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

Abstract

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.