A Comparative Study of Sulfur Poisoning and Regeneration of Precious-Metal Catalysts

This paper investigates sulfur poisoning and catalyst regeneration for alumina-supported platinum, palladium, and rhodium catalysts. Reduced catalysts and regenerated sulfur-poisoned catalysts were studied for their activity in the catalytic combustion of methane in a flow microreactor. CO adsorption, in conjunction with FTIR spectroscopy, was used to probe the metal sites on the catalysts. Spectroscopic investigations indicate that the nature of the metal species on the catalysts is different for the freshly reduced and regenerated catalysts. In the case of Pd/Al2O3, successful regeneration of the metal was evident, while for Pt/Al2O3, an increase in the high-frequency CO signal at 2075 cm-1 was observed, possibly indicative of metal−sulfur interactions which are not removed by regeneration or an increase in the metal particle size upon regeneration. Finally, in the case of Rh/Al2O3, the regenerated catalyst has an increased Rh+:Rh0 ratio compared to the freshly reduced catalyst. The reaction studies showed the order of the activity for the freshly reduced catalysts to be Pd > Rh > Pt. After exposure to H2S, it was possible to regenerate the catalysts by reduction. The regenerated Pt/Al2O3 and Rh/Al2O3 catalysts were more active in the combustion of methane than their freshly reduced analogues, while the Pd/Al2O3 catalyst was slightly less active. The success of regeneration of the active catalyst by reduction follows the order Rh > Pt > Pd.