Influence of platinum and barium precursors on the NSR behavior of Pt–Ba/Al2O3 monoliths for lean-burn engines

The influence of platinum and barium precursors on the catalytic performance of monolithic Pt–Ba/Al2O3 NOx storage catalysts was studied. The precursors used in the preparation were: tetraammineplatinum nitrate [Pt(NH3)4(NO3)2] and hexachloroplatinic acid [H2Pt(Cl)6] for incorporation of platinum by adsorption from solution (ion exchange); and barium acetate [Ba(CH3–COO)2] and barium nitrate [Ba(NO3)2] for incorporation of barium by dry impregnation. The prepared samples were characterized by XRD, H2 chemisorption and thermogravimetry, to determine the distribution and dispersion of the metallic phases. The catalytic activity of the prepared monolithic catalysts was tested for lean/rich NOx storage and reduction in a flow reactor using hydrogen as reducing agent. The catalyst prepared from tetraammineplatinum nitrate and barium acetate was the most active in the NOx storage during the lean period. NOx storage capacity (NSC) and selectivity were dependent with temperature. The higher NSC was obtained at temperature 330–350 °C. About 80% selectivity to nitrogen was achieved with catalysts prepared from tetraammineplatinum nitrate, versus 70% when the platinum was incorporated from hexachloroplatinic acid.