Zeolite nanoporous và thiết bị cảm biến nitrogen oxide - Luận án tiến sĩ

NANOPOROUS ZEOLITE AND SOLID-STATE ELECTROCHEMICAL DEVICES FOR NITROGEN-OXIDE SENSING DISSERTATION Presented in Partial Fulfillment of the Requirements for the Degree Doctor of Philosophy in the Graduate School of The Ohio State University By Jiun-Chan Yang ***** The Ohio State University 2007 Dissertation Committee: Approved by Professor Prabir K. Dutta, Advisor Professor Sheikh A. Akbar _________________________________ Professor Patrick M. Woodward Advisor Graduate Program in Chemistry Professor V.

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Box 1346 Ann Arbor, MI 48106-1346 ABSTRACT Solid-state electrochemical gas sensing devices composed of stabilized-zirconia electrolyte have used extensively in the automobile and chemical industry. Two types of electrochemical devices, potentiometric and amperometric, were developed in this thesis for total NOx (NO + NO2) detection in harsh environments. In potentiometric devices, Pt covered with Pt containing zeolite Y (PtY) and WO3 were examined as the two electrode materials. Significant reactivity differences toward NOx between PtY and WO3 led to the difference in non-electrochemical reactions and resulted in a electrode potential.

With gases passing through a PtY filter, it was possible to remove interferences from 2000 ppm CO, 800 ppm propane, 10 ppm NH3, as well as to minimize effects of 1~13% O2, CO2, and H2O. Total NOx concentration was measured by maintaining a temperature difference between the filter and the sensor. The sensitivity was significantly improved by connecting sensors in series. Amperometic devices were also developed to detect NOx passing through the PtY filter.

By applying a low anodic potential of 80 mV, NO in the NOx equilibrated mixture can be oxidized at a Pt working electrode on the YSZ electrolyte at 500°C. The PtY can be held separate from the YSZ or coated onto the YSZ as a film. This design was demonstrated to exhibit total-NOx detection capability, a low NOx detection limit (< 1 ii ppm), high NOx selectivity relative to CO and oxygen, and linear dependence on NOx concentration. The non-electrochemical reactions around the triple-phase boundary were studied to understand the origin of the superior performance of WO3 on potentiometric NOx sensing.

From TPD, DRIFTS, XRD, Raman, and catalytic activity measurements, the interfacial reactions between WO3 and YSZ were found to dramatically reduce the NOx catalytic activity of YSZ. WO3 reacted with surface Y2O3 on YSZ and formed less catalytically active yttrium tungsten oxides and monoclinic ZrO2, which suppressed the non-electrochemical reactions around the triple-phase boundary. These two products also decreased the oxygen vacancy density around the triple-phase boundary, slowed down the electrochemical oxygen reduction reaction, and in turn increased the NOx signal. The surface nanostructure of electrodes was modified by wet chemical processes to change the non-electrochemical NOx reactions.

A thin WO3 coating prepared from the peroxytungstate solution with well-defined triple-phase boundaries resulted in higher sensitivity and better response times than the electrode fabricated from commercial WO3 powders. The electrodeposited porous Pt layer greatly increased the surface area and led to a similar catalytic activity with PtY on NOx sensing. The modified electrodes demonstrated the importance of the surface nanostructure and interfacial species for potentiometric NOx sensing. The sensors composed of tungsten/H2O2 deposited sensing electrodes and more hydrothermal stable Pt-loaded siliceous zeolite Y (PtSY) reference electrodes have stable NO2 signal at 5-10% water in 600°C.

iii Dedicated to my family iv ACKNOWLEDGMENTS I would like to express my greatest gratitude to my advisor, Professor Prabir Dutta, for his encouragement and support throughout the course of this research. I am deeply indebted to Professor Sheikh Akbar, Dr. Chonghoon Lee, Dr. Ramamoorthy Ramasamy, and Dr.

Yanghee Kim, for their invaluable assistance on research and willingness to share their insight and wisdom. The current and past members of Dutta group, including Dr. Nick Szabo, Dr. Marla De Lucia, Dr.

Joe Trimboli, Dr. Bob Kristovich, Dr. John Doolittle, Dr. Kefa Onchoke, Dr.

Dipankar Sukul, Dr. Radha Vippagunta, Dr. Joe Obirai, Dr. Cheruvallil Rajesh, Toni Ruda, John Spirig, Haoyu Zhang, Mariela Oyola, Bill Schumacher, Brian Peebles, Jeremy White and Dedun Adeyemo are greatly acknowledged for their cooperation and friendship.

I must also thank Professor Henk Verweij, Professor Umit Ozkan, Professor Nitin Padture, Professor Richard McCreery, Professor Patrick Woodward, as well as the members in their groups and CISM: Dr. Jing-Jong Shyue, Dr. Sehoon Yoo, Dr. Krenar Shqau, Dr.

Jingyu Shi, Dr. Di Yu, Dr. Rick Watson, Matt Yung, Lanlin Zhang, Matt Mottern, Mike Rauscher, Inhee Lee, Jin Wang, Hong Tian, Pengbei Zhang, and Haihe Liang, for their fruitful discussion and instrumental support. v Finally, I would like to thank my parents, my wife Ju-Ya, my son Eli, and my daughter Erica, for being my solid support through this process.

vi VITA June 5, 1973. Born – Taichung, Taiwan 1995. National Chiao-Tung University, Hsinchu, Taiwan 1997. National Taiwan University, Taipei, Taiwan 1997 – 1999.

Second Lieutenant, Military Police R.Process Engineer, Taiwan Semiconductor Manufacturing Company, Tainan, Taiwan 2002 – present. Graduate Teaching and Research Associate, The Ohio State University. vii PUBLICATIONS Research Publications 1. Jiun-Chan Yang, Hsin-Yen Hwang, Che-Chen Chang “Surface Microchemistry Associated with Particle Bombardment on Ni(111)” Mat.

Jiun-Chan Yang, Prabir Dutta, “High temperature amperometric total NOx sensors with platinum-load zeolite Y modified electrodes”, Sensors and Actuators B, 2007, in press FIELDS OF STUDY Major Field: Chemistry viii TABLE OF CONTENTS Page Abstract.vii List of Tables. xvi List of Figures .1 Nitrogen oxides chemistry.2 Oxidation state +2: NO.3 Oxidation state +4: NO2, N2O4.4 Oxidation state +3 and +5: N2O3, N2O5.2 The impact and sources of NOx .3 NOx emission control with NOx sensors.4 The existing techniques of NOx sensing .1 Optical adsorption and emission .5 High temperature electrochemical NOx sensors.2 Equilibrium-Potential Type.2 Mixed-potential type.6 Selectivity of electrochemical type sensors. Promoting selectivity and sensitivity for a high temperature YSZ-based potentiometric total NOx sensor by using a Pt-loaded zeolite Y filter.1 Preparation and characterization of sensor materials.2 Catalytic NOx conversion measurements.3 Temperature programmed desorption.5 Gas sensing measurements.1 CO2, CO interference.1 Choice of electrodes.2 Role of PtY Filter .1 Interference from oxidizing gases .3 Strategies to increase sensitivity. Amperometric total NOx sensors with integrated Pt-loaded Zeolite catalytic layers.1 Pt-loaded zeolite Y preparation and characterization.3 Sensor testing setup.1 Current-voltage curves.2 Sensing response of NOx.

The influence of the interfacial reactions at the electrode-solid electrolyte interface to NOx adsorption and potentiometric NOx sensing .1 Preparation and characterization of materials .2 Sensor fabrication and electrical measurements.3 Catalytic NOx conversion measurements.4 Temperature programmed desorption measurements.5 Diffuse reflectance infrared Fourier transform spectroscopy.1 NO2 and O2 sensing behavior .3 Catalytic NOx conversion measurements.4 Temperature programmed desorption .5 X-Ray diffraction and Raman scattering.1 WO3-YSZ samples .6 Diffuse reflectance infrared Fourier transform spectroscopy .1 NO2/O2 co-adsorption on YSZ and ZrO2.2 NO2/O2 co-adsorption on Y2O3 and WO3-Y2O3.3 NO2/O2 co-adsorption on WO3-YSZ.1 NOx adsorption and conversion on WO3, ZrO2, and YSZ .2 The interfacial reactions between WO3 and YSZ .3 The influence of interfacial reactions to NOx adsorption at the triple-phase boundary .4 The influence of interfacial reactions to NOx sensing. Nanostructured Pt / WO3 electrodes and siliceous zeolite Y for sensor optimization .1 Sensor fabrication and characterization .1 Basic sensor platform .2 WO3 thick film electrode .3 WO3–coated Pt electrode .4 Peroxy-complex deposited WO3 electrode.5 Electrodeposited mesoporous Pt reference electrode.6 Pt-loaded Zeolite Y (PtY) reference electrode .7 Pt-loaded siliceous Zeolite Y (PtSY) reference electrode.1 Crystal structures and surface nanostructure of WO3 electrodes .2 Surface nanostructure of electrodeposited Pt electrodes .3 Pt-loaded zeolite Y and siliceous zeolite Y characterization .4 NO2 sensing behavior .1 Pt sensing / PtY reference (Sensor D, E) .2 WO3 sensing / PtY reference (Sensor A, B, C) .3 Pt sensing / Pt reference (Sensor G) .4 WO3 sensing / PtSY reference (Sensor F) .1 WO3 electrodes on YSZ from proxy-tungstate solutions.2 PtY and PtSY.3 Surface modified Pt electrodes. 208 xv LIST OF TABLES Table Page 1.1 Typical concentrations of exhaust gas compositions .2 Examples of the two main types of potentiometric based sensors.1 The relative changes due to the presence of CO2, CO, propane, NH3, oxygen, and water on NO signal with and without a 400oC PtY filter.1 Samples prepared in Chapter 4.155 xvi LIST OF FIGURES Figure Page 1.1 The Lewis structures of various nitrogen oxides .2 The equilibrium constants vs. temperatures for reaction 1.4 and the ratio of NO or NO2 over total NOx (NO+NO2) in 3% O2 .3 Chemical pathway of NOx formation and destruction .4 The acid deposition process.5 NOx caps under the clear sky initiative.6 The conversion efficiency of three-way catalysts .7 Conventional automotive engine control system .8 Control system for new gasoline direction inject engines .9 Illustration of depleted grain boundaries and the effects of a reducing gas on the conduction process .10 Illustration of a potentiometric gas sensor with an air reference electrode.11 Diagram of a equilibrium type NOx sensor.12(a) Mixed-potential when two electrochemical reactions have comparable kinetics.

48 (b) Mixed-potential with faster oxygen kinetics. 48 (c) Mixed-potential with slower NOx kinetics.49 (d) Mixed-potential with NO/NO2 in equilibrium.13 Mixed-potential signal of NO and NO2 at different temperatures .14 Mixed-potential type NOx sensor from Ceramatec Inc.15 Schematic cross-section of a typical amperometric oxygen sensor with a channel-type diffusion barrier .16 Principle of an amperometric two-stage cell for the simultaneous detection of oxygen and NO.17 A commercial NOx sensor from Siemens VDO / NGK.18 Design of commercial NOx sensors from NGK .19 Standard electrode potentials of various reactions at 900K with reference to reaction 1.1 Sensor testing setup (PtY = Pt-Zeolite Y) .2 Potentiometric sensors composed of YSZ, WO3 sensing electrodes, and PtY/Pt reference electrodes.3 TEM micrographs and TPD profile of NO peak (m/z =30) from a sample of PtY following adsorption of 2500 ppm NO and 5% O2 at room temperature.4 Measure of NOx equilibration as a function of temperature with 600 ppm NO2 in 3% O2.5 SEM micrographs and TPD profile of NO peak (m/z =30) from a sample of WO3 following adsorption of 2500 ppm NO and 5% O2 at room temperature. log ([NOx]) plots for a sensor at 600°C .7 Measured EMF of a signal as a function of PtY filter temperature for 10 ppm NO in 3% O2 with sensor at 600°C .8 Response curves and EMF–log ([NO]) plots for a 3-sensor array and a single sensor .9 Schematic representation of gas composition during testing of interferences from CO, CO2, propane, and NH3 .10 Response transient of 1-13 ppm NO in the presence of 3% O2 and different levels of CO2 or CO .11 Response transients from 1-13 ppm NO in the presence of 3% O2 and NH3 .12 Response curves of 1-13 ppm NO in the presence of 3% O2 and propane.13(a) Response curves of 10 ppm NO in different oxygen levels. 92 (b) EMF–oxygen level plots for NOx with or without a PtY filter at 400°C.

water level in 10% O2 with a PtY filter at 400°C .15 Stability of 1-13 ppm NO sensing signal over a 7-day test period in 3% O2 with a PtY filter at 400°C .1 Schematic representation of sensors composed of YSZ, PtY, and Pt electrodes.2 Sensor test setup.3 Homemade portable potentiostat powered by a 9V battery or an AC/DC adapter.4 The connection of sensors and electrical measuring instruments.5 I-V curves acquired in 600 ppm NO or NO2 with 3% O2 .6 I-V curves acquired on Pt and LSCFO electrodes in 3% O2.7 Calibration curves for 100-800 ppm NOx and 250-1000 ppm CO in 3% O2 .8 Comparison of responses for 1-110 ppm total NOx between a type B sensor and a chemiluminescent NOx analyzer .9 Calibration curves for a type B sensor with 1-120 ppm NOx in 3% O2 .10 Comparison of responses for 1-3 ppm total NOx between a type D sensor and a chemiluminescent NOx analyzer .11 Oxygen interference test on a type B sensor.12 Oxygen interference test on a type C sensor .13 Electrode interfacial impedance in difference oxygen partial pressure .