Sulfur poisoning and regeneration of Rh-ZSM-5 catalysts for total oxidation of methane

The activity of Rh/ZSM-5 catalysts for methane oxidation was investigated under conditions simulating the exhaust from lean burning, natural gas fueled engines to evaluate the influence of reaction atmosphere on catalytic activity. The Rh-catalysts yield high methane conversion at conditions achievable in real exhaust systems, despite the inhibiting effects of H2O and SO2. The influence of temperature and SO2 concentration (1−20 ppm) on the activity were studied. The deactivation caused by SO2 was intensified with decreasing temperature and increasing SO2 concentration, and the SO2-poisoning could be modeled as the occupation of active sites following a Temkin adsorption isotherm. At 400 °C essentially full coverage of S-species was reached with 1−2 ppm of SO2, but at 500 °C the coverage had decreased significantly, and considerable catalytic activity was preserved in the presence of SO2. Significant activity was regenerated in SO2-free gas, but the nature of the SO2-free regeneration atmosphere was unimportant.