Role of Cooperative Effects in the Transition Metal Clusters

Role of Cooperative Effects in the Transition Metal Clusters 

In this section we expand the conclusions of the previous section to bare transition metal clusters in order to test them again and to identify another, cooperative (or cluster ) effect that affects the reactivity of transition metals. In practice, transition metals are important ingredients of heterogeneous and nano-catalysts, therefore clear understanding of their reactivity at electronic level is essential to unravel the secret of their catalytic activities. Diverse classes of experimental and theoretical studies already have provided a wealth of information concerning the electronic structure, spectroscopic as well as dynamic properties of variety types of clusters, including Ptn [6],Pdn [7],Fe+ [8],COn [9], and Nbn [10]. 

To unravel the reason behind the observed variation of reactivity as a function of cluster size [6,7], we have chosen to study the detailed mechanism of H2 and CH4 activation on small Pt and Pd (n=l-6) clusters. Results of these studies have already been pubhshed [ 12]. Here, we intend to analyze the factors controlling the reactivity of these clusters. 

our studies of the reactivity of Pd/Pt clusters with H2/CH4 molecules clearly show a cooperative effect that could play a significant role in the reactivity of the transition metal clusters. Thus, the catalytically inactive metal atoms could form very active clusters  

Another important factor controlling the reactivity of transition metal centers toward o-bond is their redox activity. Indeed, it is well established that transition metal centers with low redox potential can be active catalysts [ 14]. For example, let us discuss the reactivity in hydrocarbon hydroxyiation by Methanemonooxygenase (MMO). 

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