Current Approaches to Nanostructured Catalysts

The following sections are organized into two parts. The first presents a brief overview of several approaches to preparing nanostructured supports and catalysts that are under current development. Approaches that incorporate building blocks in either part of the system (catalyst or support) will be highlighted. The second part describes a new approach to preparing nanostructured catalysts that we are currently developing in our laboratories. 

However, as mentioned above, a compromise must be made between low loading and reasonable activity. Furthermore, although hydroxyl groups may on average appear to be well separated on a dehydroxylated surface, there is evidence 

In this context, much effort has also been invested in controlling the nuclearity of the catalyst ensemble through the selection of its precursor. One area in which considerable progress has been made involves the adsorption of polynuclear clusters onto supports [33]. Examples involving the immobilization of small, preformed polynuclear clusters on supports are the reactions of carbonyl clusters of the late metals [16, 34], the binding of polyoxometalates (POMs) and their neutral alkoxy analogues [35] and heteropolyacids such as the Keggin cluster [36, 37]. 

Supported nanoparticles are related to the idea of starting with polynuclear cluster precursors. While there is no clear line that divides polynuclear clusters from nanoparticles, clusters are generally small, low nuclearity (MnL n = 3-20), structurally well-characterized species approximately 1-2 nm in size. Nanoparticles are larger ( 2 nm) and frequently defined by a size distribution rather than a discrete number of atoms and ligands [41]. In the area of catalysis, gold nanopar- 

Within a discussion of nanostructured catalysts, mention must be made of zeolitic systems. Zeolites are a broad family of natural and synthetic aluminosiU-cates that exhibit two important properties that makes them ideal for consideration as heterogeneous catalysts they are crystalline and porous. Crystallinity brings with it precise definition at the atomic scale that is absent with amorphous or polycrystaUine metal oxides. The combination of a well-defined structure and 

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