Crystal Phase-Dependent Opposite Catalytic Performance for Toluene and Chlorobenzene Oxidation in Simultaneous Elimination of NO _<i>x</i> and VOCs over V ₂ O ₅ /TiO ₂ Catalysts

Vanadium-titanium catalysts are commercially deployed for selective catalytic reduction (SCR) of industrial NO_<i>x</i> emissions. However, their performance in complex flue gases containing NO_<i>x</i>, aromatic volatile organic compounds (VOCs, e.g., toluene), and chlorinated VOCs (e.g., chlorobenzene) remains limited. This study evaluates the crystalline phase-dependence of TiO₂-supported V₂O₅ catalysts (anatase: V/TiO₂-A; rutile: V/TiO₂-R) for synergistic multipollutant control. We identify a crystal-dependent reversal in synergistic catalytic performance: V/TiO₂-A exhibits superior activity for NO_<i>x</i>-toluene coremoval, while V/TiO₂-R achieves optimal NO_<i>x</i>-chlorobenzene elimination. Mechanistic studies reveal that oxygen vacancies in V/TiO₂-A enhance toluene activation, whereas high V⁵⁺/V⁴⁺ ratios and Brønsted acidity in V/TiO₂-R promote chlorobenzene activation and HCl formation. This insight enabled the design of a tandem catalyst system (V/TiO₂-R upstream + V/TiO₂-A downstream) within a single SCR reactor, achieving >90% simultaneous conversion of NO_<i>x</i>, chlorobenzene, and toluene at 375 °C─outperforming individual catalysts, physical mixtures, and commercial benchmarks with high HCl selectivity. The configuration exploits phase-specific strengths─rutile for chlorinated VOC oxidation at high temperatures, followed by anatase for aromatic VOC degradation─avoiding separate control units and easing retrofit cost and space constraints.