Mechanistic study on the enhanced N₂ selectivity for NH₃ selective oxidation over Pt-encapsulated Cu-ZSM-5 catalysts

Ammonia (NH₃) has emerged as a promising zero‑carbon energy source for energy and transportation. However, its utilization leads to the emission of NH₃, which contributes to PM_2.5 formation and disrupts the global nitrogen cycle. Selective catalytic oxidation (SCO) represents a mainstream technology for NH₃ treatment, yet achieving both sufficient activity and high N₂ selectivity across a broad temperature window remains challenging. Here, a core-shell Pt@Cu-ZSM-5 catalyst was employed for NH₃ catalytic abatement by encapsulating metallic Pt clusters (Pt⁰) inside the channels of Cu ion-exchanged ZSM-5. The optimal sample achieved a complete NH₃ conversion below 250 °C and maintained over 92% N₂ selectivity from 250 to 500 °C due to the synergism between the Pt-Cu dual sites. Mechanistic studies revealed that NH₃ oxidation preferentially occurred on Pt⁰ sites with excellent redox capacity to produce N₂O and NO_x at relatively low and high temperatures, respectively. And the presence of Cu ions (Cu^δ+) could efficiently both inhibit the formation of N₂O on Pt⁰ sites and reduce NO_x emission, thereby improving the N₂ selectivity. At relatively low temperatures, NH₃-solvated Cu⁺(NH₃)₂ could migrate to the adjacent Pt sites and reduce the adsorbed NO* species from NH₃ oxidation, damping the formation of N₂O. At high temperatures, the NO and NO₂ emitted from Pt⁰ sites could be reduced on Cu^δ+ sites via a typical selective catalytic reduction. This study provides new insights into the rational design of bifunctional SCO catalysts and offers a comprehensive understanding of the synergistic effects in Pt-Cu dual-site systems.