Effect of basic metal additives on NO_x reduction of property of Pd-based three-way catalyst

摘要

The three-way catalytic (TWC) performance, especially CO and NOx conversion, of a Pd-only catalyst was improved by the addition of basic elements, and the activity increased as the electronegativity of the additive cations decreased (Ha > Sr > La), indicating that the basicity or electron-donating ability of the additives played a significant role in the improvement of the TWC performance. Thermal decomposition temperature ofPdO in promoted catalysts became higher with decreasing the ionelectronegativity of the promoters. XPS analysis proved that the electron density around Pd(!I) in the Ha-promoted catalyst was higher than that of Pd-only catalyst. The improvement of the TWC performance by the addition of basic promoters is discussed in terms of the stabilization of PdO, which may suppress the sintering, as well as of electron enrichment, which endows palladium with the Rh-Iike catalytic behavior.