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

The volatile molecular precursors CrO2Cl2 and VOCl3 were grafted to thermally dehydrated silica in order to obtain site-isolated, monopodal [triple bond, length as m-dash]SiO–MOxCly−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

Thermal restructuring of silica-grafted TiClx species and consequences for epoxidation catalysis

Anchoring titanium: Grafting of TiCl4 to site-isolated silanol groups on silica initially leads to freely rotating species. Upon heating, a thermal restructuring takes place, causing the elimination of TiCl4 and the formation of more strongly anchored titanium species, which were found to be highly active and stable epoxidation catalysts