Effects of Surface Fluorination on Catalytic Activities and Surface Compositions of TiO2–Al2O3 and TiO2–SiO2–Al2O3

Abstract

Abstract Studies showed that the ternary oxide having the atomic ratio of Ti/Si/Al=47.5/47.5/5 exhibited a high catalytic activity for cumene cracking after a surface fluorination using 1 wt% hydrofluoric acid. The catalytic activity for CH3OH conversion into olefins was highly dependent on the preparation method. That is, the ternary mixed oxide promoted olefin formation slightly when the mixed oxide was prepared only by coprecipitation. Surface treatment, using gaseous CF3Cl was effective in enhancing catalytic activity. Although the binary oxide, TiO2–Al2O3, itself, was catalytically inactive for olefin formation, TiO2–Al2O3 prepared by coprecipitation became active after the treatment using CF3Cl. Such an enhancement was found also for the ternary oxide, TiO2–SiO2–Al2O3, and is ascribable to increased acid strength, as determined by NH3 adsorptions at various temperatures. The XPS measurements showed that F atoms introduced into mixed metal oxides by the fluorination using CF3Cl, selectively combined with Al atoms on the mixed oxides prepared by coprecipitation. The XPS measurements of the mixed oxides before and after fluorination using CF3Cl showed that the coprecipitation preparation is more preferable than the impregnation method in maintaining surface composition during fluorination.