonium bromide, tetrabutylammonium bromide, tetramethylammonium hydroxide, tetraethylammonium hydroxide, tetrapropylammonium hydroxide, and tetrabutylammonium hydroxide, or a mixture of several thereof;

[0016] The Pt metal compound described in step (1) is any one of H2PtCl6·6H2O, PtCl2, PtCl4, Pt(NH3)4(OH)2, Pt(NH3)4Cl2·H2O, Pt(NH3)4Cl2, [Pt(NH3)4](NO3)2, or a mixture of several thereof; the organic complex is any one of diethylenetriamine, ethylenediamine, tetraethylenepentamine, triethylenetetramethyleneamine, or a mixture of several thereof;

[0017] The Zn metal compound described in step (1) is ZnCl 2、 Any one of ZnSO4 and Zn(NO3)2·6H2O or a mixture of more thereof;

[0018] The phenolic compound in step (2) is any one of phenol, catechol, resorcinol, and pyrogallol, or a mixture of several thereof;

[0019] The crystallization temperature in step (3) is 80 to 200°C; the crystallization time is 2 to 200 hours;

[0020] The drying temperature of the filtered solid product in step (3) is 80 to 180°C; the drying time is 2 to 20 hours;

[0021] The H2 reduction temperature in step (3) is 100-900°C; the treatment time is 2-20 h; and finally PtZn@molecular sieve catalysts with different grain sizes are obtained.

[0022] The c-axis size of the PtZn@ molecular sieve catalyst particles described in step (3) is 12.0 to 60.0 μm.

[0023] The method of using PtZn@ molecular sieve catalyst to dehydrogenate propane to propylene must comply with the following process conditions;

[0024] 1) Forming the PtZn@ molecular sieve catalyst into 20-80 mesh granular catalyst;

[0025] 2) Weigh a certain mass of PtZn@zeolite catalyst and mix it evenly with 2 g of quartz sand. Then, fill the reactor with a fixed-bed quartz tube with an inner diameter of 12 mm and keep the catalyst in the constant temperature range of the device's heating furnace.

[0026] 3) The catalyst is pretreated with hydrogen for a period of time and then cooled to room temperature. The temperature is then raised to the propane dehydrogenation to propylene temperature at a rate of 2°C / min. A certain amount of pure propane reaction gas is then passed through the catalyst bed to carry out the catalytic dehydrogenation reaction.

[0027] The mass of the loaded catalyst in step 2) is 0.02-1.00 g; the pure propane is industrial propane;

[0028] The hydrogen pretreatment temperature in step 3) is 100-700°C; the reduction time is 2-10 hours;

[0029] The reaction temperature in step 3) is 550-750°C;

[0030] The flow rate of the light alkane in step 3) is 2-100 mL / min, and the mass space velocity of the light alkane is WHSV=2-2000h -1 .

[0031] The PtZn@zeolite catalyst described in this invention exhibits excellent catalytic activity and stability in high-temperature propane dehydrogenation reactions. For example, in a propane dehydrogenation reaction at 600°C, the initial propane conversion rate of the PtZn@zeolite catalyst was approximately 44%. Even after 60 days of reaction, the propane conversion rate of the PtZn@zeolite catalyst with longer c-axis crystals remained very stable. In contrast, the propane conversion rate of the PtZn@zeolite catalyst with smaller crystals (Comparative Example 1) rapidly dropped to approximately 20%. These experimental results demonstrate that regulating the c-axis size of the molecular sieve catalyst crystals not only improves the catalyst's catalytic performance but also significantly enhances its stability.

[0032] The beneficial effects of the present invention are:

[0033] The catalyst described in the present invention is a PtZn@molecular sieve catalyst prepared by in-situ static crystallization of large-sized crystals. The ultra-small sub-nanometer PtZn clusters in the larger-crystal PtZn@molecular sieve catalyst can be stably present in the ten-membered ring channels of the molecular sieve at high temperatures for a long time, while the sub-nanometer PtZn clusters in the small-crystal PtZn@molecular sieve catalyst will sinter and aggregate at high temperatures, resulting in permanent deactivation. Based on the common crystallization of the molecular sieve raw material and the active metal, an appropriate amount of phenolic compound is added to form a chelate with the silicon species, reducing the nucleation rate of the silicon species during the hydrothermal crystallization reaction of the molecular sieve, thereby regulating the length of the molecular sieve c-axis. Utilizing the size effect of the molecular sieve itself not only improves the dispersion and utilization rate of the Pt active component, but most importantly, enhances the high-temperature stability of the ultra-small sub-nanometer PtZn clusters of the active component, greatly hindering the migration and aggregation of the PtZn nanoclusters. When applied to the propane dehydrogenation reaction, it exhibits excellent catalytic performance and an ultra-long high-temperature catalytic life, both of which far exceed those of currently reported Pt-based catalysts. Therefore, the PtZn@ molecular sieve with larger crystals prepared by the present invention has high propane conversion rate, high propylene yield and long-term stability at high temperature, and has industrial application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 2 are XRD patterns of the PtZn@molecular sieve catalysts prepared in Comparative Example and Examples 1 to 4.

[0035] Figure 2 This is the SEM image of the PtZn@S-1(0.25) catalyst prepared in Comparative Example 1.

[0036] Figure 3 This is the SEM image of the PtZn@S-1(12.0) catalyst prepared in Example 1.

[0037] Figure 4 This is the SEM image of the PtZn@S-1(25.0) catalyst prepared in Example 2.

[0038] Figure 5 This is the SEM image of the PtZn@S-1(35.0) catalyst prepared in Example 3.

[0039] Figure 6 This is the SEM image of the PtZn@S-1(50.0) catalyst prepared in Example 4.

[0040] Figure 7 This is the STEM image of the PtZn@S-1(50.0) catalyst prepared in Example 4.

[0041] Figure 8This is a diagram showing the catalytic activity of the PtZn@S-1(50.0) catalyst prepared in Example 4 for propane dehydrogenation for 6 consecutive months. DETAILED DESCRIPTION

[0042] In order to better understand the technical solution of the present invention, the following is a further detailed description with reference to specific embodiments and drawings, but this does not limit the scope of protection of the present invention.

[0043] Unless otherwise specified, the drugs used in the following examples were purchased from commercial sources and were not processed. Silica, tetrapropylammonium bromide (TPABr), sodium hydroxide (NaOH), chloroplatinic acid hexahydrate (HPtCl6·6H2O), zinc nitrate Zn(NO3)2·6H2O, ethylenediamine (NH2CH2CH2NH2), phenol, catechol, resorcinol, and pyrogallol were purchased from Aladdin Reagent Co., Ltd. Deionized water used in the experiments was obtained from a high-purity water system in the laboratory.

[0044] The catalyst in the examples is named PtZn@S-1(x), where Pt represents the primary active component; Zn represents the secondary active component; and x represents the c-axis size of the S-1 zeolite crystal. For example, a PtZn@zeolite catalyst with a single crystal c-axis size of 30.0 μm is designated PtZn@S-1(30.0).

[0045] Comparative Example 1 (without adding phenolic compounds)

[0046] (1) Weigh 7.2 g of silica and dissolve it in 53.2 g of deionized water. Stir in a water bath at 25 °C for 2.5 h to obtain a homogeneous solution after complete dissolution.

[0047] (2) Weigh 1.7 g of NaOH and 5.2 g of TPABr particles and add them to the above (1) successively. Continue stirring for 2.5 h to obtain a uniform mixed solution.

[0048] (3) Weigh 50.1 mg of H2PtCl6·6H2O and dissolve it in 2.0 g of deionized water. Stir the mixture in a 30 °C water bath for 1 h to form a uniform solution. Slowly add 0.5 mL of NH2CH2CH2NH2 and continue stirring for 2.5 h to obtain a uniform solution of Pt-containing organic amine complex.

[0049] (4) Weigh 52.2 mg of Zn(NO3)2·6H2O and dissolve it in 2.3 g of deionized water. Stir in a 30 °C water bath for 1.5 h to form a homogeneous solution.

[0050] (5) Mix the solutions in steps (2), (3) and (4), and continue stirring for 3.2 h to form a uniform mixed solution. Finally, the mixed solution is placed into the polytetrafluoroethylene lining of a stainless steel crystallization kettle;

[0051] (6) Place the stainless steel crystallization kettle in an oven, heat it from room temperature to 180 °C, and maintain a static hydrothermal reaction for crystallization for 5 days. After the crystallization is completed, cool, centrifuge, wash, and dry at 100 °C for 12 h to obtain the PtZn@S-1(0.25) catalyst powder precursor.

[0052] (7) The PtZn@S-1(0.25) catalyst powder precursor was placed in a high-purity H2 atmosphere in a tubular furnace, heated to 600 °C at a heating rate of 2 °C / min and maintained for 5 h for reduction, finally obtaining the PtZn@S-1(0.25) catalyst.

[0053] Figure 2 This is the SEM image of PtZn@S-1(0.25) catalyst.

[0054] Example 1

[0055] (1) Weigh 7.2 g of silica and dissolve it in 53.2 g of deionized water. Stir in a water bath at 25 °C for 2.5 h to obtain a homogeneous solution after complete dissolution.

[0056] (2) Weigh 1.7 g of NaOH and 5.2 g of TPABr particles and add them to the above (1) successively. Continue stirring for 2.5 h to obtain a uniform mixed solution.

[0057] (3) Weigh 50.1 mg of H2PtCl6·6H2O and dissolve it in 2.0 g of deionized water. Stir the mixture in a 30 °C water bath for 1 h to form a uniform solution. Slowly add 0.5 mL of NH2CH2CH2NH2 and continue stirring for 2.5 h to obtain a uniform solution of Pt-containing organic amine complex.

[0058] (4) Weigh 52.2 mg of Zn(NO3)2·6H2O and dissolve it in 2.3 g of deionized water. Stir in a 30 °C water bath for 1.5 h to form a homogeneous solution.

[0059] (5) Mix the solutions in steps (2), (3) and (4), add 5.1 g of phenol, and continue stirring for 3.2 h to form a uniform mixed solution. Finally, the mixed solution is placed in the polytetrafluoroethylene lining of a stainless steel crystallization kettle;

[0060] (6) Place the stainless steel crystallization kettle in an oven, heat it from room temperature to 180 °C, and maintain a static hydrothermal reaction for crystallization for 5 days. After the crystallization is completed, cool, centrifuge, wash, and dry at 100 °C for 12 h to obtain the PtZn@S-1 (12.0) catalyst powder precursor.

[0061] (7) The PtZn@S-1(12.0) catalyst powder precursor was placed in a high-purity H2 atmosphere in a tubular furnace, heated to 600 °C at a heating rate of 2 °C / min and maintained for 5 h for reduction, finally obtaining the PtZn@S-1(12.0) catalyst.

[0062] Figure 3 This is the SEM image of PtZn@S-1(12.0) catalyst.

[0063] Example 2

[0064] (1) Weigh 7.2 g of silica and dissolve it in 53.2 g of deionized water. Stir in a 30 °C water bath for 2.5 h to obtain a homogeneous solution after complete dissolution.

[0065] (2) Weigh 1.8 g of NaOH and 5.4 g of TPABr particles and add them to the above (1) successively. Continue stirring for 2.5 h to obtain a uniform mixed solution.

[0066] (3) Weigh 50.5 mg of H2PtCl6·6H2O and dissolve it in 2.1 g of deionized water. Stir in a 30 °C water bath for 1 h to form a uniform solution. Then slowly add 0.55 mL of NH2CH2CH2NH2 and continue stirring for 2.4 h to obtain a uniform solution of Pt-containing organic amine complex.

[0067] (4) Weigh 50.7 mg of Zn(NO3)2·6H2O and dissolve it in 2.5 g of deionized water. Stir in a 30 °C water bath for 1.5 h to form a homogeneous solution.

[0068] (5) Mix the solutions in steps (2), (3) and (4), add 6.5 g of phenol, and continue stirring for 3.5 h to form a uniform mixed solution. Finally, the mixed solution is placed in the polytetrafluoroethylene lining of a stainless steel crystallization kettle;

[0069] (6) Place the stainless steel crystallization kettle in an oven and heat it from room temperature to 185°C. Maintain a static hydrothermal reaction for crystallization for 5.5 days. After the crystallization is completed, cool, centrifuge, wash, and dry at 100°C for 12.5 hours to obtain the PtZn@S-1(25.0) catalyst powder precursor.

[0070] (7) The PtZn@S-1(25.0) catalyst powder precursor was placed in a high-purity H2 atmosphere in a tubular furnace, heated to 600 °C at a heating rate of 2 °C / min and maintained for 6 h for reduction, and finally the PtZn@S-1(25.0) catalyst was obtained.

[0071] Figure 4 This is the SEM image of PtZn@S-1(25.0) catalyst.

[0072] Example 3

[0073] (1) Weigh 7.5 g of white carbon black and dissolve it in 55.2 g of deionized water. Stir in a 30 °C water bath for 3 h to obtain a homogeneous solution after complete dissolution.

[0074] (2) Weigh 2.0 g of NaOH and 5.8 g of TPABr particles and add them to the above (1) successively. Continue stirring for 3 h to obtain a uniform mixed solution.

[0075] (3) Weigh 55.5 mg of H2PtCl6·6H2O and dissolve it in 2.5 g of deionized water. Stir the mixture in a 30 °C water bath for 2 h to form a uniform solution. Slowly add 0.65 mL of NH2CH2CH2NH2 and continue stirring for 2.7 h to obtain a uniform solution of Pt-containing organic amine complex.

[0076] (4) Weigh 51.6 mg of Zn(NO3)2·6H2O and dissolve it in 3 g of deionized water. Stir in a 30 °C water bath for 2 h to form a homogeneous solution.

[0077] (5) Mix the solutions in steps (2), (3) and (4), add 7.8 g of phenol, and continue stirring for 3.5 h to form a uniform mixed solution. Finally, the mixed solution is placed in the polytetrafluoroethylene lining of a stainless steel crystallization kettle;

[0078] (6) Place the stainless steel crystallization kettle in an oven, heat it from room temperature to 190 °C, and maintain static crystallization for 3.5 days. After the crystallization is completed, cool, centrifuge, wash, and dry at 100 °C for 12.5 h to obtain the PtZn@S-1(35.0) catalyst powder precursor.

[0079] (7) The PtZn@S-1(35.0) catalyst powder precursor was placed in a high-purity H2 atmosphere in a tubular furnace, heated to 600 °C at a heating rate of 2 °C / min and maintained for 6 h for reduction, finally obtaining the PtZn@S-1(35.0) catalyst.

[0080] Figure 5 This is the SEM image of PtZn@S-1(35.0) catalyst.

[0081] Example 4

[0082] (1) Weigh 6.2 g of silica and dissolve it in 58.2 g of deionized water. Stir in a water bath at 25 °C for 2.1 h to obtain a homogeneous solution after complete dissolution.

[0083] (2) Weigh 1.5 g of NaOH and 5.4 g of TPABr particles and add them to the above (1) successively. Continue stirring for 2.5 h to obtain a uniform mixed solution.

[0084] (3) Weigh 50.2 mg of H2PtCl6·6H2O and dissolve it in 2.0 g of deionized water. Stir in a 30 °C water bath for 1 h to form a uniform solution. Then slowly add 0.5 mL of NH2CH2CH2NH2 and continue stirring for 2.3 h to obtain a uniform solution of Pt-containing organic amine complex.

[0085] (4) Weigh 51.8 mg of Zn(NO3)2·6H2O and dissolve it in 2.5 g of deionized water. Stir in a 30 °C water bath for 1.5 h to form a homogeneous solution.

[0086] (5) Mix the solutions in steps (2), (3) and (4), add 8.9 g of phenol, and continue stirring for 3.5 h to form a uniform mixed solution. Finally, the mixed solution is placed in the polytetrafluoroethylene lining of a stainless steel crystallization kettle;

[0087] (6) The stainless steel crystallization kettle was placed in an oven and heated from room temperature to 180 °C and maintained for 6.5 days for hydrothermal crystallization. After the crystallization was completed, the catalyst was cooled, centrifuged, washed, and dried at 100 °C for 12 h to obtain the PtZn@S-1(50.0) catalyst powder precursor.

[0088] (7) The PtZn@S-1(50.0) catalyst powder precursor was placed in a high-purity H2 atmosphere in a tubular furnace, heated to 600 °C at a heating rate of 2 °C / min and maintained for 5 h for reduction, finally obtaining the PtZn@S-1(50.0) catalyst.

[0089] Figure 6 This is the SEM image of the PtZn@S-1(50.0) catalyst; Figure 7 This is the STEM image of the PtZn@S-1(50.0) catalyst; Figure 8 This is the long-term (6 months) reaction evaluation diagram of PtZn@S-1(50.0) catalyst.

[0090] Example 5

[0091] (1) Weigh 7.2 g of silica and dissolve it in 53.2 g of deionized water. Stir in a water bath at 25 °C for 2.5 h to obtain a homogeneous solution after complete dissolution.

[0092] (2) Weigh 1.7 g of NaOH and 5.2 g of TPABr particles and add them to the above (1) successively. Continue stirring for 2.5 h to obtain a uniform mixed solution.

[0093] (3) Weigh 50.1 mg of H2PtCl6·6H2O and dissolve it in 2.0 g of deionized water. Stir the mixture in a 30 °C water bath for 1 h to form a uniform solution. Slowly add 0.5 mL of NH2CH2CH2NH2 and continue stirring for 2.5 h to obtain a uniform solution of Pt-containing organic amine complex.

[0094] (4) Weigh 52.2 mg of Zn(NO3)2·6H2O and dissolve it in 2.3 g of deionized water. Stir in a 30 °C water bath for 1.5 h to form a homogeneous solution.

[0095] (5) Mix the solutions in steps (2), (3) and (4), add 8.9 g of phenol, and continue stirring for 3.2 h to form a uniform mixed solution. Finally, the mixed solution is placed in the polytetrafluoroethylene lining of a stainless steel crystallization kettle;

[0096] (6) Place the stainless steel crystallization kettle in an oven, heat it from room temperature to 180 °C, and maintain a static hydrothermal reaction for crystallization for 5 days. After the crystallization is completed, cool, centrifuge, wash, and dry at 100 °C for 12 h to obtain the PtZn@ZSM-5 (50.0) catalyst powder precursor.

[0097] (7) The PtZn@ZSM-5(50.0) catalyst powder precursor was placed in a high-purity H2 atmosphere in a tubular furnace, heated to 600°C at a heating rate of 2°C / min and maintained for 5 h for reduction, finally obtaining the PtZn@ZSM-5(50.0) catalyst.

[0098] Example 6

[0099] (1) Weigh 7.2 g of silica and dissolve it in 53.2 g of deionized water. Stir in a 30 °C water bath for 2.5 h to obtain a homogeneous solution after complete dissolution.

[0100] (2) Weigh 1.8 g of NaOH and 5.4 g of TPABr particles and add them to the above (1) successively. Continue stirring for 2.5 h to obtain a uniform mixed solution.

[0101] (3) Weigh 50.5 mg of H2PtCl6·6H2O and dissolve it in 2.1 g of deionized water. Stir in a 30 °C water bath for 1 h to form a uniform solution. Then slowly add 0.55 mL of NH2CH2CH2NH2 and continue stirring for 2.4 h to obtain a uniform solution of Pt-containing organic amine complex.

[0102] (4) Weigh 50.7 mg of Zn(NO3)2·6H2O and dissolve it in 2.5 g of deionized water. Stir in a 30 °C water bath for 1.5 h to form a homogeneous solution.

[0103] (5) Mix the solutions in steps (2), (3) and (4), add 8.9 g of catechol, and continue stirring for 3.5 h to form a uniform mixed solution. Finally, the mixed solution is placed in the polytetrafluoroethylene lining of a stainless steel crystallization kettle;

[0104] (6) Place the stainless steel crystallization kettle in an oven and heat it from room temperature to 185 °C. Maintain the static hydrothermal reaction for crystallization for 5.5 days. After the crystallization is completed, cool, centrifuge, wash, and dry at 100 °C for 12.5 h to obtain the PtZn@ZSM-11 (50.0) catalyst powder precursor.

[0105] (7) The PtZn@ZSM-11(50.0) catalyst powder precursor was placed in a high-purity H2 atmosphere in a tubular furnace, heated to 600°C at a heating rate of 2°C / min and maintained for 6 h for reduction, finally obtaining the PtZn@ZSM-11(50.0) catalyst.

[0106] Example 7

[0107] (1) Weigh 7.5 g of white carbon black and dissolve it in 55.2 g of deionized water. Stir in a 30 °C water bath for 3 h to obtain a homogeneous solution after complete dissolution.

[0108] (2) Weigh 2.0 g of NaOH and 5.8 g of TPABr particles and add them to the above (1) successively. Continue stirring for 3 h to obtain a uniform mixed solution.

[0109] (3) Weigh 55.5 mg of H2PtCl6·6H2O and dissolve it in 2.5 g of deionized water. Stir the mixture in a 30 °C water bath for 2 h to form a uniform solution. Slowly add 0.65 mL of NH2CH2CH2NH2 and continue stirring for 2.7 h to obtain a uniform solution of Pt-containing organic amine complex.

[0110] (4) Weigh 51.6 mg of Zn(NO3)2·6H2O and dissolve it in 3 g of deionized water. Stir in a 30 °C water bath for 2 h to form a homogeneous solution.

[0111] (5) Mix the solutions in steps (2), (3) and (4), add 8.9 g of resorcinol, and continue stirring for 3.5 h to form a uniform mixed solution. Finally, the mixed solution is placed in the polytetrafluoroethylene lining of a stainless steel crystallization kettle;

[0112] (6) Place the stainless steel crystallization kettle in an oven, heat it from room temperature to 190 °C, and maintain static crystallization for 3.5 days. After the crystallization is completed, cool, centrifuge, wash, and dry at 100 °C for 12.5 h to obtain the PtZn@ZSM-22 (50.0) catalyst powder precursor.

[0113] (7) The PtZn@ZSM-22(50.0) catalyst powder precursor was placed in a high-purity H2 atmosphere in a tubular furnace, heated to 600°C at a heating rate of 2°C / min and maintained for 6 h for reduction, finally obtaining the PtZn@ZSM-22(50.0) catalyst.

[0114] Example 8

[0115] (1) Weigh 6.2 g of silica and dissolve it in 58.2 g of deionized water. Stir in a water bath at 25 °C for 2.1 h to obtain a homogeneous solution after complete dissolution.

[0116] (2) Weigh 1.5 g of NaOH and 5.4 g of TPABr particles and add them to the above (1) successively. Continue stirring for 2.5 h to obtain a uniform mixed solution.

[0117] (3) Weigh 50.2 mg of H2PtCl6·6H2O and dissolve it in 2.0 g of deionized water. Stir in a 30 °C water bath for 1 h to form a uniform solution. Then slowly add 0.5 mL of NH2CH2CH2NH2 and continue stirring for 2.3 h to obtain a uniform solution of Pt-containing organic amine complex.

[0118] (4) Weigh 51.8 mg of Zn(NO3)2·6H2O and dissolve it in 2.5 g of deionized water. Stir in a 30 °C water bath for 1.5 h to form a homogeneous solution.

[0119] (5) Mix the solutions in steps (2), (3) and (4), add 8.9 g of pyrogallol, and continue stirring for 3.5 h to form a uniform mixed solution. Finally, the mixed solution is placed in the polytetrafluoroethylene lining of a stainless steel crystallization kettle;

[0120] (6) The stainless steel crystallization kettle was placed in an oven and heated from room temperature to 180 °C and maintained for 6.5 days for static hydrothermal crystallization. After the crystallization was completed, the mixture was cooled, centrifuged, washed, and dried at 100 °C for 12 h to obtain the PtZn@ZSM-48 (50.0) catalyst powder precursor.

[0121] (7) The PtZn@ZSM-48(50.0) catalyst powder precursor was placed in a high-purity H2 atmosphere in a tubular furnace, heated to 600°C at a heating rate of 2°C / min and maintained for 5 h for reduction, finally obtaining the PtZn@ZSM-48(50.0) catalyst.

[0122] The catalysts prepared in the comparative examples and examples were used for propane dehydrogenation reaction (propane conversion and propylene selectivity) and characterization. The specific experimental process was as follows: 0.5 g of the catalyst prepared in the comparative examples and examples was thoroughly mixed with 2 g of quartz sand and loaded into a quartz tube fixed-bed reactor with a diameter of 8 mm. The reactant was pure propane, the reaction temperature was 600 °C, the reaction pressure was atmospheric pressure, and the mass space velocity of propane was WHSV = 5.3 h -1 The results are shown in Table 1.

[0123] Table 1 Comparison of catalytic performance of PtZn@S-1 catalysts with different c-axis sizes

[0124]

[0125] Figure 1 The XRD patterns of the catalysts in Comparative Example 1 and Examples 1 to 4 show that the catalysts possess a regular MFI-configured pure silicon molecular sieve structure, with no diffraction peaks for Pt and Zn species observed, demonstrating the successful synthesis of the PtZn@S-1 catalyst containing highly dispersed PtZn nanoclusters. The catalytic performance results in Table 1 demonstrate that the stability of the catalysts in Examples 1, 2, 3, and 4 is significantly improved compared to the catalyst in Comparative Example 1 (which has a shorter c-axis length). The catalysts also maintain excellent overall catalytic performance under high temperature conditions, with virtually no deactivation. Furthermore, Examples 5-8 demonstrate that maintaining a constant c-axis length of 50.0 μm and varying the catalyst support type maintains high catalytic performance. This demonstrates that the addition of phenolic compounds to increase the length of the catalyst's c-axis crystallites can fundamentally stabilize the migration of PtZn nanoclusters within the catalyst and prevent sintering. Compared to similar PtZn propane dehydrogenation catalysts, the catalytic performance surpasses that of previously reported catalysts. In summary, the PtZn@S-1 catalyst with larger c-axis length grains exhibits excellent comprehensive catalytic performance and high-temperature stability for propane dehydrogenation.

[0126] The above description is only a preferred embodiment of the present invention. All equivalent changes and modifications made according to the scope of the patent application of the present invention should fall within the scope of the present invention.

Claims

1. A method for preparing a high-temperature stable PtZn@ molecular sieve catalyst for propane dehydrogenation to propylene, characterized by: The catalyst consists of a large single-crystal molecular sieve support and active component PtZn clusters. The length of the molecular sieve support crystals on the c-axis is 12.0 to 60.0 μm. The particle size of the active component PtZn clusters is 0.40 to 0.60 nm. Based on the total mass of the catalyst, the Pt loading is 0.01 to 2.00 wt%; the Zn loading is 0.01 to 2.00 wt%. The catalyst is synthesized using an in-situ hydrothermal crystallization method, encapsulating ultra-small PtZn clusters in the micropores of the large single-crystal molecular sieve. The specific preparation method comprises the following steps: (1) The silicon source, alkali source, template, organic complex, water, Pt metal compound and Zn metal compound are fully mixed and stirred to obtain a uniform mixed solution; wherein the silicon source is calculated based on the content of SiO2, and the molar ratio of the feed amount of various raw materials in the system is: silicon source / alkali source = 1:0.1~5.00; silicon source / template = 1:0.1~10.0; silicon source / organic complex = 1:0.1~10.0; silicon source / water = 1:1~50.0; (2) Slowly adding the homogeneous mixed solution obtained above into the polytetrafluoroethylene lining of a stainless steel crystallization kettle, then adding a certain amount of phenolic compound to adjust the length of the molecular sieve c axis, and continuing to stir thoroughly to obtain a homogeneous gel-like mixture; wherein the silicon source is calculated as the content of SiO2, and the molar ratio of the feeding amount of the phenolic compound is: silicon source / phenolic compound = 1:0.01~1.00; (3) placing the stainless steel crystallization kettle in a high-temperature oven and maintaining static crystallization for a certain period of time to obtain a crystallized solid product, which was filtered, washed multiple times, and dried, and finally directly reduced under a H2 atmosphere to obtain a PtZn@molecular sieve catalyst; The template agent described in step (1) is any one of tetramethylammonium bromide, tetraethylammonium bromide, tetrapropylammonium bromide, tetrabutylammonium bromide, tetramethylammonium hydroxide, tetraethylammonium hydroxide, tetrapropylammonium hydroxide, and tetrabutylammonium hydroxide, or a mixture thereof; the organic complex is any one of diethylenetriamine, ethylenediamine, tetraethylenepentamine, triethylenetetrammonium, and pentaethylenehexamine, or a mixture thereof.

2. The preparation method according to claim 1, wherein: The silicon source in step (1) is any one of white carbon black, solid silica gel, ethyl orthosilicate, silica sol, and water glass, or a mixture of several of them.

3. The preparation method according to claim 1, wherein: The alkali source in step (1) is any one of NaOH, NaHCO3, Na2CO3 or a mixture of several thereof.

4. The preparation method according to claim 1, wherein: In step (1), the Pt metal compound is any one of H2PtCl6·6H2O, PtCl2, PtCl4, Pt(NH3)4(OH)2, Pt(NH3)4Cl2·H2O, Pt(NH3)4Cl2, [Pt(NH3)4](NO3)2, or a mixture of several thereof.

5. The preparation method according to claim 1, wherein: The Zn metal compound in step (1) is ZnCl 2、 Any one of ZnSO4 and Zn(NO3)2·6H2O or a mixture of more thereof.

6. The preparation method according to claim 1, wherein: The phenolic compound described in step (2) is any one of phenol, catechol, resorcinol, and pyrogallol, or a mixture of several of them.

7. The preparation method according to claim 1, wherein: The crystallization temperature in step (3) is 80-200°C, and the crystallization time is 2-200 h; the drying temperature is 80-180°C, and the drying time is 2-20 h; the reduction temperature is 100-900°C, and the treatment time is 2-20 h.

8. The preparation method according to claim 1, wherein: The PtZn@molecular sieve catalyst described in step (3) has a crystallite c-axis length of 12.0 to 60.0 μm.

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