Step-wise dealumination of natural clinoptilolite: Structural and physicochemical characterization

The step-wise dealumination of a natural clinoptilolite has been achieved through a new milder treatment, comprising cycles of aqueous solutions of hydrochloric acid with washing steps. The course of the dealumination was monitored by XRD, FTIR, TGA, UV–vis-DRS and NMR. The XRD patterns show a contraction of cell volume during progressive dealumination steps and a decrease in crystallinity after the third dealumination cycle. The framework and OH vibrations in FTIR spectra show progressive extraction of aluminum atoms from zeolite framework and consequently the formation of silanol nests. 27Al MAS NMR indicates that low levels of octahedral aluminum species are created during the treatments.