Single-atom catalysts (SACs), in which isolated metal atoms such as palladium (Pd) are anchored on solid supports, promise breakthroughs in energy conversion and catalysis. However, balancing their activity (reaction speed) and stability (longevity) remains challenging, as the interplay between metal atoms, supports, and reactants is poorly understood. A team led by Prof. LU Junling at the University of Science and Technology of China (USTC) of the Chinese Academy of Sciences (CAS), along with Prof. WU Xiaojun from USTC and Dr. YANG Bing from the Dalian Institute of Chemical Physics of CAS, has now bridged this gap using a 1950s chemistry concept—the Frontier Molecular Orbital (FMO) theory. Published in Nature on April 2, their work reveals how tuning orbital energy levels in SACs can optimize both performance metrics.
FMO theory simplifies the complex interplay of all molecular orbitals by focusing on two critical “frontier” orbitals: the HOMO (highest occupied molecular orbital) and the LUMO (lowest unoccupied molecular orbital). In a stable molecule under normal conditions, the LUMO always resides at a higher energy level than the HOMO. When two molecules interact, their primary electronic interaction occurs between the HOMO of one molecule and the LUMO of the other. During a reaction, electrons flow from the HOMO (electron donor) into the LUMO (electron acceptor). The efficiency of this electron transfer depends critically on the energy proximity between these two orbitals.
After engineering 34 palladium SACs on 14 oxide supports, the researchers found that shrinking support particles raised their LUMO energy. By shrinking zinc oxide supports to 1.9 nanometers, the team raised the energy of support particles’ LUMO, narrowing the gap with palladium’s HOMO. This alignment strengthened metal-support bonds (boosting stability) and optimized palladium’s LUMO to grab reactants faster—delivering 25.6 min-1 reaction rate (20 times faster than conventional SACs) and 100-hour stability.
The FMO-guided design, validated through spectroscopy and microscopy, offers a universal blueprint for SACs. It also accelerates AI-driven discovery of ideal metal-support pairs for clean energy and industrial catalysis.
Schematic illustration of a single-atom catalysis (Image by Prof. LU et al., 2025)