Carboxylic acids and carboxylic anhydrides such as benzoic acid maleic anhydride phthalic anhydride or pyromellitic anhydride are produced industrially by catalytic gas-phase oxidation of aromatic hydrocarbons such as benzene o-xylene naphthalene toluene or durene in fixed-bed multitube reactors Although the processes for the oxidation of o-xylene and/or naphthalene to phthalic anhydride have been studied very intensively for decades there still is a need for improved catalysts with a selectivity to phthalic anhydride which is higher than 82 mol% We have found a novel multimetal oxide catalyst of the formula Aga-bMbV2Ox which allow significantly higher phthalic anhydride yield since the new silver vanadium oxide catalysts can oxidize o-xylene significantly more selectively to form phthalic anhydride or intermediates than by using catalysts of the vanadium oxide/anatase type By combining the new silver vanadates with conventional V2O5/TiO2 catalysts a PA yield of more than 84 mol% could be reached (C) 2010 Elsevier B V All rights reserved