Synthesis of AFI aluminophosphate molecular sieves partly substituted with magnesium by dry-gel conversion method

Abstract

Aluminophosphate molecular sieves with AFI topology, in which framework Al 3+ is partly substituted with Mg 2+ (MgAPO-5), were synthesized by dry-gel conversion (DGC, including vapor-phase transport [VPT] and steam-assisted conversion [SAC]) method using triethylamine (Et 3N) as a structure-directing agent (SDA). Systematic studies were carried out in DGC method using different compositions of gel (concentration of Mg and SDA), amount of external bulk water and period of synthesis. MgO/Al 2O 3 ratios in the range of 0.025<MgO/Al 2O 3<0.10 gave pure MgAPO-5, and further increase in Mg-content caused contamination of MgAPO-34 with CHA topology. The amount of SDA played an important role, synthesized with a SDA/Al 2O 3 ratio of 0.38–0.76. Very minute amount of external bulk water was necessary for the crystallization. Appropriate crystallization time was 12–18 h. Incorporation of Mg 2+ into the framework was suggested by generation of acid sites and the change of unit cell parameters.