Grafting of titanium alkoxides on high-surface SiO2 support: an advanced technique for the preparation of nanostructured TiO2/SiO2 catalysts

The present paper reports and discusses results on the preparation, characterization and catalytic performances of silica-supported titania (TiO2/ SiO2) catalysts. Samples were prepared by grafting titanium tetraisopropoxide (Ti-OPri)4, dissolved in toluene, onto a silica surface in an N2 atmosphere, followed by steam hydrolysis and calcination. The samples were characterized by chemical analysis, BET surface area measurements, X-ray diffraction (XRD), DR–UV–vis, FTIR and DRIFT spectroscopy analyses, TEM/EDX and NH3-TPD. The results indicated that the grafting preparation method gives rise to very strong Si–O–Ti bonds, that are responsible for high titanium dispersion. In particular, at low Ti loading, titanium species in tetrahedric coordination resulted prevalent on the catalyst surface until the maximum surface monolayer coating reached (2.2 Ti atoms/nm2). The degree of polymerization of Ti species increases with further TiO2 load increases, giving rise to a large amount of octahedrical Ti-sites grafted on SiO2. The effects on the catalytic activity of TiO2/SiO2 catalysts with increasing quantities of TiO2 were also investigated. The catalytic results obtained in the epoxidation reaction of cyclooctene with cumene hydroperoxide showed the significant effect of titanium loading on the physicochemical and reactivity/selectivity properties of the silica-supported titania catalysts.