Thermal decomposition of NH4-analcime |
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| Authors: | AYu Likhacheva S A Veniaminov E A Paukshtis |
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| Institution: | (1) Institute of Mineralogy and Petrology, pr.ak.Koptyuga 3, Novosibirsk, 90, 630090, Russia;(2) Boreskov Institute of Catalysis, pr.ak.Lavrentieva 5, Novosibirsk 90, 630090, Russia |
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| Abstract: | The thermal decomposition of ammonium-exchanged natural analcime is characterized by gas chromatography, IR spectroscopy and X-ray diffraction. The de-ammoniation and dehydroxylation proceed in parallel throughout the decomposition, which evidences the instability of the protonated analcime framework. The mechanism of degassing of NH4-analcime changes throughout its decomposition. At the initial step, the mechanism of de-ammoniation consists in thermal dissociation of NH4+ molecule onto NH3 and proton (framework OH group) and diffusion of NH3 out of the structure. Subsequent decomposition and removal of the OH groups lead to a progressive loss of crystallinity. At this step, an apparent activation energy for NH3 desorption is estimated to be 145(±13) kJ mol–1. This value is within the upper limit of the activation energy characteristic for the NH3 desorption from proton centres in large-pore zeolites. At the final step, the adsorption of NH3 and protons onto the defect centres in the amorphosed aluminosilicate framework results in a significant increase of an apparent activation energy for the de-ammoniation and dehydroxylation up to 270(±20) kJ mol–1. |
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| Keywords: | Ammonium analcime De-ammoniation Dehydroxylation Gas chromatography IR spectroscopy |
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