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

Catalytic reforming process is an important part of petrochemical industry,used to produce aromatic hydrocarbons,high-octane gasoline and hydrogen.The core of the process is the reforming catalyst supported on alumina with Pt as the active center.The monometallic Pt/Al₂O₃ catalyst has a low Pt dispersion and a large metal particle size,which is prone to carbon deposition and sintering deactivation during the reforming reaction.In the industry,metal additive Sn are often added to modify the metal and acid center of the reforming catalyst.Highly dispersed supported noble metal catalysts have high metal atom utilization and excellent catalytic performance,which has become a research hotspot of scholars in recent years.Supercritical fluid deposition method(SFD)is a new,efficient,and green micronization method.By utilizing the high diffusion,low viscosity,and zero surface tension of supercritical fluids,highly dispersed catalysts with smaller metal particles can be prepared.In this paper,highly dispersed Pt-Sn/Al₂O₃catalysts using Sn as an additives were prepared by supercritical fluid deposition method and used in catalytic reforming reaction.This topic has important theoretical research significance and practical value.In the paper,the effects of different metal Sn precursor salts and different Sn/Pt ratios during the supercritical fluid deposition process on the structure-activity relationship of the physicochemical properties and the catalytic reforming performance of Pt-Sn/Al₂O₃ catalysts were systematically researched.The study founded that,when Na₂Pt Cl₆ and Sn Cl₂ were used as the metal precursor salts and ethanol was used as the co-solvent,the metal particle size of the Pt-Sn/Al₂O₃ catalyst was the smallest,the metal Pt dispersion was the highest,the bimetals existed as Pt Sn alloys,and the catalytic reforming activity was the best.Compared with the monometallic Pt/Al₂O₃ catalyst,it was found that,after adding the metal additive Sn,the electronic and geometric effects generated between the Pt-Sn bimetals,which was beneficial to the improvement of Pt dispersion,the reduction of metal particle size and the improvement of reforming catalyst activity.In the paper,methylcyclopentane dehydroisomerization reaction was used as a model reaction for catalytic reforming.The effects of the metal particle size and reaction process conditions on the methylcyclopentane dehydroisomerization process were investigated.The metal particle size of the catalyst had a considerable effect on the methylcyclopentane dehydrogenation,showing a significant size effect.That was,the smaller the metal particle size of the catalyst,the higher the selectivity of methylcyclopentane dehydrogenation products.The Pt-Sn/Al₂O₃ catalyst prepared by the SFD method had a smaller metal particle size and better dispersion,therefore its dehydrogenation performance was significantly better than that of the catalyst prepared by the traditional impregnation method.Within the experimental temperature range,increasing the temperature can inhibit methylcyclopentane ring-opening side reaction.And it can promote the dehydrogenation of methylcyclopentane and further ring-expansion isomerization to benzene.Within the experimental pressure range,increasing the pressure was beneficial to the conversion of methylcyclopentane and the further ring-expansion isomerization of the dehydrogenation products to benzene.