Size dependence of gold clusters with precise numbers of atoms in aerobic oxidation of d-glucose

Abstract

Size-dependence is an important factor in gold nanocatalysis. In this study, we explored the catalytic performance of atomically precise Au_n(PET)_m nanocluster catalysts (where, PET = phenylethanethiolate) of different gold atoms and sizes, including Au₂₅(PET)₁₈ (∼1.2 nm), Au₃₈(PET)₂₄ (∼1.5 nm), and Au₁₄₄(PET)₆₀ (∼1.9 nm) nanoclusters. These Au_n(PET)_m gold clusters, immobilized on activated carbon (AC) and used as heterogeneous catalysts, were characterized by transmission electron microscope (TEM), BET as well as X-ray photoelectron spectroscopy (XPS). They showed good catalytic activity in the aerobic oxidation of D-glucose into gluconic acid (or gluconates) with ∼98% selectivity. We observed a distinct size dependence of the gold nanocluster in the oxidation reactions, which follows as Au₁₄₄(PET)₆₀/AC > Au₃₈(PET)₂₄/AC > Au₂₅(PET)₁₈/AC. It was primarily determined by the surface area of the nanoscopic Au nanocluster. Further, the turnover frequency (TOF) for the Au₁₄₄(PET)₆₀/AC catalyst was found to be 2.3 s⁻¹, which is comparable with that for Au/EC300 and much higher than those for the commercial Pd/AC and Pd-Bi/AC catalysts under the identical reaction conditions. On the whole, the core size of the gold nanoclusters played an important role in the catalytic process.