AVS 57th International Symposium & Exhibition
    Surface Science Tuesday Sessions
       Session SS-TuP

Paper SS-TuP25
Creation of NO Dissociation Sites Over the Pd/Al2O3 Surface

Tuesday, October 19, 2010, 6:00 pm, Room Southwest Exhibit Hall

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
T. Fujitani, National Institute of Advanced Industrial Science and Technology (AIST), Japan
Correspondent: Click to Email
The reduction of Rh in three-way catalysts is currently required. Pd catalysts, which have shown a high initial activity for NO reduction compared with that of Rh catalysts, have received much attention as possible substitutes for Rh. To develop high performance Pd catalysts, the nature of active sites must be clarified, as well as the effect of oxide supports on the supported Pd. In this study, we investigated the influence of an Al2O3 support on the electronic state and NO dissociation activity of supported Pd using a Pd-deposited Al2O3/NiAl(110) surface. NO was exposed at 300 K to the 2 ML Pd/Al2O3 surfaces annealed at different temperatures. Only molecularly adsorbed NO was observed on the Pd/Al2O3 surface after deposition of Pd at 300 K. In contrast, the formation of atomic nitrogen was seen on the Pd/Al2O3 surface annealed above 350 K, suggesting that NO dissociation sites were created after annealing. The adsorbed NO was completely dissociated over the Pd/Al2O3 surface annealed above 500 K. We compared the NO dissociation activity over the 500-K–annealed Pd/Al2O3 surface with that observed over a stepped Pd(311) single crystal surface, since the step sites on Pd surfaces are known to be active sites for NO dissociation. It was clearly shown that the NO dissociation reaction over the Pd/Al2O3 surface proceeded at a much lower temperature compared with that required for NO dissociation over the Pd(311) surface. We found that the active sites created on the annealed Pd/Al2O3 surface had a high NO dissociation ability. To clarify the nature of the Pd active sites for NO dissociation, we examined the electronic state of the Pd particles deposited on the Al2O3 surface. It was shown that the Pd was oxidized to Pdn+ (n < 2) by lattice oxygen atoms in Al2O3 after annealing above 500 K. Therefore, we concluded that the positively charged Pdn+ species created by annealing the Pd-deposited Al2O3 surface at temperatures higher than 500 K were effective for NO dissociation at low temperatures.