Catalytic Removal Of HCB Using Vanadium Catalyst Prepared By Ball Milling Method

Unintentionally formed persistent organic pollutants（UPOPs）, including polychlorinated dibenzo-p-dioxin and dibenzofuran（PCDD/Fs）, polychlorinated biphenyls（PCB）, hexachlorobenzene（HCB）, and pentachlorobenzene（PeCB）, are a group of hazardous organics emitted from thermal process like incinerators and combustion industrial processes. In addition, the HCB concentration emitted from flue gas is several orders of magnitude higher than PCDD/Fs.Compared with adsorption, catalytic destruction shows a unique advantage due to the complete decomposition of hazardous organics. Previous research reported the vanadium catalysts showed high activity and thermal ability and Cl poisoning resistance. The vanadium based catalysts are usually synthesized by wetness impregnation, sol-gel method, or polyol-mediated synthesis, which showed a poor vanadium dispersion, and low catalytic activity. Besides, these methods require complex procedures and huge amount of solvent, which is impractical for large-scale production. Several researches revealed that ball milling method can induced solid- solid, solid- liquid and solid- gas multiphase chemical reaction under room temperature or low temperature, and repaired synthesized solvent free catalyst. In this study, we developed a solvent free synthesis method based on solid state ball-milling reaction, which could rapidly synthesize doped/undoped vanadium based catalysts. The materials catalytic activity, stability, intermediates, and surface structure were tested.Compared with VTi-WI, VTi-BM catalyst showed higher HCB removal efficiency and better stability. The HCB removal efficiency of VTi-BM is 60% under 270 oC. After 10 h continuous reaction, the catalytic activity was not decreased. The reaction rate of VTi-BM is faster than VTi-WI, TCBO, TCCD, and DCMA was intermediates, and HCB were completely degradation in 30 min. The catalytic surface structure was improved in ball milling process. VTi-BM showed better dispersibility, strong redox property, and surface acidity, therefore, showed higher activity.Transition metal elements were doped into VTi-BM. VWTi, VCrTi, and VMoTi showed higher HCB removal efficiency than VTi-BM,while VCeTi, VCuTi, VMnTi, or VCo Ti showed lower HCB removal efficiency than VTi-BM。VWTi is the best catalyst for:（1） the HCB removal efficiency is over 80% at 300 oC, and can maintain high activity;（2） The HCB catalytic destruction rate of VWTi was the fastest among all doped vanadium catalysts, its intermediates also were TCBQ, TCCD, and DCMA, the HCB removal efficiency was over 90% in 20 min. VWTi possesses big surface area, WO₃ crystalline phase, more O_α concentration, and strong surface acidity, which may expose more active sites, improve VO_x dispersion, and increase surface Br?nsted acidities.In order to find the best catalyst formula, various V or W loading catalysts were synthesized in this study. According to the activity test results, the best tungsten load is about 5 at. %, and the best vanadium load is 5-7 at. %.