Wet air oxidation （WAO） is one of effective technologies to eliminate hazardous, toxic and highly concentrated organic compounds in the wastewater. In the paper, multi-walled carbon nanotubes （MWCNTs）, functionalized by 03, were used as catalysts in the absence of any metals to investigate the catalytic activity in the catalytic wet air oxidation （CWAO） of phenol, nitrobenzene （NB） and aniline at the mild operating conditions （reaction temperature of 155℃ and total pressure of 2.5 MPa） in a batch reactor. The MWCNTs were characterized with scanning electron microscopy （SEM）, transmission electron microscopy （TEM）, gas adsorption measurements （BET）, fourier transform infrared spectroscopy （FT-IR）, and X-ray photoelectron spectroscopy （XPS）. The functionalized MWCNTs showed good catalytic performance. In the CWAO of phenol over the functionalized MWCNTs, total phenol removal was obtained after 90 rain run, and the reaction apparent activation energy was ca. 40kJ · mol^-1. The NB was not removed in the CWAO of single NB, while ca. 97% NB removal was obtained and 40% NB removal was attributed to the catalytic activity after 180 min run in the presence of phenol. Ca. 49% aniline conversion was achieved after 120 min run in the CWAO of aniline.
Ru catalysts, supported on TiO 2 , CeO 2 , and CeO 2 -TiO 2 , were prepared by the impregnation method. The effect of the structure of the supports on the activity of Ru catalysts was investigated in the catalytic wet air oxidation （CWAO） of acetic acid under 230℃ and 5 MPa in a batch reactor. Physical properties including the surface area, crystalline phase, and surface components of the Ru catalysts were characterized by N 2 adsorption, X-ray powder diffraction （XRD）, and X-ray photoelectron spectroscopy （XPS）. The CeO 2 -based Ru catalysts had good activity, and the prepared RuO 2 /CeO 2 catalyst showed markedly higher activity than the RuO 2 /CeO 2 -TiO 2 catalyst. The surface structure, the high amount of chemisorbed oxygen on the catalyst surface, and the suitable pH pzc value of the supports played an important role in the activity of the Ru catalysts in CWAO of acetic acid.
The development of highly active carbon material catalysts in catalytic wet air oxidation（CWAO）has attracted a great deal of attention. In this study different carbon material catalysts（multi-walled carbon nanotubes,carbon fibers and graphite） were developed to enhance the CWAO of phenol in aqueous solution. The functionalized carbon materials exhibited excellent catalytic activity in the CWAO of phenol. After 60 min reaction,the removal of phenol was nearly100% over the functionalized multi-walled carbon,while it was only 14% over the purified multi-walled carbon under the same reaction conditions. Carboxylic acid groups introduced on the surface of the functionalized carbon materials play an important role in the catalytic activity in CWAO. They can promote the production of free radicals,which act as strong oxidants in CWAO. Based on the analysis of the intermediates produced in the CWAO reactions,a new reaction pathway for the CWAO of phenol was proposed in this study. There are some differences between the proposed reaction pathway and that reported in the literature. First,maleic acid is transformed directly into malonic acid. Second,acetic acid is oxidized into an unknown intermediate,which is then oxidized into CO2 and H2O. Finally,formic acid and oxalic acid can mutually interconvert when conditions are favorable.
