Excellent sulfur resistance of Pt/BaO/CeO(2) lean NO(x) trap catalysts

Abstract

In this work, we investigated the NO(x) storage behavior of Pt/BaO/CeO(2) catalysts, especially in the presence of SO(2). High surface area CeO(2) (similar to 110 m(2)/g) with a rod like morphology was synthesized and used as a support. The Pt/BaO/CeO(2) sample demonstrated slightly higher NO(x) uptake in the entire temperature range studied compared with Pt/BaO/gamma-Al(2)O(3). More importantly, this ceria-based catalyst showed higher sulfur tolerance than the alumina-based one. The time of complete NO(x) uptake was maintained even after exposing the sample to similar to 3 g/L of SO(2). The same sulfur exposure, on the other hand, eliminated the complete NO(x) uptake time on the alumina-based NO(x) storage catalysts. TEM images show no evidence of either Pt sintering or BaS phase formation during reductive de-sulfation up to 600 degrees 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 degrees C on the alumina-based catalysts in comparison with the ceria-based ones. All of these results strongly support that, besides their superior intrinsic NO(x) 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. (C) 2008 Elsevier B.V. All rights reserved