Role of the Mg/Al atomic ratio in hydrotalcite-based catalysts for NOx storage/reduction

1.0 wt.% Pt supported catalysts were prepared by incipient wetness impregnation of Mg-Al supports obtained by thermal decomposition of commercial hydrotalcite-type (HT) precursors with different Mg/Al atomic ratios (1.3, 2.0 and 3.0, respectively) and investigated in the storage-reduction of NOx (NSR). These catalysts showed improved performances in comparison to a Toyota-type Pt-Ba/Al2O3 catalyst at temperatures ≤ 250 °C. This behaviour can be attributed to the formation of well-dispersed cubic Mg(Al)O mixed oxides, which showed good NOx-storage properties, significantly better than those of the stoichiometric spinel MgAl2O4. Both the catalytic activity and the stability after a hydrothermal treatment of Pt/HT catalysts increased by increasing the Mg/Al atomic ratio, while the analogous Pt/MgO catalyst deactivated almost completely, evidencing the key role of the HT precursor.