1 research outputs found
PCDD/F Formation in an Iron/Potassium-Catalyzed Diesel Particle Filter
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 (Fe<sub>3</sub>O<sub>4</sub>) rather than hematite
(Fe<sub>2</sub>O<sub>3</sub>). 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