The negative impact of fossil-fuel consumption coupled with the growing energy demand has spurred the development of greener energy technologies. One attractive alternative is ethanol since it can be produced from biomass-derived synthesis gas (CO/CO2/H2). Rhodium-based catalysts are the most effective for syngas conversion to ethanol due to its ability to facilitate C-C coupling, but only when promoters are added to suppress methane formation. Both Fe and Mn promoters improve selectivity to oxygenates, but in different ways. Previous studies on Fe and Mn addition to Rh supported on TiO2 show that improved selectivity to ethanol is correlated with the presence of a RhFe alloy phase and Rh-MnO interfacial sites. Theoretical studies suggest that the role of Mn is to lower the CO insertion barrier into CHx species which leads to CHxCO intermediates that ultimately control oxygenate formation. In this work, Mn is added as a promoter to Rh supported nano-Fe2O3, which acts both as a support and an in-situ source of metallic Fe for FeRh alloy formation under reducing reaction conditions (H2 or CO+H2). The Mn-Rh/nano-Fe2O3 catalysts were tested and characterized using transmission electron microscopy (TEM), x-ray diffraction (XRD), and x-ray absorption spectroscopy (XAS). As shown in the accompanying figure, Mn addition results in substantial improvement in C2+ oxygenate selectivity at the expense of hydrocarbons, while also maintaining the CO conversion. These results will be discussed in light of in-situ x-ray structural and spectroscopy measurements which provide insight into the active Mn, Fe and Rh phases that are present under reaction conditions.

In-situ characterization of promoted Rh-based catalysts for ethanol synthesis

256th National Meeting (2018)

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