LEV-zeotype magnesium aluminophosphates with variable Mg/Al ratios

摘要

By using two different organic amines, n-methylpiperidine and 1,2-diaminocyclohexane (DACH), as the structure-directing agents (SDAs), two magnesium aluminophosphate molecular sieves (C _6H _(14)N) _2[Mg _2Al _7(PO _4) _9] and (C _6H _(14)N _2) _(1.4)(H _2O) _2H _2[Mg _2Al _5(PO _4) _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 N _2 adsorption on the calcined MgAPO-CJ67(a) sample gives the BET surface area of 386 m ~2 g ~(-1). NH _3-temperature programmed desorption (NH _3-TPD) analysis shows that MgAPO-CJ67(a) has a medium acidity.