Abatement of model molecules for dioxin total oxidation on V2O5–WO3/TiO2 catalysts: The case of substituted oxygen-containing VOC

Dioxin oxidation is generally studied on the basis of chlorinated benzene derivative models. Oxygen containing aromatic models are however also pertinent because the impact of the central O-bridge(s) of dioxins has to be evaluated. Furan was already studied as a model for the central ring of a polychlorinated dibenzofuran (PCDF), but this paper goes further as 2,5-dimethylfuran was studied in order to better take into account the steric hindrance existing around the oxygenated moiety of the modeled pollutant. The comparison of these two model compounds highlights the fact a furan ring, whether substituted or not, tends to adsorb strongly on the catalyst surface without being readily oxidized. This phenomenon leads to the formation of a carbonaceous deposit characterized by the presence of maleate species. Selective oxidation towards maleic anhydride takes place along with total oxidation in both cases. So the substitution of two methyl groups for hydrogen atoms in furan does not change the overall behavior of the pollutant towards the catalyst. This suggests that the oxygenated moiety of a PCDF – around which the steric hindrance is comparable with 2,5-dimethylfuran – could play a decisive role in the nature of the pollutant-to-catalyst interaction. Furthermore, competition tests with chlorobenzene show that the conversion of chlorobenzene is dramatically impeded in the presence of both investigated oxygen containing models. O-driven adsorption of dioxins should be envisaged as the first step of the catalytic abatement of dioxins on V-based catalysts rather than dissociative adsorption through the chlorinated end.

Chlorobenzene derivatives are widely employed as models for dioxins in the study of heterogeneous catalysts. However, the central ring of a polychlorinated dibenzofuran (PCDF) includes an oxygen bridge which could play an important role in the catalytic process. Using furan and 2,5-dimethylfuran as new models, we show that the behavior of the target pollutant could indeed be dictated by its oxygenated moiety.Figure optionsDownload as PowerPoint slide