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

Abstract

Density functional theory calculations have been performed to elucidate the mechanism of N2O 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 N2O 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 N2O molecule and a N atom. We have scanned the potential energy surface forming N2O along different pathways, which involve a trapezoid OadNNOad dimer, an inverted trapezoid ONadNadO dimer, a zigzag ONadNOad dimer, or a rhombus ONadOadN dimer. The trapezoid dimer, OadNNOad, is found to be a necessary intermediate for the formation of N2O, 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.

A DFT study of the NO dissociation on gold surfaces doped with transition metals

“…10,17,29,43 One of the intermediates observed in the reduction of NO with CO is NCO, suggesting NO dissociation followed by reaction of an N adatom with CO. Interestingly, the NCO intermediate was not observed during the NO adsorption on Au/TiO 2 ; [44][45][46][47] but the formation of dinitrosyl complexes attached to the same Au atom, e.g., Au(NO) 2 species, either in the presence or in the absence of CO, 44,45 was detected. This suggests that the energy required to cleave the N-O bond is very high on Au/TiO 2 catalysts, which is in agreement with the results from the density functional theory (DFT) studies by Wang et al 48 for NO adsorption on the Au(111) surface. They correlated the formation of (NO) 2 dimers with the high activation energy barrier for the NO dissociation on Au(111) and suggested that the (NO) 2 dimers evolve to N 2 O.…”

“…48) on Au(111) and −0.50 eV on Au(110), or on the Ag doped gold surfaces, i.e., −0.36 eV on the Ag@Au(111) surface and −0.45 eV on the Ag@Au(110) surface, to high adsorption energy values as that calculated for NO interaction with the Ir@Au(110) surface (value of −3.26 eV). Adsorption energies more negative than −2.0 eV were also calculated for Ni and Rh doped Au surfaces.…”

“…13,21,[49][50][51] Vinod et al 52 considered the Au(310) surface model catalyst for investigating NO reduction on gold, concluding that the reaction mechanism based on bond dissociation of NO species is more plausible, which is surprising taking into account the high activation energy barrier (E act = ∼3.9 eV) associated to the reaction of NO dissociation on the Au(111) surface. 48 This is a very large value, especially, when compared with the NO dissociation energy barriers on surfaces of more reactive metals such as Ir(100), 53 Rh(111), 54 Rh(100), 55,56 or Rh(211), 54 surfaces, with E act = ∼0.5 eV, ∼1.4 eV, ∼0.4 eV, and ∼0.7 eV, respectively. However, other factors, such as the presence of promoters on the catalytic surface, may have an important role in reducing the large activation energies associated with the cleavage of the N-O bond on Au surfaces.…”

NO dissociation and reduction by H 2 on Pd(1 1 1): A first-principles study

“…What is the main pathway for N 2 formation? In addition, interestingly, (NO) 2 dimer was observed at room temperature by using infrared spectroscopy on Pd(1 1 1) surface recently, as demonstrated in the literature on some other surfaces including Au [4], Ag [26], Cu [27][28][29], Mo [30], Rh [31], Al 2 O 3 [32], MgO [33], and Si-doped graphene [34]. In experiment, N 2 O was observed at low temperature on ZrO 2 -supported Pd nanocatalysts [3].…”

“…The emission of NO not only causes a series of environmental problems such as photochemical smog, acid rain and ozone depletion [1][2][3], but also has adverse effect on humans. Therefore, the catalytic removal of NO has become one of the most important problems for air pollution control and attracted remarkable attention in both academic and applied research fields [4]. In the automotive industry, platinum group metals (PGMs) such as Pt, Pd, and Rh as the main components are involved in the three-way catalysts, which have often been used for the catalytic reduction of NO for several decades [5,6].…”