Chemistry and crystallography of zeolite X: Ion exchange and metal sorption.

摘要

The crystal chemistry of hydronium ions in zeolite X has been investigated by single-crystal X-ray diffraction methods. The structure of zeolite X in equilibrium with 0.1 M aqueous Na+ at pH 6.35 was determined after partial and complete dehydration. The results show that aluminosilicate zeolites are highly selective for hydronium ions because of the strong hydrogen bonds that the hydronium. ions can make with framework oxygens and because of the formation of (H3O+)2(H2O)(Na +)2 and (H3O+)(H2O)(Na +) clusters. The structure of a single crystal of dehydrated zeolite Na-X selected from a batch grown by Petranovskii was determined. Na + ions are found at four different crystallographic sites. The disagreements between this work and three previous structural determinations can be resolved if the differences in data collection temperature and size of data set, and the possible presence of impurity ion(s) or water are considered. This work indicates that the results of many structural determinations using zeolite X crystals provided by Petranovskii are applicable to all zeolite X samples of similar composition. The structure of fully dehydrated K+-exchanged zeolite X was studied. It is much more complex than that of dehydrated Na-X; K+ ions are found at nine crystallographic sites, a large number due to cation crowding. The rate of Tl+ exchange into zeolite X single crystals was studied crystallographically. The results suggest that very long exchange times may be needed for some ions to reach near complete levels of ion exchange for crystals large enough for X-ray crystallography.;The reactions of potassium vapor with K+-exchanged zeolite X crystals at different temperatures were studied. Potassium atoms were sorbed into the zeolite crystals to form several kinds of cationic potassium clusters. The reaction of sodium vapor with a Na-X crystal at 250°C was studied. The formation of the linear Na32+ cluster is reconfirmed and the reaction conditions are clarified. The reactions of zeolite X crystals with cesium, thallium, and ytterbium vapors at different temperatures were also studied. Small numbers of cesium and thallium atoms were sorbed into the zeoliteccrystals per unit cell. No reaction occurred between ytterbium vapor and zeolite X.