title: Contribution of aluminas and aluminosilicates to the formation of PCDD/Fs on fly ashes.
abstract: 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.
authors.affiliation: Department of Chemistry, Louisiana State University, Baton Rouge, LA, USA.
authors.forename: Phillip M
authors.initials: PM
authors.lastname: Potter
authors.affiliation: Department of Chemistry, Louisiana State University, Baton Rouge, LA, USA.
authors.forename: Barry
authors.initials: B
authors.lastname: Dellinger
authors.affiliation: Department of Environmental Sciences, Louisiana State University, Baton Rouge, LA, USA. Electronic address: slomni1@lsu.edu.
authors.forename: Slawomir M
authors.initials: SM
authors.lastname: Lomnicki
mesh_terms: D000393:Air Pollutants / Q000032:analysis*; D000537:Aluminum Oxide / Q000737:chemistry*; D000538:Aluminum Silicates / Q000737:chemistry; D001572:Benzofurans / Q000032:analysis*; D002733:Chlorophenols / Q000737:chemistry*; D060729:Coal Ash / Q000032:analysis*; D000072338:Dibenzofurans, Polychlorinated; D004147:Dioxins / Q000032:analysis*; D004784:Environmental Monitoring
chemical_list: D000393:Air Pollutants; D000538:Aluminum Silicates; D001572:Benzofurans; D002733:Chlorophenols; D060729:Coal Ash; D000072338:Dibenzofurans, Polychlorinated; D004147:Dioxins; C049037:aluminosilicate; C030683:2-chlorophenol; D000537:Aluminum Oxide
keywords: Aluminosilicate; Dioxins; PCDD/Fs; Precursor pathway