Efficient synthesis of ethanol by methanol homologation using CO2 at lower temperature

Abstract

CO₂ transformation is an important topic in green chemistry, and methanol homologation using CO₂ is a promising route to produce ethanol. In this work, we studied this reaction using different homogeneous catalytic systems. It was found that a [RuCl₂(CO)₃]₂/Co₄(CO)₁₂ bimetallic catalyst using LiI as a promoter and N-ethyl-2-pyrrolidone (NEP) as the solvent was very effective under mild conditions. The reaction could proceed efficiently at 160 °C, which is much lower than that reported before. The turnover frequency (TOF) of ethanol based on Ru was as high as 7.5 h⁻¹ and the selectivity of ethanol in total products could reach 65.0 C-mol%, which are obviously higher than those reported in the literature. Ethanol was synthesized through cascade catalysis of a reverse water gas shift (RWGS) reaction and methanol homologation with syngas (CO/H₂). The outstanding performance of the catalytic system originated from the excellent cooperation of the components. The catalyst could be reused at least five times without any obvious decrease of the catalytic performance. The effect of the solvent on this reaction was studied systematically. The mechanism was also discussed based on isotope labeling tests.