(226d) Adsorption of Methanol, Ethanol, and Acetaldehyde on Small Rhodium Clusters

The production of ethanol in the United States has been growing steadily in the past few years driven by incentives to use this alcohol as a fuel additive. Of particular interest to us is the synthesis of ethanol from synthesis gas or ²syngas², a mixture of carbon monoxide and hydrogen produced from coal or biomass gasification. The hydrogenation of carbon monoxide reaction to produce ethanol reasonably selectively has been reported in the presence of highly dispersed, rhodium-based catalysts. However, the reaction also produces methane, methanol, acetaldehyde and other oxygenates and current research efforts are focused on the optimization of the reaction, via modifications of catalyst composition and structure, to maximize the reaction selectivity to ethanol. Here we discuss our quantum mechanical calculations (at the Density Functional Theory level) to develop a better understanding of the adsorption energies of methanol, ethanol, and acetaldehyde on rhodium clusters, Rh_n, where 7 ³ n ³ 11. Our results are also compared to the adsorbate-metal catalytic site interaction models proposed from experimental data (spectroscopy and thermal desorption measurements) on supported rhodium catalysts and from other calculations (at the same theory level) on single crystal rhodium surfaces.