Orbital Engineering: Breaking the Activity-Selectivity-Stability Trilemma in Low-Temperature NH3-SCR over Single-Atom Catalysts.

The persistent trade-off among high activity, optimal N2 selectivity, and robust poisoning resistance critically hinders the development of low-temperature (<250 °C) catalysts of the selective catalytic reduction with NH3 (NH3-SCR) in industrial denitrification. To resolve this trilemma, we propose an orbital engineering framework that deciphers the quantum-level interplay between spin states, orbital energetics, and electron occupancy governing catalytic performance. Our analysis reveals that elevating the lowest unoccupied molecular orbital (LUMO) energy of active sites dictates NH3-NO interactions, directly controlling activity and selectivity. Crucially, we introduce spin-orientation tuning as a novel strategy to overcome SO2 intolerance by disrupting competitive adsorption. We further outline synergistic design principles─support engineering, coordination modulation, asymmetric ligand fields, and external field regulation─to concurrently optimize all three performance metrics. This work establishes orbital engineering as the cornerstone for next-generation catalysts that transcend current limitations, enabling efficient denitrification under extremely low-temperature, high-sulfur, and humid conditions.