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 °C and a space time of 93.3 g h molCH4−1. 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, N2, H2, H2O, CO, CO2, SO2 and H2S). Cr2O3 catalyst shows to be also the most stable catalyst for the treatment of these emissions.

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 Cr2O3 was found. The pictogram shows the conversions obtained at 625 °C for the combustion of 5000 ppm of CH4 in presence of 45 ppm of SO2. Each bar correspond (from left to right) to fresh catalyst in absence of SO2, in presence of SO2, catalyst after 20 h on stream in absence of SO2, and catalyst after 20 h on stream in presence of SO2.Figure optionsDownload as PowerPoint slide