Influence of the sensitive zeolite material on the characteristics of a potentiometric hydrocarbon gas sensor

The voltage response of Na-ZSM-5 zeolite/Au electrodes with different Si/Al ratios is measured in dependence of propane partial pressure in O2/CO2/N2 atmospheres at 723 K. A mixture of two NaxCoO2 phases serves as a reference electrode. The zeolites with higher Si/Al ratios lead to higher sensitivities to propane at low concentrations (< 1000 ppm). It is shown that this is in accordance with the assumption of a sensor effect caused by changes of the Na+ ion activity due to sorption of propane in the zeolite micropores. The response times to propane concentration steps decrease with increasing propane concentration.