Selective oxidation of p-methoxytoluene to p-methoxybenzaldehyde over V2O5/CaO–MgO catalysts

Abstract The vapour phase partial oxidation of p -methoxytoluene to p -methoxybenzaldehyde was investigated over various V 2 O 5 /CaO–MgO catalysts at 673 K and under normal atmospheric pressure. Among various catalysts the 14% V 2 O 5 /CaO–MgO sample exhibited good conversion and product selectivity. The CaO–MgO mixed oxide support was prepared by a homogeneous co-precipitation method using urea as hydrolysing agent. Ammonium metavanadate was used as source of V 2 O 5 and the vanadia contents were varied from 2 to 14 weight per cent. The CaO–MgO support and various V 2 O 5 /CaO–MgO catalysts were characterized by means of X-ray diffraction, FT-infrared, electron spin resonance, scanning electron microscopy, NH 3 and CO 2 chemisorption, and BET surface area methods. Characterization results suggest that the vanadia does not form layer structures on the support surface, instead but interacts very strongly with the support oxide, in particular with MgO, and forms amorphous compounds. The NH 3 and CO 2 uptakes clearly distinguish the acid–base characteristics of the catalysts and correlate with catalytic properties.