Influence of structural, textural and chemical parameters of silver zeolites on the retention of methyl iodide

An experimental screening of silver-exchanged zeolites towards the trapping of methyl iodide was carried out with the general aim of limiting as much as possible the iodine release in case of severe nuclear accident. For the first time, a systematic study was implemented in order to better understand the effects of some important parameters such as the zeolite structural type (FAU-X and Y, MOR, 'BEA, MFI and FER) and chemical properties (namely the silver content and its speciation) on the adsorption behaviour. Characterization of 18 zeolitic sorbents, before or after iodine retention tests, was performed using elemental analyses, N-2 porosimetry at 196 degrees C, XRD, DR-IJV-Vis spectroscopy and TEM. The distribution of silver species, namely as isolated Ag+ cations or charged clusters in the internal porosity, and/or to a lesser extent as metallic nanoparticles, was found to depend mainly on the zeolite structural type and the Si/Al ratio and to a lesser extent on silver content. CH3I retention properties were evaluated from dynamic adsorption tests carried out at 100 degrees C. Quantitative exploitation of breakthrough curves showed that the silver faujasite zeolites of the Y type (Si/AI ratio = 2.5) with more than 15 wt% silver were the most efficient in order to achieve high adsorption capacities both at breakthrough and saturation. More generally, it is found that dispersed silver entities efficiently catalyze the dissociation of CH(3)i and the production of Agl precipitates. (C) 2017 Elsevier Inc. All rights reserved.