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Single-atom doping, which is the primary step toward multimetallization, on atomically size-controlled metal nanoclusters facilitates the elucidation of doping effects on catalysis. Herein, we synthesized MAu 12 (M = Au, Ir, Rh, Pt, or Pd) nanoclusters on double metal hydroxide composed of Co and Ce by thermal treatment of diphosphine-protected MAu 12 (dppe) 5 Cl 2 (dppe: 1,2-bis(diphenylphosphino)ethane). The successful formation of the MAu 12 nanocluster under an optimized thermal treatment condition (175 °C, 8 h) was confirmed by X-ray absorption fine structure spectroscopy and aberration-corrected high-angle annular dark-field scanning transmission electron microscopy. Among the five catalysts, PdAu 12 exhibited 4.4 times higher activity than Au 13 in the aqueous phase benzyl alcohol (BnOH) oxidation, while the other MAu 12 (M = Ir, Rh, or Pt) catalysts showed comparable activity to Au 13 . On the basis of the kinetic experiments under different partial pressures of O 2 with p -substituted BnOH (R-BnOH; R = MeO, Me, H, Cl, or CF 3 ), we concluded that the single Pd atom dopant plays a dual role in the oxidation depending on the nature of the R group: abstraction of H – from the adsorbed alkoxide for R = Cl or CF 3 and reductive activation of O 2 for R = MeO, Me, or H. Theoretical studies on model structures have shown that O 2 is more efficiently activated by PdAu 12 than by Au 13, thereby the different mechanism mediated by activated O 2 appears with the single Pd doping.
Masuda et al. (Wed,) studied this question.