The Reaction Performance And Deactivation Study For Dehydrofluorination Of 1,1,1,2-tetrafluoroethane Over Aluminum Base Catalysts

In fluorine chemical industry,Al-based catalyst was widely used as Lewis acid catalyst for reactions such as fluorine-chlorine exchange,dehydrohalogenation of hydrofluorocarbons and disproportionation as it possesses satisfactory Lewis acidity.Recently,more and more research work is devoted to the study of aluminium base catalyst.In the present work,the catalytic performances of alumina,aluminum fluoride and phosphorus doped alumina for the reaction of dehydrofluorination of1,1,1,2-tetreafluoroethane were investigated.The crystal structure,composition,particle size,surface acidity of fresh and spent catalysts were studied by kinds of analysis characterization,such as BET,X-ray diffraction,NH₃-TPD,SEM,EDS surface elemental analysis and so on for the mechanism of catalyst deactivation.Specific surface area,pore volume,the surface acidity of alumina affect the catalytic activity of dehydrofluorination of 1,1,1,2-tetreafluoroethane significantly.During the reaction,alumina undertakes phase transition,gradually transforming into aluminum fluoride,leading to partial catalyst deactivation.In addition,it was found that phosphorus doping in alumina by impregnation method reduces the strong acid center of the alumina surface and improve the reaction activity and stability.Aluminum fluorides were prepared by sol-gel method,precipitation method,template method respectively or commercial,which were adopted for catalytic dehydrofluorination of 1,1,1,2-tetreafluoroethane.The results show that?-Al F₃prepared by sol-gel method shows the highest activity and stability for dehydrofluorination of 1,1,1,2-tetreafluoroethane,with smallest crystal sizeand highest specific surface area among all these aluminum fluorides.?-Al F₃ prepared by template method is well crystallized,with lowest catalytic activity.The crystal size of catalysts grow with reaction time,and catalytic activity decreases gradually.It is speculated that the growth of Al F₃ crystal size is the most important factor resulting in the deactivation of the catalyst.In addition,the catalytic activity of Al F₃ catalyst drops following pre-fluorination,as well as the stability implying that pre-fluorination of catalyst is not necessary.