New Insights on the Dynamic Role of the Protecting Agent on the Reactivity of Supported Gold Nanoparticles

A very efficient catalyst (AuCePVA) was prepared by depositing gold colloids on CeO2 and using polyvinyl alcohol (PVA) as protective agent. Complete conversion and selectivity in furfural (2-FA) oxidative esterification to methyl-2-furoate (Me-2-F) was obtained without base under conventional heating at 120 °C. AuCePVA was compared with Au/CeO2 obtained by deposition-precipitation method, pointing out that along with the size of the Au nanoparticles and the surface sites of the ceria support, also PVA chains played a role during reaction. In situ FTIR spectroscopy measurements of adsorbed molecules at controlled temperature and pressure demonstrated that PVA acted not merely as gold stabilizer, but also as mediator during the 2-FA oxidative esterification, leaving both Au and ceria sites available for catalysis at the reaction temperature. In a perspective of process intensification, the microwave-assisted (MW-assisted) 2-FA oxidative esterification was carried out. Depending on the reaction time and temperature, AuCePVA favoured the oxidation of the hemiacetal into the ester rather than the re-oxidation of the acetal into the ester, due to the formation of Ce3+ sites under MW irradiation.