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 x emissions. However, their performance in complex flue gases containing NO x, aromatic volatile organic compounds (VOCs, e.g., toluene), and chlorinated VOCs (e.g., chlorobenzene) remains limited. This study evaluates the crystalline phase-dependence of TiO 2 -supported V 2 O 5 catalysts (anatase: V/TiO 2 -A; rutile: V/TiO 2 -R) for synergistic multipollutant control. We identify a crystal-dependent reversal in synergistic catalytic performance: V/TiO 2 -A exhibits superior activity for NO x -toluene coremoval, while V/TiO 2 -R achieves optimal NO x -chlorobenzene elimination. Mechanistic studies reveal that oxygen vacancies in V/TiO 2 -A enhance toluene activation, whereas high V 5+ /V 4+ ratios and Brønsted acidity in V/TiO 2 -R promote chlorobenzene activation and HCl formation. This insight enabled the design of a tandem catalyst system (V/TiO 2 -R upstream + V/TiO 2 -A downstream) within a single SCR reactor, achieving >90% simultaneous conversion of NO x, 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.