Gold has been considered catalytically inert due to its resistance to oxidation and corrosion. However, decades ago, it was discovered that gold nano-particles (<5nm) on metal oxides demonstrate superior chemical activity towards many reactions. These seminal findings spurred considerable interest in investigations of the mechanistic details of oxidative reactions on gold-based catalysts. However, the active site and structure of supported Au nanoclusters as well as the active oxygen species remains elusive. Achieving high selectivity toward partial oxidation products also remains a challenge. In this dissertation, an oxygen-covered Au(111) crystal under ultra vacuum conditions was used as a model system to gain insights into oxidative reactions in gold-based catalysis. I have been able to demonstrate that (i) surface-bound oxygen atoms are metastable at low temperature; (ii) the oxygen atoms participate in surface reactions as a Brønsted base or a nucleophilic base; and (iii) the acid-base reactions that have been observed on silver and copper may also occur on gold. Low temperature CO oxidation and the associated mechanistic aspects are investigated. CO reacts with hydroxyls formed from water-oxygen interactions to produce CO₂ on Au(111) populated with atomic oxygen at low temperatures. Directing an ¹⁶O beam toward C¹⁸O₂ pre-adsorbed Au(111), the formation of carbonate is significantly enhanced. This reaction is suggested to follow a hot-precursor-mediated mechanism. The identification of reaction pathways in oxidation of N-containing molecules such as ammonia and propylamine is presented. Abstraction of hydrogen from ammonia or propylamine by O atoms is the initial step in the surface decomposition of NHx (or RNHx-1) on Au(111). Atomic oxygen or hydroxyl-assisted dehydrogenation steps have lower barriers than the recombination steps under relevant conditions. 100% selectivity of N₂ or propionitrile can be obtained if the oxygen coverage is below the stoichiometric value. The surface oxidative chemistry of alcohols on Au(111) is also investigated. Except for methanol that is fully oxidized, alcohols initially undergo O-H bond cleavage (producing alcoxides) followed by selective β-C-H bond activation to form aldehydes or ketones. This finding reveals that the interaction of Au with the metal oxide support might not be essential to facilitate the reactions if active oxygen species are readily present, particularly at low temperatures. / text

published_or_final_version / Medical Sciences / Master / Master of Medical Sciences

published_or_final_version / Microbiology / Master / Master of Medical Sciences

published_or_final_version / Chemistry / Master / Master of Philosophy

published_or_final_version / Chinese Medicine / Doctoral / Doctor of Philosophy

Not available / text

Not available / text

In this thesis, we establish the asymptotic analysis of the singularly perturbed reaction diffusion equation [cataloger unable to transcribe mathematical equations].... Our results establish the specific dependency on the coefficients of this equation and the size of the parameter [delta] with respect to [epsilon]. The analyses include equation subject to Dirichlet and Neumann boundary conditions. In both cases, the solutions u[superscript epsilon] converge locally uniformally to the equilibria of the reaction term f. We characterize the limiting behavior of the solutions through the viscosity solution of a variational inequality. To construct the coefficients defining the variational inequality, we apply concepts developed for the homogenization of elliptic operators. In chapter two, we derive the convergence results in the Neumann case. The third chapter is dedicated to the analysis of the Dirichlet case. / text

To investigate (1) the effect of mental rehearsal (MR) on reaction time (RT), and (2) the roles of cerebral lateralization, memory, verbal and nonverbal processes in MR effects, two experiments were conducted using a total of 300 sports participants matched on age, cerebral lateralization, imagery ability, intelligence, kinaesthesis, motivation, sex, skill level and speed of reaction. It was found that (a) MR can affect significantly RT (p/0.01) because it is a powerful cognitive activity which can directly influence the memory system and make memory comparison and/or response selection processes more efficient, and (b) that there are two separate processing systems - two separate modes of thought - for verbally and nonverbally coded information, that these processing systems might be functionally discriminated along hemispheric lines, that the non-verbal processing system considerably precedes the verbal processing system, probably because it uses a more effective processing strategy, and that MR affects significantly (p/0.01) and differently the operations of the two processing systems, probably because MR is a cognitive activity more associated with the right cerebral hemisphere than with the left. The results are discussed in the light of current cerebral laterality, imagery, memory, MR and RT findings.

published_or_final_version / Chemistry / Master / Master of Philosophy