Na-A (LTA) zeolite synthesis directly from alumatrane and silatrane by sol-gel microwave techniques

Abstract

Na-A (1 μm crystal size) zeolite was successfully synthesized via a sol-gel process and microwave heating technique using alumatrane and silatrane as precursors. After fixing the SiO2:Al2O3 ratio at 1:1 and microwave heating temperature at 110 °C, increasing the Na2O concentration by adding more NaOH exponentially reduces the microwave heating time from 160 min at a Na2O:SiO2 ratio of 3:1 to 5 min at a Na2O:SiO2 ratio of 9:1. The increase of Na2O concentration strongly affects the particle size and particle size distribution, but does not affect the product composition. Small crystallite sizes are obtained from a high Na2O: SiO2 ratio (10:1) while a low Na2O:SiO2 ratio (3:1) gives large crystallite sizes (∼4.5 μm). The analyzed Si:Al:Na ratio of synthesized Na-A zeolite is 1:1:1.25. The moisture absorption ability of the synthesized Na-A zeolite is higher than that of the commercial one by approximately 20%. The increase of water ratio also affects the crystal size. As the water ratio increases, larger crystallites with a higher degree of irregularity are formed.