Catalytic Ozonation Of Phenol Over γ-Al₂O₃ Supported Metal Oxides

Heterogeneous catalytic ozonation technology is an efficient water treatment technology for the mineralization of refractory organic pollutants in industrial wastewater.It has the advantages of fast reaction rate,high utilization rate of ozone,low loss rate of catalyst and low processing cost,and the application prospect is broad.In order to promote the application of heterogeneous catalytic ozonation technology in the field of industrial organic wastewater treatment,it is necessary to develop an ozone catalyst with high catalytic activity and stability under continuous flow reaction conditions.In this paper,γ-Al₂O₃supporting different monometal oxides and bimetal oxides were prepared by redox precipitation method.The catalyst was characterized by means of SEM,EDS,BET,XRD,XPS,ICP to analyze the physical properties and composition of the catalyst.The removal effect of TOC in phenol wastewater under different preparation and operating conditions was investigated through single factor experiments,then the metal active components with the best catalytic activity and the optimal preparation process conditions were determined,and the reaction operating parameters were optimized.Finally,the reaction mechanism was discussed.Using phenol as a model pollutant to investigate the catalytic activity of different monometallic oxides supported onγ-Al₂O₃.The results of the study showed that the catalytic activity of the catalysts in descending order was:MnO_x/γ-Al₂O₃>CeO_x/γ-Al₂O₃>FeO_x/γ-Al₂O₃>CoO_x/γ-Al₂O₃,the average TOC removal rate of phenol wastewater by the MnO_x/γ-Al₂O₃catalyst in a continuous flow reaction with optimal preparation conditions was 68.4%.The MnO_x/γ-Al₂O₃catalyst has good stability:after six consecutive repeated uses of the catalyst,the average TOC removal rate of phenol wastewater was still as high as 67.2%.Using phenol as a model pollutant,and the catalytic activity of different bimetallic oxides supported onγ-Al₂O₃was further investigated under the condition that Mn was determined as the main active component.The research results showed that the catalytic activity of the catalysts in descending order was:Mn-CeO_x/γ-Al₂O₃>Mn-CoO_x/γ-Al₂O₃>Mn-FeO_x/γ-Al₂O₃,and the catalytic activities of these three catalysts were higher than MnO_x/γ-Al₂O₃.The average TOC removal rate of phenol wastewater by the Mn-CeO_x/γ-Al₂O₃catalyst in a continuous flow reaction with the optimum preparation and reaction operating conditions was80.1%.The actual total loading of Mn and Ce in the catalyst was about 1.4 wt%.The Mn-CeO_x/γ-Al₂O₃catalyst has good stability:after six consecutive repeated uses of the catalyst,the average TOC removal rate of phenol wastewater was still as high as79.6%.Compared with ozone oxidation alone,the ozone utilization rate of the Mn-CeO_x/γ-Al₂O₃catalytic ozonation system increased by 20%-32%during the continuous flow reaction process of 45 min.Mn-CeO_x/γ-Al₂O₃also showed a high mineralization rate in the process of catalytic ozonation of oxalic acid and p-nitrophenol,and the TOC removal rate was in the range of 77-83%.MnO_x/γ-Al₂O₃and Mn-CeO_x/γ-Al₂O₃both generated hydroxyl radicals in the catalytic ozone oxidation reaction system,and the hydroxyl radicals contributed to the mineralization of phenol.The introduction of Ce into the MnO_x/γ-Al₂O₃catalyst was beneficial to increase the content of Mn⁴⁺and lattice oxygen in the catalyst.Mn⁴⁺,Ce⁴⁺and lattice oxygen played important roles in the catalytic ozone oxidation reaction.