Tailoring Gold Nanoparticle Characteristics and the Impact on Aqueous-Phase Oxidation of Glycerol

Abstract

Poly(vinyl alcohol) (PVA)-stabilized 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. For each unique solvent system, there was a systematic increase in the average Au particle diameter as the temperature of the colloidal preparation increased. Generation of the Au NPs in H2O at 1°C resulted in a high observed activity compared with current Au/TiO2 catalysts (turnover frequency = 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 high angle annular dark field scanning transmission electron microscopy analysis identified the presence of isolated Au clusters (from 1 to 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.