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 Cu_NP/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.