Thermal catalytic mineralization of ortho-dichlorobenzene at low temperature: an in situ FT-IR and XPS mechanistic investigation

Abstract

Generally, the mineralization of ortho-dichlorobenzene (o-DCB) [a surrogate moiety representing dioxin and furans (D&Fs)] over mixed oxide catalysts occurs at 175 °C with the substantial participation of the lattice oxygen from the catalyst and support. However, it is necessary to reduce the mineralization temperature of any incineration process generating D&Fs from the off-gas stream. In the present work, for the first time, the above-mentioned mineralization reaction was performed at a temperature as low as 120 °C under static conditions over a biphasic catalyst in the form of V₂O₅–WO₃ dispersed on a CeO₂ support (VWC). The CeO₂ support was primarily chosen to enhance the synergistic effect of labile lattice oxygen, which primarily affects the reaction temperature and the kinetics to a great extent. The mechanistic understanding for this biphasic catalyst was developed by separately delineating the individual mechanistic role of V₂O₅–CeO₂ (VC) and WO₃–CeO₂ (WC). Effectively, the kinetics and mineralization temperature of the three catalysts (VC, WC and VWC) were different, which is attributed to the different surface intermediates formed over the catalytic surface under oxidative and non-oxidative conditions. Even in the absence of oxygen, these catalysts mineralized o-DCB, thereby substantiating their Mars–Van Krevelen (MVK)-type mechanistic behaviour. Herein, we primarily focused on the thermal catalytic reaction mechanism of o-DCB mineralization, which was established using the in situ FT-IR technique. Furthermore, the extensive XPS-based analysis revealed the different adsorption and reaction sites for particular catalysts along with the synergistic role of the CeO₂ support, which will create a new avenue for the mineralization of very toxic VOCs, such as dioxins and furans.