Studies on the V2O5–TiO2 system. Part 1.—TiO2(rutile)–V2O5

Abstract

Mechanical mixtures of separately prepared V₂O₅ and TiO₂(rutile) have been used as catalysts in the dehydration of N-ethylformamide (NEF) in the presence of oxygen. Catalytic activity has been measured as a function of the gas hourly space velocity (GHSV), the molar ratio of oxygen to NEF (O/N) and the composition of the catalysts. The characterization of fresh and used catalysts has been carried out using different physicochemical techniques: B.E.T. surface area analysis, XRD, XPS. It has been established that there exists a synergetic effect between rutile and V₂O₅ thus explaining the catalytic properties of their mechanical mixtures. V₂O₅ is dispersed over the surface of rutile grains in the course of the catalytic reaction. A simultaneous process of reduction and reoxidation of V₂O₅ takes place. The type of reduced vanadium oxide formed depends on the O/N ratio and GHSV. The deeply reduced and fully oxidized vanadium oxides are very active but are not selective. Medium reduced vanadium oxides are less active but give higher propiononitrile yields (the selective product). It was concluded that rutile disadvantages the stabilization of vanadium in a high oxidation state. It shifts the redox steady-state equilibrium of the vanadium phase towards the more reduced vanadium oxides.