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

Aluminophosphate molecular sieves with AFI topology, in which framework Al3+ is partly substituted with Mg2+ (MgAPO-5), were synthesized by dry-gel conversion (DGC, including vapor-phase transport [VPT] and steam-assisted conversion [SAC]) method using triethylamine (Et3N) 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/Al2O3 ratios in the range of 0.025<MgO/Al2O3<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/Al2O3 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 Mg2+ into the framework was suggested by generation of acid sites and the change of unit cell parameters. (C) 2004 Elsevier B.V. All rights reserved.