Zeolite catalysis structural complexity, active sites

The predominant importance of the cations in zeolites is that they form so-called active sites for selective interaction with guest molecules in sorption and catalytic processes. From the point of view of advanced material science [47] they play a significant role in the formation of quantum-sized clusters with novel optical or semiconducting properties. As they give rise to cationic conductivity, zeolites can be used as solid electrolytes, membranes in ion-selective electrodes and as host structures in solid-state batteries. Organometallic compounds and coordination complexes can be readily formed on these cations within the larger cages or channels and applied to gas separation, electron-transport relays and hybrid as well as shape-selective catalysis [48]. 

This area also includes the introduction of additional catalytic sites in zeolites by organometallic precursor compounds. Both the adjustment of Brpnsted/Lewis acidity and the directed fixation of active transition metal centers inside zeolite cages and channels seem possible, but the size and structures of these precursors will be crucial. The molecular modification appears all the more important as many catalytic processes will remain heterogeneous in nature, especially when the shape-selectivity of sodalites, zeolites, pentasils, etc. is exploited. Once again, the possible versatility of organolanthanoid complexes deserves emphasis, since these metals verify to the above-mentioned acidity and catalysis effects [92]. 

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