Discriminative sensing performances of ZSM-5, Y, mordenite, ferrierite, beta, 3A, 4A, 5A, and 13X zeolites towards sulfur dioxide

The present work is an attempt in identifying highly selective sensing materials for sulfur dioxide (SO2). The responses of various zeolites towards SO2 were investigated through the change in the electrical conductivity during the exposure to SO2 under the effects of the zeolite type, cation type, and Si/Al ratio. The zeolites were characterized by BET, FT-IR, XRD, and AAS techniques. Among all zeolites, the NH4 (+)ZSM-5 with the Si/Al ratio of 23 (NH4 (+)ZSM-5 (23)) showed the highest positive response towards SO2 with full reversibility. The cyclic response and the SO2 concentration dependence were also investigated. The relative response increased with increasing SO2 concentration. The NH4 (+)ZSM-5 (23) exhibited a reliable relative response towards SO2 down to 50 ppm. Furthermore, the pristine NH4 (+)ZSM-5 (23) was ion-exchanged with metal chloride solutions (NaCl, MgCl2, or AlCl3) to study the effect of ion valence on the sensing performance of the ion-exchanged zeolites. The ion-exchanged zeolite with Al3+ possessed the higher relative response towards SO2 at the same ion-exchange percentage than Mg2+ and Na+ due to its higher ionic charge and electronegativity. The interactions among the zeolites and the SO2 molecules were examined and proposed via infrared spectroscopy.