CO-induced morphological changes of Rh crystallites: Mechanisms, kinetics, and real-space imaging on the atomic scale
CO-induced morphological changes of Rh crystallites: Mechanisms, kinetics, and real-space imaging on the atomic scale
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CO 引起的 Rh 微晶形态变化：原子尺度的机理、动力学和实空间成像
DOI：
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发表时间：
1993
期刊：
影响因子：
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通讯作者：
A. Gaussmann
中科院分区：
文献类型：
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作者：
N. Kruse;A. Gaussmann
摘要：在 200 至 420 K 之间的不同温度和高达 10 -1 Pa 的压力下研究了 CO 与几乎半球形的 Rh 晶体（场发射器尖端）的反应。通过场离子显微镜（FIM）可以以原子分辨率观察到晶体的强烈形态变化。在 360 和 420 K 下与 CO 进行无场反应后，半球形 Rh 晶体似乎转变为多面体形状。这些晶体上不存在高折射率表面平面。也就是说，扭结位点主要用于分面。更一般地，重塑晶体的形态主要包含具有{001}、{011}、{111}和{113}对称性的平面。 CO 诱导的重组被发现是热激活的：首先在 240 K 的反应温度下观察到原子位移，但在 200 K 时不存在。使用（原子探针）脉冲场解吸质谱 (PFDMS)，在包含约 150 个原子位点的小选定表面区域中研究了潜在的反应机制和动力学。除CO 外，表面层始终含有Rh-亚羰基，Rh 0 (CO) x ( x = 1-3)。时间分辨测量（反应时间在 0.5 ms 和 0.1 s 之间）揭示了 Rh 0 (CO) 2 形成的温度依赖性延迟时间。该观察结果可以基于反应模型一致地解释，该反应模型导致在扭结位点位置中的Rh Rh 键断裂后释放移动的、吸附的Rh 0 (CO) 2 。更一般地说，在 FIM 中观察到的 Rh 晶体的结构变化很可能是由（热激活的）Rh 0 (CO) 2 在扭结处形成和分解以及整个表面的中间扩散引起的。本研究的结果表明，Rh 0 (CO) 2 可能是Rh 1 (CO) 2 形成的前体物质，正如在使用Rh/Al 2 O 3 模型催化剂的研究中观察到的那样。
Abstract The reaction of CO with Rh crystals of almost hemispherical shape (field emitter tips) was studied at various temperatures between 200 and 420 K and at pressures up to 10 −1 Pa. Strong morphological changes of the crystals could be observed with atomic resolution by field ion microscopy (FIM). After field-free reaction with CO at 360 and 420 K the hemispherical Rh crystals appeared to be transformed into polyhedral shapes. High-index surface planes were absent on these crystals. i.e.. kink sites were largely used up in faceting. More generally, the morphology of the reshaped crystals contained mainly planes with {001}, {011}, {111}, and {113} symmetry. The CO-induced restructuring was found to be thermally activated: atomic displacements were first observed at a reaction temperature of 240 K but were absent at 200 K. Using (atom-probe) pulsed field desorption mass spectrometry (PFDMS), the underlying reaction mechanisms and kinetics were studied in small selected surface areas containing about 150 atomic sites. Besides CO the surface layer always contained Rh-subcarbonyls, Rh 0 (CO) x ( x = 1-3). Time-resolved measurements (reaction times between 0.5 ms and 0.1 s) revealed temperature-dependent delay times for Rh 0 (CO) 2 formation. This observation could be consistently interpreted on the basis of a reaction model leading to the liberation of mobile, adsorbed Rh 0 (CO) 2 after Rh Rh bond breaking in kink site positions. More generally, the structural changes of Rh crystals observed in FIM were most likely caused by (thermally activated) Rh 0 (CO) 2 formation and decomposition at kinks with intermediate diffusion across the surface. The results of the present study suggest Rh 0 (CO) 2 to be the likely precursorspecies for Rh 1 (CO) 2 formation as observed in studies with Rh/Al 2 O 3 model catalysts.