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 gacetaldehyde ggold−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.

Highlights

  • Selective oxidation of alcohols over recyclable heterogeneous catalysts is an area of growing importance in green organic chemistry with the aim to replace stoichiometric reagents.[1]

  • The reaction cycle for ethanol oxidation starts with the adsorption of ethanol on one of the Au atoms located at the interface between the gold cluster and the MgCuCr2O4 support

  • We have explored for the first time the mechanism of catalytic alcohol oxidation for the highly active and selective Au/MgCuCr2O4 catalyst

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Summary

Introduction

Selective oxidation of alcohols over recyclable heterogeneous catalysts is an area of growing importance in green organic chemistry with the aim to replace stoichiometric reagents.[1]. The VebaChemie process may be employed, which involves gas-phase oxidation of ethanol over a silver catalyst at temperatures in

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