PREPARATION AND CHARACTERIZATION OF THE MAGNESIUM ALUMINOPHOSPHATE MAPO-39

MAPO-39, a small-pore magnesium aluminophosphate molecular sieve (ATN topology), has a pore opening of 4.0 angstrom and tetragonal symmetry. The preparation of MAPO-39 was studied using a one-gel composition and different crystallization periods. Pure MAPO-39 was obtained by hydrothermal crystallization of the gel (molar composition: 1.1 n-Pr2NH.0.40 MgO.0.80 Al2O3.1.02 P2O5.41 H2O) at 423 K for 96 h. Investigations on the crystal structure, morphology, thermal conversion, and surface properties of the crystalline product were carried out. The crystallinity of MAP-39 increases with increase in the crystallization period up to 96 h and decreases beyond the period of 96 h. As compared with MAPO-43 (another 8-O ring molecular sieve), MAPO-39 could be calcined at a higher temperature (up to 793 K) without any loss of the crystal structure. MAPO-39 possesses H2O-sorption capacity of 0.226 cm3 g-1. SEM investigations reveal that the crystals of MAPO-39 are irregular platelike in shape and 2.5 x 3.5 mum in size. X.p.s. analysis indicates that the concentration of aluminum is significantly higher on the surface than in the bulk and the observed binding energy of Mg2p (50.3 eV) corresponds to that of tetrahedrally coordinated magnesium.