Catalytic activity of transition metal doped Cu(111) surfaces for ethanol synthesis from acetic acid hydrogenation: a DFT study

Abstract

Transition metal (Co, Ni, Ru, Rh, Pd and Pt) doped Cu(111) models are selected to examine the effects of transition metals on Cu surface for ethanol synthesis from acetic acid hydrogenation using density functional theory (DFT) calculations. On these surfaces, the adsorption of the main intermediates and reaction barriers of key elementary steps are investigated. The calculation results indicate that oxophilic metals are projected to be more active in acetic acid adsorption and acetaldehyde adsorption compared to less-oxophilic metals. Those metals with larger C adsorption energies generally have better C–OH bond cracking activity. Additionally, a good linear Brønsted–Evans–Polanyi (BEP) correlation is established for predicting the preferences of C–OH bond scission of acetic acid on other metals. Finally, O–H bond formation in C₂-oxygenates (CH₃CO, CH₃CHO, CH₃CH₂O) hydrogenation is examined on all these surfaces. The reactions are more likely to occur on less-oxophilic metal-doped Cu surfaces. Therefore, it appears to involve an intricate balance between C–OH cracking and O–H bond formation reactions. That means those metal-doped Cu-based catalysts that are capable of preferentially activating C–OH bond without considerably inhibiting O–H bond formation of C₂-oxygenates are predicted to achieve optimum catalytic activity for ethanol synthesis from acetic acid hydrogenation. The results can provide theoretical guidance for related experiments as well as the designing of Cu-based catalysts for ethanol synthesis.