Copper ferrite supported gold nanoparticles as efficient and recyclable catalyst for liquid-phase ethanol oxidation

Abstract

Copper-containing spinel-supported gold nanoparticle catalysts are optimized toward high activity and stability in liquid-phase aerobic oxidation of aqueous bioethanol to acetic acid under mild hydrothermal conditions (3 MPa O2, 140 °C). In this work, we investigate the structure-performance relationships of supported gold catalysts by changing the composition and calcination temperature of spinel supports to gain insight into the gold-support interaction. The support effect specially acts on the rate-controlling ethanol activation step, with ferrite-spinel outperforming aluminate and chromite-spinels, and the activity increasing with the copper content in the spinels. Moreover, support calcination at 700 °C results in the optimal Au/CuFe2O4 catalyst, which can be magnetically separated and reused at least five times. The improved reusability is likely attributed to the alloying between AuNPs and Cu0 on the partially reduced CuFe2O4. The presence of negatively charged Auδ− and redox active Fe2+ species in the spent Au/CuFe2O4 catalyst points to a specific Auδ−-Fe2+ synergy for the enhanced activation of O2 and ethanol. With the help of negatively charged AuNPs, heterogeneous Fenton-like reaction is suggested to provide hydroxyl radicals for the CH bond activation of ethanol.