High temperature amperometric total NOx sensors with platinum-loaded zeolite Y electrodes

An amperometic total-NOx sensor that integrates a Pt-loaded zeolite Y (PtY) catalyst for NOx equilibration with electrochemical oxidation of NO on an yttria-stabilized zirconia (YSZ) electrolyte is described in this paper. PtY is found to be an effective catalyst for equilibrating mixtures of NO, O2 and NO2 at temperatures in excess of 400 °C. By applying a low anodic potential of 80 mV, the NO in the NOx equilibrated mixture can be oxidized at a Pt working electrode on the YSZ electrolyte at 500 °C. The current thus generated provides a measure of the total NOx in the gas stream and is the basis of the sensing measurements in this study. The PtY can be held separate from the YSZ or coated onto the YSZ as a film, the latter being more appropriate for the practical embodiment of this design. We demonstrate that this sensor exhibits total-NOx detection capability, a low NOx detection limit (<1 ppm), high NOx selectivity relative to CO and oxygen, and linear dependence on NOx concentration.