Transition metal ions in microporous crystalline aluminophosphates: Isomorphous substitution

Microporous crystalline metalloaluminophosphates (MeAPO-n) represent an imp ortant group of molecular sieves because of their potential catalytic and a dsorptive properties. Many transition metal ions are claimed to incorporate in the framework of these molecular sieves. Here, the concept of isomorpho us substitution, and the different indirect and direct tools available to v erify this substitution process for Co, Cr, V, Fe and Mn are reviewed takin g the AlPO4-5 structure as an example. In addition, it will be shown that t ransition metal ions can be used as a probe to follow the hydrothermal synt hesis process of microporous aluminophosphates.