Silica-encapsulated gold core-shell nanoparticles (Au@SiO
2) were synthesized via a bottom-up synthesis to catalyze the selective oxidation of benzyl alcohol. The pore size, morphology, and composition of Au@SiO
2 was evaluated using N
2 gas adsorption, transmission electron microscopy, and inductively-coupled plasma mass spectroscopy, respectively. The nanoparticles exhibit a pore size distribution with a peak at 27 Å, a size which enhances selectivity via preferential transport of the desired product (i.e. benzaldehyde) relative to larger, undesired products (i.e. benzoic acid/benzyl benzoate). GC-FID analysis revealed the addition of potassium carbonate during the catalytic oxidation of benzyl alcohol increased conversion from 58% to 75% while only decreasing selectivity from 98.5% to 97.7%.
These results suggest that the pore size distribution within the inert silica shell of Au@SiO2 physically inhibits the formation of undesired products to facilitate the selective oxidation of benzaldehyde despite a basic environment which would drastically reduce selectivity under typical conditions. An activation energy study revealed an unusually low activation energy of 23 kJ/mol. Combined with overwhelmingly rate-limited Thiele moduli, the particles appear to have a lower activation energy as a result of a catalyst that is not only product selective, but mechanism selective. As such, these particles are a promising platform for analysis of the impact of functionalization on mass transport and surface chemistry discretely.
