Water as the mediator is exploited to control the reaction behaviors of the aromatic carbonyl compound hydrogenation by taking advantage of its unique properties. Compared with the multifaceted effects of the aqueous solvent, the adsorbed water provides a simplified approach to gain the in-depth microbehavior mechanism of water on the palladium surface in the catalytic hydrogenation. Here we show that, with the assistance of the adsorbed water, the performance of palladium catalysts for the hydrogenation of a broad range of substrates (2-furaldehyde, benzaldehyde, anthraquinone, etc.) is enhanced. In situ experiments and DFT calculations demonstrated that hydronium ions are formed on the palladium surface via the reaction between the adsorbed water and dissociated hydrogen, accompanied by the increase in the electron density of the palladium surface via the charge separation. Mechanistic studies revealed that the former facilitates the hydrogenation of the carbonyl oxygen by promoting the hydrogen-shuttling ability, the latter favors the hydrogenation of the α-C in the hydroxyl intermediates. Meanwhile, the overstabilization of the hydroxyl intermediates by hydrogen bonds would bring about the increase in the energy barrier of the subsequent hydrogenation, resulting in the declined catalytic activity. Distinctively, the distinction in the promotional effect of water mediator for the hydrogenation of substrates is revealed to be associated with the different promotion degree of the reaction rate of the rate-determining step.

利用水作为介质，利用其独特的性质来控制芳香羰基化合物加氢的反应行为。与水性溶剂的多方面作用相比，吸附水提供了一种简化的方法来深入了解水在催化加氢过程中钯表面的微观行为机制。在这里，我们表明，在吸附水的帮助下，钯催化剂对多种底物（2-糠醛、苯甲醛、蒽醌等）的氢化性能得到提高。就地实验和 DFT 计算表明，水合氢离子是通过吸附水和解离氢之间的反应在钯表面形成的，同时通过电荷分离使钯表面的电子密度增加。机理研究表明，前者通过促进氢穿梭能力促进羰基氧的氢化，后者有利于羟基中间体中α-C的氢化。同时，氢键对羟基中间体的过度稳定会导致后续加氢的能垒增加，导致催化活性下降。与众不同的是，