Rapid mechanochemical synthesis of VOx/TiO2 as highly active catalyst for HCB removal

- Rapid one-step ball milling method was developed to synthesize VTi-BM.
- VTi-BM showed higher catalytic activity to its counterpart VTi-WI.
- Doping WOx and MoOx into VTi-BM could further enhance catalytic performance.
- DCMA, TCBQ and TCCD were identified as HCB degradation intermediate products.

A rapid (1.5 h) one-step ball milling (BM) method was developed to synthesize VOx/TiO2 (VTi-BM) and WOx or MoOx doped VOx/TiO2 (VWTi-BM or VMoTi-BM). Catalytic activity on gaseous POPs removal was tested using hexachlorobenzene (HCB) as surrogate. Catalytic performance decreased in the order of VWTi-BM (T50% = 230 °C) > VMoTi-BM (260 °C) > VTi-BM (270 °C) > VTi-WI (300 °C; VOx/TiO2 synthesized by wetness impregnation method). The intermediates from oxidation of HCB were analyzed by off gas analysis, from which 2,2,4,5-tetrachloro-4-cyclopentene-1,3-dione (TCCD), dichloromaleic anhydride (DCMA) and tetrachloro-1,4-bezoquinone (TCBQ) were identified. Furthermore, a possible mechanism for the oxidation of HCB over VOx/TiO2 catalysts was proposed. Mechanism studies showed that BM samples possess better dispersion of the VOx species and more surface chemisorbed oxygen. Doping WOx or MoOx into VOx/TiO2 by ball milling can further enhance catalytic performance by increasing surface acid sites.