The negligible volatility of ionic liquids allows them to be studied by applying ultrahigh vacuum (UHV) techniques, i.e. X-ray photoelectron spectroscopy (XPS). Consequently, this Thesis describes the XPS of ionic liquid-based metal catalytic systems. Correlation between the binding energy derived from XPS and reaction performance is extensively discussed and used to design a catalytic system for the Suzuki cross coupling reaction. To allow comparable information for the solute dissolved in ionic liquids to be obtained, pure ionic liquids and ionic liquid mixtures are analysed. Fitting models of C 1 s spectra for different ionic liquid families are presented. Charge correction methods, specifically the influence of anion basicity on charge correction, are discussed in detail. The cation-anion interaction is investigated for different families of ionic liquids with single and mixed anions. The interaction between catalysts and ionic liquids can also be demonstrated by XPS. The formation of palladium-containing ylidene complexes in ionic liquids is confirmed by XPS and ESI-MS. The influence of anion basicity on the measured binding energy of the palladium centre is explored. The binding energies of Pd 3d for a range of solutions are plotted against several established metrics, i.e. proton affinity, interaction energy and hydrogen bond acceptor ability (P), and are used to reflect the reaction rates for a model Suzuki reaction. After a proper understanding of the correlation between the binding energy of a metal centre and the reaction rate, a palladium-based catalytic system may be optimised for the Suzuki reaction. The reaction rates observed in ionic liquids with differing basicity anions are monitored and correlated back to the binding energy. XPS is also applied to investigate the interaction of catalysts with ligands in ionic liquid-based rhodium systems. The formation of different rhodium ligand-containing complexes is detected by XPS. The influence of anion basicity on the formation of different rhodium-containing complex is discussed. The measured binding energy of the rhodium centre is correlated to the reaction selectivity in the hydroformylation reaction.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:557146 |
| Date | January 2011 |
| Creators | Men, Shuang |
| Publisher | University of Nottingham |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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