Research On Efficient Catalytic Oxidation Of CVOCs At Normal Temperature

Air pollution caused by volatile organic compounds（VOCs）has received more and more attention,while chlorine-containing volatile organic compounds（CVOCs）,an important part of VOCs,is more harmful and more difficult to degrade.This paper proposed a new-type normal temperature catalytic oxidation（NTCO）method for degradation of dichloromethane at normal temperature.Compared with traditional CVOCs treatment methods,normal temperature catalytic oxidation method has significant advantages of low catalytic reaction temperature and safe treatment process.In this paper,normal temperature catalytic ozonation of dichloromethane was used as a probe reaction.Activated carbon fiber（ACF）was used as carrier to load transition metal oxides to obtain catalysts.The preparation conditions of catalyst,such as active components,calcination temperature,loading amount were investigated to get the best preparation technology.The catalysts were characterized by SEM,BET,EDS,XPS,XRD and FTIR.The results showed that MnO_x exhibited the best dichloromethane removal efficiency among the four active components of FeO_x,MnO_x,CuO_x and NiO_x.The optimum loading amount of Mn was 9 wt%and the optimum calcinations temperature was 400℃.BET test results showed that the specific surface area and pore volume of catalysts decreased with the increase of loading,and the content of micropores in the catalysts accounts for more than half.SEM characterization showed that transition metal oxide agglomeration gradually becomes obvious with the increase of active component loading.EDS characterization found that the distribution of Mn on the surface of 9 wt%MnO_x/ACF catalyst was not uniform.The XPS diagram of Mn2p showed that the predominant valence state of Mn element was+4,which accounts for 64%.Meanwhile,it also contains Mn³⁺,which accounts for 36%,indicating that the Mn was formed as composite oxides.The XPS diagram of O1s found peaks of Mn-O,C-O and Mn-O-C,revealing that MnO₂ was connected to ACF by chemical bond.XRD characterization showed that the 9 wt%loading of Mn had the strongest diffraction peak.FTIR spectra detected the peaks of products,such as formate（COO-R）and methoxy（CH₃O-）,demonstrating that dichloromethane was truly degraded.Furthermore,effect of reaction conditions were investigated on dichloromethane removal efficiency,including space velocity,ozone concentration,dichloromethane concentration and reaction temperature.The results showed that dichloromethane removal efficiency was up to 81%when the reaction temperature was at 25℃,space velocity was 7500 h^-1,ozone concentration was 2200 mg/m³,and dichloromethane concentration was declined to 100 mg/m³.Higher dichloromethane removal efficiency could be gained when reaction temperature was in the range of 25-50℃.The catalytic activity was not reduced afer 5 times cycles,indicating that catalysts have a certain ability of recycling.At the end of this work,the kinetic study was carried out based on power-rate law and the apparent activation energy（Ea）was found to be 30.43 kJ/mol.And gas hydroxyl radical（·OH）generated during the reaction process was measured by the method of salicylic acid impregnation membrane captured-high performance liquid chromatography（HPLC）.It was found that the amount of·OH was approximately between（0.64-3.63）×10¹²（individual/cm³）.