A palladium / alumina catalyst, its preparation and use

Abstract

The application relates to the technical field of catalysts, and discloses a palladium / alumina catalyst and a preparation method and application thereof. A Schiff base phosphine cyclodextrin ligand is synthesized through two-step reactions of nucleophilic substitution and Schiff base condensation, the molecular structure of the ligand covalently bridges the hydrophobic cavity of beta-cyclodextrin and the strong coordination site of diphenylphosphine through a rigid Schiff base bond; subsequently, the phosphine group of the ligand is coordinated with a palladium salt under a specific pH, and a uniform and stable palladium-ligand colloid precursor is formed under the assistance of a directing agent and a stabilizing agent; finally, the colloid is mixed with an alumina carrier for impregnation, drying, and a palladium / alumina catalyst is obtained. Through molecular design and process innovation, the problems of low activity, poor selectivity and insufficient stability of traditional catalysts are solved. When the catalyst is used for preparing hydrogen peroxide by hydrogenating anthraquinone, the hydrogenation efficiency is significantly improved, the selectivity is extremely high, and the cycle stability is excellent, so the catalyst has important industrial application value.

Description

Technical Field

[0001] This invention relates to the field of catalyst technology, specifically to a palladium / alumina catalyst, its preparation method, and its application. Background Technology

[0002] Hydrogen peroxide (H2O2), as an important green oxidant, is widely used in chemical, environmental protection, papermaking, and pharmaceutical fields. The anthraquinone process is currently the mainstream industrial process for producing hydrogen peroxide, with its core step being the catalytic hydrogenation of 2-ethylanthraquinone (EAQ). In this process, supported palladium / alumina catalysts are widely used in suspended bed hydrogenation reactors (solid-liquid-gas three-phase system) due to their relatively high activity. However, this process and existing catalyst systems still face several key technological bottlenecks that urgently need to be addressed, limiting further improvements in production efficiency and economic benefits.

[0003] Regarding catalytic activity, palladium / alumina catalysts prepared by traditional impregnation methods are prone to agglomeration of the active component, palladium nanoparticles, on the support surface, forming large and unevenly distributed active centers. This results in low effective utilization of palladium atoms per unit mass, making it difficult to achieve a breakthrough in overall hydrogenation efficiency (i.e., the ability of the working fluid to generate hydrogen peroxide). Secondly, in terms of reaction selectivity, the anthraquinone hydrogenation process involves competitive reactions between the target product (2-ethylanthraquinone, EAQH2) and over-hydrogenation byproducts (such as tetrahydro-2-ethylanthraquinone, H4EAQ), as well as various degradation products. Traditional catalysts have limited control over the reaction pathway, making them prone to deep hydrogenation and side reactions, leading to ineffective loss of effective anthraquinone and rapid aging of the working fluid system, significantly increasing production costs. Finally, regarding operational stability, during long-term cyclic reactions, especially under the influence of mechanical stirring and airflow in a suspended bed reactor, the active palladium component is prone to migration, agglomeration, and even leaching from the support surface. Simultaneously, severe wear between catalyst particles causes rapid decline in catalyst activity and selectivity, shortening its service life. Summary of the Invention

[0004] (a) Technical problems to be solved:

[0005] To address the shortcomings of existing technologies, this invention provides a palladium / alumina catalyst, its preparation method, and its application, solving the problems of low catalytic activity, poor selectivity, and severe wear of traditional catalysts.

[0006] (II) Technical Solution:

[0007] In a first aspect, the present invention provides a palladium / alumina catalyst, the palladium / alumina catalyst comprising an alumina support and a palladium active component supported thereon; the alumina support and the palladium active component are integrally modified by Schiff base phosphoyl cyclodextrin; the palladium content is 1-3 wt% based on the total weight of the catalyst; and the particle size of the catalyst is 50-300 micrometers.

[0008] Furthermore, the preparation method of Schiff base phosphoyl cyclodextrin is as follows:

[0009] Step (1): Under a nitrogen atmosphere, add mono-6-oxo-p-toluenesulfonyl-β-cyclodextrin ester, o-phenylenediamine, sodium carbonate, and N,N-dimethylformamide to a flask. Heat to 80-90℃ and stir for 12-16 hours. Filter, pour the filtrate into acetone to obtain a white precipitate. Filter, collect the solid, dissolve the solid in N,N-dimethylformamide, and separate the product in a chromatographic column to obtain mono-6-o-aminobenzylamine-β-cyclodextrin ester. The preparation reaction formula is:

[0010] .

[0011] Step (2): Under a nitrogen atmosphere, add mono-6-o-aminobenzylamine-β-cyclodextrin ester, 2-diphenylphosphine benzaldehyde, and dimethyl sulfoxide to a flask equipped with a reflux condenser. Heat to 70-80℃, stir for 10-12 hours, and distill under reduced pressure until a precipitate forms. Filter, wash with petroleum ether, and dry to obtain Schiff base phosphoyl cyclodextrin. The preparation reaction formula is:

[0012] .

[0013] Further, in step (1), the mass ratio of mono-6-oxo-p-toluenesulfonyl-β-cyclodextrin ester, o-phenylenediamine, sodium carbonate, and N,N-dimethylformamide is 10:(3-6):(1.5-3):(500-1000).

[0014] Further, in step (2), the mass ratio of mono-6-o-aminobenzylamine-β-cyclodextrin ester, 2-diphenylphosphine benzaldehyde, and dimethyl sulfoxide is 10:(10-12):(300-600).

[0015] Secondly, the present invention also provides a method for preparing a palladium / alumina catalyst, comprising the following steps:

[0016] S1. Dissolve palladium chloride in deionized water, add concentrated hydrochloric acid with a concentration of 36-38% dropwise, stir at room temperature for 2-3 hours, and add NaOH solution with a concentration of 0.1-0.5 mol / L dropwise while stirring until the pH is 4.5-5.5. Add Schiff base phosphoyl cyclodextrin, directing agent and stabilizer, stir at room temperature for 4-5 hours to obtain palladium-Schiff base phosphoyl cyclodextrin colloid.

[0017] S2. Add alumina powder to the palladium-Schiff base phospho-cyclodextrin colloid, mix evenly at room temperature, impregnate for 4-5 hours, filter, and dry the filter cake at 90-100℃ for 2-3 hours to obtain the palladium / alumina catalyst.

[0018] Furthermore, the directing agent is at least one of polyvinylpyrrolidone, cetyltrimethylammonium bromide, or hydroxyethyl cellulose; wherein the molecular weight of polyvinylpyrrolidone is 35,000-50,000.

[0019] Furthermore, the stabilizer is sodium carboxymethyl cellulose.

[0020] Furthermore, in step S1, the mass-volume ratio of palladium chloride, deionized water, concentrated hydrochloric acid, Schiff base phospho-modified cyclodextrin, directing agent, and stabilizer is 10:(500-1500):(10-30):(15-30):(8-20):(1-5).

[0021] Furthermore, in step S2, the mass ratio of palladium-Schiff base phosphoyl cyclodextrin colloid to alumina powder is 10:(20-50).

[0022] Thirdly, the present invention also provides an application of the above-mentioned palladium / alumina catalyst in the catalytic hydrogenation of anthraquinone to prepare hydrogen peroxide in a suspended bed reactor.

[0023] (III) Beneficial technical effects:

[0024] This invention first involves a nucleophilic substitution reaction between mono-6-oxo-p-toluenesulfonyl-β-cyclodextrin ester and o-phenylenediamine to obtain mono-6-o-aminobenzylamine-β-cyclodextrin ester. Then, the amino group of mono-6-o-aminobenzylamine-β-cyclodextrin ester undergoes a condensation reaction with the aldehyde group of 2-diphenylphosphine benzaldehyde to form a Schiff base bond (C=N), thereby covalently linking the diphenylphosphine functional group to the cyclodextrin, yielding the key ligand, Schiff base phosphoylated cyclodextrin. Subsequently, in a pH-controlled aqueous environment, this ligand forms a complex with a palladium salt through strong phosphine group coordination, and is dispersed into a homogeneous and stable palladium-Schiff base phosphoylated cyclodextrin colloid with the assistance of a directing agent and a stabilizer. Finally, this colloid is mixed and impregnated with an alumina support, and after drying, a palladium / alumina catalyst is obtained.

[0025] The palladium / alumina catalyst of this invention was used for the hydrogenation of anthraquinone in a suspended bed to prepare hydrogen peroxide. This catalyst exhibits excellent hydrogenation efficiency and low attrition rate. This invention integrates a strong phosphine-based coordination site, a β-cyclodextrin substrate enrichment cavity, and a rigid Schiff base bridge bond into a single "Schiff base phospho-based cyclodextrin" ligand molecule through covalent bonding. This fundamentally avoids the defects of easy separation and unsynergistic effects of functional modules in physical mixtures, achieving precise three-dimensional control of the active site in terms of electronic structure, microenvironment, and spatial configuration.

[0026] 1. The phosphine unit in the Schiff base phospho-based cyclodextrin of the present invention acts as a strong σ-electron donor. After coordination with the palladium center, it can significantly increase the electron density of palladium. This optimization of electronic structure is the electronic basis for the catalyst to achieve efficient hydrogen activation and highly selective C=O bond hydrogenation.

[0027] 2. The β-cyclodextrin unit in the Schiff base phosphoyl cyclodextrin of the present invention exhibits significant host-guest inclusion and pre-enrichment capabilities for anthraquinone substrates due to its hydrophobic cavity. This effect enables a localized high concentration distribution of substrate molecules around the catalytic active center (palladium site), effectively overcoming mass transfer limitations. Synergistically with the electronic modification effect of the active center, this effect significantly enhances the hydrogenation reaction rate.

[0028] 3. The covalent framework composed of rigid Schiff base groups in the Schiff base phosphoyl cyclodextrin of this invention provides a robust and spatially confined coordination environment for the palladium active center. This structural advantage brings a stability that cannot be achieved by traditional flexible ligands or physical adsorption. The rigid confinement strongly inhibits the thermal migration and sintering agglomeration of palladium species during the reaction and regeneration process, keeping them in a highly dispersed state for a long time, thus playing an anti-agglomeration role; the strong coordination of the phospho groups and the anchoring effect of the rigid framework together effectively prevent the leaching loss of active palladium components in the liquid phase reaction, playing an anti-leaching role. The anti-agglomeration and anti-leaching effects together endow the catalyst with excellent cycle stability and significantly extended service life, fundamentally solving the problems of easy deactivation and short life of traditional catalysts.

[0029] 4. The catalyst of this invention has a particle size controlled between 50-300 micrometers, with good sphericity and smooth surface. It has good anti-wear performance in the suspended bed reactor, with a wear rate of less than 3%, which significantly reduces the fine powder generation rate and catalyst loss. Attached Figure Description

[0030] Figure 1 This is a SEM image of the palladium / alumina catalyst prepared in Example 1 of the present invention. Detailed Implementation

[0031] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0032] Mono-6-oxo-p-toluenesulfonyl-β-cyclodextrin ester was prepared according to the method described in the journal Applied Chemistry, 2011, 28(11):1269-1273, "Heterogeneous synthesis of mono-6-oxo-p-toluenesulfonyl-β-cyclodextrin ester in alkaline aqueous solution".

[0033] All raw materials used in this invention are commercially available.

[0034] Example 1:

[0035] A method for preparing a palladium / alumina catalyst includes the following steps:

[0036] Step (1): Under a nitrogen atmosphere, add 10 parts by weight of mono-6-oxo-p-toluenesulfonyl-β-cyclodextrin ester, 4 parts by weight of o-phenylenediamine, 2 parts by weight of sodium carbonate, and 500 parts by weight of N,N-dimethylformamide to a flask, heat to 80°C, stir and react for 14 hours, filter, pour the filtrate into acetone to obtain a white precipitate, filter, collect the solid, dissolve the solid in N,N-dimethylformamide, separate the product in a chromatographic column, and obtain mono-6-o-aminobenzylamine-β-cyclodextrin ester.

[0037] Step (2): Under a nitrogen atmosphere, add 10 parts by weight of mono-6-o-aminobenzylamine-β-cyclodextrin ester, 11 parts by weight of 2-diphenylphosphine benzaldehyde, and 500 parts by weight of dimethyl sulfoxide to a flask equipped with a reflux condenser. Heat to 70°C, stir and react for 12 hours, distill under reduced pressure until the precipitate is formed, filter, wash with petroleum ether, and dry to obtain Schiff base phosphoyl cyclodextrin.

[0038] Step (3): Dissolve 10 parts by weight of palladium chloride in 1000 parts by weight of deionized water, add 20 parts by weight of concentrated hydrochloric acid with a concentration of 37%, stir at room temperature for 3 hours, and add 0.5 mol / L NaOH solution dropwise while stirring until the pH is 5. Add 22 parts by weight of Schiff base phospho-modified cyclodextrin, 14 parts by weight of polyvinylpyrrolidone, and 3 parts by weight of sodium carboxymethyl cellulose, and stir at room temperature for 4 hours to obtain palladium-Schiff base phospho-modified cyclodextrin colloid.

[0039] Step (4): Add 35 parts by weight of alumina powder to 10 parts by weight of palladium-Schiff base phospho-cyclodextrin colloid, mix evenly at room temperature, impregnate for 5 hours, filter, and dry the filter cake at 100°C for 2 hours to obtain palladium / alumina catalyst with a particle size of 50-300 micrometers and a palladium content of 1 wt%.

[0040] Example 2:

[0041] A method for preparing a palladium / alumina catalyst includes the following steps:

[0042] Step (1): Under a nitrogen atmosphere, add 10 parts by weight of mono-6-oxo-p-toluenesulfonyl-β-cyclodextrin ester, 3 parts by weight of o-phenylenediamine, 1.5 parts by weight of sodium carbonate, and 800 parts by weight of N,N-dimethylformamide to a flask, heat to 90°C, stir and react for 12 hours, filter, pour the filtrate into acetone to obtain a white precipitate, filter, collect the solid, dissolve the solid in N,N-dimethylformamide, separate the product in a chromatographic column, and obtain mono-6-o-aminobenzylamine-β-cyclodextrin ester.

[0043] Step (2): Under a nitrogen atmosphere, add 10 parts by weight of mono-6-o-aminobenzylamine-β-cyclodextrin ester, 10 parts by weight of 2-diphenylphosphine benzaldehyde, and 300 parts by weight of dimethyl sulfoxide to a flask equipped with a reflux condenser. Heat to 80°C, stir and react for 10 hours, distill under reduced pressure until the precipitate is formed, filter, wash with petroleum ether, and dry to obtain Schiff base phosphoyl cyclodextrin.

[0044] Step (3): Dissolve 10 parts by weight of palladium chloride in 500 parts by weight of deionized water, add 10 parts by weight of concentrated hydrochloric acid with a concentration of 38%, stir at room temperature for 2 hours, and add 0.1 mol / L NaOH solution dropwise while stirring until the pH is 4.5. Add 15 parts by weight of Schiff base phospho-cyclodextrin, 8 parts by weight of hexadecyltrimethylammonium bromide, and 1 part by weight of sodium carboxymethyl cellulose, and stir at room temperature for 4 hours to obtain palladium-Schiff base phospho-cyclodextrin colloid.

[0045] Step (4): Add 20 parts by weight of alumina powder to 10 parts by weight of palladium-Schiff base phospho-cyclodextrin colloid, mix evenly at room temperature, impregnate for 4 hours, filter, and dry the filter cake at 90°C for 2 hours to obtain palladium / alumina catalyst with a particle size of 50-300 micrometers and a palladium content of 2wt%.

[0046] Example 3:

[0047] A method for preparing a palladium / alumina catalyst includes the following steps:

[0048] Step (1): Under a nitrogen atmosphere, add 10 parts by weight of mono-6-oxo-p-toluenesulfonyl-β-cyclodextrin ester, 6 parts by weight of o-phenylenediamine, 3 parts by weight of sodium carbonate, and 1000 parts by weight of N,N-dimethylformamide to a flask, heat to 80°C, stir and react for 16 hours, filter, pour the filtrate into acetone to obtain a white precipitate, filter, collect the solid, dissolve the solid in N,N-dimethylformamide, separate the product in a chromatographic column, and obtain mono-6-o-aminobenzylamine-β-cyclodextrin ester.

[0049] Step (2): Under a nitrogen atmosphere, add 10 parts by weight of mono-6-o-aminobenzylamine-β-cyclodextrin ester, 12 parts by weight of 2-diphenylphosphine benzaldehyde, and 600 parts by weight of dimethyl sulfoxide to a flask equipped with a reflux condenser. Heat to 70°C, stir and react for 11 hours, distill under reduced pressure until the precipitate is formed, filter, wash with petroleum ether, and dry to obtain Schiff base phosphoyl cyclodextrin.

[0050] Step (3): Dissolve 10 parts by weight of palladium chloride in 1500 parts by weight of deionized water, add 30 parts by weight of concentrated hydrochloric acid with a concentration of 36%, stir at room temperature for 3 hours, and add 0.5 mol / L NaOH solution dropwise while stirring until the pH is 5.5. Add 30 parts by weight of Schiff base phospho-modified cyclodextrin, 20 parts by weight of hydroxyethyl cellulose, and 5 parts by weight of sodium carboxymethyl cellulose, and stir at room temperature for 5 hours to obtain palladium-Schiff base phospho-modified cyclodextrin colloid.

[0051] Step (4): Add 50 parts by weight of alumina powder to 10 parts by weight of palladium-Schiff base phospho-cyclodextrin colloid, mix evenly at room temperature, impregnate for 5 hours, filter, and dry the filter cake at 100°C for 3 hours to obtain palladium / alumina catalyst with a particle size of 50-300 micrometers and a palladium content of 3 wt%.

[0052] Comparative Example 1: The difference from Example 1 is that Schiff base phospho-substituted cyclodextrin was not added.

[0053] Comparative Example 2: The difference from Example 1 is that ordinary β-cyclodextrin is used instead of Schiff base phospho-substituted cyclodextrin.

[0054] Comparative Example 3: The difference from Example 1 is that mono-6-o-aminobenzylamine-β-cyclodextrin ester is used instead of Schiff base phospho-modified cyclodextrin.

[0055] Comparative Example 4: The difference from Example 1 is that ordinary β-cyclodextrin is used instead of mono-6-o-aminobenzylamine-β-cyclodextrin ester.

[0056] Comparative Example 5: The difference from Example 1 is that no guiding agent is added.

[0057] Comparative Example 6: The difference from Example 1 is that no stabilizer was added.

[0058] In Examples 1-3 and Comparative Examples 1-6, the hydrogenation performance of the palladium / alumina catalyst was investigated in the anthraquinone process for hydrogen peroxide preparation using a suspended bed reactor: 1.5 g of catalyst and 40 mL of working solution (containing 4 g of 2-ethylanthraquinone) were added to a 100 mL pressure reactor. After sealing, the reactor was evacuated to remove air, and then heating was initiated. When the desired reaction temperature was reached, hydrogen gas was introduced to the required reaction pressure, and stirring was started (stirring speed 800 rpm, simulating suspended bed fluidization). After the reaction, the catalyst in the hydrogenated liquid was separated by centrifugation. The hydrogenated liquid was oxidized with oxygen at 45 °C for 0.5 h, and the oxidized liquid was extracted several times with distilled water. Finally, titration was performed with KMnO4 solution in an acidic medium. The hydrogenation efficiency B (the ability of a certain amount of catalyst to catalyze the hydrogenation of a unit volume of 2-ethylanthraquinone working solution to prepare 100% H2O2, g / L) is calculated according to the following formula: B = 17 × 5cV1 / V2, where c is the concentration of KMnO4 solution (mol / L); V1 is the amount of KMnO4 solution used (mL); and V2 is the volume of the oxidation liquid (mL).

[0059] Catalyst attrition rate test: The catalyst sample was treated in an air jet mill for 5 hours. The mass percentage of fine powder with a particle size of less than 50 micrometers was calculated by sieving analysis. Attrition rate (%) = W1 / W0×100%, where W0 is the initial total mass (g) of the catalyst before the test, and W1 is the mass (g) of fine powder with a particle size of less than 50 micrometers obtained by sieving after air jet treatment.

[0060] Table 1: Test results of palladium / alumina catalyst for the hydrogenation of anthraquinone to prepare hydrogen peroxide

[0061]

[0062] As shown in the table, the palladium / alumina catalysts of Examples 1-3 exhibit excellent hydrogenation efficiency and low wear rate when used for the hydrogenation of anthraquinone to hydrogen peroxide. This is mainly due to the Schiff base phosphinized cyclodextrin molecules and their integrated modification process, which constructs a highly efficient, stable, and specific catalytic system. The phosphine units in the Schiff base phosphinized cyclodextrin molecules coordinate with the palladium center to form electron-density-rich active sites, significantly optimizing the catalytic cycle of hydrogen activation and selective hydrogenation of anthraquinone C=O bonds. The hydrophobic cavities of the cyclodextrin selectively adsorb hydrophobic anthraquinone substrates, greatly increasing the local reactant concentration at the active center. Simultaneously, the rigid coordination environment formed by Schiff base bridging provides spatial confinement for palladium species, effectively inhibiting the migration, aggregation, and leaching of active components during the reaction. Furthermore, the optimized particle size distribution and colloidal-assisted molding process endow the catalyst with excellent wear resistance.

[0063] The difference between Comparative Example 1 and Example 1 is that the palladium / alumina catalyst was prepared without the addition of Schiff base phosphoyl cyclodextrin. The catalyst in this comparative example completely lacks Schiff base phosphoyl cyclodextrin, and cannot coordinate with the palladium center to form an active site with enriched electron density, nor can it selectively adsorb hydrophobic anthraquinone substrates, ultimately resulting in poor hydrogenation efficiency.

[0064] The difference between Comparative Example 2 and Example 1 is that ordinary β-cyclodextrin replaces Schiff base phosphoyl cyclodextrin to prepare palladium / alumina catalyst. The catalyst in this comparative example lacks phospho groups and Schiff base bonds. Ordinary β-cyclodextrin has weak interaction with palladium and cannot form a stable and highly active coordination center; it also cannot produce a spatial confinement effect on palladium species, resulting in poor hydrogenation efficiency.

[0065] The difference between Comparative Example 3 and Example 1 is that mono-6-o-aminobenzylamine-β-cyclodextrin ester was used to replace Schiff base phospho-modified cyclodextrin in the preparation of palladium / alumina catalyst. The catalyst in this comparative example lacks phosphine group, and the amino group of mono-6-o-aminobenzylamine-β-cyclodextrin ester has a weaker coordination ability with palladium than that of phosphine group, resulting in unstable active sites and low activity.

[0066] The difference between Comparative Example 4 and Example 1 is that ordinary β-cyclodextrin was used to replace mono-6-o-aminobenzylamine-β-cyclodextrin ester in the preparation of palladium / alumina catalyst. In this comparative example, ordinary β-cyclodextrin was directly mixed with 2-diphenylphosphine benzaldehyde without chemical bond linkage. The phosphine group and cyclodextrin were not combined, making it difficult for them to act on the same palladium center simultaneously. The phosphine ligand was easy to dissociate from the palladium center and could not provide a stable confinement, resulting in poor hydrogenation efficiency.

[0067] The difference between Comparative Example 5 and Example 1 is that no directing agent was added to prepare the palladium / alumina catalyst. The catalyst in this comparative example lacks a directing agent, which disrupts the uniformity of the colloidal precursor. When forming the palladium-cyclodextrin complex, it lacks steric hindrance protection and is prone to local aggregation, resulting in uneven dispersion of the palladium active component and poor hydrogenation efficiency.

[0068] The difference between Comparative Example 6 and Example 1 is that no stabilizer was added to prepare the palladium / alumina catalyst. The catalyst in this comparative example lacks a stabilizer, which compromises the stability of the colloidal precursor and the reproducibility of the process. The colloid is unstable, and the composite colloid settles or aggregates before impregnation, resulting in uneven loading and poor hydrogenation efficiency.

[0069] Figure 1 This is a scanning electron microscope (SEM) image of the palladium / alumina catalyst prepared in Example 1 of this invention. Test conditions: accelerating voltage EHT = 5.00 kV, detector type signal A = SE2, working distance WD = 5.4 mm, magnification Mag = 1.00 KX (1000x). Figure 1It can be seen that the palladium / alumina catalyst prepared by this invention has good particle sphericity and smooth surface, and the particle size of the palladium / alumina catalyst prepared by this invention is 50-300 micrometers.

[0070] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A palladium / alumina catalyst, characterized in that, The palladium / alumina catalyst comprises an alumina support and a palladium active component supported thereon; the alumina support and the palladium active component are integrally modified by Schiff base phosphoyl cyclodextrin. The palladium content is 1-3 wt% based on the total weight of the catalyst; the particle size of the catalyst is 50-300 micrometers. The method for preparing the Schiff base phosphoyl cyclodextrin is as follows: Mono-6-oxo-p-toluenesulfonyl-β-cyclodextrin ester undergoes a nucleophilic substitution reaction with o-phenylenediamine to obtain mono-6-o-aminobenzylamine-β-cyclodextrin ester; then, the amino group of mono-6-o-aminobenzylamine-β-cyclodextrin ester undergoes a condensation reaction with the aldehyde group of 2-diphenylphosphine benzaldehyde to form a Schiff base bond, thereby covalently linking the diphenylphosphine functional group to the cyclodextrin to obtain the Schiff base phosphoyl cyclodextrin.

2. The palladium / alumina catalyst according to claim 1, characterized in that, The preparation method of the Schiff base phosphoyl cyclodextrin is as follows: Step (1): Under a nitrogen atmosphere, add mono-6-oxo-p-toluenesulfonyl-β-cyclodextrin ester, o-phenylenediamine, sodium carbonate, and N,N-dimethylformamide to a flask, heat to 80-90℃, stir and react for 12-16 hours, filter, pour the filtrate into acetone to obtain a white precipitate, filter, collect the solid, dissolve the solid in N,N-dimethylformamide, separate the product in a chromatographic column to obtain mono-6-o-aminobenzylamine-β-cyclodextrin ester; Step (2): Under a nitrogen atmosphere, add mono-6-o-aminobenzylamine-β-cyclodextrin ester, 2-diphenylphosphine benzaldehyde, and dimethyl sulfoxide to a flask equipped with a reflux condenser. Heat to 70-80℃, stir and react for 10-12 hours, distill under reduced pressure until the precipitate is formed, filter, wash with petroleum ether, and dry to obtain Schiff base phosphoyl cyclodextrin.

3. The palladium / alumina catalyst according to claim 2, characterized in that, In step (1), the mass ratio of mono-6-oxo-p-toluenesulfonyl-β-cyclodextrin ester, o-phenylenediamine, sodium carbonate, and N,N-dimethylformamide is 10:(3-6):(1.5-3):(500-1000).

4. The palladium / alumina catalyst according to claim 2, characterized in that, In step (2), the mass ratio of mono-6-o-aminobenzylamine-β-cyclodextrin ester, 2-diphenylphosphine benzaldehyde, and dimethyl sulfoxide is 10:(10-12):(300-600).

5. A method for preparing the palladium / alumina catalyst according to any one of claims 1-4, characterized in that, Includes the following steps: S1. Dissolve palladium chloride in deionized water, add concentrated hydrochloric acid with a concentration of 36-38% dropwise, stir at room temperature for 2-3 hours, and add NaOH solution with a concentration of 0.1-0.5 mol / L dropwise while stirring until the pH is 4.5-5.

5. Add Schiff base phosphoyl cyclodextrin, directing agent and stabilizer, stir at room temperature for 4-5 hours to obtain palladium-Schiff base phosphoyl cyclodextrin colloid. S2. Add alumina powder to the palladium-Schiff base phospho-cyclodextrin colloid, mix evenly at room temperature, impregnate for 4-5 hours, filter, and dry the filter cake at 90-100℃ for 2-3 hours to obtain the palladium / alumina catalyst.

6. The method for preparing the palladium / alumina catalyst according to claim 5, characterized in that, The directing agent is at least one of polyvinylpyrrolidone, hexadecyltrimethylammonium bromide, or hydroxyethyl cellulose.

7. The method for preparing the palladium / alumina catalyst according to claim 5, characterized in that, The stabilizer is sodium carboxymethyl cellulose.

8. The method for preparing the palladium / alumina catalyst according to claim 5, characterized in that, The mass ratio of palladium chloride, deionized water, concentrated hydrochloric acid, Schiff base phospho-modified cyclodextrin, directing agent, and stabilizer in step S1 is 10:(500-1500):(10-30):(15-30):(8-20):(1-5).

9. The method for preparing the palladium / alumina catalyst according to claim 5, characterized in that, In step S2, the mass ratio of palladium-Schiff base phospho-based cyclodextrin colloid to alumina powder is 10:(20-50).

10. The application of a palladium / alumina catalyst as described in any one of claims 1-4, characterized in that, The palladium / alumina catalyst is used in a suspended bed reactor for the catalytic hydrogenation of anthraquinone to prepare hydrogen peroxide.

Images