Elucidation of distinct C-Cl/H activation and dioxin formation on Pt- and Ru-supported TiO2 for catalytic oxidation of chlorinated volatile organic compounds.

Noble metal catalysts are widely employed for the catalytic oxidation of chlorinated volatile organic compounds (CVOCs). However, the distinct roles of different noble metals in the deep oxidation of CVOCs remain poorly understood, representing a critical bottleneck in the development of more efficient abatement technologies. Herein, the catalytic performance of Pt/TiO2 and Ru/TiO2 was evaluated for the oxidation of both saturated (monochloroethane, monochloromethane) and unsaturated (vinyl chloride, chlorobenzene) CVOCs. Experiments combined with density functional theory calculations demonstrate that C-Cl bond cleavage for CVOCs occurs on TiO2 Lewis acid sites, and subsequent C-H activation and O2 utilization determine distinct catalytic performances. Pt/TiO2 exhibits higher activity toward unsaturated CVOCs owing to relatively moderate O2 adsorption and abundant reactive chemisorbed oxygen on the Pt0 species, enabling efficient oxygen-insertion pathways. By contrast, Ru/TiO2 preferentially converts saturated CVOCs owing to its relatively superior C-H bond dissociation capability relative to Pt/TiO2. The resulting polychlorinated dibenzo-p-dioxin and furan (PCDD/F) formation on the catalyst surface and in the gas phase is strongly associated with Cl-removal pathways: Ru/TiO2 promotes Cl2 generation via Deacon reactions, enhancing gas-phase PCDD/F formation, whereas Pt/TiO2 stabilizes oxygenated phenoxy-type intermediates on the catalyst surface, favoring PCDD/F formation on the catalyst. These findings thus elucidate the distinct roles of Pt and Ru in governing reaction pathways and secondary pollutant formation, offering critical guidance for the development of catalytic systems that balance high removal efficiency with minimal environmental risks.