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When referring to this work, full bibliographic details including the author, title, awarding institution and date of the thesis must be given e.g. AUTHOR (year of submission) "Full thesis title", University of Southampton, name of the University School or Department, PhD Thesis, pagination http://eprints.soton.ac.uk UNIVERSITY OF SOUTHAMPTON FACULTY OF NATURAL AND ENVIRONMENTAL SCIENCES Chemistry Design of Hybrid Nanomaterials as Sustainable Heterogeneous Oxidation Catalysts by Christopher Stephen Hinde Thesis for the degree of Doctor of Philosophy April 2015 UNIVERSITY OF SOUTHAMPTON ABSTRACT FACULTY OF NATURAL AND ENVIRONMENTAL SCIENCES Chemistry Thesis for the degree of Doctor of Philosophy DESIGN OF HYBRID NANOMATERIALS AS SUSTAINABLE HETEROGENEOUS OXIDATION CATALYSTS Christopher Stephen Hinde Anion exchange properties of a microporous copper chlorophosphate have been exploited to demonstrate, for the first time, a method for generating monodisperse and uncapped noble metal nanoparticles by thermal extrusion. Confirmed initially by structural characterisation with PXRD, SEM and TEM studies, the microporous framework supported Au, Pt and Pd nanoparticles were shown to activate molecular oxygen for the environmentally benign oxidation of benzyl alcohol to benzaldehyde. Probing of the kinetic properties demonstrated contrasting catalytic features for each of the NP catalysts, with the Pt NP catalyst showing heightened activity and a propensity for selectivity toward benzaldehyde. In-depth physico-chemical analysis of the metal NP catalysts revealed a dependence of the activation/extrusion parameters to the activity and catalytic properties of the resulting materials. Utilising X-ray techniques such as XAS (EXAFS and XANES) and XPS, coupled with the investigation of catalytic properties toward aerobic oxidation of vanillyl alcohol to vanillin, it was established that reduction in the presence of H at moderate temperatures is a 2 much more efficient process to calcination in air at much higher temperatures, to afford the complete extrusion of complex anions for active NP formation. Structure-property correlations were harnessed to rationalise the superior catalytic properties of the Pt catalyst compared with the Au and Pd counterparts, exposing the extent of extrusion and revealing a contrast in the nature of complex anion-support interactions. To further exemplify the scope of hybrid metal nanoparticle/microporous nanomaterials in the pursuit of new, efficient, green and industrially applicable catalysts, the highly robust UiO-66 type MOFs have been utilised as NP hosts for tandem catalytic applications. A facile method of NP deposition on UiO-66 has been demonstrated using established colloidal synthesis methods with PVP, to generate active Au NP materials for the selective oxidation of cinnamyl alcohol to cinnamaldehyde using simple peroxides. By introducing amine functionality to the MOF with 2-aminoterephthalic acid to form the isoreticular NH -UiO-66 as a host for Au NPs, an effective catalyst for the two step process 2 involving the aforementioned oxidation with subsequent Knoevenagel condensation reaction (coupling the aldehyde with an activated methylene compound at the –NH sites on the MOF) has been achieved in good yield. 2 Table of Contents ABSTRACT ................................................................................................................................ i Table of Contents ............................................................................................................. iii List of Tables .......................................................................................................................ix List of Schemes ............................................................................................................... xiii List of Figures ................................................................................................................... xv DECLARATION OF AUTHORSHIP ........................................................................... xxv Acknowledgements ................................................................................................... xxvii Abbreviations ................................................................................................................ xxix Chapter 1: Introduction ............................................................................................ 1 1.1 Catalysis ................................................................................... 1 1.1.1 Mechanisms and Fundamental Theory ............................ 1 1.1.1.1 Heterogeneous and Homogeneous Catalysis ........ 5 1.1.1.2 Active sites .......................................................... 6 1.1.1.3 Immobilisation Concepts ..................................... 7 1.1.1.4 Reactions at Surfaces ........................................... 8 1.1.1.5 Measurement of Activity .................................... 10 1.1.2 Catalysis in Industry ..................................................... 11 1.1.2.1 Sustainable Chemistry ....................................... 12 1.1.2.2 Oxidation Catalysis ........................................... 14 1.2 Nanoparticles as Catalysts ....................................................... 16 1.2.1 Metal Nanoparticles and the Quantum Size Effect .......... 17 1.2.2 Localised Surface Plasmon Resonance (LSPR) ................. 18 1.2.3 Control of Size and Shape ............................................. 20 1.2.4 Synthesis and Immobilisation of Nanoparticles .............. 22 1.2.4.1 Impregnation .................................................... 22 1.2.4.2 Deposition-Precipitation Strategy ....................... 23 1.2.4.3 Colloidal Deposition .......................................... 24 1.2.4.4 Encapsulation .................................................... 25 iii 1.2.4.5 Multimetallic Nanoparticles ............................... 27 1.2.5 Host Materials .............................................................. 28 1.2.5.1 Microporous Inorganic Frameworks ................... 29 1.2.5.2 Metal-Organic Frameworks ................................ 31 1.2.5.3 Mesoporous Materials ....................................... 34 1.2.6 Catalytic Oxidation Reactions with Noble Metal Nanoparticles ............................................................... 35 1.2.6.1 Oxidation of Carbon Monoxide .......................... 36 1.2.6.2 Oxidation of Alcohols ........................................ 37 1.2.6.3 Oxidation of Hydrocarbons ............................... 44 1.3 Aims and Discussion ............................................................... 48 1.3.1 Rationale for Development of NP Catalysts .................... 48 1.3.2 Design, Characterisation and Implementation ............... 49 1.4 References .............................................................................. 51 Chapter 2: Experimental ....................................................................................... 63 2.1 Synthetic Techniques ............................................................... 63 2.1.1 Hydrothermal Synthesis ................................................ 63 2.1.2 Solvothermal Synthesis ................................................. 65 2.1.3 Activation of MOFs ....................................................... 65 2.1.4 Synthesis of Nanoparticle-Polymer Colloids ................... 66 2.2 Catalytic Techniques ............................................................... 67 2.2.1 Reactions in the Batch .................................................. 67 2.2.1.1 High Pressure Batch Reactions ........................... 67 2.2.1.2 Batch Reactions at Ambient Pressure ................. 69 2.2.2 Gas Chromatography (GC) ............................................ 70 2.2.2.1 Quantitative Analysis by GC ............................... 72 2.3 Characterisation Techniques .................................................... 74 2.3.1 Powder X-Ray Diffraction .............................................. 74 iv 2.3.2 Electron Microscopy ..................................................... 77 2.3.2.1 Scanning Electron Microscopy (SEM) ................... 77 2.3.2.2 Transmission Electron Microscopy (TEM) ............ 80 2.3.2.3 Energy Dispersive X-Ray Spectroscopy (EDX) ...... 81 2.3.3 X-Ray Photoelectron Spectroscopy (XPS) ........................ 83 2.3.4 X-ray Absorption Spectroscopy (XAS) ............................. 85 2.3.4.1 Extended X-Ray Absorption Fine Structure Spectroscopy (EXAFS) ........................................ 86 2.3.4.2 X-Ray Absorption Near-Edge Spectroscopy (XANES) ......................................................................... 88 2.3.5 Inductively Coupled Plasma – Optical Emission Spectroscopy (ICP-OES) ................................................. 89 2.3.6 Thermogravimetric Analysis (TGA) ................................ 90 2.3.7 Gas Adsorption Surface Analysis Studies ....................... 90