Sol-immobilized vs deposited-precipitated Au nanoparticles supported on CeO2 for furfural oxidative esterification

The non-edible nature of lignocellulose makes this an important raw material for future biorefineries. This work concerns the oxidative esterification of furfural (a C5 compound) to alkyl furoates, which find applications in the fine chemical industry. RESULTS: Very efficient Au/CeO2 catalysts for furfural oxidative esterification were prepared by deposition of gold colloids using polyvinyl alcohol as protective agent. The catalysts provided complete conversion and selectivity without the presence of a base. Sol-immobilized catalysts displayed better catalytic performances than Au/CeO2 prepared by deposition–precipitation (74% conversion). It was proposed that polyvinyl alcohol molecules act not only as gold stabilizer, but they leave ceria support uncovered and available for catalysis. The reaction is extremely sensitive to temperature, but can be carried out at very low pressures. Sol-immobilized catalysts do not require any preliminary calcination to be activated and can be recovered by simple filtration: no oxidation of the exhausted catalyst is required for at least six catalytic runs. CONCLUSION: The new catalyst is active, selective, recyclable and suitable for an industrial chemistry application based on renewable resources. Furoate ester can be obtained with optimal yields by a greener process than is presently used.

BACKGROUND: The non-edible nature of lignocellulose makes this an important raw material for future biorefineries. This work concerns the oxidative esterification of furfural (a C5 compound) to alkyl furoates, which find applications in the fine chemical industry.RESULTS: Very efficient Au/CeO2 catalysts for furfural oxidative esterification were prepared by deposition of gold colloids using polyvinyl alcohol as protective agent. The catalysts provided complete conversion and selectivity without the presence of a base. Sol-immobilized catalysts displayed better catalytic performances than Au/CeO2 prepared by deposition-precipitation (74% conversion). It was proposed that polyvinyl alcohol molecules act not only as gold stabilizer, but they leave ceria support uncovered and available for catalysis. The reaction is extremely sensitive to temperature, but can be carried out at very low pressures. Sol-immobilized catalysts do not require any preliminary calcination to be activated and can be recovered by simple filtration: no oxidation of the exhausted catalyst is required for at least six catalytic runs.CONCLUSION: The new catalyst is active, selective, recyclable and suitable for an industrial chemistry application based on renewable resources. Furoate ester can be obtained with optimal yields by a greener process than is presently used. (C) 2017 Society of Chemical Industry