A density functional theory study of NO reduction promoted by Au4+ and Au4

Density functional theory (DFT) is used to study the NO reduction by H₂ on Au⁴⁺ and Au₄ clusters. The reaction mechanism is explored along two possible entrances: one involves the complexes of the clusters with H₂ and the other is related to the complexes of the clusters with NO. In all cases, it is found that the catalytic cycle involves two sequential elementary steps: the rupture of the H-H bond in H₂ and the formation of H₂O and N₂O molecule. The calculated results show that the reaction mediated by Au⁴⁺ is energetically most favorable compared to that promoted by Au₄, indicating that the charge state of Au clusters plays an essential role for the catalyzed NO reduction. The present theoretical study rationalizes the early experimental findings well and enriches our understanding of the catalytic NO reduction by Au-based catalysts.