Dual Pd2+ and Pd0 sites on CeO2 for benzyl alcohol selective oxidation

• Pd/CeO 2 catalysts with a stable high Pd 2+ /(Pd 0 + Pd 2+ ) ratio are prepared by ALD . • Pd/CeO 2 catalysts exhibit excellent performance in benzyl alcohol oxidation. • The TOFs exhibit a volcano relationship with the Pd 2+ /(Pd 0 + Pd 2+ ) ratio. • A dual-site catalyzed oxygen-promoted β-H elimination mechanism was proposed. Solvent-free aerobic oxidation of benzyl alcohol is a green approach for synthesizing fine chemicals. Pd-based catalysts are extensively investigated due to their excellent catalytic activity compared to other metal catalysts. Most researchers believe that metallic Pd species (Pd 0 ) provide active centers. However, the critical role of active oxygen and the function of Pd 2+ is neglected. Herein, supported Pd clusters on CeO 2 (Pd/CeO 2 ) with a stable high Pd 2+ /(Pd 0 + Pd 2+ ) ratio are prepared by atomic layer deposition (ALD). The turnover frequency (TOF) and activity on as-prepared Pd/CeO 2 catalysts in solvent-free aerobic oxidation of benzyl alcohol reach 3.50 × 10 5 h −1 and 1.85 × 10 5 mol/(mol Pd ·h), respectively, which are much superior to previously reported results. As the Pd loading increases, the TOFs exhibit a volcano relationship with the Pd 2+ /(Pd 0 + Pd 2+ ) ratio, pointing to a dual Pd 0 and Pd 2+ sites catalyzed mechanism. O 2 kinetic isotopic effect and further evidence support a dual-site catalyzed oxygen-promoted β-hydride elimination mechanisms, in which benzyl alcohol is selectively adsorbed to Pd 2+ sites and reacts with active oxygen species on nearby Pd 0 sites during the reaction.