Metallophosphate Zeotypes and Related Materials

A wider and chemically different range of heteroatomic substitutions is possible in aluminophosphates than in zeolites. This is partly because the framework 

Divalent metals that have been substituted for aluminium in the framework include Mg, Mn, Fe, Co and Zn. Typically the negative charge imparted to the framework is balanced in the as-prepared sample by protonated amines or alkylammonium cations incorporated during synthesis, and a typical composition can be described as 

Removal of the templates from MgAPOs by calcination in oxygen can result in bridging hydroxyl groups or in the generation of Lewis acid sites which are thought to be Mg cations that are not fully tetrahedrally coordinated within the framework. In the case of transition metals such as Mn, Fe and Co , calcination in oxygen results in the oxidation of some or all of the cations to the trivalent state. These can then be reduced back to the divalent state and protons introduced (Chapters 3 and 9). For substituted metal cations that show no redox behaviour, such as calcination results in solid acid catalysts, 

Phosphorus has been most successfully substituted by silicon, although there are many reports that other elements, including titanium and vanadium, can be introduced. The direct replacement of isolated phosphorus atoms by silicon atoms results in a negatively charged framework and, upon calcination, an add site. Since this can take the form of a bridging hydroxyl between aluminium and silicon atoms, it is similar in character to those found in aluminosilicate zeolites. 

Metal phosphates with distinctive, fully tetrahedrally coordinated frameworks have also been prepared for metals such as beryUium, cobalt, zinc and gallium, although gallophosphates often show mixed coordination geometry. Pure templated cobalt phosphates and cobalt aluminium phosphates with high 

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