(641b) Methane Activation on Subsurface Boron Doped Copper: First Principles Investigation of the Structure, Activity and Electronic Properties of the Catalyst

Quang Thang Trinh,^1,2 Samir H. Mushrif ^1,*

¹School of Chemical and Biomedical Engineering, Nanyang Technological University, 62 Nanyang Drive, Singapore 637459, Singapore.

²Cambridge Centre for Advanced Research in Energy Efficiency in Singapore (CARES), Campus for Research Excellence and Technological Enterprise (CREATE), Singapore 138602, Singapore.

^*Email: SHMushrif@ntu.edu.sg

Abstract: Methane, the primary component of commercially exploitable resources like natural gas, shale gas and gas hydrates, with great potential to be converted to a variety of value added chemicals, still remains hugely underutilized.^1,2 Although being a commercial catalyst in the synthesis of methanol from syngas, or in the fabrication of graphene by chemical vapor deposition, high activation barriers on Copper (Cu) for C-H bond activation limits its application in methane utilization.^2,3 However in this study, using first principles calculations, we predict that Copper catalyst, when doped with a monolayer of subsurface Boron (Cu-B), can efficiently activate the C-H bond of Methane and can facilitate the C-C coupling reaction. Boron binds strongest in the subsurface octahedral site of Cu and the thermodynamic driving force for B diffusion from on-surface to the sub-surface position in Cu is stronger than that for Ni. Since, Ni doped with subsurface B was experimentally synthesized, ^4,5 we suggest that Cu doped with subsurface B (Cu-B) is also synthesizable. The presence of the monolayer subsurface B creates corrugated step-like structure on Cu surface and significantly brings down the methane C-H activation barrier from 170 kJ/mol on Cu(111) to only 74 kJ/mol on Cu-B. One of the major issues in methane activation on other transition metals is the complete decomposition of methane to carbon; but it is not the case for Cu-B. The dissociation of surface CH₂ on Cu-B is inhibited due to the high activation barrier of 161 kJ/mol. Moreover, C-C coupling between CH₂ fragments is feasible, with the activation barrier of only 53 kJ/mol; suggesting that Methane activation on Cu-B catalyst might have higher selectivity towards olefins. Evaluation of C-H activation on Cu(110) surface which has similar step-like structure as Cu-B shows that the geometrical/corrugation effect of Cu-B surface is not solely responsible for its high activity. Further analysis on Bader charge and Density of states reveal that there is a charge transfer from B to Cu, which synergistically promotes the C-H activation together with the geometrical/corrugation effect and makes the Cu-B as active for C-H activation as other expensive transition metals (Rh and Ni).⁶

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