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

The thioresistance of different bulk transition metal oxides used as catalysts for the combustion of methane–air lean mixtures is studied in this work. A superb behaviour of Cr 2O 3 was found. The pictogram shows the conversions obtained at 625 °C for the combustion of 5000 ppm of CH 4 in presence of 45 ppm of SO 2. Each bar correspond (from left to right) to fresh catalyst in absence of SO 2, in presence of SO 2, catalyst after 20 h on stream in absence of SO 2, and catalyst after 20 h on stream in presence of SO 2. ▪ Different bulk metal oxides (NiO, CuO, Mn 2O 3, Cr 2O 3 and Co 3O 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 2O 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 2O 3 catalyst is caused by the absence of formation of surface sulphates. By contrast, Mn 2O 3 and Co 3O 4 are more active than Cr 2O 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 2O 3 catalysts was compared to the corresponding to Pd/Al 2O 3 catalyst and to a highly sulphur-tolerant perovskite (La 0.9Ce 0.1CoO 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 2O, CO, CO 2, SO 2 and H 2S). Cr 2O 3 catalyst shows to be also the most stable catalyst for the treatment of these emissions.