University of South Carolina Scholar Commons Theses and Dissertations Fall 2018 Three-Way Catalysts in Passive Selective Catalytic Reduction Systems Calvin Thomas Follow this and additional works at: https://scholarcommons.sc.edu/etd Part of the Chemical Engineering Commons Recommended Citation Thomas, C.(2018). Three-Way Catalysts in Passive Selective Catalytic Reduction Systems. (Doctoral dissertation). Retrieved from https://scholarcommons.sc.edu/etd/5067 This Open Access Dissertation is brought to you by Scholar Commons. It has been accepted for inclusion in Theses and Dissertations by an authorized administrator of Scholar Commons. For more information, please contact [email protected]. THREE-WAY CATALYSTS IN PASSIVE SELECTIVE CATALYTIC REDUCTION SYSTEMS by Calvin Thomas Bachelor of Chemical Engineering Auburn University, 2013 Submitted in Partial Fulfillment of the Requirements For the Degree of Doctor of Philosophy in Chemical Engineering College of Engineering and Computing University of South Carolina 2018 Accepted by: Jochen Lauterbach, Major Professor William Mustain, Committee Member Erdem Sasmaz, Committee Member Todd Toops, Committee Member Cheryl L. Addy, Vice Provost and Dean of the Graduate School © Copyright by Calvin Thomas, 2018 All Rights Reserved. ii DEDICATION This work is dedicated to my brothers and sisters: Micah, Megan, Charles, Jessica, and Alexandra. They have been with me through my whole life and I wouldn’t be where or who I am without them. It is also dedicated to my dog Fritz because he is a very good boy. iii ACKNOWLEDGEMENTS First and foremost, I would like to thank my advisor, Professor Jochen Lauterbach for accepting me into the Strategic Approaches to the Generation of Electricity (SAGE) research group. My time in this research group has helped me grow tremendously as researcher, and it has been an honor working with him on throughout my PhD research. I would also like to thank Dr. Todd Toops and Josh Pihl in the Fuels, Engines, and Emissions Research Center (FEERC) at Oak Ridge National Laboratory (ORNL). During my visits to the facilities at ORNL, both Dr. Toops and Mr. Pihl provided me with extensive guidance and mentorship. Finally, I would like to thank all the members of both the SAGE research group at USC and the FEERC at ORNL. Both research groups have been welcoming and helpful during my work at their respective institutions. iv ABSTRACT Conventional gasoline-powered engines operate with a stoichiometric air-fuel ratio (AFR), but greater fuel economy is achieved in lean burn engines by increasing the AFR. The primary drawback to these engines is the nitrogen oxide (NOX) emissions, which cannot be reduced over a conventional three-way catalyst (TWC). Passive selective catalytic reduction (SCR) is a promising approach for the control of NOX emissions in lean burn systems. By periodically decreasing the AFR to fuel-rich levels, ammonia (NH3) can be produced over a TWC and stored on a downstream SCR catalyst for the reduction of NOX during normal lean operation. While passive SCR has shown promise, work to date has not sufficiently examined the effects of physical or chemical degradation on the TWC in a passive SCR system or how these factors are affected by the transient nature of passive SCR. Furthermore, many questions about the formulation of the TWC have yet to be answered. This work is focused on answering these questions to better understand NH3 production over TWCs and the degradation mechanisms of passive SCR. Using commercially formulated TWCs, the effects of hydrothermal aging and sulfur dioxide (SO2) are examined, while model catalysts are synthesized to investigate the roles of ceria on the catalyst. Hydrothermal aging at 920°C for 100 hours results in significant noble metal sintering as well as degradation of both oxygen storage and NOX storage components. Long term exposure to 2 ppm SO2 results in significant deactivation of catalyst activity, which is attributed primarily to the deactivation of water gas shift and v steam reformation reactions. These sulfur effects can be partially mitigated by lowering the AFR during rich operation. Finally, in the investigation of ceria, it was found that low levels of ceria promote water gas shift, but elevated levels result in inhibition of catalyst reduction. vi TABLE OF CONTENTS Dedication .......................................................................................................................... iii Acknowledgements ............................................................................................................ iv Abstract ................................................................................................................................v List of Tables .......................................................................................................................x List of Figures .................................................................................................................... xi List of Abbreviations .........................................................................................................xv Chapter 1: Introduction ........................................................................................................1 1.1: Motivation .........................................................................................................1 1.2: Three-way catalyst activity ...............................................................................6 1.3: Three-way catalyst composition .....................................................................10 1.4: Evaluating three-way catalysts for passive selective catalytic reduction .......12 Chapter 2: Experimental ....................................................................................................17 2.1: Experimental techniques .................................................................................17 2.2: Catalysts and Reactors ....................................................................................21 Chapter 3: The Effects of Hydrothermal Aging on Three-Way Catalyst Performance in Passive Selective Catalytic Reduction Systems .................................................................27 3.1: Introduction .....................................................................................................27 3.2: Experimental ...................................................................................................29 3.3: Results and discussion ....................................................................................35 3.4: Conclusions .....................................................................................................50 vii Chapter 4: The Effects of Sulfation on Three-Way Catalyst Performance in Simulated Passive Selective Catalytic Reduction Exhaust .................................................................53 4.1: Introduction .....................................................................................................53 4.2: Experimental ...................................................................................................55 4.3: Results and Discussion ...................................................................................57 4.4: Conclusions .....................................................................................................72 Chapter 5: The Effects of Sulfation on Three-Way Catalyst Performance in Isolated Reactions for Passive Selective Catalytic Reduction.........................................................74 5.1: Introduction .....................................................................................................74 5.2: Experimental ...................................................................................................75 5.3: Results and Discussion ...................................................................................78 5.4: Conclusions .....................................................................................................88 Chapter 6: The Effects of Rich Phase Lambda on the Sulfated Three-Way Catalyst Performance in Simulated Passive Selective Catalytic Reduction Exhaust ......................90 6.1: Introduction .....................................................................................................90 6.2: Experimental ...................................................................................................92 6.3: Results and Discussion ...................................................................................94 6.4: Conclusions .....................................................................................................98 Chapter 7: The Effects of Ceria Loading on Three-Way Catalysts for Passive Selective Catalytic Reduction ..........................................................................................................100 7.1: Introduction ...................................................................................................100 7.2: Experimental .................................................................................................102 7.3: Results and Discussion .................................................................................104 7.4: Conclusions ...................................................................................................107 Chapter 8: Conclusions and Future Work ........................................................................109 viii References ........................................................................................................................117