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

Abstract

WOx/CeO2 catalysts prepared by wet impregnation with (NH4)6H2W12O40 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, N2 isothermal adsorption and desorption, Raman, XPS, H2-TPR, O2-TPD and NH3-TPD shows that CeO2 exists as a form of face-centered cubic fluorite structure, while WOx 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 WOx and CeO2, which increases oxygen vacancy and promotes the reducibility and acidity of WOx/CeO2 catalysts. In CB or 1,2-DCB oxidation, WOx/CeO2 catalysts with monotungstate WOx 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% H2O or 5% CO2 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 Brönsted acid sites is promoted by gas oxygen. Partial oxidation products are oxidized to COx by surface oxygen.