MULTIFUNCTIONAL (NOx/CO/O2) SOLID-STATE SENSORS FOR COAL COMBUSTION CONTROL
Sensing properties of a La{sub 2}CuO{sub 4}- and WO{sub 3}-based potentiometric NO{sub x} sensor were investigated both in N{sub 2} and in a simulated exhaust gas. We performed temperature programmed reaction (TPR) and desorption (TPD) experiments to determine the reaction and adsorption characteristics of O{sub 2}, NO{sub x}, CO, CO{sub 2}, and their mixtures on the electrodes, and related the results to sensor performance. The relative responses of the La{sub 2}CuO{sub 4}-based sensor under varied concentrations of NO, NO{sub 2}, CO, CO{sub 2} and O{sub 2} were studied. The results showed a very high sensitivity to CO and NO{sub 2} at 450 C in 3% O{sub 2}, whereas the response to O{sub 2} and CO{sub 2} gases was negligible. The NO response at 400-500 C agreed with the NO adsorption behavior. The high NO{sub 2} sensitivity at 450 C was probably related to heterogeneous catalytic activity of La{sub 2}CuO{sub 4}. The adsorption of NO was not affected by the change of O{sub 2} concentration and thus the sensor showed selective detection of NO over O{sub 2}. However, the NO sensitivity was strongly influenced by the existence of CO, H{sub 2}O, NO{sub 2}, and CO{sub 2}, as the adsorption behavior of NO was influenced by these gases. The WO{sub 3}-based sensor was able to selectively detect NO in the presence of CO{sub 2} in 3% O{sub 2} and at 650 C. The NO sensitivity, however, was affected by the variation of the NO{sub 2}, CO, and H{sub 2}O concentration. No gas-solid reactions were observed using TPR in the NO containing gas mixture, indicating that the NO response was not obtained by the conventionally accepted mixed-potential mechanism. At the same condition the sensor had high sensitivity to {approx}10 ppm NO{sub 2} and selectivity in the presence of CO, CO{sub 2}, and H{sub 2}O, showing it to be applicable to the monitoring of NO{sub 2}. Significantly different sensing properties of NO in simulated exhaust gas suggested the occurrence of gas composition change by the gas-phase and gas-solid reactions, and strong adsorption of water on the electrodes. The NO{sub 2} sensitivity in simulated exhaust gas was modified by O{sub 2} and H{sub 2}O, but not by CO and CO{sub 2}. A positive voltage response was obtained for NO{sub 2} but negative for NO at 650 C with the n-type semiconducting WO{sub 3}-based sensor. In contrast the opposite response direction for NO{sub x} was observed at 450 C with the La{sub 2}CuO{sub 4} (p-type semiconductor).
- Research Organization:
- University of Florida (US)
- Sponsoring Organization:
- (US)
- DOE Contract Number:
- FG26-02NT41533
- OSTI ID:
- 840269
- Resource Relation:
- Other Information: PBD: 21 Mar 2005
- Country of Publication:
- United States
- Language:
- English
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MULTIFUNCTIONAL (NOx/CO/O2) SOLID-STATE SENSORS FOR COAL COMBUSTION CONTROL