Formation of Ammonia during the NO−H2 Reaction over Pt/ZrO2

The mechanism for the formation of NH 3 during the NO−H 2 reaction over Pt/ZrO 2 was studied. Steady-state isotopic transient kinetic analysis was carried out with isotopic switching from 15 NO−D 2 to 14 NO−D 2, and the results revealed that formation of N 2 and N 2 O was associated with linearly adsorbed NO on the Pt surface, whereas ammonia formation was associated with ND x species adsorbed on ZrO 2 . The adsorbed NH x species were not observed on the surface of ZrO 2 during NH 3 adsorption. From transient kinetic experiments, the formation rates of NH x species and of gaseous NH 3 agreed with each other, suggesting that the NH x species on ZrO 2 was an ammonia intermediate. The ND x species did not react with D 2 directly, but H−D exchange occurred easily. The addition of H 2 O to the NO−H 2 feed gas enhanced the formation of NH 3 . In situ diffuse reflectance spectra and transient kinetic analysis revealed that H 2 O enhanced the conversion of NH x species to NH 3 .