Arrangement and Diffusive Mobility of Extraframework Species in the Hydrated Ammonium Forms of Zeolites Clinoptilolite and Chabazite |
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Authors: | N K Moroz Yu V Seryotkin I S Afanassyev V V Bakakin |
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Institution: | (1) Institute of Inorganic Chemistry, Siberian Branch, Russian Academy of Sciences, Novosibirsk |
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Abstract: | The location and diffusive mobility of ammonium ions and water molecules in the channels of the NH4substituted forms of the natural zeolites clinoptilolite (NH4)6.5Al6.5Si29.5O72] · 12.6H2O and chabazite (NH4)9.6Ca0.6Na0.3Al11.1Si24.9O72] · 25.8H2O were studied by Xray diffraction analysis and 1H NMR spectroscopy. The arrangement of the extraframework subsystem was shown to be largely determined by hydrogen bonds N—H...O(H2O) of length 2.7–2.9 . The diffusive mobility of the ions was found to correspond to abnormally low energy barriers, similar to those for H2O diffusion. The activation parameters for the diffusion jumps of the ions and molecules are E(NH4) = E(H2O) = 31(2) kJ/mole, 0(NH4) = 2 · 1011 sec-1, 0(H2O) = 4 · 1012 sec-1 in NH4chabazite and E(NH4) = E(H2O) = 25(1) kJ/mole, 0(NH4) = 2 · 1010 sec-1, 0(H2O) = 3 · 1011 sec-1 in NH4clinoptilolite. It is suggested that the development of ion and molecular diffusion is caused by the same defects, whose formation with temperature rise is controlled by Hbond rearrangement. |
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