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 (Pd⁰) provide active centers. However, the critical role of active oxygen and the function of Pd²⁺ is neglected. Herein, supported Pd clusters on CeO₂ (Pd/CeO₂) with a stable high Pd²⁺/(Pd⁰ + Pd²⁺) ratio are prepared by atomic layer deposition (ALD). The turnover frequency (TOF) and activity on as-prepared Pd/CeO₂ catalysts in solvent-free aerobic oxidation of benzyl alcohol reach 3.50 × 10⁵ h⁻¹ and 1.85 × 10⁵ 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 Pd²⁺/(Pd⁰ + Pd²⁺) ratio, pointing to a dual Pd⁰ and Pd²⁺ sites catalyzed mechanism. O₂ 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 Pd²⁺ sites and reacts with active oxygen species on nearby Pd⁰ sites during the reaction.

苯甲醇的无溶剂好氧氧化是合成精细化学品的绿色途径。与其他金属催化剂相比，Pd 基催化剂由于其优异的催化活性而被广泛研究。大多数研究人员认为金属 Pd 物质 (Pd ⁰ ) 提供活性中心。然而，活性氧的关键作用和Pd ²⁺的作用却被忽略了。在此，通过原子层沉积（ALD）制备具有稳定的高Pd ²⁺ /（Pd ⁰  + Pd ^{2+ ）比率的CeO} ₂（Pd/CeO ₂ ）上负载的Pd簇。_{制备的 Pd/CeO 2}上的周转频率 (TOF) 和活性苯甲醇的无溶剂好氧氧化催化剂分别达到3.50 × 10 ⁵ h ^-1和1.85 × 10 ⁵  mol/(mol _Pd ·h)，远远优于先前报道的结果。随着 Pd 负载量的增加，TOF 与 Pd ²⁺ /(Pd ⁰  + Pd ²⁺ ) 比率呈现火山关系，表明存在双重 Pd ⁰和 Pd ²⁺位点催化机制。O ₂动力学同位素效应和进一步的证据支持双位点催化氧促进的 β-氢化物消除机制，其中苯甲醇选择性吸附到 Pd ^{2+位点并在反应过程中与附近 Pd 0}位点上的活性氧物质发生反应。