title: Dechlorination of polychlorinated biphenyls by iron and its oxides.
abstract: The decomposition efficiency of polychlorinated biphenyls (PCBs) was determined using elemental iron (Fe) and three iron (hydr)oxides, i.e., α-Fe2O3, Fe3O4, and α-FeOOH, as catalysts. The experiments were performed using four distinct PCB congeners (PCB-209, PCB-153, and the coplanar PCB-167 and PCB-77) at temperatures ranging from 180 °C to 380 °C and under an inert, oxidizing or reducing atmosphere composed of N2, N2+O2, or N2+H2. From these three options N2 showed to provide the best reaction atmosphere. Among the iron compounds tested, Fe3O4 showed the highest activity for decomposing PCBs. The decomposition efficiencies of PCB-209, PCB-167, PCB-153, and PCB-77 by Fe3O4 in an N2 atmosphere at 230 °C were 88.5%, 82.5%, 69.9%, and 66.4%, respectively. Other inorganic chlorine (Cl) products which were measured by the amount of inorganic Cl ions represented 82.5% and 76.1% of the reaction products, showing that ring cleavage of PCBs was the main elimination process. Moreover, the dechlorination did not require a particular hydrogen donor. We used X-ray photoelectron spectroscopy to analyze the elemental distribution at the catalyst's surface. The O/Fe ratio influenced upon the decomposition efficiency of PCBs: the lower this ratio, the higher the decomposition efficiency. X-ray absorption near edge structure spectra showed that α-Fe2O3 effectively worked as a catalyst, while Fe3O4 and α-FeOOH were consumed as reactants, as their final state is different from their initial state. Finally, a decomposition pathway was postulated in which the Cl atoms in ortho-positions were more difficult to eliminate than those in the para- or meta-positions.
authors.affiliation: School of Chemistry and Environment, Beihang University, Beijing 100191, China.
authors.forename: Yifei
authors.initials: Y
authors.lastname: Sun
authors.affiliation: School of Chemistry and Environment, Beihang University, Beijing 100191, China.
authors.forename: Xiaoyuan
authors.initials: X
authors.lastname: Liu
authors.affiliation: Department of Environmental Engineering, Kyoto University, Kyoto 615-8540, Japan.
authors.forename: Masashi
authors.initials: M
authors.lastname: Kainuma
authors.affiliation: School of Environment, Tsinghua University, Beijing 100084, China.
authors.forename: Wei
authors.initials: W
authors.lastname: Wang
authors.affiliation: Department of Environmental Engineering, Kyoto University, Kyoto 615-8540, Japan. Electronic address: takaoka.masaki.4w@kyoto-u.ac.jp.
authors.forename: Masaki
authors.initials: M
authors.lastname: Takaoka
authors.affiliation: Department of Environmental Engineering, Kyoto University, Kyoto 615-8540, Japan.
authors.forename: Nobuo
authors.initials: N
authors.lastname: Takeda
mesh_terms: D002384:Catalysis; D004785:Environmental Pollutants / Q000737:chemistry*; D005290:Ferric Compounds / Q000737:chemistry*; D054879:Halogenation; D007501:Iron / Q000737:chemistry*; D011078:Polychlorinated Biphenyls / Q000737:chemistry*; D013696:Temperature
chemical_list: D004785:Environmental Pollutants; D005290:Ferric Compounds; C000499:ferric oxide; D011078:Polychlorinated Biphenyls; D007501:Iron
keywords: Coplanar PCBs; Hydrogen donor; Iron catalysts; O/Fe ratio; Reaction pathway; X-ray absorption near edge structure (XANES); X-ray photoelectron spectroscopy