Promoting selectivity and sensitivity for a high temperature YSZ-based electrochemical total NOx sensor by using a Pt-loaded zeolite Y filter

Potentiometric sensors provide a promising approach for NOx detection in harsh environments, but typically suffer from interferences with other gases. Potentiometric sensors use two electrodes, and both chemical and electrochemical reactivity at each electrode are critical to sensor performance. In this study, we have examined Pt electrode covered with Pt containing zeolite Y (PtY) and WO3 as the two electrode materials. Temperature programmed desorption of NO from NOx/O2-exposed PtY and WO3 was studied. In addition, the ability of PtY and WO3 to equilibrate a mixture of NO and O2 was examined over the temperature range of 200–600 °C. Significant reactivity differences were found between PtY and WO3, with the latter being largely inactive toward NOx equilibration. With gases passing through a PtY filter, it was possible to remove interferences from 2000 ppm CO, 800 ppm propane, 10 ppm NH3, as well as minimize effects of 1–13% O2, CO2, and H2O. By maintaining a temperature difference between the filter (typically at 400 °C) and the sensor at 600 °C, total NOx concentration (NO + NO2) was measured. By connecting three sensors in series, the sensitivity was also significantly improved.