In addition to their natural appeal as crystalline solids possessing a void intracrystalline volume consisting of channels
and cages, sometimes interconnected, zeolites also have remarkable features resulting from the surface curvature of their
internal surface. These features involve non-covalent interactions between the framework of the zeolite and molecules
adsorbed in their intracrystalline free space. These interactions extend beyond the molecular level and are thus of
supramolecular nature. They are at the origin of confinement effects which govern their behaviour as sorbents and catalysts.
By contrast to molecular shape selective effects which result from short range repulsions imposing restrictions on sorbates or
reactants, reaction transition states, andror products, the van der Waals interactions responsible for confinement effects are
long ranged and attractive. They favour the adsorption of certain molecules vs. others, sometimes at specific locations in the
intracrystalline volume, stabilise reaction transition states, and may eventually enhance the probability of bimolecular
reactions. Because of such confinement effects, zeolites can be assimilated to solid solvents and several of their
characteristics can be described using solvent effects as an analogy. This review analyses recent literature supporting this
view with specific attention to the application of zeolites in selective adsorption and separation and their use as catalysts for
fine chemicals synthesis. Some other consequences of confinement effects will also be discussed, in particular those relating
to the measurement and optimal use of the acidic properties of zeolites.
In addition to their natural appeal as crystalline solids possessing a void intracrystalline volume consisting of channelsand cages, sometimes interconnected, zeolites also have remarkable features resulting from the surface curvature of theirinternal surface. These features involve non-covalent interactions between the framework of the zeolite and moleculesadsorbed in their intracrystalline free space. These interactions extend beyond the molecular level and are thus ofsupramolecular nature. They are at the origin of confinement effects which govern their behaviour as sorbents and catalysts.By contrast to molecular shape selective effects which result from short range repulsions imposing restrictions on sorbates orreactants, reaction transition states, andror products, the van der Waals interactions responsible for confinement effects arelong ranged and attractive. They favour the adsorption of certain molecules vs. others, sometimes at specific locations in theintracrystalline volume, stabilise reaction transition states, and may eventually enhance the probability of bimolecularreactions. Because of such confinement effects, zeolites can be assimilated to solid solvents and several of theircharacteristics can be described using solvent effects as an analogy. This review analyses recent literature supporting thisview with specific attention to the application of zeolites in selective adsorption and separation and their use as catalysts forfine chemicals synthesis. Some other consequences of confinement effects will also be discussed, in particular those relatingto the measurement and optimal use of the acidic properties of zeolites.
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