Characterization and catalytic activity of V2O5/Al2O3-TiO2 for selective oxidation of 4-methylanisole

The vapour phase selective oxidation of 4-methylanisole to p-anisaldehyde and p-anisic acid was investigated over V2O5/Al2O3-TiO2 catalysts containing various amounts of V2O5 (2-16 wt.%) in the temperature range 523-723 K under normal atmospheric pressure. The Al2O3-TiO2 (1:1.3 mole ratio) binary oxide support was prepared by a homogenous coprecipitation method using urea as precipitating reagent. The V2O5/Al2O3TiCl2 catalysts were prepared by a wet impregnation method from ammonium metavanadate dissolved in oxalic acid solution. The Al2O3-TiO2 support and V2O5/Al2O3-TiO2 catalysts were subjected to various calcination temperatures (773-1073 K) to understand the dispersion and thermal stability of catalysts and were characterized by means of X-ray diffraction, FT-infrared, X-ray photoelectron spectroscopy, O-2 chemisorption and BET surface area methods. The physicochemical characterization results reveal that the Al2O3-TiO2 mixed oxide is homogeneous and thermally quite stable retaining titania-anatase phase up to 1073 K. The alumina-titania support also accommodates a monolayer equivalent of V2O5 in a highly dispersed state when calcined at 773 K. This observation is supported from XRD, FTIR and O-2 uptake results. The XPS studies reveal that titania, alumina and vanadia are in Ti(IV), Al(III) and V(V) oxidation states irrespective of calcination temperature employed. The O 1s, Ti 2p, Al 2p and V 2p photoelectron peaks of the V2O5/Al2O3-TiO2 samples are highly sensitive to the calcination temperature as well as V2O5 coverage. The 16 wt.% V2O5/Al2O3-TiO2 catalyst exhibits more conversion and more product selectivity top-anisaldehyde when compared to other samples. (c) 2006 Elsevier B.V. All rights reserved.