The Diesel Oxidation Catalyst (DOC) is subjected to harsh conditions, causing its performance to
diminish over time as the result of different aging mechanisms, which either decreases or lowers the
accessibility to the catalyst’s active sites. Previous work using chemisorption to quantify aging progression
has resulted in a reproducibility of 17%. In this study it has been attempted to lower this, while
also performing performance evaluations to see if correlations exist between dispersion and Light-Off
Two catalysts have been investigated, LLC (Low Loading Catalyst) and HLC (High Loading Catalyst).
These were hydrothermally aged at 600 C, 700 C and 800 C. In addition to these, two HLC engine cell
samples were also investigated.
To ensure sample homogeneity, different sample preparation methods were investigated. Catalyst samples
were crushed, or had their washcoat layer removed, or were milled and then sieved. A total of 5 runs were
done using fresh catalysts of LLC and HLC to calculate the standard deviation. Evaluation of performance
was done on all samples using Synthetic Catalyst Activity Testing (SCAT).
It was deemed that the only viable sample preparation method was to mill and sieve as other methods
would be hard to reproduce. The results showed that the reproducibility for LLC was %STD = 4% and
for HLC %STD = 2%. For LLC, a correlation between catalytic activity and dispersion was found. The
activity dropped with respect to the dispersion in a close to linear fashion without a large effect on BET
surface area. For HLC the dispersion decreased largely upon hydrothermal aging, however no correlation
was found with the activity; only when aged at 800 C a significant change in LOT was noted. The BET
surface area measurements were inconsistent. Lower dispersion sometimes resulted in higher surface area.
Engine cell samples exhibited notable decrease in dispersion, but not in surface area, and did not correlate
to the hydrothermally aged catalysts, which might be due to other effects inhibiting CO chemisorption