C–H Bond Activation of Methane through Electronic Interaction with Pd(110)

The adsorption and interaction of methane on Pd(110) were investigated by vibrational spectroscopy, synchrotron-based X-ray spectroscopy, and first-principles density functional theory (DFT) calculations. The vibrational modes of methane are significantly perturbed by the interaction with the Pd surface. A redshifted C–H stretching vibration was detected by infrared reflection-absorption spectroscopy, indicating that C–H bonds in methane molecules are softened through the interaction with the Pd(110) surface. The electronic interaction was evidenced by carbon K-edge near-edge X-ray absorption fine structure spectroscopy, which shows the mixing between methane molecular orbitals and the substrate d-band. The adsorption configuration and vibrational modes of methane were calculated by the DFT method. The combined experimental and theoretical studies revealed that the interaction between methane and Pd(110) depends significantly on the adsorbed conformation of methane molecules, which is affected by the intermolecular interaction at a high methane coverage. The methane–substrate interaction is suppressed when oxygen is preadsorbed on Pd(110). The obtained spectroscopic results indicate that the coverage of oxygen is a key factor in the activation of methane on metal catalysts.