Highly efficient synthesis of LTA-type aluminophosphate molecular sieve by improved ionothermal method with low dosage of structure-directing agent

Abstract

Aluminophosphate molecular sieve with LTA topology was efficiently synthesized by seed-assisted and improved ionothermal method with low dosages of organic amines and ionic liquids (ILs). The influences of organic amine type, crystallization temperature, amount of organic species, and seed crystals on the synthesis of LTA-type material were investigated, to refine the synthetic conditions. The results indicate that LTA-type molecular sieve is synthesized even by adding small amount of seed crystal into initial gels, of which both molar ratios of ILs/Al2O3 and Amine/Al2O3 are decreased to 0.67. Utilization rate of inorganic raw materials during as-synthesis is up to 86% under optimal conditions. Structure and morphology of the products, together with organic species occluded in cavities were fully analyzed by XRD, SEM, N2 physisorption, TG-DTA, CHN elemental analysis, and liquid 13C NMR. The results show that the resultant LTA molecular sieve is a hierarchically porous material with both micropores and mesopores inside. It is the cooperative structure-directing effect between morpholine and 1-ethyl-3-methylimidazolium cations that guides the formation of LTA molecular sieve.