Sensitivity of the glycerol oxidation reaction to the size and shape of the platinum nanoparticles in Pt/SiO2 catalysts

The structure sensitivity of the catalytic oxidation of glycerol with atmospheric O-2 in neutral pH water solutions was evaluated by using three series of silica-supported platinum catalysts. Transmission electron microscopy and CO titration experiments with infrared absorption spectroscopy detection were used to characterize the catalysts. Higher loadings led to larger average Pt nanoparticle sizes, but comparisons across catalysts made by different methods were unreliable because of differences in particle size distributions. Nevertheless, strong dependences of the selectivity for oxidation at the terminal versus central alcohol groups were identified as a function of both the extent of reaction and Pt particle size, with high conversions and large nanoparticles favoring terminal-carbon oxidation. Additional increases in turnover frequencies were also observed with increasing average metal nanoparticle size and with cuboctahedral versus tetrahedral Pt nanoparticles. On the other hand, no significant trends were seen in terms of further oxidation of glyceraldehyde to glyceric acid. The reported trends were ascribed to the general need for multi-atom surface Pt ensembles for conversion and to a possible unique access to the central carbonyl in glycerol only at low-coordination Pt sites. (C) 2015 Elsevier Inc. All rights reserved.