Insights into the mechanism of ethanol synthesis and ethyl acetate inhibition from acetic acid hydrogenation over Cu2In(100): a DFT study

Developing low-cost and high-efficiency non-noble metal catalysts is beneficial for industrially massive synthesis of ethanol from acetic acid, which can be obtained from renewable biomass. Understanding the detailed mechanism of the reaction from a molecular level provides insights that can be used to tailor catalysts to improve their performance. In this study, alternative mechanisms for ethanol synthesis from acetic acid hydrogenation over Cu2In(100) have been investigated using periodic density functional theory (DFT) calculations. The pathway of CH3COOH → CH3COO → CH3CHOO → CH3CHO → CH3CH2O → CH3CH2OH was found to be most favorable. The high activation barriers for CH3COO hydrogenation to CH3CHOO (1.33 eV) and CH3CH2O hydrogenation to CH3CH2OH (1.04 eV) indicate that these two steps are the rate-limiting steps. In addition, the results also show that there are probably two more active intermediate species of CH3CO and CH3CH(OH)O besides CH3COO. Furthermore, the synergy and the role of copper and indium in the Cu–In bimetallic catalyst were discussed. The adsorption strength of copper will be improved by indium. Indium, however, has high chemical inertness in Cu2In. They evenly divided the surface into small reaction areas which could significantly inhibit ethyl acetate formation through the hindrance effect.