Effect of H2S on the hydrogenation of carbon dioxide over supported Rh catalysts

The hydrogenation of CO2 was studied on supported noble metal catalysts in the presence of H2S. In the reaction gas mixture containing 22 ppm H2S the reaction rate increased on TiO2 and on CeO2 supported metals (Ru, Rh, Pd), but on all other supported catalysts or when the H2S content was higher (116 ppm) the reaction was poisoned. FTIR measurements revealed that in the surface interaction of H2 + CO2 on Rh/TiO2 Rh carbonyl hydride, surface formate, carbonates and surface formyl were formed. On the H2S pretreated catalyst surface formyl species were missing. TPD measurements showed that adsorbed H2S desorbed as SO2, both from TiO2-supported metals and from the support. IR, XP spectroscopy and TPD measurements demonstrated that the metal became apparently more positive when the catalysts were treated with H2S and when the sulfur was built into the support. The promotion effect of H2S was explained by the formation of new centers at the metal/support interface.