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Effects of trace elements in biodiesel on the performance of diesel oxidation catalysts in heavy-duty vehicles

Time: Fri 2020-10-23 13.00

Location:, Stockholm (English)

Subject area: Chemical Engineering

Doctoral student: Jonas Granestrand , Kemisk teknologi, Process Technology

Opponent: Dr. Todd J. Toops, Oak Ridge National Laboratory, Tennessee, USA

Supervisor: Lars Pettersson, Processteknologi

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To reduce net greenhouse gas emissions, a shift towards adoption of biofuels is ongoing in the transport sector. Heavy-duty diesel vehicles are equipped with aftertreatment equipment, comprising of catalysts and filters, and how this equipment is affected by the use of biofuels is not yet fully understood. Fatty Acid Methyl Ester (FAME) biodiesel may contain high loadings of different trace elements stemming either from the biomass used as raw material, or from the production process. These trace elements could act as poisons that deactivate the aftertreatment catalysts.

The objective of this work was to study how the diesel oxidation catalyst (DOC) is affected by the presence of trace elements in FAME biodiesel. The DOC reduces emissions of CO and hydrocarbons, but furthermore, it generates NO2 from NO present in the exhaust, which is essential for downstream aftertreatment components to operate optimally. Because the DOC is located at the inlet of the aftertreatment system, it is subjected to high concentrations of trace elements, compared to downstream components.

An investigation of a DOC that had been used for an entire lifetime in a vehicle operating on FAME biodiesel revealed that phosphorus appeared to have the largest effect on DOC activity, causing considerable deactivation in the NO oxidation reaction. Na and Ca, on the other hand, appeared to have little effect. The largest cause of deactivation was thermal aging, rather than poisoning by trace components.

In-situ X-ray Absorption Spectroscopy studies of poisoned model catalysts showed a strong electronic interaction between P and catalytically active Pt/Pd particles during CO oxidation reaction conditions. In contrast, such effects were not observed for Na and K. Elemental mapping with Energy dispersive spectroscopy (EDS) of scanning transmission electron micrographs showed that phosphorus was co-located with Pt-Pd, whereas Na and K, on the other hand, were evenly distributed throughout the Al2O3 washcoat support.