This document is downloaded from DR‑NTU (https://dr.ntu.edu.sg) Nanyang Technological University, Singapore. Improving selectivity of gold nanoparticles for glycerol electro‑oxidation via interaction with non‑noble metals Thia, Larissa Yi Ping 2017 Thia, L. Y. P. (2017). Improving selectivity of gold nanoparticles for glycerol electro‑oxidation via interaction with non‑noble metals. Doctoral thesis, Nanyang Technological University, Singapore. http://hdl.handle.net/10356/70202 https://doi.org/10.32657/10356/70202 Downloaded on 29 Sep 2021 18:20:57 SGT IMPROVING SELECTIVITY OF GOLD NANOPARTICLES FOR GLYCEROL ELECTRO-OXIDATION VIA INTERACTION WITH NON-NOBLE METALS THIA YI PING LARISSA Interdisciplinary Graduate School NEWRI-Residues & Resource Reclamation Centre 2016 IMPROVING SELECTIVITY OF GOLD NANOPARTICLES FOR GLYCEROL ELECTRO-OXIDATION VIA INTERACTION WITH NON-NOBLE METALS THIA YI PING LARISSA Interdisciplinary Graduate School NEWRI- Residues & Resource Reclamation Centre A thesis submitted to the Nanyang Technological University in partial fulfilment of the requirement for the degree of Doctor of Philosophy 2016 To my parents, with gratitude. Acknowledgements First and foremost, I would like to thank my supervisor, Prof Wang Xin, for giving me the opportunity to join his research group and work on this project. Your patience and support over the course of my PhD studies has been instrumental in helping me persist despite my numerous failures. I have also benefited greatly from the academic advice you have given me. To my lab mates, both past and present, including: Zhou Huiming, Yan Ya, Xiao Peng, Xia Baoyu, Peng Yuecheng and Nsanzimana Jean Marie Vianney thanks for the help and support. Special thanks goes out to: Li Nan, for your encouragement when I needed it the most. Also for help with the XPS tests. Xie Mingshi, for helping me in countless large and small ways (certainly too many to be listed). Wang Jiong and Lu Yizhong for the insightful discussions that I have had with you guys over the past 8 months. Also for help with ICP and TEM. Finally, to Wang Haibo, thanks for pulling me through the past year (and all the times in between) as I worked towards completing my thesis and publications. I couldn’t have done it without you. To the friends that I have made during my PhD studies: Yan Yibo, Chen Xiaoping, Zhao Jun and Huang Lin, thanks for all the laughter, friendship and generosity. To Jaslyn, thanks for being such a pal. Glad to have made it through this PhD journey with you. I would also like to thank my other friends, especially Bri and Angie, for their unwavering support and encouragement. Thanks for always being available. Lastly, my gratitude goes out to my parents for the immense sacrifices they have made for me over the years. Thanks for giving me the best in life and for always believing in me despite all the odds. This thesis is dedicated to the both of you. i Abstract This thesis begins by examining the current state of the art for glycerol electro-oxidation. Extensive research has been carried out to determine the effect of size, morphology, shape, support, experimental conditions and catalyst preparation methods on the catalytic performance of both Au and Pt based catalysts. While the effect of non-noble metal promoters has been relatively well studied for Pt group catalysts, the same cannot be said for Au based catalysts. Thus, the research work presented in this thesis aims to demonstrate how the selectivity of carbon supported Au nanoparticles for glycerol electro-oxidation can be improved via interaction of Au/C with non-noble metals. Enhanced selectivity towards C3 products, glycerate and tartronate, was achieved by simple electro-deposition of Cu onto Au nanoparticles. Initial studies showed that the most selective catalysts were obtained when Cu electro-deposition occurred at -0.1 V and +0.015 V for 30 min. Enhancement in C3 selectivity was attributed to the presence of an Au+ species that was generated via electron transfer between Au and electro-deposited Cu2O. C3 selectivity was maximized at double that of pure carbon supported Au nanoparticles when Cu electro- deposition took place at +0.015 V for 90 min. This result is attributed to the doubling of Au+ content that takes place at this experimental condition. Electro-deposition of Ni onto Au nanoparticles also gave rise to enhanced C3 selectivity. The most selective catalysts were obtained when Ni electro-deposition occurred at -0.3 V for 40 min. Au+ species was similarly identified post Ni electro-deposition and it was generated due to electron transfer between Au and NiOOH species. When Ni electro-deposition occurred at more negative potentials, the resultant thick Ni surface layer partially shielded Au from the reaction medium thus reduced access of glycerol molecules to the Au active sites. As such, C3 selectivity of the Ni-Au/CB catalysts prepared under these conditions were relatively similar ii to that of pure Au/CB. Any possible synergistic effect between Au and Ni was thus nullified by the thick Ni surface coverage. Lastly, residual Ag containing porous Au structures were prepared and tested for glycerol electro-oxidation. These catalysts were highly active and selective towards C-C bond breaking products, glycolate and formate. Porous Au catalysts were obtained by etching alloyed AuAg sheets in concentrated nitric acid. However, etching does not completely remove all traces of Ag, hence small amounts are still present. Additionally, low temperature annealing enhanced selectivity and product conversion due to the increase in mixed Au-Ag sites after annealing. Keywords: glycerol electro-oxidation, Cu electro-deposition, Ni electro-deposition, porous Au, Au nanoparticles iii Table of Contents Acknowledgements .................................................................................................................. i Abstract .................................................................................................................................... ii Table of contents ..................................................................................................................... iv List of figures ......................................................................................................................... viii List of tables............................................................................................................................. xi List of publications ................................................................................................................. xii Chapter 1: Introduction and Scope of Thesis ...................................................................... 1 1.1. Introduction ................................................................................................................... 1 1.2. Rationale: the need to valorise glycerol via electro-oxidation .................................... 1 1.3. Scope of thesis .............................................................................................................. 3 1.3.1. Objectives ............................................................................................................... 3 1.3.2. Hypothesis............................................................................................................... 4 Chapter 2: Literature Review ................................................................................................ 6 2.1. Introduction ................................................................................................................... 6 2.2. Glycerol Oxidation....................................................................................................... 6 2.2.1. Platinum group catalysts ......................................................................................... 6 2.2.1.2. Disadvantages ................................................................................................... 7 2.2.2. Gold based catalysts ................................................................................................ 7 2.2.2.1. Advantages ........................................................................................................ 7 2.2.2.2. Size Effect ......................................................................................................... 8 2.2.2.3. Effect of preparation method ............................................................................ 9 2.2.2.4. Influence of protecting agent .......................................................................... 11 2.2.2.5. Influence of platinum group metals on catalytic performance of Au ............ 12 2.2.3. Effect of support .............................................................................................. 17 2.2.3.1. Carbon supports ......................................................................................... 17 2.2.3.2. Oxide supports ........................................................................................... 20 2.2.3.2.1. Influence of basic/acidic nature of oxide supports .............................. 20 2.2.3.2.2. Nickle oxide supports .......................................................................... 21 2.2.3.2.3. Copper oxide supports ......................................................................... 22 2.2.4. Influence of reactor design ................................................................................... 22 2.2.5. Copper based catalysts .........................................................................................