Alkali ions secure hydrides for catalytic hydrogenation

Abstract

Catalytic hydrogenation is one of the backbones of the chemical industry. Controlling the reaction behaviour of the activated hydrogen species over oxide-supported metal catalysts is essential. Aside from the expected addition to substrates, the activated hydrogen species would also destroy the active structures. Here we show that, with the assistance of alkali cations, the atomically dispersed Ru(iii) on Al2O3 exhibits enhanced performance in the hydrogenation of a broad range of substrates. The alkali cations facilitate the hydrogenation mediated by heterolytic hydrogen species, which not only restrain the hydride species from migrating to interfacial oxygen, thus suppressing the reduction and aggregation of ruthenium, but also stabilize the negatively charged transition states and intermediates through enhanced Columbic attraction. Distinctively, an inverse H/D isotope effect related to H2 splitting as the rate-determining step over the atomically dispersed ruthenium-catalysed hydrogenation is predicted and confirmed. Alkali metals have been traditionally used to promote heterogeneous catalysts, albeit their mode of action remains controversial. Now, the authors demonstrate the multifaceted role of sodium ions in promoting atomically dispersed Ru(iii) on Al2O3, resulting in a superior hydrogenation catalyst.