The formation mechanism of the initial C-C chain in ethanol synthesis on γ-AlOOH(100)

An in-depth understanding of the reaction mechanism at the molecular level is the key to guide the synthesis of ethanol over the CuZnAl catalyst, which is one of the major challenges for ethanol application in energy. Reported herein is a density functional theory study of ethanol synthesis from mixed methanol and syngas on the γ-AlOOH(100) surface. The possible elementary reactions are unambiguously identified and for the first time we confirm the high reactivity of the γ-AlOOH(100) surface for the initial C-C chain formation via CO insertion into CH₃, which has a 62.8 kJ mol^-1 (0.65 eV) activation barrier that is significantly lower than the barriers previously reported. And its corresponding reaction energy is -288.2 kJ mol^-1 (-2.99 eV). Bader charge analyses indicate that it is advantageous for the nucleophilic attack of CO to the neighboring CH₃ on the γ-AlOOH(100) surface. Our calculations show that ethanol synthesis starts with CH₃OH dissociation, goes through CH₃O dissociation to yield CH₃, subsequently, CO inserts into CH₃ to form CH₃CO, which is further hydrogenated to yield CH₃CHO and eventually obtain C₂H₅OH. And the formation of intermediate CH₃ is the rate-determining step of the overall reaction. The results not only provide new mechanistic insights into the role of γ-AlOOH but also may be useful for the rational designing and optimizing of the CuZnAl catalyst for ethanol synthesis.