CRYSTAL-STRUCTURES OF THE POTASSIUM CLUSTERS IN THE SODALITE CAVITIES OF ZEOLITE-A AND ZEOLITE-X

Single crystals of fully dehydrated sodium zeolite A, Na12Al12Si12O48 per unit cell, and zeolite X, Na92Al92Si100O384 per unit cell, reacted with potassium vapor at 300-degrees-C. Their structures were determined by X-ray diffraction methods at 24-degrees-C in the cubic space groups Pm3mBAR and Fd3BAR, respectively. Not only have all Na+ ions been replaced with K+ by redox reaction, but additional potassium atoms were sorbed to give K15Al12Si12O48 per 12.298(2) angstrom unit cell for K-A.K, and K142Al92Si100O384 per 25.197(3) angstrom unit cell for K-X-K. Crystallographic results show that tetrahedral K4n+ clusters form in the sodalite cavities of zeolite A and that one-, two-, and three-dimensional cationic continua form within the channel systems of zeolites A and X. Isolated K4n+ and K3m+ Clusters may exist in zeolite X at early stages of potassium sorption, but these become linked by potassium ions at site I at higher loadings. The partially reduced ions of the tetrahedral clusters interact primarily with oxygen atoms (ions) of the zeolite structure. The size of the cluster (the K-K distance) depends upon the distortion of the sodalite unit within its zeolite.