Abstract
High-temperature phase transformations of K-LTA zeolite were investigated in the temperature range 800-1800°C. The nano-structured KAlSiO4 precursor was prepared at 850°C and after annealing at 1000°C, the first polymorph of KAlSiO 4, synthetic kaliophilite was formed. With increasing temperature, the following polymorphs were synthesized: kalsilite (1100°C), low KAlSiO 4-O 1 (1200°C), KAlSiO 4-ANA (1300°C), and high KAlSiO 4-O 2 at (1430°C). Synthetic kaliophilite and KAlSiO 4-ANA phases are the new polymorphs in the system studied. Consequently, the KAlSiO 4-ANA phase is the ANA-type end member of the zeolite framework having the ratio Si/Al = 1. From XRD powder patterns a distorted leucite unit cell for a KAlSiO 4-ANA phase was calculated: a 0 = 13.638(6) Å, b 0 = 13.811(8) Å, c = 13.817(9) Å, α 0 = 99.98(4)°, β 0 = 102.28(4)°, and γ 0 = 62.80(4)°. 29Si MAS NMR chemical shifts at -89.08 and -98.01 ppm suggest that the KAlSiO 4-ANA phase has an ordered framework cation topology.
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