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Theoretical Mechanism Investigation on Catalytic Ozonation by Metal Oxide

Author: HuXiaoHong
Tutor: ZhouXin
School: Harbin Institute of Technology
Course: Physical and chemical
Keywords: the mechanism of ozonation metal oxide DFT calculation solid-liquidinteraction competitive adsorption
CLC: O643.32
Type: Master's thesis
Year: 2013
Downloads: 131
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Abstract


Studies have been investigated that metal oxidant can catalyze ozone producemore OH radicals, which have a strong ability to oxidize refractory organics andhave almost no selectivity for substances. The catalytic ozonation in the presence ofmetal oxidant is thought as a kind of promising water treatment technology. Inrecent decades, many metal oxidants such as MnO2, TiO2, FeOOH and Al2O3havebeen proved with high efficiency. Unfortunately the mechanism of the generation ofOH radicals is still fuzzy in this process until now. One of the main reasons is thatthe catalytic process is very complex in aqueous solution. Ozone molecules andwater molecules will compete with each other on the reactive center of metal oxidecatalysts, leading to the interference for speculating the mechanisms. Moreover it isof difficulty to capture the intermediates and free radicals and to test the adsorptionof ozone and organic molecules in the solid-liquid interface in the experiments.Some results suggested the adsorption of organic substances on the catalyst’ssurface was not compulsory for effective oxidation; in fact organic adsorptionseems to inhibit the catalytic effect. But the others found that the organiccompounds tested were not adsorbed on metal oxide catalysts （TiO2, Al2O3, MnO2）in wastewater, suggesting an absence of surface interaction with organics. Itindicated that under reaction conditions the adsorption of organics did not takeplace at all or that a limited adsorption did not result in an energetically favoredroute for the catalytic reaction, as a result, this research excluded the mechanismsbased on the adsorption of organics on metal oxide catalysts. In order to becatalytically active for the material, it must adsorb at least one of the substrates ofthe ozonation reaction. So finally the mechanisms based on the adsorption oforganics on oxides （Al2O3） were excluded, it is reasonable to put forward that theadsorption of ozone considering the strong adsorption of water is followed by thefurther oxidation of organic molecules.In my thesis, the dissociation of water molecule, the competition behavior ofwater and ozone and the influence of the coverage on molecules adsorption wereinvestigated on the γ-Al2O3surfaces firstly with DFT method. Further, themechanism of generation of hydroxyl radical was explored on γ-Al2O3（110） surfacein detail. Extensive calculations based on DFT method also were explored to revealthe chemisorptions and physisorption of formic acid, oxalate and pyridine byγ-Al2O3（110） surface. Meanwhile the adsorption and dissociation of ozonemolecule on γ-AlOOH （100） and α-FeOOH （010） surfaces were researchedcompared with that on γ-Al2O3（110） surface. It was demonstrated that the watermolecule would be dissociated into surface hydroxyl, which would prefer to take place at AlIsite on （110） surface, and the increasing coverage of hydroxyl favorsmolecules adsorption. In results ozone would be more easily absorbed anddissociated at AlI-OH and AlIII-OH sites on0.375ML surface. It was also indicatedthat properties of organic matters play an effective role on their adsorption on metaloxides, and γ-Al2O3surface has the highest ability of absorption compared withγ-AlOOH surface and α-FeOOH surface.

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CLC: > Mathematical sciences and chemical > Chemistry > Physical Chemistry ( theoretical chemistry ),chemical physics > Chemical kinetics,catalysis > Catalytic > Catalytic reaction
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