Preparation Of Immobilized Nano-gold Catalyst And Its Application In Photo-assisted Selective Reduction

With the development of fine chemicals and pharmaceutical industry,the commercial value of aromatic alcohols,one of necessary raw materials in the above fields is becoming more and more important.In general,the selective hydrogenation of aromatic ketones to the corresponding aromatic alcohols has been considered as one of cost-optimal processes to produce aromatic alcohols.However,green and energy-efficient hydrogenation of aromatic ketones still is a huge challenge for industrial circles.In recent years,owing to the increasing energy-related and environmental issues,more and more photocatalytical processes have received appreciable attentions and various semiconductor materials have been used as photocatalysts in photolysis of water to produce hydrogen,alcohol oxidation,ketone reduction,degradation of harmful organic volatiles?VOCs?,etc.Metal nanoparticles as dopants of semiconductor materials can effectively increase efficiency/range of absorbing visible light,moreover,the synergistic effects can improve the separation efficiency of the photogenerated charge and accelerate the migration rate.This is of great significance for photocatalytic reactions.In order to effectively hydrogenate aromatic ketones to aromatic alcohols under mild conditions,in this dissertation,the advantages of photocatalysis were combined with the physicochemical properties of cerium oxide and metal nanoparticles.More specifically,Au?Pd?nanoparticles were supported on nano-cerium oxide by using sodium borohydride to reducing the corresponding noble metal precursors,then,the catalytic performance of the resultant supported catalysts in photocatalytic reaction was investigated systematically.The main contents discussed were as follows:?1?Cerium oxide with particle size<200 nm was selected as support and HAuCl₄ as Au precursor.The Au/CeO₂ photocatalysts were prepared by sodium borohydride reduction.The effects of temperature,time and pH on the size of Au nanoparticles were investigated.The catalyst prepared under the optimal conditions was subjected to the photocatalytic hydrogenation of styrene oxide.The effects of catalyst dosage,type of alkali,amount of alkali,amount of solvent,reaction temperature,reaction time and light intensity on the catalytic performance were investigated systematically.It was found that,under the optimal conditions,the catalyst exhibits good photocatalytic performance for the hydrogenation of styrene oxide.The conversion of styrene oxide is as high as 60.2%,with 99.9%selectivity to styrene.Furthermore,the catalyst can be reused for 4 times without loss of activity.?2?In view of the fact that the above Au/CeO₂ catalyst shows unacceptable catalytic performance in hydrogenation reduction of acetophenone,palladium was invoked to enhance performance of the photocatalyst of Au/CeO₂.During the preparation processes of the bimetal AuPd/CeO₂,the effects of Au-Pd loading mode,the ratio of Au to Pd,and the contents of noble metals were investigated in detail.Under the optimal reaction conditions,the catalyst of AuPd/CeO₂ shows outstanding catalytic activity.The conversion of acetophenone is as high as 95.6%with 82.2%selectivity to 1-phenylethanol.The catalyst can be reused for 2 times without significant loss of catalytic activity.In order to investigate the reasons for the high catalytic activity,the catalysts were characterized by TEM,XPS,and electrochemical analysis and possible reason was discussed.