Location of extra-framework Co2+, Ni2+,Cu2+ and Zn2+ cations in natural dealuminated clinoptilolite

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Comprehensive Analysis of the Copper Exchange Implemented in Ammonia and Protonated Forms of Mordenite Using Microwave and Conventional Methods

This article presents the results of a comprehensive study of copper-exchanged mordenite samples prepared from its ammonia and protonated forms (Si/Al = 10) using two different ion exchange methods: conventional and microwave (MW)-assisted. The protonated H-MOR-10 sample was obtained by calcination of commercial NH4-MOR-10; in this case, a slight degradation of the mordenite framework was observed, but the resulting defects were partially restored after the first ion-exchange procedure of protons for copper ions. The level of copper exchange in the studied materials was found to be limited to 70%. Regardless of the exchange procedure, the replacement of ammonium or proton ions with copper led to a linear increase in the a/b ratio of cell parameters in accordance with an increase in the level of copper exchange, which means that all Cu2+ cations are ion-exchangeable and enter the main mordenite channel. Thermal analysis indicated a correlation between the replacement of various ammonium and hydroxyl groups by copper ions during the exchange treatment and their dehydroxylation energy during thermal decomposition. As a conclusion: MW-assisted treatment proved itself as an efficacious method for the synthesis of copper-exchanged mordenites, which not only significantly reduces preparation time but leads to a systematically higher copper exchange level

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

International audienceThe 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