The selective hydrogenation of lignin-derived phenols under mild conditions is still a challenging work. In this study, 2.0 wt% Pd/γ-Al₂O₃ catalyst was found to show high catalytic performance for the selective hydrogenation of lignin-derived phenols, giving 100% conversion of substrate and 94.9% yield of cyclohexanols under optimized conditions. The excellent catalytic performance of the 2.0 wt% Pd/γ-Al₂O₃ catalyst could be possibly ascribed to its higher percentage (93.6%) of surface Pd⁰ species than other catalysts. The turnover number (TON) of substrate was 1363 with apparent activation energy (Ea) of 22.7 and 13.6 kJ mol⁻¹ for the hydrogenation of 4-ethyl phenol to 4-ethyl cyclohexanone and subsequent hydrogenation for C=O bond over Pd/γ-Al₂O₃, respectively. The lower Ea could possibly explain the excellent catalytic activity for the full hydrogenation of 4-ethyl phenol to 4-ethyl cyclohexanol. Furthermore, this catalyst showed higher selectivity to hydrolysis and hydrogenation than to hydrogenolysis for the conversion of β-O-4, 4-O-5 and α-O-4 linked lignin-derived dimeric compounds with excellent substrate conversion and cyclohexanol product yield, offering great opportunity and potential for upgrading of lignin-derived phenols to well-defined end products.

在温和条件下对木质素衍生的酚类进行选择性加氢仍然是一项具有挑战性的工作。在本研究中，发现 2.0 wt% Pd/γ-Al ₂ O ₃催化剂对木质素衍生酚的选择性加氢具有较高的催化性能，在优化条件下，底物转化率为 100%，环己醇产率为 94.9%。2.0 wt% Pd/γ-Al ₂ O ₃催化剂的优异催化性能可能归因于其表面Pd ⁰物种的百分比（93.6%）高于其他催化剂。底物的转换数 (TON) 为 1363，表观活化能 ( Ea ) 为 22.7 和 13.6 kJ mol ^-1分别用于在 Pd/γ-Al ₂ O ₃上将 4-乙基苯酚氢化成 4-乙基环己酮和随后的 C=O 键氢化。较低的Ea可能解释了 4-乙基苯酚完全加氢生成 4-乙基环己醇的优异催化活性。此外，该催化剂对β-O-4、4-O-5和α-O-4连接的木质素衍生的二聚化合物的转化显示出比氢解更高的水解和氢化选择性，具有优异的底物转化率和环己醇产物收率，为将木质素衍生的酚类升级为明确定义的最终产品提供了巨大的机会和潜力。