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.