Small Silver Particles: Characterization by Nuclear MagneticResonance, Conduction-Electron Spin Resonance, and CatalyticBehavior in Partial Oxidation Reactions

该项目由两个奖项资助：CTS 90-17692，普渡大学 大学和CTS 90-19612宾夕法尼亚州 大学 这是一项研究， 微晶尺寸、电性能和催化性能 在氧化铝上高度分散的银颗粒的行为， 粒径为1 ~ 30 nm的二氧化硅。 实验 进行的包括固态核磁共振， 在干净的银和 用氧-16或氧-17覆盖的银;导电 电子自旋共振的传导电子的小 (less小于5 nm）银微晶;和同位素瞬变 乙烯部分氧化反应动力学研究 环氧乙烷）而不是银。 以前的研究已经表明 分散良好的二氧化硅负载的银催化剂不 部分氧化期间烧结;这些催化剂还表现出 选择性与分散不良的银/α- 氧化铝催化剂，但在低得多的促进剂（二氯乙烷） 浓度的 环氧乙烷的详细机理 在银上的形成是未知的，但是表面下的氧具有 被证明是存在的，并动态耦合到 反应 本研究在一系列的研究中考察了这些现象。 控制条件。 乙烯的双氧化是一个世界性的，非常有竞争力的， 数十亿美元的业务;即使是适度的改善， 流程效率对竞争力有重大影响 位置 这项工作直接解决了这个问题， 对其他过程也有影响。

This project is funded by two awards: CTS 90-17692 to Purdue University and CTS 90-19612 to the Pennsylvania State University. It is a study of the correlations between crystallite size, electrical properties, and catalytic behavior of highly dispersed silver particles on alumina or silica with particle diameters of 1 to 30 nm. Experiments performed include solid-state nuclear magnetic resonance of adsorbed species containing carbon-13 on clean silver and on silver covered with oxygen-16 or oxygen-17; conduction electron spin resonance of the conduction electrons of small (less than 5 nm) silver crystallites; and isotopic transient kinetic studies of the partial oxidation of ethylene (to ethylene oxide) over silver. Previous studies have shown that well-dispersed, silica-supported silver catalysts do not sinter during partial oxidation; these catalysts also exhibit selectivities comparable to poorly dispersed silver/alpha- alumina catalysts, but at much lower promoter (dichloroethane) concentrations. The detailed mechanism of ethylene oxide formation on silver is not known, but subsurface oxygen has been shown to be present and dynamically coupled to the reaction. This study examines these phenomena under a series of controlled conditions. The expoxidation of ethylene is a worldwide, very competitive, multibillion-dollar business; even modest improvements in process efficiency can have major impact on competitive position. This work addresses this issue directly, and also has implications for other processes.