| AVS 55th International Symposium & Exhibition | |
| Surface Science | Tuesday Sessions |
| Session SS-TuP |
| Session: | Surface Science Poster Session |
| Presenter: | I. Nakamura, National Institute of Advanced Industrial Science and Technology (AIST), Japan |
| Authors: | I. Nakamura, National Institute of Advanced Industrial Science and Technology (AIST), Japan A. Takahashi, National Institute of Advanced Industrial Science and Technology (AIST), Japan T. Fujitani, National Institute of Advanced Industrial Science and Technology (AIST), Japan |
| Correspondent: | Click to Email |
The reduction of the noble metal content in the three-way automotive catalyst (Rh, Pt, Pd/Al2O3-ZrO2-CeO2) is currently required. In order to reduce noble metal loading, the enhancement of atomic efficiency and suppression of oxidation and sintering of noble metal are important subjects. To overcome these subjects, the clarification of the supported metal state is necessary. In this study, we investigated the influence of oxide support on the structure of Rh and the NO reactivity using the Rh/Al2O3 and Rh/ZrO2 model catalysts. The model catalysts were prepared by deposition of Rh onto the Al2O3 and ZrO2 thin films. The NO dissociation activity on the Rh/Al2O3 model catalyst was higher than that on Rh(111). In contrast, the activity for the Rh/ZrO2 model catalyst was the same as Rh(111). Furthermore, the dissociation activity on the Rh/Al2O3 model catalyst increased by heating, but no enhancement by heating treatment was observed for the Rh/ZrO2 model catalyst. We thus considered that the Al2O3 support promotes the NO dissociation activity by changing the Rh surface structure. To clarify the effect of Al2O3 support on Rh, we examined the NO adsorption state on the model catalysts. The IRAS peak due to NO adsorbed on bridge site was observed at 1645 cm-1 for the Rh/Al2O3 model catalyst. For the Rh/ZrO2 model catalyst, the peak was seen at 1616 cm-1, which was attributed to NO on hollow site. These results indicate that the surface structures of Rh are (100) and (111) faces for the Rh/Al2O3 and Rh/ZrO2 model catalysts, respectively. We also confirmed that the exposed surfaces of Rh supported on Al2O3 and ZrO2 are the (100) and (111) face from a comparison with the rate and apparent activation energy for NO dissociation on Rh(100) and Rh(111). Thus, we found that the effect of Al2O3 support on Rh for an enhancement of NO dissociation activity is to stabilize the surface structure of the (100) face with a high NO dissociation ability. AFM measurements confirmed that the small Rh particles with 2.5 nm diameter were formed on the Rh/Al2O3 model catalyst. We concluded that the Al2O3 support affected the morphology of the Rh surface by stabilization of small Rh particle, resulting in the enhancement of NO dissociation activity.