Catalytic destruction of PCDD/Fs over vanadium oxide-based catalysts

Abstract

Vanadium oxide-based catalysts were developed for the destruction of vapour phase PCDD/Fs (polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans). A vapour phase PCDD/Fs generating system was designed to supply stable PCDD/Fs steam with initial concentration of 3.2 ng I-TEQ Nm⁻³. Two kinds of titania (nano-TiO₂ and conventional TiO₂) and alumina were used as catalyst supports. For vanadium-based catalysts supported on nano-TiO₂, catalyst activity is enhanced with operating temperature increasing from 160 to 300 °C and then reduces with temperature rising further to 350 °C. It is mainly due to the fact that high volatility of organic compounds at 350 °C suppresses adsorption of PCDD/Fs on catalysts surface and then further inhibits the reaction between catalyst and PCDD/Fs. The optimum loading of vanadium on nano-TiO₂ support is 5 wt.% where vanadium oxide presents highly dispersed amorphous state according to the Raman spectra and XRD patterns. Excessive vanadium will block the pore space and form microcrystalline V₂O₅ on the support surface. At the vanadium loading of 5 wt.%, nano-TiO₂-supported catalyst performs best on PCDD/Fs destruction compared to Al₂O₃ and conventional TiO₂. Chemical states of vanadium in the fresh, used and reoxidized VOx(5 %)/TiO₂ catalysts at different operating temperature are also analysed by XPS.

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