Effect of Li Promoter on Catalytic Performance of Rh-Mn/SiO2 for CO Hydrogenation to C-2-Oxygenates

The influence of Li loading on the catalytic activity of Li-promoted Rh-Mn/SiO2 catalyst for the synthesis of C-2-oxygenates through CO hydrogenation was investigated. The catalyst samples were characterized by volumetric chemisorption, temperature-programmed reduction, temperature-programmed desorption of CO, and temperature-programmed surface reaction. The addition of Li significantly suppressed the formation of CH4 on the Rh-based catalyst, while the selectivity for higher hydrocarbons was little affected. The Li promoter largely enhanced the selectivity for C-2-oxygenates, especially that of acetic acid. However, the activity of the Rh-based catalyst for CO hydrogenation gradually decreased with the increase in Li loading. It was suggested that the role of Li was to decrease the CO dissociation ability and to reduce the number of active sites for CO dissociation. The uptakes of H-2 and CO on the Li-promoted Rh-based catalyst were almost the same as those on the Rh-Mn/SiO2 catalyst, which implied that most of Li was positioned on the support, and only a small part of the added Li was positioned on the top of Rh particles