Establishing the occupation of supercage sites by silver ions using the response of partially silver-exchanged zeolite X- and Y-modified electrodes

Abstract

Exclusive occupancy of the sodalite cage and hexagonal-prism (small-channel network) sites of zeolites X and Y by silver ions results in an attenuated electrochemical response of zeolite-modified electrodes (ZMEs) compared with the case where silver ions occupy supercage sites. When silver ions located in the small-channel network, the initial redox current was a minimum, and grew slowly as the electrode was repeatedly cycled. Electrodes showed the reverse behavior when silver ions resided in the supercages, in that the initial redox current was a maximum and decayed rapidly. The maximum current due to silver ions in the small-channel network, computed using the peak current for the oxidation recorded in NaNO₃, is less than 10 µA per Ag⁺ ion per unit cell (uc). In contrast, modified electrodes in which silver ions occupy supercage sites produced maximum peak currents of ca. 200 µA per Ag⁺ ion per uc in the same electrolyte. In this paper we use this information to identify the general locations of silver ions in X and Y zeolites. At less than 5 Ag⁺ ions uc^-1, silver ions preferentially occupy supercage sites in zeolite Y. In zeolite X silver ions exclusively locate in the small-channel network at loadings of less than 5 Ag⁺ ions uc^-1.