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Four samples from each of two field-aged catalysts subjected to different field test conditions were investigated. The light-off and conversion performance of each sample was measured in a synthetic exhaust flow reactor system. Time-resolved laser IR spectroscopy was used to investigate the catalyst behaviour under transient conditions. Significant differences in light-off temperatures and transient conversion performance between the samples was observed. The samples taken from the inlet side of the monolith were more deactivated than the corresponding ones from the outlet. However, samples taken from peripheral positions always showed better performance than samples originating from the centre. In order to explain observed variations in activity, the following surface properties were examined: oxygen uptake, specific metal area (CO chemisorption), total surface area (BET) and chemical composition (XPS analysis).

A standard commercial three-way catalyst was aged at 950°C for 24 hours in dry N2 with 2% O2. The performance of the aged and a fresh samples were characterized using a synthetic exhaust flow system. The light-off temperature for all three pollutants on the aged sample was more than 70°C higher than for the fresh one. The effect of aging on steady-state performance at higher temperatures (>400°C) was more moderate. In order to explain the decrease in activity the samples were analysed for their bulk and surface composition using electron microscopy (TEM/STEM/EDS), photoelectron spectroscopy (XPS) and X-ray diffraction (XRD). In addition the precious metal dispersion were determined by CO chemisorption and the total area by standard BET measurement. TEM micrographs showed that the metal particles containing platinum had an average diameter between 3-4 nm in the fresh sample but grow considerably in size upon aging.

This paper will review several different emission control systems for heavy duty diesel (HDD) applications aimed at future legislations. The focus will be on the (DOC+CSF+SCR+ASC) configuration. As of today, various SCR technologies are used on commercial vehicles around the globe. Moving beyond EuroVI/US10 emission levels, both fuel consumption savings and higher catalyst system efficiency are required. Therefore, significant system optimization has to be considered. Examples of this include: catalyst development, optimized thermal management, advanced urea dosing calibrations, and optimized SCR inlet NO:NO2 ratios. The aim of this paper is to provide a thorough system screening using a range of advanced SCR technologies, where the pros and cons from a system perspective will be discussed. Further optimization of selected systems will also be reviewed. The results suggest that current legislation requirements can be met for all SCR catalysts under investigation.