Alkaline- and alkaline-earth oxides based Lean NOx Traps: Effect of the storage component on the catalytic reactivity

The introduction of lean-burn engine technology has prompted the development of NOx storage-reduction (NSR or Lean NOx Traps, LNT) catalysts, which are currently based on a PtBa/Al2O3 system. Potassium is another element that has shown potentials as a storage component. This work explores the role of K during the NOx storage phase and the subsequent reduction using transient activity data and FT-IR analyses over a PtK/Al2O3 powdered catalyst. The catalytic behaviour of a PtK/Al2O3 system has been compared with that of a PtBa/Al2O3 catalyst. NOx storage experiments indicate similar storage efficiency in the two cases. The storage pathways are similar on both the storage components: nitrites and nitrates are formed, the first ones only at the beginning of the storage, quickly transformed in nitrates. The reduction of NOx stored over both systems is also analyzed when H2 is used as reductant. An in series 2-steps process is herein reported, involving at first the formation of NH3 upon reaction of nitrates with H2 (step 1), followed by the reaction of NH3 with residual nitrates to give N2 (step 2). The influence of the storage component on the Pt sites modifies the reactivity of H2 towards stored nitrates.

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