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Nitrogen Oxides Gas Sensor Utilizing Microporous

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Nitrogen Oxides Gas Sensor Utilizing Microporous DEVELOPMENT OF HARSH ENVIRONMENT NITROGEN OXIDES SOLID- STATE GAS SENSORS DISSERTATION Presented in Partial Fulfillment of the Requirements for the Degree Doctor of Philosophy in the Graduate School of The Ohio State University By Nicholas F. Szabo, M.S. ***** The Ohio State University 2003 Dissertation Committee: Approved by Dr. Prabir Dutta, Adviser Dr. Sheikh Akbar ______________________ Adviser Dr. Patrick Woodward Department of Chemistry ABSTRACT The goal of this dissertation was to study and develop high temperature solid-state sensors for combustion based gases. Specific attention was focused on NOx gases (NO and NO2) as they are of significant importance with respect to the environment and the health of living beings. This work is divided into four sections with the first chapter being an introduction into the effects of NOx gases and current regulations, followed by an introduction to the field of high temperature NOx sensors and finally where and why they will be needed in the future. Chapter 2 focuses on the development of a gas sensor for NOx capable of operation in harsh environments. The basis of the sensor is a mixed potential response at 500/600°C generated by exposure of gases to a platinum-yttria stabilized zirconia (Pt- YSZ) interface. Asymmetry between the two Pt electrodes on YSZ is generated by covering one of the electrodes with a zeolite, which helps to bring NO/NO2 towards equilibrium prior to the gases reaching the electrochemically active interface. Three sensor designs have been examined, including a planar design that is amenable to packaging for surviving automotive exhaust streams. Automotive tests indicated that the sensor is capable of detecting NO in engine exhausts. ii Chapter 2 concluded that it is difficult to measure NO or NO2 selectively especially when both gases are present at the same time thus we have developed a strategy in chapter 3 to measure the total NOx level (NO +NO2) in a background of O2 and N2 at high temperatures with minimal CO interference by combining a catalytic filter bed with the existing YSZ sensor device. The filter bed was composed of a Pt catalyst dispersed onto a zeolite Y support placed before a YSZ sensor having an air reference with a Cr2O3 or Pt sensing electrode. Chapter 4 explores the reasons for the difference in sensitivity of metal oxide electrodes, Cr2O3 and a mixed conducting perovskite La0.6Sr0.4Fe0.8Co0.2Ox, with the goal of ultimately developing a systematic method of electrode screening as compared to the random screening often found in the literature. iii Dedicated to my parents Barbara and Frederick Szabo and grandparents Nida and Nicholas Coreno iv ACKNOWLEDGMENTS I would like to thank my adviser Dr. Prabir Dutta, for his patience, support, and encouragement, especially when the direction was not necessarily clear, which made this dissertation possible. I thank Dr. Sheikh Akbar for offering suggestions on material and fabrication issues as well as support and encouragement. I also am grateful for Dr. Perena Gouma and Dr. Ramasamy Ramamoorthy for microstructural characterization work done on sensor materials. Actual fabrication of the sensor designs and testing facilities could not have been accomplished without the help of Mr. Jim Brooke, Mr. Tim Henthorne, and Mr. Ken Kushner. To them I am grateful for all of their help. My thanks go to Dr. Ahmed Solimon, Mr. Alan Ida, and Mr. Byongho Lee for their help in automotive testing and for running the dynamometer set-up. I am grateful for the help and stimulating discussions amongst my colleagues in the Dutta group present (Marla, Joe, John, Bob, Kefe, Toni, Pramatha, Rama, Yanghee) and past (Hyunjung, Ramsharan, Anand, Nancy, Estelle, Astrid). Thanks for sitting patiently through my research talks in this minute diversion from "normal" chemistry and the comfort from those in the 'sensor crew' - Nancy, Marla and Joe. I also thank the numerous people who have come through the Center for Industrial Sensors and Measurements research group, including Dr. Hongbin Du, Dr. v Ramachandra Rao, Dr. Shaestagir Chowdhury, Badri Naranayan, and especially Chong Hoon Lee. I would also like to acknowledge CISM and the Department of Chemistry for fiscal support throughout the years with graduate teaching and research positions and a research fellowship. vi VITA December 10, 1974 ......................................... Born - Parma, Ohio, USA 1997 ................................................................ B.S. Chemistry and Mathematics, Bowling Green State University, Bowling Green, Ohio, USA 2000.................................................................M.S. Chemistry, The Ohio State University, Columbus, Ohio, USA 1997 - present ................................................. Graduate Fellow, Teaching and Research Associate, The Ohio State University PUBLICATIONS Research Publications 1. Nicholas F. Szabo, Prabir K. Dutta, “Strategies for Total NOx Measurement with Minimal CO interference Utilizing a Microporous Zeolitic Catalytic Filter," Sensors and Actuators B, 88 (2003) 168-177. vii 2. N. F. Szabo, H. Du, S. A. Akbar, A. Soliman, P. K. Dutta, “Microporous Zeolite Modified Yttria Stabilized Zirconia (YSZ) Sensors for Nitric Oxide (NO) Determination in Harsh Environments,” Sensors and Actuators B, 82 (2002) 142- 149. 3. Nicholas F. Szabo, Prabir K. Dutta, A. Soliman, “A NOx Sensor for Feedback Control and Emissions Reduction,” SAE Technical Paper Series, 2002-01-0029 (2002). FIELD OF STUDY Major Field: Chemistry viii TABLE OF CONTENTS Page Abstract ..............................................................................................................................ii Dedication ..........................................................................................................................iv Acknowledgments ..............................................................................................................v Vita ...................................................................................................................................vii List of Tables ....................................................................................................................xv List of Figures ..................................................................................................................xvi Chapters: 1. Introduction..............................................................................................................1 1.1 The need for harsh environment NOx sensors.............................................2 1.1.1 The environmental, health effects and sources of NOx...................2 1.1.2 Legislation on NOx emissions..........................................................4 1.1.3 Methods to control NOx emissions and where a NOx sensor is needed..............................................................................................7 1.1.3.1 Vehicles (mobile sources)................................................7 1.1.3.2 Coal-fired boilers (stationary sources)...........................11 1.2 Future NOx sensor requirements................................................................11 1.3 The existing types of high temperature NOx gas sensors..........................13 1.4 Potentiometric sensors...............................................................................15 1.4.1 Electrolyte types.............................................................................15 ix 1.4.2 Sensor electrodes...........................................................................15 1.4.3 Measurement principle..................................................................16 1.4.4 A real world example: the potentiometric O2 sensor.....................16 1.5 Potentiometric NOx sensors in the literature..............................................17 1.6 Mechanism of potentiometric NOx sensor response..................................23 1.6.1 Operating principles of potentiometric designs.............................24 1.6.1.1 Equilibrium potential type sensors..................................24 1.6.1.2 Mixed potential type potentiometric sensors..................25 1.7 Issues of selectivity between NO an NO2 in existing NOx sensors...........29 Chapter 1: Figures..................................................................................................31 2. Proof of Concept: The Use of Microporous Zeolite NaY to Create a High- Temperature Combustion Gas Sensor...................................................................49 2.1 Experimental..............................................................................................50 2.1.1 Sensor designs...............................................................................50 2.1.2 Sensing apparatus and testing.......................................................52 2.1.3 Prototype design for automotive exhaust gas sensing...................53 2.2 Results........................................................................................................55 2.2.1 Testing with a YSZ air reference based sensor..............................55 2.2.2 Testing of a planar sensor blank (Type III)...................................59 2.2.3 Type I, II, III testing results...........................................................60 2.2.3.1 NO sensing......................................................................60 2.2.3.2 Interference effects..........................................................60 2.2.3.2.1 Oxygen..........................................................60
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