Abstract
The effect of Li and Mn promoters on the structure and selectivity of supported Rh catalysts on CO hydrogenation reaction was examined. Infrared spectroscopy and X-ray absorption were used to investigate the adsorption of reactants and local structure of Rh. These techniques were used in combination with reactivity and temperature programmed studies to correlate structural characteristics with activity and selectivity during CO hydrogenation of the unpromoted Rh/TiO2 and three promoted Rh catalysts: Rh-Li/TiO2, Rh-Mn/TiO2, and Rh-Li-Mn/TiO2. The presence of a promoter slightly decreases the Rh clusters size, however no evidence for an electronic effect induced by the presence of Li and Mn was found. The Li promoter introduces a weakened CO adsorption site that appears to enhance the selectivity to C2+ oxygenates. The selectivity to these products varies inversely with the reducibility of Rh metal, i.e., the lower the reducibility, the higher the selectivity.