The Performance of Pd, Pt, and Pd-Pt Catalysts in Lean Exhaust

A matrix of pelleted catalysts composed of Pt, Pd, Pt co-impregnated with Pd, and Pt physically mixed with Pd supported on A l₂O₃ were compared with the same noble metal formulations supported on CeO₂/Al₂O₃ for lightoff and warmed-up performance in net lean exhaust. These catalysts were tested as prepared (fresh) and following a relatively severe thermal aging treatment (cycled between net lean and net rich environment at 1000°C for 4 h).

Pd showed better lightoff performance than Pt for catalyzing the oxidation of propylene, while Pt showed better lightoff and warmed-up performance than Pd for catalyzing the oxidation of propane. Having both Pt and Pd present as a result of co-impregnation or physical mixture results in good lightoff and warmed-up performance for the conversion of both types of hydrocarbons. The presence of CeO₂ generally decreases lightoff performance for most of these catalysts.