面对饮用水水源水质的日益恶化和严格的饮用水水质标准，臭氧消毒技术、臭氧预氧化技术以及臭氧活性炭等深度氧化技术越来越多地被人们所采用。但臭氧氧化技术也有其局限性，一是臭氧不能彻底矿化水体中的天然有机物及其他微量污染物，小分子有机羧酸、醛、酮和酮酸往往是臭氧氧化后的副产物。二是臭氧氧化含溴离子的水源水时会有潜在致癌物溴酸根的生成，沿海及部分内陆城市水源水中普遍含Br-且浓度较高是限制臭氧氧化技术推广的主要原因之一。 丙酮酸（PA）是臭氧氧化天然水体和含芳香族化合物废水的主要副产物之一，难以被臭氧进一步氧化。研究发现负载型氧化物PdO/CeO2可有效催化臭氧降解PA。此外，PdO/CeO2还可快速催化臭氧降解其它酮酸为小分子饱和酸，一方面降低了溶液的TOC，另一方面提高了水体的可生化性，易于后续生物活性碳净化。PdO/CeO2催化臭氧降解PA是一个微界面反应过程，表面CeO2是吸附络合PA的活性位，而表面PdO是吸附分解臭氧的活性位。吸附在催化剂表面的臭氧分解生成氧自由基（•O），•O可与臭氧进一步反应生成超氧自由基（•O2-）。这些自由基对吸附在催化剂表面的PA进行氧化降解。此外，CeO2的存在增加了•O与Pd的结合强度，从而减少了•O与臭氧的进一步反应生成较弱氧化剂•O2-的几率。 分子筛Ce-MCM-48可在常用饮用水处理pH范围内高效地控制BrO3-的生成。介孔材料MCM-48能略微降低液相的臭氧浓度，而Ce-MCM-48则通过抑制臭氧的分解使液相的臭氧浓度提高了30%。因此，Ce掺杂抑制了臭氧的羟基自由基（•OH）分解，减弱了•OH在BrO3-生成中的作用。Ce-MCM-48对BrO3-生成过程中的重要中间产物次溴酸（HOBr/OBr-）有一定的吸附作用，从而减少了HOBr/OBr-被液相中•OH继续氧化生成BrO3-的反应。相比于MCM-48，Ce的掺杂使Ce-MCM-48对HOBr/OBr-有更强的吸附能力。另一方面， Ce的掺杂可促进臭氧的分解产物H2O2进一步分解成•OH，从而促进BrO3-的生成。综合上述两个因素，Ce的含量应有一个合理范围，实验表明最佳Si/Ce比为66~100。此外，Ce-MCM-48还可以强化臭氧对难降解有机物农药莠去津和氧乐果的降解，增强了O3/Ce-MCM-48工艺在水处理中的应用性。

      Along with the continuous deterioration of water sources and the more stringent drinking water standards, ozone disinfection, ozone pre-oxidation, and advanced treatment with ozone followed by biological activated carbon (BAC) have been extensively applied. However, ozonation has its own limitations. First, ozone can hardly mineralize natural organic matter and other micro-organic pollutants in water, so carboxylic acids, ketones and aldehydes are common by-products post ozonation. Second, bromate (BrO3-), a potentially carcinogenic by-product, will be generated from ozonation of water containing bromide (Br-). The common presence of a considerably high level of Br- in water sources of coastal and some inland cities largely limits the application and propagation of ozonation technologies. Herein, a number of catalysts were prepared in this study to promote the degradation of small organic acids or to inhibit the formation of BrO3- during ozonation. Their catalytic efficacy and mechanism were investigated in detail, so as to provide useful reference for future application of the catalytic ozonation technology. Pyruvic acid (PA) is a major by-product formed during ozonation of water containing dissolved aromatic compounds or natural organic matter, which can hardly be further oxidized by ozone. This study found that a composite metal oxide, PdO/CeO2, could significantly enhance the degradation of PA in water during ozonation. The surface property of PdO/CeO2 was systematically characterized with X-ray diffraction, transmission electron microscopy, X-ray photoelectron spectroscopy, BET surface area and zeta potential, and the relationship between the surface property and the catalytic activity was examined and discussed in detail. Results indicated that PdO/CeO2 with 4.0% of Pd loading and calcined at 550 oC had the highest catalytic activity in PA degradation by ozone. Complete PA (5 mg L-1) removal was quickly achieved in catalytic ozonation at 5 min and pH 4.7. Kinetic experiments revealed that the rate constant of PA degradation could be increased by 130-fold based on the unit catalyst dose (i.e., g/L). PdO/CeO2 maintained a persistently high activity and structural stability throughout the semi-continuous experiment for the ozonation of PA. In addition, PdO/CeO2 exhibited a high efficiency in catalyzing the degradation of other keto acids by ozone, with even smaller carboxylic acids formed as byproducts. This not only reduced the concentration of total organic carbon (TOC), but also improved the biodegradability of the water to favor the subsequent BAC purification. With regard to the catalytic mechanism of PdO/CeO2 for PA degradation by ozone, the adsorptive decomposition of ozone on the catalyst surface was proposed. Synergetic effect was observed between the two component metal oxides (i.e., PdO and CeO2) on PA adsorption, aqueous ozone decomposition, and catalytic ozonation of PA. The addition of tert-butyl alcohol promoted PA degradation, while 1 mM phosphate significantly inhibited PA degradation by ozone, which implies that the catalytic ozonation of PA with PdO/CeO2 was actually a micro-interfacial reaction process. ATR-FTIR and in-situ Raman spectroscopy analyses revealed that the surface CeO2 acted as active sites for PA adsorption, and the surface PdO acted as active sites for ozone adsorption. The adsorbed ozone was first decomposed to oxygen radicals (•O) on the catalyst surface, which may further react with ozone to produce peroxide radicals (•O2-). These radicals mainly accounted for the degradation of PA adsorbed on the catalyst surface. Moreover, the presence of CeO2 consolidated the combination of •O with Pd, and thus suppressed the reaction between •O and ozone to form the relatively weaker oxidant, •O2-. The above results substantiated the synergy between PdO and CeO2 for catalyzing PA degradation by ozone. Regarding the problem of BrO3- formation during the ozonation process, our experimental results indicated that a variety of commonly-used catalysts, such as MnO2, Fe3O4, TiO2, Co3O4 and CeO2, could all inhibit the formation of BrO3- to some extent. The composite catalysts prepared with two or three metal oxides were proved to have higher and more stable efficiencies in inhibiting BrO3- formation during ozonation, among which the cerium incorporated mesoporous sieve (Ce-MCM-48) was highly effective in reducing BrO3- formation over a pH range suitable for drinking water treatment (i.e., 6.0-9.0). Aqueous ozone concentration was slightly decreased in the presence of MCM-48, while notably increased by 30% in the presence of Ce-MCM-48. This means that Ce-doping inhibited ozone decomposition to hydroxyl radicals (•OH), and thus decreased the contribution of •OH to BrO3- formation. Moreover, Ce-MCM-48 could partially adsorb HOBr/OBr-, an important intermediate formed during bromate formation, so suppressed the further oxidation of HOBr/OBr- to BrO3-. As compared to MCM-48, Ce-doping also improved the ability of Ce-MCM-48 for adsorbing HOBr/OBr-. On the other side, it was reported that Ce-doping could promote the decomposition of H2O2 (a byproduct formed from ozone decomposition) into •OH, which would enhance BrO3- formation. To trade off the positive and negative effects, our experimental results indicated that the optimal Si/Ce ratio of Ce-MCM-48 ranged from 66 to 100. Besides, the Ce-MCM-48 could also catalyze the degradation of two recalcitrant pesticides (atrazine and omethoate) by ozone, which increased the applicability of the O3/Ce-MCM-48 process to water treatment for simultaneously minimizing BrO3- formation and promoting organic degradation.