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

小银颗粒：通过核磁共振、传导电子自旋共振和部分氧化反应中的催化行为进行表征

基本信息

批准号：
9019612
负责人：
M. Albert Vannice
金额：
$ 21.55万
依托单位：
Pennsylvania State Univ University Park
依托单位国家：
美国
项目类别：
Standard Grant
财政年份：
1991
资助国家：
美国
起止时间：
1991-09-01 至 1994-08-31
项目状态：
已结题

来源：
https://www.nsf.gov/awardsearch/showAward?AWD_ID=9019612&HistoricalAwards=false
关键词：
Small Silver Particles Characterization Nuclear

项目摘要

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.

该项目由两个奖项资助：普渡大学的 CTS 90-17692 和宾夕法尼亚州立大学的 CTS 90-19612。它研究粒径为 1 至 30 nm 的氧化铝或二氧化硅上高度分散的银颗粒的微晶尺寸、电性能和催化行为之间的相关性。进行的实验包括在干净的银和覆盖有氧 16 或氧 17 的银上吸附含有碳 13 的物质的固态核磁共振；小（小于 5 nm）银微晶的传导电子的传导电子自旋共振；乙烯在银上部分氧化（生成环氧乙烷）的同位素瞬态动力学研究。先前的研究表明，分散良好的二氧化硅负载的银催化剂在部分氧化过程中不会烧结；这些催化剂还表现出与分散不良的银/α-氧化铝催化剂相当的选择性，但助催化剂（二氯乙烷）浓度低得多。银上形成环氧乙烷的详细机制尚不清楚，但已证明地下氧的存在并与反应动态耦合。这项研究在一系列受控条件下检查了这些现象。乙烯氧化是一项全球性的、竞争非常激烈、价值数十亿美元的业务；即使流程效率的微小改进也会对竞争地位产生重大影响。这项工作直接解决了这个问题，并且对其他过程也有影响。