Preparation Of Sulfur-doped Mesoporous Carbon Supported Palladium Catalyst And Its Application In Hydrogenation Of Chloronitrobenzene

Catalytic hydrogenation is one of the most important chemical methods in synthetic organic chemistry,and carbon material supported precious metal catalysts are widely used in such reactions.In the catalytic hydrogenation reaction system,when the reaction substrate contains a plurality of reducing functional group compounds,excessive hydrogenation may be caused due to the high activity of the noble metal catalyst,thereby lowering the reaction selectivity,and also causing troubles for subsequent product purification.Many scientific research work shows that doping modification of carbon supports can effectively improve the hydrogenat io n performance of precious metal catalysts.Among them,the vulcanization treatment of the noble metal catalyst can improve the selectivity of the hydrogenation reaction well,but the sulfurized noble metal catalyst in the reaction process has a phenomenon of loss of sulfur atoms,thereby still affecting the selectivity of the hydrogenation reaction.Therefore,we envisage that a sulfur atom is introduced into a carbon carrier,and the sulfur atom is bonded to the carbon skeleton in the form of a covalent bond,so that the problem of loss of sulfur atoms can be well suppressed,so that the selectivity of the hydrogenation reaction can be improved.Improve the stability of the catalyst in the catalytic hydrogenation process.This led to the research content of this article:In this paper,a novel sulfur-doped mesoporous carbon-supported palladium metal catalyst is reported,which is a high-temperature carbonization of a sulfur-r ic h organic polymer in an inert gas,and then the resulting sulfur-doped carbon carrier is supported by a metal palladium to obtain a sulfur-doped carbon-supported palladium.catalyst.We have evaluated that it has a selectivity of up to 99.9% in the reaction of hydrogenation of o-chloronitrobenzene to o-chloroaniline,and the reaction substrate can be completely converted within 3 hours.The sulfur-doped mesoporous carbonsupported palladium catalyst maintained high catalytic performance after six cycles of application,exhibiting 100% conversion and more than 99.9% hydrogenat io n selectivity.We obtained the characterization of sulfur-doped mesoporous carbonsupported palladium catalysts by XRD,TEM,XRF,EDX,XPS and TPD-MS.The results show that there is an interaction between the sulfur atom and the metal palladium in the sulfur-doped catalyst.force.The sulfur atom will take the external electrons of the metal palladium due to its electronegativity,and it will exhibit a high valence state.Compared with the zero-valent palladium,the hydrogenation activity of the high-va le nt palladium will be significantly weakened.Therefore,the interaction between the sulfur atom and the metal palladium reduces the ability of the palladium to dissociate and adsorb hydrogen,inhibits the occurrence of hydrogenation side reactions,and the sulfur-doped palladium interaction catalyst is moderate in the hydrogenation reaction.Excel ent selectivity.On the other hand,the sulfur-doped catalyst with the best hydrogenation performance also showed excel ent stability in the hydrogenat io n reaction.The cycle was applied 6 times,and the hydrogenation performance was maintained at a high level,which confirmed our It is envisaged that the sulfur atom is introduced into the carbon skeleton in the form of a covalent bond,which is more stably present in the catalyst and continuously interacts with the noble metal in the catalyst.Subsequently,we have tried a series of oxidation treatments to process the obtained sulfur-doped catalyst Pd/CS to obtain a hydrogenation catalyst with better catalytic activity.As assessed by the hydrogenation of o-chloronitrobenzene,the time required for these oxidized sulfur-doped catalysts to catalyze the complete conversion of the hydrogenation substrate is significantly reduced,and still maintains a hydrogenation selectivity of greater than 98%.After XRD,TEM,EDX,XRF and XPS characterization,we obtained that the proportion of oxygen-containing groups in Pd/CS after oxidation treatment increased,and the chemical form of bulk sulfur also changed,that is,the proportion of sulfur oxide increased..Therefore,we speculate that the cause of the increase in catalyst hydrogenation activity is the introduction of oxygen atoms.