Few-Atom Copper Cluster Facilitates H2O2 Activation to Promote Selective Oxidation of Benzene to Phenol.

The catalytic oxidation of benzene faces challenges in achieving high activity and selectivity. While single-atom catalysts present intriguing potential for this transformation, their practical implementation is hindered by intrinsic limitations in the mass-specific activity. In this context, few-atom cluster catalysts have emerged as an alternative, leveraging well-defined metal ensemble effects that enable precisely tailored active sites and enhanced interatomic synergies. Herein, we introduce an atomic cluster supported on a graphitic carbonitride (CN) catalyst (Cu3/CN), exhibiting excellent catalytic performance for selective oxidation of benzene to phenol, with superior turnover frequency (TOF) to that of single-atom Cu1/CN (719 h-1 vs 280 h-1) and suppressing phenol selectivity to that of nanoparticle CuNP/CN (95.3% vs 77.2%). Multimodal mechanistic investigations unambiguously identify the critical role of the adsorbed O* on the Cu site (Cu═O*) for C-H-oxidation, verified by both in situ spectroscopic monitoring and ex situ surface analysis. Complementary density functional theory calculations validate Cu atomic cluster (Cu3) site features a higher d-band center and larger charge transfer with the H2O2 molecule than that of the isolated Cu1 site. The sufficient charge transfer stretches the O-O bond in H2O2 to facilitate the formation of the Cu═O* species. Furthermore, the resulting Cu═O* in the Cu3 site demonstrates a significant hybridization of the O 2p orbitals and Cu 3d orbitals at the Fermi level, which endows it with high activity for benzene activation. The appropriate ensemble effect of the unique Cu3 architecture is the key to its higher catalytic performances. This work establishes a structure-performance correlation that highlights the critical role of atomic cluster architecture in optimizing catalytic functionality.