(186z) Diffusion of Species in Functionalized Micro/Mesoporous Au@SiO2 Core-Shell Nanoparticles

Silica-encapsulated gold core-shell nanoparticles (Au@SiO₂) were synthesized via a bottom-up synthesis to catalyze the selective oxidation of benzyl alcohol. The pore size and morphology of the catalyst allows for the unique opportunity to investigate the impacts of silica functionalization on mass transport and surface chemistry discretely. The nanoparticles exhibit a pore 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. Tuning the average pore diameter can allow the investigation of mass transport independent from surface chemistry. Diffusion-Order Spectroscopy NMR (DOSY-NMR) was performed on catalysts with varying pore size and functionality, revealing larger pores exhibited both lower diffusion coefficients and lower selectivity.