A PGM-free NOx adsorber + selective catalytic reduction catalyst system (AdSCR) for trapping and reducing NOx in lean exhaust streams at low temperature†
Low-temperature operation of urea/NH3-SCR converters, required by recent emission regulations, is challenging due to technological limits related to poor catalytic activity, difficult urea decomposition and undesired ammonium nitrate formation. Herein, we present a novel concept of a catalytic device, which adds a NOx storage functionality to a typical SCR catalyst. This enables capture and storage of NOx in lean exhaust streams already at room temperature, with significant efficiencies under dry conditions, as well as direct reduction of the stored NOx at higher temperatures. The proposed system (AdSCR = adsorption + selective catalytic reduction) is intrinsically different from the well-known existing NOx storage reduction (LNT) + SCR systems. In fact, it is free of PGM materials and does not require lean–rich cycling, being operated just like an SCR catalyst. It has therefore potential advantages both in terms of costs and flexibility of the aftertreatment configuration: in principle, it can be integrated into conventional SCR converters, leading to improved deNOx efficiencies without additional modifications of the aftertreatment architecture.