Ultrafast synthesis of discrete submicron AlPO4-LTA molecular sieve crystals and their application in molecular sieve membrane

Abstract

Ultrafast synthesis of nanosized and submicron zeolite materials is challenging but highly desired due to their wide applications. Herein, discrete LTA-type aluminophosphate molecular sieve (AlPO4-LTA) submicron crystals have been synthesized in an open glass beaker under oil bath heating for only 10 min. The influences of the synthesis parameters, including the ratios of tetramethylammonium hydroxide (TMAOH)/Al and HF/Al, and the heating methods were investigated thoroughly. The optimized product exhibits exceptional properties, including good crystallinity, small particle size (ca. 130 nm) and large BET surface areas (867 m2/g). The time-dependent study reveals the formation process of submicron AlPO4-LTA crystals: the primary worm-like amorphous first aggregated into loosely assembled spheres, then the crystallinity of the spheres enhances while keeping the particle size unchanged. Using the submicron AlPO4-LTA crystals as the seed layer, an AlPO4-LTA membrane was synthesized via secondary growth approach. For binary mixtures at 298 K, the separation factors for H2/N2, H2/O2, H2/CO2 and H2/CH4 are 4.8, 6.2, 7.3 and 5.9, respectively, suggesting the good gas separation performance of the membrane.