Sulphur poisoning of LaCr0.5−xMnxMg0.5O3·yMgO catalysts for methane combustion

LaCr0.5−xMnxMg0.5O3·yMgO catalysts (x=0, 0.25, y=0, 17) were prepared, characterised (X-ray diffraction, BET analysis, scanning electron microscopy–energy dispersion spectroscopy, transmission electron microscopy, FTIR spectroscopy, chemical and atomic absorption analyses), tested for high-temperature methane combustion and aged in presence of SO2 to investigate the effect of sulphur on their catalytic activity. The role of chromium presence in the perovskite structure have been assessed by comparison with earlier studies on Cr-free perovskites: (i) it worsens the activity of catalysts in the fresh state; (ii) owing to its acidic nature, it makes perovskites less prone to adsorb SO2 and so more resistant to sulphur poisoning; (iii) it renders catalyst regeneration by NH3 leaching less effective because of the partial solubility of chromium oxide in basic media. Conversely, MgO promotes catalytic activity of fresh LaCr0.5Mg0.5O3·yMgO catalysts and slows down sulphur poisoning of the LaCr0.25Mn0.25Mg0.5O3·17MgO catalyst only.