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

Department of Chemistry, The Ohio State University, Columbus, OH 43210-1185, USA
Sensors and Actuators B Chemical (Impact Factor: 4.29). 05/2007; 123(2):929-936. DOI: 10.1016/j.snb.2006.10.052

ABSTRACT 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.

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    • "The need for nitric oxide (NO) sensing is critical in a diverse variety of applications ranging from high temperature combustion [1] [2] [3] [4] [5] to clinical analysis [6] [7]. An example of a high temperature combustion application is monitoring and minimization of NO x emissions produced by lean burn engines [8]. "
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    • "OSU NO sensors fabricated using two different approaches. (a) Standard fabrication approach used to produce the sensors described elsewhere [28]. (b) Basic sensor design fabricated using microprocessing techniques. "
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    • "These sensors exhibit stability on the order of months, with no indication of failure upon test comple- tion. We have also reported on an amperometric total NO x sensor based on measuring current upon application of a low anodic potential (∼80 mV) to Pt electrodes on a YSZ electrolyte [12]. Pt-loaded zeolite Y (PtY), an active NO x equilibration catalyst with high thermal stability and surface area, was used as a coating on the YSZ to equilibrate the NO x. "
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    ABSTRACT: Simultaneous measurement of total NOx and O2 using two electrochemical methods are demonstrated using metal/metal oxide internal oxygen reference electrode-based sensors at high temperatures. The Pd/PdO-containing reference chamber was sealed within a stabilized zirconia superstructure by a high pressure/temperature plastic deformation bonding method exploiting grain boundary sliding between the ceramic components. Amperometric and potentiometric NOx sensing devices were assembled on the outside of the sensor. Pt-loaded zeolite Y was used to obtain total NOx capability. Both the amperometric and potentiometric type sensors showed total NOx response, with the potentiometric device showing better NOx/O2 signal stability and lower NOx–O2 cross-interference. Since these sensors do not require plumbing for reference air, there is more flexibility in the placement of such sensors in a combustion stream.
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