Research On Key Materials For Efficient Removal Of CVOCs In Engineering Survey And Construction

The Chlorinated Volatile Organic Compounds（CVOCs）occur in contaminated cultivated soil and shallow buried stratum mainly come from the volatilization of crude oil on the ground during the oil extraction process,the leakage of oil pipelines,the degradation of sludge sites and solid waste landfills,etc.,because of their high toxicity,Volatile and other characteristics,causing continuous occurrence of dangerous incidents to survey and construction personnel;delays in project progress,resulting in waste of personnel and resources as well as economic losses.Besides,CVOCs cause different degrees of pollution to soil,groundwater and the ecological environment.Therefore,development of high efficiency,environmentally friendly and anti-chlorine poisoning catalysts is urgent.Catalytic oxidation is deemed as the one of the most effience technologies for CVOCs oxidation.Catalyst is the key to this technology.Amongst,VO_x catalyst has excellent resistance to chlorine poisoning to the degradation of CVOCs.CeO₂ has good oxygen mobility and oxygen storage and release performance,which is conducive to the deep oxidation of CVOCs,and is often used as a catalyst carrier.Therefore,this paper uses 1,2-dichloroethane as the pollutant and VO_x/CeO₂catalyst as the main body,and systematically studies the effect of different V/Ce molar ratios and CeO₂ morphology on the catalytic performance of the catalyst for the degradation of CVOCs.The specific content is as follows:（1）The hollow sphere CeO₂ was prepared by the hydrothermal method.VO_x/CeO₂catalysts with different V/Ce molar ratios（0.025:1,0.05:1,0.1:1 and 0.2:1）were prepared using the impregnation method and to investigate catalytic efficiency and reaction mechanism of 1,2-DCE oxidation.It is found that the V_0.05Ce catalyst has the best activity because of its excellent low-temperature redox ability,a large number of Ce³⁺species and chemically absorbed oxygen（O^-and O₂^-）species.Moreover,V_0.05Ce catalyst has high stability and chlorine poisoning resistance.It is observed that the abundant acidic sites and the strong VO_x-CeO₂ interaction can effectively inhibit chlorine by-products（CHCl₃,CCl₄,C₂HCl₃ and C₂H₃Cl₃）production.It is verified that the presence of water（1～5%）can effectively remove the Cl species from the catalyst surface,which is beneficial to the activation and oxidation of1,2-DCE.It is confirmed that the removal of lattice oxygen species led to the more Ce³⁺formation,which in turn caused the formation of more oxygen vacancies,and improved the catalytic efficiency of the V_0.05Ce catalyst.Combining the in situ DRIFTS and chlorine by-products distribution results,the reaction mechanism of 1,2-DCE over V_0.05Ce catalyst was proposed.（2）Based on the above work,VO_x/CeO₂ catalysts with different morphologies were synthesised via impregnation means（V/Ce=0.05:1）and further to investigate the effect of CeO₂ morphology on the catalytic performance of VO_x/CeO₂ catalyst.VO_x/CeO₂-s F catalyst has the best catalytic performance(T₉₀=281°C)for 1,2-DCE oxidation.The VO_x/CeO₂-s F catalyst has a large specific surface area,excellent low-temperature redox ability,abundant oxygen vacancies and a large number of chemically absorbed oxygen species,which are favorable for surface active oxygen species absorption on the oxygen vacancies,thereby ensuring its excellent catalytic activity.It is revealed that the removal of lattice oxygen species resulted in larger amounts of Ce³⁺generation,which further more oxygen vacancies formation.Subsequently,surface active oxygen species were absorbed on the oxygen vacancies and further improved the migration ability of active oxygen species,which promotes the deep oxidation of 1,2-DCE.