X-ray spectroscopic studies of the high temperature reduction of Cu(II)0 by 2-chlorophenol on a simulated fly ash surface

The reaction of 2-chlorophenol on Cu(11)0 at 375 degreesC is studied using X-ray absorption near edge structure (XANES) spectroscopy. A mixture of copper(II) oxide and silica is prepared to serve as a surrogate for fly ash in combustion systems. 2-Chlorophenol is utilized as a model precursor for formation of polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans (PCDD/F). The Cu K-edge spectra shift to lower binding energy, reflecting the reduction of the copper. The substrate is found to form a mixture of COO, Cu(I), and Cu(0), with the dominant species being Cu(I). The data are fitted well with a first-order reaction scheme, with a time constant at 375 degreesC of 76 s. This is the first application of XANES spectroscopy for studying the kinetics and mechanism of heterogeneous reactions relevant to combustion processes, and the results demonstrate the utility and desirability of such X-ray spectroscopic studies.