Partial Oxidation of Methane with Molecular Oxygen to Produce Hydrogen Catalyzed by Rh 3 O 2 + Clusters

Catalytic partial oxidation of methane (POM) in the presence of molecular oxygen represents a highly promising strategy for the conversion of methane to hydrogen under mild conditions; however, it remains quite challenging due to the kinetic inertness of methane and catalyst instability under an oxidative atmosphere. Herein, benefiting from dual-ion-trap mass spectrometric experiments in conjunction with quantum chemical calculations, we successfully identify that the Rh 3 O 2 + cluster cation can catalyze the POM reaction with O 2 to produce 2H 2 + CO 2 under thermal collision conditions. The ligand effect of the oxygen atoms to enhance the activity and stability of a cluster catalyst has been clarified. The coordinated oxygen atoms can tune the contribution of the active Rh 4d-orbital in the frontier orbitals of Rh 3 O 0-2 + clusters, enabling enhancement of cluster reactivity toward C–H activation. The stability of reaction intermediate Rh 3 O 3 + under an oxygen atmosphere is also ensured by the bridging oxygen atoms that can regulate the highest occupied orbitals of the active [Rh 3 ] site, dominated by the Rh 4d z 2 orbital that is disadvantageous for reaction with O 2 . This work not only provides an insightful guide in the design of excellent ligand-protected metal cluster catalysts in direct conversion of CH 4 with O 2 under mild conditions but also reveals the molecular-level mechanism of efficient hydrogen production in the POM process.