Dynamic Frustrated Lewis Pairs on Ceria for Direct Nonoxidative Coupling of Methane

While the regulation of surface oxygen vacancy (V_O) of ceria is an effective methodology to construct solid frustrated Lewis pairs (FLPs), the intrinsic properties and potential applications of solid FLPs are not well-demonstrated. Herein, we present a theoretical study on the formation rules and dynamic behaviors of FLPs on CeO₂(110) and their performance on nonoxidative conversion of methane. The density functional theory studies show that the formation of solid FLPs on CeO₂(110) is dependent on the number of oxygen vacancies (V_Os). The FLPs constructed by three or more V_Os are stable in thermodynamics, whereas the FLPs containing few V_Os (i.e., V_O monomer and V_O dimer) are less stable but can be dynamically formed via thermal fluctuation and reactant-adsorption, as observed by ab initio molecular dynamics simulations. Hence, the general existence of FLPs on reduced CeO₂(110) surface under reaction conditions is revealed. Calculations on methane activation show that FLPs are active for C-H bond breaking with an activation energy as low as 0.63 eV, attributed to the enhanced acidity and basicity of FLPs. Because of the structure of FLPs, the subsequent dissociation of a second methane and the C-C coupling of CH₃ to form C₂H₆ is relatively prevailing at FLP sites, different from the popular gas-phase coupling mechanism. Ethane can be further dehydrogenated at FLP sites to form more valuable ethylene. On the basis of these findings, our study provides insights into the formation and dynamic behaviors of solid FLPs on CeO₂ and more importantly predicts a promising strategy for nonoxidative coupling of methane into more valuable chemicals on abundant oxide-based catalysts.