Ionothermal synthesis process for aluminophosphate molecular sieves in the mixed water/ionic liquid system

Abstract

The synthesis process of aluminophosphate AlPO₄-11 molecular sieve in the mixed water/1-butyl- 3-methylimidazolium bromide ([bmim]Br) ionic liquid was investigated by XRD, multinuclear solid-state NMR, scanning electron microscopy (SEM) and X-ray energy dispersive spectroscopy (EDS). It was observed that a tablet phase, named SIZ-2, was formed at the early stage of crystallization. During crystallization metastable SIZ-2 with an incompletely condensed framework phosphorus disappeared gradually, and the phosphorous species became fully condensed through hydroxyl reaction with tetrahedral aluminum to form thermodynamically stable AlPO₄-11 in the final product. It was found that [bmim]Br, acting as the structure-directing agent, was occluded into the AlPO₄-11 channel.