Characterization of silicated anatase powders

Abstract

Silicated titanias have been prepared by reaction of commercial anatase-based TiO₂ powders with tetraethylorthosilicate, followed by calcination. At low loadings orthosilicate species are found, that interact mainly with surface defects of anatase where surface hydroxy groups are located. At higher loadings polysilicate species are found, while amorphous silica is observed if the nominal loading is comparable to that allowing the coverage of the entire TiO₂ surface with a silicate layer. Surface silicate species progressively mask the TiO₂ surface, and do not generate Brønsted acidity that is sufficiently strong to protonate pyridine. Silication strongly hinders anatase crystal growth and loss of surface area upon heating, as well as the anatase-to-rutile phase transformation. Thus, supported silica in small amounts can act as an efficient morphology and structure promoter of anatase TiO₂-based catalysts, although it also perturbs the TiO₂ surface chemistry significantly.