NOVEL, CRYSTALLINE, LARGE-PORE MAGNESIUM ALUMINOPHOSPHATE MOLECULAR-SIEVE OF TYPE-50 - PREPARATION, CHARACTERIZATION, AND STRUCTURAL STABILITY

A large-pore magnesium aluminophosphate molecular sieve with AFY topology (MAPO-50) has been synthesized. The magnesium aluminophosphate molecular sieve has a three-dimensional pore structure and trigonal (three-fold) symmetry. Pure MAPO-50 was crystallized hydrothermally from a gel of composition of 2.6 n-Pr2NH (di-n-propylamine):O.30 MgO:0.85 Al2O3:1.0 P2O5:50 H2O at 423 K for 140 h. The effects of the crystallization period, the concentration of magnesium and the organic template (di-n-propylamine) in the gel on the crystallinity and phase purity of MAPO-50 were examined. The as-synthesized materials were characterized by the XRD, SEM, t.g.d.t.g.d.t.a., FT i.r., and XPS techniques, The effects of thermal treatment on the structural stability of MAPO-50 have also been investigated, The crystal structure collapse starts above 583 K and is complete above 646 K. MAPO-50 exhibits lower thermal stability than MAPO-5, MAPO-11, MAPO-36, and MAPO-46. The magnesium content in the AIPO(4) framework and the large structural void volume and the 8- and 12-ring pore openings are mainly responsible for the lower thermal stability of MAPO-50.