Tight-Binding Quantum Chemical Molecular Dynamics of Oxygen Migration of Rh-supporting CeO 2 Surfaces
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Tight-Binding Quantum Chemical Molecular Dynamics of Oxygen Migration of Rh-supporting CeO2 Surfaces Ai Suzuki, Ryuji Miura, Nozomu Hatakeyama, Akira Miyamoto 1
New Industry Creation Hatchery Center (NICHe), Tohoku University, Sendai, 980-8579, Japan
ABSTRACT The electronic properties of the interface between Rh clusters and CeO2 (111), (110) and (100) surfaces were studied using an isothermal-isobaric (NPT) ensemble at 773 K and 101.343 kPa using the tight binding-quantum chemical molecular dynamics (TB-QCMD) method. The amount of electronic exchange by interaction at the interface between the supported Rh55 clusters and each CeO2 surface was investigated quantitatively. A comparison of the mean square displacement (MSD) showed that the topmost oxygens on the Rh-supporting CeO2 surface exhibited higher mobility than those of the bare CeO2 surface. Although the mobility of the topmost oxygens on the bare CeO2 surface was in the order (100) > (110) > (111), this sequence was altered by the presence of Rh, so that the oxygen mobility for the more open (110) surface was the largest. The amount of electron exchange that occurred between Rh and the CeO2 (110) surface was also larger than for the (111) or (100) surface. The Ce 4f orbitals on the CeO2 (110) surface exhibited the strongest mixing with Rh 4d orbitals, which simultaneously caused restructuring and instability of the topmost Ce-O bonds. This enhancement of oxygen migration in the presence of Rh was occurred together with an increase in the number of oxygen vacancies on the ceria surface. This was because the topmost oxygens was shifted to have a stronger affinity with Rh and thus formed stronger bonds with Rh than with Ce.
INTRODUCTION Chemical interaction between noble metals and the cerium oxide is a prerequisite for industrially important catalytic reactions such as the three way catalysts. Especially, there are two prominent important characteristics in the noble metals/cerium oxide system those have been intensively investigated so far, the one is the SMSI (strong metal-support interaction) and the other is the OSC (Oxygen storage and release capacity). The former affects on the tendency of sinterability and durability of supported noble metal catalysts, and the latter governs the reactivity of catalysis. To clarify these two fundamental features with deep insight into the surface atomic mobility has a definable impact on the advancement of science, technology, and the field of physical chemistry. In particular, the combination of the Rh-CeO2 has the most
prominent for both effects among the various possible noble metals-CeO2 combinations. Therefore, new theoretical methodology was developed and applied to cover the surface mobility and analyze the electronic structure. We have introduced tight-binding quantum chemical molecular dynamics (TB-QCMD) method for better understanding of the influence of Rh on both the SMSI and the enhancement of oxygen mobility governing the OSC. This study explains the reason why the oxygen migration was enhanced in the
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