Study On Preparation And Performance Of CNTs As Catalysts In The Catalytic Wet Air Oxidation Of The Organics

Catalytic wet air oxidation （CWAO） has been proved as one of effective advanced oxidative processes for eliminating the hazardous, toxic and highly concentrated organic compounds, and a great deal of attention has been paid in the application of the CWAO. In this study, multi-walled carbon nanotubes（MWNTs） used as catalyst were modified by different chemical oxidation methods, and investigated in the CWAO of phenol in the batch reactor. The effect of reaction conditions on the performance of the functionalized MWNTs was studied, and the stability of the MWNTs was measured in the CWAO of phenol in the reactor. Meanwhile, the CWAO of aniline and nitrobenzene was performed over the functionalized MWNTs.The MWNTs were treated with the different oxidizing oxidants, such as HNO3-H2SO4, ozone, H2O2, Air and hydrothermal reaction, respectively. The MWNTs were characterized by scanning electron microscope （SEM）, the surface area, Raman, Fourier transform infrared spectroscopy （FT-IR）, X-ray photoelectron spectroscopy （XPS） and the point of zero charge (pH_pzc). The results showed that oxygen-containing functional groups were introduced on the surface of the functionalized MWNTs. The functionalized MWNTs were very active catalysts in the CWAO of phenol. The activity orders of the catalysts in the CWAO of phenol were:MWNTs-O（g）-3>MWNTs-H> MWNTs-O（l）>MWNTs-NS-1>MWNTs-NS-3> MWNTs-A> MWNTs-NS-2> MWNTs-T. Moreover, the03-functionalized MWNTs showed the best activity at155℃and total pressure of2.5MPa, in the initial phenol concentration of1000mg/L and catalyst loading of0.4g/L,100%phenol and78%total organic carbon（TOC） were removed after120min reaction. The oxygen-containing functional groups played the important role in the good performance of the functionalized MWNTs in the CWAO of phenol.The effect of the operating conditions on the performance of the MWCNTs-O（g） catalysts were investigated in the CWAO of phenol. The optimal operating conditions was:at temperature of155℃, total pressure of2.5MPa, phenol initial concentration of1000mg/L and catalyst loading of0.4g/L. Compared to the fresh MWNTs-O（g） catalysts, the used catalysts in the cyclic reactions showed the better activity and the MWNTs-O（g） had the perfect stability in the CWAO of phenol. In the CWAO of aniline over the functionalized MWNTs-O（g）, ca.49%aniline was removed after120min reaction, under the reaction temperature of155℃, the total pressure of2.5MPa, the initial aniline concentration of2000mg/L and loading catalyst of0.8g/L, the catalysts showed the better activity. Under the same operating conditions （155℃,2.5MPa,0.4g/L）, the nitrobenzene adsorption on the MWNTs played the important role in the nitrobenzene removal, and the MWNTs-O（g） had inefficiency in the CWAO of nitrobenzene. In the CWAO of the mixed pollutants containing phenol and nitrobenzene, it is found that:（1） the addition of phenol to the same system obviously improved the nitrobenzene removal and ca.30%conversions was achieved over the MWNTs-O（g）;（2） Moreover, phenol removal was also improved in the presence of nitrobenzene, and the removal increased from75to100%after75min in the CWAO of phenol and nitrobenzene.