Uwins P J, Millar G J, Nelson M L
Centre for Microscopy and Microanalysis, University of Queensland, Brisbane, Australia.
Microsc Res Tech. 1997 Mar 1;36(5):382-9. doi: 10.1002/(SICI)1097-0029(19970301)36:5<382::AID-JEMT8>3.0.CO;2-N.
Polycrystalline silver catalysts are used extensively for the partial oxidation of methanol to formaldehyde, which is then primarily incorporated in the synthesis process for adhesives and resins. In order to maximize formaldehyde production it is essential to gain a comprehensive understanding of the complex microstructural changes which occur in the catalyst during reaction conditions. However, conventional electron microscopic techniques are incapable of imaging catalysts at high temperatures and in the presence of a gaseous atmosphere. Therefore, an environmental scanning electron microscope (ESEM) has been used to image polycrystalline silver catalysts during simulated industrial conditions. The most dramatic effect of heating various catalysts to 700 degrees C in the ESEM chamber was the formation of "pinholes" in the silver surface. These "pinholes" occur at specific temperatures and are inherently associated with the catalytic process, resulting from near-surface explosions caused by subsurface hydroxyl recombination. Of particular interest was the nature and location of the holes, which preferentially occur in the vicinity of surface defects such as platelets and edge structures. To the best of our knowledge, this study represents the first time that the progress of a catalytic reaction has been observed under in situ conditions by scanning electron microscopy.
多晶银催化剂广泛用于将甲醇部分氧化为甲醛，而甲醛随后主要用于粘合剂和树脂的合成过程。为了使甲醛产量最大化，全面了解催化剂在反应条件下发生的复杂微观结构变化至关重要。然而，传统的电子显微镜技术无法在高温及气态气氛存在的情况下对催化剂进行成像。因此，环境扫描电子显微镜（ESEM）已被用于在模拟工业条件下对多晶银催化剂进行成像。在ESEM腔室中将各种催化剂加热到700摄氏度的最显著影响是在银表面形成“针孔”。这些“针孔”在特定温度下出现，并且与催化过程内在相关，是由亚表面羟基复合引起的近表面爆炸导致的。特别令人感兴趣的是这些孔的性质和位置，它们优先出现在诸如薄片和边缘结构等表面缺陷附近。据我们所知，这项研究首次通过扫描电子显微镜在原位条件下观察到催化反应的进程。
