Theoretical study of the crystal plane effect and ion-pair active center for C–H bond activation by Co3O4 nanocrystals

Abstract

Methane has attracted extensive interest in recent years due to its potential application as a replacement of oil and a feedstock for valuable chemicals. Due to the large C–H bond energy, the conversion of methane into useful products has been a challenge. In the present study, density functional theory (DFT) calculations were performed to study the activation of the C–H bond of methane on the (001) and (011) planes of Co3O4, which showed that CH4 activation on Co3O4 nanocrystals was fairly easy with only small energy barriers (less than 1.1 eV). Surface Co–O ion pairs are the active site for C–H bond activation, where the two ions provide a synergistic effect for the activation of the strong C–H bond and yield surface Co-CH3 and O–H species. The Co3O4(011) surface is shown to be more reactive for C–H bond activation than the Co3O4(001) surface, which is consistent with previous experimental results. Our results suggest that methane oxidation on Co3O4 nanocrystals has strong crystal plane effect and structure sensitivity and the ion-pair active center plays a significant role in activating the strong C–H bond.