US-Poland Joint Fund Research on Reactivity of Silver Clusters in Zeolites

这个由华沙核化学与技术研究所辐射化学与技术系的Jacek Michalik博士和休斯顿大学化学系的Larry Kevan博士共同资助的美国-波兰Marie Sklodowska-Curie联合基金研究项目，题目是“沸石中银团簇的反应性”。研究人员将探索小银团簇的反应性，作为银团簇在多相催化中的应用的一个入口。本研究的关键在于将聚类大小控制在较窄的范围内。许多生成方法导致较大的尺寸分布。限制这种情况的一种方法是在分子筛中发现的分子筛分子筛中，在分子大小的笼子或通道中产生金属团簇。除了ESR和相关的光谱学（红外和漫反射），研究人员提出了一种称为电子自旋回波调制（ESEM）的脉冲ESR方法，作为表征沸石中银簇物种反应性的主要新工具。通过分析与弱电子-核偶极相互作用相关的调制信号，可以确定顺磁性物质与吸附分子的配位几何。在有利的情况下，它应该提供其他技术难以获得的结构细节，如吸附质分子的数量，它们的取向以及反应过程中配位几何的变化。因此，结合ESR、ESEM、漫反射光谱和红外光谱，这将提高我们对金属团簇的多相催化机理的认识。该放射化学项目通过使波兰和美国的领先专家在共同感兴趣和能力强的领域结合互补人才和汇集资源，实现了推进科学知识的计划目标。

This US-Poland Marie Sklodowska-Curie Joint Fund research project between Dr. Jacek Michalik of the Department of Radiation Chemistry and Technology, Institute of Nuclear Chemistry and Technology, Warsaw, and Dr. Larry Kevan, Department of Chemistry, University of Houston, is on "Reactivity of Silver Clusters in Zeolites." The researchers will explore the reactivity of small silver clusters as an entry into the utilization of silver cluster species in heterogenous catalysis. The critical aspect of this study is to control the cluster size within narrow range. Many generation methods lead to a broad size distribution. One method to limit this is to produce the metal clusters within a molecular size cage or channel as one finds in molecular sieves called zeolites. In addition to ESR and associated optical spectroscopies (infared and diffuse reflectance), the researchers propose a pulse ESR method known as Electron Spin Echo Modulation (ESEM) as a major new tool in characterizing the reactivity of silver cluster species in zeolites. By analyzing the modulation signal associated with weak electron-nuclear dipolar interactions, it is possible to determine the coordination geometry of paramagnetic species with adsorbed molecules. In favorable cases this should provide the structure details, not readily obtainable by other techniques, such as the number of adsorbate molecules, their orientation as well as the changes of coordination geometry in the course of reaction. Thus, rather detailed structural information about reaction intermediates can be obtained by using a combination of ESR, ESEM, diffuse relectance and infrared spectroscopies which will improve our knowledge about the mechanism of heterogenous catalysis on metal clusters. This project in radiation chemistry fulfills the program objective of advancing scientific knowledge by enabling leading experts in Poland and the United States to combine complementary talents and pool resources in areas of strong mutual interest and competence.