Isotopic studies of NOx reduction over Pt-Ba/Al2O3 LNT catalyst

NOx storage and reduction (NSR) catalysts (or lean NOx trap, LNT) are considered to be one of the most promising solutions for NOx removal from lean burn engine exhausts. In a recent study by some of us , a mechanism for the reduction by H2 of NOx stored onto a Pt-Ba/Al2O3 LNT model catalyst has been proposed. In particular it has been suggested that the formation of N2 occurs via a 2-steps in series molecular pathway involving at first the formation of NH3 upon reaction of stored NOx with H2 (step 1), followed by the reaction of NH3 with residual stored NOx to give N2 (step 2). It has also been found that step 1 is faster than step 2, which is rate determining in the formation of N2. The present study aims to better elucidate the pathways involved in the reduction of the stored NOx, and in particular the second step of the proposed mechanism for N2 formation involving stored NOx and ammonia. For this purpose experiments have been carried out using isotopically labelled molecules and different reductants, including H2 and NH3.