title: Formation of dioxins in the catalytic combustion of chlorobenzene and a micropollutant-like mixture on Pt/gamma-Al2O3.
abstract: Catalytic combustion over a 2 wt % Pt/gamma-Al2O3 catalyst of chlorobenzene (PhCl) and of a micropollutant-like mixture representative for a primary combustion offgas has been investigated. Typical conditions were 1000-1500 ppm of organics in the inflow, contact times approximately 0.3 s, 16% O2 in nitrogen at approximately 1 bar, and temperature range 200-550 degrees C. PhCl reacts considerably slower than when processing Cl-free compounds such as heptane. At intermediate temperatures--and incomplete conversion--byproducts are formed, especially polychlorobenzenes (PhClx). These are accompanied by polychlorinated dibenzo-p-dioxins (PCDDs) and dibenzofurans (PCDFs) at levels of about 10(-6) relative to PhClx. Additional HCI--made by co-reacting PhCl with tert-butylchloride--leads to much higher levels of PhClx and PCDD/Fs. Using the micropollutant-like mixture, the total chlorine input is reduced almost 20-fold, but it nevertheless leads to a 30-fold higher PCDD/F output. This is ascribed to reaction of the small amounts of (chloro)phenols in the mixture. The congener/isomer patterns of the PCDD/Fs for the mixture and with PhCl per se are quite comparable with those found in emissions from incinerators. As carbon is not present nor formed on the catalyst surface, de-novo formation therefrom cannot be involved. Rather condensation of phenolic entities or like precursors must have occurred. Consequences and options to ensure safe application are briefly discussed as well.
authors.affiliation: Center for Chemistry and the Environment, Leiden Institute of Chemistry, Gorlaeus Laboratories, Leiden University, NL-2300 RA Leiden, The Netherlands.
authors.forename: Vincent
authors.initials: V
authors.lastname: De Jong
authors.forename: Mariusz K
authors.initials: MK
authors.lastname: Cieplik
authors.forename: Robert
authors.initials: R
authors.lastname: Louw
mesh_terms: D000537:Aluminum Oxide / Q000737:chemistry; D002384:Catalysis; D002722:Chlorobenzenes; D004147:Dioxins / Q000737:chemistry*; D005740:Gases; D017745:Incineration; D010984:Platinum / Q000737:chemistry
chemical_list: D002722:Chlorobenzenes; D004147:Dioxins; D005740:Gases; D010984:Platinum; C031294:chlorobenzene; D000537:Aluminum Oxide