Design Strategies for High-Performance NH3–SCO Catalysts: Identifying and Modulating Direct Anchoring Sites for Ag on TiO2

Ammonia (NH₃) slip from diesel vehicle aftertreatment systems and internal combustion engines fueled by NH₃ or NH₃/H₂ poses serious environmental problems. Ag-based catalysts are widely used for the selective catalytic oxidation of NH₃ to N₂ (NH₃-SCO), and their performance is greatly dependent on the state of Ag, which is influenced by the anchoring sites on the support. Despite efforts to identify the direct anchoring sites of metal atoms on TiO₂, conflicting views persist. Here, we compared the correlation between Ag dispersion and the content of hydroxyl (OH) groups or defects on TiO₂ and conducted density functional theory (DFT) calculations, and the results confirmed that the surface OH groups of TiO₂ serve as the direct anchoring sites for Ag. By modulating the OH group content through thermal induction, the optimal OH group content on TiO₂-800 resulted in more metallic Ag nanoparticles (Ag⁰ NPs) in larger sizes, leading to the development of an excellent NH₃-SCO catalyst. Moreover, in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), kinetic studies, and DFT calculations suggested that more Ag⁰ NPs in larger sizes on 10Ag/TiO₂-800 were conducive to O₂ activation and NH₃ dissociation. Our findings provide new insights for designing efficient NH₃-SCO catalysts, and OH groups as direct anchoring sites could be extended to other metals and supports for the rational design of catalysts.