Reaction mechanism of methanol synthesis from CO, H2, and H2S over Cu-modified RuO2 catalyst. The reaction mechanisms for methanol synthesis from CO, H2, and H2S have been investigated in the absence and presence of copper metal over RuO2-based catalysts. It was found that the copper species of Cu+ and Cu2+ were not responsible for the enhanced activity and stability of methanol synthesis over Cu/RuO2-based catalysts. The surface Cu metal species of Cu(+) and Cu2+ were observed on RuO2-based catalysts, and the copper species had no catalytic effect on methanol synthesis from CO, H2, and H2S over RuO2-based catalysts. However, the coexistence of surface Cu(+) and Cu2+ with Ru(+) in Cu/RuO2 catalysts showed that the Cu(+) species inhibited the formation of methanol and promoted its further oxidation to dimethyl ether by weakening the C-H bond cleavage and weakening the C-O bond formation. On the basis of these observations, the reaction mechanism of methanol synthesis from CO, H2, and H2S over Cu/RuO2 catalysts was proposed.