A bifunctional catalyst having metal and acid sites, and methods of making and use

Abstract

This invention discloses a bifunctional catalyst with both metal and acid sites, its preparation method, and its applications, relating to the field of catalytic materials. The invention uses an oxide with a high hydroxyl density on its surface as a support. Metal active centers dispersed on the support surface and acidic sites surrounding the metal centers constitute a bifunctional catalytic unit. The acidic sites are anchored to the support surface by Si-O-Si bonds and terminated with -SO3H groups. The effective spacing between the metal and acidic sites is limited by the chain length and configuration of the introduced thiol ligands. This avoids the acidic groups from becoming too close to the metal surface and poisoning the metal hydrogenation sites, while ensuring controllable proximity and synergistic effects at the nanoscale. Structurally, this forms a ring of acidic sites distributed along the outer edge of the metal with a certain distance between them.

Description

Technical Field

[0001] This invention relates to the field of catalytic materials, and in particular to a metal-acid site proximity controllable bifunctional catalyst, its preparation method, and its application in the one-step hydrogenation of nitrobenzene to p-aminophenol. Background Technology

[0002] p-Aminophenol ( p α-Aminophenol (PAP) is an important organic chemical intermediate, and its downstream product, p-acetaminophenol, is a commonly used antipyretic and analgesic drug. In recent years, researchers and companies have been committed to developing low-environmental-pollution, high-quality p-aminophenol preparation routes. Using nitrobenzene as a raw material, the one-step hydrogenation method to prepare p-aminophenol is an industrially significant and efficient route with advantages such as short production process, low energy consumption, and high product quality. However, the use of large amounts of sulfuric acid in this process leads to problems such as catalyst poisoning, equipment corrosion, high wastewater treatment costs, and difficulties in product separation, which limit its industrial application.

[0003] Currently, solid acid materials such as molecular sieves, sulfuric acid sulfonate, and metal oxides have been developed as alternatives to sulfuric acid and have shown selectivity for p-aminophenol in this process. However, these solid acid catalysts generally suffer from low acid density, making it difficult to provide a sufficient proton environment, resulting in low PAP selectivity; and acid site leaching occurs during the reaction, causing rapid catalyst deactivation, which severely limits the reusability of these solid acids.

[0004] Based on reaction kinetics studies, it was found that the intermediate phenylhydroxylamine undergoes further hydrogenation to the byproduct aniline much faster than the Bamberger rearrangement to p-aminophenol under proton attack. Regulating the Bamberger rearrangement rate above the over-hydrogenation rate is key to achieving high PAP selectivity. Recent studies have shown that the synergistic effect between metal and acid sites plays a crucial role in regulating catalytic reaction pathways, particularly affecting PAP selectivity. Current catalyst design mainly focuses on controlling the catalyst's geometry / electronic structure in sulfuric acid solution to suppress over-hydrogenation of the intermediate to aniline. There is an urgent need to develop new strategies to achieve short-range synergy between the active and acid sites at the mesoscale, promoting rapid rearrangement reactions and suppressing over-hydrogenation. Therefore, using metal-acid bifunctional catalysts with controllable sites can integrate complex reactions on a single support, improve acid site utilization by controlling the metal-acid center distance, and achieve high selectivity for p-aminophenol under limited acid density. Summary of the Invention:

[0005] This invention provides a bifunctional catalyst with gold and acid sites, its preparation, and its application. An oxide with a high hydroxyl density on its surface serves as a support. Metal active centers dispersed on the support surface and acid sites surrounding the metal centers constitute a bifunctional catalytic unit. The acid sites are anchored to the support surface by Si-O-Si bonds and terminated with -SO3H groups. The effective spacing between the metal and acid sites is limited by the chain length and configuration of the introduced thiol ligand. This avoids the acid groups from becoming too close to the metal surface and poisoning the metal hydrogenation sites, while ensuring controllable proximity and synergistic effect at the nanoscale. Structurally, this forms a ring of acid sites distributed along the outer edge of the metal with a certain distance between them.

[0006] A bifunctional catalyst with metal and acid sites, wherein the bifunctional catalyst uses an oxide with high hydroxyl density as a support, the surface of the support is dispersed with metal centers, and acid sites are surrounding the metal centers. The acidic sites are anchored to the support surface by Si-O-Si bonds and terminated with -SO3H groups; thiol ligands are introduced into the metal center and the acidic sites; Thiol ligands are adsorbed on the surface of the metal center to serve as a sacrificial template. The oxides with high hydroxyl density are silicon oxide, aluminum oxide, zirconium oxide, and titanium oxide; The metal center is gold, palladium, platinum, nickel, or ruthenium, with a metal loading of 0.1% to 5%. The thiol ligands are ethanethiol, benzylthiol, phenylethanethiol, n-dodecylthiol, n-octadecylthiol, 2-naphthiophenol, and biphenyl-4-thiol.

[0007] Preferably, the bifunctional catalyst has silicon dioxide as the oxide with high hydroxyl density, platinum as the metal center, and phenylethyl mercaptan as the thiol ligand. Or the bifunctional catalyst, wherein the oxide with high hydroxyl density is zirconium oxide, the metal center is ruthenium, and the thiol ligand is benzyl mercaptan; Or the bifunctional catalyst described herein, wherein the oxide with high hydroxyl density is alumina, the metal center is platinum, and the thiol ligand is ethanethiol; Or the bifunctional catalyst, wherein the oxide with high hydroxyl density is titanium oxide, the metal center is nickel, and the thiol ligand is n-dodecanethiol.

[0008] Preferably, the metal loading is 0.1%, 0.3%, 0.5%, or 1.0%.

[0009] The preferred bifunctional catalysts are 0.1% Pt / SiO2-SO3H, 0.1% Pt / Al2O3-SO3H, 0.3% Ru / Al2O3-SO3H, and 0.3% Ru / SiO2-SO3H.

[0010] A method for preparing a bifunctional catalyst with controllable metal-acid site distance: Step 1: After dispersing the support in a metal salt solution and obtaining the supported catalyst precursor Metal / support by wet impregnation, the supported catalyst precursor Metal / support is dispersed in a thiol / ethanol solution to obtain the Thiol-Metal / Support catalyst. Step 2: Disperse the Thiol-Metal / Support catalyst in an aqueous solution, add mercaptosilane coupling agent, adjust the acidity of the system, stir at room temperature for 5-10 h, transfer to a high temperature and high pressure reactor, react at 80-150 °C for 10 h, cool to room temperature, wash and dry; add oxidant to the obtained powder sample, wash until neutral, and dry to obtain the bifunctional catalyst.

[0011] Preferably, the diameter of the carrier in step one is 0.02-3 mm, and the dispersion of the carrier is 5%-10%; the concentration of the thiol is 0.1 M; and the concentration of the hydrochloric acid in step three is 0.1 M.

[0012] Preferably, the silane coupling agent in step two is 3-mercaptopropyltrimethoxysilane or 3-mercaptopropyltriethoxysilane; the oxidant is an acidic aqueous solution of 30% hydrogen peroxide, potassium persulfate, or potassium permanganate.

[0013] Preferably, the mass ratio of the carrier to the silane coupling agent is 2:1; the acidification sulfuric acid concentration is selected as a 10% sulfuric acid aqueous solution.

[0014] A bifunctional catalyst with metal and acid sites is used in the hydrogenation of nitrobenzene to prepare p-aminophenol.

[0015] This invention utilizes the strong electron affinity between a specific metal and thiol groups to construct an in-situ, adjustable-thickness thiol self-assembled layer on the metal surface. This self-assembled layer, through the steric hindrance formed by thiol ligands, provides a nanoscale buffer zone at the structural level for subsequently introduced acidic groups, thereby limiting the excessive approach of acidic sites to the metal surface and forming a controllable metal-acid site spacing around the metal. The condensation reaction between a silane coupling agent and a high-hydroxyl-density support anchors the thiol-containing silane coupling agent on the support surface via Si-O-Si bonds. Here, the thiol ligands adsorbed on the metal surface act as a sacrificial spacer template: under oxidizing conditions, they oxidize and release the metal center from the metal surface, and facilitate the conversion of thiol groups in the silane coupling agent anchored on the support surface into sulfonic acid groups. This invention achieves precise control of the distance between metal and acid sites without significantly sacrificing metal hydrogenation activity, enabling the catalyst to simultaneously possess highly efficient metal hydrogenation centers and spatially adjacent but controllably separated acid catalytic centers within the same structural unit, thereby optimizing the selectivity and activity in the tandem reaction process.

[0016] Beneficial effects 1) By utilizing the self-assembled layer constructed through the electronic interaction between metal and thiol groups, the steric hindrance effect generated by thiol molecules can achieve the controllable synthesis of the distance between metal sites and sulfonic acid sites, overcoming the difficulty of precisely controlling the metal and acid sites in traditional metal-acid bifunctional catalysts. 2) By precisely controlling the metal-acid site spacing, the catalyst can simultaneously possess excellent hydrogenation function and tunable acid catalyst capability without significantly reducing the metal hydrogenation activity, thereby significantly improving the activity and selectivity in multi-step tandem reactions. 3) The method of this invention is highly versatile and can be extended to other noble metal / oxide support systems and various mercaptosilane coupling agents, providing a simple, efficient and scalable new approach for constructing bifunctional solid catalysts with adjustable metal-acid site spacing. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the structure of the catalyst prepared in Example 1 of the present invention.

[0018] Figure 2 The X-ray electronic spectrum of the catalyst prepared in Example 2 of this invention.

[0019] Figure 3 Transmission electron microscopy (TEM) images and elemental distribution of the catalyst prepared in Example 3 of this invention.

[0020] Figure 4 The ammonia adsorption-desorption curve is shown for the catalyst prepared in Example 4 of this invention.

[0021] Figure 5 The X-ray diffraction pattern is shown for the catalyst and support prepared in Example 5 of this invention.

[0022] Figure 6 This is the infrared spectrum of Embodiment 6 of the present invention.

[0023] Figure 7 The thermogravimetric analysis curve is shown for the catalyst prepared in Example 7 of this invention.

[0024] Figure 8 This is a summary of the catalytic activity and selectivity of the one-step preparation of p-aminophenol from nitrobenzene in Examples 1-8 of the present invention. Detailed Implementation

[0025] The above-mentioned solution will be further described below with reference to specific embodiments; it should be understood that these embodiments are used to illustrate the basic principles, main features and advantages of the present invention, and the present invention is not limited to the scope of the following embodiments; the implementation conditions used in the embodiments can be further adjusted according to specific requirements, and the implementation conditions not specified are usually the conditions in conventional experiments.

[0026] Where specific experimental steps or conditions are not specified in the examples, they can be performed according to the conventional experimental steps or conditions described in the literature in this field. Unless otherwise specified in the following examples, all raw materials are commercially available or prepared by conventional methods in this field.

[0027] Example 1: (1) 0.6 g H2PtCl6· . 6H₂O was dissolved in 50 mL of deionized water to form a homogeneous solution. Then, 200 g of silica powder was added to the solution while stirring, and the mixture was impregnated for 5 h with an equal volume. After impregnation, the wet sample was dried in a 120 °C oven to constant weight to obtain a dry solid containing the platinum precursor.

[0028] (2) The above-mentioned dry solid was ground into powder and placed in a muffle furnace. The temperature was increased to 200 °C at 2 °C / min under a flowing air atmosphere, and calcined for 4 h. Then it was naturally cooled to room temperature. The sample was then transferred to a tube furnace and heated to 300 °C at 5 °C / min under a 5 vol.% H2 / N2 mixed atmosphere. The sample was reduced for 4 h and then cooled to room temperature to obtain a 0.1% Pt / SiO2 precursor.

[0029] (3) Weigh 200 g of 0.1% Pt / SiO2 precursor and disperse it in 1 L of anhydrous ethanol. Stir the mixture mechanically until it is homogeneous. Add phenylethyl mercaptan to the dispersion to obtain a 0.1 M phenylethyl mercaptan solution. Stir continuously for 8 h to allow the mercaptan to form a self-assembled layer on the metal surface. After the reaction is complete, filter the solution and wash it with anhydrous ethanol to obtain the mercaptan-modified intermediate.

[0030] (4) The above intermediate was dispersed in 1 L of deionized water and mechanically stirred to form a uniform suspension. The pH was adjusted to 1-2 with hydrochloric acid. 200 mL of 3-mercaptopropyltrimethoxysilane was added under continuous stirring. After reacting at room temperature for 5 h, the system was heated to 100 °C and the reaction continued for another 5 h. After the reaction was completed, the mixture was filtered to obtain a solid powder. The solid was added to 2 L of 30% H2O2 solution, and a small amount of sulfuric acid was added to make the system acidic. The mixture was fully oxidized for 5 h under stirring to remove the phenylethyl mercaptan on the surface. After oxidation, the mixture was filtered and washed with deionized water until the filtrate was nearly neutral. Then it was dried at 80 °C to constant weight to obtain the bifunctional catalyst 0.1% Pt-phenylethyl mercaptan / SiO2-SO3H. The metal loading was determined by ICP-MS.

[0031] Figure 1 This is a schematic diagram of the catalyst prepared in Example 1 of the present invention. The central nanocluster is the metal catalytic center, and the surrounding structure consists of acidic sites. The catalyst in Example 1 is Pt / SiO2-SO3H. In the figure, red, blue, green, gray, white, and gold represent silicon, oxygen, carbon, hydrogen, and platinum atoms, respectively.

[0032] Example 2: (1) Weigh 1.8 g of [Ru(NH3)6]Cl3 and dissolve it in 50 mL of deionized water. Stir until completely dissolved, then add 200 g of zirconium oxide powder and stir evenly. Impregnate the mixture with an equal volume for 5 h. After impregnation, dry the mixture in a 120 °C forced-air drying oven to constant weight to obtain a dry solid containing gold precursor.

[0033] (2) The dried solid was ground and placed in a muffle furnace. The temperature was increased to 250 °C at 2 °C / min under an air atmosphere, and calcined for 4 h. The temperature was then cooled to room temperature. The sample was then transferred to a tube furnace and heated to 600 °C at 5 °C / min under a 5 vol.% H2 / N2 mixed atmosphere. The temperature was reduced for 3 h. The sample was then cooled to room temperature to obtain a 0.3% Ru / ZrO2 precursor.

[0034] (3) Weigh 200 g of 0.3% Ru / ZrO2 precursor and add it to 1 L of anhydrous ethanol. Stir mechanically to disperse it evenly. Add benzyl mercaptan to make the concentration of benzyl mercaptan 0.1 M. Stir continuously at room temperature for 8 h to allow benzyl mercaptan to form a self-assembled layer on the surface of gold particles. After the reaction is complete, filter and wash with anhydrous ethanol to obtain thiol-modified 0.3% Au / ZrO2 intermediate.

[0035] (4) Disperse the intermediate in 1 L of deionized water and stir to form a uniform slurry. Adjust the pH to 1-2 with hydrochloric acid. Add 200 mL of 3-mercaptopropyltrimethoxysilane to the system and react at room temperature for 5 h. Then raise the temperature to 100 °C and continue the reaction for 5 h. After the reaction is complete, filter to obtain a solid. Add 2 L of 0.1 M potassium permanganate aqueous solution (pH = 3), oxidize fully at 70 °C for 3 h, and remove benzyl mercaptan adsorbed on the metal surface. Add ascorbic acid until the solution is milky white. After filtering to obtain powder, disperse in sulfuric acid aqueous solution (pH = 1) and acidify for 2 h. Separate the solid and wash with deionized water until the filtrate is neutral to obtain the bifunctional catalyst. After filtration, wash with deionized water until the filtrate is close to neutral and dry at 100-120 °C to constant weight to obtain 0.3% Au-benzyl mercaptan / ZrO2–SO3H bifunctional catalyst.

[0036] Figure 2 The X-ray electronic spectrum of the catalyst prepared in Example 2 of this invention shows that S in the catalyst mainly exists in the form of high-valence S, which is -SO3H.

[0037] Example 3: (1) Weigh 2.7 g of H2PtCl6·6H2O and dissolve it in 50 mL of deionized water, stirring until completely dissolved. Add 200 g of γ-Al2O3 powder with high hydroxyl density to the solution, stir and mix, and impregnate with an equal volume for 5 h. After impregnation, place the wet sample in a drying oven at 120 °C and dry to constant weight.

[0038] (2) After grinding the dried sample evenly, it was placed into a porcelain boat and calcined in a muffle furnace at 2 °C / min to 300 °C under an air atmosphere for 4 h. After natural cooling, the sample was transferred to a tube furnace and calcined at 5 °C / min to 350 °C under a 5 vol.% H2 / N2 atmosphere for 4 h. After cooling to room temperature, a 0.5% Pt / γ-Al2O3 precursor was obtained.

[0039] (3) Weigh 200 g of 0.5% Pt / γ-Al2O3 precursor and add it to 1 L of anhydrous ethanol. Stir mechanically to disperse it evenly. Add ethanethiol at room temperature to obtain a 0.1 M ethanethiol solution. Stir continuously for 8 h to allow the thiol to form a self-assembled layer on the surface of the platinum particles. After the reaction is complete, filter and wash with anhydrous ethanol to obtain the ethanethiol-modified Pt-ethanethiol / γ-Al2O3 intermediate.

[0040] (4) Disperse the intermediate in 1 L of deionized water, stir until homogeneous, and adjust the pH to 1-2 with hydrochloric acid. Add 200 mL of 3-mercaptopropyltrimethoxysilane, react at room temperature for 5 h, then heat the system to 100 °C and continue the reaction for 5 h. After the reaction is complete, filter to obtain a solid. Add the solid to 2 L of 30% H2O2 solution and add a small amount of sulfuric acid to make the system acidic. Oxidize under stirring for 5 h to remove the ethanethiol adsorbed on the metal surface. After oxidation is complete, filter, wash with deionized water until the filtrate is nearly neutral, and dry at 100-120 °C to constant weight to obtain a 0.5% Pt-ethanethiol / γ-Al2O3-SO3H bifunctional catalyst.

[0041] Figure 3 The images show transmission electron microscopy (TEM) images and elemental distribution of the catalyst prepared in Example 3 of this invention. The sulfur element is concentrated around the metal, while it is randomly distributed on the support further away.

[0042] Example 4: (1) Weigh 9.0 g Ni(NO3)2·6H2O and dissolve it in 50 mL of deionized water, stirring to form a clear solution. Add 200 g of titanium dioxide powder to the solution, stir evenly, and then impregnate it with an equal volume for 5 h. After impregnation, dry it in a drying oven at 120 °C until constant weight.

[0043] (2) The dried solid was ground and placed into a ceramic boat, which was then placed in a muffle furnace. The temperature was increased to 350 °C at 2 °C / min under an air atmosphere and held for 4 h to complete the calcination. After cooling to room temperature, the sample was transferred to a tube furnace and heated to 400 °C at 5 °C / min under a 5 vol.% H2 / N2 atmosphere. The sample was reduced for 4 h and then cooled to room temperature to obtain a 1.0% Ni / TiO2 precursor.

[0044] (3) Weigh 200 g of Ni / SiO2 precursor and add it to 1 L of anhydrous ethanol. Stir mechanically to disperse it evenly. Add n-dodecanethiol solution at room temperature to obtain a 0.1 M solution. Continue stirring for 8 h. After the reaction is complete, filter and wash with anhydrous ethanol to obtain 1.0% Ni-n-dodecane / TiO2 intermediate modified with thiol.

[0045] (4) Disperse the intermediate in 1 L of deionized water, stir to form a uniform suspension, and adjust the pH to 1-2 with hydrochloric acid. Add 200 mL of 3-mercaptopropyltriethoxysilane, react at room temperature for 5 h, then heat the system to 100 °C and continue the reaction for 5 h. After filtering to obtain the solid, add it to an acidic oxidation system prepared with 1 L of 30% H2O2 and 1 L of 0.5 M dilute nitric acid, and stir at 50-60 °C for 6 h to fully oxidize and remove the n-dodecanethiol adsorbed on the surface. After oxidation, filter, wash with deionized water until the filtrate is close to neutral, and dry at 100-120 °C to constant weight to obtain a 1.0% Ni-n-dodecane / TiO2-SO3H bifunctional catalyst.

[0046] Figure 4 The ammonia adsorption-desorption curve of the catalyst prepared in Example 4 of this invention shows the ammonia desorption peak at 450 °C at strong acid sites, indicating the successful introduction of acid sites into the catalyst and the removal of most of the thiols on the Pt surface.

[0047] Example 5: (1) Weigh 0.88 g of PdCl2 into a beaker, add a small amount of 0.1 M hydrochloric acid to aid dissolution, and then add deionized water to a total volume of 50 mL. Stir to form a clear solution. Add 200 g of silica powder to the solution while stirring, and impregnate for 5 h with equal volume. After impregnation, place the wet sample in a 120 °C drying oven to constant weight.

[0048] (2) The dried solid was ground and placed into a ceramic boat, which was then placed in a muffle furnace. The temperature was increased to 300 °C at 2 °C / min under an air atmosphere and held for 4 h to complete the calcination. After cooling to room temperature, it was transferred to a tube furnace and heated to 300 °C at 5 °C / min under a 5 vol.% H2 / N2 atmosphere. The furnace was reduced for 4 h and then cooled to room temperature to obtain a 0.3% Pd / SiO2 precursor.

[0049] (3) Weigh 200 g of Pd / SiO2 precursor and add it to 1 L of anhydrous ethanol, and disperse it by mechanical stirring. After adding n-hexadecylthiol, a 0.1 M n-hexadecylthiol solution is obtained. Stir continuously at room temperature for 8 h to allow the thiol to form a self-assembled layer on the surface of the palladium particles. After the reaction is complete, filter and wash with anhydrous ethanol to obtain the thiol-modified Pd / SiO2 intermediate.

[0050] (4) Disperse the intermediate in 1 L of deionized water, stir until homogeneous, and adjust the pH to 1-2 with hydrochloric acid. Add 200 mL of 3-mercaptopropyltriethoxysilane to the system, react at room temperature for 5 h, then heat the system to 100 °C and continue the reaction for 5 h. After the reaction is complete, filter to obtain a solid, add it to 2 L of 30% H2O2 solution, add a small amount of sulfuric acid to adjust to acidity, and oxidize under stirring for 5 h to convert the mercapto groups to sulfonic acid groups and remove the thiol ligands on the metal surface. After filtration, wash with deionized water until the filtrate is nearly neutral, and dry at 100-120 °C to constant weight to obtain a 0.3% Pd-n-hexadecylthiol / SiO2-SO3H bifunctional catalyst.

[0051] Figure 5 The X-ray diffraction pattern of the catalyst and support prepared in Example 5 of this invention shows that, due to the low metal loading and good dispersion, there are no obvious metal diffraction peaks.

[0052] Example 6: (1) Weigh 1.2 g of H2PtCl6·6H2O and dissolve it in 50 mL of deionized water, stirring until homogeneous. Add 200 g of silica powder and impregnate for 5 h with an equal volume. After impregnation, dry in a 120 °C drying oven to constant weight.

[0053] (2) The dried solid was ground and placed in a muffle furnace. The temperature was increased to 200 °C at 2 °C / min under an air atmosphere and held for 4 h to complete the calcination. After cooling, it was transferred to a tube furnace and heated to 300 °C at 5 °C / min under a 5 vol.% H2 / N2 atmosphere. The temperature was reduced for 4 h to obtain a 0.2% Pt / SiO2 precursor.

[0054] (3) Weigh 200 g of 0.2% Pt / SiO2 precursor and add it to 1 L of anhydrous ethanol, and stir to disperse. Add 2-naphthiophenol to obtain a 1.0 M 2-naphthiophenol ethanol solution, and stir at room temperature for 6 h. After the reaction is complete, filter and wash with anhydrous ethanol to obtain 0.2% Pt-2-naphthiophenol / SiO2 intermediate modified with 2-naphthiophenol.

[0055] (4) Disperse the intermediate in 1 L of deionized water, stir until homogeneous, and adjust the pH to 1-2 with hydrochloric acid. Add 200 mL of 3-mercaptopropyltrimethoxysilane, react at room temperature for 5 h, then heat the system to 100 °C and continue the reaction for 5 h. After filtering to obtain the solid, add it to 2 L of 30% H2O2 solution, and add a small amount of sulfuric acid to make the system acidic. Oxidize under stirring for 5 h to remove the thiol ligands on the metal surface. Filter and wash with deionized water until the filtrate is nearly neutral, and dry at 100-120 °C to constant weight to obtain a 0.2% Pt-2-naphthiophenol / SiO2–SO3H bifunctional catalyst.

[0056] Figure 6 The infrared spectrum of Example 6 of this invention shows that the presence of the methylene group proves the successful introduction of the acid site.

[0057] Example 7: (1) Weigh 1.2 g of H2PtCl6·6H2O and dissolve it in 50 mL of deionized water, stirring until clear. Add 200 g of γ-alumina to the solution, stir and mix, and impregnate with an equal volume for 5 h. After impregnation, place the wet sample in a 120 °C drying oven and dry to constant weight.

[0058] (2) The dried solid was ground and placed into a porcelain boat. The temperature was increased to 200 °C at 2 °C / min in an air atmosphere in a muffle furnace and held for 4 h. After cooling, the sample was transferred to a tube furnace and the temperature was increased to 300 °C at 5 °C / min in a 5 vol.% H2 / N2 atmosphere and reduced for 4 h to obtain a 0.2% Pt / Al2O3 precursor.

[0059] (3) Weigh 200 g of 0.2% Pt / Al2O3 precursor and add it to 1 L of anhydrous ethanol, then disperse it by mechanical stirring. Add biphenyl-4-thiol to obtain a 0.1 M biphenyl-4-thiol ethanol solution. Stir continuously at room temperature for 10 h to allow biphenyl-4-thiol to form an aromatic self-assembled confinement layer on the platinum surface. After the reaction is complete, filter the solution and wash it several times with anhydrous ethanol to obtain 0.2% Pt-biphenyl-4-thiol / Al2O3 modified with biphenyl-4-thiol.

[0060] (4) Disperse the intermediate in 1 L of deionized water, stir until homogeneous, and adjust the pH to 1-2 with hydrochloric acid. Add 200 mL of 3-mercaptopropyltriethoxysilane to the system, react at room temperature for 5 h, then raise the temperature to 100 °C and continue the reaction for 6 h. After solid-liquid separation, add the obtained solid to 2 L of 30% H2O2 solution, add a small amount of sulfuric acid to adjust to acidity, and stir at 50-60 °C for 6-8 h to remove the thiol ligands adsorbed on the metal surface. Filter and wash with deionized water until the filtrate is nearly neutral, and dry at 100-120 °C to constant weight to obtain a 0.2% Pt-biphenyl-4-thiol / Al2O3-SO3H bifunctional catalyst.

[0061] Figure 7 The thermogravimetric analysis curve of the catalyst prepared in Example 7 of this invention shows that the organic sulfonic acid sites desorbed after 200 °C, indicating that the catalyst has good thermal stability.

[0062] Example 8: (1) Weigh 5 g of HAuCl4·3H2O and dissolve it in 50 mL of deionized water, stirring to form a clear solution. Add 200 g of ZrO2 powder with abundant surface hydroxyl groups, stir evenly, and then impregnate the sample with an equal volume for 5 h. After impregnation, place the wet sample in a drying oven at 120 °C and dry to constant weight.

[0063] (2) After grinding the dried solid, it was placed in a porcelain boat and placed in a muffle furnace. The temperature was increased to 400 °C at 2 °C / min under an air atmosphere and held for 3-4 h to complete the calcination. After cooling to room temperature, the sample was transferred to a tube furnace and heated to 300 °C at 5 °C / min under a 5 vol.% H2 / N2 mixed atmosphere. The sample was reduced for 4 h and then cooled to room temperature to obtain a 1% Au / ZrO2 precursor.

[0064] (3) Weigh 200 g of 1% Au / ZrO2 precursor and add it to 1 L of anhydrous ethanol. Disperse the precursor by mechanical stirring. Add benzyl thiol to prepare an ethanol solution of 0.1 M benzyl thiol and stir at room temperature for 8 h. After the reaction is complete, filter the solution and wash it with anhydrous ethanol to obtain thiol-modified 1% Au-benzyl thiol / ZrO2.

[0065] (4) Add the intermediate to 1 L of deionized water, stir to disperse, and adjust the pH to 1-2 with hydrochloric acid. Add 200 mL of 3-mercaptopropyltriethoxysilane, react at room temperature for 5 h, then raise the temperature to 100 °C and continue the reaction for 5 h. After solid-liquid separation, add the obtained solid to an acidic oxidizing solution containing potassium persulfate (prepared by dissolving an appropriate amount of KHSO5 composite salt in dilute sulfuric acid to form 2 L of oxidizing solution), and stir to oxidize at 50-60 °C for 6-8 h to fully remove the surface-adsorbed thiols. After oxidation, filter, wash with deionized water until the filtrate is nearly neutral, and dry at 100-120 °C to constant weight to obtain a 1% Au-benzyl mercaptan / ZrO2 bifunctional catalyst.

[0066] Comparative Example 1: (1) Weigh 200 g of commercial SiO2 powder and place it in a dry three-necked flask. Slowly add 300 mL of anhydrous chlorosulfonic acid (ClSO3H) while controlling the system temperature at 0-5 °C. The addition process takes about 2 h. After the addition is complete, heat the system to 60 °C and continue stirring for 6 h to allow the hydroxyl groups on the SiO2 surface to be fully sulfonated to form ‒SO3H. After the reaction is complete, pour the solid into a large amount of ice water to quench it, filter it, and wash it repeatedly with deionized water until the pH of the washing solution is close to neutral. Dry the washed solid at 120 °C for 12 h to obtain sulfonated SiO2 support SiO2-SO3H.

[0067] (2) Weigh 1.2 g of H2PtCl6·6H2O and dissolve it in 50 mL of deionized water to form a clear solution. Gradually add 200 g of SiO2-SO3H powder to the above solution while stirring, and impregnate for 5 h with equal volume. After impregnation, dry in a drying oven at 120°C to constant weight, grind and sieve to obtain a dry sample of platinum precursor.

[0068] (3) The dried sample was placed in a porcelain boat and placed in a muffle furnace. The temperature was increased to 250 °C at 2 °C / min under an air atmosphere and held for 3 h. After cooling to room temperature, it was transferred to a tube furnace and the temperature was increased to 300 °C at 5 °C / min under a 5 vol.% H2 / N2 atmosphere. The reduction was carried out for 4 h and then cooled to obtain the catalyst Pt / SiO2-SO3H of Comparative Example 1.

[0069] Comparative Example 2: (1) Take 200 g of NH4-β molecular sieve powder, put it into a porcelain boat, heat it to 550 °C at 2 °C / min in air atmosphere, and keep it at that temperature for 6 h to complete the NH4 + → H + The conversion yields H-β molecular sieve.

[0070] (2) Weigh 1.2 g of H2PtCl6·6H2O and dissolve it in 50 mL of deionized water, stirring until completely dissolved. Add 200 g of H-β powder to the platinum salt solution, stir evenly, and impregnate with an equal volume for 5 h. After impregnation, dry in a drying oven at 120 °C until constant weight, and grind for later use.

[0071] (3) Calcination and reduction The dried sample was placed in a muffle furnace and heated to 400 °C in air at a rate of 1–2 °C / min, and held at this temperature for 4 h to stabilize the Pt species and molecular sieve framework. After cooling, it was transferred to a tube furnace and heated to 300 °C at a rate of 5 °C / min in a 5 vol.% H2 / N2 atmosphere for reduction for 3–4 h. After cooling, the Pt / H-β bifunctional catalyst was obtained.

[0072] Comparative Example 3: (1) Preparation of Pt / SiO2: 1.2 g of H2PtCl6·6H2O was weighed and dissolved in 50 mL of deionized water. 200 g of SiO2 powder was added to the solution and impregnated for 5 h with an equal volume. The mixture was then dried at 120 °C to constant weight. The dried sample was ground and calcined in air at 200 °C for 4 h. Then it was reduced in 5 vol.% H2 / N2 at 300 °C for 4 h to obtain Pt / SiO2.

[0073] (2) Preparation of SiO2-SO3H: SiO2 powder was dispersed in 1 L of deionized water. Hydrochloric acid was added under stirring to adjust the pH to 1-2. 200 ml of 3-mercaptopropyltrimethoxysilane was added under continuous stirring, and the mixture was reacted at room temperature for 5 h. Then, the temperature was raised to 100 °C and the reaction was continued for another 5 h. The granular material was filtered, and 2 L of 30% H2O2 was added. A small amount of sulfuric acid was added to make the system acidic. After 5 h of complete oxidation, the filtrate was washed until it was close to neutral and then dried to obtain SiO2-SO3H solid acid. When using, the two are mixed in a 1:1 ratio.

[0074] Comparative Example 4: (1) Weigh 200 g of powdered activated carbon (pre-dried and dehumidified at 110 °C) and place it in an acid-resistant three-necked flask. Slowly add 500 mL of concentrated sulfuric acid (98% by mass), control the system temperature at 80-100 °C, and stir the reaction in an oil bath for 10 h to introduce -SO3H onto the carbon surface. After the reaction is complete, slowly pour the slurry into a large amount of ice water to dilute and cool it, filter it, and wash it repeatedly with deionized water until the pH of the washing solution is close to neutral. Dry the filtered sulfonated activated carbon at 120 °C for 12 h to obtain the C-SO3H support.

[0075] (2) Weigh 1.0 g of H2PtCl6·6H2O and dissolve it in 50 mL of deionized water. Add 100 g of C-SO3H to the above platinum salt solution and stir to impregnate for 5 h. After impregnation, dry at 120 °C to constant weight and grind. Load the dried Pt / C-SO3H precursor into a tube furnace and heat it to 250 °C at 5 °C / min under N2 atmosphere, switch to 5 vol.% H2 / N2, and reduce for 3 h. Cool to room temperature to obtain the Pt / sulfonated activated carbon bifunctional catalyst.

[0076] Comparative Example 5: (1) Weigh 1.2 g of H2PtCl6·6H2O and 10.0 g of H3PW 12 O 40 • xH2O (phosphotungstic acid) was dissolved in 200 mL of deionized water and stirred until completely dissolved to obtain a co-impregnation solution containing Pt and heteropoly acid.

[0077] (2) Gradually add 200 g of SiO2 powder to the above solution and stir thoroughly to ensure the solution uniformly wets the carrier surface. Continue stirring for 4-5 h to ensure the metal salt reacts with H3PW. 12 O 40 Sufficient adsorption. After impregnation, the slurry is slowly evaporated in a water bath at 80-100 °C to remove most of the water, resulting in a wet paste-like solid. The wet solid is then dried in a drying oven at 120 °C until constant weight, and then ground for later use.

[0078] (3) Place the dried sample into a muffle furnace and heat it to 250 °C at a rate of 1-2 °C / min under air atmosphere, and keep it at that temperature for 3 h to allow H3PW to precipitate. 12 O 40 The Pt species were uniformly fixed on the SiO2 surface. After cooling, the Pt was transferred to a tube furnace and heated to 250-280 °C at a rate of 5 °C / min under a 5 vol.% H2 / N2 atmosphere for 3 h to reduce some Pt ​​species to the metallic state, while phosphotungstic acid existed as a strong Brønsted acid. After cooling to room temperature, the catalyst H3PW was obtained. 12 O 40 / SiO2.

[0079] Catalytic performance test In a high-pressure stainless steel reactor equipped with mechanical stirring, 5.0 g of catalyst and 1 mL of nitrobenzene as substrate were added, followed by 100 mL of deionized water to prepare the reaction solution. The reactor was purged with hydrogen five times to replace the air inside, and finally, hydrogen was introduced to an initial reaction pressure of 1.0 MPa. The temperature was raised to 100 °C under mechanical stirring, and the reaction was carried out for 6 h. Throughout the reaction, thorough stirring was maintained to ensure good contact between the gas, liquid, and solid phases. After the reaction was completed, the reactor was cooled to room temperature and the pressure was slowly released. The reaction solution was removed, and after filtration to remove the solid catalyst, high-performance liquid chromatography (HPLC) was used for qualitative and quantitative analysis of nitrobenzene and reaction products (such as p-aminophenol and aniline). The conversion rate of nitrobenzene and the selectivity of each product were calculated to evaluate the hydrogenation activity and selectivity of the catalyst.

[0080]

[0081]

[0082] After cooling to room temperature, the reaction mixture was diluted with 70% methanol solution. High-performance liquid chromatography (Agilent HPLC 2016) was used to analyze the conversion of nitrobenzene and the selectivity of each product. The detector was a UV detector, the eluent was 70% methanol solution, the injection volume was 10 μl, the flow rate was 1 ml / min, and the column temperature was 30 °C. The products were quantified using the external standard method, with chlorobenzene selected as the external standard.

[0083] Figure 8 This is a summary of the catalytic activity and selectivity of the catalysts in Examples 1-8 of the present invention for the one-step preparation of p-aminophenol from nitrobenzene.

[0084] Using the catalyst of Example 1, the conversion rate of nitrobenzene to p-aminophenol in the one-step hydrogenation reaction of nitrobenzene was 98.5%, and the selectivity of p-aminophenol was 91.5%.

[0085] Using the catalyst of Example 2, the conversion rate of nitrobenzene to p-aminophenol in the one-step hydrogenation reaction of nitrobenzene was 98.3%, and the selectivity of p-aminophenol was 88.7%.

[0086] Using the catalyst of Example 3, the conversion rate of nitrobenzene to p-aminophenol in the one-step hydrogenation reaction of nitrobenzene was 92.4%, and the selectivity of p-aminophenol was 88.2%.

[0087] Using the catalyst of Example 4, the conversion rate of nitrobenzene to p-aminophenol in the one-step hydrogenation reaction of nitrobenzene was 89.6%, and the selectivity of p-aminophenol was 90.3%.

[0088] Using the catalyst of Example 5, the conversion rate of nitrobenzene to p-aminophenol in the one-step hydrogenation reaction of nitrobenzene was 91.2%, and the selectivity of p-aminophenol was 83.1%.

[0089] Using the catalyst of Example 6, the conversion rate of nitrobenzene to p-aminophenol in the one-step hydrogenation reaction of nitrobenzene was 93.5%, and the selectivity of p-aminophenol was 82.4%.

[0090] Using the catalyst of Example 7, in the one-step hydrogenation reaction of p-nitrobenzene to p-aminophenol, the conversion rate of nitrobenzene was 88.9% and the selectivity of p-aminophenol was 87.3%.

[0091] Using the catalyst of Example 8, the conversion rate of nitrobenzene to p-aminophenol in the one-step hydrogenation reaction of nitrobenzene was 89.7%, and the selectivity of p-aminophenol was 85.8%.

[0092] Using the catalyst of Comparative Example 1, the conversion rate of nitrobenzene to p-aminophenol in the one-step hydrogenation reaction of nitrobenzene was 73.5%, and the selectivity of p-aminophenol was 75.0%.

[0093] Using the catalyst of Comparative Example 2, the conversion rate of nitrobenzene to p-aminophenol in the one-step hydrogenation reaction of nitrobenzene was 79.0%, and the selectivity of p-aminophenol was 64.0%.

[0094] Using the catalyst of Comparative Example 3, the conversion rate of nitrobenzene to p-aminophenol in the one-step hydrogenation reaction of nitrobenzene was 68.0%, and the selectivity of p-aminophenol was 70.0%.

[0095] Using the catalyst of Comparative Example 4, the conversion rate of nitrobenzene to p-aminophenol in the one-step hydrogenation reaction of nitrobenzene was 71.0%, and the selectivity of p-aminophenol was 66.0%.

[0096] Using the catalyst of Comparative Example 5, the conversion rate of nitrobenzene to p-aminophenol in the one-step hydrogenation reaction of nitrobenzene was 77.0%, and the selectivity of p-aminophenol was 68.0%.

Claims

1. A bifunctional catalyst having both metal and acid sites, characterized in that: The bifunctional catalyst uses an oxide with a high hydroxyl density as a support, with metal centers dispersed on the surface of the support and acidic sites surrounding the metal centers. The acidic sites are anchored to the support surface by Si-O-Si bonds and terminated by -SO3H groups; The distance between the metal center and the acidic site is determined by adsorbing thiol ligands on the surface of the metal center as a sacrificial template; The oxides with high hydroxyl density are silicon oxide, aluminum oxide, zirconium oxide, and titanium oxide; The metal center is gold, palladium, platinum, nickel, or ruthenium, with a metal loading of 0.1% to 5%. The thiol ligands are ethanethiol, benzylthiol, phenylethanethiol, n-dodecylthiol, n-octadecylthiol, 2-naphthiophenol, and biphenyl-4-thiol.

2. The bifunctional catalyst according to claim 1, characterized in that: The aforementioned bifunctional catalyst, The oxide with high hydroxyl density is silicon dioxide, the metal center is platinum, and the thiol ligand is phenylethyl mercaptan; Or the bifunctional catalyst, wherein the oxide with high hydroxyl density is zirconium oxide, the metal center is ruthenium, and the thiol ligand is benzyl mercaptan; Or the bifunctional catalyst described herein, wherein the oxide with high hydroxyl density is alumina, the metal center is platinum, and the thiol ligand is ethanethiol; Or the bifunctional catalyst, wherein the oxide with high hydroxyl density is titanium oxide, the metal center is nickel, and the thiol ligand is n-dodecanethiol.

3. The bifunctional catalyst according to claim 1, characterized in that: The mass ratio of the metal center to the carrier is 1:1000, 3:1000, 1:200, or 1:

100.

4. The bifunctional catalyst according to claim 1, characterized in that: The bifunctional catalysts are 0.1% Pt / SiO2-SO3H, 0.1% Pt / Al2O3-SO3H, 0.3% Ru / Al2O3-SO3H, and 0.3% Ru / SiO2-SO3H.

5. The method for preparing the bifunctional catalyst according to any one of claims 1-4, characterized in that: Step 1: After dispersing the support in a metal salt solution and obtaining the supported catalyst precursor Metal / support by wet impregnation, the supported catalyst precursor Metal / support is dispersed in a thiol / ethanol solution to obtain the Thiol-Metal / Support catalyst. Step 2: Disperse the Thiol-Metal / Support catalyst in an aqueous solution, add mercaptosilane coupling agent, adjust the acidity of the system, stir at room temperature for 5-10 h, transfer to a high temperature and high pressure reactor, react at 80-150 °C for 10 h, cool to room temperature, wash and dry; add oxidant to the obtained powder sample, wash until neutral, and dry to obtain the bifunctional catalyst.

6. The preparation method according to claim 5, characterized in that: In step one, the diameter of the carrier is 0.02-3 mm, and the dispersion of the carrier is 5%-10%; the concentration of the thiol is 0.1 M; and in step three, the concentration of the hydrochloric acid is 0.1 M.

7. The preparation method according to claim 5, characterized in that: In step two, the silane coupling agent is 3-mercaptopropyltrimethoxysilane or 3-mercaptopropyltriethoxysilane; the oxidant is 30% hydrogen peroxide, potassium persulfate aqueous solution or potassium permanganate acidic aqueous solution.

8. The preparation method according to claim 7, characterized in that: The mass ratio of the carrier to the silane coupling agent is 2:1; the acidification sulfuric acid concentration is selected as a 10% sulfuric acid aqueous solution.

9. The bifunctional catalyst according to any one of claims 1-4 or the bifunctional catalyst obtained by any one of claims 5-8 is used in the hydrogenation reaction of nitrobenzene to prepare p-aminophenol.

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