lundi 25 juin 2018 à 14H00

CINaM - Salle Raymond Kern

Hisato Yasumatsu

Cluster Research Laboratory, Toyota Technological Institute: In East Tokyo Laboratory, Genesis Research Institute, Inc., Ichikawa, Chiba 272-0001, Japan

Low-temperature catalysis of electron donation owing to strong electronic interaction between platinum cluster and silicon substrate

It has been found that O₂ molecules are dissociated on a Pt cluster disk bound to a Si substrate, Pt_N/Si (N=10-60), at lower temperature by 150 K [1,2] than on the Pt(111) single-crystal surface [3], resulting in low-temperature CO oxidation. Considering the O₂ dissociation is driven by electron transfer to anti-bonding molecular orbitals of O₂, the cluster acts as a highly-efficient electron donor. Indeed, it has been found in our STM observation that electrons are accumulated at the sub-nano interface between Pt_N and the Si substrate [4,5] owing to strong electronic cluster-surface interaction. In this presentation, low-temperature dissociation of NO on the cluster disk is reported to show the universality of this cluster as well as in connection with catalytic NO reduction, which is indispensable to clean environment in use of combustion engines particularly at high air-to-fuel ratios (lean combustion) having high fuel efficiency but substantial nitrogen oxides, NOx, at low temperature. The size-selected cluster disks were prepared by cluster-impact [6] of size-selected cluster ions. The initiation temperature of the NO reduction was measured by means of temperature-programed desorption (TPD) of N₂ produced, while its turnover-rate (TOR) by continuous gas-flow reactions [7]. It was observed that the NO reduction proceeds on Pt_N/Si at lower temperature by 70 K than on the Pt(100) single-crystal surface [8]. Its rate-determining step was found to be the NO dissociation, so that it is reliable that the NO dissociation on Pt_N/Si takes place at the lower temperature. Furthermore, the TOR measurements show high chemical selectivity such that only N₂ but neither N₂O nor NO₂ are produced even with excess O₂, mimicking the exhaust gas of the lean combustion. It is concluded that the low-temperature catalysis of electron donation by Pt_N/Si has been demonstrated universally, considering the NO dissociation is also driven by the electron transfer to the anti-bonding molecular orbitals of NO. The resulting N adsorbates are combined each other to be N₂ with high efficiency, but combination between NO and N/O adsorbates are negligible. It is promising that this activity derives from the accumulated electrons.

[1] H. Yasumatsu, Encyclopedia of Interfacial Chemistry: Surface Science and Electrochemistry, ed. Klaus Wandelt (Editor-in-Chief), Elsevier, in press (2018); Book ISBN: 9780128097397.

[2] H. Yasumatsu and N. Fukui, J. Phys. Chem. C 119, 11217 (2015).

[3] J. Yoshinobu and M. Kawai, J. Chem. Phys. 103, 3220 (1995).

[4] H. Yasumatsu, T. Hayakawa and T. Kondow, Chem. Phys. Lett. 487, 279 (2010).

[5] H. Yasumatsu, P. Murugan and Y. Kawazoe, Phys. Stat. Solidi B 6, 1193 (2012).

[6] H. Yasumatsu and T. Kondow, Rep. Prog. Phys. 66, 1783 (2003).

[7] H. Yasumatsu and N. Fukui, Catal. Sci. Technol. 6, 6910 (2016).

[8] Y. Ohno et al. Chem. Phys. Lett. 373, 161 (2003).

Invitation : Claude Henry - Entrée libre