Transition Metal Ions in Microporous Crystalline Aluminophosphates: Isomorphous Substitution

Microporous crystalline metalloaluminophosphates (MeAPO-n) represent an important group of molecular sieves because of their potential catalytic and adsorptive properties. Many transition metal ions are claimed to incorporate in the framework of these molecular sieves. Here, the concept of isomorphous substitution, and the different indirect and direct tools available to verify this substitution process for Co, Cr, V, Fe and Mn are reviewed taking the AlPO4-5 structure as an example. In addition, it will be shown that transition metal ions can be used as a probe to follow the hydrothermal synthesis process of microporous aluminophosphates.