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/Al2O3-TiO2 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, O2 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 O2 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 to p-anisaldehyde when compared to other samples.

The Al2O3-TiO2 support accommodates a monolayer equivalent of V2O5 in a highly dispersed state and exhibits good catalytic activity for oxidation of 4-methylanisole to p-anisaldehyde and p-anisic acid in vapour phase under normal atmospheric pressure. These catalysts were characterized by means of XRD, FTIR, XPS, O2 chemisorption and BET surface area methods to correlate with catalytic properties. Figure optionsDownload as PowerPoint slide