Atomic Ni-doped ZrO₂ with subnanometric Fe clusters for tandem C-C bond cleavage and coupling

The sustainable valorization of lignin β-O-4 compounds into high-value natural products through one-pot tandem catalysis presents an urgent yet scientifically challenging frontier in biomass conversion. Herein, we report a mesoporous Fe₃@Ni₁-ZrO₂ catalyst featuring subnanometric Fe-O clusters anchored on atomic Ni-doped ZrO₂ nanosheets. This engineered architecture enables the one-pot tandem conversion of lignin β-O-4 segments to flavones under aerobic and base-free conditions, delivering 56.2% yield with a space-time yield (STY) of 3.3 g g_cat ^-1 h^-1 in continuous flow operation. Moreover, the system demonstrates exceptional substrate versatility through efficient conversion of diverse lignin β-O-4 dimers and substituted 2'-phenoxyacetophenones into bioactive flavones. Mechanistic investigations combining controlled experiments and density functional theory (DFT) calculations reveal a cooperative catalytic mechanism, i.e., ZrO₂ nanosheets mediate selective oxidative cleavage of C-C bonds in β-O-4 segments, and subnanometric Fe₃ clusters activate aldol condensation of cleavage intermediates, while atomic Ni sites suppress competing pathways to govern the selectivity. This synergistic interplay within the Fe₃@Ni₁-ZrO₂ framework establishes a robust catalytic microenvironment to enable a high-efficiency tandem process.