LEV-zeotype magnesium aluminophosphates with variable Mg/Al ratios

Abstract

By using two different organic amines, n-methylpiperidine and 1,2-diaminocyclohexane (DACH), as the structure-directing agents (SDAs), two magnesium aluminophosphate molecular sieves |(C₆H₁₄N)₂|[Mg₂Al₇(PO₄)₉] and |(C₆H₁₄N₂)_1.4(H₂O)₂H₂|[Mg₂Al₅(PO₄)₇], denoted as MgAPO-CJ67(a) and MgAPO-CJ67(b), have been synthesized under hydrothermal conditions. They are the first example of Mg incorporated aluminophosphates with the LEV-zeotype structure. The magnesium and aluminum atoms co-occupy the same crystallographic positions in the frameworks of MgAPO-CJ67(a) and MgAPO-CJ67(b), but with different Mg/Al ratios of 1 : 3.5 and 1 : 2.5, respectively. MgAPO-CJ67(a) exhibits higher thermal stability upon calcination than MgAPO-CJ67(b), and its framework keeps intact after the removal of occluded organic SDAs. The N₂ adsorption on the calcined MgAPO-CJ67(a) sample gives the BET surface area of 386 m² g⁻¹. NH₃-temperature programmed desorption (NH₃-TPD) analysis shows that MgAPO-CJ67(a) has a medium acidity.