Abstract
Understanding Pd effects on NO(x) storage and release is crucial for designing passive NO(x) adsorber (PNA) to control NO(x) emissions during diesel cold-starts. Herein, we report two oxidation states of Pd species on Ce(x)Zr(1-x)O(2) regulated by metal-support interaction. Pd(δ+) (0 < δ < 2) in Pd/Ce(0.25)Zr(0.75)O(2) exhibits a high affinity for O(2) adsorption, which promotes the oxidation of adsorbed NO to nitrates at 100 °C. These nitrates are thermally unstable due to electron transfer from the Pd atom to the N-O bond, facilitating the decomposition of nitrates to NO(2) above 200 °C. In contrast, Pd(2+) in Pd/Ce(0.75)Zr(0.25)O(2) prefer to NO adsorption. A large amount of adsorbed NO and nitrites accumulate on Pd(2+) and Ce(4+) results in high levels of NO release below 200 °C. For the potential application in PNA, Pd/Ce(0.25)Zr(0.75)O(2) is recommended due to its proper NO(x) release temperature as well as better water and SO(2) resistance.