Biofuel-Promoted
Polychlorinated Dibenzodioxin/furan
Formation in an Iron-Catalyzed Diesel Particle Filter
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Abstract
Iron-catalyzed diesel particle filters
(DPFs) are widely used for
particle abatement. Active catalyst particles, so-called fuel-borne
catalysts (FBCs), are formed <i>in situ</i>, in the engine,
when combusting precursors, which were premixed with the fuel. The
obtained iron oxide particles catalyze soot oxidation in filters.
Iron-catalyzed DPFs are considered as safe with respect to their potential
to form polychlorinated dibenzodioxins/furans (PCDD/Fs). We reported
that a bimetallic potassium/iron FBC supported an intense PCDD/F formation
in a DPF. Here, we discuss the impact of fatty acid methyl ester (FAME)
biofuel on PCDD/F emissions. The iron-catalyzed DPF indeed supported
a PCDD/F formation with biofuel but remained inactive with petroleum-derived
diesel fuel. PCDD/F emissions (I-TEQ) increased 23-fold when comparing
biofuel and diesel data. Emissions of 2,3,7,8-TCDD, the most toxic
congener [toxicity equivalence factor (TEF) = 1.0], increased 90-fold,
and those of 2,3,7,8-TCDF (TEF = 0.1) increased 170-fold. Congener
patterns also changed, indicating a preferential formation of tetra-
and penta-chlorodibenzofurans. Thus, an inactive iron-catalyzed DPF
becomes active, supporting a PCDD/F formation, when operated with
biofuel containing impurities of potassium. Alkali metals are inherent
constituents of biofuels. According to the current European Union
(EU) legislation, levels of 5 μg/g are accepted. We conclude
that risks for a secondary PCDD/F formation in iron-catalyzed DPFs
increase when combusting potassium-containing biofuels