Preparation of ∼1 nm Gold Clusters Confined within Mesoporous Silica and Microwave-Assisted Catalytic Application for Alcohol Oxidation

A simple, effective method has been demonstrated to immobilize ∼1 nm Au clusters within mesoporous silicas (SBA-15, MCF, HMS) using triphenylphosphine-protected Au11 (Au11:TPP) clusters as precursors, which were deposited on the silica surface in an organic medium. A unique feature of this method is the ability to disperse Au11:TPP homogeneously over a large surface area by optimizing the solvent-mediated interaction. The Au11:TPP−silica composite was then carefully calcined to remove the protecting ligands while suppressing the aggregation of the resulting Au clusters. For SBA-supported Au clusters, the absence of the surface plasmon band in the reflectance spectrum indicated that contamination by AuNPs larger than 2 nm was negligibly small. The Au cluster size supported on SBA was estimated to be 0.8 ± 0.3 nm by HAADF-STEM observations. The SBA-supported Au clusters exhibited catalytic activity for oxidation of various alcohols by H2O2 under microwave irradiation and were found to be reusable.