Remarkable Enhancement in Hydrogenation Ability by Phosphidation of Ruthenium: Specific Surface Structure Having Unique Ru Ensembles

A series of transition metals and metal phosphides supported on silica (M/SiO2 and MxPy/SiO2, M = Pt, Pd, Ir, Rh, Ru, Ni, and Co) were prepared and tested as catalysts for hydrogenation of toluene as a hydrogen carrier. Catalytic activities were reduced greatly by phosphidation of noble metals, such as Pt, Pd, Ir, and Rh. Catalytic activity of Ru, however, showed a remarkable increase in turnover frequency-26 times higher than that of bare Ru. Ru2P/SiO2 with a much lower cost exhibited a catalytic performance comparable with those of other platinum group metals. A combination of kinetic, infrared, and computational studies revealed that (1) strong adsorption of toluene on Ru2P promoted hydrogenation and (2) a specific surface structure of Ru2P having large ensembles of electron-deficient Ru allowed the strong adsorption.