Novel low temperature NOx storage-reduction catalysts for diesel light-duty engine emissions based on hydrotalcite compounds.

A series of Pt and Pt,Cu supported catalysts were prepared by wet impregnation of Mg–Al supports obtained from hydrotalcite-type (HT) precursor compounds. These novel NOx storage-reduction (NOxSR) catalysts show improved performances in NOx storage than Pt,Ba/alumina NOxSR catalysts at reaction temperatures lower than 200 C. These catalysts show also improved resistance to deactivation by SO2. The effect is attributed to the formation of well dispersed Mg(Al)O particles which show good NOx storage properties. The promoted low temperature activity is explained by the lower basicity of the Mg(Al)O mixed oxide in comparison to BaO, which induces on one hand a lower inhibition on Pt activity (NO to NO2 oxidation and/or hydrocarbon oxidation) due to electronic effect, and on the other hand a lower thermal stability of the stored NOx . The presence of Cu slightly inhibits activity at low temperature, although improves activity and resistance to deactivation at 300 °C. On these catalysts FT-IR characterization evidences the formation of a Pt–Cu alloy after reduction.