Prepa Ration Of MnO₂/?-Al₂O₃ Catalyst And Catalytic Ozonation Degradation Of Phenol Effluent

Ozone oxidation has been widely used in the industrial wastewater treatment as the product of the ozone decomposition was harmless to the environment.But the low efficiency of ozone was the important issues that could not be ignored.Heterogeneous catalytic ozonation could improve the oxidation efficiency and there was no metal ions removal problems.So,the refractory organic wastewater can be degraded deeply.MnO2/?-Al2O3 heterogeneous catalysts were prepared by wet impregnation method and were characterized by X-ray Diffraction(XRD),Scanning Electron Microscope(SEM),nitrogen adsorption(BET),Fourier Transform Infrared Spectrometer(FT-IR),and temperature programmed desorption of ammonia(NH3-TPD).The process of catalytic oxidation for treatment of phenol with O3 as oxidant in the presence of MnO2/?-Al2O3 catalyst was investigated.The catalysts activity was evaluated by the removal of phenol and COD(chemical oxygen demand).The effects of different factors on the activity of MnO2/?-Al2O3 were investigated,respectively.The optimum preparation methods for catalysts with the best performance were as follows:10wt.%of the manganese loading,calcinate 5 h under the temperature of 500?.Under the best reaction conditions for oxidation of 100 mg/L phenol,initial pH 6.5(not adjust),T=25?,2 g/L catalyst,0.96 mg/min ozone,600 rmp/min rotating speed,76.3%of phenol and 56.6%COD removal were achieved in 60 min.But there was a little decrease on catalytic activity after 5 times recycle of the catalyst.Meanwhile,the intermediate products were determined by High Performance Liquid(HPLC).The results showed that there were four main kinds of intermediate products,catechol,hydroquinone,resorcinol and p-benzoquinone,respectly.The intermediate products were oxidized to quinones firstly,then further degraded into tartaric acid,oxalic acid,acetic acid and formic acid,and finally were degraded into CO2 and H2O.Adsorption of the small molecule acid on the catalyst surface was the main reason for the decrease of the catalytic activity.Based on the MnO2/?-Al2O3 catalysts a small amount of alkali metal elements were doped in it using impregnation by step to improve its catalytic performance,stability and reusability.Related characteration and evaluation of activity were also made in the experiments-The results revealed that when the doping content of sodium was 2%,compared with other catalysts,the catalyst shows the best catalytic activity.The phenol removal is almost complete and the COD degradation is about 73.5%in 60 min at steady-state conditions under the best operation conditions.And there was almost no decrease on catalytic activity after 5 times recycle of the catalyst.Besides,the effects of tert-butyl alcohol and p-benzoquinone on the phenol degradation demonstrated that the reaction followed·OH and·O2-oxidation mechanism.