Molecular Sieves: Aluminophosphates

Abstract

Aluminophosphate molecular sieves exhibit structural and compositional diversity. Their frameworks can be modified by other elements, thus providing novel silicoaluminophosphate (SAPO), metaloaluminophosphate (MAPO), and metalosilicoaluminophosphate (MAPSO) materials. They possess the characteristics of both zeolites and aluminophosphates, all of which result in unique catalytic, ion-exchange, and adsorbent properties. Aluminophosphate molecular sieves have been prepared hydrothermally in nonaqueous reaction media. The crystallization process depends on a number of variables including temperature, time, molar ratio of the reactants, and pH. The most commonly investigated metal ions incorporated into aluminophosphate frameworks are transition metal ions of first transition series. Different characterization techniques are used for studying their oxidation number, location, and coordination environment within aluminophosphate frameworks. These parameters, together with structural characteristics of the framework such as pore size, pore shape, and geometry, significantly affect the catalytic performance of aluminophosphate materials. Methanol-to-olefin conversion and oxidation reactions are instances of industrially important reaction systems where aluminophosphate molecular sieves demonstrate an important catalytic performance