CHARACTERIZATION OF SILICATED ANATASE POWDERS

Silicated titanias have been prepared by reaction of commercial anatas e-based TiO2 powders with tetraethylorthosilicate, followed by calcina tion. At low loadings orthosilicate species are found, that interact m ainly with surface defects of anatase where surface hydroxy groups are located. At higher loadings polysilicate species are found, while amo rphous silica is observed if the nominal loading is comparable to that allowing the coverage of the entire TiO2 surface with a silicate laye r. Surface silicate species progressively mask the TiO2 surface, and d o not generate Bronsted acidity that is sufficiently strong to protona te pyridine. Silication strongly hinders anatase crystal growth and lo ss of surface area upon heating, as well as the anatase-to-rutile phas e transformation. Thus, supported silica in small amounts can act as a n efficient morphology and structure promoter of anatase TiO2-based ca talysts, although it also perturbs the TiO2 surface chemistry signific antly.