Cluster Structure and Reactions: Gaining Insights into Catalytic Processes
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Cluster Structure and Reactions: Gaining Insights into Catalytic Processes A. W. Castleman Jr.
Received: 18 July 2011 / Accepted: 18 July 2011 / Published online: 9 August 2011 Ó The Author(s) 2011. This article is published with open access at Springerlink.com
Abstract To many researchers outside the field of cluster science it may come as a surprise that much can be learned of its relevance to catalysis, even restricting the discussion to ionized systems. This perspective is largely focused on catalytic oxidation reactions in which oxygen radical centers on transition metal oxides play a dominant role. The objective is to present how fundamental insights into reaction mechanisms can be gained through employing alternative approaches that complement rather than supersede more conventional methods in t he field of catalysis. In view of the well acknowledged role of defect centers in effecting reactivity, and the preponderance of recent papers presenting evidence of the importance of charged sites, the need/desire to conduct repetitive experiments is clear. Presented herein are approaches using clusters to accomplish this in order to unravel fundamental catalytic reaction mechanisms, and to use identified superatoms and the concepts of element mimics to tailor catalysts with desired functionality. Keywords Heterogeneous catalysis Catalysis Gas-phase kinetics Elementary kinetics Reaction intermediates Superatoms
1 Introduction Considering the global need for new sources of energy, enhanced methods of pollution abatement, advanced approaches to the production of fine chemicals, sensors for A. W. Castleman Jr. (&) Departments of Chemistry and Physics, The Pennsylvania State University, University Park, PA 16802, USA e-mail: [email protected]
the detection of harmful materials, as well as new methods of evaluating medical and biological issues, it is clear that catalysis, which impacts all of these, is one of the most important subjects for scientific investigation [1]. In view of the large diversity of reactions and accompanying physical phenomena involved, unraveling the fundamentals of catalytic processes requires a wide range of studies [2]. Clearly no single approach is sufficient to elucidate all of the issues which arise in unraveling catalytic processes, and advances in the subject benefit from well devised investigations of many types [3–6]. One valuable approach employs the use of clusters whose chemistry can be used to follow the course of reactions influenced by various reactive centers/defect sites, and the present invited perspective focuses on past developments and future prospects in this area [2, 5, 7–10]. While acquiring reproducible defect sites for the purpose of elucidating their influence on the course of catalytic reactions is an arduous task, it is a relatively straight forward procedure to recreate and conduct repetitive studies on model clusters which mimic specific reaction centers. There is growing evidence that sites of differing charge density can greatly influence reactions and the eff
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