A mechanism of gas-phase alcohol oxidation at the interface of Au nanoparticles and a MgCuCr2O4 spinel support

Abstract

The catalytic oxidation of bio-ethanol to acetaldehyde entails a promising route for valorization of biomass into many important chemicals that are currently mainly being produced from fossil-based ethylene feedstock. We employ here DFT calculations to understand the unprecedented synergy between gold clusters and a MgCuCr₂O₄ spinel support, which shows excellent catalytic performance for the oxidation of ethanol to acetaldehyde (space-time yield of 311 g_acetaldehyde g_gold⁻¹ h⁻¹ at 250 °C). The investigations support a mechanism involving catalytic reactions at the gold–support interface. Dissociative adsorption of ethanol is facilitated by cooperative action of a gold atom at the metal cluster–support interface and a basic oxygen atom of the support. The most difficult step is the recombinative desorption of water from the surface. The oxygen vacancy formation energy is found to be a good performance descriptor for ethanol oxidation of Au/MgMeCr₂O₄ (Me = Cu, Ni, Co) catalysts. The high selectivity towards acetaldehyde stems from the facile desorption of acetaldehyde as compared to the cleavage of the remaining α-C–H bond in the product. The opposite holds for methanol oxidation, explaining why experimentally we observe complete methanol oxidation over Au/MgCuCr₂O₄ under conditions where ethanol is selectively converted to acetaldehyde.