POISON-RESISTANT CATALYSTS FOR THE SIMULTANEOUS CONTROL OF HYDROCARBON, CARBON-MONOXIDE, AND NITROGEN-OXIDE EMISSIONS

The paper investigates several features of the operation of noble metal catalysts in automobile exhaust near the stoichiometric air:fuel ratio ( A F). These features include the extent of intrapellet diffusion limitations as a function of feedstream stoichiometry, the mechanism of poisoning, the effects of noble metal (Pt, Rh, Pd) impregnation profiles on activity and poison resistance, and the effects of A F oscillations on catalyst performance. A pellet configuration, containing an external shell of Pt and internal rings of Rh and Pd, was found to have improved poison resistance and lightoff characteristics. The addition of Ce improved the catalyst's initial performance in transient operation. © 1979.