AbstractTwo vanadia/titania catalysts, containing 1 and 8 wt% vanadia on anatase, have been investigated for the selective oxidation ofo‐xylene to phthalic anhydride. In a comparative study, activity and selectivity ino‐xylene oxidation were measured using an integral reactor and a reactor with external product recirculation, with the objective of studying the influence of backmixing in the latter on the reaction behaviour. Adsorbed surface species were investigated by means ofin‐situdiffuse reflectance FT‐IR spectroscopy, using an environmental chamber which corresponds to an integral reactor. No difference in activity and selectivity ino‐xylene oxidation was observed between the two catalysts. FT‐IR studies showed adsorbedo‐xylene, benzoate and a high concentration of phthalic anhydride on the surface of both catalysts.o‐Xylene oxidation follows a sequential reaction path, witho‐tolualdehyde as the first intermediate and phthalide, phthalic anhydride and maleic anhydride as sequential products. No evidence was found for a direct oxidation‐path ofo‐xylene to phthalic anhydride. Total oxidation products CO and CO2are formed by direct oxidation of theo‐xylene and by oxidation of the reaction products. Due to greatly reduced concentration and temperature gradients, the recycle reactor proved to be highly suitable for studying the extremely exotherm