Pt-based catalysts supported on aluminas of different morphologies and methods of making and use

Abstract

The application provides a Pt-based catalyst with different morphologies of alumina, a preparation method and application, and the active component of the catalyst is Pt-Sn, and the carrier is granular, rod-shaped, nanoflower-shaped, filamentous or rhombic flake-shaped gamma-Al2O3. The simple and controllable synthesis method is used to realize accurate regulation of the surface structure and pore characteristics of the catalyst, to enhance the anchoring capacity of the active component and to optimize the acid distribution, so as to effectively inhibit the side reaction, and to significantly improve the anti-carbon deposition performance and propylene selectivity of the catalyst.

Description

Technical Field

[0001] This invention relates to the field of catalytic material preparation and efficient conversion and utilization of low-carbon alkanes, specifically to Pt-based catalysts supported on alumina with different morphologies, their preparation methods, and applications. Background Technology

[0002] Propylene is an important basic raw material for organic chemicals, widely used in the production of polypropylene, acrylonitrile, propylene oxide, and other chemical products. It is a fundamental raw material for the three major synthetic materials (plastics, rubber, and fibers). In recent years, the demand for propylene has continued to grow both domestically and internationally. The two traditional oil-to-olefins routes, naphtha cracking and catalytic cracking, are energy-intensive and highly polluting, necessitating clean and efficient olefin production technologies. my country has abundant reserves of oil and gas resources such as shale gas, but these raw material gases are currently mainly used for combustion, failing to achieve efficient utilization. Shale gas contains large amounts of propane gas, and propane dehydrogenation (PDH) is a novel industrial process for producing propylene. This process achieves a highly efficient conversion of gaseous fuels into chemical products. Compared to traditional oil-to-propylene production routes, it offers advantages such as cleanliness and efficiency, high propylene selectivity, abundant raw material sources, and simple and easily separable product composition, attracting widespread attention both domestically and internationally.

[0003] Propane dehydrogenation is a strongly endothermic reaction, and the core and key to this process lies in the selection and performance optimization of the catalyst. Currently, commercial propane dehydrogenation processes mainly employ noble metal catalysts and metal oxides such as CrO₂. x Catalyst. Compared to metal oxides CrO x Precious metal catalysts, with their advantages of high catalytic activity, excellent propylene selectivity, and non-toxicity, have become the primary choice for propane dehydrogenation. However, precious metal catalysts also have some problems. Metal particles are prone to sintering and agglomeration at high temperatures, and their high catalytic activity can easily induce deep dehydrogenation reactions, leading to coking and rapid catalyst deactivation. This significantly reduces catalyst stability and increases the operating and regeneration costs of industrial production. Furthermore, the strong acid sites on the γ-Al₂O₃ support are prone to deep dehydrogenation, forming irreversible coking, which significantly affects the dispersion state of the active metal and its interaction with the support, further limiting the dehydrogenation performance of Pt-based catalysts.

[0004] Existing research on the modification of Pt-based catalysts mainly focuses on two directions: support modification and active component structure optimization. However, both have corresponding limitations. Patent CN 118577266 A effectively improves the dispersion of Pt by doping Sn into the alumina framework to form anchoring sites. Its core is support component modification, but its preparation process is complex, and Sn doping can easily lead to changes in acidic sites on the support surface, potentially triggering side reactions. Patent CN 116212861 B reduces the Pt loading to 0.01-0.1 wt% and forms a sub-nano alloy. Its core is active component structure optimization. Although the low-loading PtSn disordered alloy reduces the amount of precious metal used, it requires a precise high-temperature reduction process to form the sub-nano alloy, making industrial scale-up difficult. At the same time, the propylene selectivity of the catalyst in this invention fluctuates greatly (80.5%-97.6%).

[0005] Therefore, it is of great significance to develop a catalyst technology that is not prone to sintering and deactivation during alkane dehydrogenation, has excellent anti-coking properties, and exhibits stable selectivity for propylene. Summary of the Invention

[0006] In view of the shortcomings of the prior art, the purpose of this invention is to provide a catalyst with different morphologies supported on Pt groups, its preparation method and application.

[0007] The microstructure of γ-Al₂O₃ supports (e.g., granular, rod-shaped, nanoflower-like, filamentous, rhombic flake-like, etc.) directly determines the exposed crystal faces, surface atomic coordination state, pore structure, and acidity distribution. The exposed crystal faces directly determine the Al coordination environment, while the Al coordination state, through electronic interactions and spatial effects, regulates the existence form (valence state, dispersion, and crystal phase) of the active metal centers, thus affecting the catalyst's activity, resistance to coking, and sintering stability. When γ-Al₂O₃ grows along high surface energy crystal faces in rod-like or flake-like forms, the proportion of five-coordinated Al significantly increases, with a small amount of four-coordinated Al present. Five-coordinated Al is a strong electron acceptor, effectively promoting the stability of high-valence metal species. Four-coordinated Al has weaker electron-accepting ability but can modulate metal-catalyst interactions. Precise control of the surface properties of the support at the microscopic level can effectively inhibit the high-temperature sintering and agglomeration of active metal particles, improve the dispersion and exposure of active metals, and strengthen the interaction between active metals and the support. On the other hand, it can reduce strong acid sites on the support surface that are prone to coking and inhibit the occurrence of side reactions such as deep dehydrogenation, thereby simultaneously improving the catalytic activity, propylene selectivity and anti-coking stability of Pt-based catalysts.

[0008] This invention addresses the core technical challenges of traditional alkane dehydrogenation catalysts, such as easy sintering and deactivation, poor anti-coking performance, and low propylene selectivity, by controlling the morphology of different γ-Al2O3 supports. It solves the problems of easy deactivation and weak anti-coking performance in the preparation of olefins from alkane dehydrogenation in existing technologies. By controlling the morphology of γ-Al2O3 supports, the catalytic activity, propylene selectivity, and anti-coking stability of Pt-based catalysts are improved simultaneously.

[0009] Specifically, the catalysts of the present invention, which are Pt-based catalysts supported on alumina with different morphologies, have Pt-Sn as the active component and γ-Al2O3 as the support in the form of granular, rod-shaped, nano-flower-shaped, filament-shaped, or rhomboid-shaped sheets. The mass of the active component is calculated in terms of metal elements, and the mass of the support is calculated in terms of γ-Al2O3. Pt is 0.5 wt.% of the support weight and Sn is 1 wt.% of the support weight.

[0010] γ-Al2O3 with different morphologies, such as granules, rods, nanoflowers, filaments, and rhombic flakes, was prepared by precise control via hydrothermal or aluminum alkoxide methods. By controlling the morphology of the support, Pt species were highly dispersed and anchored, thereby improving the propane dehydrogenation activity, propylene selectivity, and anti-coking stability of the catalyst.

[0011] This invention also provides a method for preparing Pt-based catalysts supported on alumina with different morphologies as described above. When the support is granular, rod-shaped, nanoflower-shaped, or filamentous γ-Al2O3, the preparation method specifically includes the following steps: Step 1: Dissolve the aluminum source in deionized water to obtain an aluminum source aqueous solution, and stir at 400 r / min for 30 min; Step 2: Weigh the precipitant, dissolve it in deionized water, and let it stand for 30 minutes to obtain an aqueous solution of the precipitant; Step 3: Add the precipitant aqueous solution to the aluminum source aqueous solution and stir to mix; stir at 400 r / min for 1 h; in Step 3, the granular, rod-shaped, and nano-flower-shaped Pt-Sn / γ-Al2O3 catalyst is added directly to the aluminum source aqueous solution, or the precipitant aqueous solution is added dropwise to the aluminum source aqueous solution at a dropping rate of 1 drop / second, and stirring is continued at 400 r / min for 1 h.

[0012] Furthermore, in step three, the filamentous Pt-Sn / γ-Al2O3 catalyst is prepared by adding the precipitant aqueous solution dropwise to the aluminum source aqueous solution at a dropping rate of 1 drop / second, and stirring continuously for 1 hour at a speed of 400 r / min.

[0013] The reason why granular, rod-shaped, and nano-flower-shaped Pt-Sn / γ-Al2O3 catalysts can directly add the precipitant aqueous solution to the aluminum source aqueous solution is that the precipitant used in these catalysts is urea, which does not directly ionize to release OH-. -It hydrolyzes very slowly at room temperature, and the solution is neutral. It will not promote the hydrolysis and precipitation of aluminum ions after being added dropwise, so it can be added directly.

[0014] The reason for adding the filamentous Pt-Sn / γ-Al2O3 catalyst dropwise to the aluminum source aqueous solution is that the precipitant used in this catalyst is ammonium carbonate. At room temperature, aluminum ions and carbonate ions in the solution will undergo a double hydrolysis reaction, which will quickly precipitate and release carbon dioxide. It is necessary to add it slowly to control the precipitation rate and prevent a large amount of carbon dioxide from being generated, which would cause the solution to overflow.

[0015] Controlling the dropping speed to 1 drop / second also controls the sedimentation rate; sedimentation that is too fast will also affect the final morphology.

[0016] Step 4: Pour the mixed solution into a hydrothermal reactor for crystallization; the conditions for the hydrothermal reactor crystallization reaction are 100-200 ℃ for 10-40 h; the temperature and time of the crystallization reaction are used to precisely control atomic diffusion, crystallization rate and grain growth during the crystallization process, and ultimately determine the morphology of the resulting product.

[0017] Step 5: After crystallization is complete and the product has cooled to room temperature, centrifuge, wash, and dry the product.

[0018] Step 6: Grind and calcine the product to obtain γ-Al2O 3。

[0019] Step 7: Pt and Sn sources are impregnated onto γ-Al2O3 using an evaporation impregnation method. After impregnation, the mixture is dried at 80-100 °C for 8-12 h, and then calcined in a muffle furnace at 500-600 °C for 2-4 h to obtain granular, rod-shaped, nano-flower-like, and filamentous Pt-Sn / γ-Al2O3 catalysts.

[0020] Furthermore, in step one, the aluminum source is one or a combination of several of Al(NO3)3·9H2O, Al2(SO4)3·18H2O, and AlCl3·6H2O; The molar ratio of aluminum source to deionized water is 1-2 : 110-250; In step two, the precipitant is one or a combination of CO(NH2)2 and (NH4)2CO3. The molar ratio of precipitant to deionized water is 1:12-30; The molar ratio of the aluminum source in step one to the precipitant in step two is 1:3-9.

[0021] Furthermore, in the preparation of the filamentous Pt-Sn / γ-Al2O3 catalyst, in step one, after dissolving the aluminum source in deionized water to obtain an aqueous solution of the aluminum source, 0.5-1 ml of an aqueous solution of 1-butyl-2,3-dimethylimidazolium chloride with a concentration of 0.5 g / ml is added, and stirring is continued for 30 min at a speed of 400 r / min.

[0022] The role of 1-butyl-2,3-dimethylimidazolium chloride: [BdMIM] in this chloride salt + The cation has a planar aromatic structure and can act as a structure directing agent, adsorbing on nonpolar crystal planes and promoting their growth. Ultimately, it grows along a single crystal plane to form a filamentous structure.

[0023] Furthermore, in step five, the product after crystallization is washed 3-4 times with 30-50 mL of deionized water, filtered, and the solid product is dried in an 80 ℃ oven for 8-12 h; the precursor ground to a powder larger than 80 mesh in step six is ​​placed in a muffle furnace and heated to 500-600 ℃ at 2 ℃ / min, and calcined for 2-6 h to obtain γ-Al2O3.

[0024] Further, in step seven, the co-impregnation solution is prepared first: 0.5 wt.% Pt source and 1 wt.% Sn source are added to 2-5 ml of anhydrous ethanol and allowed to stand for 60 min, where the Pt source is H2PtCl6·6H2O and the Sn source is SnCl2·2H2O; then 1-3 g of γ-Al2O3 is added to 15-40 ml of anhydrous ethanol, stirred, and then sonicated at a stirring speed of 350 r / min and an ultrasonic intensity of 40 kHz for 30 min each; finally, the anhydrous ethanol solution of γ-Al2O3 is placed in an oil bath, and the co-impregnation solution is added dropwise to the anhydrous ethanol solution of γ-Al2O3 at a dropping rate of 2 drops / second. After the addition is complete, the mixture is heated at 90 ℃ for 2-4 h to impregnate the Pt and Sn sources onto the γ-Al2O3.

[0025] Furthermore, when the support is rhomboid sheet-like γ-Al2O3, the preparation method specifically includes the following steps: Step S1: High-purity aluminum shavings react with n-pentanol to produce aluminum alkoxy; Step S2: Hydrolysis and crystallization of alkoxyaluminum to prepare the precursor pseudoboehmite; Step S3: The precursor is dried, ground, and calcined to obtain γ-Al2O3; Step S4: Pt source and Sn source are impregnated onto γ-Al2O3 by evaporation impregnation. After impregnation, the mixture is dried at 100 °C overnight and then calcined in a muffle furnace at 500-600 °C for 2-4 h to obtain rhomboid plate-shaped Pt-Sn / γ-Al2O3 catalyst.

[0026] Furthermore, in step S1, aluminum shavings are placed in a three-necked flask containing n-pentanol, wherein the molar ratio of aluminum shavings to n-pentanol is 0.9-1.2 : 2.7-3.6, and reflux is added, and the reaction is carried out at 130-150 °C for 4-6 h.

[0027] Furthermore, the specific steps of step S2 are as follows: Step S21: Heat aluminum alkoxy to 90-100 °C and stir at 500 r / min. Add deionized water dropwise to start hydrolysis. The molar ratio of deionized water to aluminum is 1.8-5.7 : 0.07-0.22, and the dropping rate of deionized water is 1 drop / second. Step S22: After the deionized water is added dropwise, continue stirring at 90-100 °C for 1 h to end the hydrolysis and then cool down; Step S23: After cooling to room temperature, take the lower layer of white slurry into a hydrothermal reactor, add 18-54 ml of deionized water, and crystallize at 120-180 ℃ for 12-24 h. The crystallized product is the precursor pseudoboehmite.

[0028] Furthermore, in step S3, the precursor is dried at 120 °C for 8-12 h, and the dried product is ground into a powder with a mesh size greater than 80. The powder precursor is placed in a muffle furnace and heated to 500-600 °C at a rate of 2 °C / min, and calcined for 2-6 h to obtain γ-Al2O3. In step S4, the co-impregnation solution is prepared first: 0.5 wt.% Pt source and 1 wt.% Sn source are added to 2-5 ml of anhydrous ethanol and allowed to stand for 60 min, where the Pt source is H2PtCl6·6H2O and the Sn source is SnCl2·2H2O; then 1-3 g of γ-Al2O3 is added to 15-40 ml of anhydrous ethanol, stirred, and then sonicated. The stirring speed is 350 r / min, the sonication intensity is 40 kHz, and the stirring and sonication time are both 30 min; finally, the anhydrous ethanol solution of γ-Al2O3 is placed in an oil bath, and the co-impregnation solution is added dropwise to the anhydrous ethanol solution of γ-Al2O3 at a dropping rate of 2 drops / second. After the addition, the solution is heated at 90 ℃ for 2-4 h to impregnate the Pt source and Sn source onto the γ-Al2O3.

[0029] The reason why different aluminum sources are needed for γ-Al₂O₃ with different morphologies: the anions (Cl) in aluminum salts - NO 3- SO4 2- The morphology and structure of the product are greatly affected by the different hydrolysis capabilities and adsorption coordination of different anions, which leads to different nucleation rates and crystal face growth of alumina, ultimately resulting in differences in microstructure.

[0030] The reason for different amounts of aluminum source and deionized water is that different aluminum ion concentrations result in different nucleation rates and different final morphologies. Changing the amount of aluminum source and deionized water changes the aluminum ion concentration.

[0031] The reason for the different types and amounts of precipitants: The core function of precipitants is to regulate the pH of the system, thereby regulating the hydrolysis-precipitation kinetics of aluminum ions. Different precipitants have different pH regulation capabilities, and the hydrolysis and precipitation rates of aluminum ions are different, which will ultimately affect their microstructure.

[0032] The present invention also provides the application of the Pt-based catalysts supported on alumina with different morphologies in the propane dehydrogenation reaction.

[0033] Compared with the prior art, the beneficial effects of the present invention are as follows: it can achieve precise control of the surface structure and pore characteristics of the catalyst using a simple and controllable synthesis method, enhance the anchoring ability of the active components and optimize the acidity distribution, thereby effectively suppressing side reactions and significantly improving the catalyst's anti-coking performance and propylene selectivity. Attached Figure Description

[0034] Figure 1 The XRD patterns of the catalysts prepared in Examples 1-5 and Comparative Example 1 before and after loading are shown in (a) before loading and (b) after loading. Figure 2 SEM images of alumina with different morphologies prepared in Examples 1-5 and Comparative Example 1: (a) granular, (b) rod-shaped, (c) nanoflower-shaped, (d) rhomboid flake-shaped, (e) filament-shaped, (f) commercial alumina; Figure 3 Comparison of TEM and EDS images of the catalysts prepared in Examples 2-3 and 5; Figure 4 The catalysts prepared in Examples 1-5 and the nitrogen adsorption-desorption isotherms and pore size distribution diagrams compared with Comparative Example 1 are shown. (a) Nitrogen adsorption-desorption isotherm, (b) Pore size distribution diagram. Figure 5 The graph shows the relationship between the amount of NH3 desorption and temperature in the NH3-TPD test of the catalysts prepared in Examples 1-5 and Comparative Example 1. Figure 6 The figures show the catalysts prepared in Examples 1-5 and their propane dehydrogenation reaction performance compared with Comparative Example 1. Figure 7 The XRD patterns of the catalyst prepared in Example 5 before and after the reaction are shown in (a) and (b) are the relationship between the amount of CO2 generated in O2-TPO after the reaction and the temperature. Detailed Implementation

[0035] The present invention will be further described below with reference to specific embodiments, but the embodiments do not limit the present invention in any way. Unless otherwise stated, the raw materials and reagents used in the embodiments of the present invention are conventionally purchased raw materials and reagents.

[0036] The technical solution of the present invention will be further explained below with reference to implementation examples.

[0037] Example 1 This embodiment provides a method for preparing particulate Pt-Sn / γ-Al2O3-particle catalysts, with the following steps: Step 1: Weigh 3.7513 g Al(NO3)3·9H2O and dissolve it in 40 ml of deionized water. Stir at 400 r / min for 30 min to obtain an aluminum source aqueous solution. Step 2: Weigh 5.4036 g of CO(NH2)2, dissolve it in 20 ml of deionized water, and let it stand for 30 min to obtain an aqueous solution of the precipitant; Step 3: Add the CO(NH2)2 precipitant aqueous solution to the aluminum source aqueous solution and stir for 1 h at a speed of 400 r / min; Step 4: Pour the well-stirred mixed solution into a hydrothermal reactor for crystallization, and react at 100 °C for 12 h; Step 5: After crystallization, the product is washed 4 times with 30 mL of deionized water, filtered, and the solid product is dried in an 80℃ oven for 12 h. Step 6: Grind the product into a powder with a mesh size greater than 80, place it in a muffle furnace and heat it to 600 °C at a rate of 2 °C / min, and calcine it for 2 h to obtain γ-Al2O3; Step 7; First, prepare the co-impregnation solution: Add 0.5 wt.% Pt source and 1 wt.% Sn source to 3 ml of anhydrous ethanol and let stand for 60 min. The Pt source is H2PtCl6·6H2O, and the Sn source is SnCl2·2H2O. Then, add 1.5 g of granular γ-Al2O3 to 20 ml of anhydrous ethanol, stir, and then sonicate. The stirring speed is 350 rpm, the sonication intensity is 40 kHz, and the stirring and sonication time are both 30 min. Finally, place the anhydrous ethanol solution of γ-Al2O3 in an oil bath, and then add the co-impregnation solution dropwise to the anhydrous ethanol solution of γ-Al2O3 at a dropping rate of 2 drops / second. After the addition is complete, heat at 90 ℃ for 4 h to impregnate the Pt source and Sn source onto the γ-Al2O3. After impregnation, dry at 100 ℃ for 12 h, and then heat in a muffle furnace at 500 ℃. Particle-shaped Pt-Sn / γ-Al2O3 catalyst was obtained by calcination at ℃ for 2 h, and is denoted as Pt-Sn / γ-Al2O3-particle.

[0038] Example 2 This embodiment provides a method for preparing a rod-shaped Pt-Sn / γ-Al2O3-rod catalyst. The specific method is the same as in Example 1. The difference between this embodiment and Example 1 is that in step four, the hydrothermal reactor crystallization reaction is carried out at 100 °C for 36 h, and in step seven, 1.5 g of rod-shaped γ-Al2O3 is used.

[0039] Example 3 This embodiment provides a method for preparing a nanoflower-like Pt-Sn / γ-Al2O3-nanoflower catalyst. The specific method is the same as in Example 1. The difference between this embodiment and Example 1 is as follows: In step one, in the preparation of the Pt-Sn / γ-Al2O3 catalyst, the aluminum source is Al2(SO4)3·18H2O, the amount is 7.1 g, and the amount of deionized water is 40 ml; In step two, the amount of CO(NH2)2 is 2.3670 g, and the amount of deionized water is 20 ml; In step four, the hydrothermal reactor crystallization reaction is carried out at 180℃ for 24 h; In step seven, 1.5 g of nanoflower-like γ-Al2O3 is used.

[0040] Example 4 This embodiment provides a method for preparing a filamentous Pt-Sn / γ-Al2O3-thread catalyst. The specific method is the same as in Example 1, but the difference between this embodiment and Example 1 is as follows: In step one, the aluminum source is AlCl3·6H2O, with an amount of 4.83 g and deionized water volume of 19.24 ml. The aluminum source and deionized water are stirred at 400 r / min for 30 min, and then 0.76 ml of an aqueous solution of 1-butyl-2,3-dimethylimidazolium chloride with a concentration of 0.5 g / ml is added, followed by stirring for another 30 min. In step two, the precipitant is (NH4)2CO3, with an amount of 9.61 g and deionized water volume of 40 ml. In step three, the precipitant aqueous solution is added dropwise to the aluminum source aqueous solution at a dropping rate of 1 drop / second.

[0041] Example 5 This embodiment provides a method for preparing a rhomboid sheet-like Pt-Sn / γ-Al2O3-rhombus catalyst, as detailed below: Step S1: Place 4 g of aluminum shavings in a three-necked flask containing 57 ml of n-pentanol, add reflux condenser, and react at 150°C for 5 h; Step S2: After heating aluminum alkoxy to 100 °C, stir at 500 r / min and add 68 ml of deionized water dropwise to start hydrolysis. The drop rate of deionized water is 1 drop / second. After the deionized water is added, continue stirring at 100 °C for 1 h to stop the hydrolysis and cool down. After cooling to room temperature, take the lower white slurry into a hydrothermal reactor, add 35 ml of deionized water, and crystallize at 180 °C for 24 h. The crystallized product is the precursor pseudoboehmite. Step S3: The precursor pseudoboehmite was dried at 120 °C for 12 h. The dried product was ground into powder. The powdered precursor was placed in a muffle furnace and heated to 600 °C at 2 °C / min. It was then calcined for 2 h to obtain γ-Al2O3. Step S4: Add 0.5 wt.% Pt source and 1 wt.% Sn source to 3 ml of anhydrous ethanol and let stand for 60 min. The Pt source is H2PtCl6·6H2O, and the Sn source is SnCl2·2H2O. Then add 3 g of γ-Al2O3 to 40 ml of anhydrous ethanol, stir, and then sonicate. The stirring speed is 350 r / min, the sonication intensity is 40 kHz, and the stirring and sonication time are both 30 min. Finally, place the anhydrous ethanol solution of γ-Al2O3 in an oil bath, and then add the co-impregnation solution dropwise to the anhydrous ethanol solution of γ-Al2O3 at a dropping rate of 2 drops / second. After the addition, heat at 90 ℃ for 4 h to impregnate the Pt and Sn sources onto the γ-Al2O3. After impregnation, dry at 100 ℃ overnight, and then calcine in a muffle furnace at 600 ℃ for 2 hours. The rhombic sheet-like Pt-Sn / γ-Al2O3 catalyst was obtained and denoted as Pt-Sn / γ-Al2O3-rhombus.

[0042] Comparative Example 1 This invention also provides a method for preparing a commercial Pt-Sn / γ-Al2O3-commercial catalyst. The specific method is described in Example 1. The difference between this example and Example 1 is that the support used is commercial alumina, and the supported catalyst is prepared using the same method as step seven in Example 1.

[0043] Propane dehydrogenation reaction performance test: First, 1 g of the 40-60 mesh catalyst prepared in Examples 1-5 and Comparative Example 1 was mixed with 1 g of quartz sand (the mass ratio of quartz sand to catalyst was 10). After uniform mixing, the mixture was loaded into a stainless steel tube. Next, the device was heated and the catalyst was pretreated. The feed gas concentration was 40% C3H8 / N2 mixture, the total flow rate was 20 ml / min, and the reaction temperature was 550 ℃. The device was heated to 550 ℃ at a heating rate of 10 ℃ / min under N2 atmosphere (30 ml / min). After stabilizing for 10 min, the atmosphere was switched to air (30 ml / min) for oxidation for 30 min, then switched to N2 (30 ml / min) for purging for 5 min, then switched to 5% H2 / Ar (30 ml / min) mixture for reduction for 30 min, then switched to N2 (12 ml / min) for purging for 5 min. Finally, C3H8 (8 mL / min) was introduced to test the propane dehydrogenation reaction performance. The composition of the reaction products was analyzed by gas chromatography using a GC-2011 gas chromatograph (Beijing Zhongke Huijie Analytical Technology Co., Ltd.).

[0044] Figure 1 The figures show the XRD patterns of the Pt-Sn / γ-Al2O3 catalysts with different morphologies prepared in Examples 1-5 and Comparative Example 1 before and after loading (tested using a Rigaku Ultima IV X-ray diffractometer, Japan. CuKα radiation was used in this experiment at a voltage of 40 kV, a current of 100 mA, and a scan rate of 10 ° / min). The figures show that all catalysts exhibit a distinct γ-Al2O3 structure before and after loading, and the structure of γ-Al2O3 remains unchanged, indicating successful synthesis of γ-Al2O3. Furthermore, no obvious characteristic diffraction peaks corresponding to Pt and Sn were observed in the figures, likely due to low Pt and Sn content or highly dispersed Pt and Sn particles.

[0045] Figure 2 SEM images of γ-Al₂O₃ with different morphologies prepared in Examples 1-5 and Comparative Example 1 (tested using a JSM7401F scanning electron microscope manufactured by JEOL Ltd., Tokyo, Japan. The test voltage was 10 kV and the working distance was approximately 8.6 mm). These images clearly show... Figure 2 In (ae), γ-Al2O3 exhibits regular granular, rod-shaped, nanoflower-like, filamentous, and rhomboid plate-like structures, and the particle size varies with the morphology, corresponding to the morphology of γ-Al2O3 in Examples 1-5, while the morphology of γ-Al2O3 in Comparative Example 1 is a regular blocky structure.

[0046] Figure 3Comparison of TEM (Figs. a, e, i) and EDS images of the catalysts prepared in Examples 2 (ad), 3 (eh), and 5 (il) (To analyze the microstructure and crystal phase structure of the samples, a Thermo Fisher Scientific Talos F200X field emission transmission electron microscope (TEM) was used. In this experiment, the instrument operating voltage was set to 200 kV, and the elemental composition and surface distribution of the catalysts were systematically characterized using the energy dispersive X-ray spectroscopy (EDS) module integrated in the instrument. The energy resolution of this spectral system was 136 eV). The EDS comparison images include the distribution of all elements (Figs. b, f, j), Al elemental distribution (Figs. c, g, k), and Pt elemental distribution (Figs. d, h, l). It can be clearly observed that the surface Pt particles of the rod-shaped, nanoflower-shaped, and rhomboid sheet-shaped catalysts are relatively uniform, mainly exposing the

[200] crystal planes, and exhibiting a highly dispersed state, indicating that the preparation method of the present invention can better disperse the active sites.

[0047] Figure 4 The catalysts prepared in Examples 1-5 and the nitrogen adsorption-desorption isotherms and pore size distribution diagrams compared with Comparative Example 1 are shown (tested using Quantachrome Autosorb IQ from Quanta Computer to analyze structural parameters such as specific surface area and pore size distribution of the samples. Before testing, the catalysts need to be pretreated at 300 °C for 4 h). Figure 4 It can be observed that all several catalysts exhibit distinct type IV N2 adsorption-desorption isotherms, and all have microporous structures. Figure 4 b. It can be observed that the pore size of several catalysts is mesoporous. Among them, the nano-sized catalyst has more micropores. Overall, the morphology adjustment has a greater impact on the specific surface area and pore structure of the catalyst, which is beneficial to the control of the active specific surface area of ​​the catalyst.

[0048] Figure 5 The graphs show the relationship between the amount of NH3 desorption and temperature in the NH3-TPD test of the catalysts prepared in Examples 1-5 and Comparative Example 1. It can be observed that the acidity of the catalyst changes with the morphology. The commercial alumina catalyst in Comparative Example 1 has the largest acidity and is more likely to initiate side reactions such as cracking and deep dehydrogenation. The rhomboid plate catalyst in Example 5 has the smallest acidity.

[0049] The catalyst evaluation results are shown in Table 1: Table 1. Propane dehydrogenation performance of Pt-Sn / γ-Al2O3 catalysts with different morphologies prepared in Examples 1-5 Catalyst morphology Particles Rod-shaped Nanoflower-like filamentous rhombus flake Initial conversion of propane / % 10.1 15.1 13.8 6.6 18.6 Initial selectivity of propylene / % 97.4 98.2 98.2 95.0 98.7 See further Figure 6It can be observed that the catalysts with morphologically controlled supports in Examples 1-5, compared with the commercial alumina catalyst in Comparative Example 1, show that morphological control significantly improves dehydrogenation activity. The synthesized catalysts still exhibit propylene selectivity of over 98% even with a catalyst dosage of only 0.1 g. Among them, the rhombic sheet-like catalyst in Example 5 has a propane conversion rate as high as 18.6% and a propylene selectivity as high as 98.7%, with the slowest deactivation rate, making it the best-performing catalyst. This is due to its good Pt dispersion, low acidity, and fewer side reactions. The catalyst with the nanoflower-like support in Example 3 has high initial performance but deactivates the fastest. This is because the nanoflower structure has many micropores, which is not conducive to Pt dispersion and mass transfer. Furthermore, the interaction between Pt and the support is weak, leading to easy sintering and aggregation. The filamentous catalyst in Example 4 has slightly lower initial activity than the commercial alumina in Comparative Example 1, but the overall activity difference is not significant.

[0050] Figure 7 As shown in Figure a, the rhomboid-shaped catalyst in Example 5 still maintains a distinct γ-Al₂O₃ structure after five regeneration cycles. Furthermore, no characteristic diffraction peaks corresponding to Pt and Sn were observed in the figure, indicating that the Pt dispersion remained relatively good after the reaction. Additionally, calculations using the Scherrer equation revealed a slight increase in catalyst grain size after the reaction, indicating that some metal underwent sintering and growth, but this was not significant. Figure 7 As can be seen from Example 5, after one reaction and five regeneration cycles, the amount of carbon deposited by the rhomboid catalyst is not much different. Most of the carbon deposits are below 550 °C, and these carbon deposits can be eliminated during regeneration. Only a small amount of carbon deposits above 550 °C are difficult to eliminate, and the amount of these carbon deposits is also relatively small. The catalyst has good anti-carbon deposit performance.

[0051] It can be seen that the catalyst in this invention, compared with commercial alumina, exhibits significantly improved propane dehydrogenation activity after morphology adjustment, while also possessing high resistance to coking.

[0052] The embodiments described above are merely examples of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention.

Claims

1. Catalysts supported on Pt groups in alumina with different morphologies, characterized in that, The active component is Pt-Sn, and the support is γ-Al2O3 in the form of particles, rods, nanoflowers, filaments, or rhomboid sheets. The mass of the active component is calculated in terms of metal elements, and the mass of the support is calculated in terms of γ-Al2O3. Pt is 0.5 wt.% of the support weight and Sn is 1 wt.% of the support weight.

2. The method for preparing Pt-based catalysts with different morphologies of alumina according to claim 1, characterized in that, The support is γ-Al2O3 in the form of particles, rods, nanoflowers, or filaments; specifically, it includes the following steps: Step 1: Dissolve the aluminum source in deionized water to obtain an aqueous solution of the aluminum source; Step 2: Weigh the precipitant, dissolve it in deionized water, and let it stand for 30 minutes to obtain an aqueous solution of the precipitant; Step 3: Add the precipitant aqueous solution to the aluminum source aqueous solution and stir to mix; Step 4: Pour the mixed solution into a hydrothermal reactor for crystallization; Step 5: After crystallization is complete and the product has cooled to room temperature, centrifuge, wash, and dry the product. Step 6: Grind and calcine the product to obtain γ-Al2O3; Step 7: Pt and Sn sources are impregnated onto γ-Al2O3 using an evaporation impregnation method. After impregnation, the mixture is dried at 80-100 °C for 8-12 h, and then calcined in a muffle furnace at 500-600 °C for 2-4 h to obtain granular, rod-shaped, nano-flower-like, and filamentous Pt-Sn / γ-Al2O3 catalysts.

3. The preparation method according to claim 2, characterized in that, In step one, the aluminum source is one or a combination of several of Al(NO3)3·9H2O, Al2(SO4)3·18H2O, and AlCl3·6H2O. The molar ratio of aluminum source to deionized water is 1-2 : 110-250; In step two, the precipitant is one or a combination of CO(NH2)2 and (NH4)2CO3. The molar ratio of precipitant to deionized water is 1:12-30; The molar ratio of the aluminum source in step one to the precipitant in step two is 1:3-9.

4. The preparation method according to claim 2, characterized in that, In the preparation of filamentous Pt-Sn / γ-Al2O3 catalyst, in step one, after dissolving the aluminum source in deionized water to obtain an aqueous solution of the aluminum source, 0.5-1 ml of an aqueous solution of 1-butyl-2,3-dimethylimidazolium chloride with a concentration of 0.5 g / ml is added.

5. The preparation method according to claim 2, characterized in that, In step five, the product after crystallization is washed 3-4 times with 30-50 mL of deionized water, filtered, and the solid product is dried in an 80 ℃ oven for 8-12 h; the precursor ground to a powder larger than 80 mesh in step six is ​​placed in a muffle furnace and heated to 500-600 ℃ at 2 ℃ / min, and calcined for 2-6 h to obtain γ-Al2O3.

6. The preparation method according to claim 2, characterized in that, In step seven, the co-impregnation solution is prepared first: 0.5 wt.% Pt source and 1 wt.% Sn source are added to 2-5 ml of anhydrous ethanol and allowed to stand for 60 min. The Pt source is H2PtCl6·6H2O, and the Sn source is SnCl2·2H2O. Then, 1-3 g of γ-Al2O3 is added to 15-40 ml of anhydrous ethanol, stirred, and then sonicated. Finally, the anhydrous ethanol solution of γ-Al2O3 is placed in an oil bath, and the co-impregnation solution is added dropwise to the anhydrous ethanol solution of γ-Al2O3 at a rate of 2 drops / second. After the addition is complete, the mixture is heated at 90 °C for 2-4 h to impregnate the Pt and Sn sources onto the γ-Al2O3.

7. The method for preparing Pt-based catalysts with different morphologies of alumina according to claim 1, characterized in that, The support is rhomboid sheet-like γ-Al2O3; specifically, the following steps are included: Step S1: High-purity aluminum shavings react with n-pentanol to produce aluminum alkoxy; Step S2: Hydrolysis and crystallization of alkoxyaluminum to prepare the precursor pseudoboehmite; Step S3: The precursor is dried, ground, and calcined to obtain γ-Al2O3; Step S4: Pt source and Sn source are impregnated onto γ-Al2O3 by evaporation impregnation. After impregnation, the mixture is dried at 100 °C overnight and then calcined in a muffle furnace at 500-600 °C for 2-4 h to obtain rhomboid plate-shaped Pt-Sn / γ-Al2O3 catalyst.

8. The preparation method according to claim 7, characterized in that, In step S1, aluminum shavings are placed in a three-necked flask containing n-pentanol, wherein the molar ratio of aluminum shavings to n-pentanol is 0.9-1.2 : 2.7-3.6, and reflux is added. The reaction is carried out at 130-150℃ for 4-6 h.

9. The preparation method according to claim 7, characterized in that, The specific steps of step S2 are as follows: Step S21: Heat aluminum alkoxy to 90-100 °C and stir at 500 r / min. Add deionized water dropwise to start hydrolysis. The molar ratio of deionized water to aluminum is 1.8-5.7 : 0.07-0.22, and the dropping rate of deionized water is 1 drop / second. Step S22: After the deionized water is added dropwise, continue stirring at 90-100 °C for 1 h to end the hydrolysis and then cool down; Step S23: After cooling to room temperature, take the lower layer of white slurry into a hydrothermal reactor, add 18-54 ml of deionized water, and crystallize at 120-180 ℃ for 12-24 h. The crystallized product is the precursor pseudoboehmite.

10. The application of the Pt-based catalysts with different morphologies of alumina supported by any one of claims 1-9 in the propane dehydrogenation reaction.

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