Supported Gold Nanoparticles for Furfural Valorization in the Future Bio-based Industry

Gold nanoparticles prepared by sol immobilization using PVA as protecting agent were supported over different oxides (CeO₂, ZrO₂ and TiO₂). The activity of the gold catalysts was tested in the oxidative esterification of furfural by an efficient and sustainable process. The samples supported on ceria and zirconia (AuCe and AuZr) have shown complete conversion and selectivity under mild reaction conditions. The catalytic performances are better than those obtained with the reference commercial AuTiWGC. The DR UV–Vis spectroscopic results indicate that gold nanoparticles that give rise to similar plasmonic band, as in the case of AuCe and AuZr, are very active and highly selective. The extent of crystallinity of the gold particles seems to have no influence on the activity of the sol immobilized catalysts. The null selectivity of the catalyst supported on titania is probably due to the presence of residual sulphate groups. The effect of the oxygen pressure on the furfural conversion is almost negligible for all the samples and, despite of the oxygen pressure lowering, it is possible to obtain always high conversion and selectivity. The selectivity of the process is unaffected by using air instead of oxygen, even at very low pressures. On the contrary, the presence of PVA seems to influence the conversion when working in air at low pressures, due to a dilution effect of the oxidant atmosphere. This is confirmed by the results obtained for a sample synthesized by deposition precipitation of gold on zirconia, where the high metal dispersion and the absence of the protecting agent allowed to reach high conversion even in low air pressure.