The deactivation kinetics of a V/Ti oxide catalyst were studied in partial oxidn. of toluene to PhCHO and PhCO2H at 523-573 K. The catalyst consists of a monolayer of VOx species, and after oxidative pretreatment, contains isolated monomeric and polymeric metavanadate-like vanadia species under dehydrated conditions as was shown by FT Raman spectroscopy. Under the reaction conditions via in situ DRIFTS, fast formation of adsorbed carboxylate and benzoate species was obsd. accompanied by disappearance of the band of monomeric species. Slow accumulation of maleic anhydride, coupling products and/or PhCO2H on the surface causes deactivation of the catalyst during the reaction. Temp.-programmed oxidn. after the reaction showed formation of high amts. of CO, CO2 and water. Rate consts. for the toluene oxidn. steps were derived via math. modeling of reaction kinetics at low conversion and const. O/toluene ratio of 20:1. The model allows prediction of deactivation dynamics, steady-state rates and selectivity. The highest rate const. was found for the transformation of PhCHO to PhCO2H, which explains the low yield of PhCO2H. [on SciFinder (R)]