NO Reduction Activity of Pd Catalyst Modified with Rare Earth Oxides

Abstract

Reductions of NO over fresh and aged Pd-rare earth catalysts supported on α-Al₂O₃ were investigated through activity examination, TPD-, and adsorption-measurements of NO. Sixteen kinds of rare earths, including yttrium, were used and NO reducing activities were measured using a simulated exhaust gas under the stoichiometric conditions.
It was found that the NO conversion of Pd-rare earth catalysts at lo wer temperatures were better than that of nonmodified Pd catalyst (Figs.1 and 5). Among the catalysts tested, La, Pr, Nd, and Sm were the most effective components (Figs.4 and 8). Except for Ce, the Pd-rare earth catalysts had better activities and selectivities for the NO-H₂ reaction below 300°C than the Pd catalyst (Fig.10) and FI, reacted with NO more easily than with O₂ (Fig.11). The reason why the Pd-rare earth catalysts had the excellent activity for NO reduction by H₂ is as follows: The amount of NO chemisorption on Pd-rare earth catalysts was higher than that on the Pd catalyst (Table 1) and also, the NO chemisorbed on Pd-rare earth catalysts were dissociated more easily than that on the Pd catalyst (Fig.12).