NOx Sensing Performances in Various Mixed Gases at High Temperature for Complex Impedance-Based Zirconia Sensor

Abstract

We have already reported that a new-type complex impedance-based zirconia sensor using a ZnCr₂O₄ sensing-electrode (SE) could detect total NOx content even at 700°C. Thus, we examined here the influence of various other gases on the NOx sensitivity of the present sensor. As a result, we found that the sensitivities to H₂O as well as CO₂ were little and the NOx sensitivity was hardly affected by the presence of H₂O and CO₂ with rather high concentrations. Although we found that the sensitivities to H₂, C₃H₆ and C₃H₈ were relatively high, they might be reduced by installing an oxidation catalyst in the upper stream of the sensor element. Here, we confirmed that the NO sensitivity was almost equal to the NO₂ sensitivity and a linear relationship was observed between sensitivity and NOx concentration even in the coexistence of 8 vol% H₂O and 15 vol% CO₂. Furthermore, it was found that the NOx sensitivity was affected by the change in concentration of oxygen in the sample gas.