Dehydration and rehydration of mesolite: An in situ FTIR study

The dehydration and rehydration processes of mesolite belonging to NAT group of zeolites were investigated using in situ Fourier Transform Infrared spectroscopy (FTIR). The thermal induced variations of the water molecule bending (ν₂), the stretching (ν₃ and ν₁) modes and the corresponding second order modes in the wavenumber region 4000–8000 cm⁻¹ were followed as indicative of the dehydration process. Observed spectral variations were well correlated with thermogravimetric studies and indicate that the mesolite dehydrates in three stages (470; 510 and 650 K). Anomalous spectral variations of 4600 cm⁻¹ at first stage indicate that the dehydration is triggered by the expulsion of water coordinating AlO₄ tetrahedron. Partial rehydration (up to 85%) at second stage indicates disordering of natrolite and scolecite layers. During the third stage mesolite completely dehydrates, causing the destruction of framework.