Low temperature decomposition of PCDD/PCDF, chlorobenzenes and PAHs by TiO_2-based V_2O_5-WO_3 catalysts

摘要

The oxidation of representative congeners of polychlorinated dibenzo-p-dioxins (PCDDs). polychlorinated dibenzofurans (PCDFs). polychlorinated chlorobenzenes (PCBzs), and of polyaromatic hydrocarbons (PAHs) was investigated on two commercial V_2O_5-WO_3/TiO_2-based catalysts, optimized for the combined reduction of nitrogen oxides and decomposition of dioxins. The non-chlorinated polyaromatic compounds (including non-chlorinated dibenzodioxin and dibenzofuran) are destroyed at temperatures as low as 150 deg C with an efficiency of more than 95%. PCDD and PCDF were also removed from the gas phase with an efficiency of >98%. However, at 150 deg C they remained mainly unchanged (up to 75%) adsorbed on the catalyst. A decrease in the oxidation rate with increasing chlorine substitution was found for the PCDD/PCDF. This could be explained by an increasing "redox potential" with increasing chlorine substitution due to the electron withdrawing effect of the chlorine. For the more volatile monoaromatic PCBz, however, the effect of lowering the volatility with increasing chlorine substitution (resulting in longer residence time on the catalyst ) over-compensates the effect of the increasing "redox potential" with higher degree of chlorination.