Structures and CO oxidation activities of size-selected Au nanoparticles in mesoporous titania-coated silica aerogels

Abstract

We have prepared Au/Titania-coated silica aerogel catalysts from Au nanoparticles (AuNPs) having well-regulated sizes in the range 1.4–6.4 nm, through heat-treatment of thiol-capped AuNPs, size-separation through fractional precipitation, and adsorption of the AuNPs on the support in a nonpolar solvent. The Au particle size was preserved during calcination of the catalyst samples at 673 K and subsequent CO oxidation. The turnover frequency for CO oxidation of the catalysts changed drastically when their sizes varied from 4 to 5 nm, but it did not change appreciably in other size regions. X-ray absorption spectroscopy and X-ray diffraction measurements revealed that lattice contraction and structural changes become prominent at Au diameters of less than 4–5 nm. Thus, the structural changes that occurred in the AuNPs in this diameter region are consistent with the enhanced catalytic activity.