Preparation And Catalytic Performance Of Highly Dispersed Pt/Al₂O₃ Catalysts By Supercritical Fluid Deposition

Supported noble metal catalysts have a wide range of applications.Highly dispersed noble metal catalysts can improve the utilization of metal atoms and catalytic efficiency,which has become a research hotspot of scholars in recent years.Supercritical Fluid Deposition（SFD）is a green micronization method.By utilizing the special dissolution and transport properties of supercritical fluids,highly dispersed catalysts with smaller metal particles and more uniform size can be prepared.In this paper,highly dispersed Pt/Al₂O₃ catalysts were prepared by supercritical fluid deposition method and used in catalytic reforming reaction.This topic has important theoretical significance and practical value.Firstly,the dissolution process in supercritical fluid deposition was studied by investigating different metal precursor salts,co-solvents and carrier pretreatment methods.It was found that when Na₂PtCl₆ was used as precursor salt and ethanol as co-solvent,the particle size of Pt/Al₂O₃ prepared was the smallest and the metal dispersion was the highest.The catalyst prepared by ethanol pretreatment is not significantly different from the catalyst prepared by untreated carrier in terms of Pt particles,metal dispersion and loading,but the catalyst prepared by thiol modified carrier after dehydroxylation has decreased in all aspects.In this paper,the temperature,pressure,time,load and reduction conditions affecting the deposition process in SFD method were systematically investigated.According to the dispersion of Pt particles,the optimum preparation conditions of Pt/Al₂O₃ catalyst were selected:deposition temperature as 40℃,pressure as 11 MPa,time as 3 h,nominal load 0.5 wt.%,and reduction was carried out by N₂ atmosphere thermal decomposition.The catalytic reforming reaction model of benzene from cyclohexane dehydrogenation was used to evaluate the activity of the catalyst with better dispersion.It can be found that the catalysts prepared by SFD with 0.12 wt.%,0.24 wt.%and 0.37wt.%exhibit excellent catalytic activity.The higher the Pt loading,the higher the catalytic activity.Compared with the traditional impregnation method,SFD method shows obvious size effect and effect of reducing the quantity of precious metal:0.12wt.%catalyst is better than the catalyst prepared by ordinary impregnation method with 0.4 wt.% catalyst.