Studies on the V2O5–TiO2system. Part 3.—Monolayers of V2O5

Abstract

The catalytic behaviour of anatase– and rutile–vanadium monolayer-like catalysts has been studied in the dehydration of N-ethylformamide (NEF) in the presence of oxygen. The catalysts were prepared using two methods: grafting and impregnation. Physicochemical characterizations of the fresh and used samples were carried out using B.E.T. surface analysis and XRD, XPS and FTIR techniques. The grafted samples are composed of the vanadium monolayer over the surface of anatase which undergoes sintering in the course of the catalytic reaction, probably forming V₆O₁₃. The vanadium monolayer formed on the anatase can protect it against the influence of the V₂O₅ crystals and may inhibit the anatase-into-rutile transformation during the calcination of catalysts. The impregnated samples are composed of fine grains of dispersed V₂O₅ in contact with the anatase grains. Calcination of these impregnated samples leads to the formation of a thin rutile-like layer on the surface of the anatase grains. The catalytic behaviour of these samples is similar to that of the V₂O₅–TiO₂(rutile) catalysts. There is no difference between the two rutile samples. Their catalytic properties seem to be a superposition of those found in pure rutile and V₂O₅.