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Keywords:

Science & Technology, Physical Sciences, Chemistry, Physical, Chemistry

Abstract:

The crystal structure of calcium mordenite has been studied at 150, 300, 450, and 20°C by single-crystal X-ray diffraction methods The cation distribution changes with temperature although the framework is not affected. One calcium ion, in the small channel, is bonded to six framework oxygens and to two water molecules. This ion does not move on heating, but the water occupancy is reduced to that of the calcium ion. The second calcium ion, in the large channel, is bonded at room temperature to seven water molecules. As the temperature rises, water is lost and the cation becomes distributed over two pairs of sites in both of which it is bonded to framework oxygens of the wall of the large channel and up to 150°C also to water molecules. The site in the small channel has the best coordination for calcium, and its occupancy increases as the temperature rises. © 1987 American Chemical Society.