Evidence for the presence of Mo(VI), W(VI) or Re(VII) species in silica-based materials. New approaches to highly dispersed oxo-species in mesoporoussilicates

d(o) Transition metal-containing mesoporous molecular sieves are synthesize d by the hydrolysis of tetraethyl orthosilicate in aqueous acid, in the pre sence of neutral or anionic low-condensed Mo(VI) or W(VI) oxo-peroxo or Re( VII) polyoxo species and a cationic surfactant; the materials have a nearly homogeneous distribution of the dopants and promising catalytic activities .