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Issue 17, 2015
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Energetics of sodium–calcium exchanged zeolite A

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Abstract

A series of calcium-exchanged zeolite A samples with different degrees of exchange were prepared. They were characterized by powder X-ray diffraction (XRD) and differential scanning calorimetry (DSC). High temperature oxide melt drop solution calorimetry measured the formation enthalpies of hydrated zeolites CaNa-A from constituent oxides. The water content is a linear function of the degree of exchange, ranging from 20.54% for Na-A to 23.77% for 97.9% CaNa-A. The enthalpies of formation (from oxides) at 25 °C are −74.50 ± 1.21 kJ mol−1 TO2 for hydrated zeolite Na-A and −30.79 ± 1.64 kJ mol−1 TO2 for hydrated zeolite 97.9% CaNa-A. Dehydration enthalpies obtained from differential scanning calorimetry are 32.0 kJ mol−1 H2O for hydrated zeolite Na-A and 20.5 kJ mol−1 H2O for hydrated zeolite 97.9% CaNa-A. Enthalpies of formation of Ca-exchanged zeolites A are less exothermic than for zeolite Na-A. A linear relationship between the formation enthalpy and the extent of calcium substitution was observed. The energetic effect of Ca-exchange on zeolite A is discussed with an emphasis on the complex interactions between the zeolite framework, cations, and water.

Graphical abstract: Energetics of sodium–calcium exchanged zeolite A

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Publication details

The article was received on 24 Feb 2015, accepted on 20 Mar 2015 and first published on 25 Mar 2015


Article type: Paper
DOI: 10.1039/C5CP01133G
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Phys. Chem. Chem. Phys., 2015,17, 11198-11203

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    Energetics of sodium–calcium exchanged zeolite A

    H. Sun, D. Wu, X. Guo, B. Shen and A. Navrotsky, Phys. Chem. Chem. Phys., 2015, 17, 11198
    DOI: 10.1039/C5CP01133G

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