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

Abstract

Abstract Different bulk metal oxides (NiO, CuO, Mn 2 O 3 , Cr 2 O 3 and Co 3 O 4 ) were prepared and tested for the combustion of methane–air lean mixtures (5000 ppmV of CH 4 ) in presence of SO 2 (40 ppmV). Methane combustion experiments were carried out at ambient pressure, 425 and 625 °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 SO 2 , 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 Cr 2 O 3 is not deactivated at the studied conditions, whereas all the other materials present fast deactivation in presence of SO 2 . Aged catalysts characterisation reveals that the outstanding behaviour of the Cr 2 O 3 catalyst is caused by the absence of formation of surface sulphates. By contrast, Mn 2 O 3 and Co 3 O 4 are more active than Cr 2 O 3 for methane oxidation in absence of sulphur species, but they are strongly deactivated in presence of SO 2 . Finally, the performance of the Cr 2 O 3 catalysts was compared to the corresponding to Pd/Al 2 O 3 catalyst and to a highly sulphur-tolerant perovskite (La 0.9 Ce 0.1 CoO 3 ) for the oxidation of methane in a real industrial emission from a coke oven, containing different inorganic gases (NH 3 , N 2 , H 2 , H 2 O, CO, CO 2 , SO 2 and H 2 S). Cr 2 O 3 catalyst shows to be also the most stable catalyst for the treatment of these emissions.