title: PCDD/F formation in an iron/potassium-catalyzed diesel particle filter.
abstract: Catalytic diesel particle filters (DPFs) have evolved to a powerful environmental technology. Several metal-based, fuel soluble catalysts, so-called fuel-borne catalysts (FBCs), were developed to catalyze soot combustion and support filter regeneration. Mainly iron- and cerium-based FBCs have been commercialized for passenger cars and heavy-duty vehicle applications. We investigated a new iron/potassium-based FBC used in combination with an uncoated silicon carbide filter and report effects on emissions of polychlorinated dibenzodioxins/furans (PCDD/Fs). The PCDD/F formation potential was assessed under best and worst case conditions, as required for filter approval under the VERT protocol. TEQ-weighted PCDD/F emissions remained low when using the Fe/K catalyst (37/7.5 μg/g) with the filter and commercial, low-sulfur fuel. The addition of chlorine (10 μg/g) immediately led to an intense PCDD/F formation in the Fe/K-DPF. TEQ-based emissions increased 51-fold from engine-out levels of 95 to 4800 pg I-TEQ/L after the DPF. Emissions of 2,3,7,8-TCDD, the most toxic congener (TEF = 1.0), increased 320-fold, those of 2,3,7,8-TCDF (TEF = 0.1) even 540-fold. Remarkable pattern changes were noticed, indicating a preferential formation of tetrachlorinated dibenzofurans. It has been shown that potassium acts as a structural promoter inducing the formation of magnetite (Fe3O4) rather than hematite (Fe2O3). This may alter the catalytic properties of iron. But the chemical nature of this new catalyst is yet unknown, and we are far from an established mechanism for this new pathway to PCDD/Fs. In conclusion, the iron/potassium-catalyzed DPF has a high PCDD/F formation potential, similar to the ones of copper-catalyzed filters, the latter are prohibited by Swiss legislation.
authors.affiliation: Laboratory for Analytical Chemistry, Empa, Swiss Federal Laboratories for Materials Testing and Research, Überlandstrasse 129, CH-8600 Dübendorf, Switzerland.
authors.forename: Norbert V
authors.initials: NV
authors.lastname: Heeb
authors.forename: Markus
authors.initials: M
authors.lastname: Zennegg
authors.forename: Regula
authors.initials: R
authors.lastname: Haag
authors.forename: Adrian
authors.initials: A
authors.lastname: Wichser
authors.forename: Peter
authors.initials: P
authors.lastname: Schmid
authors.forename: Cornelia
authors.initials: C
authors.lastname: Seiler
authors.forename: Andrea
authors.initials: A
authors.lastname: Ulrich
authors.forename: Peter
authors.initials: P
authors.lastname: Honegger
authors.forename: Kerstin
authors.initials: K
authors.lastname: Zeyer
authors.forename: Lukas
authors.initials: L
authors.lastname: Emmenegger
authors.forename: Peter
authors.initials: P
authors.lastname: Bonsack
authors.forename: Yan
authors.initials: Y
authors.lastname: Zimmerli
authors.forename: Jan
authors.initials: J
authors.lastname: Czerwinski
authors.forename: Markus
authors.initials: M
authors.lastname: Kasper
authors.forename: Andreas
authors.initials: A
authors.lastname: Mayer
mesh_terms: D001572:Benzofurans; D002384:Catalysis; D005374:Filtration / Q000379:methods*; D007501:Iron / Q000737:chemistry*; D000072317:Polychlorinated Dibenzodioxins / Q000031:analogs & derivatives* / Q000737:chemistry; D011188:Potassium / Q000737:chemistry*
chemical_list: D001572:Benzofurans; D000072317:Polychlorinated Dibenzodioxins; D007501:Iron; D011188:Potassium; C014211:2,3,7,8-tetrachlorodibenzofuran