Mechanism of N2O Formation During NO Reduction on the Au(111) Surface

Density functional theory calculations have been performed to elucidate the mechanism of N 2 O formation over the Au(111) surface during NO reduction. It is shown that the dissociation of NO into an N atom and an O atom involves a barrier as high as 3.9 eV, implying that the formation of N 2 O does not occur via the direct dissociation mechanism of NO. Alternatively, we find that the reaction may occur via a dimer mechanism; i.e., two NO molecules initially associate into a dimeric (NO) 2, which then dissociates into a N 2 O molecule and a N atom. We have scanned the potential energy surface forming N 2 O along different pathways, which involve a trapezoid O ad NNO ad dimer, an inverted trapezoid ON ad N ad O dimer, a zigzag ON ad NO ad dimer, or a rhombus ON ad O ad N dimer. The trapezoid dimer, O ad NNO ad, is found to be a necessary intermediate for the formation of N 2 O, and the calculated barrier for the rate-determining step along the energetically most favorable pathway is only 0.34 eV. The present results rationalize the early experimental findings well and enrich our understanding of the reduction of NO on the Au surface.