The microscopic adsorption behavior of molecules including SO2 and NO on ultrafine precious metal particles was investigated by the density functional quantum chemical calculations. The precious metals particles, which are the sites of activation in the catalyst, were modeled by Pt5, Kh5 and Pd5 clusters. The adsorption energies (Eads) of the molecules calculated on the metal clusters were calculated. Three geometries of SO2 on the apex of Pt5 cluster (X) were considered(a) two O atoms interact with X (C2v symmetry; model-1), (b) one S atom interacts with X (C2v symmetry; model-2), and (c) one O atom interacts with X (Cs symmetry; model-3). The order of Eads values for the SO2 adsorption states on Pt5 clusters can be described as model-2 > model-3 > model-1. This result revealed the adsorption state of SO2 in which one Pt-S bond formed is the most stable energetically. The order of Eads for the SO2 adsorption state on different metal clusters can be described as Pt > Pd > Rh. It was also determined that the adsorption state of SO2 on metal clusters is less stable than that of NO and the order of adsorption stability on metal clusters is different for SO2 and NO molecules.
- Adsorption energy
- Density functional calculations
- Metal cluster
- Molecular adsorption