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Thesis Title PALLADIUM AND GOLD CATALYSTS FOR SUSTAINABLE CHEMICAL PROCESSING YUFEN HAO A dissertation submitted for the degree of Doctor of Philosophy Heriot-Watt University School of Engineering and Physical Sciences July 2015 This copy of the thesis has been supplied on condition that anyone who consults it is understood to recognise that the copyright rests with its author and that no quotation from the thesis and no information derived from it may be published without the prior written consent of the author or of the University (as may be appropriate). Abstract The main focus of this thesis is the investigation of sustainable routes for the production of commercially important higher and functionalised aliphatic and aromatic amines through the application of (oxide and carbon) supported palladium and gold catalysts. In the hydrogenation of butyronitrile as a model aliphatic nitrile, unsupported Pd promoted the formation of primary and secondary amines. The acid-base character of the support and available surface reactive hydrogen are critical catalyst variables. The greater acidity of Pd/C (relative to Pd/Al2O3) resulted in the predominant formation of the tertiary (tributyl-) amine where spillover hydrogen serves to elevate hydrogenation rate. The combination of Ba with Pd (supported bimetallic) proved effective in promoting hydrogenation activity with 100% selectivity to the secondary amine, which is attributed to a decrease in acidity and modification to Pd dispersion that enhances surface hydrogen. The feasibility of an alternative route for the synthesis of higher aliphatic secondary and tertiary amines from primary and secondary amine feedstock has been demonstrated. Control of contact time is key where the use of a multiple catalyst beds in series facilitates higher yields. This is accounted for in terms of surface reaction mechanism. This configuration was also efficient for the synthesis of benzylamine from benzonitrile. Hydrogenation selectivity was further assessed by considering the reduction of functionalized nitroarenes (p-chloronitrobenzene (p-CNB) and p-nitrobenzonitrile (p- NBN)). It is shown that the redox nature of the support has a direct impact on the activity and selectivity response. The formation of Pdδ+ (on carbon) activates the nitro group with subsequent C-Cl bond scission with the formation of p-chloroaniline (p- δ- CAN) and aniline (AN). The occurrence of Pd (on SiO2 and Al2O3) favours interaction via the aromatic ring that activates both –NO2 and –Cl for attack generating AN and nitrobenzene. The formation of a PdZn alloy (established by XPS analysis) in addition 0 to Pd selectively activates the –NO2 group and promotes the sole formation of p-CAN at all levels of conversion (and close to 100%). Exclusive conversion of p-NBN to p- aminobenzonitrile was achieved over a series of oxide (CeO2, Fe2O3, Fe3O4, TiO2, ZrO2 and Al2O3) supported (1 mol %) Au catalysts. Hydrogen uptake is structure sensitive and favoured by smaller nano-scale metal particles with a consequent increase in activity. Reaction over Au/TiO2 delivered the highest specific hydrogenation rate, which is explained on the basis of –NO2 activation at the metal-support interface that is i facilitated by Nδ+ interaction with electron rich gold (Auδ-, demonstrated by XPS). This effect is shown to extend to TiO2 supported Ag and Pd. Supported Au is also effective in the selective hydrogenation of benzaldehye in liquid phase operation using water as a green solvent. 100% yield of the target benzyl alcohol was attained over Au/Al2O3 whereas Pt/Al2O3 generated toluene and benzene as significant (hydrogenolysis) by-products. Solvent effects were evaluated where a direct correlation between selective hydrogenation rate and dielectric constant is demonstrated and ascribed to competitive adsorption, which was more severe for less polar alcohol solvents. Solvation by polar water facilitated benzaldehyde activation. The same activity and selectivity trends were found to also apply to continuous gas phase reaction. The results presented in this thesis demonstrate, for the first time, direct participation of the support in the catalytic hydrogenation of aliphatic nitriles over Pd- based catalysts. This can be harnessed to enhance amine production in a sustainable continuous flow gas operation process. Moreover, secondary and tertiary aliphatic amines can be selectively produced from the correspondent primary and secondary amines over Pd in continuous mode. The use of reducible supports can result in the formation of an alloy phase and surface defects with beneficial selectivity and activity effects in the production of functionalized amines. The selective catalytic action of supported Au catalysts has been established in achieving 100% yield of benzyl alcohol (from benzaldehyde) using water as a benign solvent. ii Dedication To my grandparents Yaoer Zhang and Jiacai Hao iii Acknowledgements This thesis could not have been completed without the help and support of my supervisor, colleagues, friends and family. I would like to take this opportunity to express my utmost gratitude to them. My greatest appreciation goes to my supervisor Professor Mark A. Keane. I thank him for the guidance, encouragement and advice that he has provided throughout my PhD studies. I do appreciate his enthusiasm for research work, rich experience in directing research projects. Thanks also goes to Dr. Fernando Cárdenas-Lizana for his patience in discussion and suggestions on the research projects and also the modification of the thesis. I would also like to thank Dr. Humphrey Yiu for his support in access to the usage of experimental equipments. The fancial support from Scottish Overseas Research Student Awards Scheme is also acknowleged and very much appreciated for without it, I would not have been able to commence and complete this work. I am enormously delighted to have the privilege of knowing my colleagues of past and present, namely, Noemie Perret, Xiaodong Wang, Maoshuai Li, I thank you for all the discussions/suggestions in the research projects and wonderful moments in life. I would also like to thank my friends Ivan Ku, Na Wang, Dalia Capao, Eilidh Duncan, Craig Callahan, Natalia Felenta, Gregor, Pedro, Kamil and Yi Jin for making my life easier away from PhD studies. I would personally thank my close friends Shuhua Dong, Peggy Zhu and Rajiv for their consistent support when I was through any difficult times. My appreciation is also extended to all the technicians in Chemical engineering department for helping me with the installation/maintaining of experimental equipments. Just name a few of them, Ronnie (who has retired now); Curtis; Richard; Craig Bell etc. Last but not least, my special gratitude goes to my parents and two younger sisters for their unconditional love and unwavering support. iv Table of Contents Abstract ......................................................................................................................................................... i Dedication ................................................................................................................................................... iii Acknowledgments ....................................................................................................................................... iv Table of Contents ........................................................................................................................................ v Lists of Tables ........................................................................................................................................... ixx Lists of Figures ............................................................................................................................................ xi Lists of Schemes ...................................................................................................................................... xvv Glossary .................................................................................................................................................. xvii Symbols .................................................................................................................................................... xvi List of Publications by the Candidate ...................................................................................................... xixx List of Presentations by the Candidate ..................................................................................................... xxx Chapter 1: Introduction and Scope of the Thesis ........................................................................................ 1 1.1 Sustainable Chemical Processing and Amine Synthesis ............................................................. 1 1.2 Scope and Organization of the Thesis ........................................................................................ 1 1.3 References .................................................................................................................................. 3 Chapter 2: Support Effects in the Gas Phase Hydrogenation of Butyronitrile over Palladium ................. 5 2.1 Introduction ................................................................................................................................ 5 2.2 Experimental Method ................................................................................................................. 6 2.2.1 Catalyst Characterization ......................................................................................................
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