Thermal restructuring of silica-grafted –CrO2Cl and –VOCl2 species

Abstract

The volatile molecular precursors CrO2Cl2 and VOCl3 were grafted to thermally dehydrated silica in order to obtain site-isolated, monopodal ≡SiO-MO(x)Cl(y-1) species (M = V, Cr). Thermal restructuring under dynamic vacuum was investigated up to 450 °C with different spectroscopic techniques (viz., NMR, UV-Vis, IR, Raman and XPS). During this thermal restructuring, VOCl3 or CrO2Cl2 is partially eliminated from the surface, whilst the remaining surface species become multiply bound to the silica surface. This restructuring increases both the chemical and thermal stability of these materials, and has significant consequences for their performance as heterogeneous catalysts.