Deactivation of after-treatment catalysts for bio-fuelled engines

To decrease the emissions of anthropogenic CO2 from vehicles one option is to increase the utilization of biobased fuels. However, there are challenges with this transition, one being the mitigation of emissions of the potent greenhouse gas methane, which is the main constituent of biogas. Another relates to the presence of catalyst poisons in biofuels due to a wide variety of raw materials that are used for the production of these fuels.In this thesis, the aim is to investigate how exhausts from biogas and biodiesel impact the emission control system of a heavy-duty vehicle. The catalysts in the emission control system are studied individually and as a system, with commercial biobased fuels and synthetic gas feeds containing catalyst poisons. After exposure to biogas exhaust for 900 h in an engine-bench, the Pd/Pt-Al2O3 oxidation catalyst was found to be severely deactivated in terms of CH4 oxidation activity. A decrease in low-temperature activity for NO oxidation to NO2 was observed, which impacts the performance of the SCR-catalyst down-stream in the system. This loss in activity is explained by the finding of catalyst poisons as well as metal segregation and sintering of the noble metal particles.The V2O5-WO3/TiO2 SCR-catalyst in the engine-bench system remained active for NOx reduction after long-term ageing, however, the decrease in NO2 formation over the oxidation catalyst at low temperatures could cause an increase in NOx emissions even if the SCR catalyst itself is still active. Except for the vanadium-based SCR catalyst also a Cu-CHA catalyst was studied. Both types of SCR catalysts were found to be sensitive to phosphorus poisoning and the Cu-CHA catalyst was also found to be sensitive to sulfur.From results obtained we propose that the SO2 exposure leads to the formation of Cu-bisulfate species that reduce the amount of copper sites available for NOx reduction in the Cu-CHA SCR catalyst. The degree of deactivation is also dependent on the reaction condition where the standard SCR reaction is more impacted than the fast SCR reaction