Ambient 5 Cluster Catalysts Under Applied Conditions

The results of investigations of supported size-selected Pt cluster catalysts under ambient and more applied conditions is described in this chapter. Based on the successful experiments with unselected clusters and application under electrochemical conditions [1 ], within this work both unselected and selected cluster materials (of different sizes) are investigated. Exemplarily for selected sizes, in a highly collaborative approach, results on characterization, stability and reactivity are presented. 

With respect to experiments under ambient conditions, the previous approach [20] of cluster transfer for ex situ studies (see Sect. 2.3) is followed up, however with size-selected clusters. As a first step, characterization of the prepared materials is performed. Further, for reactivity studies a knowledge on the stability under reactive conditions is a prerequisite and thus the clusters are tested towards their temperature stability. Last, the reactivity of cluster catalysts is probed under different conditions, towards two different reactions. Various new experimental means are applied to probe and analyze Pt) clusters and serve as a perspective for future testing and application of cluster based materials. 

In the presented work different aspects of supported Pt cluster catalysts were studied under well defined UHV and applied ambient conditions. In the following the achieved results and gained insights are summarized. 

With respect to cluster catalysis under ambient and applied conditions, the results and the achieved insights can be benchmarked with the requirements for a successful catalyst material stated in the introduction (Fig. 1.2). A reproducible preparation, with respect to both size and coverage is evidenced on both local and integral level. In particular, the STEM results and the computer assisted analysis are introduced as a tool to monitor the deposition as well as changes after treatments. Using the data... 

Studying the influence of the precise size of the catalytically active species on reactivity is of major interest in catalytic research but is still extremely demanding. There are few examples carried out in the UHV showing that a catalytic process can indeed be tuned by the precise number of atoms in the catalyst. Under more realistic conditions, e.g. ambient pressure or liquid environment, such investigations are almost completely missing. Florian Schweinberger tackled in his doctoral thesis Catalysis with Supported Size-Selected Platinum Clusters Fundamental UHV and Applied Ambient Experiments both topics and presents results both from UHV and ambient studies. His work has been exceptionally well received and the doctoral thesis is particularly well written. 

Investigating the reactivity of supported size-selected metal clusters in order to contribute to the understanding of heterogeneous catalysis on a molecular level is the focus of interest in the nanocat lab. To work out the origin of size effects [23] and structure insensitivity [24] of heterogeneous catalysts, different systems and techniques have been successfully applied [20, 25-29]. Major milestones were the investigation of Pt, Au, Pd clusters towards their reactivity in the CO oxidation reaction [30-35] and the acetylene cyclotrimerization [24, 31, 36, 37] on Pd clusters. Further, in the last years successful experiments with clusters under ambient conditions have been performed [20, 38-40] and showed the possibility to use clusters for application to more realistic problems in heterogeneous catalysis. 

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