Synthesis and characterization of AlPO4-36 and MAPO-36 with different magnesium content

The objective of this work was to perform a systematic study regarding the effect of different synthesis parameters on the crystallization of AlPO4-36 and MAPO-36 (aluminophosphate molecular sieve type 36, ATS, structure), MA PO-36 samples were synthesized from gels containing different magnesium con tents in order to obtain catalysts with different degrees of acidity, Under the synthesis conditions employed in this work, the formation of AlPO4-36 and MAPO-36 increased when the reaction mixture was aged at room temperatur e; however, small amounts of AlPO4-5 always crystallize parallel to the ATS materials. The presence of magnesium in the reaction mixture can also favo r the formation of the ATS structure; nevertheless, the synthesis of pure M APO-36 from reaction mixtures having very low magnesium content was not pos sible under several conditions. Pseudobehmite was a better aluminum source than aluminum isopropoxide for the formation of MAPO-36. A practically pure ATS structure was obtained from reaction mixtures containing molar fractio ns of Mg between 0.033 and 0.133, For higher magnesium contents, traces of another unidentified phase were detected. Energy-dispersive spectrometry an alysis indicates a uniform chemical composition of the MAPO-36 particles, a nd Scanning electron microscopy shows that the ATS samples have a needlelik e morphology. Thermogravimetric analysis of ATS samples reveals that the we ight loss corresponding to the decomposition of protonated amine is linearl y correlated with magnesium content in the solid up to 0.8 mmol of magnesiu m per gram of solid.