Promoting effects of lithium on Pd/CeO2 catalysts in carbon monoxide-hydrogen reactions

At a low percentage, lithium (0.15%) increases the methanol activity and selectivity of a Pd/CeO2 catalyst. Higher lithium loadings result in the appearance of ethanol (23.4% ethanol selectivity on 3% Pd-1% Li/CeO2) but with a decreased overall catalytic activity. The maximum amounts of surface formyl species and of adsorbed carbon monoxide correspond to the most active methanol synthesis catalyst (3% Pd-0.15% Li/CeO2). These results suggest that lithium can stabilize adsorbed carbon monoxide and surface formyl species. An increase in the temperature of desorption of carbon monoxide after carbon monoxide-hydrogen reaction (from 470 to 590 K) is attributed to an interaction between adsorbed CO and Li+. This interaction can both favour carbon monoxide dissociation and carbon monoxide insertion reactions. Temperature-programmed desorption after ethanol adsorption was performed and a mechanism of ethanol formation is proposed.