Tailoring gold nanoparticle characteristics and the impact on aqueous-phase oxidation of glycerol

Polyvinylalcohol (PVA)-stabilised Au nanoparticles (NPs) were synthesized by colloidal methods, in which temperature variations (−75 to 75°C) and mixed H2O/EtOH solvent ratios (0, 50 and 100 vol:vol) were used. The resulting Au NPs were immobilized on TiO2 (P25) and their catalytic performance was investigated for the liquid phase oxidation of glycerol. There was a systematic increase in average Au particle size as the temperature of colloidal preparation increases, for each unique solvent system. Generation of the Au NPs in H2O at 1°C resulted in a high observed activity compared to current Au/TiO2 catalysts (TOF = 915 h-1). Interestingly, Au catalysts with similar average particle sizes but prepared under different conditions had contrasting catalytic performance. For the most active catalyst, aberration-corrected HAADF STEM analysis identified the presence of isolated ultra small Au clusters (from 1-5 atoms) for the first time using a modified colloidal method, which was supported by experimental and computational CO adsorption studies. It is proposed that the variations in the populations of these species, in combination with other solvent/PVA effects, is responsible for the contrasting catalytic properties.