Methane is a potential feedstock for the production of petroleum and coal derived chemicals and fuels. Screening potential metal/metal oxide catalysts for its selective activation and deriving mechanistic insights into the activation processes are pertinent for developing/optimizing processes for its utilization. Metal oxides have been shown to be effective in activating C-H bonds of methane1-2 and of sugars3. In this investigation, we evaluate the potential of CuO as a catalyst for the C-H bond activation of methane and derive insights into the roles of the metal and lattice oxygen atoms in the activation process. First principles calculations reveal that the C-H bond of methane can be dissociated with barriers as low as 76.6 kJmol-1 on the CuO(111) surface, if the under-coordinated lattice Cu-O pair synergistically participates in the process. The significantly low activation barrier is due to 1) the stabilization of the transition state (TS) and 2) the stabilization of the co-adsorbed products of dissociation. The surface copper atom adds to the C-H bond of methane, while the surface lattice oxygen simultaneously abstracts the hydrogen via a 4-centered (CH3-(Cu)--H-(O)) TS. The charge transfer interactions in this mechanism (Cu→CH3---H→ O→ Cu) generate Cu--CH3 and O--H dipoles, stabilizing the TS by their interaction. Both, CuO(111) and CuO(-111), surfaces are more efficient than chemisorbed oxygen containing Cu(111) surface in activating methane by this mechanism. Alternatively, methane activation may also proceed via a mechanism involving only hydrogen abstraction by the oxygen species, with higher activation barriers though. Further dissociation of the surface CH3 moiety and coupling reactions of the dissociated species on CuO(111) have significantly higher barriers, suggesting the potential of this surface to selectively generate CH3 species.4 The nature and strength of metal-oxygen bonding in the metal oxide and their different facets have implications on the stabilization of both, the TS and the products of dissociation, and thus may dictate reaction pathways on these surfaces. The mechanistic insights on the role of metal-oxygen site pair towards activation of methane can be extended to other transition metal oxides. REFERENCES 1. Chin et al., J. Am. Chem. Soc. 2013, 135, 15425 2. Weaver et al., Chem. Soc. Rev. 2014, 43, 7536 3. Amaniampong et al., Angew. Chem. Int. Ed. 2015, 54, 8928 4. Guo et al., Science 2014, 344, 616

Metal-lattice oxygen site pairs in four-centered C-H bond activation of methane

251st National Meeting (2016)

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