Observing copper chloride during dioxin formation using dispersive XAFS

摘要

The incineration of municipal solid waste generates dioxins. To control dioxins, it is necessary to determine the mechanism of their formation. Because copper chloride (CuCl2) is one of the strongest catalysts of dioxin formation in fly ash, it is important to study the chemical changes of this compound. To determine the chemical changes of copper, Cu-K x-ray absorption near edge structure (XANES) spectra were examined during the heating of model fly ash using a time-resolved dispersive x-ray absorption fine structure (DXAFS) technique. The change in the absorption edge of the Cu-K XANES spectrum revealed a change in the valence of copper and the temperature dependence of the reduction and oxidation of CuCl2. From room temperature to 270 degrees C, CuCl2 was reduced, and from >270 to 300 degrees C, copper was reoxidized in the presence of 10% oxygen. At a constant temperature of 210 or 300 degrees C, copper was dynamically reduced and oxidized. In experiments using different gas streams, HCl gas had no effect on the reaction of copper, while oxygen gas was essential for the reoxidation of copper. Our results suggest that dioxin formation in fly ash occurs via the chlorination of carbon with the reduction of CuCl2 and carbon gasification catalyzed by copper oxides. Copyright (C) 2008 John Wiley & Sons, Ltd.