OXIDATION OF O-XYLENE TO PHTHALIC-ANHYDRIDE OVER V2O5 TIO2 CATALYSTS .1. INFLUENCE OF CATALYST COMPOSITION, PREPARATION METHOD AND OPERATING-CONDITIONS ON CONVERSION AND PRODUCT SELECTIVITIES/

The oxidation of o-xylene and of o-tolualdehyde over V2O5/ TiO2 (anata se) catalysts has been studied at 533-633 K under steady state conditi ons; catalysts were prepared either by wet impregnation employing NH4V O3 solution or by a grafting technique with VO(O-i-C4H9)(3). At lower temperatures and lower contact times, for both o-xylene and o-tolualde hyde, part of the reactant feed disappeared due to the formation of an involatile polymeric residue, the formation of which was enhanced at lower temperatures, lower contact times, and higher organic reactant c oncentrations, At lower contact times, the part of the residue deposit ed on the catalyst surface constituted an important CO2 source, The ca talyst prepared by grafting showed higher phthalic anhydride selectivi ty and less of the residue, The formation of nonselective oxidation pr oducts seems to be favoured by uncoated TiO2 since 0.6% V2O5/TiO2 show ed higher CO2 selectivity than other catalysts. Crystalline V2O5 cause d greater residue formation. (C) 1995 Academic Press, Inc.