In situ FT-IR studies of CO and CO₂ hydrogenation over titania supported Rh and Rh-Li catalysts

The conversion of coal-derived synthesis gas into ethanol provides a unique opportunity to develop an affordable and readily reformable hydrogen carrier that can be distributed and stored using the nation's existing infrastructure. One of the challenges is that the catalysts investigated to date suffer from poor overall yields even in cases where the selectivity is reasonably high. A key technical issue in the ethanol production reaction is to keep a high selectivity to ethanol without formation of methane.1,2 Rh-based catalysts are the most widely studied catalyst for hydrogenation of CO to oxygenate compounds and promoters can be used to increase conversion and to inhibit the methanation pathway.1 However, little is known on the reasons as to why the promoters affect the activity and CO bond cleavage. Therefore it is our goal to investigate the effect of promoters on the reaction pathways. More specifically, we examined the effects of Li on the properties of Rh/TiO2 for CO and CO2 hydrogenation by using in-situ infrared spectroscopy in a transient reactor at ambient pressure and elevated temperatures. The goal is to identify the mechanistic factors that govern the reaction pathway, such as CO adsorption states, CO bond breaking, and the selectivity to methane vs alcohol. The in-situ surface spectroscopy experiments revealed that the presence of the Li promoter does not seem to alter the electronic structure of Rh, but rather it may introduce structural changes that could alter the Rh dispersion and/or bonding with CO.