Vanadia/titania catalysts for gas phase partial toluene oxidation - Spectroscopic characterisation and transient kinetics study

Formation of vanadia species during the calcination of ball milled mixture of V2O5 with TiO2 was studied by Raman spectroscopy in situ and at ambient conditions. It is found that calcination in air leads to fast (1-3 h) sprea ding of vanadia over TiO2 followed by a slower process leading to the forma tion of a monolayer vanadia. The calcinated catalyst showed higher activity during toluene oxidation than the uncalcinated one, but the selectivity to wards C-7-oxygenated products (benzaldehyde and benzoic acid) remains uncha nged. The activity of the catalysts is ascribed to the formation of vanadia species in the monolayer. The details of the parallel-consecutive reaction scheme of toluene oxidation are presented from steady-state and transient kinetics studies. Different oxygen species seem to participate in the deep and partial oxidation of toluene. Coke formation was observed during the re action presenting an average composition C2nH1.1n. The amount of coke on th e catalyst was not dependent on the calcination step and the vanadium conte nt in the catalyst. Coke formation was seen to be responsible for the deact ivation of the catalyst. (C)2000 Elsevier Science B.V. All rights reserved.