水滑石负载钯催化剂上的醇无氧脱氢反应

 研究了多种载体负载 Pd 催化剂上苯甲醇无氧脱氢反应. 结果发现, 以兼具较强酸性和碱性的水滑石 (HT) 为载体时, Pd 催化剂具有优异的苯甲醇转化活性和苯甲醛选择性, 当 Pd 含量为 0.32%~0.55% 时催化性能最佳. Pd/HT 催化剂可重复使用, 且对于含推电子取代基的芳香醇、2-噻吩甲醇、α,β-不饱和醇与环状脂肪醇等的直接脱氢反应均具有较好催化性能. HT 表面的 Pd(II) 物种反应后转变为平均粒径为 2.0~2.5 nm 的 Pd 纳米粒子或纳米簇. 具有较高分散度的 Pd(II) 物种易转变为较小的 Pd 纳米粒子, 从而具有较佳的催化性能. 本文推测, 催化剂表面的碱性位可促进苯甲醇 O–H 键的活化, 形成 Pd-苯甲氧基中间体, 该中间体进一步脱氢生成苯甲醛和 Pd-H 物种; 而催化剂表面的质子酸位可与 Pd-H 作用, 促进 H2 的脱除.

Oxidant-Free Dehydrogenation of Alcohols over Hydrotalcite-Supported Palladium Catalysts

Pd catalysts supported on various supports have been studied for the oxidant-free dehydrogenation of alcohols. The Pd catalyst loaded on hydrotalcite (HT), which is an acid-base bifunctional support, demonstrates superior benzyl alcohol conversion and benzaldehyde selectivity. Detailed studies using the Pd/HT catalyst reveal that the best performance can be obtained over the catalyst with w(Pd) = 0.32%–0.55%. The Pd/HT can be used repeatedly without significant deactivation and can efficiently catalyze the dehydrogenation of various alcohols including the substituted benzylic alcohols, 2-thiophenemethanol, α,β-unsaturated alcohols, and cyclic aliphatic alcohols. The characterization results show that the Pd(II) species over the HT are transformed into Pd nanoparticles or nanoclusters with mean size of 2.0–2.5 nm during the reaction. The highly dispersed Pd(II) species in the catalyst precursors can lead to the formation of smaller Pd nanoparticles, favoring the catalytic performance. We speculate that the basicity of the catalyst may promote the activation of the O-H bond of alcohol to form a Pd-benzyl alcoholate intermediate, which undergoes β-H abstraction by Pd nanoparticles, and the Brönsted acid sites on the catalyst surface may facilitate the release of H2 by the interaction with the formed hydride species on Pd nanoparticles.