A platinum-based catalyst for the dehydrogenation of cyclohexane and a process for its preparation

Abstract

This invention relates to the field of catalyst technology and discloses a platinum-based catalyst for cyclohexane dehydrogenation and its preparation process. The invention first prepares a titanium dioxide-nitrogen-doped graphene composite support via a microwave hydrothermal method, then loads platinum and rhenium metal precursors onto the support, and finally forms platinum-rhenium alloy nanoparticles under mild conditions using a UV-assisted chemical reduction method. After post-treatment, the platinum-based catalyst for cyclohexane dehydrogenation is obtained. This invention creatively constructs a composite structure with titanium dioxide nanoparticles as the core, nitrogen-doped graphene as the shell, and platinum-rhenium alloy nanoparticles positioned at the interface. Utilizing the stabilizing effect of the titanium dioxide core, the conductive and anchoring function of the nitrogen-doped graphene shell, and the synergistic catalytic effect of the platinum-rhenium alloy, a significant improvement in the catalyst activity, selectivity, and stability in the cyclohexane dehydrogenation reaction is achieved. This method is green, safe, and simple to operate, and the resulting catalyst exhibits excellent catalytic performance.

Description

Technical Field

[0001] This invention relates to the field of catalyst technology, specifically to a platinum-based catalyst for cyclohexane dehydrogenation and its preparation process. Background Technology

[0002] Cyclohexane dehydrogenation is a crucial industrial process for producing benzene and hydrogen, widely used in the petrochemical and fine chemical industries. Benzene, as a fundamental chemical raw material, holds an irreplaceable position in industries such as synthetic fibers, plastics, rubber, pharmaceuticals, and pesticides. The cyclohexane dehydrogenation reaction is strongly endothermic and typically occurs at high temperatures, placing high demands on the activity, selectivity, and stability of the catalyst.

[0003] Currently, the most commonly used cyclohexane dehydrogenation catalysts in industry are mainly noble metal catalysts, among which platinum (Pt)-based catalysts have attracted much attention due to their excellent dehydrogenation activity and benzene selectivity. Traditional platinum-based catalysts typically use alumina, silica, or activated carbon as supports, and platinum nanoparticles are loaded via impregnation. However, several problems still exist in the practical application of this type of catalyst: First, platinum metal is prone to sintering and migration at high temperatures, leading to a reduction in active sites and catalyst deactivation; second, there is still room for improvement in the selectivity of the catalyst for benzene, and byproducts such as cracked gas and carbon deposits can affect product purity and catalyst lifetime; third, the dispersion of platinum in traditional preparation processes is not high, resulting in low utilization and waste of precious metal resources.

[0004] Several improvement strategies have been developed in the prior art. Publication No. CN111686718B discloses a cyclohexane dehydrogenation catalyst and its preparation method. The catalyst is a metal-supported catalyst, comprising a metal active component and a support. The metal active component is Pt, and the support is γ-Al₂O₃. This invention increases the steric hindrance of the metal-supported compound in the impregnation solution through ammonia complexation. Furthermore, alkaline conditions can further reduce the active metal loading rate, prevent metal particle aggregation, and improve the dispersibility and uniformity of the catalyst's active component. However, while traditional alumina (Al₂O₃) supports have a high specific surface area, their surface acidic sites are prone to initiating side reactions such as cracking and isomerization, affecting the selectivity of benzene.

[0005] Therefore, developing a platinum-based cyclohexane dehydrogenation catalyst with high activity, high selectivity, good dispersibility of platinum-based active materials, and simple preparation process and reasonable cost is of great industrial significance and application prospect. Summary of the Invention

[0006] (a) Technical problems to be solved:

[0007] To address the shortcomings of existing technologies, this invention provides a platinum-based catalyst for cyclohexane dehydrogenation and its preparation process, solving problems such as low activity, insufficient selectivity, and inadequate stability of traditional catalysts.

[0008] (II) Technical Solution:

[0009] A platinum-based catalyst for cyclohexane dehydrogenation, comprising a titanium dioxide-nitrogen-doped graphene composite support and a platinum-based active component supported thereon.

[0010] The titanium dioxide-nitrogen-doped graphene composite carrier consists of a core and a shell, wherein the core is titanium dioxide nanoparticles and the shell is a nitrogen-doped graphene layer.

[0011] The platinum-based active component is platinum-rhenium alloy nanoparticles with an average particle size of 1-3 nm.

[0012] The platinum-based active component is located between the nitrogen-doped graphene outer shell and the titanium dioxide core.

[0013] Furthermore, in the platinum-rhenium alloy nanoparticles, the molar ratio of rhenium to platinum is (0.1-0.5):1.

[0014] Furthermore, the preparation process of the platinum-based catalyst for cyclohexane dehydrogenation includes the following steps:

[0015] S1. Preparation of composite carrier:

[0016] Titanium dioxide nanoparticles were dispersed in water, and graphene oxide and a nitrogen source were added. The mixture was ultrasonically stirred for 1-2 hours to obtain a mixture. The mixture was then added to a microwave hydrothermal reactor and microwaved at 150-200℃ for 2-4 hours. After cooling, the supernatant was removed by centrifugation. The mixture was washed three times alternately with deionized water and anhydrous ethanol to obtain a titanium dioxide-nitrogen-doped graphene composite carrier.

[0017] S2, Loaded metal precursor:

[0018] Titanium dioxide-nitrogen-doped graphene composite carrier was added to ethanol and ultrasonically dispersed for 30-60 min. Then ammonium perrhenate and chloroplatinic acid were added, and ultrasonic treatment was continued for 30-60 min. Then the mixture was stirred at room temperature in the dark for 1-2 h to obtain a slurry loaded with metal precursors.

[0019] S3, UV-assisted chemical reduction:

[0020] Sodium borohydride was added to the slurry loaded with the metal precursor under a nitrogen atmosphere, and the mixture was heated to 25-60°C in a water bath. It was then irradiated with ultraviolet light for 2-3 hours to reduce the platinum precursor chloroplatinic acid and the rhenium precursor ammonium perrhenate. Platinum-rhenium alloy nanoparticles were formed at the interface of the composite carrier, yielding the platinum-based active component.

[0021] S4. Post-processing:

[0022] The platinum-based active component of platinum-rhenium alloy nanoparticles loaded on a titanium dioxide-nitrogen-doped graphene composite support was washed three times with deionized water and anhydrous ethanol, dried, and activated by heat treatment to obtain a platinum-based catalyst for cyclohexane dehydrogenation.

[0023] Furthermore, the nitrogen source in S1 is one of urea, melamine, ammonia, polyaniline, or ethylenediamine.

[0024] Furthermore, the mass ratio of titanium dioxide nanoparticles, water, graphene oxide, and nitrogen source in S1 is 10:(800-1200):(15-25):(40-80).

[0025] Furthermore, the mass-to-volume ratio of titanium dioxide-nitrogen-doped graphene composite support to ethanol in S2 is 10:(100-200); the molar ratio of ammonium perrhenate to chloroplatinic acid in S2 is (0.1-0.5):1; and the amount of chloroplatinic acid added is such that platinum accounts for 0.5-3% of the total mass of the catalyst.

[0026] Furthermore, the amount of sodium borohydride added in S3 is 2-5 times the total molar amount of ammonium perrhenate and chloroplatinic acid.

[0027] Furthermore, the dominant wavelength of ultraviolet light in S3 is 254nm, and the power is 100-160W.

[0028] Furthermore, in S4, the heat treatment activation method is as follows: under a hydrogen atmosphere, the dried product is reduced at 130℃ for 2 hours and then at 300-400℃ for 2-5 hours.

[0029] (III) Beneficial technical effects:

[0030] 1. This invention first prepares a titanium dioxide-nitrogen-doped graphene composite support by microwave hydrothermal method, then loads platinum and rhenium metal precursors on the support, and finally forms platinum-rhenium alloy nanoparticles under mild conditions by ultraviolet light-assisted chemical reduction method, and then obtains a platinum-based catalyst for cyclohexane dehydrogenation after post-processing.

[0031] 2. This invention creatively constructs a composite structure with titanium dioxide nanoparticles as the core, nitrogen-doped graphene as the shell, and platinum-rhenium alloy nanoparticles positioned at the interface. This design achieves multiple synergistic enhancement effects: the titanium dioxide core stabilizes the metal particles and modulates their electronic properties through metal-carrier interactions; the nitrogen-doped graphene shell not only provides highly conductive channels to promote electron transfer, but its surface nitrogen defect sites also serve as efficient metal anchoring points, preventing metal sintering and ensuring high dispersion of the active components; the precise positioning of the platinum-rhenium alloy nanoparticles at the core-shell interface allows them to be simultaneously electronically regulated by titanium dioxide and physically confined by graphene, enabling rapid desorption of benzene molecules, fundamentally improving selectivity and anti-carbon deposition capabilities, and achieving a synergistic enhancement of activity, selectivity, and stability.

[0032] 3. This invention employs a green preparation process—ultraviolet light-assisted chemical reduction—that utilizes photogenerated electrons to instantaneously and synchronously reduce platinum and rhenium precursors under mild conditions, fundamentally suppressing metal migration and Ostwald ripening caused by traditional high-temperature thermal reduction. This process results in platinum-rhenium alloy nanoparticles with an average particle size of 1-3 nm, uniform size distribution, and high atomic utilization, providing precise structural assurance for the high performance of the catalyst. Furthermore, this process eliminates the need for flammable and explosive hydrogen or strong reducing agents, ensuring high production safety and environmental friendliness.

[0033] 4. This invention introduces rhenium as a co-catalyst to form an alloy with platinum. The addition of rhenium, through electronic and geometric effects, further optimizes the d-band center position of platinum, adjusts the adsorption / desorption energy barriers for reactants and products, significantly improves the selectivity of benzene, effectively suppresses carbon deposition side reactions, and extends the catalyst lifespan.

[0034] 5. This invention utilizes a microwave-assisted hydrothermal method to synthesize a composite support in one step, resulting in a simple and efficient process. The uniformity and speed of microwave heating ensure the in-situ growth and complete coating of nitrogen-doped graphene on the surface of titanium dioxide particles. The resulting composite support has a stable structure and uniform composition, laying the foundation for a high-performance catalyst. This efficient preparation method significantly shortens the process flow, reduces energy consumption, and has promising prospects for industrial application.

[0035] 6. The platinum-based catalyst for cyclohexane dehydrogenation prepared in this invention has a robust mechanical framework provided by its titanium dioxide core, while the nitrogen-doped graphene layer surrounding it acts like a tough "armor," effectively preventing the support structure from breaking and pulverizing during intense reactions and regeneration cycles. This excellent physical stability ensures that the catalyst maintains its intact morphology after multiple recyclings, which is the foundation for recycling and reuse. Positioning platinum-rhenium alloy nanoparticles at the interface between the core and the shell, this structure achieves dual anchoring of active sites through the synergistic effect of the two support materials. During reaction, regeneration, and even recycling, the metal nanoparticles are less likely to detach from the support, migrate, or sinter and grow, ensuring that active sites are not easily lost during recycling, and the recovered catalyst can still maintain high activity. Attached Figure Description

[0036] Figure 1 Activation energy diagrams of methylcyclohexane dehydrogenation catalyzed by platinum-based catalysts in the examples and comparative examples of cyclohexane dehydrogenation.

[0037] Figure 2 The average particle size diagram shows the platinum-based catalysts used for cyclohexane dehydrogenation in the examples and comparative examples. Detailed Implementation

[0038] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0039] Example 1:

[0040] A method for preparing a platinum-based catalyst for cyclohexane dehydrogenation includes the following steps:

[0041] S1. Preparation of composite carrier:

[0042] Ten parts by weight of titanium dioxide nanoparticles were dispersed in 1000 parts by weight of water, and 20 parts by weight of graphene oxide and 60 parts by weight of urea were added. The mixture was ultrasonically stirred for 1 hour to obtain a mixture. The mixture was added to a microwave hydrothermal reactor and microwaved at 160°C for 3 hours. After cooling, the supernatant was removed by centrifugation. The mixture was washed three times alternately with deionized water and anhydrous ethanol to obtain a titanium dioxide-nitrogen-doped graphene composite carrier.

[0043] S2, Loaded metal precursor:

[0044] Ten parts by weight of titanium dioxide-nitrogen-doped graphene composite carrier were added to 150 parts by weight of ethanol and ultrasonically dispersed for 40 min. Then, 0.13 parts by weight of ammonium perrhenate and 0.55 parts by weight of chloroplatinic acid were added, and ultrasonic treatment was continued for 50 min. Then, the mixture was stirred at room temperature in the dark for 1 h to obtain a slurry loaded with metal precursors.

[0045] S3, UV-assisted chemical reduction:

[0046] The slurry of the loaded metal precursor obtained in S2 was subjected to nitrogen atmosphere protection, and 0.27 parts by weight of sodium borohydride were added. The mixture was heated to 40°C in a water bath and then irradiated with ultraviolet light with a main wavelength of 254 nm and a power of 120 W for 2 hours to reduce the platinum precursor chloroplatinic acid and the rhenium precursor ammonium perrhenate. Platinum-rhenium alloy nanoparticles were formed at the interface of the composite support, and platinum-based active components were obtained.

[0047] S4. Post-processing:

[0048] The platinum-based active component of platinum-rhenium alloy nanoparticles loaded on a titanium dioxide-nitrogen-doped graphene composite support was washed three times alternately with deionized water and anhydrous ethanol, dried, and then reduced at 130°C for 2 h and 300°C for 5 h under a hydrogen atmosphere to obtain a platinum-based catalyst for cyclohexane dehydrogenation.

[0049] Example 2:

[0050] A method for preparing a platinum-based catalyst for cyclohexane dehydrogenation includes the following steps:

[0051] S1. Preparation of composite carrier:

[0052] Ten parts by weight of titanium dioxide nanoparticles were dispersed in 800 parts by weight of water, and 15 parts by weight of graphene oxide and 80 parts by weight of ethylenediamine were added. The mixture was ultrasonically stirred for 2 hours to obtain a mixture. The mixture was added to a microwave hydrothermal reactor and microwaved at 200°C for 2 hours. After cooling, the supernatant was removed by centrifugation. The mixture was washed with deionized water and anhydrous ethanol alternately and centrifuged three times to obtain a titanium dioxide-nitrogen-doped graphene composite carrier.

[0053] S2, Loaded metal precursor:

[0054] Ten parts by weight of titanium dioxide-nitrogen-doped graphene composite carrier were added to 100 parts by weight of ethanol and ultrasonically dispersed for 60 min. Then, 0.01 parts by weight of ammonium perrhenate and 0.14 parts by weight of chloroplatinic acid were added, and ultrasonic treatment was continued for 30 min. Finally, the mixture was stirred at room temperature in the dark for 1 h to obtain a slurry loaded with metal precursors.

[0055] S3, UV-assisted chemical reduction:

[0056] The slurry of the loaded metal precursor obtained in S2 was subjected to nitrogen atmosphere protection, and 0.02 parts by weight of sodium borohydride was added. The mixture was heated to 25°C in a water bath and then irradiated with ultraviolet light with a main wavelength of 254 nm and a power of 100 W for 3 hours to reduce the platinum precursor chloroplatinic acid and the rhenium precursor ammonium perrhenate. Platinum-rhenium alloy nanoparticles were formed at the interface of the composite support, and platinum-based active components were obtained.

[0057] S4. Post-processing:

[0058] The platinum-based active component of platinum-rhenium alloy nanoparticles loaded on a titanium dioxide-nitrogen-doped graphene composite support was washed three times alternately with deionized water and anhydrous ethanol, dried, and then reduced at 130°C for 2 h and 400°C for 2 h under a hydrogen atmosphere to obtain a platinum-based catalyst for cyclohexane dehydrogenation.

[0059] Example 3:

[0060] A method for preparing a platinum-based catalyst for cyclohexane dehydrogenation includes the following steps:

[0061] S1. Preparation of composite carrier:

[0062] Ten parts by weight of titanium dioxide nanoparticles were dispersed in 1200 parts by weight of water, and 25 parts by weight of graphene oxide and 40 parts by weight of melamine were added. The mixture was ultrasonically stirred for 2 hours to obtain a mixture. The mixture was added to a microwave hydrothermal reactor and microwaved at 150°C for 4 hours. After cooling, the supernatant was removed by centrifugation. The mixture was washed with deionized water and anhydrous ethanol alternately and centrifuged three times to obtain a titanium dioxide-nitrogen-doped graphene composite carrier.

[0063] S2, Loaded metal precursor:

[0064] Ten parts by weight of titanium dioxide-nitrogen-doped graphene composite carrier were added to 200 parts by weight of ethanol and ultrasonically dispersed for 30 min. Then, 0.24 parts by weight of ammonium perrhenate and 0.96 parts by weight of chloroplatinic acid were added, and ultrasonic treatment was continued for 60 min. Finally, the mixture was stirred at room temperature in the dark for 2 h to obtain a slurry loaded with metal precursors.

[0065] S3, UV-assisted chemical reduction:

[0066] The slurry of the loaded metal precursor obtained in S2 was subjected to nitrogen atmosphere protection, and 0.52 parts by weight of sodium borohydride were added. The mixture was heated to 60°C in a water bath and then irradiated with ultraviolet light with a main wavelength of 254 nm and a power of 160 W for 3 h to reduce the platinum precursor chloroplatinic acid and the rhenium precursor ammonium perrhenate. Platinum-rhenium alloy nanoparticles were formed at the interface of the composite support, and platinum-based active components were obtained.

[0067] S4. Post-processing:

[0068] The platinum-based active component of platinum-rhenium alloy nanoparticles supported on a titanium dioxide-nitrogen-doped graphene composite support was washed three times with deionized water and anhydrous ethanol, dried, and then reduced at 130°C for 2 h and 300°C for 4 h under a hydrogen atmosphere to obtain a platinum-based catalyst for cyclohexane dehydrogenation.

[0069] Comparative Example 1: The difference from Example 1 is that titanium dioxide nanoparticles are not added in the step of preparing the composite support in S1.

[0070] Comparative Example 2: The difference from Example 1 is that the composite support is prepared without adding a nitrogen source in step S1.

[0071] Comparative Example 3: The difference from Example 1 is that the composite carrier was prepared by physical mixing.

[0072] S1. Preparation of the carrier: 20 parts by weight of graphene oxide and 60 parts by weight of urea were dispersed in 900 parts by weight of water and ultrasonically stirred for 1 hour to obtain a mixture. The mixture was added to a microwave hydrothermal reactor and microwaved at 160°C for 3 hours. After cooling, the supernatant was removed by centrifugation. The mixture was washed and centrifuged three times alternately with deionized water and anhydrous ethanol to obtain a nitrogen-doped graphene composite carrier. 10 parts by weight of titanium dioxide nanoparticles dispersed in 100 parts by weight of ethanol were added to obtain a physically mixed carrier.

[0073] The other methods and steps are the same as in Example 1.

[0074] Comparative Example 4: The difference from Example 1 is that ammonium perrhenate is not added in the step of loading the metal precursor in S2.

[0075] Comparative Example 5: The difference from Example 1 is that S3 does not use ultraviolet light-assisted chemical reduction, but uses conventional H2 thermal reduction.

[0076] S3. Chemical reduction without ultraviolet light: The slurry of the metal precursor obtained in S2 is mixed with 0.25 parts by weight of sodium borohydride under a hydrogen atmosphere, heated to 400°C, and stirred for 2 hours to obtain the platinum-based active component.

[0077] The other methods and steps are the same as in Example 1.

[0078] In Examples 1-3 and Comparative Examples 1-5, the platinum-based catalyst for cyclohexane dehydrogenation was evaluated using the following method: 50 mg of catalyst #1 was weighed and uniformly mixed with 0.5 g of 40-60 mesh quartz sand. The mixture was placed in a quartz reaction tube, and a hydrogen-nitrogen mixture with a total volume flow rate of 60 mL / min and a hydrogen volume concentration of 10% was introduced. The mixture was pretreated at 400°C for 1 h. After pretreatment, the reactor temperature was set to 300°C, and nitrogen was purged at 15 mL / min for 30 min. Then, nitrogen was introduced and the methylcyclohexane feed pump was turned on at a flow rate of 0.02 mL / min and a methylcyclohexane feed volume concentration of 19%. Methylcyclohexane and nitrogen were premixed in a preheating furnace at a temperature of 120°C. Samples were taken periodically during the reaction, and the composition of the products was analyzed using gas chromatography.

[0079] Table 1. Test results of platinum-based catalysts for cyclohexane dehydrogenation

[0080]

[0081] The platinum-based catalysts for cyclohexane dehydrogenation in Examples 1-3 possess a three-in-one synergistic catalytic system of "core-shell-interface." The core of this system lies in constructing a composite support with titanium dioxide as the core and nitrogen-doped graphene as the shell, precisely positioning platinum-rhenium alloy nanoparticles at the interface between the two. The titanium dioxide core provides a robust anchor for the metal particles through strong metal-support interactions, effectively suppressing sintering at high temperatures. The nitrogen-doped graphene shell not only promotes electron transfer with its high conductivity but also strongly fixes the metal precursor at its nitrogen-deficient sites, ensuring high dispersion of active sites. The alloy formed by platinum and rhenium modulates the d-band center of platinum through electronic effects, optimizing the adsorption behavior of reactants and products, enabling rapid desorption of benzene molecules, thus achieving both high activity and high benzene selectivity at the source.

[0082] The platinum-based catalysts for cyclohexane dehydrogenation in Examples 1-3 were prepared using a green process called UV-assisted chemical reduction. This process utilizes photogenerated electrons to instantaneously and synchronously reduce the precursors of platinum and rhenium under mild conditions, fundamentally suppressing metal migration and Ostwald ripening caused by traditional high-temperature thermal reduction. This allows for the precise construction of ultrafine and uniform active sites at the platinum-rhenium alloy interface. Ultimately, the stability of the support structure, the intrinsic high selectivity of the active components, and the precise control of the microstructure by the preparation process are deeply coupled, producing a synergistic effect of "1+1+1>3", jointly overcoming the challenge of simultaneously achieving activity, selectivity, and stability in the cyclohexane dehydrogenation reaction.

[0083] The difference between Comparative Example 1 and Example 1 is that the step of preparing the composite support in S1 does not involve the addition of titanium dioxide nanoparticles. The resulting catalyst loses the core function of the titanium dioxide nanoparticle core and lacks the crucial strong metal-support interaction between titanium dioxide and the metal. Consequently, the platinum-rhenium nanoparticles lack solid anchoring points in the high-temperature reaction environment, making them highly susceptible to migration, agglomeration, and sintering, leading to a rapid reduction in active sites and a sharp decline in stability. Furthermore, from an electronic effect perspective, the modulating effect of titanium dioxide on the electronic structure of platinum also disappears, making it impossible to optimize the intrinsic activity and selectivity of the active sites.

[0084] The difference between Comparative Example 2 and Example 1 is that the composite support preparation step in S1 does not involve adding a nitrogen source, resulting in the catalyst losing the anchoring sites provided by nitrogen doping. Undoped graphene oxide has a strong chemical inertness on its surface, making it unable to effectively immobilize the metal precursor. During reduction, metal atoms easily migrate freely and aggregate into larger, more uneven particles, leading to a significant reduction in the metal dispersion of the catalyst and an insufficient total number of exposed active sites, thus directly causing a decrease in catalytic activity.

[0085] The difference between Comparative Example 3 and Example 1 lies in the fact that the composite support was prepared through physical mixing. The resulting catalyst could not construct a precise "core-shell-interface" structure solely through physical mixing. The interaction between titanium dioxide and graphene was merely a simple physical contact, rather than a tight coupling at the atomic level. This leads to two serious consequences: first, the expected synergistic stabilizing effect and electronic modulation effect are significantly weakened; second, the active metal cannot be precisely confined to the optimal interfacial environment and may be randomly distributed on any support, meaning that most active sites are not in the optimal catalytic microenvironment, resulting in low overall efficiency.

[0086] The difference between Comparative Example 4 and Example 1 is that ammonium perrhenate was not added in the S2 step of supporting the metal precursor. The resulting catalyst lacked rhenium. This absence of rhenium prevented platinum from achieving crucial electronic modulation, and its d-band center could not be optimized to the ideal position. This led to excessive adsorption of benzene products, making desorption difficult. This not only reduced benzene selectivity but also promoted deep dehydrogenation and coking. Coking covering the active sites is the fundamental reason why its stability is far inferior to that of the examples, resulting in poorer selectivity and stability.

[0087] The difference between Comparative Example 5 and Example 1 is that S3 did not use ultraviolet light-assisted chemical reduction, but instead used conventional H2 thermal reduction. The resulting catalyst exhibited poor performance due to inherent defects in the preparation process. The high-temperature thermal reduction process provided excessively high migration energy to the metal atoms, leading to Ostwald ripening of the platinum-rhenium alloy particles. This resulted in significant grain coarsening and uneven distribution, reducing the number of active sites and decreasing intrinsic activity, thus affecting both the initial activity and selectivity of the catalyst.

[0088] The above are merely specific embodiments of the present invention, but the technical features of the present invention are not limited thereto. Any simple changes, equivalent substitutions, or modifications made based on the present invention to solve essentially the same technical problems and achieve essentially the same technical effects are all covered within the protection scope of the present invention.

Claims

1. A platinum-based catalyst for the dehydrogenation of cyclohexane, characterized in that, The platinum-based catalyst for cyclohexane dehydrogenation comprises a titanium dioxide-nitrogen-doped graphene composite support and a platinum-based active component supported thereon. The titanium dioxide-nitrogen-doped graphene composite carrier consists of a core and a shell, wherein the core is titanium dioxide nanoparticles and the shell is a nitrogen-doped graphene layer. The platinum-based active component is platinum-rhenium alloy nanoparticles with an average particle size of 1-3 nm; The platinum-based active component is positioned between the nitrogen-doped graphene outer shell and the titanium dioxide core; The preparation process of the platinum-based catalyst for cyclohexane dehydrogenation includes the following steps: S1. Preparation of composite carrier: Titanium dioxide nanoparticles were dispersed in water, graphene oxide and a nitrogen source were added, and the mixture was ultrasonically stirred for 1-2 hours to obtain a mixture. The mixture was then added to a microwave hydrothermal reactor and microwaved at 150-200℃ for 2-4 hours. After cooling, the supernatant was removed by centrifugation, and the mixture was washed and centrifuged three times alternately with deionized water and anhydrous ethanol to obtain a titanium dioxide-nitrogen-doped graphene composite carrier. S2, Loaded metal precursor: Titanium dioxide-nitrogen-doped graphene composite carrier was added to ethanol and ultrasonically dispersed for 30-60 min. Then ammonium perrhenate and chloroplatinic acid were added, and ultrasonic treatment was continued for 30-60 min. Then the mixture was stirred at room temperature in the dark for 1-2 h to obtain a slurry loaded with metal precursors. S3, UV-assisted chemical reduction: Sodium borohydride was added to the slurry loaded with metal precursors under a nitrogen atmosphere, and the mixture was heated to 25-60°C in a water bath and then irradiated with ultraviolet light for 2-3 hours to reduce the platinum precursor chloroplatinic acid and the rhenium precursor ammonium perrhenate. Platinum-rhenium alloy nanoparticles were formed at the interface of the composite support, and platinum-based active components were obtained. S4. Post-processing: The platinum-based active component of platinum-rhenium alloy nanoparticles loaded on a titanium dioxide-nitrogen-doped graphene composite support was washed three times with deionized water and anhydrous ethanol, dried, and activated by heat treatment to obtain a platinum-based catalyst for cyclohexane dehydrogenation.

2. The platinum-based catalyst for the dehydrogenation of cyclohexane according to claim 1, characterized in that, In the platinum-rhenium alloy nanoparticles, the molar ratio of rhenium to platinum is (0.1-0.5):

1.

3. The platinum-based catalyst for cyclohexane dehydrogenation according to claim 1, characterized in that, The nitrogen source in S1 is one of urea, melamine, ammonia, polyaniline, or ethylenediamine.

4. The platinum-based catalyst for the dehydrogenation of cyclohexane according to claim 1, characterized in that, The mass ratio of titanium dioxide nanoparticles, water, graphene oxide, and nitrogen source in S1 is 10:(800-1200):(15-25):(40-80).

5. The platinum-based catalyst for the dehydrogenation of cyclohexane according to claim 1, characterized in that, The mass-volume ratio of titanium dioxide-nitrogen-doped graphene composite support and ethanol in S2 is 10:(100-200); the molar ratio of ammonium perrhenate to chloroplatinic acid in S2 is (0.1-0.5):1; the amount of chloroplatinic acid added is such that platinum accounts for 0.5-3% of the total mass of the catalyst.

6. The platinum-based catalyst for cyclohexane dehydrogenation according to claim 1, characterized in that, The amount of sodium borohydride added in S3 is 2-5 times the total molar amount of ammonium perrhenate and chloroplatinic acid.

7. The platinum-based catalyst for the dehydrogenation of cyclohexane according to claim 1, characterized in that, The dominant wavelength of the ultraviolet light in S3 is 254nm, and the power is 100-160W.

8. The platinum-based catalyst for the dehydrogenation of cyclohexane according to claim 1, characterized in that, In S4, the heat treatment activation method is as follows: under a hydrogen atmosphere, the dried product is reduced at 130°C for 2 hours and then at 300-400°C for 2-5 hours.

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