Evaluation of PCDD/F oxidation catalysts: confronting studies on model molecules with tests on PCDD/F-containing gas stream.

Titania supported vanadium oxide is a renowned catalyst for the abatement of polychlorinated dibenzo-p-dioxins and furans (PCDD/Fs) from gas effluents. To develop more active formulations, researchers mainly rely on lab-scale experiments on "PCDD/Fs-mimicking substances", like (chloro)-benzene. Using such model compounds is convenient whereas handling PCDD/Fs in the laboratory is potentially hazardous and complicated. Recent studies, however, challenged some foremost conclusions of model compound based studies, starting from the observation that different model compounds gave contrasted results. Thus the present work aims at confronting some of these dubious conclusions with direct experimental tests on PCDD/Fs. One reference V(2)O(5)/TiO(2) catalyst and three modified formulations (V(2)O(5)/TiO(2)-SO(4), V(2)O(5)-MoO(3)/TiO(2), and V(2)O(5)-WO(3)/TiO(2)) have been evaluated. A dedicated apparatus was used which allows safe and reliable tests on a mixture of PCDD/Fs congeners. Some of the previously proposed catalyst improvement strategies actually prove to be disadvantageous in the removal of PCDD/Fs. In particular, MoO(3)- and WO(3)-modified catalysts were significantly less active than the reference catalyst. These observations show that conclusions from model compound based studies must be drawn with care and should ideally be confronted with tests on the actual target pollutants.