Modifications of Surface Properties of a H2-treated RuS2/SiO2 Catalyst: A Parallel between Low-Temperature CO FTIR Spectroscopy and Model Reactions

A silica-supported ruthenium sulfide catalyst was progressively reduced by hydrogen at increasing temperatures (423–673 K). The resulting modification of the surface properties was characterized by low-temperature CO adsorption FTIR spectroscopy and by test reactions such as CH3SH condensation and 1-butene hydrogenation. On the nonreduced catalyst, CO adsorption spectra showed the presence of bands, indicating various CO forms on Ru sites in a sulfur-rich environment. When sulfur was progressively removed from the ruthenium sulfide phase, the number of coordinatively unsaturated Ru sites increased with the simultaneous formation of metallic Ru microdomains. A comparison of measurements of adsorption and catalytic activity showed that a rich sulfur environment was needed for the condensation of CH3SH to CH3SCH3, a reaction that required acidic sites, while butene hydrogenation required highly depleted Ru sites. These results show that, upon reduction, RuS2 became less acidic and increasingly more metallic.