Paper SS-TuP25
Reaction Properties of NO over the Rh/Al₂O₃/NiAl(110) Model Catalyst

Tuesday, October 16, 2007, 6:00 pm, Room 4C

The reduction of the noble metal content in the three-way automotive catalyst is currently required. In order to reduce noble metal loading, the enhancement of atomic efficiency of noble metal is an important subject. In this study, we investigated the NO reaction properties using Rh supported model catalyst. The model catalyst was prepared by deposition of Rh onto the Al₂O₃ thin film. It was shown that the NO dissociation activity on Rh deposited on Al₂O₃ is higher than that on Rh(111). Furthermore, we found that the NO dissociation activity on the Rh supported model catalyst increased by annealing treatment, where the activity increased with increasing heating temperature up to 500 K, and then decreased above 600 K. These results indicate that the atomic efficiency of Rh for NO dissociation is enhanced by supporting on Al₂O₃. To clarify the effect of Al₂O₃ support on Rh, we examined the NO adsorption state on the Rh supported model catalyst using IRAS. The IRA peak due to NO adsorbed on hollow site was observed at 1615 cm^-1 for the surface without heating, which agreed with the frequency observed for Rh(111). In contrast, the peak due to NO adsorbed on bridge site was newly observed at 1645 cm^-1 for the surface annealed to 500 K. Thus, we considered that the Rh surface structure changes from (111) face to (100) face by heating to 500 K. We previously found that the NO dissociation activity on Ir(100) was about twice of that on Ir(111), which was consistent with the relationship between the Rh supported model catalyst annealed to 500 K and Rh(111). Therefore, the enhancement of atomic efficiency of Rh is due to a change of the Rh surface structure to (100) face with a high NO dissociation ability. We concluded that the effect of Al₂O₃ support on NO dissociation is not electronic effect on Rh, but stabilization of (100) Rh surface structure.