(24f) NOx Reduction Over Perovskite Based Lean NOx Trap | AIChE

(24f) NOx Reduction Over Perovskite Based Lean NOx Trap

Authors 

Qi, G. - Presenter, General Motors Global R&D


Abstract

Conventional Lean NOx Trap (LNT) catalysts contain high loadings of Pt in order to oxidize NO to NO2, a critical reaction in LNT application, and NO2 is stored as nitrates/nitrites on NOx trap materials (such as BaO) during lean periods and reduced to nitrogen/ammonia during shorter rich periods.  Hence it is highly desirable to develop non-Pt catalysts with high NO oxidation activities.  We have recently reported that perovskites are active catalysts for NO oxidation.  This paper presents our investigation on using perovskites to substitute Pt in LNT catalysts.  LNT catalysts based on LaMO3 and Sr-LaMO3 (M = Mn, Fe and Co) perovskites were evaluated and their thermal durability under reducing conditions, required for desulfation was probed.  Temperature Programmed Reduction (TPR) and X-ray Diffraction (XRD) results show that Co-perovskite is not stable in reducing environmentat temperatures above 500oC, whereas both Fe and Mn-perovskites could be stable at 700oC under the same condition. Considering both NOoxidation to NO2 efficiency and thermal durability under rich condition, Mn-perovskite is likely the best choice for LNT applications.  Similar NOx reduction performance was achieved over a Mn-perovskite based LNT when compared with a Pt based LNT, and its sulfation and desulfation characteristics were evaluated.

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