Designing Au nanocatalysts supported on nanosized metal oxides has drawn much attention due to remarkable nanoscale influenced metal-support interactions and their favorable role in heterogeneous catalysis. This work reports development of Au nanocatalysts dispersed on nanosized CeO₂ and CeO₂-ZrO₂ supports for solvent- and base-free oxidative coupling of benzylamines into N-benzylbenzaldimines using O₂ as a green oxidant. The physicochemical characterization of nanocatalysts has been undertaken using HRTEM, UV–vis DRS, XRD, Raman, BET, TG-DTA, AAS, and XPS techniques. HRTEM images reveal the formation of nanosized CeO₂ and CeO₂-ZrO₂ supports with an average diameter of ∼10 and 7 nm, respectively. HRTEM images also indicated that Au/CeO₂-ZrO₂ catalyst has smaller Au nanoparticles (∼2.1 nm) compared with that of Au/CeO₂ catalyst (∼3.7 nm). Raman and XPS studies showed that the addition of ZrO₂ to CeO₂ leads to abundant oxygen vacancies and higher concentration of Ce³⁺, respectively. The Au/CeO₂-ZrO₂ catalyst exhibited a higher efficiency in benzylamine conversion (∼95%) followed by Au/CeO₂ (∼78%), CeO₂-ZrO₂ (∼51%), and CeO₂ (∼39%). The Au/CeO₂-ZrO₂ catalyst was also found to effective for oxidative coupling of various benzylamines, and moderate to good product yields were obtained. The presence of smaller Au particles (2.1 nm) and improved surface-defect properties of nanoscale CeO₂-ZrO₂ support are found to be key factors for high performance of Au/CeO₂-ZrO₂ catalyst. Additionally, the reaction temperature is one of the important factors for the performance of catalysts. Remarkably, ∼99.6–99.9% selectivity for N-benzylbenzaldimines was found in the amine oxidation, which highlights the significance of present work in the selective oxidation catalysis.

中文翻译：

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有前景的纳米结构金/金属氧化物催化剂，可在环境友好的条件下进行苄胺的氧化偶联

由于纳米级影响显着的金属-载体相互作用及其在非均相催化中的有利作用，设计负载在纳米级金属氧化物上的金纳米催化剂引起了广泛的关注。这项工作报道了分散在纳米尺寸CeO ₂和CeO ₂ -ZrO ₂载体上的Au纳米催化剂的开发，该载体用于使用O ₂作为绿色氧化剂将苄胺无溶剂和无碱地氧化偶联为N-苄基苯二胺。纳米催化剂的理化特性已经使用HRTEM，UV-vis DRS，XRD，拉曼，BET，TG-DTA，AAS和XPS技术进行了表征。HRTEM图像揭示了纳米CeO ₂和CeO ₂ -ZrO _2的形成支撑物的平均直径分别约为10和7 nm。HRTEM图像还表明，金/的CeO ₂ -ZrO ₂与金/铈的催化剂相比，具有更小的Au纳米颗粒（~2.1纳米）₂催化剂（~3.7纳米）。拉曼和XPS研究表明，向CeO _2中添加ZrO _2分别导致大量的氧空位和更高的Ce ³⁺浓度。Au / CeO ₂ -ZrO ₂催化剂的苄胺转化率较高（〜95％），其次是Au / CeO ₂（〜78％），CeO ₂ -ZrO ₂（〜51％）和CeO ₂（〜39） ％）。Au / CeO ₂还发现-ZrO ₂催化剂对于各种苄胺的氧化偶联有效，并且获得了中等至良好的产物产率。发现较小的Au颗粒（2.1nm）的存在和纳米级CeO ₂ -ZrO ₂载体的改善的表面缺陷性质是高性能Au / CeO ₂ -ZrO ₂催化剂的关键因素。另外，反应温度是影响催化剂性能的重要因素之一。值得注意的是，在胺氧化中发现N-苄基苯甲二胺的选择性约为99.6–99.9％，这突出了目前在选择性氧化催化中的工作意义。