Hydrogenation of CO₂ over SiO₂ Supported Rh–Co-alkalimetal Catalysts

Abstract

CO₂ hydrogenation was carried out over alkali metals such as Li, Na and K promoted silica-supported Rh–Co catalysts (Rh–Co–M/SiO₂). Na additive was most effective of the three alkali metals for ethanol formation over 5 wt% Rh–Co(1 : 1)/SiO₂. The added amount of Na influenced product selectivity as well as CO₂ conversion. The highest ethanol selectivity was obtained over 5 wt% Rh–Co–Na (1 : 1 : 0.5)/SiO₂ catalyst. The mechanism of promotion effect of Na added amount was investigated by means of in situ FT-IR observation during reaction. The variation of Na added amount changed the ratio of Rh₂–(CO)₃ and bridged type adsorbed CO species to linear type one. This finding suggested that the amount of Na affected on the hydrogenation ability of Rh–Co/SiO₂ catalysts, leading to the difference in CO₂ hydrogenation activity.