Catalytic decomposition of PCDD/Fs on a V₂O₅-WO₃/nano-TiO₂ catalyst: effect of NaCl

The effect of NaCl addition on the properties, activity, and deactivation of a V₂O₅-WO₃/nano-TiO₂ catalyst was investigated during catalytic decomposition of gas-phase polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans (PCDD/Fs). The extent of deactivation relates directly to the NaCl loading of the catalyst. Poisoning by sodium neutralizes acid sites, interacts strongly with active VO_x species, and reduces the redox capacity of catalysts. In addition, NaCl is also a chlorine source and may actually accelerate the synthesis of new PCDD/Fs. Washing a catalyst with dilute sulfuric acid largely restores catalytic activity, breaking the interaction of Na⁺ ions and dispersed vanadia and removing Na from the catalyst surface. Consequently, catalyst acidity and redox capacity almost recover. Furthermore, sulfate residues react with surface adsorbed water to generate Brønsted acid sites, ensuing a surge of strong acidity of the catalysts.