Catalytic Degradation Of Chlorobenzene Over Ce-Mn Supported Anatase TiO₂ Catalysts With Different Crystal Faces

The control of chlorobenzene in industrial process plays an important role in ecological environment and human health.Among the current control technologies,catalytic oxidation technology has attracted extensive attention for the reason that it can completely destroy the pollutants at relatively low temperature and generate non-toxic or low toxic products such as water and carbon dioxide.In catalytic oxidation technology,the choice of catalyst is the key factor of the degradation efficiency.Anatase TiO₂itself has good oxidation activity and is widely used in catalytic degradation.Improving the exposure rate of anatase TiO₂crystal surface is a good means and effective method to enhance the intrinsic activity of the catalyst.Simultaneously,using composite metal oxide as catalyst has the advantages of significantly reducing the cost and improving the catalytic activity.However,the effect of TiO₂with different crystal faces on the degradation activity of chlorobenzene and the interaction between Ce and Mn are still the key problems to be investigated.Therefore,in order to solve the above key problems and provide technical support for the control and reduction of pollutants such as chlorobenzene in the environment,we prepared TiO₂with different crystal facet exposed and supported Mn and Ce transition metal oxide catalysts.The main research of this paper is as follows:（1）Above all,three kinds of TiO₂catalysts with different exposed crystal planes:TiO₂{001},TiO₂{101}and TiO₂{201}were prepared,their physical properties were characterized,and their catalytic activities for chlorobenzene degradation were explored.Firstly,the preparation methods of TiO₂{201},{101}and{001}crystal face catalysts were investigated and optimized.The physicochemical properties of TiO₂{001},TiO₂{101}and TiO₂{201}catalysts were characterized by Scanning Electron Microscopy（SEM）,Transmission Electron Microscopy（TEM）,X-ray photoelectron spectroscopy（XPS）and X-ray diffraction,respectively.The results showed that three kinds of TiO₂materials with different crystal faces exposed were successfully synthesized.Meanwhile,{001}TiO₂had the largest specific surface area,followed by TiO₂{101}and TiO₂{201}.Subsequently,three kinds of catalysts were applied to the catalytic degradation of chlorobenzene.It was found that TiO₂{001}had the highest catalytic activity of more than 50%at 300°C,while{101}and{201}TiO₂crystal planes did not show good catalytic activity,and the degradation efficiency was below 20%.It suggested that the catalytic activity of different crystal planes exposed TiO₂had the same trend with the specific surface area,but had no significant relationship with the crystal plane energy.Situ DRIFTs was used to explore the reaction mechanism of Chlorobenzene on the surface of various catalysts.The results indicated that the interface interaction between{001}TiO₂and chlorobenzene was strong.And chlorobenzene was gradually degraded to benzaldehyde,maleic acid and other intermediate products,and finally mineralized to form CO₂.（2）Besides,in order to further improve the catalytic activity of TiO₂with different crystal facet exposed to chlorobenzene,and to explore the interaction between Ce,Mn and different crystal faces,as well as the influence of different loading ratio of Ce and Mn on the catalytic activity,we synthesized{001}TiO₂,{101}TiO₂and{201}TiO₂.Composite oxide catalysts with different ratios of Mn,Ce and Ti,respectively（0.05-0.1）:（0.05-0.1）:1,and applied to the catalytic degradation of chlorobenzene.It was found that the activity of the catalysts with Mn and Ce supported on each exposed crystal surface was improved,especially with regard to{201}TiO₂and{101}TiO₂.The increase of Mn and Ce loading will improve the activity of the catalyst to a certain extent,but it will also have a certain inhibition effect when the loading amount is too much.When the ratio of Ti:Mn:Ce is1:0.1:0.05,the chlorobenzene degradation efficiency could reach 100%and the mineralization efficiency is more than 85%.（3）In order to explore the reasons for the increase in catalyst activity after loading of Mn and Ce,this study carried out the characterization of physical and chemical properties of the three different crystal plane TiO₂supported Ce and Mn catalysts with a ratio of Ti:Mn:Ce=1:0.1:0.05.The research results showed that the interaction between Ce,Mn and crystal planes played a vital effect during the process of catalytic oxidation of chlorobenzene over composite oxides,while the specific surface area did not have a significant influence on its catalytic activity.Different crystal planes had different interactions with cerium and manganese.Among them,{201}TiO₂had the strongest interaction with cerium-manganese,which promoted the generation of active oxygen species and increased the concentration of oxygen vacancies,thereby greatly improving catalytic oxidation activity for chlorobenzene.{101}TiO₂also had a certain interaction with cerium and manganese,while{001}TiO₂featured the weakest interaction.In situ diffuse reflectance Fourier transform infrared spectroscopy was used to characterize the interfacial reaction between the catalyst and chlorobenzene at 300℃and 5%oxygen,and the related degradation mechanism was explored.The results show that during the catalytic oxidation process,chlorobenzene first generates benzoquinone and other carbonyl-rich compounds,benzoquinone is decomposed into carboxylates,and finally mineralized to CO₂and H₂O.GC-MS results showed that the derivatives contained benzene,butanol,phenol,butyl formate,chlorobenzene,dichlorobenzene and trichlorobenzene,while ion chromatography showed that formic acid,acetic acid and a large number of chloride ions were generated after catalytic degradation.