Catalytic combustion of chlorinated aromatics over WOx/CeO2 catalysts at low temperature

Abstract WO x /CeO 2 catalysts prepared by wet impregnation with (NH 4 ) 6 H 2 W 12 O 40 and (COOH) 2 aqueous solution were used in the catalytic combustion of chlorobenzene (CB) and 1,2-dichloro- benzene (1,2-DCB). Characterization by XRD, N 2 isothermal adsorption and desorption, Raman, XPS, H 2 -TPR, O 2 -TPD and NH 3 -TPD shows that CeO 2 exists as a form of face-centered cubic fluorite structure, while WO x is identified as the forms of monoxo and dioxo monotungstate, polytungstate and nano-particle, depending on W content. W-O-Ce is formed as a result of interaction between WO x and CeO 2 , which increases oxygen vacancy and promotes the reducibility and acidity of WO x /CeO 2 catalysts. In CB or 1,2-DCB oxidation, WO x /CeO 2 catalysts with monotungstate WO x present excellent stable activity with TOF at 250 °C based on W-O-Ce in a range of 4.7–7.2 × 10 −4 s -1 . 90% conversion is obtained below 350 °C, at which chlorination is almost completely inhibited. The activity in feed containing 5% H 2 O or 5% CO 2 is depending on their effects on the availability of surface oxygen. In situ FT-IR shows that the adsorbed CB species can be oxidized by surface lattice oxygen into phenolate, carboxylates and carbonate, while the formation of acetaldehyde on Bronsted acid sites is promoted by gas oxygen. Partial oxidation products are oxidized to CO x by surface oxygen.