A New Approach to Single-Atom Catalysts by Tuning Metal-Support Frontier Orbital Interactions
Single-atom catalysts (SACs) have emerged as a frontier in catalysis, yet their activity is not reliably correlated with the charge state of the central metal atom. Traditional d-band theory fails for discrete energy levels, and electronic metal-support interactions (EMSI) complicate the rational design of advanced SACs. This highlight examines a joint study by Lu, Wu, and Yang (2025) that establishes a linear relationship between the catalytic activity of Pd1 SACs on metal oxide (MOx) supports and the lowest unoccupied molecular orbital (LUMO) positions of the MOx. Through atomic layer deposition, 34 Pd1/MOx SACs with 0.1 wt% Pd loading were synthesized, including 14 MOx compositions (ZnO, CoOx, NiOx, TiO2, Ga2O3) of varying particle sizes on SiO2. Decreasing MOx particle size elevates the LUMO, narrowing the gap with the Pd1 HOMO, enhancing orbital coupling and EMSI. For ZnO, reducing particle size from ~46 nm to ~1.9 nm shifts the LUMO from -0.35 V to -1.12 V (vs. NHE) and broadens the band gap from 3.29 eV to 5.82 eV. In acetylene semi-hydrogenation, Pd1/ZnO-1.9 nm achieves a turnover frequency (TOF) of 25.6 min-1, far exceeding 1.0 min-1 for bulk ZnO, with exceptional stability and selectivity over 100 h. This frontier orbital descriptor offers a general principle for designing efficient SACs.