Interaction between soot and stored NOx during operation of LNT catalysts

Diesel-equipped vehicles are considered as one of the primary sources of NOx and particulate (soot) emissions in industrialized countries. Accordingly, in the transport sector remarkable research efforts are being made to find viable solutions to limit their emission. Recently the potential use of LNT catalyst in the simultaneous removal of soot and NOx has been proposed according to the DPNR (Diesel Particulate-NOx Reduction) concept. In previous works of our group the potentiality of both Ba- and K-based LNT catalysts in the simultaneous removal of soot and NOx has been investigated. It has been shown that during the lean phase soot oxidation occurs by NO2 (formed upon NO oxidation), while NOx are being stored on the catalyst surface. More recently it has also been shown that NOx species stored onto the trapping component of the catalyst may participate in the combustion of soot via the release of NOx upon nitrate decomposition and/or by directly reacting with soot according to a surface reaction. Aim of this work is to provide new insights on the interplay existing between soot combustion and NOx storage, and in particular on the interactions between soot and the stored NOx. The investigation has been carried out over PtBa/Al2O3 and PtK/Al2O3 catalysts and over the corresponding Pt-free binary samples to evaluate the role of Pt in the reaction.