Tandem confinement of sub-nanometer Pt–Cu sites in USY zeolite enables high NH3-SCO selectivity across an ultra-wide temperature window

Abstract

Selective catalytic oxidation of ammonia (NH₃-SCO) to N₂ is crucial for abating residual NH₃ emissions, but existing catalysts struggle to combine low-temperature activity with high N₂ selectivity due to competitive Pt-NO interactions. Here we design a tandem confinement catalyst by depositing sub-nanometer Pt clusters (∼0.72  nm) inside the supercages of a Cu-exchanged USY zeolite via atomic layer deposition (ALD), creating intimately paired Pt–Cu active sites. This confined Pt/Cu-USY ALD catalyst achieves >90 % NH₃ conversion and >90 % N₂ selectivity across an exceptionally broad 170-300°C window under simulated exhaust conditions, surpassing all previously reported Pt-based NH₃-SCO catalysts. The simultaneously enhanced low-temperature activity and high-temperature N₂ selectivity of the Pt/Cu-USY ALD catalyst can be attributed to the spatial confinement of Pt clusters within the Cu-USY framework, which leads to an expanded NO desorption window (150–350 °C). Detailed in situ studies further reveal that N₂O₄ species preferentially serve as NO storage intermediates on the Pt/Cu-USY ALD catalyst surface at low temperatures, exhibiting significantly lower formation barriers compared to free nitrates, which dominate as intermediates in conventional Pt–Cu systems. This effectively mitigates free nitrate–induced site poisoning and overcomes the typical activity–selectivity trade-offs observed in conventional Pt–Cu dual-site catalysts.