Formation mechanisms of N2O and NH3 on Pd/ZrO2 and Pd/Al2O3 for NO reduction.

[Display omitted] • The Pd/Al 2 O 3 produced less N 2 O and NH 3 than the Pd/ZrO 2 under fuel-rich cycle. • The N 2 O generation is related to the activity of nitrates after NO x adsorption. • The NH 3 is originated from the reaction of nitrates with surface hydroxyls or steam. • ZrO 2 rather than Al 2 O 3 acts as an electron acceptor from Pd for NO adsorption. Reducible and nonreducible supports usually display distinct properties on the size, valence, and coordination of Platinum group elements in supported metal oxide. However, there are few reports on the regulation of main and side reaction rates and inhibition of byproducts from the perspective of reaction kinetics. Here, we compare the N 2 O and NH 3 formations of Pd supported on Al 2 O 3 and ZrO 2 in NO reductions. Pd/Al 2 O 3 produces less N 2 O and NH 3 in quantity than Pd/ZrO 2 , which could be due to the moderate metal-support interactions between Pd with higher average valence and Al 2 O 3 with lower ability of electrons transfer. ZrO 2 acted as an electron acceptor in NO reduction facilitating the formations of unstable nitrates and surface hydroxyls. In-situ DRIFTS and NAP-XPS results suggest that the N 2 O generation is directly related to nitrates with different stabilities: bridging, bidentate, and partial monodentate nitrates are active on Pd/ZrO 2 , whereas, only nitro and partial bridging nitrates are active on Pd/Al 2 O 3. The NH 3 is mainly originated from the reaction of nitrates to surface hydroxyls with different coordination numbers. This work clarifies the byproducts formation mechanism in NO reduction and opens up the research topics using in-situ spectroscopy methodology. [ABSTRACT FROM AUTHOR]