Aerobic Oxidation of Cyclohexane Catalyzed by Size-Controlled Au Clusters on Hydroxyapatite: Size Effect in the Sub-2 nm Regime

In this work, we synthesized gold clusters, Au-n (n = 10, 18, 25, 39), with atomically controlled sizes on hydroxyapatite (HAP) and studied the catalysis for aerobic oxidation of cyclohexane. These Au-n/HAP catalysts could efficiently oxidize cyclohexane to cyclohexanol and cyclohexanone. The turnover frequency monotonically increased with an increase in the size, reaching values as high as 18 500 h(-1) Au atom(-1) at n = 39, and thereafter decreased with a further increase in n up to n similar to 85. This finding provides a fundamental insight into size-specific catalysis of gold in the cluster,regime (diameter < 2 nm) and a guiding principle for rational design of Au cluster-based catalysts.