The dual states of pd on catalyst Pd/γ-Al₂O₃

Effects of different reduction atmospheres on the catalytic activity of 7% Pd/γ-Al₂O₃ catalyst were investigated using simulated exhaust gas and XPS. The results are: Once the catalysts were treated by lean-hold/lean-down or rich-hold/lean-down step, the catalyst lost their activities and Palladium particles on the catalysts existed in oxidation states. While the catalysts treated by lean-hold/rich- down, rich-hold/rich-down or stoichiometric steps, these catalysts were activated and Palladium particles on the catalysts occurred in metallic states. The catalytic activity of Pd° was higher than that of PdO in the experimental condition. The activity of this kind of catalyst was reversible. Stoichiometric gas could keep the activity of the catalyst.