Preparation Of Magnetic Palladium-carbon Catalyst And Experimental Study On Its Catalytic Hydrogenation Reaction

Aromatic amines and their derivatives are used widely.Catalytic hydrogenation reduction using supported noble metal catalyst has a good application prospect because of its high conversion and selectivity.However,the cost of precious metal catalyst is high due to the low atomic utilization rate and the loss of catalyst in the separation and recovery process,which restricts its application in industrial practice.Therefore,it is a research hotspot to design a catalyst with high activity,dispersibility and interaction ability between carrier and active component.In this study,magnetic palladium-carbon（Pd/C）bimetallic catalyst doped with nanometer zero-valent iron（n ZVI）was prepared by calcination method.This catalytic material has high magnetic properties and meets the performance of magnetic separation and recovery of industrial catalytic materials.The modified magnetic Pd/C catalyst after calcination has obvious Pd crystal structure,and the nanosized zero-valent iron particles are successfully doped into the Pd crystal structure to form Fe-Pd bimetallic active component.The obtained catalyst was directly applied to pressurized selective hydrogenation of nitro with 5-nitro-2-benzimidazolone as the substrate and deionized water as the solvent.The theoretical Pd content was 3%under dry base condition,and the influence of iron content change on catalytic performance was determined by controlling doping iron content.3Fe⁰-3Pd/C had the strongest initial activity.5Fe⁰-3Pd/C has the best stability,with 99.6%conversion and 96.5%selectivity at lower temperature and pressure.The initial activity of the catalyst is high and the reaction conditions are mild and easy to implement.High temperature thermal reduction resulted in the loss of Pd active site,and the gradual inactivation of Fe⁰resulted in the decrease of catalytic activity gradually.Therefore,the preparation method of magnetic Pd/C catalyst doped with n ZVI should be improved.Under the complexation dispersion and reduction of sodium citrate and sodium borohydride,a highly dispersive zero-valent Fe-Pd bimetallic alloy catalyst was prepared by taking advantage of the electron-donating properties of Fe²⁺and Fe⁰generated during the reduction process.The prepared catalyst was applied to the selective hydrogenation of 5-nitro-2-benzimidazolone with a conversion rate of 99.8%and selectivity of 97.0%under mild conditions.The Fe-Pd bimetallic active component formed in the catalyst inhibits the passivation and deactivation of the nanometer zero-valent iron,which makes the catalyst have higher catalytic activity and service life under mild reaction conditions.Among them,n ZVI,as the active component,improved the unsaturated coordination sites on the surface of the material.The feasibility of using n ZVI to reduce Pd load in the catalyst was proved by comparing the reduction of Pd load with that of palladium-carbon catalyst under the constant loading of Fe.The performance of magnetic separation and recovery of catalytic materials was further enhanced by the introduction of Fe₃O₄.The catalyst is easy to prepare and recover.It also has high stability,less cost and meet the actual demand of enterprise production.