Ab Initio Study of the Adsorption of NO on the Rh₆⁺ Cluster

Abstract

The process of NO adsorption on the cationic cluster Rh(6)(+) is investigated using the density-functional theory (DFT) with the generalized gradient approximation (GGA) to exchange and correlation. We determine the geometries, electronic structure, and relevant energies for different structural and spin isomers of Rh(6)(0,±), and we study the consecutive adsorption of two NO molecules on the cationic cluster Rh(6)(+). With regard to the first NO molecule, different adsorption energies are found for the ground state octahedral structure of the bare cationic cluster and for the first isomer, which, having a prism-type structure, undergoes a structural transition to an octahedral symmetry upon dissociative adsorption of NO. Several dissociative NO adsorption processes are analyzed in comparison with molecular adsorption of NO to give support to the first step of the reaction inferred from experiments. With regard to the adsorption of a second NO molecule, the intermediate with lowest energy contains a preformed N(2) molecule. The energy of that complex is about 0.7 eV smaller than the sum of the free N(2) energy plus the lowest energy of the Rh(6)(+)-O(2) complex. This complex is composed of two separated O atoms occupying adjacent 2-fold bridging positions of the nearly undistorted Rh(6)(+) octahedral cluster. These findings are in qualitative agreement with experiments.

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.…”

Catalytic reduction of NO by CO on Rh4+clusters: a density functional theory study

“…One is made up of the (4), (5), and 2 × (6) reactions through N-O bond cleavage in the absence of CO, and another is composed of the (7), (8), (5), and (6) reactions through N-O bond cleavage in the presence of CO, denoted as the reaction pathways A and P IJRP-A and RP-P), respectively. In the side reaction (3) of NO + 3CO → CN + 2CO 2 , there is a unique reaction pathway that comprises the (7), (9), (10), and (6) reactions through N-O bond cleavage in the presence of CO. There is a unique reaction pathway in the side reaction (2) of NO + 2CO → NCO + CO 2 that is composed of the (7) and (9) reactions through N-O bond cleavage in the presence of CO.…”

“…By means of density functional theory (DFT) calculations, Ghosh et al have studied the binding of NO to small rhodium clusters including those composed of one to five atoms, 9 indicating that rhodium clusters may be good catalysts for NO reduction. 10 Xie et al have analyzed the NO adsorption and decomposition reaction mechanism on Rh 7 + clusters, which includes NO adsorption, NO decomposition to N and O atoms, and the reaction of the N atom with the second adsorbed NO and then reduction to the N 2 molecule. 10 Xie et al have analyzed the NO adsorption and decomposition reaction mechanism on Rh 7 + clusters, which includes NO adsorption, NO decomposition to N and O atoms, and the reaction of the N atom with the second adsorbed NO and then reduction to the N 2 molecule.…”

DENSITY FUNCTIONAL CALCULATIONS ON SPECTRUM AND ELECTRONIC PROPERTIES OFWNCO(N= 1 ~ 6) CLUSTERS

“…In the past few years, gas molecules adsorbed on transition metal clusters has been widely investigated owing to their unique physical and chemical properties, [1][2][3][4][5][6][7][8][9][10] such as extreme hardness, high melting point, chemical inertness, interesting catalytic behavior, etc. Carbon monoxide is one of the most important gases which participate in catalytic processes in heterogeneous phase.…”