Substrate-Dependent\nRole of a Pd Dopant in PdAu<sub>12</sub> Catalysts in the Oxidation\nof <i>p</i>‑Substituted\nBenzyl Alcohols: Promotion of Hydride Abstraction and Reductive Activation\nof O<sub>2</sub>

Single-atom\ndoping, which is the primary step toward\nmultimetallization,\non atomically size-controlled metal nanoclusters facilitates the elucidation\nof doping effects on catalysis. Herein, we synthesized MAu<sub>12</sub> (M = Au, Ir, Rh, Pt, or Pd) nanoclusters on double metal hydroxide\ncomposed of Co and Ce by thermal treatment of diphosphine-protected\nMAu<sub>12</sub>(dppe)<sub>5</sub>Cl<sub>2</sub> (dppe: 1,2-bis(diphenylphosphino)ethane).\nThe successful formation of the MAu<sub>12</sub> nanocluster under\nan optimized thermal treatment condition (175 °C, 8 h) was confirmed\nby X-ray absorption fine structure spectroscopy and aberration-corrected\nhigh-angle annular dark-field scanning transmission electron microscopy.\nAmong the five catalysts, PdAu<sub>12</sub> exhibited 4.4 times higher\nactivity than Au<sub>13</sub> in the aqueous phase benzyl alcohol\n(BnOH) oxidation, while the other MAu<sub>12</sub> (M = Ir, Rh, or\nPt) catalysts showed comparable activity to Au<sub>13</sub>. On the\nbasis of the kinetic experiments under different partial pressures\nof O<sub>2</sub> with <i>p</i>-substituted BnOH (R-BnOH;\nR = MeO, Me, H, Cl, or CF<sub>3</sub>), we concluded that the single\nPd atom dopant plays a dual role in the oxidation depending on the\nnature of the R group: abstraction of H<sup>–</sup> from the\nadsorbed alkoxide for R = Cl or CF<sub>3</sub> and reductive activation\nof O<sub>2</sub> for R = MeO, Me, or H. Theoretical studies on model\nstructures have shown that O<sub>2</sub> is more efficiently activated\nby PdAu<sub>12</sub> than by Au<sub>13</sub>, thereby the different\nmechanism mediated by activated O<sub>2</sub> appears with the single\nPd doping.