Excellent sulfur resistance of Pt/BaO/CeO2 lean NOx trap catalysts

In this work, we investigated the NOx storage behavior of Pt/BaO/CeO2 catalysts, especially in the presence of SO2. High surface area CeO2 (∼110 m2/g) with a rod like morphology was synthesized and used as a support. The Pt/BaO/CeO2 sample demonstrated slightly higher NOx uptake in the entire temperature range studied compared with Pt/BaO/γ-Al2O3. More importantly, this ceria-based catalyst showed higher sulfur tolerance than the alumina-based one. The time of complete NOx uptake was maintained even after exposing the sample to ∼3 g/L of SO2. The same sulfur exposure, on the other hand, eliminated the complete NOx uptake time on the alumina-based NOx storage catalysts. TEM images show no evidence of either Pt sintering or BaS phase formation during reductive de-sulfation up to 600 °C on the ceria-based catalyst, while the same process over the alumina-based catalyst resulted in both a significant increase in the average Pt cluster size and the agglomeration of a newly formed BaS phase into large crystallites. XPS results revealed the presence of about five times more residual sulfur after reductive de-sulfation at 600 °C on the alumina-based catalysts in comparison with the ceria-based ones. All of these results strongly support that, besides their superior intrinsic NOx uptake properties, ceria-based catalysts have (a) much higher sulfur tolerance and (b) excellent resistance against Pt sintering when they are compared to the widely used alumina-based catalysts.