Liberating Active Metals from Reducible Oxide Encapsulation for Superior Hydrogenation Catalysis

The strong metal-support interaction (SMSI) is of significant importance to heterogeneous catalysis. The electronic modification and encapsulation of active metals by reducible supports are the intrinsic properties of the SMSI, where the latter would decrease or even cease the catalytic activity of transition metals. Here, we demonstrate for the first time that alkalies are the functional additives that can effectively manipulate the SMSI for better hydrogenation catalysis. Specifically, both thermodynamic analyses and experimental results show that the addition of alkalies to the Ru/TiO₂ catalyst could form a titanate top layer that effectively hampers the migration of TiO_2- to the surface of Ru nanoparticles. In the meantime, a substantially enhanced reduction of the support is achieved, leading to an even stronger electron donation from the support to Ru. The alkali-modified Ru/TiO₂ exhibits superior low-temperature catalytic activity in the hydrogenation of aromatics, which is ca. an order of magnitude higher than that of the commercial Ru/Al₂O₃ catalyst and is in clear contrast to that of the neat Ru/TiO₂ catalyst that shows negligible activity due to the severe encapsulation of Ru by TiO_2-.