FUNDAMENTAL STUDIES OF CATALYTIC DEHYDROGENATION ON ALUMINA-SUPPORTED SIZE-SELECTED PLATINUM CLUSTER MODEL CATALYSTS by Eric Thomas Baxter A dissertation submitted to the faculty of The University of Utah in partial fulfillment of the requirements for the degree of Doctor of Philosophy Department of Chemistry The University of Utah May 2018 Copyright © Eric Thomas Baxter 2018 All Rights Reserved T h e U n iversity of Utah Graduate School STATEMENT OF DISSERTATION APPROVAL The dissertation of Eric Thomas Baxter has been approved by the following supervisory committee members: Scott L. Anderson , Chair 11/13/2017 Date Approved Peter B. Armentrout , Member 11/13/2017 Date Approved Marc D. Porter , Member 11/13/2017 Date Approved Ilya Zharov , Member 11/13/2017 Date Approved Sivaraman Guruswamy , Member 11/13/2017 Date Approved and by Cynthia J. Burrows , Chair/Dean of the Department/College/School of Chemistry and by David B. Kieda, Dean of The Graduate School. ABSTRACT The research presented in this dissertation focuses on the use of platinum-based catalysts to enhance endothermic fuel cooling. Chapter 1 gives a brief introduction to the motivation for this work. Chapter 2 presents fundamental studies on the catalytic dehydrogenation of ethylene by size-selected Ptn (n = 4, 7, 8) clusters deposited onto thin film alumina supports. The model catalysts were probed by a combination of experimental and theoretical techniques including; temperature-programmed desorption and reaction (TPD/R), low energy ion scattering spectroscopy (ISS), X-ray photoelectron spectroscopy (XPS), plane wave density-functional theory (PW-DFT), and statistical mechanical theory. It is shown that the Pt clusters dehydrogenated approximately half of the initially adsorbed ethylene, leading to deactivation of the catalyst via (coking) carbon deposition. The catalytic activity was observed to be size-dependent and strongly correlated to the cluster structure, with Pt7 demonstrating the highest activity. In Chapter 3 the focus turns to selectively doping Pt7 clusters with boron. A combination of experiment and theory were used investigate the alkene-binding affinity of the bimetallic (PtnBm/alumina) model catalysts. A comparison of the theoretical and experimental results show that doping the Pt clusters with boron modifies the alkene- binding affinity and thus the tendency toward dehydrogenation to coke precursors. Chapter 4 describes a way to produce bimetallic (PtnBm/alumina) model catalysts by exposing prepared Ptn/alumina samples to diborane and heating. It is shown that the diborane exposure/hearting procedure results in the preferential binding of B to the Pt clusters. iv TABLE OF CONTENTS ABSTRACT ...................................................................................................................... iii ACKNOWLEDGMENTS ............................................................................................... vii Chapters 1. INTRODUCTION .......................................................................................................... 1 1.1 Motivation ................................................................................................................. 2 1.2 References ................................................................................................................. 4 2. ETHYLENE DEHYDROGENATION ON Pt4, 7, 8 CLUSTERS ON Al2O3: STRONG CLUSTER SIZE DEPENDENCE LINKED TO PREFERRED CATALYST MORPHOLOGIES ...................................................................................... 6 2.1 Overview ................................................................................................................... 7 2.2 Introduction ............................................................................................................... 7 2.3 Results and Discussion ............................................................................................. 9 2.3.1 Cluster Catalyst Structures .................................................................................. 9 2.3.2 Size-Dependent Catalytic Activity ................................................................... 11 2.3.3 Routes of Deactivation ...................................................................................... 22 2.4 Conclusions ............................................................................................................. 31 2.5 Methodology ........................................................................................................... 32 2.5.1 Experimental Section ........................................................................................ 32 2.5.2 Computational ................................................................................................... 37 2.6 Acknowledgments................................................................................................... 39 2.7 References ............................................................................................................... 39 3. BORON SWITCH FOR SELECTIVITY OF CATALYTIC DEHYDROGENATION ON SIZE-SELECTED Pt CLUSTERS ON Al2O3 ................. 53 3.1 Overview ................................................................................................................. 54 3.2 Introduction ............................................................................................................. 54 3.3 Results and Discussion ........................................................................................... 56 3.4 Conclusion .............................................................................................................. 68 3.5 Methods................................................................................................................... 68 3.5.1 Experimental Section ........................................................................................ 68 3.5.2 Computational ................................................................................................... 70 3.6 Acknowledgements ................................................................................................. 71 3.7 References ............................................................................................................... 72 4. DIBORANE INTERACTIONS WITH Pt7/ALUMINA: PREPARATION OF SIZE-CONTROLLED BORATED Pt MODEL CATALYSTS WITH IMPROVED COKING RESISTANCE ................................................................................................. 80 4.1 Overview ................................................................................................................. 81 4.2 Introduction ............................................................................................................. 81 4.3 Methods................................................................................................................... 83 4.3.1 Computational ................................................................................................... 84 4.3.2 Experimental ..................................................................................................... 85 4.4 Results ..................................................................................................................... 89 4.4.1 Temperature Programmed Desorption/Reaction Following Adsorption of B2H6 and D2 ........................................................................................................... 89 4.4.2 X-Ray Photoelectron Spectroscopy .................................................................. 93 4.4.3 Temperature-Dependent Ion Scattering Spectroscopy ..................................... 95 4.4.4 DFT Results for Adsorption of Diborane on Pt7 Clusters................................. 97 4.4.5 Molecular Dynamics Simulations of Diborane/Pt7/Alumina Thermal Chemistry ................................................................................................................... 99 4.4.6 Pt4B4/Alumina ................................................................................................. 102 4.5 Discussion ............................................................................................................. 104 4.5.1 Decomposition of Diborane on Pt7/Alumina .................................................. 104 4.6 Conclusion ............................................................................................................ 113 4.7 Acknowledgement ................................................................................................ 113 4.8 References ............................................................................................................. 114 5. CONCLUSION ........................................................................................................... 127 Appendices A: SUPPORTING INFORMATION FOR CHAPTER 2 .............................................. 130 B: SUPPORTING INFORMATION FOR CHAPTER 3 .............................................. 155 C: SUPPORTING INFORMATION FOR CHAPTER 4 .............................................. 177 vi ACKNOWLEDGMENTS I would like to thank Scott L. Anderson for giving me the opportunity to work in his laboratory, first as an undergraduate student, and then as a graduate student. His willingness to have discussions, share his experiences, and to provide encouragement has played a vital role in my development as a research scientist. I would also like to thank the other members of my committee: Professor Peter B. Armentrout, Professor Marc