The chemistry of the palladium phase in Pd/Ce/Al2O3 during ammonia formation

The formation of NH3 from NO is a crucial reaction for passive-selective catalytic reduction applications. In this application, an in situ supply of NH3 is formed in oxygen-lean conditions, which can subsequently be used to reduce NO to N2 in the presence of excess O2 [1]. On the fundamental level, producing NH3 from NO through heterogeneous catalytic processes involves fascinating surface chemistry that is not yet well understood. In the presence of stoichiometric and excess oxygen concentrations, NH3 formation is suppressed. However, we have previously shown that Pd/Ce/Al2O3 is a promising formulation, able to temporarily facilitate the formation of ammonia under globally slightly-oxidizing but locally rich conditions [2].This work uses in situ X-ray absorption spectroscopy (XAS) to identify how the oxidation state of the catalytically active phase is affected during transient pulses of O2 in the presence of either pure NO or a combination of NO, CO and H2