Hydrogenation of molecular oxygen to hydroperoxyl： An alternative pathway for O2 activation on nanogold catalysts

Activation of molecular O2 is the most critical step in gold-catalyzed oxidation reactions; however, the underlying mechanisms of this process remain under debate. In this study, we propose an alternative O2 activation pathway with the assistance of hydrogen-containing substrates using density functional theory. It is demonstrated that the co-adsorbed H-containing substrates （R-H） not only enhance the adsorption of O2, but also transfer a hydrogen atom to the adjacent O2, leading to O2 activation by its transformation to a hydroperoxyl （OOH） radical species. The activation barriers of the H-transfer from 16 selected R-H compounds （H2O, CH3OH, NH2CHCOOH, CH3CH=CH2, （CH3）2SiH2, etc.） to the co-adsorbed O2 are lower than 0.50 eV in most cases, indicating the feasibility of the activation of O2 via OOH under mild conditions. The formed OOH oxidant, with an increased O-O bond length of -1.45 A, either participates directly in oxidation reactions through the end-on oxygen atom, or dissociates into atomic oxygen and hydroxyl （OH） by crossing a fairly low energy barrier of 0.24 eV. Using CO oxidation as a probe, we have found that OOH has superior activity than activated O2 and atomic oxygen. This study reveals a new pathway for the activation of O2, and may provide insight into the oxidation catalysis of nanosized gold.