Materials Science Division, Lawrence Berkeley National Lab, Berkeley, CA 94720, USA.
Science. 2010 Feb 12;327(5967):850-3. doi: 10.1126/science.1182122.
Stepped single-crystal surfaces are viewed as models of real catalysts, which consist of small metal particles exposing a large number of low-coordination sites. We found that stepped platinum (Pt) surfaces can undergo extensive and reversible restructuring when exposed to carbon monoxide (CO) at pressures above 0.1 torr. Scanning tunneling microscopy and photoelectron spectroscopy studies under gaseous environments near ambient pressure at room temperature revealed that as the CO surface coverage approaches 100%, the originally flat terraces of (557) and (332) oriented Pt crystals break up into nanometer-sized clusters and revert to the initial morphology after pumping out the CO gas. Density functional theory calculations provide a rationale for the observations whereby the creation of increased concentrations of low-coordination Pt edge sites in the formed nanoclusters relieves the strong CO-CO repulsion in the highly compressed adsorbate film. This restructuring phenomenon has important implications for heterogeneous catalytic reactions.
阶梯状单晶表面被视为实际催化剂的模型，这些催化剂由暴露大量低配位位点的小金属颗粒组成。我们发现，当铂（Pt）表面在高于 0.1 托的一氧化碳（CO）压力下暴露时，会发生广泛而可逆的重构。在接近环境压力的室温下的气态环境中进行的扫描隧道显微镜和光电子能谱研究表明，随着 CO 表面覆盖率接近 100%，原本平坦的（557）和（332）取向 Pt 晶体的梯级会分裂成纳米级簇，并在抽出 CO 气体后恢复到初始形态。密度泛函理论计算为这些观察结果提供了依据，即在形成的纳米簇中增加低配位 Pt 边缘位点的浓度可以缓解高度压缩吸附物膜中强的 CO-CO 排斥力。这种重构现象对多相催化反应具有重要意义。
