Effect of Li Promoter on titania-supported Rh catalyst for ethanol formation from CO hydrogenation

The addition of 0.10 wt% Li to Rh/TiO2 more than doubled the CO conversion for CO hydrogenation while increasing ethanol selectivity. The addition of Li also increases formation of C2 oxygenates at the expense of C1 species, methanol and methane. This is attributed to enhanced dispersion of Rh by Li that appears to reduce dissociation of CO, which previous studies have shown requires large ensembles of Rh atoms on the surface. Li promotion appears to increase the associatively adsorbed CO, allowing for increased H2 chemisorption on the surface compared to the dissociative adsorption of the same number of CO atoms. This increases selectivity to ethanol compared to the unpromoted catalysts. CO-TPD shows more reactive adsorbed CO species on the Li-promoted catalyst. FTIR results suggest that Li promotion alters CO bonding at bridged or interfacial sites and its effect is more structural than electronic.