Characterization of the Platinum–Hydrogen Bond by Surface-Sensitive Time-Resolved Infrared Spectroscopy

The vibrational dynamics of Pt–H on a nanostructured platinum surface has been examined by ultrafast infrared spectroscopy. Three bands are observed at 1800, 2000, and 2090 cm^–1, which are assigned to Pt–CO in a bridged and linear configuration and Pt–H, respectively. Lifetime analysis revealed a time constant of (0.8 ± 0.1) ps for the Pt–H mode, considerably shorter than that of Pt–CO because of its stronger coupling to the metal substrate. Two-dimensional attenuated total reflection infrared spectroscopy provided additional evidence for the assignment based on the anharmonic shift, which is large in the case of Pt–H (90 cm^–1), in agreement with the density functional theory calculations. The absorption cross section of Pt–H is smaller than that of the very strong Pt–CO vibration by only a modest factor of ∼1.5–3. Because Pt–H is transiently involved in catalytic water splitting on Pt, the present spectroscopic characterization paves the way for in-operando kinetic studies of such reactions

Origin of Efficient Catalytic Combustion of Methane over Co₃O₄(110): Active Low-Coordination Lattice Oxygen and Cooperation of Multiple Active Sites

A complete catalytic cycle for methane combustion on the Co₃O₄(110) surface was investigated and compared with that on the Co₃O₄(100) surface on the basis of first-principles calculations. It is found that the 2-fold coordinated lattice oxygen (O_2c) would be of vital importance for methane combustion over Co₃O₄ surfaces, especially for the first two C–H bond activations and the C–O bond coupling. It could explain the reason the Co₃O₄(110) surface significantly outperforms the Co₃O₄(100) surface without exposed O_2c for methane combustion. More importantly, it is found that the cooperation of homogeneous multiple sites for multiple elementary steps would be indispensable. It not only facilitates the hydrogen transfer between different sites for the swift formation of H₂O to effectively avoid the passivation of the active low-coordinated O_2c site but also stabilizes surface intermediates during the methane oxidation, optimizing the reaction channel. An understanding of this cooperation of multiple active sites not only might be beneficial in developing improved catalysts for methane combustion but also might shed light on one advantage of heterogeneous catalysts with multiple sites in comparison to single-site catalysts for catalytic activity