DEACTIVATION OF V2O5/TIO2 CATALYSTS IN THE OXIDATION OF O-XYLENE TO PHTHALIC-ANHYDRIDE

The transient regime of o-xylene oxidation over 1 % V2O5/TiO2 was studied at different temperatures and contact times. At lower temperatures and lower contact times, an initial strong decrease of conversion, always accompanied by residual selectivity increase, was observed. Results obtained for residual selectivity, time to reach steady state and conversion suggested that catalyst deactivation might be associated to the formation of heavy by-products. Catalytic samples after operation with o-xylene/air mixtures were analysed by Temperature Programmed Oxidation and FTIR. Organic molecules containing aromatic rings could be detected over the catalytic surface, changing their characteristics with the experimental conditions under which samples were tested. Larger contents of organic ''residue'' were obtained at lower temperatures and lower contact times. For some experimental conditions, a constant amount of such compounds was observed on the catalytic surface after one hour of exposure to the reactant mixture.