Atomically Dispersed Pt/Pd Enables Cascade Adsorption–Oxidation for Enhanced Chemiresistive Ammonia Sensing

Atomically dispersed noble-metal sensitizers offer an effective means of enhancing semiconductor metal oxide gas sensors, yet a single type of atomic noble-metal site is often insufficient to optimize both gas adsorption and catalytic oxidation. Here, atomically dispersed Pt and Pd sites are co-engineered on mesoporous SnO2 nanospheres to establish a cascade adsorption–oxidation pathway for enhanced NH3 sensing. The Pt/Pd–SnO2 sensor exhibits 4.1-, 6.2-, and 26-fold higher NH3 sensitivity than Pt–SnO2, Pd–SnO2, and mesoporous SnO2, respectively, with a calculated detection limit of 100 ppb and a response time of approximately 2 s. In situ spectroscopy, temperature-programmed desorption, and density functional theory calculations reveal that Pd-associated defect motifs promote the adsorption of NH3 and O2, whereas Pt–O–Sn motifs facilitate the subsequent oxidation of adsorbed NH3-derived species. The coexistence of atomically dispersed Pt and Pd dual-sensitizers therefore couples enhanced adsorption with accelerated catalytic oxidation, providing an atomic-scale noble-metal engineering strategy for high-performance gas sensing.