Preparation Of Nano-Gold/Rice Husks Carbon Catalyst And Its Application In Oxidation Of Benzyl Alcohol

Benzaldehyde has been used in medical,dyeing,spices,and other industries widely.Previously,the benzaldehyde is mainly prepared via the hydrolysis of benzyl chloride and the oxidation of toluene,the former causes severe chlorine contamination,while the conditions of high temperature and pressure result in poor product selectivity.Nowadays,benzaldehyde is mainly synthesized via the liquid-phase oxidation of benzyl alcohol.In industry,stoichiometric chromates/permanganate was generally used to oxidize benzyl alcohol,such processes are expensive and environmentally-unfriendly.Recently,highly efficient and environmentally-friendly catalytic oxidation systems have attracted the attention of researchers,such as the systems with H₂O₂ or O₂ as oxidants,which produce no harmful residues with water being the only by-product.In this context,the main challenge of clean catalytic oxidation of benzyl alcohol in industry is to develop highly active and selective catalysts.In this dissertation,by combining the characteristics of bimetal with semiconductor,a series of Au-based catalysts were prepared and used to catalyze selective oxidation of benzyl alcohol to benzaldehyde under mild conditions.The main contents were as follows:?1?The carrier of the Au-based catalysts was prepared by organo-functionalizing the carbon-silicon compound derived from biomass of rice husk.A series of AuPd bimetallic composite catalysts were obtained by simple reduction of HAuCl₄ and PdCl₂ with sodium borohydride.The resultant composite catalysts were characterized by XRD,ICP-AES,TEM etc.Catalytic performance of the catalysts in solvent-free selective oxidation of benzyl alcohol with O₂ as oxidant was evaluated,yielding the best bimetallic catalyst of Au_0.25Pd_0.5-N-SiO₂/C-600-2:1.Under the optimum conditions,the conversion of benzyl alcohol and the selectivity to benzaldehyde were 68.3%and 86.5%,respectively,while TOF value was 2962 h^-1;furthermore,the catalyst could be reused for 3 times without significant loss of catalytic activity.?2?On the basis of the section 1),a series of microporous carbon supports with high surface areas were prepared by impregnating rice husk with KOH and successive carbonization.With HAuCl₄ as Au precursor and Ce?NO₃?₃ as cerium dioxide precursor,a series of Au/CeO₂-AC catalysts were prepared via a spontaneous redox process under nitrogen protection.The resultant catalysts were characterized by XRD,ICP-AES,TEM etc.The catalytic performance of the catalysts in the photocatalytic oxidation of benzyl alcohol was investigated,yielding the best catalyst of Au₃/20CeO₂-AC-700-1:1.Under the optimal conditions,the conversion of benzyl alcohol and benzaldehyde selectivity were 34.7%and 99.99%,respectively.Finally,the mechanism of the photocatalytic oxidation reaction was discussed by introducing different kinds of free radical quenchers.