Abstract
Ph.D. (Chemistry)
Catalysis has increasingly become a crucial enabling technology permitting the functionalization and utilization of a myriad of raw materials. Within this thesis we report on the kinetic analysis and catalytic activity of γ-Al2O3 supported copper and gold nanoparticles on the rate of oxidation of various reactions under mild conditions. The organothiol adsorption-based technique, using the Langmuir approach for the determination of specific surface area of these supported copper and gold nanoparticles is also reported. Alumina, γ-Al2O3 and the mixed oxide Li2O/γ-Al2O3 were used as supports for the copper and gold particles. The synthesis of copper and gold nanoparticles is simply carried out via homogeneous deposition precipitation using CO(NH2)2 as precipitating agent, and thereafter reduced using NaBH4 resulting in the formation of small particles with a fairly narrow size distribution. Cationic imidazolium ionic liquids, 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIM][BF4]) and 1-butyl-3-methylimidazolium hexafluorophosphate ([BMIM][PF6]) were used as stabilizers for copper and gold nanoparticles. These catalysts were evaluated in the oxidation of methylene blue, morin and benzyl alcohol. The effects of Li2O as additive, and that of ionic liquids as stabilizers were investigated. A fair agreement was found between particle sizes obtained from ligand adsorption and TEM methods. The particle sizes of both methods deviate in the order of 3–13% for γ-Al2O3-containing copper catalysts, and 0-15% for gold-based catalyst. Copper and gold-based catalysts were revealed to be very active in the investigated reactions, especially when Li2O is used as additive, and imidazolium ionic liquids as stabilizing agents. The kinetic data obtained could be modeled in terms of the Langmuir–Hinshelwood model; that is both reactants are assumed to be adsorbed on the surface of the nanoparticles. The apparent reaction rate could therefore be related to the surface S of the nanoparticles, to the kinetics constant k, related to the rate determining steps, and to the adsorption constant of the reactants. Atomic absorption spectroscopy (AAS), X-ray diffraction spectrometry (XRD), N2-physisorption Brunauer–Emmet–Teller (BET), transmission electron microscopy (TEM), scanning electron microscopy (SEM), thermogravimetric analysis (TGA) and temperature programmed reduction (TPR) are used for the full characterization of the catalysts. The ligand adsorption was followed by ultraviolet-visible spectroscopy (UV-vis), while the oxidation reactions were followed by UV-vis, gas chromatography (GC-FID), and gas chromatography–mass spectrometry (GC-MS).