Elucidation of deactivation or resistance mechanisms of CrOx, VOx, and MnOx supported phases in the total oxidation of chlorobenzene via ToF-SIMS and XPS analyses

VOx, CrOx and MnOx supported on TiO2 are all efficient catalysts in the total oxidation of benzene. However, in the oxidation of chlorobenzene, they exhibit different behaviors in terms of their resistance to deactivation by the chlorinated reactant and/or products of the reaction (Cl-2, HCl). Precisely: VOx catalysts present a very good resistance; conversely, MnOx catalysts present a huge deactivation and CrOx catalysts exhibit an intermediate behavior. This contribution leads to a better understanding of the mechanisms and origins of the respective deactivation (or resistance to deactivation) of the catalysts via a postmortem characterization by 'X-ray photoelectron spectroscopy' (XPS) and 'time of flight - secondary ion mass spectroscopy' (ToF-SIMS). (i) The different behaviors are correlated to the atomic ratio of chlorine/transition metal at the surface of the used catalysts and (ii) the nature of the chlorinated species responsible for the deactivation is elucidated: namely, CrOx catalysts deactivate because of a firm adsorption at the surface of the chlorinated volatile organic compounds (VOC) or of chlorinated intermediates of reaction, while MnOx catalysts deactivate because of the formation of (oxy)chlorides at their surface. Copyright (c) 2008 John Wiley & Sons, Ltd.