Role of the Interface between Pd and PdO in Methane Dissociation

Dissociation of the first C-H bond of methane was investigated at the interface of partial PdO(101) monolayer and supporting Pd(100) surface with density functional calculations. Activation pathways of CH(4) on the bulk PdO(100), PdO(101), Pd(100), and Pd(100) supported PdO(101) monolayer surfaces were also examined. The PdO(101)@:Pd(100) boundary enables several new routes for methane dissociation compared to the bulk surfaces, the lowest activation energy barrier being 0.8 eV. The barrier on the most stable and dominant bulk PdO(100) surface is as high as 1.2 eV, whereas on the lower proportion bulk PdO(101) surface it is only 0.5 eV. However, the corresponding barrier increases to 1.2 eV in the case of supported PdO(101) monolayer. A low activation energy of 0.7 eV is observed also on the Pd(100) surface, however, the reaction enthalpy on the metal surface is not as favored as on oxide surfaces or at the phase boundary. Hydrogen diffusion from metal to oxide phase can improve the reaction enthalpy, but it causes increase in the total activation energy. Overall, the results indicate that the presence of phase boundary between PdO and Pd enhances the activity in methane combustion, rationalizing experimental findings.