Structural and catalytic studies of novel Au/Ni enantioselective catalysts
Abstract
Heterogeneous enantioselective catalysis strives to create new successful catalysts. One of the
most researched examples is the hydrogenation β-ketoesters using nickel-based catalysts. A
hindrance in the industrial scale-up of this enantioselective hydrogenation reaction is the lack
of exact details of how chirality is bestowed onto this achiral metal surface. While a number
of mechanisms have been proposed to explain the enantioselective behaviour of this system,
these are predominantly based on catalytic studies. An alternative approach is through surface
science studies examining the morphology, structure and composition of this catalytic
system. A range of ultrahigh vacuum based model studies investigating the structure and
composition of ultrathin Ni films and Ni/Au surface alloys on Au{111} using the techniques
of Scanning Tunnelling Microscopy (STM) and Medium Energy Ion Scattering (MEIS) are
presented in this thesis. In addition, the adsorption of the chiral modifier (S)-glutamic acid
has been studied on these surfaces using vibrational spectroscopy (Reflection Absorption
Infrared Spectroscopy (RAIRS)) and Temperature Programmed Desorption (TPD).
Furthermore, MEIS has been used to investigate the influence of (S)-glutamic acid on the
surface composition of Au/Ni model catalysts detecting effects such as adsorbate induced
segregation and de-alloying behaviour.
In addition, colloidal preparative routes have been used to synthesise bimetallic Au/Ni
nanoparticles supported on mesoporous silica. The catalysts are then modified by the
adsorption of the chiral ligand, (R,R)-tartaric acid. Finally, the catalysts are tested for their
activity and enantioselectivity with respect to methylacetoacetate hydrogenation. At each
stage the catalysts are characterised by a combination of Extended X-ray Absorption Fine
Structure (EXAFS); Transmission Electron Microscopy (TEM), Energy Dispersive X-ray
Spectrometry (EDS) and Atomic Absorption Spectroscopy (AAS).
Type
Thesis, PhD Doctor of Philosophy
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