(673b) Silver Single Atom Catalysts on Different Supports with Distinct Catalytic Performance for the Selective Oxidation of Ammonia

The selective catalytic oxidation of NH₃ (NH₃-SCO) is an efficient route to remove NH₃ from the NH₃ slip of vehicle emission control. Supported metal catalysts such as Pt, Pd and Cu catalysts are widely reported, but the high cost and high N₂O yield limited their application [1]. Ag, with relatively low price and superior catalytic activity, recently attracted great attention and showed high potential for NH₃-SCO reaction. However, to date, very few works have reported the preparation and application of Ag single atom catalysts (Ag₁ SACs) for NH₃-SCO reaction, particularly the effect of supports on Ag coordination environments and catalytic performance.

We herein report the preparation and application of Ag catalysts with 1wt.% Ag loading on three different supports including CeO₂, Al₂O₃ and ZrO₂ for NH₃-SCO reaction. By means of TEM, UV-vis DRS and EXAFS, it was verified that Ag is present as single atom phase within all the three catalysts. Under different testing conditions with or without H₂O, NH₃-SCO activity on the catalysts decreased by the order of Ag₁/CeO₂ > Ag₁/ZrO₂ > Ag₁/Al₂O₃ (Figure 1), with the Ag₁/CeO₂ catalyst performing the best. H₂-temperature programed reduction (H₂-TPR) results indicated that Ag₁/CeO₂ exhibited the best low-temperature reducibility. In accompanying density functional theory-based calculation, we believe that the greatest advantage offered by the Ag SACs on CeO₂ is the formation of hydrogen bonds between NH₃ and surface oxygen atoms, providing a drastically smaller activation energy barrier corresponding to shorter distances required for the hydrogen to dissociate.

References:

[1]. G.Y. Xu, Y. Zhang, J.G. Lin, Y.B. Wang, X.Y. Shi, Y.B. Yu, and H. He. ACS Catalysis 11(9): 5506-5516, 2021.