Ni-Al composite oxide supported Pt catalyst for methyl cyclohexane dehydrogenation and preparation method thereof

Abstract

The preparation method comprises the following steps: combining a solvent confinement hydrolysis-polymerization volatilization method with a roasting crystal transformation in-situ metal doping technology to prepare a mesoporous Ni-Al composite oxide carrier with an excellent structure, texture and surface properties, and carrying out in-situ metal doping on the mesoporous Ni-Al composite oxide carrier to prepare the Pt-loaded Ni-Al composite oxide catalyst for dehydrogenation of methylcyclohexane, so as to obtain the Pt-loaded Ni-Al composite oxide catalyst for dehydrogenation of methylcyclohexane. The preparation method comprises the following steps: loading a low-loading-capacity Pt active component by virtue of an impregnation method, realizing highly uniform dispersion and stable immobilization of Pt active sites on the surface of a carrier in a single atomic cluster form by virtue of a strong bonding effect between coordinated unsaturated aluminum species on the surface of the carrier and a Pt precursor, improving an electronic structure of the metal Pt active sites, and preparing the catalyst. The catalytic activity of the catalyst on a low-temperature dehydrogenation reaction of methylcyclohexane is improved. The Pt dispersity of the Ni-Al composite oxide loaded Pt catalyst reaches 60.0% or above, and the Ni-Al composite oxide loaded Pt catalyst shows extremely high catalytic activity, selectivity, stability and reproducible and reusable performance in a low-temperature dehydrogenation reaction of methylcyclohexane.

Description

Technical Field

[0001] This invention belongs to the technical field of inorganic mesoporous catalytic material preparation, and relates to a supported Pt-based mesoporous catalytic material with a well-developed mesoporous structure, high specific surface area and pore volume, large and uniformly distributed mesopores, and highly uniformly dispersed Pt active sites in the form of atomic clusters. The Pt-based catalyst prepared in this invention exhibits extremely high low-temperature catalytic activity, selectivity, stability, and reproducible reusability in the dehydrogenation reaction of methylcyclohexane. Background Art

[0002] Hydrogen energy has the advantages of being clean, efficient, and renewable, making it the best green energy alternative to traditional fossil fuels (Liu M., Issues and opportunities facing hydrolytic hydrogen production materials. Chem. Eng. J ., 2023, 461, 141918). However, how to improve the high-density storage and safe, long-distance transportation of hydrogen has become the key to realizing the "hydrogen society" (Anand C., Green hydrogen for a asustainable future: A review of production methods, innovations, and applications. Int. J. Hydrogen Energy , 2025, 111, 319-341).

[0003] Compared with traditional hydrogen storage technologies, reversible catalytic hydrogenation-dehydrogenation cyclic hydrogen storage technology based on liquid organic hydrogen carriers (LOHCs) has the advantages of high hydrogen storage density, long hydrogen storage cycle, convenient transportation, high safety, and good reversible recycling. It is considered an important way to achieve large-scale, efficient and safe hydrogen storage (Prieto C., A two-step methodology for the selection and process optimization of Liquid Organic Hydrogen Carriers (LOHCs). Int. J. Hydrogen Energy , 2025, 135, 69-85).

[0004] Among the many LOHC hydrogen storage systems, the methylcyclohexane-toluene system has become the focus of current LOHC hydrogen storage due to its excellent cyclic stability, low toxicity, and good compatibility with existing petrochemical industry infrastructure (Gao J., The progress of research based on methylcyclohexane dehydrogenation technology: Areview. Int. J. Hydrogen Energy , 2024, 85, 865-880).

[0005] While current toluene catalytic hydrogenation technology is relatively mature, the catalytic dehydrogenation of methylcyclohexane is highly endothermic, leading to the deactivation of supported metal catalysts at high temperatures (>350°C) due to sintering of the active metal and / or carbon deposition (Yue Y., Active and stable Pt-Ga2O3 / Al2O3 catalyst for dehydrogenation of methylcyclohexane. Catal. Today , 2024, 433, 114688). Therefore, the development of low-temperature dehydrogenation catalysts with high activity, high selectivity and high stability has become the key to the industrial application of methylcyclohexane-toluene hydrogen storage technology.

[0006] The noble metal Pt exhibits excellent catalytic activity and selectivity in the dehydrogenation of methylcyclohexane due to its excellent C-H bond cleavage ability (Wu Y., Insights into size effects of Pt / Al2O3 catalysts on hydrogen production from methylcyclohexane dehydrogenation. Catal. Sci. Technology . 2024, 14, 1791-1801). However, the high price severely limits the practical application of supported Pt-based catalysts.

[0007] Selecting mesoporous alumina with a high specific surface area to support the Pt active component can effectively improve the utilization of Pt atoms while significantly reducing the Pt loading, thereby reducing catalyst preparation costs and improving the catalyst's activity in the low-temperature dehydrogenation of methylcyclohexane (Li C., Efficient and stable dehydrogenation of methylcyclohexane over Pt supported on mesoporous alumina with excellent textural properties. Int. J. Hydrogen Energy , 2024, 74, 297-306). In addition, the introduction of other metal promoters is beneficial to changing the geometric / electronic structure of the Pt active sites loaded on the support surface, thereby improving its catalytic activity for the dehydrogenation of methylcyclohexane (Nakaya Y, Distorted Surface Ensembles in Platinum-Antimony for the Durable Catalytic Dehydrogenation of Methylcyclohexane. JACS Au , 2025, 5, 1956).

[0008] Among many metal additives, Ni has the ability to combine with Pt, x The introduction of species into the support surface can effectively disperse Pt and enhance the dehydrogenation activity of Pt-based catalysts through interfacial charge transfer (Alconada K, Evaluation of bimetallic Pt-Co and Pt-Ni catalysts in LOHC dehydrogenation. Int. J. Hydrogen Energy , 2024, 51, 243-55). However, it is difficult to achieve NiO by traditional impregnation method. x The highly uniform dispersion of species on the support surface cannot significantly improve the low-temperature dehydrogenation catalytic activity of methylcyclohexane of supported Pt-based catalysts by reducing the nickel loading.

[0009] Therefore, how to develop a Ni-Al composite oxide support material with a developed mesoporous structure, a high surface area and a strong bonding interaction with the Pt precursor, so as to achieve highly uniform dispersion of low-loaded Pt in the form of atomic-level or ultra-small nanoclusters, effectively increase the number of Pt active sites, improve the utilization rate of Pt atoms, and achieve the purpose of reducing the catalyst preparation cost and improving the low-temperature dehydrogenation reaction activity and selectivity of the prepared catalyst for methylcyclohexane. At the same time, by improving the mass transfer / heat transfer efficiency of the catalyst, the anti-sintering and anti-carbon deposition properties of the Pt-based catalyst are improved. This has become a core issue that needs to be addressed in the current development of Pt-based catalysts for low-temperature and efficient dehydrogenation of methylcyclohexane. Summary of the Invention

[0010] The purpose of the present invention is to provide a Ni-Al composite oxide-supported Pt catalyst for methylcyclohexane dehydrogenation and a preparation method thereof, so as to achieve highly uniform dispersion of low-loaded Pt active sites in the form of single-atom clusters, thereby significantly improving the low-temperature reaction activity, selectivity, stability and regeneration performance of the supported Pt catalyst in the methylcyclohexane dehydrogenation reaction.

[0011] To achieve the above-mentioned purpose of the invention, the Ni-Al composite oxide supported Pt catalyst for methylcyclohexane dehydrogenation of the present invention is as follows: a hydrolyzate composed of a mixture of anhydrous organic alcohol and deionized water is slowly added dropwise to an anhydrous organic alcohol solution containing an aluminum source, thereby promoting a controlled hydrolysis-polymerization reaction of the aluminum source at the molecular level to obtain an oligomeric aluminum hydroxyl species sol; the aluminum hydroxyl species sol is volatilized to obtain a pseudo-boehmite crystal phase mesoporous alumina material; a nickel salt is loaded on the surface of the mesoporous alumina material by an impregnation method, and metallic nickel atoms are in situ uniformly doped into the pore walls of the mesoporous alumina by a calcination-transformation doping strategy to form Ni-O-Al bonds, thereby obtaining a Pt catalyst. c -Al2O3 crystalline mesoporous Ni-Al composite oxide carrier, loaded with Ni-Al composite oxide loaded Pt catalyst obtained by calcination with chloroplatinic acid and can be used for low-temperature and efficient dehydrogenation of methylcyclohexane.

[0012] The specific surface area of ​​the Ni-Al composite oxide supported Pt catalyst for methylcyclohexane dehydrogenation obtained in the present invention is 400 to 700 m 2 / g, pore volume 0.6~1.2cm 3 / g, with a mesopore diameter of 4.0 to 8.0 nm. It not only has a well-developed mesoporous channel structure, high specific surface area and pore volume, and a large and uniform mesopore diameter, but also has highly uniformly dispersed Pt active sites in the form of single-atom clusters, with a Pt dispersion of more than 60.0%. Therefore, it shows relatively excellent catalytic performance in the low-temperature dehydrogenation reaction of methylcyclohexane, achieving efficient conversion of methylcyclohexane at 300°C, with a maximum dehydrogenation rate of up to 2500 mmol / g. Pt / min or more, and can still maintain more than 80% of the initial catalytic activity during the 100h reaction process or regeneration and repeated use.

[0013] Furthermore, in the Ni-Al composite oxide supported Pt catalyst for methylcyclohexane dehydrogenation of the present invention, the raw aluminum source is one of aluminum isopropoxide, aluminum isobutoxide, aluminum tert-butoxide, aluminum nitrate, aluminum chloride or aluminum sulfate, or a mixture of several of them in any proportion.

[0014] Furthermore, in the Ni-Al composite oxide supported Pt catalyst for methylcyclohexane dehydrogenation of the present invention, the anhydrous organic alcohol is one of methanol, ethanol, isopropanol, ethylene glycol or propylene glycol, or a mixture of several of them in any proportion.

[0015] Furthermore, the anhydrous organic alcohol used to form the hydrolysis solution and the anhydrous organic alcohol used to dissolve the aluminum source can be the same anhydrous organic alcohol or different anhydrous organic alcohols.

[0016] The present invention also provides a method for preparing a Ni-Al composite oxide-supported Pt catalyst suitable for dehydrogenation of methylcyclohexane, the method comprising:

[0017] 1) Dissolve the aluminum source completely in anhydrous organic alcohol at a molar ratio of anhydrous organic alcohol to aluminum source of 20 to 300:1 under stirring at room temperature to obtain a clear aluminum source alcohol solution;

[0018] 2) Mixing 10 to 100 times the molar amount of the aluminum source used in step 1) with deionized water and 10 to 150 times the molar amount of anhydrous organic alcohol to obtain a clarified hydrolyzate;

[0019] 3) Under stirring and reflux conditions at 60-160°C, slowly and uniformly add the hydrolyzate to the aluminum source alcohol solution, maintain the temperature and continue stirring and reflux reaction to promote partial hydrolysis of the aluminum source molecules in the reaction solution while inhibiting the polymerization and cross-linking between the aluminum hydroxyl monomer species obtained by hydrolysis to obtain an oligomeric aluminum hydroxyl species sol;

[0020] 4) The aluminum hydroxyl species sol is volatilized in an open state at 40-100° C. to evaporate the solvent organic alcohol and deionized water to obtain a mesoporous alumina material having a mesoporous structure and a pseudo-boehmite crystal phase;

[0021] 5) According to the molar ratio of aluminum source: nickel salt = 100-500:1, the mesoporous alumina material is placed in an ethanol solution containing nickel salt and stirred evenly, and then dried and calcined at 350-550°C to obtain c -Mesoporous Ni-Al composite oxide support of Al2O3 crystal phase;

[0022] 6) According to the molar ratio of aluminum source: chloroplatinic acid = 300-800:1, the mesoporous Ni-Al composite oxide support is placed in an ethanol solution dissolved with chloroplatinic acid and stirred evenly. After drying, the support is calcined at 400-600° C. to obtain a Ni-Al composite oxide supported Pt catalyst.

[0023] The preparation method of the present invention first uses a homogeneous mixed solution of anhydrous organic alcohol and deionized water as a hydrolyzing solution, and slowly and uniformly adds it dropwise to the organic alcohol solution in which the aluminum source is dissolved during stirring and refluxing at 60-160°C, thereby promoting partial hydrolysis-polymerization and local cross-linking of the aluminum source molecules dispersed between the anhydrous organic alcohol molecules to obtain an oligomeric aluminum hydroxyl species sol.

[0024] Preferably, the above preparation method is more specifically to slowly and uniformly add the hydrolyzate to the aluminum source alcohol solution at a dropping rate of 1.0 to 5.0 mL / min, and continue stirring and refluxing at the maintained temperature for 1 to 4 hours.

[0025] In the above-mentioned preparation method of the present invention, the solvent volatilization treatment is followed by promoting further polymerization and cross-linking of oligomeric aluminum hydroxyl species in the sol, and removing organic pure water molecules present in the mesoporous channels, thereby obtaining a mesoporous alumina material with a developed mesoporous channel structure and a pseudo-boehmite crystal phase.

[0026] Preferably, the above preparation method is more specifically to volatilize the solvent of the aluminum hydroxy species sol in an open state at 40 to 100° C. for 6 to 48 hours.

[0027] In the above preparation method of the present invention, the mesoporous Ni-Al composite oxide carrier is prepared by loading nickel salt by impregnation on the above mesoporous alumina material with developed mesoporous structure and pseudo-boehmite crystal phase, and then undergoing calcination and nickel in-situ doping process.

[0028] Preferably, the preparation method is more specifically to dry the mesoporous alumina material impregnated with nickel salt at 60° C. and then calcinate the material at 350-550° C. for 2-4 hours.

[0029] In the above preparation method of the present invention, a mesoporous Ni-Al composite oxide with a developed mesoporous structure and highly uniformly doped Ni atoms on the pore wall surface at a near-atomic level is ultimately used as a carrier for highly uniform and stable loading of low-loading Pt active components.

[0030] Preferably, the preparation method is more specifically to dry the mesoporous Ni-Al composite oxide support impregnated with chloroplatinic acid at 60° C. and then calcinate it at 400-600° C. for 2-4 hours.

[0031] More preferably, the drying time described in the above preparation method of the present invention should be no less than 24 hours.

[0032] The key to the preparation method of the Ni-Al composite oxide supported Pt catalyst for methylcyclohexane dehydrogenation of the present invention is the preparation of a mesoporous Ni-Al composite oxide support with excellent structure, texture and surface properties.

[0033] By slowly adding the hydrolysis solution drop by drop into the anhydrous organic alcohol solution in which the aluminum precursor is dissolved, the deionized water molecules highly dispersed in the anhydrous organic alcohol and the aluminum precursor molecules highly uniformly dispersed in the solution have a small contact probability, resulting in a slow partial hydrolysis-polymerization reaction of the aluminum precursor molecules and the generation of oligomeric aluminum hydroxyl species; in the subsequent stirring and reflux process, the oligomeric aluminum hydroxyl species are locally cross-linked between the organic alcohol molecules to generate nano-clustered aluminum hydroxyl species; the organic alcohol molecules filling the gaps between the nano-clustered aluminum hydroxyl species are removed by volatilization, combined with further polymerization-cross-linking between the aluminum hydroxyl species, a mesoporous alumina material with a developed mesoporous channel structure and a pseudo-boehmite crystal phase is prepared; and then the material is loaded with nickel salt and calcined, and the mesoporous alumina is transformed from the pseudo-boehmite crystal phase to the c -NiO produced by thermal decomposition of nickel salt during the phase transformation of Al2O3 x The species can be in situ doped on the pore wall surface of mesoporous alumina to obtain a mesoporous Ni-Al composite oxide support material with a developed mesoporous channel structure, high specific surface area and pore volume, and highly uniform Ni atoms doped at the near-atomic level.

[0034] The formation of a large number of Ni-O-Al bonds on the surface leads to the presence of a large number of coordinately unsaturated aluminum species on the surface of the mesoporous Ni-Al composite oxide support, which can interact with the chlorine atoms in the chloroplatinic acid molecules through coordination bonding, thereby achieving highly uniform dispersion of the chloroplatinic acid molecules on the pore wall surface of the mesoporous Ni-Al composite oxide support; through calcination, thermal decomposition of the chloroplatinic acid molecules and hydrogen reduction treatment, the metal Pt active sites are finally highly uniformly dispersed in the form of single-atom clusters on the pore wall surface of the mesoporous Ni-Al composite oxide, resulting in a supported Pt-based mesoporous catalytic material that shows excellent catalytic activity, selectivity, stability and renewable and reusable performance in the low-temperature dehydrogenation reaction of methylcyclohexane.

[0035] The present invention optimizes the solution-sol-gel process, regulates the degree of hydrolysis, polymerization and cross-linking of aluminum source molecules, synthesizes a mesoporous alumina material with a developed mesoporous channel structure and a pseudo-boehmite crystal phase, and uses the calcination crystallization metal doping technology to impregnate the NiO impregnated on the pore wall surface of the pseudo-boehmite phase mesoporous alumina. x Species are uniformly doped in situ into the mesoporous walls of alumina to obtain c-Al2O3 crystal phase and highly uniform dispersion of Ni atoms on the pore wall surface at the near-atomic level. Using this as a carrier, a Ni-Al composite oxide-supported Pt catalyst for methylcyclohexane dehydrogenation with low-loaded Pt active sites in the form of highly uniformly dispersed single-atom clusters was prepared, thereby significantly improving the low-temperature reaction activity, selectivity, stability and reproducible reusability of the supported Pt-based catalyst in the methylcyclohexane dehydrogenation reaction. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 Nitrogen adsorption-desorption isotherm (a) and wide-angle XRD spectrum (b) of mesoporous alumina material.

[0037] Figure 2 (a) N2 adsorption-desorption isotherm and (b) wide-angle XRD spectrum of the mesoporous Ni-Al composite oxide support.

[0038] Figure 3 The mesoporous Ni-Al composite oxide carrier before and after loading chloroplatinic acid 27 Al MAS NMR spectrum.

[0039] Figure 4 (a) Nitrogen adsorption-desorption isotherm and (b) wide-angle XRD spectrum of Ni-Al composite oxide supported Pt catalyst.

[0040] Figure 5 It is the element mapping spectrum of Ni-Al composite oxide supported Pt catalyst.

[0041] Figure 6 This is a spherical aberration corrected HAADF-STEM image of the Ni-Al composite oxide supported Pt catalyst.

[0042] Figure 7 The performance of the low-temperature dehydrogenation reaction of methylcyclohexane before and after regeneration of the Ni-Al composite oxide supported Pt catalyst.

[0043] Figure 8 This is a graph showing the change in methylcyclohexane conversion and dehydrogenation rate over the Ni-Al composite oxide supported Pt catalyst at 300°C as a function of methylcyclohexane feed rate. DETAILED DESCRIPTION

[0044] The following embodiments are only used to more clearly illustrate the technical solutions of the present invention so that those skilled in the art can better understand and utilize the present invention, but are not intended to limit the scope of protection of the present invention.

[0045] Unless otherwise specified, the production processes, experimental methods or detection methods involved in the embodiments of the present invention are all conventional methods in the prior art, and their names and / or abbreviations are conventional names in the field and are very clear and unambiguous in the relevant fields of use. Those skilled in the art can understand the conventional process steps based on the names and apply the corresponding equipment to implement them according to conventional conditions or the conditions recommended by the manufacturer.

[0046] The various instruments, equipment, raw materials or reagents used in the embodiments of the present invention are not particularly limited in their sources and are all conventional products that can be purchased through regular commercial channels or prepared according to conventional methods well known to those skilled in the art.

[0047] The following examples of the present invention are prepared according to the following method for the dehydrogenation of methylcyclohexane using a Ni-Al composite oxide supported Pt catalyst:

[0048] 1) Dissolve the aluminum source completely in anhydrous organic alcohol at a molar ratio of anhydrous organic alcohol to aluminum source of 20 to 300:1 under stirring at room temperature to obtain a clear aluminum source alcohol solution;

[0049] 2) Mixing 10 to 100 times the molar amount of the aluminum source with deionized water and 10 to 150 times the molar amount of anhydrous organic alcohol to obtain a clarified hydrolyzate;

[0050] 3) Under stirring and reflux conditions at 60-160° C., slowly and uniformly add the above hydrolyzate to the above aluminum source alcohol solution at a dropping rate of 1.0-5.0 mL / min, maintain the temperature and continue stirring and reflux for 1-4 hours to promote partial hydrolysis of the aluminum source molecules in the reaction solution while inhibiting the polymerization and cross-linking between the aluminum hydroxyl monomer species obtained by hydrolysis to obtain an oligomeric aluminum hydroxyl species sol;

[0051] 4) In an open state at 40-100° C., the aluminum hydroxyl species sol is volatilized to remove the solvent for 6-48 hours, and the organic alcohol and deionized water are removed to obtain a mesoporous alumina material with a developed mesoporous channel structure and a pseudo-boehmite crystal phase;

[0052] 5) According to the molar ratio of aluminum source: nickel salt = 100-500:1, the mesoporous alumina material is placed in an ethanol solution containing nickel salt and stirred evenly, dried at 60°C for 24 hours, and calcined at 350-550°C for 2-4 hours to obtain c -Mesoporous Ni-Al composite oxide support of Al2O3 crystal phase;

[0053] 6) According to the molar ratio of aluminum source: chloroplatinic acid = 300-800:1, the mesoporous Ni-Al composite oxide support was placed in an ethanol solution dissolved with chloroplatinic acid and stirred evenly, dried at 60°C for 24 hours, and calcined at 400-600°C for 2-4 hours to obtain a Ni-Al composite oxide supported Pt catalyst. Example

[0054] Example 1

[0055] At room temperature, 8.17 g of aluminum isopropoxide was completely dissolved in 80 mL of anhydrous ethanol to obtain a clear solution. Subsequently, 80 mL of a hydrolyzate solution (an 8:2 volume ratio of anhydrous ethylene glycol to deionized water) was added dropwise at a rate of 5.0 mL / min under stirring and reflux at 70°C. After stirring and refluxing for 2 hours, the resulting alumina sol was subjected to solvent evaporation at 60°C for 24 hours to obtain the mesoporous alumina material.

[0056] Depend on Figure 1 (a) shows that the N2 adsorption-desorption isotherm shows a type IV adsorption isotherm and an H1 hysteresis loop, indicating that it has a well-developed mesoporous channel structure. Figure 1 The wide-angle XRD spectrum of (b) shows that the 2θ values ​​of the material are 28.2 o , 38.3 o , 48.9 o and 64.9 o The characteristic diffraction peaks corresponding to the (120), (031), (200) and (002) crystal planes of pseudo-boehmite are shown [JCPDS No. 21-1307], indicating that the mesoporous alumina material has a pseudo-boehmite crystal phase.

[0057] The above-mentioned mesoporous alumina material was added to 80 mL of anhydrous ethanol solution containing 0.052 g of nickel nitrate hexahydrate, stirred at room temperature for 2 h, and then dried at 60° C. for 24 h and calcined at 400° C. for 4 h to obtain a mesoporous Ni-Al composite oxide support.

[0058] Depend on Figure 2 From the N2 adsorption-desorption isotherm in (a), it can be seen that the mesoporous Ni-Al composite oxide support also shows a type IV adsorption isotherm and an H1 type hysteresis loop, and shows a steeper capillary condensation curve in the relative pressure range of 0.5 to 0.8, indicating that the mesoporous Ni-Al composite oxide support has a well-developed mesoporous channel structure, a large specific surface area and pore volume, and a large and uniformly distributed mesopore diameter. In addition, Figure 2The wide-angle XRD spectrum of (b) shows that, unlike the pseudo-boehmite phase mesoporous alumina material, the mesoporous Ni-Al composite oxide support has a 2θ value of 66.7. o The corresponding c -The characteristic diffraction peak of Al2O3(440) crystal plane [JCPDS No. 10-0425] indicates that the mesoporous alumina crystal phase undergoes a transformation during the calcination process, from pseudo-boehmite crystal phase to c -Al2O3 crystal phase.

[0059] 1.0 g of a mesoporous Ni-Al composite oxide support was weighed and immersed in 60 mL of an anhydrous ethanol solution containing 0.013 g of chloroplatinic acid hexahydrate. The support was stirred at room temperature for 24 h, and then dried at 60 ° C for 24 h and calcined at 500 ° C for 3 h to prepare a Ni-Al composite oxide supported Pt catalyst. The mass fraction of Pt in the catalyst was 0.50%.

[0060] Figure 3 The mesoporous Ni-Al composite oxide support before and after loading chloroplatinic acid is given. 27 Al MAS NMR spectrum. As shown in the figure, before loading with chloroplatinic acid, the mesoporous Ni-Al composite oxide support exhibits three peaks at 8.8, 38.5, and 69.1 ppm, corresponding to hexa-, penta-, and tetra-coordinated aluminum species, respectively. The penta- and tetra-coordinated aluminum species can be considered coordinatively unsaturated aluminum species, with contents of 9.6% and 20.9%, respectively. After impregnation with chloroplatinic acid, the peaks at 38.5 and 69.1 ppm on the mesoporous Ni-Al composite oxide support significantly weaken, accompanied by a significant increase in the intensity of the peak signal for the hexa-coordinated saturated aluminum species. Calculations show that the contents of hexa-, penta- and tetra-coordinated aluminum species in the mesoporous Ni-Al composite oxide after loading with chloroplatinic acid are 73.8%, 8.9% and 17.3%, respectively. Compared with before loading with chloroplatinic acid, the contents of tetra- and penta-coordinated unsaturated aluminum species in the mesoporous Ni-Al composite oxide support are significantly reduced, indicating that there is a coordination interaction between the chloroplatinic acid molecules and the coordinated unsaturated aluminum species on the pore wall surface of the mesoporous Ni-Al composite oxide support, thereby being anchored on the pore wall surface of the mesoporous Ni-Al composite oxide support.

[0061] Depend on Figure 4 (a) It can be seen that after the calcination of the mesoporous Ni-Al composite oxide support loaded with chloroplatinic acid, the obtained Ni-Al composite oxide loaded Pt catalyst shows a well-developed mesoporous channel structure, a high specific surface area and pore volume, and a large and uniformly distributed mesopore diameter. By calculation, the specific surface area, pore volume and average mesopore diameter of the catalyst are 539m 2 / g, 0.89cm 3 / g and 5.6nm. In addition, Figure 4 In (b), no Pt crystal diffraction peak was detected, indicating that the Pt active component was highly dispersed on the surface of the mesoporous Ni-Al composite oxide support.

[0062] Figure 5 The elemental mapping of the Ni-Al composite oxide-supported Pt catalyst is further presented, showing that the Ni and Pt atoms are highly uniformly dispersed in the catalyst at a near-atomic level.

[0063] 0.2 g of the obtained Ni-Al composite oxide supported Pt catalyst was taken and reduced at 400° C. with 20 mL / min of hydrogen for 2 h.

[0064] Depend on Figure 6 The spherical aberration corrected HAADF-STEM image shows that after the Ni-Al composite oxide supported Pt catalyst is treated with hydrogen reduction, the metal Pt is uniformly dispersed on the surface of the mesoporous Ni-Al composite oxide support in the form of ultrasmall clusters; after further magnification, it was found that the metal Pt ultrasmall clusters are composed of aggregations of Pt single atoms.

[0065] CO pulse chemisorption characterization results confirmed that the dispersion of metallic Pt on the surface of the mesoporous Ni-Al composite oxide support was as high as 70.4%. Calculations showed that the average size of the metallic Pt single-atom clusters was 1.32 nm, consistent with the spherical aberration-corrected HAADF-STEM characterization results.

[0066] 0.2 g of the obtained Ni-Al composite oxide-loaded Pt catalyst was taken and filled in the middle of the quartz reaction tube of the fixed-bed microreactor. After reduction treatment with 20 mL / min of hydrogen at 400°C for 2 h, the temperature was lowered to 300°C, and 6.0 mL / h of methylcyclohexane vapor was brought into the reactor with nitrogen at a flow rate of 10 mL / min for methylcyclohexane dehydrogenation reaction.

[0067] Depend on Figure 7 It can be seen that after 1 hour of reaction, the conversion rate of the catalyst for methylcyclohexane is as high as 65.6%, the selectivity of toluene in the product reaches 100%, and the dehydrogenation rate reaches 1583mmol / g / min. Moreover, during the continuous reaction process of up to 100 hours, the conversion rate and dehydrogenation rate of the catalyst for methylcyclohexane are always maintained above 57.6% and 1390mmol / g / min, respectively.

[0068] More importantly, after calcination and hydrogen reduction regeneration treatment, the catalyst can still maintain more than 88.9% of its initial activity, and its activity only decreases by 8.2% during the 100-hour reaction process.

[0069] Figure 8The methylcyclohexane conversion and corresponding hydrogen evolution rate of the Ni-Al composite oxide supported Pt catalyst at different methylcyclohexane feed rates at 300°C are shown. As can be seen from the figure, when the nitrogen flow rate is constant, the catalyst can almost completely convert methylcyclohexane when the methylcyclohexane feed rate is 2.0 mL / h, and the hydrogen evolution rate at this time is 796 mmol / g. Pt / min. As the methylcyclohexane feed rate increases, the catalyst shows a significantly increased dehydrogenation rate accompanied by a gradual decrease in the methylcyclohexane conversion rate. When the methylcyclohexane feed rate increases to 38.0 mL / h, the methylcyclohexane conversion rate decreases to about 20.0%. This conversion rate can be used to calculate the maximum dehydrogenation rate of the catalyst, which is as high as 3057 mmol / g. Pt / min.

[0070] Example 2

[0071] At room temperature, 8.25 g of aluminum isopropoxide was completely dissolved in 100 mL of anhydrous ethylene glycol to obtain a clear solution. Subsequently, 80 mL of a hydrolyzate solution (an 8:2 volume ratio of anhydrous isopropanol to deionized water) was added dropwise at a rate of 3.0 mL / min under stirring and reflux at 80°C. After stirring and refluxing for 3 hours, the resulting alumina sol was subjected to solvent evaporation at 80°C for 36 hours to obtain a mesoporous alumina material.

[0072] The above-mentioned mesoporous alumina material was added to 80 mL of anhydrous ethanol solution containing 0.060 g of nickel nitrate hexahydrate, stirred at room temperature for 2 h, and then dried at 60° C. for 24 h and calcined at 500° C. for 3 h to obtain a mesoporous Ni-Al composite oxide support.

[0073] XRD and N2 adsorption-desorption characterization results confirmed that the mesoporous alumina material has a well-developed mesoporous channel structure and pseudo-boehmite crystal phase. After loading nickel nitrate and then calcining it, the obtained mesoporous Ni-Al composite oxide carrier showed c -Al2O3 crystal phase structure. 27 The Al MAS NMR characterization results confirmed that Ni atoms were highly uniformly dispersed in the pore walls of alumina mesopores at a near-atomic level and Ni-O-Al bonds were formed on the pore wall surface, resulting in the generation of a large number of tetracoordinate and pentacoordinate unsaturated aluminum species on the surface of the mesoporous Ni-Al composite oxide support.

[0074] 1.0 g of the above-mentioned mesoporous Ni-Al composite oxide support was weighed and immersed in 60 mL of an anhydrous ethanol solution containing 0.013 g of chloroplatinic acid hexahydrate. After stirring at room temperature for 24 h, the support was dried at 60°C for 24 h and calcined at 500°C for 3 h to prepare a Ni-Al composite oxide-supported Pt catalyst. The mass fraction of Pt in the catalyst was 0.50%.

[0075] The results of N2 adsorption-desorption and CO pulse chemical adsorption characterization confirmed that the obtained catalyst has a well-developed mesoporous channel structure, uniform mesopore diameter, high specific surface area and pore volume, and the Pt active sites are highly uniformly dispersed in the form of atomic clusters. Calculations show that the specific surface area and pore volume of the Ni-Al composite oxide supported Pt catalyst are 486 m 2 / g and 0.78cm 3 / g, the mesopore diameter is 5.85nm, the Pt dispersion is 69.3%, and Pt is uniformly dispersed on the pore wall surface of the mesoporous Ni-Al composite oxide support in the form of single atomic clusters with an average size of 1.35nm.

[0076] 0.2 g of the resulting Ni-Al composite oxide-supported Pt catalyst was placed in the middle of a fixed-bed microreactor's quartz reaction tube and subjected to a reduction treatment at 400°C with 20 mL / min of hydrogen for 2 hours. Methylcyclohexane dehydrogenation was then carried out at 300°C using 6.0 mL / h of methylcyclohexane vapor introduced into the reactor with a nitrogen flow rate of 10 mL / min.

[0077] Test results show that under the above reaction conditions, the catalyst can completely convert 63.8% of methylcyclohexane into toluene with a dehydrogenation rate of 1540mmol / g / min. Moreover, during a continuous reaction process of up to 100 hours or during regeneration and repeated use, the catalyst's conversion rate and dehydrogenation rate for methylcyclohexane always remain above 55.4% and 1337mmol / g / min, respectively.

[0078] More importantly, under the condition of keeping the nitrogen flow rate constant, by increasing the feed rate of methylcyclohexane to 37 mL / h, the catalyst showed a high concentration of 2977 mmol / g Pt The maximum dehydrogenation rate is 2.177kJ / min.

[0079] Example 3

[0080] At room temperature, 9.86 g of aluminum isobutoxide was completely dissolved in 100 mL of anhydrous ethanol to obtain a clear solution. Subsequently, 100 mL of a hydrolyzate solution (a mixture of anhydrous isopropanol and deionized water in a volume ratio of 7:3) was added dropwise at 4.0 mL / min under stirring and reflux at 100°C. After stirring and refluxing for 4 hours, the resulting alumina sol was subjected to solvent evaporation at 90°C for 12 hours to obtain a mesoporous alumina material.

[0081] The above-mentioned mesoporous alumina material was added to 50 mL of anhydrous ethanol solution containing 0.085 g of nickel nitrate hexahydrate, stirred at room temperature for 2 h, and then dried at 60° C. for 24 h and calcined at 500° C. for 3 h to obtain a mesoporous Ni-Al composite oxide support.

[0082] XRD and N2 adsorption-desorption characterization results confirmed that the mesoporous alumina material has a well-developed mesoporous channel structure and pseudo-boehmite crystal phase. After loading nickel nitrate and then calcining it, the obtained mesoporous Ni-Al composite oxide carrier showed c -Al2O3 crystal phase structure. 27 The Al MAS NMR characterization results confirmed that Ni atoms were highly uniformly dispersed in the pore walls of alumina mesopores at a near-atomic level and Ni-O-Al bonds were formed on the pore wall surface, resulting in the generation of a large number of tetracoordinate and pentacoordinate unsaturated aluminum species on the surface of the mesoporous Ni-Al composite oxide support.

[0083] 1.0 g of the above-mentioned mesoporous Ni-Al composite oxide support was weighed and immersed in 50 mL of an anhydrous ethanol solution containing 0.013 g of chloroplatinic acid hexahydrate. After stirring at room temperature for 24 h, the support was dried at 60°C for 12 h and calcined at 550°C for 3 h to prepare a Ni-Al composite oxide-supported Pt catalyst. The mass fraction of Pt in the catalyst was 0.50%.

[0084] The results of N2 adsorption-desorption and CO pulse chemical adsorption characterization confirmed that the obtained catalyst has a well-developed mesoporous channel structure, uniform mesopore diameter, high specific surface area and pore volume, and the Pt active sites are highly uniformly dispersed in the form of atomic clusters. Calculations show that the specific surface area and pore volume of the Ni-Al composite oxide-supported Pt catalyst are 503 m 2 / g and 0.76cm 3 / g, the mesopore diameter is 5.07nm, the Pt dispersion is 68.3%, and Pt is uniformly dispersed on the pore wall surface of the mesoporous Ni-Al composite oxide support in the form of single atomic clusters with an average size of 1.36nm.

[0085] 0.2 g of the resulting Ni-Al composite oxide-supported Pt catalyst was placed in the middle of a fixed-bed microreactor's quartz reaction tube and subjected to a reduction treatment at 400°C with 20 mL / min of hydrogen for 2 hours. Methylcyclohexane dehydrogenation was then carried out at 300°C using 6.0 mL / h of methylcyclohexane vapor introduced into the reactor with a nitrogen flow rate of 10 mL / min.

[0086] Test results show that under the above reaction conditions, the catalyst can completely convert 62.5% of methylcyclohexane into toluene, with a dehydrogenation rate of 1509 mmol / g / min. Moreover, during a continuous reaction process of up to 100 hours or regeneration and repeated use, the catalyst's conversion rate and dehydrogenation rate for methylcyclohexane always remain above 54.6% and 1318 mmol / g / min, respectively.

[0087] More importantly, under the condition of keeping the nitrogen flow rate constant, by increasing the feed rate of methylcyclohexane to 36 mL / h, the catalyst showed a high concentration of 2896 mmol / g Pt The maximum dehydrogenation rate is 2.177kJ / min.

[0088] Example 4

[0089] At room temperature, 15.0 g of aluminum nitrate was completely dissolved in 100 mL of anhydrous ethanol to obtain a clear solution. Subsequently, 100 mL of a hydrolyzate solution (a mixture of anhydrous ethanol and deionized water in a 9:1 volume ratio) was added dropwise at 5.0 mL / min under stirring and reflux at 120°C. After stirring and refluxing for 4 hours, the resulting alumina sol was subjected to solvent evaporation at 80°C for 48 hours to obtain a mesoporous alumina material.

[0090] The above-mentioned mesoporous alumina material was added to 60 mL of anhydrous ethanol solution containing 0.065 g of nickel nitrate hexahydrate, stirred at room temperature for 2 h, and then dried at 60° C. for 24 h and calcined at 450° C. for 4 h to obtain a mesoporous Ni-Al composite oxide support.

[0091] XRD and N2 adsorption-desorption characterization results confirmed that the mesoporous alumina material has a well-developed mesoporous channel structure and pseudo-boehmite crystal phase. After loading nickel nitrate and then calcining it, the obtained mesoporous Ni-Al composite oxide carrier showed c -Al2O3 crystal phase structure. 27 The Al MAS NMR characterization results confirmed that Ni atoms were highly uniformly dispersed in the pore walls of alumina mesopores at a near-atomic level and Ni-O-Al bonds were formed on the pore wall surface, resulting in the generation of a large number of tetracoordinate and pentacoordinate unsaturated aluminum species on the surface of the mesoporous Ni-Al composite oxide support.

[0092] 1.0 g of the above-mentioned mesoporous Ni-Al composite oxide support was weighed and immersed in 50 mL of an anhydrous ethanol solution containing 0.013 g of chloroplatinic acid hexahydrate. After stirring at room temperature for 24 h, the support was dried at 60°C for 24 h and calcined at 500°C for 3 h to prepare a Ni-Al composite oxide-supported Pt catalyst. The mass fraction of Pt in the catalyst was 0.50%.

[0093] The results of N2 adsorption-desorption and CO pulse chemical adsorption characterization confirmed that the obtained catalyst has a well-developed mesoporous channel structure, uniform mesopore diameter, high specific surface area and pore volume, and the Pt active sites are highly uniformly dispersed in the form of atomic clusters. Calculations show that the specific surface area and pore volume of the Ni-Al composite oxide supported Pt catalyst are 529 m 2 / g and 0.98cm 3 / g, the mesopore diameter is 6.91nm, the Pt dispersion is 67.1%, and Pt is uniformly dispersed on the pore wall surface of the mesoporous Ni-Al composite oxide support in the form of single atomic clusters with an average size of 1.39nm.

[0094] 0.2 g of the resulting Ni-Al composite oxide-supported Pt catalyst was placed in the middle of a fixed-bed microreactor's quartz reaction tube and subjected to a reduction treatment at 400°C with 20 mL / min of hydrogen for 2 hours. Methylcyclohexane dehydrogenation was then carried out at 300°C using 6.0 mL / h of methylcyclohexane vapor introduced into the reactor with a nitrogen flow rate of 10 mL / min.

[0095] Test results show that under the above reaction conditions, the catalyst can completely convert 61.8% of methylcyclohexane into toluene, with a dehydrogenation rate of 1491 mmol / g / min. Moreover, during a continuous reaction process of up to 100 hours or regeneration and repeated use, the catalyst's conversion rate and dehydrogenation rate for methylcyclohexane always remain above 53.7% and 1296 mmol / g / min, respectively.

[0096] More importantly, under the condition of keeping the nitrogen flow rate constant, by increasing the feed rate of methylcyclohexane to 35 mL / h, the catalyst showed a high concentration of 2816 mmol / g Pt The maximum dehydrogenation rate is 2.177kJ / min.

[0097] Example 5

[0098] At room temperature, 10.23 g of aluminum tert-butoxide was completely dissolved in 100 mL of anhydrous methanol to obtain a clear solution. Subsequently, 150 mL of a hydrolyzate solution (a mixture of anhydrous methanol and deionized water in a volume ratio of 7:3) was added dropwise at 80°C under stirring and reflux at a rate of 2.0 mL / min. After stirring and refluxing for 4 hours, the resulting alumina sol was subjected to solvent evaporation at 100°C for 12 hours to obtain a mesoporous alumina material.

[0099] The above-mentioned mesoporous alumina material was added to 60 mL of anhydrous ethanol solution containing 0.080 g of nickel nitrate hexahydrate, stirred at room temperature for 2 h, and then dried at 60° C. for 24 h and calcined at 550° C. for 2 h to obtain a mesoporous Ni-Al composite oxide support.

[0100] XRD and N2 adsorption-desorption characterization results confirmed that the mesoporous alumina material has a well-developed mesoporous channel structure and pseudo-boehmite crystal phase. After loading nickel nitrate and then calcining it, the obtained mesoporous Ni-Al composite oxide carrier showed c -Al2O3 crystal phase structure. 27 The Al MAS NMR characterization results confirmed that Ni atoms were highly uniformly dispersed in the pore walls of alumina mesopores at a near-atomic level and Ni-O-Al bonds were formed on the pore wall surface, resulting in the generation of a large number of tetracoordinate and pentacoordinate unsaturated aluminum species on the surface of the mesoporous Ni-Al composite oxide support.

[0101] 1.0 g of the above-mentioned mesoporous Ni-Al composite oxide support was weighed and immersed in 50 mL of an anhydrous ethanol solution containing 0.013 g of chloroplatinic acid hexahydrate. After stirring at room temperature for 24 h, the support was dried at 60°C for 24 h and calcined at 500°C for 3 h to prepare a Ni-Al composite oxide-supported Pt catalyst. The mass fraction of Pt in the catalyst was 0.50%.

[0102] The results of N2 adsorption-desorption and CO pulse chemical adsorption characterization confirmed that the obtained catalyst has a well-developed mesoporous channel structure, uniform mesopore diameter, high specific surface area and pore volume, and the Pt active sites are highly uniformly dispersed in the form of atomic clusters. Calculations show that the specific surface area and pore volume of the Ni-Al composite oxide supported Pt catalyst are 529 m 2 / g and 0.88cm 3 / g, the mesopore diameter is 6.21nm, the Pt dispersion is 66.5%, and Pt is uniformly dispersed on the pore wall surface of the mesoporous Ni-Al composite oxide support in the form of single atomic clusters with an average size of 1.42nm.

[0103] 0.2 g of the resulting Ni-Al composite oxide-supported Pt catalyst was placed in the middle of a fixed-bed microreactor's quartz reaction tube and subjected to a reduction treatment at 400°C with 20 mL / min of hydrogen for 2 hours. Methylcyclohexane dehydrogenation was then carried out at 300°C using 6.0 mL / h of methylcyclohexane vapor introduced into the reactor with a nitrogen flow rate of 10 mL / min.

[0104] Test results show that under the above reaction conditions, the catalyst can completely convert 60.8% of methylcyclohexane into toluene with a dehydrogenation rate of 1467mmol / g / min. Moreover, during a continuous reaction process of up to 100 hours or during regeneration and repeated use, the catalyst's conversion rate and dehydrogenation rate for methylcyclohexane always remain above 53.1% and 1282mmol / g / min, respectively.

[0105] More importantly, under the condition of keeping the nitrogen flow rate constant, by increasing the feed rate of methylcyclohexane to 34 mL / h, the catalyst showed a high concentration of 2736 mmol / g Pt The maximum dehydrogenation rate is 2.177kJ / min.

[0106] Example 6

[0107] At room temperature, 9.85 g of aluminum tert-butoxide was completely dissolved in 100 mL of anhydrous ethanol to obtain a clear solution. Subsequently, 100 mL of a hydrolyzate solution (a mixture of anhydrous propylene glycol and deionized water in a volume ratio of 8:2) was added dropwise at 3.0 mL / min under stirring and reflux at 90°C. After stirring and refluxing for 4 hours, the resulting alumina sol was subjected to solvent evaporation at 60°C for 48 hours to obtain a mesoporous alumina material.

[0108] The above-mentioned mesoporous alumina material was added to 60 mL of anhydrous ethanol solution containing 0.045 g of nickel nitrate hexahydrate, stirred at room temperature for 2 h, and then dried at 60° C. for 24 h and calcined at 550° C. for 2 h to obtain a mesoporous Ni-Al composite oxide support.

[0109] XRD and N2 adsorption-desorption characterization results confirmed that the mesoporous alumina material has a well-developed mesoporous channel structure and pseudo-boehmite crystal phase. After loading nickel nitrate and then calcining it, the obtained mesoporous Ni-Al composite oxide carrier showed c -Al2O3 crystal phase structure. 27 The Al MAS NMR characterization results confirmed that Ni atoms were highly uniformly dispersed in the pore walls of alumina mesopores at a near-atomic level and Ni-O-Al bonds were formed on the pore wall surface, resulting in the generation of a large number of tetracoordinate and pentacoordinate unsaturated aluminum species on the surface of the mesoporous Ni-Al composite oxide support.

[0110] 1.0 g of the above-mentioned mesoporous Ni-Al composite oxide support was weighed and immersed in 50 mL of an anhydrous ethanol solution containing 0.013 g of chloroplatinic acid hexahydrate. After stirring at room temperature for 24 h, the support was dried at 60°C for 24 h and calcined at 500°C for 3 h to prepare a Ni-Al composite oxide-supported Pt catalyst. The mass fraction of Pt in the catalyst was 0.50%.

[0111] The results of N2 adsorption-desorption and CO pulse chemical adsorption characterization confirmed that the obtained catalyst has a well-developed mesoporous channel structure, uniform mesopore diameter, high specific surface area and pore volume, and the Pt active sites are highly uniformly dispersed in the form of atomic clusters. Calculations show that the specific surface area and pore volume of the Ni-Al composite oxide supported Pt catalyst are 546 m 2 / g and 0.91cm 3 / g, the mesopore diameter is 5.56nm, the Pt dispersion is 65.8%, and Pt is uniformly dispersed on the pore wall surface of the mesoporous Ni-Al composite oxide support in the form of single atomic clusters with an average size of 1.45nm.

[0112] 0.2 g of the resulting Ni-Al composite oxide-supported Pt catalyst was placed in the middle of a fixed-bed microreactor's quartz reaction tube and subjected to a reduction treatment at 400°C with 20 mL / min of hydrogen for 2 hours. Methylcyclohexane dehydrogenation was then carried out at 300°C using 6.0 mL / h of methylcyclohexane vapor introduced into the reactor with a nitrogen flow rate of 10 mL / min.

[0113] Test results show that under the above reaction conditions, the catalyst can completely convert 59.7% of methylcyclohexane into toluene, with a dehydrogenation rate of 1441 mmol / g / min. Moreover, during a continuous reaction process of up to 100 hours or regeneration and repeated use, the catalyst's conversion rate and dehydrogenation rate for methylcyclohexane always remain above 52.6% and 1270 mmol / g / min, respectively.

[0114] More importantly, under the condition of keeping the nitrogen flow rate constant, by increasing the feed rate of methylcyclohexane to 33 mL / h, the catalyst showed a high concentration of 2655 mmol / g Pt The maximum dehydrogenation rate is 2.177kJ / min.

[0115] Comparative Example 1

[0116] At room temperature, 8.17 g of aluminum isopropoxide was completely dissolved in 80 mL of anhydrous ethanol to obtain a clear solution. Subsequently, 80 mL of a hydrolyzate solution (a mixture of anhydrous ethylene glycol and deionized water in a volume ratio of 8:2) was added dropwise at 5.0 mL / min under stirring and reflux at 70°C. After stirring and refluxing for 2 hours, the resulting alumina sol was subjected to solvent evaporation at 60°C for 24 hours, yielding a mesoporous alumina material with a pseudo-boehmite crystalline phase.

[0117] The above mesoporous alumina material was calcined at 550℃ for 2h to obtain c -Mesoporous alumina support with Al2O3 crystal phase.

[0118] N2 adsorption-desorption and 27 Al MAS NMR characterization results confirmed that the mesoporous alumina support showed a well-developed mesoporous channel structure and c The formation of -Al2O3 crystal phase is conducive to the transformation of hexacoordinated saturated aluminum species to tetracoordinated and pentacoordinated unsaturated aluminum species. c In the mesoporous alumina support with -Al2O3 crystal phase, the contents of penta-coordinated and tetra-coordinated unsaturated aluminum species are 7.0% and 18.6%, respectively.

[0119] 1.0 g of a mesoporous alumina support was weighed and immersed in 60 mL of an anhydrous ethanol solution containing 0.013 g of chloroplatinic acid hexahydrate. The solution was stirred at room temperature for 24 h, dried at 60 ° C for 24 h, and calcined at 500 ° C for 3 h to prepare a mesoporous alumina-supported Pt catalyst. The mass fraction of Pt in the catalyst was 0.50%.

[0120] The N2 adsorption-desorption characterization results confirmed that the catalyst prepared above has a well-developed mesoporous channel structure, uniform mesopore diameter, high specific surface area and pore volume. Its specific surface area, pore volume and mesopore diameter are 521m 2 / g, 1.01cm 3 The results of CO pulse chemisorption characterization confirmed that the dispersion of metallic Pt on the support surface was 60.1%, and the average size of the Pt nanoclusters was calculated to be 1.57 nm.

[0121] 0.2 g of the mesoporous alumina-loaded Pt catalyst was filled in the middle of the quartz reaction tube of the fixed-bed microreactor. After reduction treatment with 20 mL / min of hydrogen at 400°C for 2 h, 6.0 mL / h of methylcyclohexane vapor was brought into the reactor at 300°C with nitrogen at a flow rate of 10 mL / min for methylcyclohexane dehydrogenation reaction.

[0122] Test results show that the catalyst can completely convert 56.8% of methylcyclohexane into toluene, and the dehydrogenation rate reaches 1371mmol / g Pt When the feed rate of methylcyclohexane was further increased to 25 mL / h, the catalyst showed a Pt The maximum dehydrogenation rate is 2.177kJ / min.

[0123] Compared with Example 1, it can be seen that during the calcination and crystallization process of mesoporous alumina, nickel atoms are highly and uniformly doped in the pore walls of the alumina mesopores at a near-atomic level, which is conducive to the generation of more tetra-coordinate and penta-coordinate unsaturated aluminum species, and thus is more conducive to the uniform anchoring of chloroplatinic acid molecules on the pore wall surface of the mesoporous alumina support through coordination bonding. As a result, after calcination, thermal decomposition of chloroplatinic acid molecules and hydrogen reduction treatment, the Pt active sites can be highly uniformly dispersed in the form of single-atom clusters, causing Pt to show higher low-temperature dehydrogenation activity of methylcyclohexane due to its smaller particle size and higher utilization efficiency.

[0124] Comparative Example 2

[0125] At room temperature, 8.17 g of aluminum isopropoxide was completely dissolved in 80 mL of anhydrous ethanol to obtain a clear solution. Subsequently, 80 mL of a hydrolyzate solution (a mixture of anhydrous ethylene glycol and deionized water in a volume ratio of 8:2) was added dropwise at 5.0 mL / min under stirring and reflux at 70°C. After stirring and refluxing for 2 hours, the resulting alumina sol was subjected to solvent evaporation at 60°C for 24 hours, yielding a mesoporous alumina material with a pseudo-boehmite crystalline phase.

[0126] The above mesoporous alumina material was calcined at 400 ° C for 2 h, added into 80 mL of anhydrous ethanol solution containing 0.052 g of nickel nitrate hexahydrate, stirred at room temperature for 2 h, dried at 60 ° C for 24 h and calcined at 400 ° C for 4 h to obtain mesoporous alumina loaded with NiO x Species carrier.

[0127] The results of N2 adsorption-desorption characterization confirmed that the mesoporous alumina loaded NiO x The species carrier has a developed mesoporous structure and a high specific surface area and pore volume.

[0128] XRD characterization results show that the carrier has a 2θ value of 66.7 o The corresponding c -Al2O3(440) crystal plane characteristic diffraction peak [JCPDS No. 10-0425], at 2θ value of 75.6 oThe characteristic diffraction peak corresponding to the NiO (311) crystal plane is shown at [JCPDS No. 71-1179]. According to the Debye-Scherrer formula, the average size of NiO nanoparticles is 3.15 nm. It can be seen that the traditional impregnation method cannot achieve the desired effect of NiO. x Highly uniform dispersion of species on the mesoporous alumina surface.

[0129] 27 Al MAS NMR characterization results confirmed that NiO x The contents of penta-coordinated and tetra-coordinated unsaturated aluminum species in the species carrier were 7.0% and 18.6%, respectively, indicating that the traditional method can effectively prepare the unsaturated aluminum species with c -Al2O3 crystal phase mesoporous alumina surface loaded with NiO x Species do not promote the formation of coordinatively unsaturated aluminum species.

[0130] Weigh 1.0 g of mesoporous alumina loaded with NiO x The species carrier was immersed in 60 mL of anhydrous ethanol solution containing 0.013 g of chloroplatinic acid hexahydrate, stirred at room temperature for 24 h, and then dried at 60 ° C for 24 h and calcined at 500 ° C for 3 h to prepare a mesoporous alumina-supported Ni-Pt catalyst with a Pt mass fraction of 0.50%.

[0131] The N2 adsorption-desorption characterization results confirmed that the catalyst prepared above has a developed mesoporous channel structure, uniform mesopore diameter, high specific surface area and pore volume. Its specific surface area, pore volume and mesopore diameter are 501m 2 / g, 0.85cm 3 The results of CO pulse chemisorption characterization confirmed that the dispersion of metallic Pt on the support surface was 63.6%, and the average size of the Pt nanoclusters was calculated to be 1.49 nm.

[0132] 0.2 g of the mesoporous alumina-loaded Ni-Pt catalyst was filled in the middle of the quartz reaction tube of the fixed-bed microreactor, and after reduction treatment with 20 mL / min of hydrogen at 400°C for 2 h, 6.0 mL / h of methylcyclohexane vapor was brought into the reactor at 300°C with nitrogen at a flow rate of 10 mL / min for methylcyclohexane dehydrogenation reaction.

[0133] Test results show that the catalyst can completely convert 58.5% of methylcyclohexane into toluene, and the dehydrogenation rate reaches 1419mmol / g Pt When the feed rate of methylcyclohexane was further increased to 27 mL / h, the catalyst showed a 2275 mmol / g Pt The maximum dehydrogenation rate is 2.177kJ / min.

[0134] Compared with Comparative Example 1, it can be seen that c -Al2O3 crystal phase mesoporous alumina surface loaded with NiO x The species are beneficial to the dispersion of Pt, thereby improving the utilization efficiency of Pt and the reaction activity of the obtained catalyst in the low-temperature dehydrogenation reaction of methylcyclohexane. However, compared with Example 1, it is found that the conventional impregnation method is c -Al2O3 crystal phase mesoporous alumina surface loaded with NiO x species, because it is impossible to achieve NiO x The highly uniform dispersion of species and the generation of a larger amount of coordinatively unsaturated aluminum species make it difficult for the Pt active sites to be highly uniformly dispersed on the surface of the mesoporous alumina support in the form of single-atom clusters, resulting in the resulting catalyst showing relatively low low-temperature dehydrogenation activity of methylcyclohexane.

[0135] Comparative Example 3

[0136] At room temperature, 8.17 g of aluminum isopropoxide was completely dissolved in 80 mL of anhydrous ethanol to obtain a clear solution. Subsequently, 80 mL of a hydrolyzate solution (an 8:2 volume ratio of anhydrous ethylene glycol to deionized water) was added dropwise at a rate of 5.0 mL / min under stirring and reflux at 70°C. After stirring and refluxing for 2 hours, the resulting alumina sol was subjected to solvent evaporation at 60°C for 24 hours to obtain the mesoporous alumina material.

[0137] XRD and N2 adsorption-desorption characterization results confirmed that the mesoporous alumina material has a developed mesoporous channel structure and pseudo-boehmite crystal phase. 27 The Al MAS NMR characterization results showed that the mesoporous alumina material exhibited only one signal peak at 8.8 ppm, indicating that only hexacoordinated saturated aluminum species existed in the mesoporous alumina material with pseudo-boehmite crystal phase.

[0138] 1.0 g of mesoporous alumina material was weighed and immersed in 60 mL of anhydrous ethanol solution containing 0.013 g of chloroplatinic acid hexahydrate. After stirring at room temperature for 24 h, the material was dried at 60 ° C for 24 h and calcined at 500 ° C for 3 h to prepare a mesoporous alumina-supported Pt catalyst. The mass fraction of Pt in the catalyst was 0.50%.

[0139] The results of N2 adsorption-desorption characterization confirmed that the catalyst prepared above has a well-developed mesoporous channel structure, uniform mesopore diameter, high specific surface area and pore volume. Its specific surface area, pore volume and mesopore diameter are 415m 2 / g, 0.78cm 3The results of CO pulse chemisorption characterization confirmed that the dispersion of metallic Pt on the surface of the material was only 46.6%, and the average size of the Pt nanoclusters was calculated to be 2.05 nm.

[0140] 0.2 g of the mesoporous alumina-loaded Pt catalyst was filled in the middle of the quartz reaction tube of the fixed-bed microreactor, and after reduction treatment with 20 mL / min of hydrogen at 400°C for 2 h, 6.0 mL / h of methylcyclohexane vapor was brought into the reactor at 300°C with nitrogen at a flow rate of 10 mL / min for methylcyclohexane dehydrogenation reaction.

[0141] Test results show that the catalyst can only completely convert 28.6% of methylcyclohexane into toluene, and the dehydrogenation rate is only 690mmol / g. Pt Increasing the methylcyclohexane feed rate to 12 mL / h, the catalyst showed a 965 mmol / g Pt The maximum dehydrogenation rate is 2.177kJ / min.

[0142] Compared with Example 1 and Comparative Example 1, it can be seen that when the mesoporous alumina material with a developed mesoporous channel structure and a pseudo-boehmite crystal phase is used as a carrier, since there are no coordinatively unsaturated aluminum species on its surface, it is impossible to achieve highly uniform dispersion of Pt active sites in the form of single-atom clusters through coordination bonding, resulting in the obtained catalyst showing relatively poor catalytic activity for the low-temperature dehydrogenation of methylcyclohexane.

[0143] Comparative Example 4

[0144] According to the existing literature (Pan D,. Solvothermal-assisted evaporation-induced self-assembly of ordered mesoporous alumina with improved performance. J. Colloid Interface Sci . 2018, 529, 432-43) method, a solvent-thermal-assisted volatilization-induced self-assembly method was used to prepare high surface area mesoporous alumina materials, and Pt-based catalysts were prepared using them as supports.

[0145] The specific preparation process is as follows: under strong stirring at 32°C, 3.2g of triblock nonionic surfactant F127, 0.4g of citric acid, 1.6g of 37wt% concentrated hydrochloric acid and 3.26g of aluminum isopropoxide are completely dissolved in 20mL of anhydrous ethanol in sequence, and the temperature is maintained and stirring is continued for 24h; the reaction solution is transferred to a reactor and solvent thermally treated at 80°C for 24h; the reaction sol obtained by the reaction is transferred to a culture dish, and subjected to solvent volatilization treatment at 60°C for 24h and calcination treatment at 550°C for 2h to prepare mesoporous alumina material.

[0146] XRD and N2 adsorption-desorption characterization results confirmed that the mesoporous alumina material has a highly regular and ordered two-dimensional hexagonal mesoporous channel structure and a high specific surface area, and the pore wall is an amorphous phase structure.

[0147] 1.0 g of mesoporous alumina material was weighed and immersed in 60 mL of anhydrous ethanol solution containing 0.013 g of chloroplatinic acid hexahydrate. After stirring at room temperature for 24 h, the material was dried at 60 ° C for 24 h and calcined at 500 ° C for 3 h to prepare a mesoporous alumina-supported Pt catalyst. The mass fraction of Pt in the catalyst was 0.50%.

[0148] The N2 adsorption-desorption characterization results confirmed that the prepared catalyst has a two-dimensional hexagonal ordered mesoporous structure, uniform mesopore diameter, high specific surface area and pore volume. The specific surface area, pore volume and mesopore diameter are 311m 2 / g, 0.41cm 3 The results of CO pulse chemical adsorption characterization confirmed that the dispersion of metallic Pt on the material surface was only 36.3%. Pt was dispersed on the pore wall surface of the mesoporous alumina material in the form of nanoparticles with an average size of 2.21 nm.

[0149] 0.2 g of the mesoporous alumina-loaded Pt catalyst was filled in the middle of the quartz reaction tube of the fixed-bed microreactor, and after reduction treatment with 20 mL / min of hydrogen at 400°C for 2 h, 6.0 mL / h of methylcyclohexane vapor was brought into the reactor at 300°C with nitrogen at a flow rate of 10 mL / min for methylcyclohexane dehydrogenation reaction.

[0150] Test results show that the catalyst can only completely convert 26.9% of methylcyclohexane into toluene, and the dehydrogenation rate is only 714mmol / g. Pt / min. Increasing the methylcyclohexane feed rate to 10mL / h, the catalyst showed 890mmol / g Pt The maximum dehydrogenation rate is 2.177kJ / min.

[0151] Compared with Example 1 and Comparative Example 1, it can be seen that compared with the solvent confined hydrolysis-polymerization volatilization method, the mesoporous alumina material obtained by the solvent thermal assisted volatilization induced self-assembly method shows a relatively low specific surface area, which is not conducive to the highly uniform dispersion of Pt active sites, resulting in the obtained catalyst showing relatively poor catalytic activity for the low-temperature dehydrogenation of methylcyclohexane.

[0152] Comparative Example 5

[0153] Use commercially available c -Al2O3 is used as a carrier for the preparation of loaded Pt catalyst.

[0154] Weigh 1.0g of commercial c -Al2O3 was immersed in 60mL of anhydrous ethanol solution containing 0.013g of chloroplatinic acid hexahydrate, stirred at room temperature for 24h, dried at 60℃ for 24h and calcined at 500℃ for 3h to prepare commercial c -Al2O3-loaded Pt catalyst, the mass fraction of Pt in the catalyst is 0.50%.

[0155] The N2 adsorption-desorption characterization results confirmed that the obtained catalyst had a low specific surface area and pore volume, and the specific surface area, pore volume and pore diameter were 98m 2 / g, 0.17cm 3 The results of CO pulse chemisorption characterization confirmed that the Pt dispersion in the catalyst was only 21.9%, and Pt was dispersed on the pore wall surface of the alumina support in the form of nanoparticles with an average size of 4.30 nm.

[0156] Take the business c -Al2O3-loaded Pt catalyst 0.2 g was filled in the middle of the quartz reaction tube of the fixed-bed microreactor and reduced with 20 mL / min of hydrogen at 400°C for 2 h. Then, 6.0 mL / h of methylcyclohexane vapor was introduced into the reactor at 300°C with nitrogen at a flow rate of 10 mL / min for methylcyclohexane dehydrogenation reaction.

[0157] Test results show that the catalyst can only completely convert 15.8% of methylcyclohexane into toluene, and the maximum dehydrogenation rate is only 381mmol / g Pt / min.

[0158] Compared with Examples 1 to 6 and Comparative Examples 1 to 4, it can be seen that commercial c -Al2O3, due to its low specific surface area and pore volume, is not conducive to the highly uniform dispersion of Pt active sites, resulting in the obtained catalyst showing poor catalytic activity for the low-temperature dehydrogenation of methylcyclohexane.

[0159] The above embodiments of the present invention do not describe all details in detail, nor do they limit the present invention to the above embodiments. Various changes, modifications, substitutions, and variations made by those skilled in the art without departing from the principles and purpose of the present invention are intended to be included within the scope of protection of the present invention.

Claims

1. A Ni-Al composite oxide-supported Pt catalyst for methylcyclohexane dehydrogenation, comprising slowly dropping a hydrolyzate consisting of a mixture of anhydrous organic alcohol and deionized water into an anhydrous organic alcohol solution containing an aluminum source, thereby causing the aluminum source to undergo a controlled hydrolysis-polymerization reaction at the molecular level to produce an oligomeric aluminum hydroxyl species sol; volatilizing the aluminum hydroxyl species sol to produce a pseudo-boehmite crystalline mesoporous alumina material; and loading a nickel salt onto the surface of the mesoporous alumina material by an impregnation method. Using a calcination-transformation doping strategy, metallic nickel atoms are in situ uniformly doped into the pore walls of the mesoporous alumina to form Ni-O-Al bonds, thereby producing a Pt catalyst. γ -Al2O3 crystalline mesoporous Ni-Al composite oxide support, loaded with a Ni-Al composite oxide-loaded Pt catalyst obtained by calcining with chloroplatinic acid and used for low-temperature and efficient dehydrogenation of methylcyclohexane. The catalyst has highly uniformly dispersed Pt active sites in the form of single-atom clusters, with a Pt dispersion of more than 60.0%.

2. The Ni-Al composite oxide supported Pt catalyst for dehydrogenation of methylcyclohexane according to claim 1, characterized in that The aluminum source is one of aluminum isopropoxide, aluminum isobutoxide, aluminum tert-butoxide, aluminum nitrate, aluminum chloride or aluminum sulfate, or a mixture of any proportions of the above.

3. The Ni-Al composite oxide supported Pt catalyst for dehydrogenation of methylcyclohexane according to claim 1, characterized in that The anhydrous organic alcohol is one of methanol, ethanol, isopropanol, ethylene glycol or propylene glycol, or a mixture of several of them in any proportion.

4. The Ni-Al composite oxide supported Pt catalyst for dehydrogenation of methylcyclohexane according to claim 3, characterized in that The anhydrous organic alcohol used to constitute the hydrolysis solution may be the same as or different from the anhydrous organic alcohol used to dissolve the aluminum source.

5. The method for preparing the Ni-Al composite oxide supported Pt catalyst for methylcyclohexane dehydrogenation according to any one of claims 1 to 4, comprising: 1) Dissolve the aluminum source completely in anhydrous organic alcohol at a molar ratio of anhydrous organic alcohol to aluminum source of 20 to 300:1 under stirring at room temperature to obtain a clear aluminum source alcohol solution; 2) Mixing 10 to 100 times the molar amount of the aluminum source used in step 1) with deionized water and 10 to 150 times the molar amount of anhydrous organic alcohol to obtain a clarified hydrolyzate; 3) Under stirring and reflux conditions at 60-160°C, slowly and uniformly add the hydrolyzate to the aluminum source alcohol solution, maintain the temperature and continue stirring and reflux reaction to promote partial hydrolysis of the aluminum source molecules in the reaction solution while inhibiting the polymerization and cross-linking between the aluminum hydroxyl monomer species obtained by hydrolysis to obtain an oligomeric aluminum hydroxyl species sol; 4) The aluminum hydroxyl species sol is volatilized in an open state at 40-100° C. to evaporate the solvent organic alcohol and deionized water to obtain a mesoporous alumina material having a mesoporous structure and a pseudo-boehmite crystal phase; 5) According to the molar ratio of aluminum source: nickel salt = 100-500:1, the mesoporous alumina material is placed in an ethanol solution containing nickel salt and stirred evenly, and then dried and calcined at 350-550°C to obtain γ -Mesoporous Ni-Al composite oxide support of Al2O3 crystal phase; 6) According to the molar ratio of aluminum source: chloroplatinic acid = 300-800:1, the mesoporous Ni-Al composite oxide support is placed in an ethanol solution dissolved with chloroplatinic acid and stirred evenly. After drying, the support is calcined at 400-600° C. to obtain a Ni-Al composite oxide supported Pt catalyst.

6. The method for preparing a Ni-Al composite oxide supported Pt catalyst for dehydrogenation of methylcyclohexane according to claim 5, characterized in that The hydrolyzate was slowly and uniformly added dropwise to the aluminum source alcohol solution at a dropping rate of 1.0-5.0 mL / min, and the temperature was maintained while stirring and reflux reaction was continued for 1-4 h.

7. The method for preparing a Ni-Al composite oxide supported Pt catalyst for dehydrogenation of methylcyclohexane according to claim 5, characterized in that The aluminum hydroxy species sol is allowed to evaporate the solvent in an open state at 40 to 100° C. for 6 to 48 hours.

8. The method for preparing a Ni-Al composite oxide supported Pt catalyst for dehydrogenation of methylcyclohexane according to claim 5, characterized in that The mesoporous alumina material impregnated with nickel salt is dried at 60° C. and then calcined at 350-550° C. for 2-4 hours.

9. The method for preparing a Ni-Al composite oxide supported Pt catalyst for dehydrogenation of methylcyclohexane according to claim 5, characterized in that The mesoporous Ni-Al composite oxide support impregnated with chloroplatinic acid is dried at 60° C. and then calcined at 400-600° C. for 2-4 hours.

10. The method for preparing the Ni-Al composite oxide supported Pt catalyst for dehydrogenation of methylcyclohexane according to claim 5, characterized in that The drying time in steps 5) and 6) is no less than 24 hours.

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