SYNTHESIS AND PROPERTIES OF MGAPO-5

Magnesium aluminophosphate molecular sieves with the AlPO4-5 structure have been synthesized with varying Mg : (Mg + Al + P) mole ratios usi ng triethylamine as an organic template. The results indicated that hi ghly crystalline MgAPO-5 material can be obtained using starting react ion gel compositions containing up to 50 mol% of Mg. The MgAPO-5 produ ct was associated with small amounts of MgAPO-47 below 20 mol% Mg addi tion and in the range 30-50 mol% Mg it was associated with an unknown phase designated as phase (1). In either case, the contribution due to the impurity phase was <5%. Substitution of Mg into the AlPO4-5 frame work was demonstrated by the variation in the unit-cell volume wth Mg mole fraction, thermogravimetric study of the amount of occluded amine , chemical analysis and Al-27 and P-31 NMR data. The Al-27 NMR spectra of MgAPO-5 samples containing up to 50 mol% Mg showed a single peak a t 39 ppm which is assigned to Al(4P). The P-31 NMR spectra showed a ma jor peak at -29 ppm followed by low intensity peaks with decrease in i ntensity order at -23, -17 and -11 ppm corresponding to P(4Al), P(3Al, 1Mg), P(2Al, 2Mg)P and (1Al, 3Mg) units, respectively. The magnesium phosphate sample prepared in the absence of aluminium gave a symmetric al single P-31 NMR peak near 0 ppm due to P(4Mg) units. Temperature-pr ogrammed desorption of pyridine indicated that the MgAPO-5 samples con tain structural Bronsted acid sites.