Pd-based catalysts have been widely applied in selective hydrogenation of phenol. However, avoiding excessive hydrogenation of C=O functional groups is still challenging. Here, we synthesized Pd nanoclusters supported by N-doped C-AlO (Pd/CN-AlO) catalyst for phenol hydrogenation. Remarkably, the cyclohexanone yield shows a volcano trend with the doping of carbon content, where Pd/CN-AlO with carbon content of 6.76 % (Pd/CN-AlO-2) exhibits the highest cyclohexanone yield. Under the optimized conditions, the phenol conversion and cyclohexanone selectivity over Pd/CN-AlO-2 are 99.5 % and 96.7 %, respectively. The corresponding TOF value is 1731.7 h, which is 5.8 times higher than that of Pd/AlO (299.7 h). Mechanism studies reveal the excellent catalytic performance of Pd/CN-AlO-2 is mainly attributed to the synergistic effect of electron-deficient Pd clusters and Lewis acid sites. Pd nanoclusters with moderate electron-deficient state and moderate Lewis acid density are beneficial to the adsorption of phenol and the desorption of cyclohexanone, thereby exhibiting the best phenol conversion and cyclohexanone selectivity. This work provides a carbon modification strategy to regulate the structure of Pd-based catalysts, which is a helpful guide for the hydrogenation reactions.

中文翻译：

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通过碳掺杂调节Pd纳米团簇的电子态和路易斯酸密度协同增强绿色溶剂中的苯酚加氢


钯基催化剂在苯酚选择性加氢中得到了广泛的应用。然而，避免C=O官能团的过度氢化仍然具有挑战性。在这里，我们合成了 N 掺杂 C-Al2O (Pd/CN-Al2O) 催化剂负载的 Pd 纳米团簇，用于苯酚加氢。值得注意的是，环己酮产率随着碳含量的掺杂呈现火山趋势，其中碳含量为6.76%的Pd/CN-AlO(Pd/CN-AlO-2)表现出最高的环己酮产率。在优化条件下，Pd/CN-AlO-2的苯酚转化率和环己酮选择性分别为99.5%和96.7%。相应的TOF值为1731.7 h，是Pd/Al2O (299.7 h)的5.8倍。机理研究表明Pd/CN-AlO-2优异的催化性能主要归因于缺电子Pd簇和路易斯酸位的协同作用。具有中等缺电子态和中等路易斯酸密度的Pd纳米团簇有利于苯酚的吸附和环己酮的解吸，从而表现出最好的苯酚转化率和环己酮选择性。这项工作提供了一种碳改性策略来调节钯基催化剂的结构，这对加氢反应有帮助。