Effect of Ce additive on CO_2 hydrogenation over Rh/SiO_2 catalysts

摘要

The effects of Ce additive on CO_2 hydrogenation over Rh/SiO_2 catalysts were studied.Ce addition drastically increased CO_2 conversion.The main roduct was CO over unpromoted Rh/SiO_2 catalyst,but methaneover Ce promoted Rh/SiO_2 catalyst.oreover,Ce additive promoted ethanol production.The mechanism of the promotion effect of Ce was investigated by XRD,TEM,EDX and FT-IR.The mean metal particle size of Rh-Ce/SiO_2 estimated by XRD and TEM analysis was smaller than that for Rh/SiO_2 and Ce/SiO_2.In-situ FT-IR during reaction and CO-2 adsorption.However,a new peakattributd to carboxylate species was observed at around 1570 cm~(-1) by CO_2 adsorptionon the catalyst,leading to increased activity.The new adsroption band at around 1700 cm~(-1) may be attributed to a CO molecule bonded through both the carbonand oxygen atoms due to higher metal dispersion.These findings suggest that the Ce additive enhanced CO dissociation and CO insertion over Rh/SiO_2 catalysts,resulting in promotion of CH_4 and ethanol formation.