Effect of Ceria on the Storage and Regeneration Behavior of a Model Lean NO x Trap Catalyst Yaying Ji Æ Todd J. Toops Æ Mark Crocker Received: 6 June 2007 / Accepted: 17 July 2007 / Published online: 4 August 2007 Ó Springer Science+Business Media, LLC 2007 Abstract In this study the effect of ceria addition on the performance of a model Ba-based lean NO x trap (LNT) catalyst was examined. The presence of ceria improved NO x storage capacity in the temperature range 200–400 °C under both continuous lean and lean-rich cycling condi- tions. Temperature-programmed experiments showed that NO x stored in the ceria-containing catalyst was thermally less stable and more reactive to reduction with both H 2 and CO as reductants, albeit at the expense of additional reductant consumed by reduction of the ceria. These find- ings demonstrate that the incorporation of ceria in LNTs not only improves NO x storage efficiency but also posi- tively impacts LNT regeneration behavior. Keywords NO x Á Storage Á Reduction Á LNT Á Ceria 1 Introduction Lean-burn engines, including diesel and gasoline direct injection engines, are generally more fuel-efficient than stoichiometric gasoline engines and emit less carbon dioxide. Thus there are both economic and environmental incentives to increase the use of lean-burn vehicles. However, the development of effective after treatment methods for the abatement of lean exhaust emissions rep- resents a challenge to the automotive industry. While conventional three-way catalysts are highly effective for control of nitrogen oxides (NO x ), CO and hydrocarbons (HCs) from stoichiometric exhaust, the technology for removal of NO x from lean exhaust is still not fully devel- oped. Specifically, the excess oxygen present in lean exhaust competes with NO x for available reductants (H 2 , CO, HCs), and significantly decreases NO x reduction efficiency. Of the several technologies proposed for lean NO x removal, the lean NO x trap (LNT), also known as the NO x Storage-Reduction (NSR) catalyst or the NO x Adsorber Catalyst (NAC), is considered a promising candidate. LNT catalysts contain precious metals (generally Pt and Rh) and an alkali or alkaline-earth metal storage component (most commonly BaO) supported on a high surface area material (usually alumina). Under typical lean exhaust conditions, NO is oxidized to NO 2 over precious metal sites and reversibly stored as nitrates or nitrites on the storage materials. Stored NO x species are subsequently decom- posed, released and reduced to N 2 during short periodic excursions to rich (i.e., net reducing) conditions. The trapping ability of the LNT catalyst is thus restored after a lean-rich cycle. A major issue still remaining for LNT catalysts is that of deactivation due to sulfur poisoning. Decomposition of barium sulfate requires high temperatures (around 700 °C) and reducing conditions. Such treatments reduce the high fuel efficiency of lean-burn engines and result in catalyst deterioration due to sintering of the precious metal and NO x storage components, as well as the occurrence of unwanted reactions between washcoat components. Therefore, the improvement of LNT durability represents a key challenge. Y. Ji Á M. Crocker (&) Center for Applied Energy Research, University of Kentucky, 2540 Research Park Drive, Lexington, KY 40511-8479, USA e-mail: crocker@caer.uky.edu T. J. Toops Fuels, Engines and Emissions Research Center, Oak Ridge National Laboratory, 2360 Cherahala Blvd, Knoxville, TN 37932-1563, USA 123 Catal Lett (2007) 119:257–264 DOI 10.1007/s10562-007-9226-2