Preparation Of Pd/C Catalysts For Selective Hydrogenation Of Halogenated Aromatic Compounds And Study Of Catalytic Properties

Halogenated aromatic amines are widely used in materials chemistry,organic chemistry and pharmaceutical chemistry.They are important intermediates in the synthesis of dyes,insecticides and herbicides.Catalysis of hydrogenated halogenated aromatic nitro compounds by Pd/C catalysts is an important way to prepare halogenated aromatic amines.In this study,the effects of preparation conditions of Pd/C catalysts on their activity were investigated by changing the preparation conditions of Pd/C catalysts,evaluating the decomposition reaction of formic acid,and characted FTIR,XRD,N₂ physical adsorption and SEM of Pd/C catalysts.The pretreatment of activated carbon with inorganic acids could effectively remove ash content and impurities on the surface of activated carbon.The most oxygen-containing functional groups were introduced in activated carbon treated with HNO₃.When the concentration of nitric acid was 5%,the treatment of activated carbon not only introduced many oxygen-containing functional groups,but also did not destroy the pore structure on the surface of activated carbon.The activities of five catalysts for preparation of activated carbon with different sources and morphologies were compared,demonstrating that the catalysts for preparation of activated carbon with large surface area had small Pd particles,dispersive distribution and high catalytic activity.When hydrogen was used as reducing agent to prepare catalysts,the reduction of Pd ions was complete,and hydrogen enhanced the interaction between Pd particles and carriers.Therefore,using activated carbon with large specific surface area in irregular bulk as carrier,catalysts prepared by hydrogen reduction under 5%nitric acid treatment showed smaller Pd particles and more dispersive distribution,and the activity in the decomposition of formic acid reached 50%.The selectivity of the catalysts was evaluated by the synthesis of the intermediate of indoxacarb,2-?phenylmethyl?-7-chloroindeno[1,2-e][1,3,4]oxadiazine-2,4a?3H,5H?-4a methyl dicarboxylate?YCW-5?,to7-chloro-2,5-dihydroindeno[1,2-e][1,3,4]oxadiazine-4a?3H?-carboxylic acid methyl ester?YWC-6?by catalytic hydrogenation.The relationship between catalyst activity and selectivity in the synthesis of the intermediate of indoxacarb,2-?phenylmethyl?-7-chloroindeno[1,2-e][1,3,4]oxadiazine-2,4a?3H,5H?-4a methyl dicarboxylate?YCW-5?,to 7-chloro-2,5-dihydroindeno[1,2-e][1,3,4]oxadiazine-4a?3H?-carboxylic acid methyl ester?YWC-6?by catalytic hydrogenation was investigated,revealing that high activity of Pd/C catalysts promoted the occurrence of side reactions in catalytic hydrogenation of halogenated aromatic compounds.Amination catalyst was prepared by modifying catalyst with ethylenediamine as additive.The experiment showed that 20g catalyst aminated with 1 ml ethylenediamine had high activity in the reaction,with conversion rate of 99.3%and dechlorination rate of only 0.8%.Application for many times presented good performances.Therefore,it has good industrial prospects.