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

Activation of molecular O-2 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 O-2 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 O-2, but also transfer a hydrogen atom to the adjacent O-2, leading to O-2 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)(2)SiH2, etc.) to the co-adsorbed O-2 are lower than 0.50 eV in most cases, indicating the feasibility of the activation of O-2 via OOH under mild conditions. The formed OOH oxidant, with an increased O-O bond length of similar to 1.45 , 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 O-2 and atomic oxygen. This study reveals a new pathway for the activation of O-2, and may provide insight into the oxidation catalysis of nanosized gold.