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Carbon nanotube supported platinum catalysts for the ozonation of oxalic acid in aqueous solutions Zheng-Qian Liu, Jun Ma*, Yu-Hong Cui School of Municipal and Environmental Engineering, Harbin Institute of Technology, P.

O. Box 2627,

202 Haihe Road, Harbin 150090, PR China A R T I C L E I N F O Article history: Received

21 October

2007 Accepted

16 February

2008 Available online

29 February

2008 A B S T R A C T Ozonation of oxalic acid in the presence of carbon nanotube (CNT) supported platinum (Pt/CNT) catalyst in aqueous solution was studied. The activity and stability of Pt/CNT, the in?uence of preparation conditions on Pt/CNT activity and the ozonation mechanism of oxalic acid with Pt/CNT were investigated. It was found that Pt/CNT was more active for oxalic acid removal and more resistant to ozonation compared with the case of acti- vated carbon supported Pt catalyst. The Pt loading, reduction temperature and pyrolysis atmosphere signi?cantly in?uenced the Pt/CNT activity, especially for pyrolysis atmo- sphere. By means of X-ray diffraction and X-ray photoelectron spectroscopy analysis, the aggregation of Pt and the existence of chemisorbed oxygen with Pt were found when the Pt/CNT catalyst was prepared by calcination, which are unfavorable for its performance. The CNT was oxidized and some acidic groups were generated in calcination, which also cause a decrease of Pt/CNT activity. A free radical mechanism was proposed which involves ozone decomposition and hydrogen peroxide formation for oxalic acid degradation on Pt/ CNT. The redox couple of Ptred/Ptox was suggested to be crucial for the improvement of CNT activity. The Pt/CNT has a good stability after ?ve re-uses without any leaching of Pt. ?

2008 Published by Elsevier Ltd. 1. Introduction Recently, activated carbon (AC) used as catalysts or catalyst supports are gaining increasing attentions in heterogeneous catalytic ozonation [1C6]. However, AC is easily oxidized in the process of ozonation, and a certain concentration of dis- solved total organic carbon (TOC) was generated during the ozonation of AC in the absence of organic compounds [2]. Car- bon nanotube (CNT) may be more suitable for catalyst sup- ports than AC in the liquid phase reactions due to its extraordinary mechanical, electrical, chemical and thermal properties [7]. The excellent activity of CNT used as catalyst [8] or catalyst support [9] has been proved in catalytic wet air oxidation. However, to the best of our knowledge, CNT has never been examined in heterogeneous catalytic ozonation. Transition metal oxides were usually adopted as catalysts in heterogeneous catalytic ozonation [10C12], while the use of noble metal were seldom reported as active component of catalysts in these processes [13,14]. It was found that the cata- lyst supported with Pt showed a high ef?ciency for the decom- position of aqueous ozone [15], and Pt/TiO2 showed a good activity for the degradation of atrazine [16]. It is well known that the preparation conditions have great impact on catalyst performance, however, only a few works focused on the prep- aration and optimization of catalyst in ozonation [11,13]. Oxalic acid is often observed as a by-product of the ozon- ation of many refractory organic compounds and it is refrac- tory to ozonation with a reaction rate kO3 lower than 0.04 M?1 s?1 [17]. In addition, oxalic acid can be oxidized di- rectly to CO2 and water without the formation of other by-products [4], which simpli?es the analysis. So, in the 0008-6223/$ - see front matter ?

2008 Published by Elsevier Ltd. doi:10.1016/j.carbon.2008.02.018 * Corresponding author: Fax: +86