published_or_final_version / Chemistry / Doctoral / Doctor of Philosophy

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In recent years, the catalytic properties of finely dispersed gold particles on oxide support materials have attracted much attention. Such catalysts are active for several types of oxidation reactions, in particular low-temperature carbon monoxide oxidation. The watergas- shift (WGS) reaction and the selective oxidation of CO in the presence of hydrogen are possible applications of gold-based catalysts. In this thesis we attempted to detail the key issues relevant to the deactivation of supported gold catalysts. A new aspect of the CO oxidation deactivation mechanism was comprehensively discussed. It was found that titanate nanotube supported gold catalyst (Au/TN), prepared by deposition precipitation, deactivated due to the formation of bicarbonate species on gold-sites. Moisture prevented the formation and accumulation of these species and also promoted the reaction. The Au/TN catalyst was characterised by HRTEM, in-situ DRIFTS-Mass spectrometry, BET, etc. Titanium dioxide (TiO2) is widely used as support material for various important industrial catalysts and its modification may suite specific catalytic requirements. In this work we have confirmed that the incorporation of nitrogen (N) into TiO2 increases the concentration of oxygen ion vacancies. When tested for CO oxidation, the nitrogendoped titania supported gold catalyst, Au/TiO2-xNx, was found to be a poor and unstable catalyst compared to the pure titania supported gold catalyst, Au/TiO2. Both catalysts were characterised by XRD, Raman spectroscopy, DRS-UV visible spectroscopy, TPO, BET, HRTEM etc. New Cu-based methanol synthesis catalysts, prepared by co-precipitation and deposition precipitation, were physically mixed with _-Al2O3 and tested for the direct single-step DME synthesis from syngas. The catalysts exhibited good CO conversion and DME selectivity. The loading of gold on the methanol synthesis components of the bifunctional catalysts promoted CO conversion and the WGS reaction. In addition, Au suppressed iv methanation on the bifunctional catalysts. The catalysts were characterised by TPR, XRD, BET and XRF spectroscopy.

Tris-2-chloroethyl phosphate (TCEP) is a biorecalcitrant flame retardant and plasticizer. It is a toxic and carcinogenic compound that is frequently detected in wastewater effluents and water bodies, including those used for drinking water, around the world. Due to the incomplete removal of TCEP from current wastewater and drinking water treatment facilities, effective treatment processes must be identified that will remove TCEP from water. This research investigated the effectiveness of Fenton's oxidation for removing TCEP from water. In laboratory scale experiments, batch reactions of aqueous TCEP solutions were conducted at different pH conditions and dosages of H2O2:Fe2+:TCEP molar ratios. Samples were tested at pH values ranging from 2.5 to 4.5 and H2O2:Fe2+:TCEP molar ratios from 5.0:0.5:1 to 200:5.0:1. TCEP concentrations were quantified by solid phase micro-extraction (SPME) followed by gas chromatography (GC). Complete removal of TCEP was achieved at equilibrium conditions with a molar ratio dose of 150:5:1 H2O2:Fe2+:TCEP. The kinetics of TCEP removal were also investigated. Pseudo-first order rate constants for TCEP removal were obtained. The effectiveness of ozonation was also investigated in this research. Batch reactions of aqueous TCEP at different doses of ozone were conducted at pH 7.0 ± 0.1. Ozonation was found to have no effect on the degradation of TCEP.

The effect of over-oxidation on periodate oxidation of cellulose was studied. It was found that the over-oxidation process has a significant effect on the overall reaction. An integrated rate equation was formulated. The oxidation of internal glucose units is second-order overall, first order with respect to both periodate and cellulose; while the oxidation of the reducing end group is first order overall, that with respect to periodate. It was also found that prolonged oxidation degrades cellulose to a considerable extent, which is thought to be the direct result of random chain scission. The periodate breaks up cellulose polymer into fragments, some of which are so small that they go into the solution. / Graduation date: 1989

Municipal wastewater treatment using biological nutrient removal generates large amounts of waste sludge. An effort is made to solubilize nutrients from sludge and reuse them in subsequent processes. The microwave-enhanced advanced oxidation (MW/H₂O₂-AOP) process using hydrogen peroxide as the oxidant was applied to the treatment of different organic slurries including wasted sludge, blood meal, and fish silage. The factors controlling phosphates, ammonia, and COD release into solution included inorganic acid addition, hydrogen peroxide dosage, treatment times and temperatures. Higher dosages and treatment temperatures yielded better solubilization of phosphates and ammonia. It was found that approximately all of the COD was solubilized at a treatment temperature of 80°C. Volatile fatty acid (VFA) concentrations were also found to have increased with the amount of inorganic acid added into treatment. Up to 25% of soluble COD was composed of acetic acid. Higher irradiation levels tended to be more effective in the solubilization of nutrients. In terms of trends of particle size distribution, detectable particles increased in size in acidic conditions, with the largest fraction of larger particles in a given sample being the treatment with highest irradiation power. In neutral condition treatments, the higher the irradiation power provided to the samples, the more spread out the particle sizes range. In alkaline condition treatments, an increase in smaller particles were found after treatment; higher power irradiation yielded significantly higher numbers of smaller particles. This study provided an insight into the athermal effects of theMW/H₂O₂-AOP. Blood meal solubilization for the purpose of its application as an organic feritilizer was investigated using theMW/H₂O₂-AOP. It was found that over the treatment temperature range of 60 to l20C, solids particle reduction, ammonia and orthophosphate production were achieved. Maximum solubility of chemical oxygen demand (COD) occurred at 80°C. Without the addition of acid, soluble COD decreased due to protein denaturation and coagulation out of the solution. Fish silage is also a valuable fertilizer for organic greenhouse hydroponics operations, but a pretreatment step is required. It was found that up to 26% of total Kjeldahl nitrogen could be released as ammonia with 6% hydrogen peroxide dosage at 170°C. An increase of nitrate/nitrite concentration was observed with higher hydrogen peroxide dosage and higher microwave temperature.

Thesis (Ph. D.)--University of Hong Kong, 1989.

published_or_final_version / Chemistry / Doctoral / Doctor of Philosophy