Assessing Dual Rh/Ru Cascade Catalysts in One-Pot Homogeneous Synthesis of Ethanol from Syngas and Methanol

Abstract

The direct conversion of cheap syngas into value-added ethanol at an industrial scale is in high demand. Herein we disclose a one-pot homogeneous homologation of methanol to ethanol with syngas via a rhodium/ruthenium bimetallic catalytic approach. By introducing a catalytic amount of methyl iodide, methanol can be converted to ethanol with high selectivity (>91% ethanol). A syngas ratio of H2/CO = 4:1 was found to be optimal. Among various phosphine ligands tested, Rh-dppp catalyst gave the highest aldehyde pathway selectivity, thus providing an effective route for the synthesis of ethanol upon coupling with a Ru hydrogenation catalyst. The bite angle of the bisphosphine ligands dramatically influences the selectivity of the dual Rh/Ru metallic cascade catalysts. In line with the experimental findings, theoretical calculations predicted a rational trend of the selectivity of different bisphosphine ligands via varying bite angle properties.