Conversion of Methane with Oxygen to Produce Hydrogen Catalyzed by Triatomic Rh₃ ^- Cluster Anion

Metal catalysts, especially noble metals, have frequently been prepared upon downsizing from nanoparticles to subnanoclusters to catalyze the important reaction of partial oxidation of methane (POM) in order to optimize the catalytic performance and conserve metal resources. Here, benefiting from mass spectrometric experiments in conjunction with photoelectron spectroscopy and quantum chemical calculations, we successfully determine that metal cluster anions composed of only three Rh atoms (Rh₃ ^-) can catalyze the POM reaction with O₂ to produce 2H₂ + CO₂ under thermal collision conditions (∼300 K). The interdependence between CH₄ and O₂ to protect Rh₃ ^- from collapse and to promote conversion of CH₄ → 2H₂ has been clarified. This study not only provides a promising metal cluster displaying good catalytic behavior in POM reaction under mild conditions but also reveals a strictly molecular-level mechanism of direct partial oxidation for the production of hydrogen, a promising renewable energy source in the 21st century.