In this work, Gold and Copper oxidation catalysts supported on a range of metal oxides were synthesised via 2 previously uninvestigated preparation methods. In the first chapter, Gold nanoparticle catalysts were deposited onto TiO2, CeO2 and ZrO2 nanoparticles via the non-aqueous Modified Photodeposition procedure. This method was found to produce smaller Gold particle sizes following intrinsic excitation of the support than the conventional aqueous phase method, with surface physisorbed water apparently acting as the sacrificial reductant. The as prepared catalysts were drastically more active than those prepared by the conventional method and under standardised tests were directly comparable to those prepared by the Deposition Precipitation Method. The second part of the work, explored the preparation of metal oxide supported Copper catalysts via the Flame Spray Pyrolysis process. CO Oxidation tests established the following order of activity for 4wt% Cu loaded on the various supports: Cu-CeO2 > Cu-TiO2 > Cu-ZrO2 > Cu-Al2O3 > Cu-SiO2. CO-TPD studies found that more active materials tended to adsorbed more CO and reacted higher proportions of this with lattice oxygen to form CO2 at lower temperatures. The addition of Cu to each metal oxide surface was found to induce lengthening of the average Metal-Oxygen bond length, with higher electron density on surface O. This phenomenum is proposed as being responsible for the widely reported ???synergistic effect??? reported for similar Cu catalysts. Cu-CeO2 (0-12wt%) catalysts were tested in the Preferential CO Oxidation (COPROX) reaction. Increasing Cu content, varied the Cu morphology from monomers, through to dimers and ultimately CuO crystallites. DFT simulations of the Cu dimer structure revealed higher levels of bonding ionicity in this morphology, relative to the monomeric structure. This coincided with higher levels of activity, reinforcing the earlier finding that highly ionic bonds are conducive to higher levels of activity. High levels of activity and selectivity were maintained until approximately 423 K. Surface redox properties of the 4wt% Cu-CeO2 catalyst were assessed using temperature-programmed reduction (CO, H2) and desorption (CO) experiments, as well as in situ and phase-resolved infrared spectroscopy to study the transition to nonselective conditions. For the first time, it was demonstrated that CO and H2 react at identical surface sites, with CO2 formation proceeding simultaneously via three distinct Cux+-CO carbonyl species. Under non-selective conditions, a gradual red-shift and loss of intensity in the carbonyl peak was observed, indicating reduction of Cu+ to Cu0 and the onset of an alternate non-selective redox-type oxidation mechanism. These results for Cu-CeO2 suggest that improved low temperature catalytic activity will only be achieved at the expense of reduced high temperature selectivity and vice versa. The final section of work explored the use of Cu-based catalysts for the low temperature oxidation of Acetaldehyde (ACA). Based on this work, it is concluded that the ACA oxidation activity of these materials is determined by two main factors: the basicity of the metal oxide support (and its subsequent ability to convert ACA to carboxylates) and the availability of surface oxygen during acetate decomposition. It is proposed that a high concentration of reducible sites (either by Cu addition or naturally occurring on CeO2) accelerates the activation and provision of oxygen and also potentially provides sites for the stabilization of methoxy intermediates resulting from the acetate decomposition.
| Identifer | oai:union.ndltd.org:ADTP/272585 |
| Date | January 2009 |
| Creators | Kydd, Richard Berwick, Chemical Sciences & Engineering, Faculty of Engineering, UNSW |
| Publisher | Awarded by:University of New South Wales. Chemical Sciences & Engineering |
| Source Sets | Australiasian Digital Theses Program |
| Language | English |
| Detected Language | English |
| Rights | Copyright Kydd Richard Berwick., http://unsworks.unsw.edu.au/copyright |
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