Reduction and Oxidation Chemistry

It is possible to oxidise and reduce atoms in the framework and also those within the pores of microporous (and mesoporous) solids of appropriate chemical compositions. Although pure aluminosilicate, silicate and aluminophosphate frameworks cannot be oxidised or reduced, transition metal and some lanthanide cations within the framework can exist in different oxidation states. Also, although typical alkali, alkali metal and most lanthanide cations in extraframework positions possess no redox chemistry, transition metal cations such as nickel, copper and platinum do. In the case of the transition metals, this enables them to become important catalysts. The included sulfide species in ultramarine-related pigments described above are also prepared through the reduction of sulfate species. 

1 Reduction of Extra-framework Transition Metal Cations 

Transition metal cations such as Ni , Pd and Pt present as charge balancing cations as the result of cation exchange (for Pd and Pt as the ammine 

2 Redox Behaviour of Framework Transition Metal Cations 

In the examples discussed above, the transition metals are heteroatoms that occupy tetrahedral sites within the framework. There are also examples where transition metals occupy octahedral framework sites within a porous silicate framework. In the much studied titanosilicate ETS-10, in which the structure contains a mixture of octahedral titanium and tetrahedral silicon, a small fraction of the octahedral titanium may be reduced to Ti(III) by hydrogen. In addition, it is possible to include the lanthanide cerium into the mixed coordination microporous silicate AV-5. As described in Section 2.5.1, this 

---