In Situ Structural Study of Manganese and Iron Oxide Promoted Rhodium Catalysts for Oxygenate Synthesis

In situ x-ray diffraction (XRD) and absorption spectroscopy (XAS) was used to characterize the structure and phase composition of a novel Mn and Fe double-promoted Rh-based catalyst for CO hydrogenation to oxygenates. Catalysts with different Mn:Rh molar ratios were prepared by combining Mn and Rh precursors with Fe2O3 powder, which were then calcined in air and reduced under hydrogen. The resulting MnRh/Fe2O3 catalysts are found to be highly selective for ethanol synthesis (similar to 40 %) for CO hydrogenation under mild conditions (similar to 1 bar, 240 degrees C). Comparison of the reactivity results with quantitative phase information from in situ XRD measurements suggest that reduced metal oxides, MnO and FeOx, and metallic Rh co-exist as active phases to promote oxygenate selectivity. The results of this work also highlight the importance of in situ characterization for extracting meaningful information on the active phases of such complex, ternary catalysts which can vary under reaction conditions.