Atomic design of dual-metal hetero-single-atoms for high-efficiency synthesis of natural flavones

Single-atom (SA) catalysts provide extensive possibilities in pursuing fantastic catalytic performances, while their preparation still suffers from metal aggregation and pore collapsing during pyrolysis. Here we report a versatile medium-induced infiltration deposition strategy for the fabrication of SAs and hetero-SAs (MaN4/MbN4@NC; Ma = Cu, Co, Ni, Mn, Mb = Co, Cu, Fe, NC = N-doped carbon). In-situ and control experiments reveal that the catalyst fabrication relies on the “step-by-step” evolution of Ma-containing metal-organic framework (MOF) template and Mb-based metal precursor, during which molten salt acts as both pore generator in the MOF transformation, and carrier for the oriented infiltration and deposition of the latter to eventually yield metal SAs embedded on hierarchically porous support. The as-prepared hetero-SAs show excellent catalytic performances in the general synthesis of 33 kinds of natural flavones. The highly efficient synthesis is further strengthened by the reliable durability of the catalyst loaded in a flow reactor. Systematic characterizations and mechanism studies suggest that the superior catalytic performances of CuN4/CoN4@NC are attributed to the facilitated O2 activating-splitting process and significantly reduced reaction energy barriers over CoN4 due to the synergetic interactions of the adjacent CuN4.