Cluster-Catalysed Hydrogenation Reactions

Although the true nature of the catalyst is not always clear when mononuclear complexes are used as pre-catalysts in hydrogenation reactions, with cluster compounds employed as the pre-catalyst, it is frequently found that the active species is colloidal and review articles are available on how to distinguish between homogeneous and heterogeneous regimes.[43,441 A summary of hydrogenation reactions with metal-clusters in ionic liquids is provided in Table 3.4. 

The performance of four different anionic carbonyl clusters in the hydrogenation of styrene, viz [HFe3(CO)n], [HWOs3(CO)i4] , [H3Os4(CO)i2] and 

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Table 3.4 Cluster-catalysed hydrogenation reactions in ionic liquids...

Catalysis by Metal Ousters in Zeolites. There is an increasing interest in the use of metal clusters stabilized in zeolites. One objective of such work is to utilize the shape and size constraints inherent in these support materials to effect greater selectivities in typical metal-catalysed reactions. Much work has been concerned with carbon monoxide hydrogenation, and although the detailed nature of the supported metals so obtained is not well understood, there is clear evidence of chain limitation in the Fischer-Tropsch process with both RuY zeolites and with HY and NaY zeolites containing Fe3(CO)22- In the former case there is a drastic decline in chain-growth probability beyond C5- or C10-hydrocarbons depending upon the particle size of the ruthenium metal. 

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