ABSTRACT
Zeolites are a class of crystalline aluminosilicates and silicalites in which silicon and aluminum atoms are tetrahedrally linked by oxygen bridges, constructing threedimensional (3D) networks containing channels, pores, cages, and cavities.1 Zeolites then possess the properties of a high specic surface area and adsorption capacity. Having well-dened crystalline structures, zeolites contain quite uniform pores of molecular dimensions and the sizes of which are usually in the micropore region.2 This unique porosity endows zeolites with molecule-sieving abilities for discriminating guest molecules and partitioning of reactants/products. Only those molecules with the dimensions smaller than the entrance windows are allowed to diffuse into and out of the pores and channels, while the larger ones are excluded outside. The chemical compositions of the zeolite frameworks are changeable, not only in silica to alumina ratios but also in coordinated metal ions. Other than Si and Al, transition metals and many group elements, for example, P,3 B,4 Ga,5 Fe,6 Ti,7 Sn,8 Ge,9 Zr,10 V,11 and so on, can also be incorporated into the framework occupying the tetrahedral sites. Among them, the zeotype microporous materials of titanosilicate, tinsilicate, gemenosilicate, and ALPO, SAPO, and MeAPO are also recognized as zeolites with the enlargement and denition of zeolites. By introducing metal ions into the zeolite framework, the catalytic active sites and ion-exchange sites are generated.
