Surface Properties and Structures of Binary Oxides Containing Ti0₂, Prepared from Metal Alkoxides

Abstract

Ti0₂-SiO₂ and Ti0₂-Al₂0₃ binary oxides were prepared by simultan eous hydrolysis of a mixed solution of the respective metal alkoxides, and relationship between the structures and the surface properties of the binary oxides was studied. Both binary oxides calcined at 773 K were foun d to form finely-divided Ti0₂ particles by XRD and EXAFS measurements and to have strong acid sites on the surfaces. Ti0₂ particles in the Ti0₂-Al₂03 were observed to grow with the elevation of the calcination temperature and transformed from an anatase to a rutile structure at about 973 K. While in the Ti0, Si0₂, the growth of TiO₂ particles as well as the phase transformation was strongly suppressed even after a calcination at 1273 K, suggesting the presence of some interactions between the Ti0₂ and SiO₂ particles. The types of acid sites generated on the binary oxides were m easured by infrared spectroscopy of pyridine adsorbed on the surfaces. The results showed that only Lewis acids, sprung from pure TiO₂ and Al₂0₃ particles still remained on the Ti0₂-Al₂0₃, whereas BrOnsted acids were created on the Ti0₂-Si0₂. The generation of the BrOnsted acid sites is considered to be ascribed to the interactions between the component oxide particles in the binary oxide, probably originated in Ti-O-Si bonds. The isomerization of 1-butene was remarkably accelerated by the presence of the BrOnsted acid sites on the surface of Ti0₂Si0₂.