Effect of SO2 and H2S on CO preferential oxidation in H2-rich gas over Ru/Al2O3 and Pt/Al2O3 catalysts

The influence of the addition of 2.1 or 21 ppm SO2 or 2.1, 4.3 or 48 ppm H2S to reaction gas composed of 51.5 vol.% H2, 0.3 vol.% CO, 13.0 vol.% CO2, 0.5 vol.% O2, 6.0 vol.% N2, and 28.8 vol.% H2O on the activity for the CO preferential oxidation was investigated. The catalysts used for the reaction tests were monolith Ru/Al2O3 and Pt/Al2O3 catalysts with Ru loading of 1.6 g/l and Pt loading of 3.1 g/l, respectively. Pellet 3.8 wt.% Ru/Al2O3 and 3.8 wt.% Pt/Al2O3 catalysts were also used to elucidate the deactivation mechanisms. The addition of a high concentration of SO2 or H2S decreased the activity for the CO preferential oxidation. The XPS and IR spectrum for the SO2-poisoned Ru/Al2O3 catalyst showed that Ru particles adsorbed SO42− species, while the XPS for both SO2- and H2S-poisoned Pt/Al2O3 catalysts showed that Pt particles adsorbed S2− species. The activities of the Ru/Al2O3 catalyst for both CO and H2 oxidations were lowered in the presence of the sulfur compounds; the selectivity of CO oxidation was almost constant during the poisoning reaction. On the other hand, the activity of the Pt/Al2O3 catalyst for CO oxidation was lowered by small amounts of the sulfur compounds, while the activity for H2 oxidation was almost constant; the selectivity of CO oxidation decreased. The poisoned Pt catalysts were regenerated by the calcination at 175 °C, and the covering S2− species was oxidized to SO42− species, which migrated to the Al2O3 support.