Chemistry of Mesoporous Solids

Typical mesoporous silicas are more weakly acidic and less hydrothermally stable than zeolites, particularly at elevated temperatures, and for these reasons cannot be used as high-temperature cracking catalysts. Their chemistry is much 

Functionalised mesoporous silicas can be used for subsequent immobilisation of catalytic complexes. The large available pore space enables a very wide range of functional molecules and complexes to be immobilised in this way. Mesoporous silicas functionalised with alkylammonium ions can be used for anion exchange. This can be used to prepare the solids as the hydroxide form, which demonstrates basic character, or to ion exchange in anionic metal complexes, such as [AuCls] or [PtCU] . These species can subsequently be reduced to prepare finely dispersed metal particles throughout the pores.  

Although a common view of microporous solids is as fixed frameworks which are neutral or have a negative charge that permits cation exchange behaviour, they are rarely completely inert. To be of use, they should not lose their regular order upon template removal and should be able to withstand changes in 

The frameworks of some inorganic microporous solids show changes in dimensions and symmetry, for example as a result of dehydration or cation relocation much greater flexibility is observed in some MOFs where flexible organic linkers can change configuration and adapt to adsorption. In addition, the frameworks of aluminophosphates can tolerate redox behaviour of included transition metal cations and both AlPOs and silicates show variation in coordination around framework cations e.g. aluminium atoms in AlPOs, titanium atoms in zeotypic titanosilicates, and both aluminium and silicon atoms in fluoride-containing, as-prepared aluminophosphates or silicas, respectively). 

Zeolites were used as well-defined hosts with well-defined nanospaces that can be filled or used as reactors long before nanotechnology achieved its current popularity. Ship-in-a-bottle complexes, laser dyes and chromophore species, nanoparticulate oxides and sulfides and conducting wires and polymers have all been assembled in regular arrays within the pores. At present, cata-lytically active nanoparticles of supported metals remain the most widely applied of such composites. 

---