Influence of calcination treatment on the structure of grafted WOx specieson titania

TiO2/WOx supported metal oxide materials were prepared by grafting a tungst en(V)ethoxide precursor onto a titania support. The supported metal oxides were characterized by Raman spectroscopy under ambient conditions in oxygen and inert gas atmosphere. Measured under ambient conditions, the samples a re sensitive to a variation in laser power. This effect is a function of th e tungsten loading. During calcination of the samples in either inert gas a tmosphere (N-2) or oxidizing atmosphere (O-2), this sensitivity is not obse rved. After cooling the samples to room temperature under inert gas conditi ons, a sensitivity of the surface structures to a laser power variation is again recorded. The structural changes are due to thermal effects and not t o an adsorption of water. The composite band structure in the Raman spectra of the samples leads to the conclusion that octahedrally and tetrahedrally coordinated WOx surface structures as well as polytungstates are co-existi ng on the surface, and are forming cross linked structures. According to th e XPS data, the structure of the metal oxide species depends on the monolay er coverage on the support. (C) 1999 Elsevier Science B.V. All rights reser ved.