Dry Reforming of Methane Over Ru2/CeO2: Dynamic Behavior of Lattice Oxygen

The reverse oxygen spillover (ROS) process is a critical factor in the dry reforming of methane (DRM). However, the detailed mechanism remains unclear. In this study, we investigate the ROS process in Ru/CeO₂(111) (where n = 1, 2, 3, 4) using ab initio molecular dynamics simulations at realistic DRM reaction temperatures (1000 K). Our findings indicate that the ROS phenomenon is observed exclusively in the Ru₂/CeO₂ system, while it is absent in the Ru₁, Ru₃, and Ru₄/CeO₂ systems. Furthermore, additional investigations involving other transition metal (TM) systems, specifically TM₂/CeO₂ (where TM = Co, Ni, Pd, and Pt), reveal that ROS can also occur in the Co₂/CeO₂(111) system. The phenomenon of ROS is primarily attributed to two factors. First, an electronic structure analysis suggests that the strong metal–support interaction and strong “oxophilic” properties of certain transition metals, such as Ru and Co, are significant contributors to the ROS. Second, from a geometric perspective, the coordination between Ru₂ and the surface oxygen atoms of CeO₂(111) is asymmetric, with two Ru atoms coordinating to three surface oxygen atoms. This configuration provides for the possibility that one of the surface oxygen atoms spillover into the Ru₂ cluster. Notably, the coordination environment of the Ru clusters plays a more critical role than electronic properties in determining the occurrence of ROS. Through detailed calculations of the DRM reaction mechanism, we demonstrate that the oxygen vacancy created by the spillover process can facilitate CO₂ activation, while the lattice oxygen that spills from the interface can lower the energy barrier associated with the oxidation process. We anticipate that our findings will provide theoretical insights for the design of high-performance catalysts for DRM, emphasizing the importance of considering metal–support interactions at the metal–support interface.