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      Contribution of aluminas and aluminosilicates to the formation of PCDD/Fs on fly ashes

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      Chemosphere
      Elsevier BV

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          Abstract

          <p class="first" id="P2">Chlorinated aromatics undergo surface-mediated reactions with metal oxides to form Environmentally Persistent Free Radicals (EPFRs) which can further react to produce polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs). Previous work using laboratory-made fly ash surrogates composed of transition metal oxides deposited on silica powder has confirmed their ability to mimic fly ash in the production of PCDD/Fs. However, little is known about the propensity of aluminas and aluminosilicates, other components of fly ash, to form PCDD/Fs. A fly ash sample containing both alumina and mullite, an aluminosilicate, was tested for PCDD/F formation ability and compared to PCDD/F yields from the thermal degradation of 2-monochlorophenol (2-MCP) precursor over γ-alumina, α-alumina, and mullite. A packed-bed flow reactor was used to investigate the thermal degradation of 2-MCP over the various catalysts at 200–600 °C. Fly ash gave similar PCDD/F yields to surrogates made with similar transition metal content. γ-alumina, which is thermodynamically unfavorable, was very catalytically active and gave low PCDD/F yields despite a high destruction of 2-MCP. Mullite and α-alumina, the thermodynamically favorable form of alumina, yielded higher concentrations of dioxins and products with a higher degree of chlorine substitution than γ-alumina. The data suggest that certain aluminas and aluminosilicates, commonly found in fly ash, are active catalytic surfaces in the formation of PCDD/Fs in the post-flame cool zones of combustion systems and should be considered as additional catalytic surfaces active in the process. </p>

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          Author and article information

          Journal
          Chemosphere
          Chemosphere
          Elsevier BV
          00456535
          February 2016
          February 2016
          : 144
          : 2421-2426
          Article
          10.1016/j.chemosphere.2015.11.009
          4695248
          26615490
          bb8e7cbc-ac81-41b4-a555-ac4dc1ba836a
          © 2016

          https://www.elsevier.com/tdm/userlicense/1.0/

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