Thermogravimetric and High-Temperature X-ray Diffraction study on the desorption of humic monomers from Y zeolites

This study examined the thermal behavior of p-hydroxybenzaldehyde (HBA) desorption from Y zeolites using both isothermal and non-isothermal methods, in order to obtain a detailed structural and kinetic interpretation of the process. Rietveld refinement of in situ powder XRD data and thermal analysis revealed that HBA thermal degradation occurred in the temperature range of about 250–480 °C. This process has a considerable impact on the framework's geometry, resulting in cooperative tilting of the tetrahedra and deformation of both the 6MRs and 12MR rings. For comparison, the HBA desorption experiment was also repeated in isothermal conditions at four different temperatures (200, 250, 350, and 400°C). There were no significant differences between isothermal and non-isothermal kinetic data. Overall, the results of both experimental conditions suggest that the cooperative tilting of tetrahedra and the deformation of rings play a crucial role in HBA desorption. The similar activation energies obtained from isothermal and non-isothermal kinetics further validate the accuracy of the experimental methods employed in this study. These findings provide valuable insights into the mechanisms involved in the desorption process of HBA.