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On the H-form of natrolite

¹ Institute of Mineralogy and Petrography, pr. ak. Koptyuga 3, 630090 Novosibirsk 90, Russia
² Boreskov Institute of catalysis, pr. ak. Lavrentieva 5, 630090 Novosibirsk 90, Russia

^* e-mail: alih{at}uiggm.nsc.ru

To resolve the problem of existence of the H-form of natrolite, the thermal decomposition of NH₄-exchanged natrolite (as a precursor of the H-form) was studied by gas chromatography, IR spectroscopy and X-ray diffraction. Throughout the decomposition, the de-ammoniation is immediately followed by dehydroxylation, which is evidence for the instability of the H-natrolite formed after the removal of NH₃, and leads to a negligibly small concentration of the OH-groups. The natrolite structure can not persist after the removal of NH₃.

In the final step of decomposition, the adsorption of NH₃ onto Lewis centres accumulated in the amorphosed framework hinders the de-ammoniation. This seems to be one of the major factors which influence the observed increase in the activation energy for NH₃ desorption from 117 (±13) kJ/mol in the initial step to 270 (±20) kJ/mol.

Smooth vacuum degassing of NH₄-natrolite at 550 K leads to partial de-ammoniation, rather than formation of H-natrolite.

Key-words: natrolite, H-natrolite, ammonium natrolite, de-ammoniation, dehydroxylation, amorphisation, gas chromatography, IR spectroscopy.