Novel reactivity and physical properties on transition metal carbide surfaces by controlling atomic structures and surface electronic states

通过控制原子结构和表面电子态来实现过渡金属碳化物表面的新颖反应性和物理性质

基本信息

批准号：
12450019
负责人：
IWASAWA Yasuhiro
金额：
$ 9.02万
依托单位：
The University of Tokyo
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (B)
财政年份：
2000
资助国家：
日本
起止时间：
2000 至 2001
项目状态：
已结题

项目摘要

Since the finding in 1970's that early transition metal carbides behave like noble metals rather than the native transition metals in surface catalysis, this class of materials has accepted great interests as potential substitutes for the precious noble metals in catalytic applications. The materials also show high activities for hydrodesulfurization and hydrodenitrogenation of hydrocarbons, which are relevant to environmental catalysis. Other than the catalysis, transition metal carbides of Group 4-6 have unique properties combining those of both metal and ceramics ; they are good electrical and thermal conductors typical of metals, while they possess ultra-hardness, very high melting points, and stable sub-stoichiometry typical of ceramics. Up to date, however, few groups have presented their investigations on single crystal surfaces of the chemically active transition metal carbides at atomic scale resolution which would address key issues for unique catalytic performances of the ma … More terials. We have successfully prepared well-ordered C-terminated surfaces on Mo_2C(0001) and obtained their images by scanning tunneling scanning tunneling microscopy (STM) for the first time.The structure of an α-Mo_2C(0001) surface varies depending on surface coverage of C atoms which was regulated by the annealing temperature and its period. By careful control of the preparation procedure, well-ordered C-terminated surfaces with (ν3xν3)R30-honeycomb structure and c(2x4)-zigzag row structure were successfully prepared and imaged by STM. It was revealed that each C atom inside the structures became visible as a shallow sombrero protrusion at low tunneling resistance less than 1 MΩ.Novel selective etching reaction of the surface carbon atoms by oxygen gas was found to occur even at room temperature. On a carbon terminated Mo_2C(0001) surface with both (ν3xν3)R30-honeycomb and c(2x4)-zigzag row structures, the etching reaction selectively occurred on the c(2x4)-zigzag row structure, leading to exposure of underlying (1x1) Mo layer. Less

自1970年代发现，早期过渡金属碳化物的行为像贵金属，而不是表面催化中的天然过渡金属，这类材料已经接受了极大的兴趣，作为催化应用中贵重金属的潜在底物。这些材料还显示出与环境催化有关的氢化氢化和氢化剂的高活性。除催化外，第4-6组的过渡金属碳化物具有将金属和陶瓷的特性结合在一起的独特特性。它们是典型的金属电气和热导体，同时具有超硬性，非常高的熔点以及典型的陶瓷的稳定的亚化学计量法。然而，最新的小组对原子尺度分辨率的化学活性过渡金属碳化物的单晶表面进行了研究，这将解决MA…更多terials的独特催化性能的关键问题。我们已经成功地在MO_2C（0001）上成功准备了良好的C端表面，并首次通过扫描隧道扫描隧道显微镜（STM）获得了图像。第一次。α-MO_2C（0001）表面的结构根据表面覆盖率而变化，该结构根据汽车原子的表面覆盖率而变化，而汽车原子及其被重新维护温度及其定期。通过仔细控制制备程序，通过（ν3xν3）R30-Honeycomb结构和C（2x4）-Zigzag行结构成功地制备了良好的C端表面。据揭示，由于低隧穿电阻在低于1MΩ的浅层浅骨突出时，结构内部的每个C原子都变得可见。即使在室温下，也发现了氧气通过氧气对表面碳原子的选择性蚀刻反应。在碳终止的MO_2C（0001）表面上，具有（ν3xν3）R30-HoneyComb和C（2x4） - Zigzag行结构，在C（2x4）-Zigzag行结构上选择性地发生蚀刻反应，导致下层MO层暴露于下层（1x1）MO层。较少的