Sulphur poisoning of transition metal oxides used as catalysts for methane combustion

Different bulk metal oxides (NiO, CuO, Mn2O3, Cr2O3 and Co3O4) were prepared and tested for the combustion of methane-air lean mixtures (5000 ppmV of CH4) in presence of SO2 (40 ppmV). Methane combustion experiments were carried out at ambient pressure, 425 and 625 degrees C and a space time of 93.3 g h mol(CH4)(-1). Catalysts aged (60 h on stream) both in absence and in presence of SO2, were characterised by nitrogen physisorption (BET), X-ray diffraction (XRD), scanning electron microscopy (SEM), temperature-programmed desorption (TPD-MS) and infrared spectroscopy (DRIFTS). It was observed that Cr2O3 is not deactivated at the studied conditions, whereas all the other materials present fast deactivation in presence of SO2. Aged catalysts characterisation reveals that the outstanding behaviour of the Cr2O3 catalyst is caused by the absence of formation of surface sulphates. By contrast, Mn2O3 and Co3O4 are more active than Cr2O3 for methane oxidation in absence of sulphur species, but they are strongly deactivated in presence of SO2. Finally, the performance of the Cr2O3 catalysts was compared to the corresponding to Pd/Al2O3 catalyst and to a highly sulphur-tolerant perovskite (La0.9Ce0.1CoO3) for the oxidation of methane in a real industrial emission from a coke oven, containing different inorganic gases (NH3, N-2, H-2, H2O, CO, CO2, SO2 and H2S). Cr2O3 catalyst shows to be also the most stable catalyst for the treatment of these emissions. (C) 2008 Elsevier B.V. All rights reserved.