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Basic Research on the Mechanism of Catalytic Activity of Metal/Oxide Nano-Hetero Interfaces

金属/氧化物纳米异质界面催化活性机理的基础研究

基本信息

批准号：
16360319
负责人：
KOHYAMA Masanori
金额：
$ 9.79万
依托单位：
National Institute of Advanced Industrial Science and Technology (AIST)
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (B)
财政年份：
2004
资助国家：
日本
起止时间：
2004 至 2005
项目状态：
已结题

项目摘要

In order to elucidate the mechanism of catalytic activity of metal/oxide interfaces such as gold catalysts, we have applied the three methods ; electron microscopy observation, scanning probe microscopy (SPM) observation, and ab initio calculation, closely combined to each other. For Au/TiO_2 interfaces, the SPM observation has shown that the reduced Ti-rich TiO_2 surfaces have stronger attractive interactions with Au atoms or clusters, which is consistent with ab initio calculations indicating that Ti-rich or O-rich TiO_2 surfaces can make stronger adhesion with Au layers than stoichiometric surfaces. By ab initio calculations, we have made comparison between the simulated scanning tunneling microscopy (STM) image and the experimental STM image for the Au adsorption on the reduced Ti-rich surface, and we have also examined Pt/TiO_2 and Ag/TiO_2 systems for comparison. By applying the electron holography through the electron microscope to Au/TiO_2 catalysts, we observed that the mean inner potential in Au clusters suddenly increases for the cluster sizes less than 2-4 nm. The dependence of this phenomenon on the methods of sample preparation has been examined, and it seems that the interface dipole associated with O-rich interfaces is important for the potential increase. In this way, it can be said that the interface stoichiometry is the key for the catalytic activity. About the Au/CeO_2 system with remarkable catalytic activity, we have found dynamic and reversible shape changes of Au clusters deposited on CeO_2 during the electron microscopy observation, in accordance with easy formation and ordering of O-vacancies by electron beams. During this phenomenon, we have observed that the interface layer itself is tightly attached to the CeO_2 surface, where the interface is supposed to be off-stoichiometric. In any case, the dynamical shape changes of deposited metal clusters according to the atmosphere should be closely concerned with the catalytic activity.

为了阐明金催化剂等金属/氧化物界面的催化活性机理，我们采用了三种方法：电子显微镜观察，扫描探针显微镜（SPM）观察，从头计算，紧密结合在一起。对于Au/TiO_2界面，SPM观测表明，还原态富Ti的TiO_2表面与Au原子或团簇之间有较强的吸引作用，这与从头算结果表明富Ti或富O的TiO_2表面与Au层之间的粘附力比化学计量比表面更强相一致。通过从头计算，我们比较了Au在还原态富Ti表面吸附的模拟扫描隧道显微镜（STM）图像和实验STM图像，并比较了Pt/TiO_2和Ag/TiO_2体系。用电子显微镜对Au/TiO_2催化剂进行电子全息照相，发现当团簇尺寸小于2-4 nm时，Au团簇的平均内电位突然增大。这种现象的样品制备方法的依赖性已被检查，它似乎是与富O界面的界面偶极子是重要的电位增加。因此，可以说界面化学计量比是催化剂活性的关键。对于具有显著催化活性的Au/CeO_2体系，我们在电镜观察中发现了沉积在CeO_2上的Au团簇的动态可逆的形状变化，这与电子束作用下O空位的易形成和有序化是一致的。在这一过程中，我们观察到界面层本身与CeO_2表面紧密结合，这表明界面层是非化学计量的。在任何情况下，沉积的金属团簇的形状随气氛的动态变化应与催化活性密切相关。