Characteristics of Pt-BaO/CeO2 lean NOx trap catalysts: the role of the CeO2 support in the desulfation process

Introduction Removal of harmful NOx emissions from lean burn and diesel engines in the presence of excess oxygen presents a great challenge. Lean-NOx traps (LNTs, aka NOx storage/reduction (NSR) catalysts or NOx adsorbers) are one of the promising technologies to remove NOx effectively. In the LNT technology, an active (alkali and/or alkaline earth) oxide material takes up NOx under lean engine operation conditions and stores them as nitrates [1], which are released from the active oxide catalyst component, and then reduced to N2 on the precious metal component of the catalyst during a rich cycle. However, the stability of LNT materials against SO2 poisoning remains a critical issue. In a previous publication [2], our group reported the superior intrinsic NOx uptake of Pt-BaO/CeO2 sample over Pt-BaO/Al2O3 over typical operating temperature ranges. In addition, the ceria-supported sample showed significantly improved sulfur resistance than the latter. From a practical point of view for ceria supported samples, however, a question arises about its desulfation behavior compared with the alumina-supported sample reported previously [3]. In this contribution, we explore the characteristics of Pt-BaO/CeO2 sample by focusing on the role of ceria in the desulfation, compared with that for the similarly prepared alumina supported one. For this purpose, we used temperature programmed reaction (H2 TPRX), synchrotron time resolved x-ray diffraction (TR-XRD) and in situ sulfur K-edge x-ray absorption near-edge spectroscopy (XANES) techniques.