posted on 2017-11-01, 00:00authored byTianchao Niu, Zhao Jiang, Yaguang Zhu, Guangwen Zhou, Matthijs A. van Spronsen, Samuel A. Tenney, J. Anibal Boscoboinik, Dario Stacchiola
The
role of oxygen in the activation of C–H bonds in methane
on clean and oxygen-precovered Cu(111) and Cu2O(111) surfaces
was studied with combined in situ near-ambient-pressure scanning tunneling
microscopy and X-ray photoelectron spectroscopy. Activation of methane
at 300 K and “moderate pressures” was only observed
on oxygen-precovered Cu(111) surfaces. Density functional theory calculations
reveal that the lowest activation energy barrier of C–H on
Cu(111) in the presence of chemisorbed oxygen is related to a two-active-site,
four-centered mechanism, which stabilizes the required transition-state
intermediate by dipole–dipole attraction of O–H and
Cu–CH3 species. The C–H bond activation barriers
on Cu2O(111) surfaces are large due to the weak stabilization
of H and CH3 fragments.