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金属及合金的微晶(尺寸在0.5～30纳米)淀积在氧化物(Al_2O_3或SiO_2等)载体上作为化学反应活化中心的催化剂,在石油、化学等工业部门有着广泛的应用。对一种节约贵金属并有高的选择性和稳定性的Pt—Sn双金属催化剂(大连化物所研制)进行了高分辨电镜微观结构的研究。观察到Pt—Sn催化剂中具有规则外形(六角形、五角形、四角形等)并显示出一维及二维点阵象的微晶颗粒,以及在这些微粒中存在的微孪晶(多重孪晶)。甚至还观察到原子列的错排形成的位错。高分辨的点阵象结合选区电子衍射的分析结果,揭示了这种双金属催化剂中不同相的组成和结构。图1是一个铂—锡催化剂小颗粒的高分辨点阵象,揭示出小颗粒的微晶体本质。样品用环氧树脂包埋再用金刚石刀切成极薄的、适合高分辨观察的无衬底的小颗粒的试片。此外,在合成氨用的氧化铁催化剂中观察到氧化铁部分还原后,形成1～20纳米尺寸的纯铁微晶作为反应的活化中心,嵌在剩余的氧化铁的载体上。
Crystals of metals and alloys (0.5-30 nm in size) are deposited on oxides (Al 2 O 3 or SiO 2, etc.) as catalysts for the activation of chemical reactions and are widely used in petroleum, chemical and other industrial sectors. The microstructure of high-resolution electron microscopy was studied on a Pt-Sn bimetallic catalyst with high selectivity and stability, which is precious metal and has high selectivity. In the Pt-Sn catalyst, microcrystal particles having a regular shape (hexagonal, pentagonal, tetragonal, etc.) and exhibiting one-dimensional and two-dimensional lattice images and micro-twins (multiple twins) existing in these microparticles were observed . Dislocations formed by the misalignment of the atom columns were even observed. High-resolution dot matrix images combined with the analysis of selected area electron diffraction revealed the composition and structure of the different phases in this bimetallic catalyst. Figure 1 is a high-resolution lattice image of a small platinum-tin catalyst particle revealing the crystallite nature of small particles. Samples were embedded with epoxy resin and then diamond knife cut into very thin, suitable for high-resolution substrate-free small particles of the test piece. In addition, it was observed in the iron oxide catalyst for ammonia synthesis that partial reduction of iron oxide resulted in the formation of pure iron crystallites of 1 to 20 nanometers in size as the activation center for the reaction, embedded in the remaining iron oxide support.