Controlled Synthesis Of Highly Dispersible And Highly Thermally Stable Au Catalysts And Their Properties In Benzyl Alcohol Oxidation

Supported gold catalysts are widely used in many reactions,due to their superior catalytic performance.Typically,high dispersion is desirable for better utilization of gold catalysts,and those particles with size below 5 nm usually show unique catalytic activity.However,the size of gold nanoparticles spontaneously sinter with time,especially,under the condition of high pressure and temperature,because of its high surface free energy,and low Huttig and Tamman temperature.The preparation of supported nano-gold catalysts with high dispersion and high stability is of great significance in the field of catalysis.In this paper,a controlled impregnation method was employed to prepare Au-based catalysts.The microstructures of the catalysts were characterized by physical adsorption,X-ray diffractometer,temperature programmed reduction and high resolution transmission electron microscopy.Moreover,the possible formation mechanism of the catalysts was proposed.Finally,the catalytic performance of the catalysts was tested in aerobic oxidation of benzyl alcohol.The main research contents are as follows:(1)The AuPtCu catalysts with high dispersion,high activity and good thermal stability was prepared by a controlled impregnation method.The effects of the directing role of configuration ions and the interaction between Au(and Pt)and Cu on the particle sizes,thermal stability and catalytic performance of the catalysts were studied.The results showed that the catalysts had high dispersion and thermal stability when indroduced the configuration ions as a directing reagents.The size of AuPtCu nanoparticles was 4.7 nm when calcination temperature was increased to 600 °C,while the nanoparticles prepared by traditional method were grown up to 10.5 nm.The study also indicated that doping of the high-melting metal Pt could inhibit the agglomeration of nanoparticles.The high thermal stability of AuPtCu nanoparticles was due to the simultaneous employment of multiple additional effects.Finally,the catalysts prepared by this method was tested in aerobic oxidation of benzyl alcohol,and it was found that the yield of benzaldehyde was above 85%.(2)A more in-depth analysis of the formation on the high dispersion Au catalysts was studied.The reserach showed that the configurational ions had an impact on the dispersion and structure of Au nanoparticles during the catalysts perparation.First,it has been proved that the configuration ions of Cu or Ni could keep the high dispersion of Au nanoparticles by controlling the valence change of the precursor in drying process.Second,in the process of reduction,configuration ions could offer the positioning effect for the Au deposition,and a metal interaction between Au and Cu could be generated,which may form a high dispersion and semi-emdded AuCu nanocatalysts.However,Au nanoparticles were randomly dispersed on the surface of supports and had worse dispersion,when the supports did not contain configuration ions.Finally,the activity in aerobic oxidation of benzyl alcohol showed that the size of Au nanoparticles had a great influence on the catalytic performance.