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Kinetics of Nitric Oxide and Oxygen Gases on Porous Y-Stabilized ZrO2-Based Sensors
Chemical Engineering and Institute for Micromanufacturing, Louisiana Tech University, Ruston, LA 71272, USA
Institute for Micromanufacturing, Louisiana Tech University, Ruston, LA 71272, USA
* Author to whom correspondence should be addressed.
Received: 15 July 2013; in revised form: 8 August 2013 / Accepted: 13 August 2013 / Published: 16 August 2013
Abstract: Using impedance spectroscopy the electrical response of sensors with various porous Y-stabilized ZrO2 (YSZ) microstructures was measured for gas concentrations containing 0–100 ppm NO with 10.5%O2 at temperatures ranging from 600–700 °C. The impedance response increased substantially as the sensor porosity increased from 46%–50%. Activation energies calculated based on data from the impedance measurements increased in magnitude (97.4–104.9 kJ/mol for 100 ppm NO) with respect to increasing YSZ porosity. Analysis of the oxygen partial pressure dependence of the sensors suggested that dissociative adsorption was the dominant rate limiting. The PWC/DNP theory level was used to investigate the gas-phase energy barrier of the 2NO+O2→2NO2 reaction on a 56-atom YSZ/Au model cluster using Density Functional Theory and Linear Synchronous Transit/Quadratic Synchronous Transit calculations. The reaction path shows oxygen surface reactions that begin with NO association with adsorbed O2 on a Zr surface site, followed by O2 dissociative adsorption, atomic oxygen diffusion, and further NO2 formation. The free energy barrier was calculated to be 181.7 kJ/mol at PWC/DNP. A qualitative comparison with the extrapolated data at 62% ± 2% porosity representing the YSZ model cluster indicates that the calculated barriers are in reasonable agreement with experiments, especially when the RPBE functional is used.
Keywords: NOx; diesel emissions; YSZ; NO sensing; porous; density functional theory; reaction mechanism
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Killa, S.; Cui, L.; Murray, E.P.; Mainardi, D.S. Kinetics of Nitric Oxide and Oxygen Gases on Porous Y-Stabilized ZrO2-Based Sensors. Molecules 2013, 18, 9901-9918.
Killa S, Cui L, Murray EP, Mainardi DS. Kinetics of Nitric Oxide and Oxygen Gases on Porous Y-Stabilized ZrO2-Based Sensors. Molecules. 2013; 18(8):9901-9918.
Killa, Sajin; Cui, Ling; Murray, Erica P.; Mainardi, Daniela S. 2013. "Kinetics of Nitric Oxide and Oxygen Gases on Porous Y-Stabilized ZrO2-Based Sensors." Molecules 18, no. 8: 9901-9918.