Synergistic Enhancement of Hydrolysis–Oxidation Drives Efficient Catalytic Elimination of Chlorinated Aromatics over VOx/TiO2 Catalysts at Low Temperature

Abstract

The efficient catalytic elimination of toxic chlorinated aromatics (i.e., dioxins, chlorobenzenes, etc.) at low temperature is still a great challenge. Based on the VO_x/TiO₂ catalyst, a hydrolysis-oxidation strategy (CeO_x and WO_x doping) was built for desirable low-temperature catalytic activity, product selectivity, H₂O tolerance, and chlorine desorption. The in situ and ex situ experimental characterizations and density functional theory calculations revealed that hydrolysis sites favored molecular adsorption, C–Cl cleavage, and HCl formation; meanwhile, oxidation sites enhanced the activation of reactive oxygen species and improved oxygen mobility and redox properties. The enhanced oxygen storage/release capacity (33–53 fold) and extended redox cycle (e.g., from V⁵⁺↔V⁴⁺ to V⁵⁺↔V⁴⁺↔V³⁺) favored the deep oxidation. The introduction of H₂O triggered the hydrolysis–oxidation process that promoted the catalytic activity and chlorine desorption due to the elevated generation of ·O₂^– and higher-activity ·OH. Furthermore, the water resistance of the VO_x/TiO₂-based catalyst was enhanced after the application of the hydrolysis–oxidation strategy. The V–Ce–W/Ti catalyst exhibited remarkable removal efficiency of dioxins (96.7–98.2%), which was reduced from 0.34–0.48 ng I-TEQ Nm^–3 to 0.006–0.016 ng I-TEQ Nm^–3 during pilot tests at 160–180 °C, achieving ultralow emissions. This work provides practical guidance for industry development for efficiently eliminating chlorinated organics in flue gas.