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 ∼ 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.