Carbon nanotube supported platinum catalysts for the ozonation of oxalic acid in aqueous solutions

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 influence 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 activated carbon supported Pt catalyst. The Pt loading, reduction temperature and pyrolysis atmosphere significantly influenced the Pt/CNT activity, especially for pyrolysis atmosphere. 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 five re-uses without any leaching of Pt.