X-ray Spectroscopic Studies of the High Temperature Reduction of Cu(II)O by 2-Chlorophenol on a Simulated Fly Ash Surface

Abstract

The reaction of 2-chlorophenol on Cu(II)O at 375 degrees C 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 shiftto lower binding energy, reflecting the reduction of the copper. The substrate is found to form a mixture of Cu(II), Cu(I), and Cu(O), with the dominant species being Cu(I). The data are fitted well with a first-order reaction scheme, with a time constant at 375 degrees C 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.

Formation of PCDD/Fs from oxidation of 2-monochlorophenol over an Fe2O3/silica surface

“…We have previously demonstrated that 2-MCP interacts with the surfaces of metal oxides through a chemisorption mechanism (Farquar et al, 2003; Lomnicki and Dellinger, 2003a; Vejerano et al, 2011). Two pathways of chemisorption have been proposed for chlorophenols: i) elimination of H 2 O (upper path in Scheme 1) and ii) elimination of both H 2 O and HCl (lower path Scheme 1) (Lomnicki et al, 2008; Nganai et al, 2009).…”

“…Some of these radicals are resonance stabilized and can exist as primarily oxygen-centered or carbon-centered mesomers (cf. Scheme 1 Species II and III) (Farquar et al, 2003). …”

Influence of iron and copper oxides on polychlorinated diphenyl ether formation in heterogeneous reactions

“…This could be induced by a competitive reaction between the absorbed species and a gas-phase molecule (Farquar et al 2003;Lomnicki and Dellinger 2003a). The surfaceassociated chlorophenoxyl can react with gas-phase chlorobenzenes to form PCDEs, with another vicinal chlorophenoxyl via a Langmuir-Hinshelwood pathway to form PCDF, and with gas-phase polychlorophenol via an EleyRideal pathway to form PCDD.…”

Formation of environmentally persistent free radicals (EPFRs) on ZnO at room temperature: Implications for the fundamental model of EPFR generation

“…EPFR-containing PM has been demonstrated to produce pulmonary and cardiovascular dysfunction in animal models, with greater toxicity than non-EPFR-containing PM 5–11 . EPFRs were first proposed to form through the reduction of metal oxides by high-temperature exposure (above 150°C) to simple substituted aromatics, which electron and X-ray spectroscopy has shown to occur on CuO 12,13 and TiO 2 14 model systems. However, the longest-lived EPFR species observed to date are phenoxy radicals generated on ZnO 15 , which presents a significant challenge to the generic model of EPFR formation because it is usually not possible to create a Zn(I) oxidation state except under rare conditions 16–20 .…”