Subsurface Ru-Triggered Hydrogenation Capability of TiO_2–x Overlayer for Poison-Resistant Reduction of N-Heteroarenes

Transition-metal-based catalysts are applied widely in the hydrogenation reaction of different organic compounds. However, serious deactivation occurs when the substrate contains strong coordinating functional groups or impurities. In this paper, we reported that a TiO2-x overlayer that formed over Ru NPs (Ru@TiO2-x/TiO2) under reduction conditions worked as a chemoselective, durable, and sulfur-resistant catalyst for the partial hydrogenation of quinoline and other N-heteroarenes. Mechanistic studies revealed that the inhibition of quinoline and its reduced product on the H-2 activation over the Ru NPs was eliminated on the active nonmetal overlayer of Ru@TiO2-x. The oxygen vacancies of the Ru@TiO2-x overlayer were determined to be the active sites for H-2 activation. The synergy between the TiO2-O-v (TiO2-x) active sites with the subsurface Ru particles effectively reduced the barriers of H-2 dissociation and H addition steps, enabling the nonmetal TiO2-O-v shell to catalyze the hydrogenation reaction at mild conditions with remarkable stability and poisoning resistance.