Conversion of Syngas to Ethanol over a RhFe Alloy Catalyst.

Abstract

The direct conversion of syngas to ethanol is a promising route for the sustainable production of value-added chemicals and fuels. While Fe-promoted Rh-based catalysts have long been studied because of their notable activity and selectivity toward ethanol, the catalyst structure and the nature of Rh-Fe interaction remain poorly understood under reaction conditions, due to the intrinsic complexity of heterogeneous catalysts prepared by conventional approaches. In this work, we construct well-defined RhFe@SiO₂ model catalysts via surface organometallic chemistry, composed of small and narrowly distributed nanoparticles supported on silica. Such a RhFe@SiO₂ catalyst converts syngas into ethanol, reaching an overall ethanol selectivity of 38% among all products at 8.4% CO conversion, while the nonpromoted Rh@SiO₂ catalyst mostly yields methane (selectivity >90%) and no ethanol. Detailed in situ X-ray absorption spectroscopy and diffuse-reflectance infrared Fourier transform spectroscopy studies reveal that the RhFe@SiO₂ catalyst corresponds to an Rh-Fe alloy with ca. 3:1 Rh/Fe ratio alongside residual Fe^II single sites. The alloy is stable under working conditions, promoting high activity and ethanol selectivity.