Methanol-Selective Oxidation Pathways on Au Surfaces: A First-Principles Study

With density functional theory, all elementary steps of methanol (CH 3 OH) dehydrogenation and oxidation on atomic-oxygen-covered or OH-covered Au (111) surfaces are systematically studied. Our results suggest that on low oxygen coverage Au (111) surface the production of CH 2 O and CO start from α-H elimination and β-H elimination, respectively. The selective oxidation pathway is controlled by thermodynamics of the first step rather than kinetics. The overall energy barrier to produce CO is 0.39 eV corresponding to gas-phase methanol, which indicates that the reaction can proceed at low temperature. On high oxygen coverage Au (111) surface, the elimination of α-H and one β-H can take place simultaneously to form CH 2 O for the cooperative interaction of two nearby atomic oxygen. The missing observation of CH 2 O may come from the fact that the newly formed CH 2 O is ready to react with surface atomic oxygen and hydroxyl to form CH 2 OO(H) rather than desorption from the surface. The rate-limiting step of the oxidation of CH 2 OO(H) is the dehydrogenation of CHO 2 with an energy barrier of 0.95 eV. Also, the newly formed CH 2 O can be dehydrogenated by surface atomic oxygen to form CO and then to CO 2 with low energy barrier. Our results give good explanation for experimental observations and make up the discrepancy between experimental observation and previous theoretical work.