ZSM-5, Y, and Mordenite Zeolites as Sensing Materials for Ethanol Vapor

The effects of the framework type, the charge balancing cation type, and the Si/Al ratio of ZSM-5, Y, and Mordenite zeolites on the electrical conductivity responses towards ethanol vapor have been investigated. All zeolites were characterized using XRD, FT-IR, SEM, TGA, BET, and NH$_{3}$-TPD techniques. For the effect of the framework type, H$^{+}$Y has a higher electrical conductivity sensitivity value than that of H$^{+}$MOR because of a greater pore volume and available surface area. For the effect of the charge balancing cation, all NH$_{4}^{+}$ZSM-5 zeolites (Si/Al = 23, 50, 80, 280) show negative responses, whereas the H$^{+}$Y zeolites (Si/Al = 30, 60, 80) and the H$^{+}$MOR zeolites (Si/Al = 30, 200) show positive responses. These differing behaviors can be traced to the interactions between ethanol molecules and the reactive sites of the zeolites. For the effect of Si/Al ratio, the electrical conductivity sensitivity towards the ethanol decreases with increasing Si/Al ratio or decreasing Al content, and there is a lesser degree of interaction between ethanol molecules and the active sites of the zeolites. The interactions between the ethanol molecules and the zeolites were investigated through infrared spectroscopy.