Methane Activation on Metal-Doped (111) and (100) Ceria Surfaces with Charge-Compensating Oxygen Vacancies

Reducing the temperature for methane activation is an important objective that would benefit many technological applications. In this work, we explore the possibility to achieve this goal using single-atom catalysts (SACs) on ceria surfaces. We focus on Ag SACs, which have recently been suggested to be promising catalysts for both H-2 and CH4 oxidation. Using first-principles calculations, we investigate methane activation on CeO2 (111) and CeO2 (100), two frequently exposed surfaces on ceria nanoparticles. The presence of Ag is found to reduce the activation energy for methane dissociation on both surfaces. On Ag-doped CeO2 (111), the formation of methanol via the Mars-van Krevelen mechanism has a slightly lower energy barrier than the dissociation to CH3 + H, suggesting that methanol is a likely product of methane activation on this surface. A novel aspect of this work is the focus on stable surface structures where each Ag dopant substituting Ce forms a complex with a charge-compensating surface oxygen vacancy. These complexes are found to play a critical role and accounting for their presence is essential for a proper description of the surface reactivity.