The synergetic effect of support oxygen groups and Pt particle size in the oxidation of α-D-glucose: a proximity effect in adsorption

The influence of the support-oxygen groups and Pt particle size on the catalytic performance of Pt/AC for the aerobic oxidation of α-D-glucose to gluconic acid (glycolate) was studied. Surface-oxygen groups were introduced by treating the activated carbon support with diluted HNO ₃ without significantly affecting the support porosity. The platinum particle size could be decreased on both the treated and untreated support by adding an additional calcination step to the synthesis. The presence of oxygen-containing groups is shown to be highly beneficial (∼4 fold increase in the turnover frequency) only for the smallest Pt particle size (1.8–2.5 nm, determined by TEM). For the catalyst with the larger Pt size (3.4–3.6 nm), the presence of additional oxygen-contacting groups does not significantly enhance the activity. Since the size of the smaller Pt particles is close to the product/substrate molecular diameter (glucose/gluconic acid, ∼0.9 nm) the observed effect can be attributed to the effective repulsion by the negatively charged oxygen groups in close proximity to the glycolate reaction product. The increase in activity originates from the resulting enhanced desorption of glycolate by alleviating the product inhibition presence due to the strong interaction of glycolate with Pt.