Boosting Catalytic Hydrogen Transfer Cascade Reactions via Tandem Catalyst Design by Coupling Co Single Atoms with Adjacent Co Clusters

The catalytic hydrogen transfer (CHT) cascade reaction coupling alcohols with nitro compounds to synthesize imines is highly significant due to its remarkable efficiency and atom economy. However, the complicated multistep reaction process makes single-site catalysts exhibit unsatisfactory catalytic performance for the CHT cascade reaction. Herein, inspired by the findings of DFT calculations that Co nanocluster (Co_NC) and Co single atom (Co_SA) can act as the optimal active sites for alcohol oxidation and nitro reduction, respectively, one dual-active site catalyst (Co_SA-Co_NC/CN), containing Co_SA and Co_NC sites, was synthesized by a two-step vacuum pyrolysis strategy. Benefiting from the relay-like tandem catalysis of Co_NC and Co_SA, Co_SA-Co_NC/CN achieved an impressive 93% nitrobenzene conversion and 99% imine selectivity at 160 °C in 4 h, with a record turnover frequency of 20.9 h^-1. This work provides insights into the functions of single-atom and nanocluster active sites in the CHT cascade reaction and sheds light on the rational preparation of tandem catalysts.