A high specific surface area mesoporous alumina material with surface rich in hydroxyl groups, and a method for its preparation and use

Abstract

A high specific surface area mesoporous alumina material with a surface rich in hydroxyl groups is produced by dissolving an aluminum source in an anhydrous organic alcohol solvent containing organic carboxylic acids, slowly and uniformly adding an aqueous ethanol solution to form an alumina sol, drying to obtain an alumina gel, and then treating with high-temperature steam at 400–650°C to obtain a material with... c Mesoporous alumina materials with Al2O3 crystal phase structure, well-developed mesoporous channel structure, high specific surface area and pore volume, and containing 5.0-10.0 mmol / g aluminum hydroxyl groups on the surface of mesoporous pore walls are suitable as catalyst supports for dehydrogenation reactions. The highly uniform loading of metal Pt active components significantly improves the low-temperature reaction activity, selectivity and stability of the catalyst for efficient dehydrogenation of liquid organic hydrogen supports.

Description

Technical Field

[0001] This invention belongs to the field of inorganic porous materials and catalyst preparation technology, and relates to a high specific surface area mesoporous alumina material, particularly a high specific surface area mesoporous alumina material with hydroxyl groups rich in the pore wall surface and whose content is adjustable, and its preparation method. The hydroxyl-rich high specific surface area mesoporous alumina material of this invention can be applied to the development of liquid organic hydrogen carrier dehydrogenation catalysts, realizing the practical application of liquid organic hydrogen carrier hydrogen storage technology. Background Technology

[0002] Mesoporous alumina materials have become ideal catalysts or catalyst supports in the chemical and petroleum industries due to their good stability, large specific surface area and pore volume, and tunable surface acidity / basicity. They have broad application prospects in reactions such as hydrocracking, hydrorefining, hydroreforming, dehydrogenation, and automobile exhaust purification (Journal of Colloid and Interface Science, 2018, 529, 432-443; ACS Applied Materials & Interfaces, 2023, 16, 454-466).

[0003] Studies have shown that when mesoporous alumina materials are used as supports, their specific surface area, pore volume, mesopore diameter, and surface aluminum hydroxyl content directly affect the catalytic performance of supported catalysts (International Journal of Hydrogen Energy, 2024, 57, 52-59; Environmental Science & Technology, 2022, 56, 10916-10924).

[0004] Increasing the specific surface area and surface aluminum hydroxyl content of mesoporous alumina supports is beneficial for the highly uniform dispersion of metal active components on the support surface (Nature Communications, 2024, 15, 3874; Molecular Catalysis, 2023, 535, 112817), exposing more catalytic active sites, increasing the probability of contact between reactants and active sites, and enhancing the reactivity of supported catalysts. In addition, larger and more uniformly distributed mesoporous pore sizes are beneficial for improving the mass transfer and diffusion performance of reactants and products within the catalyst channels, effectively suppressing the occurrence of side reactions and the formation of carbon deposits, and playing a positive role in improving the selectivity and stability of catalysts (International Journal of Hydrogen Energy, 2022, 47, 4704-4715; Nanomaterials, 2023, 13, 728).

[0005] Therefore, the preparation of mesoporous alumina materials with high specific surface area, large mesopore size and a large number of aluminum hydroxyl groups on the pore wall surface has become a hot topic in the research of mesoporous alumina materials.

[0006] Currently, there are many methods for preparing high specific surface area mesoporous alumina materials, mainly including precipitation, microwave, template, and sol-gel methods (Microporous and Mesoporous Materials, 2018, 260, 9-16; Chemistry of Materials, 2019, 32, 3-26). Among them, the sol-gel method has the advantages of being simple, convenient, reproducible, having mild reaction conditions, low energy consumption, and wide applicability, and has become a commonly used method for synthesizing mesoporous alumina materials.

[0007] The chemical process of the sol-gel method involves the hydrolysis of aluminum salts dissolved in a solvent to generate aluminum hydroxide monomers. These monomers then undergo polymerization-crosslinking reactions to form a sol, which in turn forms a gel. Finally, drying and heat treatment yield nano-alumina with a mesoporous structure (Microporous and Mesoporous Materials, 2016, 223, 203-212). However, due to the low electronegativity of aluminum, it readily undergoes nucleophilic reactions, resulting in a rapid and difficult-to-control hydrolysis-polymerization rate of aluminum salts. This leads to a small specific surface area (generally below 400 μm²) in mesoporous alumina materials obtained by the traditional sol-gel method. 2 The pore size distribution is relatively wide (generally in the range of 3 to 25 nm), and the aluminum hydroxyl content in the pore walls is relatively low, which seriously affects its practical application in the design and development of high-efficiency supported catalysts (Chemistry of Materials, 2019, 32, 3-26; Materials, 2021, 14, 1761).

[0008] How to control the hydrolysis-polymerization rate and crosslinking degree of aluminum source through a simple and reproducible preparation process, optimize the solution-sol-gel formation process, and improve the content of aluminum hydroxyl groups on the pore wall surface of mesoporous alumina materials with well-developed pore structure, high specific surface area and pore volume, large mesopore size and uniform pore size distribution, has become the focus and challenge of high-performance mesoporous alumina carrier material research. Summary of the Invention

[0009] The purpose of this invention is to provide a high specific surface area mesoporous alumina material with a surface rich in hydroxyl groups, its preparation method and application. Through a simple and controllable preparation process, a mesoporous alumina material with a well-developed mesoporous channel structure, uniform and adjustable mesoporous pore size, extremely high specific surface area and pore volume, and a surface rich in aluminum hydroxyl groups with adjustable content can be obtained, so as to significantly enhance its practical application value as a catalyst support.

[0010] The high specific surface area mesoporous alumina material with hydroxyl-rich surface described in this invention is prepared by dissolving an aluminum source in an anhydrous organic alcohol solvent containing organic carboxylic acids, slowly and uniformly adding an aqueous ethanol solution to induce a slow hydrolysis-polymerization reaction of the aluminum source to form an alumina sol, drying to obtain an alumina gel with a mesoporous structure, and then treating it at a high temperature of 400-650°C in a water vapor environment to obtain a material with... γ -Mesoporous alumina materials with an Al2O3 crystal phase structure have a specific surface area, pore volume, and mesopore diameter of 500–900 μm. 2 / g, 0.8~1.8cm 3 / g and 5.0~12.0nm, and contains 5.0~10.0mmol / g of aluminum hydroxyl groups on the surface of the mesoporous pore walls.

[0011] In the high specific surface area mesoporous alumina material with hydroxyl-rich surface described in this invention, the aluminum source can be one or a mixture of several of aluminum isopropoxide, aluminum isobutoxide, aluminum tert-butoxide, aluminum nitrate, aluminum chloride, or aluminum sulfate in any proportion.

[0012] Furthermore, the organic carboxylic acid is citric acid, glacial acetic acid, oxalic acid, or tartaric acid.

[0013] Furthermore, the anhydrous organic alcohol solvent is one of methanol, ethanol, or isopropanol, or a mixture of several in any proportion.

[0014] The high specific surface area mesoporous alumina material with a surface rich in hydroxyl groups described in this invention is preferably prepared according to the following method:

[0015] 1) Dissolve the organic carboxylic acid and aluminum source in an anhydrous organic alcohol solvent to obtain a clear solution;

[0016] 2) Under stirring and reflux conditions at 50–150°C, an aqueous ethanol solution is slowly and uniformly added dropwise as a hydrolysate to the clarified solution to promote a slow hydrolysis-polymerization reaction of the aluminum source within the confined space of the organic alcohol solvent, thereby obtaining alumina sol.

[0017] 3) The solvent in the alumina sol is removed by natural evaporation in an open state to obtain a blocky alumina gel with a mesoporous structure;

[0018] 4) The alumina gel is subjected to high-temperature treatment in a water vapor environment of 400–650℃ to prepare a product with… γ -A high specific surface area mesoporous alumina material with an Al2O3 crystal phase structure and a surface rich in aluminum hydroxyl groups.

[0019] In the clarified solution, the molar ratio of organic carboxylic acids and anhydrous organic alcohols to the aluminum source is preferably 0.01–10:5–200:1.

[0020] More preferably, in the clarified solution, the molar ratio of organic carboxylic acids and anhydrous organic alcohols to the aluminum source is 0.1–1:10–100:1.

[0021] The amount of the ethanol aqueous solution used is 5 to 15 times the mass of the aluminum source.

[0022] More specifically, the volume percentage of the ethanol-water solution is preferably 50-90%.

[0023] Furthermore, the present invention preferably involves slowly and uniformly adding the ethanol aqueous solution to the clarified solution at a dropping rate of 2 to 15 mL / min, thereby causing the aluminum source molecules in the solution to undergo a slow hydrolysis-polymerization reaction within the confined space of the organic alcohol solvent to obtain alumina sol.

[0024] Furthermore, after adding the ethanol-water hydrolysate, the temperature is maintained and the mixture is stirred and refluxed for 0.5–3 hours to ensure that the aluminum source is fully hydrolyzed to obtain alumina sol.

[0025] Preferably, the present invention specifically involves subjecting the obtained alumina sol to volatilization drying treatment at 40–100°C in an open state to remove alcohol and water present in the alumina sol, thereby obtaining a blocky alumina gel with a mesoporous structure.

[0026] More preferably, the process of removing the solvent by natural evaporation in the open state is maintained for 6 to 72 hours.

[0027] In the preparation method of this invention, the alumina gel is subjected to high-temperature treatment in a steam environment at 400–650°C to remove organic carboxylic acid molecules that coordinate with aluminum atoms and to promote the alumina crystal phase from the pseudoboehmite crystal phase to the crystalline phase. γ During the Al2O3 crystal phase transformation, the unstable Al-O-Al bonds on the surface of mesoporous alumina are broken by the hydrolysis of high-temperature water vapor, and a large amount of surface Al-OH is generated. This results in a mesoporous alumina material with uniform and adjustable pore size, large specific surface area and pore volume, and rich aluminum hydroxyl content on the pore wall surface.

[0028] More specifically, the present invention involves treating the alumina gel at high temperature in water vapor at a flow rate of 10-30 mL / min, with the treatment time preferably being 0.5-3 h.

[0029] This invention first uses an aqueous ethanol solution as the hydrolysate, which is slowly and uniformly added dropwise to an anhydrous organic alcohol solvent containing an aluminum source and an organic carboxylic acid. By heating and refluxing under normal pressure, water molecules uniformly dispersed between ethanol molecules come into contact with aluminum source molecules that are highly uniformly dispersed in the reaction solution. This causes the aluminum source molecules to undergo local hydrolysis within the molecular confinement space of the organic alcohol solvent. At this time, the organic carboxylic acid molecules dissolved in the reaction solution can also undergo coordination reactions with the partially hydrolyzed monomeric aluminum hydroxyl species, thereby effectively inhibiting the polymerization and cross-linking between aluminum hydroxyl species, resulting in an oligomeric aluminum hydroxyl species sol that is highly uniformly dispersed between organic alcohol solvent molecules.

[0030] Secondly, during the subsequent volatilization process of this invention, the volatilization and precipitation of organic alcohol solvent molecules and water molecules filling the spaces between oligomeric aluminum hydroxyl species, as well as the further polymerization and crosslinking between aluminum hydroxyl species, ultimately produce an alumina gel with a well-developed mesoporous structure.

[0031] Furthermore, through the high-temperature steam treatment of mesoporous alumina gel according to this invention, organic carboxylic acid molecules coordinated with aluminum atoms are removed, and the alumina crystal phase is induced to change from the pseudoboehmite crystal phase to the... γ During the Al2O3 crystal phase transformation, the unstable Al-O-Al bonds on the surface of the mesoporous alumina are broken by the hydrolysis of high-temperature water vapor, and a large amount of surface Al-OH is generated. In this way, a mesoporous alumina material with a well-developed mesoporous channel structure, uniform pore size, large specific surface area and pore volume, and rich aluminum hydroxyl content on the surface of the mesoporous pore walls that can be adjusted is finally obtained.

[0032] The present invention provides a simple, easy-to-implement, and reproducible method for preparing high-specific-surface-area mesoporous alumina materials rich in hydroxyl groups. Compared with traditional mesoporous alumina preparation methods, the method of slowly and uniformly adding an ethanol aqueous solution as a hydrolysate to an organic alcohol solvent containing dissolved aluminum source and organic carboxylic acid ligands can effectively control the hydrolysis rate of the aluminum source and the degree of polymerization-crosslinking between aluminum hydroxyl species. This enables the controllable synthesis of mesoporous alumina materials with well-developed mesoporous channel structure and high specific-surface-area. The hydrolysis of unstable Al-O-Al bonds on the pore wall surface of mesoporous alumina by high-temperature steam promotes the generation of a large amount of surface Al-OH. By controlling the amount of steam introduced, the treatment temperature and time, and the adjustment of the texture properties of mesoporous alumina, the surface Al-OH content of the mesoporous alumina material can be effectively controlled, which is beneficial for the large-scale preparation of high-specific-surface-area mesoporous alumina materials rich in hydroxyl groups.

[0033] Based on the excellent structure, texture and surface properties of the high specific surface area mesoporous alumina material with hydroxyl-rich surface prepared by the present invention, it is suitable for use as a catalyst support to achieve highly uniform dispersion of metal active components at the near atomic level on its pore wall surface.

[0034] More specifically, the high specific surface area mesoporous alumina material with hydroxyl-rich surface described in this invention is suitable as a support for preparing liquid organic hydrogen carrier dehydrogenation catalysts. By loading metal active components onto it, the low-temperature reaction activity, selectivity and stability of the mesoporous alumina-supported metal catalyst in the efficient dehydrogenation reaction of liquid organic hydrogen carriers can be significantly improved.

[0035] Furthermore, this invention also provides a low-temperature, high-efficiency dehydrogenation catalyst for liquid organic hydrogen supports. The catalyst uses the high-specific-surface-area mesoporous alumina material with a surface rich in hydroxyl groups as described in this invention as a support, and loads a metal Pt active component. When applied to the low-temperature dehydrogenation reaction of liquid organic hydrogen supports, it can achieve highly efficient and selective dehydrogenation of liquid organic hydrogen supports at reaction temperatures of 280–350°C, with a hydrogen evolution rate as high as 900 mmol / g. Pt The catalyst's catalytic activity and selectivity remained almost unchanged during the long reaction period of 100 hours, with a reaction rate of over 900 min. Attached Figure Description

[0036] Figure 1 This is the XRD pattern of the high specific surface area mesoporous alumina material with hydroxyl-rich surface in Example 1.

[0037] Figure 2 This is a TEM image of the high specific surface area mesoporous alumina material with hydroxyl-rich surface in Example 1.

[0038] Figure 3 The N2 adsorption-desorption isotherm and pore size distribution curve are for the high specific surface area mesoporous alumina material with hydroxyl-rich surface in Example 1.

[0039] Figure 4 This is the in-situ FT-IR spectrum of the high specific surface area mesoporous alumina material with hydroxyl-rich surface in Example 1 after high vacuum dehydration treatment.

[0040] Figure 5 The thermogravimetric curve is shown in Example 1 for a high specific surface area mesoporous alumina material with a surface rich in hydroxyl groups.

[0041] Figure 6 The N2 adsorption-desorption isotherm and pore size distribution curve are shown in Comparative Example 1, which shows the high specific surface area mesoporous alumina material.

[0042] Figure 7 The thermogravimetric curves of the high specific surface area mesoporous alumina material in Comparative Example 1 are shown.

[0043] Figure 8 The N2 adsorption-desorption isotherm and pore size distribution curve of the mesoporous alumina material in Comparative Example 2 are shown.

[0044] Figure 9The thermogravimetric curves of the mesoporous alumina material in Comparative Example 2 are shown.

[0045] Figure 10 This is a STEM image of the catalyst material obtained by loading 0.5 wt% Pt onto a high specific surface area mesoporous alumina material rich in hydroxyl groups on the surface in Example 1.

[0046] Figure 11 This is a graph showing the performance of the catalyst obtained by loading 0.5 wt% Pt onto a high specific surface area mesoporous alumina material rich in hydroxyl groups in Example 1 for the dehydrogenation reaction of methylcyclohexane at 280°C. Detailed Implementation

[0047] The specific embodiments of the present invention will be further described in detail below with reference to the accompanying drawings and examples. The following examples 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, and are not intended to limit the scope of protection of the present invention.

[0048] Unless otherwise specified, the production processes, experimental methods, or testing methods involved in the embodiments of this invention are all conventional methods in the prior art, and their names and / or abbreviations are all conventional names in the field, which are very clear and distinct in the relevant application areas. Those skilled in the art can understand the conventional process steps based on the names and apply the corresponding equipment, and implement them according to conventional conditions or the conditions recommended by the manufacturer.

[0049] The various instruments, equipment, raw materials or reagents used in the embodiments of this invention are not subject to any special restrictions on their source. They are all conventional products that can be purchased through regular commercial channels and can be prepared according to conventional methods known to those skilled in the art. Example

[0050] Example 1

[0051] Under stirring and reflux conditions at 75°C, 0.86 g of glacial acetic acid and 8.25 g of aluminum isopropoxide were completely dissolved in 60 mL of anhydrous ethanol to obtain a clear solution.

[0052] Keeping the stirring and reflux conditions unchanged, 100 mL of hydrolysate, which is a mixture of anhydrous ethanol and deionized water in a volume ratio of 8:2, was added dropwise to the clear solution at a dropping rate of 8.0 mL / min. After the addition was completed, stirring and reflux were continued for 2 h to obtain alumina sol.

[0053] The obtained alumina sol was subjected to solvent evaporation treatment at 80℃ for 24 hours to obtain a blocky alumina gel with a mesoporous structure.

[0054] A high specific surface area mesoporous alumina material with hydroxyl-rich surface was prepared by calcining the alumina gel in water vapor at a flow rate of 20 mL / min at 550 °C for 2 h.

[0055] Figure 1 The XRD pattern of the alumina material prepared in Example 1 is shown. Figure 1 The small-angle XRD pattern in (A) shows a strong diffraction peak at 2θ = 0.89°, proving that the alumina material has a mesoporous channel structure; furthermore, the large-angle XRD pattern in (B) shows peaks at 45.5° and 67.0° corresponding to... γ The two weak diffraction peaks of the Al2O3 (400) and (440) crystal planes indicate that the material possesses γ -Al2O3 crystal phase structure and small nanocrystals.

[0056] Figure 2 TEM characterization results further confirmed that the prepared alumina material has a highly developed mesoporous channel structure.

[0057] Depend on Figure 3 The N2 adsorption-desorption isotherm (A) and the corresponding pore size distribution curve (B) show that the alumina material exhibits a typical Type IV adsorption isotherm and an H1 hysteresis loop, characteristic of cylindrical pores. Furthermore, it displays a very steep capillary condensation curve within the relative pressure range of 0.5–0.8, indicating that the alumina material possesses a large and uniformly distributed pore size. Calculations show that the specific surface area and pore volume of the alumina material are 818 m² / s. 2 / g and 1.35cm 3 / g, with a mesopore size of 6.92nm.

[0058] Figure 4 Furthermore, in-situ high-vacuum FT-IR spectra of the alumina material were provided. After high-vacuum dehydration treatment at 300℃ for 2 hours, the FT-IR spectra were obtained at 1640 cm⁻¹. -1 No bending vibration absorption peak corresponding to the hydroxyl group in the water molecule was detected at this location, indicating that the adsorbed water present in the mesoporous channels of the alumina material was completely removed after high-temperature vacuum treatment. Meanwhile, at this point, the absorption peak at 3300–3900 cm⁻¹... -1 The presence of multiple strong absorption peaks corresponding to the stretching vibration of hydroxyl groups within the range fully demonstrates that the alumina material contains a large number of different types of aluminum hydroxyl groups (Al-OH) on the pore wall surface.

[0059] Thermogravimetric analysis was performed on the alumina material prepared in Example 1, and the results were obtained. Figure 5The thermogravimetric curves are shown. It is evident that the alumina material exhibits significant weight loss behavior between 180 and 600 °C, corresponding to the polymerization and dehydration of Al-OH on the pore wall surface. Calculations show that the Al-OH content on the pore wall surface of the alumina material is as high as 8.91 mmol / g, which is consistent with the results determined by Grignard titration.

[0060] Example 2

[0061] Under stirring and reflux conditions at 90°C, 1.26 g of citric acid and 6.40 g of aluminum tert-butoxide were completely dissolved in 80 mL of anhydrous isopropanol to obtain a clear solution.

[0062] Keeping the stirring and reflux conditions unchanged, 85 mL of hydrolysate, which is a mixture of anhydrous ethanol and deionized water in a volume ratio of 9:1, was added dropwise to the clear solution at a dropping rate of 10.0 mL / min. After the addition was completed, stirring and reflux were continued for 2 h to obtain alumina sol.

[0063] The obtained alumina sol was subjected to solvent evaporation treatment at 100℃ for 6 hours to obtain a blocky alumina gel with a mesoporous structure.

[0064] Alumina gel was calcined in steam at 500°C for 3 hours at a flow rate of 25 mL / min to prepare a high specific surface area mesoporous alumina material with hydroxyl-rich surface.

[0065] Characterization results from XRD, TEM, and N2 adsorption-desorption confirmed that the prepared alumina material possesses a well-developed mesoporous channel structure, uniform mesopore size, high specific surface area, and high pore volume. Calculations showed that the specific surface area and pore volume of the alumina material were 780 m² / s. 2 / g and 0.95cm 3 / g, mesopore diameter 7.36nm.

[0066] High-vacuum in-situ FT-IR, thermogravimetric analysis and Grignard reagent titration results confirmed that the surface of the pore wall of the alumina material contains a large amount of aluminum hydroxyl groups, with a content as high as 8.09 mmol / g.

[0067] Example 3

[0068] Under stirring and reflux conditions at 80°C, 1.80 g of tartaric acid and 8.16 g of aluminum isopropoxide were completely dissolved in 60 mL of anhydrous methanol to obtain a clear solution.

[0069] Keeping the stirring and reflux conditions unchanged, 60 mL of hydrolysate, which is a mixture of anhydrous ethanol and deionized water in a volume ratio of 1:1, was added dropwise to the clear solution at a dropping rate of 10.0 mL / min. After the addition was completed, stirring and reflux were continued for 2 h to obtain alumina sol.

[0070] The obtained alumina sol was subjected to solvent evaporation treatment at 60℃ for 48 hours to obtain a blocky alumina gel with a mesoporous structure.

[0071] A high specific surface area mesoporous alumina material with hydroxyl-rich surface was prepared by calcining the alumina gel in water vapor at a flow rate of 15 mL / min at 500 °C for 2 h.

[0072] Characterization results from XRD, TEM, and N2 adsorption-desorption confirmed that the prepared alumina material possesses a well-developed mesoporous channel structure, uniform mesopore size, high specific surface area, and high pore volume. Calculations showed that the specific surface area and pore volume of the alumina material were 690 m² / s. 2 / g and 1.05cm 3 / g, mesopore diameter 9.69nm.

[0073] High-vacuum in-situ FT-IR, thermogravimetric analysis, and Grignard reagent titration results confirmed that the surface of the pore wall of the alumina material contains a large amount of aluminum hydroxyl groups, with a content as high as 7.38 mmol / g.

[0074] Example 4

[0075] Under stirring and reflux conditions at 120°C, 0.84 g of citric acid and 10.6 g of aluminum nitrate were completely dissolved in 70 mL of isopropanol to obtain a clear solution.

[0076] Keeping the stirring and reflux conditions unchanged, 80 mL of hydrolysate, which is a mixture of anhydrous ethanol and deionized water in a volume ratio of 6:4, was added dropwise to the clear solution at a dropping rate of 5.0 mL / min. After the addition was completed, stirring and reflux were continued for 2 h to obtain alumina sol.

[0077] The obtained alumina sol was subjected to solvent evaporation treatment at 50℃ for 48 hours to obtain a blocky alumina gel with a mesoporous structure.

[0078] A high specific surface area mesoporous alumina material with hydroxyl-rich surface was prepared by calcining the alumina gel in water vapor at a flow rate of 28 mL / min at 450 °C for 4 h.

[0079] Characterization results from XRD, TEM, and N2 adsorption-desorption confirmed that the prepared alumina material possesses a well-developed mesoporous channel structure, uniform mesopore size, high specific surface area, and high pore volume. Calculations showed that the specific surface area and pore volume of the alumina material were 725 m² / s. 2 / g and 0.97cm 3 / g, mesopore size 10.20nm.

[0080] High-vacuum in-situ FT-IR, thermogravimetric analysis, and Grignard reagent titration results confirmed that the surface of the pore wall of the alumina material contains a large amount of aluminum hydroxyl groups, with a content as high as 8.03 mmol / g.

[0081] Example 5

[0082] Under stirring and reflux conditions at 100°C, 0.68 g of glacial acetic acid and 11.2 g of aluminum isopropoxide were completely dissolved in 100 mL of isopropanol to obtain a clear solution.

[0083] Keeping the stirring and reflux conditions unchanged, 100 mL of hydrolysate, which is a mixture of anhydrous ethanol and deionized water in a volume ratio of 8:2, was added dropwise to the clear solution at a dropping rate of 10.0 mL / min. After the addition was completed, stirring and reflux were continued for 2 h to obtain alumina sol.

[0084] The obtained alumina sol was subjected to solvent evaporation treatment at 80℃ for 36 hours to obtain a blocky alumina gel with a mesoporous structure.

[0085] A high specific surface area mesoporous alumina material with hydroxyl-rich surface was prepared by calcining the alumina gel in water vapor at a flow rate of 10 mL / min at 600 °C for 3 h.

[0086] Characterization results from XRD, TEM, and N2 adsorption-desorption confirmed that the prepared alumina material possesses a well-developed mesoporous channel structure, uniform mesopore size, high specific surface area, and high pore volume. Calculations showed that the specific surface area and pore volume of the alumina material were 672 m² / s. 2 / g and 1.23cm 3 / g, mesopore size 10.96nm.

[0087] High-vacuum in-situ FT-IR, thermogravimetric analysis, and Grignard reagent titration results confirmed that the surface of the pore wall of the alumina material contains a large amount of aluminum hydroxyl groups, with a content as high as 6.04 mmol / g.

[0088] Example 6

[0089] Under stirring and reflux conditions at 140°C, 0.92 g of oxalic acid and 9.2 g of aluminum isobutoxide were completely dissolved in 90 mL of ethanol to obtain a clear solution.

[0090] Keeping the stirring and reflux conditions unchanged, 100 mL of hydrolysate, which is a mixture of anhydrous ethanol and deionized water in a volume ratio of 7:3, was added dropwise to the clear solution at a dropping rate of 3.0 mL / min. After the addition was completed, stirring and reflux were continued for 1 h to obtain alumina sol.

[0091] The obtained alumina sol was subjected to solvent evaporation treatment at 60℃ for 48 hours to obtain a blocky alumina gel with a mesoporous structure.

[0092] A high specific surface area mesoporous alumina material with hydroxyl-rich surface was prepared by calcining the alumina gel in water vapor at a flow rate of 30 mL / min at 600 °C for 2 h.

[0093] Characterization results from XRD, TEM, and N2 adsorption-desorption confirmed that the prepared alumina material possesses a well-developed mesoporous channel structure, uniform mesopore size, high specific surface area, and high pore volume. Calculations showed that the specific surface area and pore volume of the alumina material were 615 m² / s. 2 / g and 1.12cm 3 / g, mesopore diameter 8.04nm.

[0094] High-vacuum in-situ FT-IR, thermogravimetric analysis, and Grignard reagent titration results confirmed that the surface of the pore walls of the alumina material contains a large amount of aluminum hydroxyl groups, with a content as high as 6.56 mmol / g.

[0095] Comparative Example 1

[0096] Under stirring and reflux conditions at 75°C, 0.86 g of glacial acetic acid and 8.25 g of aluminum isopropoxide were completely dissolved in 60 mL of anhydrous ethanol to obtain a clear solution.

[0097] Keeping the stirring and reflux conditions unchanged, 100 mL of hydrolysate, which is a mixture of anhydrous ethanol and deionized water in a volume ratio of 8:2, was added dropwise to the clear solution at a dropping rate of 8.0 mL / min. After the addition was completed, stirring and reflux were continued for 2 h to obtain alumina sol.

[0098] The obtained alumina sol was subjected to solvent evaporation treatment at 80℃ for 24 hours to obtain a blocky alumina gel with a mesoporous structure.

[0099] High specific surface area mesoporous alumina material was prepared by calcining alumina gel in air at 550℃ for 2 hours.

[0100] Figure 6 The N2 adsorption-desorption isotherm (A) and pore size distribution curve (B) show that the alumina material prepared in Comparative Example 1 also has a well-developed mesoporous channel structure, uniform mesopore size, high specific surface area and pore volume. The calculated specific surface area and pore volume of the alumina material are 722 m² / s. 2 / g and 1.25cm 3 / g, with a mesopore diameter of 6.30nm, which is not significantly different from the performance of the alumina material in Example 1.

[0101] However, according to Figure 7The thermogravimetric curve of the alumina material in Comparative Example 1 and the results of the Grignard reagent titration method confirmed that the Al-OH content on the pore wall surface of the alumina material in Comparative Example 1 was only 3.69 mmol / g, which was significantly lower than the aluminum hydroxyl content in Example 1.

[0102] Comparative Example 2

[0103] Under stirring and reflux conditions at 75°C, 0.86 g of glacial acetic acid and 8.25 g of aluminum isopropoxide were completely dissolved in 60 mL of anhydrous ethanol to obtain a clear solution.

[0104] Keeping the stirring and reflux conditions unchanged, 20 mL of deionized water was added dropwise to the clear solution at a dropping rate of 8.0 mL / min. After the addition was completed, stirring and reflux were continued for 2 h to obtain alumina sol.

[0105] The obtained alumina sol was subjected to solvent evaporation treatment at 80℃ for 24 hours to obtain a blocky alumina gel with a mesoporous structure.

[0106] Mesoporous alumina material was prepared by calcining alumina gel in air at 550°C for 2 hours.

[0107] Figure 8 The N2 adsorption-desorption isotherm (A) and pore size distribution curve (B) show that although the alumina material prepared in Comparative Example 2 also has a mesoporous channel structure, the mesopore size distribution is wider and the specific surface area and pore volume are relatively low. Its specific surface area and pore volume are calculated to be only 334 m². 2 / g and 0.30cm 3 / g.

[0108] Furthermore, according to Figure 9 The thermogravimetric curves of the alumina material in Comparative Example 2, combined with the results of Grignard reagent titration, confirm that the aluminum hydroxyl content on the pore wall surface of the alumina material in Comparative Example 2 is only 1.70 mmol / g.

[0109] Comparing Comparative Examples 1 and 2 with Example 1, it can be seen that using an aqueous ethanol solution instead of pure water as the hydrolysis solution, and slowly and uniformly adding it to an anhydrous organic alcohol solvent containing aluminum source and organic carboxylic acid, can effectively reduce the hydrolysis-polymerization-crosslinking rate and degree of aluminum source molecules. This is beneficial for preparing mesoporous alumina materials with larger specific surface area and pore volume. At the same time, the use of high-temperature steam treatment is more conducive to increasing the surface Al-OH content of the prepared mesoporous alumina material.

[0110] Application Example 1

[0111] 1.0 g of the high specific surface area mesoporous alumina material with hydroxyl-rich surface prepared in Example 1 was weighed as a carrier and immersed in 40 mL of anhydrous ethanol solution containing 0.013 g H2PtCl6. After stirring at room temperature for 24 h, it was successively subjected to volatilization drying at 60 °C and calcination at 500 °C for 4 h to prepare the mesoporous alumina-supported Pt-based catalytic material.

[0112] Depend on Figure 10 The STEM images of the prepared catalytic material show that the active metal Pt nanoclusters with a size of less than 1.5 nm can be highly uniformly dispersed on the surface of the pore walls of the support.

[0113] Take 0.20 g of the catalyst material prepared above and fill it into a fixed-bed microreactor. At 280 °C, use nitrogen gas with a flow rate of 10 mL / min as the carrier gas to introduce methylcyclohexane at a flow rate of 2.5 mL / h into the microreactor to carry out the methylcyclohexane dehydrogenation reaction.

[0114] Depend on Figure 11 It is evident that, after 1 hour of reaction, the catalytic material achieved a conversion rate of 98.0% for methylcyclohexane, a toluene selectivity of 100% in the product, and a hydrogen evolution rate as high as 985 mmol / g / min. More importantly, during a continuous reaction of 100 hours, the conversion rate of methylcyclohexane and the hydrogen evolution rate consistently remained above 95.2% and 957 mmol / g / min, respectively.

[0115] Therefore, the catalytic material obtained by loading Pt onto a high specific surface area mesoporous alumina material rich in hydroxyl groups exhibits extremely high catalytic activity, selectivity and stability in the low-temperature dehydrogenation reaction of methylcyclohexane.

[0116] Application Example 2

[0117] 1.0 g of the high specific surface area mesoporous alumina material with hydroxyl-rich surface prepared in Example 2 was weighed as a carrier and immersed in 40 mL of anhydrous ethanol solution containing 0.013 g H2PtCl6. After stirring at room temperature for 24 h, it was successively treated by volatilization drying at 70 °C and calcination at 600 °C for 4 h to prepare the mesoporous alumina-supported Pt-based catalytic material.

[0118] 0.20 g of the above-mentioned catalyst material was packed into a fixed-bed microreactor. At 280 °C, nitrogen gas with a flow rate of 10 mL / min was used as the carrier gas to introduce methylcyclohexane at a flow rate of 27.0 mL / h into the microreactor for the methylcyclohexane dehydrogenation reaction.

[0119] After 1 hour of reaction, the conversion rate of methylcyclohexane by the catalyst was 20.1%, the selectivity of toluene in the product was 100%, and the hydrogen evolution rate was 2183 mmol / g / min. During the continuous reaction for 100 hours, the conversion rate of methylcyclohexane and the hydrogen evolution rate remained above 16.1% and 1749 mmol / g / min, respectively.

[0120] Application Example 3

[0121] 1.0 g of the high specific surface area mesoporous alumina material with hydroxyl-rich surface prepared in Example 3 was weighed as a carrier and immersed in 40 mL of anhydrous ethanol solution containing 0.013 g H2PtCl6. After stirring at room temperature for 24 h, it was successively subjected to volatilization drying at 70 °C and calcination at 500 °C for 4 h to prepare the mesoporous alumina-supported Pt-based catalytic material.

[0122] 0.20 g of the above-mentioned catalyst material was packed into a fixed-bed microreactor. At 280 °C, nitrogen gas with a flow rate of 10 mL / min was used as the carrier gas to introduce cyclohexane at a flow rate of 3.0 mL / h into the microreactor for cyclohexane dehydrogenation reaction.

[0123] After 1 hour of reaction, the catalytic material achieved a 92.1% conversion rate of cyclohexane, a 100% selectivity for benzene in the product, and a hydrogen evolution rate of 1280 mmol / g / min. Furthermore, during a continuous reaction of 100 hours, the cyclohexane conversion rate and hydrogen evolution rate remained above 89.0% and 1237 mmol / g / min, respectively.

[0124] Application Example 4

[0125] 1.0 g of the high specific surface area mesoporous alumina material with hydroxyl-rich surface prepared in Example 4 was weighed as a carrier and immersed in 40 mL of anhydrous ethanol solution containing 0.013 g H2PtCl6. After stirring at room temperature for 24 h, it was successively treated by volatilization drying at 60 °C and calcination at 550 °C for 4 h to prepare mesoporous alumina-supported Pt-based catalytic material.

[0126] Take 0.20 g of the above-mentioned catalyst material and fill it into a fixed-bed microreactor. At 280 °C, use nitrogen gas with a flow rate of 10 mL / min as the carrier gas to carry cyclohexane at a flow rate of 20.0 mL / h into the microreactor to carry out the cyclohexane dehydrogenation reaction.

[0127] After 1 hour of reaction, the catalytic material achieved a cyclohexane conversion rate of 22.3%, a benzene selectivity of 100% in the product, and a hydrogen evolution rate of 2067 mmol / g / min. Furthermore, during the continuous reaction for 100 hours, the cyclohexane conversion rate and hydrogen evolution rate remained above 18.3% and 1696 mmol / g / min, respectively.

[0128] Application Example 5

[0129] 1.0 g of the high specific surface area mesoporous alumina material with hydroxyl-rich surface prepared in Example 5 was weighed as a carrier and immersed in 40 mL of anhydrous ethanol solution containing 0.013 g H2PtCl6. After stirring at room temperature for 24 h, it was successively treated by volatilization drying at 80 °C and calcination at 450 °C for 5 h to prepare mesoporous alumina-supported Pt-based catalytic material.

[0130] 0.20 g of the above-mentioned catalyst material was packed into a fixed-bed microreactor. At 280 °C, nitrogen gas with a flow rate of 10 mL / min was used as the carrier gas to introduce decahydronaphthalene into the microreactor at a flow rate of 5.0 mL / h for decahydronaphthalene dehydrogenation reaction.

[0131] After 1 hour of reaction, the conversion rate of decahydronaphthalene by the catalyst was 68.2%, the naphthalene selectivity in the product was 100%, and the hydrogen evolution rate was 1107 mmol / g / min. Furthermore, during the continuous reaction for 100 hours, the conversion rate of decahydronaphthalene and the hydrogen evolution rate remained above 50.6% and 821 mmol / g / min, respectively.

[0132] Application Example 6

[0133] 1.0 g of the high specific surface area mesoporous alumina material with hydroxyl-rich surface prepared in Example 6 was weighed as a carrier and immersed in 40 mL of anhydrous ethanol solution containing 0.013 g H2PtCl6. After stirring at room temperature for 24 h, it was successively treated by volatilization drying at 60 °C and calcination at 500 °C for 3 h to prepare the mesoporous alumina-supported Pt-based catalytic material.

[0134] 0.20 g of the above-mentioned catalyst material was packed into a fixed-bed microreactor. At 280 °C, nitrogen gas with a flow rate of 10 mL / min was used as the carrier gas to introduce decahydronaphthalene into the microreactor at a flow rate of 28.0 mL / h for decahydronaphthalene dehydrogenation reaction.

[0135] After 1 hour of reaction, the conversion rate of decahydronaphthalene by the catalyst was 21.6%, the naphthalene selectivity in the product was 100%, and the hydrogen evolution rate was 1902 mmol / g / min. Furthermore, during the continuous reaction for 100 hours, the conversion rate of decahydronaphthalene and the hydrogen evolution rate remained above 15.9% and 1401 mmol / g / min, respectively.

[0136] Application Example 7

[0137] 1.0 g of the high specific surface area mesoporous alumina material prepared in Comparative Example 1 was weighed as a carrier and immersed in 40 mL of anhydrous ethanol solution containing 0.013 g of H2PtCl6. After stirring at room temperature for 24 h, the material was successively subjected to volatilization drying at 60 °C and calcination at 500 °C for 4 h to prepare the mesoporous alumina-supported Pt-based catalyst material.

[0138] Take 0.20 g of the catalyst material prepared above and fill it into a fixed-bed microreactor. At 280 °C, use nitrogen gas with a flow rate of 10 mL / min as the carrier gas to introduce methylcyclohexane at a flow rate of 2.5 mL / h into the microreactor to carry out the methylcyclohexane dehydrogenation reaction.

[0139] After 1 hour of reaction, the conversion rate of methylcyclohexane by the catalyst was 78.1%, the selectivity of toluene in the product was 100%, and the hydrogen evolution rate was 785 mmol / g / min.

[0140] Under the same conditions, after 100 h of continuous reaction, the conversion rate and hydrogen evolution rate of methylcyclohexane decreased to 65.2% and 656 mmol / g / min, respectively.

[0141] Compared with Application Example 1, the supported Pt-based catalyst with Pt metal supported on it exhibited relatively poor low-temperature dehydrogenation catalytic activity due to the lower surface aluminum hydroxyl content of Comparative Example 1. It was only 79.7% of the Pt catalyst supported on the mesoporous alumina material in Application Example 1. Moreover, after a long reaction time of 100 h, the catalytic activity decreased by 16.5%, which was significantly lower than the catalytic stability of the Pt catalyst supported on the mesoporous alumina material in Application Example 1.

[0142] Application Example 8

[0143] 1.0 g of the mesoporous alumina material prepared in Comparative Example 2 was weighed and impregnated in 40 mL of anhydrous ethanol solution containing 0.013 g H2PtCl6. After stirring at room temperature for 24 h, the material was successively subjected to volatilization drying at 60 °C and calcination at 500 °C for 4 h to prepare the mesoporous alumina-supported Pt-based catalytic material.

[0144] Take 0.20 g of the catalyst material prepared above and fill it into a fixed-bed microreactor. At 280 °C, use nitrogen gas with a flow rate of 10 mL / min as the carrier gas to introduce methylcyclohexane at a flow rate of 2.5 mL / h into the microreactor to carry out the methylcyclohexane dehydrogenation reaction.

[0145] After 1 hour of reaction, the conversion rate of methylcyclohexane by the catalyst was 33.7%, the selectivity of toluene in the product was 100%, and the hydrogen evolution rate was 339 mmol / g / min.

[0146] Under the same conditions, after 100 h of continuous reaction, the conversion rate and hydrogen evolution rate of methylcyclohexane decreased to 21.2% and 213 mmol / g / min, respectively.

[0147] Compared with Application Example 1, Comparative Example 2, due to its lower specific surface area and surface aluminum hydroxyl content, is not conducive to the highly uniform dispersion of metallic Pt. As a result, the supported Pt-based catalyst with Pt metal supported on it exhibits poor low-temperature dehydrogenation catalytic activity and stability. Its catalytic activity is only 34.4% of that of the Pt catalyst supported on the mesoporous alumina material in Application Example 1. Moreover, after a long reaction time of 100 h, the catalytic activity decreased by 37.1%, which is significantly lower than the catalytic stability of the Pt catalyst supported on the mesoporous alumina material in Application Example 1.

[0148] The above embodiments of the present invention do not describe all details exhaustively, nor do they limit the present invention to the embodiments described above. Various changes, modifications, substitutions, and variations made by those skilled in the art to these embodiments without departing from the principles and spirit of the present invention should be included within the scope of protection of the present invention.

Claims

1. A high specific surface area mesoporous alumina material with a surface rich in hydroxyl groups, comprising dissolving an aluminum source in an anhydrous organic alcohol solvent containing an organic carboxylic acid at a molar ratio of organic carboxylic acid and anhydrous organic alcohol to aluminum source of 0.01–10:5–200:1, and slowly and uniformly adding an aqueous ethanol solution at a rate of 2–15 mL / min under stirring and reflux conditions at 50–150 °C to induce a slow hydrolysis-polymerization reaction of the aluminum source to form an alumina sol, drying to obtain an alumina gel with a mesoporous structure, and then treating it at a high temperature of 400–650 °C in a steam environment to obtain a material with… γ -Mesoporous alumina materials with an Al2O3 crystal phase structure have a specific surface area, pore volume, and mesopore diameter of 500–900 μm. 2 / g, 0.8~1.8cm 3 / g and 5.0~12.0nm, and contains 5.0~10.0mmol / g of aluminum hydroxyl groups on the surface of the mesoporous pore walls.

2. The high specific surface area mesoporous alumina material with a surface rich in hydroxyl groups according to claim 1, characterized in that... The aluminum source is one or a mixture of aluminum isopropoxide, aluminum isobutoxide, aluminum tert-butoxide, aluminum nitrate, aluminum chloride, or aluminum sulfate in any proportion; the organic carboxylic acid is citric acid, glacial acetic acid, oxalic acid, or tartaric acid; and the anhydrous organic alcohol solvent is one or a mixture of methanol, ethanol, or isopropanol in any proportion.

3. The method for preparing the high specific surface area mesoporous alumina material with hydroxyl-rich surface as described in claim 1, comprising the following steps: 1) Dissolve the organic carboxylic acid and aluminum source in an anhydrous organic alcohol solvent to obtain a clear solution, according to the molar ratio of organic carboxylic acid and anhydrous organic alcohol to aluminum source of 0.01-10:5-200:

1. 2) Under stirring and reflux conditions at 50–150°C, an aqueous ethanol solution is slowly and uniformly added dropwise at a rate of 2–15 mL / min to the clarified solution as a hydrolysate to promote a slow hydrolysis-polymerization reaction of the aluminum source within the confined space of the organic alcohol solvent, thereby obtaining alumina sol. 3) The solvent in the alumina sol is removed by natural evaporation in an open state to obtain a blocky alumina gel with a mesoporous structure; 4) The alumina gel is subjected to high-temperature treatment in a water vapor environment of 400–650℃ to prepare a product with… γ -A high specific surface area mesoporous alumina material with an Al2O3 crystal phase structure and a surface rich in aluminum hydroxyl groups.

4. The preparation method according to claim 3, characterized in that: The amount of ethanol aqueous solution used is 5 to 15 times the mass of the aluminum source.

5. The preparation method according to claim 3, characterized in that: After the ethanol-water solution is added slowly and at a uniform rate, the temperature is maintained and the mixture is stirred and refluxed for 0.5 to 3 hours.

6. The preparation method according to claim 3, characterized in that: The alumina sol was volatilized at 40–100°C in an open state for 6–72 hours.

7. The preparation method according to claim 3, characterized in that: The alumina gel was treated at high temperature in steam at a flow rate of 10–30 mL / min for 0.5–3 h.

8. The application of the high specific surface area mesoporous alumina material with hydroxyl-rich surface as described in claim 1 as a catalyst support.

9. The application of the high specific surface area mesoporous alumina material with hydroxyl-rich surface as described in claim 1 as a dehydrogenation catalyst support for liquid organic hydrogen.

10. A low-temperature, high-efficiency dehydrogenation catalyst for liquid organic hydrogen support, comprising a high specific surface area mesoporous alumina material rich in hydroxyl groups as described in claim 1, loaded with a metal Pt active component, for use in low-temperature dehydrogenation reactions of liquid organic hydrogen support.

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