Characterization of Y zeolites dealuminated by solid-state reaction with ammonium hexafluorosilicate

In the present work the solid-state dealumination of Y zeolite with ammonium hexafluorosilicate for various reaction times was studied. A detailed characterization of the porosity of the samples, and their hydrophobic-hydrophilic properties, was made. The characterization techniques used, besides the low temperature nitrogen adsorption and the room temperature water adsorption, include also the FTIR, the powder XRD and the Al-27 and Si-29 MAS NMR. These techniques showed evidence for the complex mechanism of dealumination that for sufficiently long times of reaction allows the partial reconstitution of the structure. Due to this mechanism the evolution of the Si/Al ratio, as well as the porosity and the hydrophobic-hydrophilic properties, do not run monotonically with the time.