Nitric Oxide Adsorption and Reduction Reaction Mechanism on the Rh₇⁺ Cluster: A Density Functional Theory Study

Abstract

The transition metal rhodium has been proved the effective catalyst to convert from NO(x) to N(2.) In the present work, we are mainly focused on the NO adsorption and decomposition reaction mechanism on the surface of the Rh(7)(+) cluster, and the calculated results suggest that the reaction can proceed via three steps. First, the NO can adsorb on the surface of the Rh(7)(+) cluster; second, the NO decomposes to N and O atoms; finally, the N atom reacts with the second adsorbed NO and reduces to a N(2) molecule. The N-O bond breaks to yield N and O atoms in the second step, which is the rate-limiting step of the whole catalytic cycle. This step goes over a relatively high barrier (TS(12)) of 39.6 kcal/mol and is strongly driven by a large exothermicity of 55.1 kcal/mol during the formation of stable compound 3, accompanied by the N and O atoms dispersed on the different Rh atoms of the Rh(7)(+) cluster. In addition, the last step is very complex due to the different possibilities of reaction mechanism. On the basis of the calculations, in contrast to the reaction path II that generates N(2) from two nitrogen atoms coupling, the reaction path I for the formation of intermediate N(2)O is found to be energetically more favorable. Present work would provide some valuable fundamental insights into the behavior of the nitric oxide adsorption and reduction reaction mechanism on the Rh(7)(+) cluster.

Geometrical Structures of Partially Oxidized Rhodium Cluster Cations, Rh6Om+ (m = 4, 5, 6), Revealed by Infrared Multiple Photon Dissociation Spectroscopy

“…36 12 In our calculations, those in Rh6Om + were found to have a capped pyramidal geometry for m = 4 and a prismatic geometry for m = 5 and 6, which are now confirmed by the current spectroscopic experiments. The change of geometry of the Rh framework at m = 4 reduces the number of triangular hollow sites, on which N atoms prefer to sit when NO adsorbs dissociatively, from eight to six, 38,39 with only two triangular hollow sites available for Rh6O4 + . For Rh6O5 + , which has a prismatic structure, no sites are left.…”

Thermal Desorption and Reaction of NO Adsorbed on Rhodium Cluster Ions Studied by Thermal Desorption Spectroscopy

“…Xie and coworkers obtained a potential energy surface for the adsorption and dissociation of an NO molecule on the Rh 7 + cluster, as shown in Figure 1. 15 They found that the NO molecule first adsorbs on a hollow Rh 7 + site in molecular form, with an adsorption energy of −2.0 eV. In addition, it was found that a transition state exists for the dissociation of NO, with an energy barrier of 1.7 eV.…”

Structural isomers and low-lying electronic states of gas-phase M+(N2O)n (M = Co, Rh, Ir) ion–molecule complexes

“…Rhodium in particular plays a prominent role in the N 2 O reduction in the automobile three-way catalytic converter. This in turn led to many fundamental studies of rhodium cluster reactions with nitrogen oxides, 19,[25][26][27][28][29][30] including infrared-driven cluster surface reactions. [31][32][33] Here, we report a combined experimental and quantum chemical study of group 9 ion -N 2 O complexes, M + (N 2 O) n (M = Co, Rh, Ir) with the aim of investigating the fundamental interactions involved in the early stages of nitrous oxide reduction at heterogeneous catalysts.…”