Construction of Rh-N4 single atoms and Rh clusters dual-active sites for synergistic heterogeneous hydroformylation of olefins with ultra-high turnover frequency

The design and construction of Rh-based heterogeneous catalysts with excellent catalytic activity and high atom utilization for hydroformylation of olefins is extremely important but still challenging. Herein, we report a robust dual-active sites coupling catalyst containing triphenyl phosphine-coordinated Rh clusters and Rh-N4 single atomic sites (PPh3-RhAC-SA/N-C) for hydroformylation of olefins. The PPh3-RhAC-SA/N-C exhibits ultra-high activity to the hydroformylation of 1-hexene among the reported Rh-based catalysts, achieving the turnover frequency value of 6599 h-1, which is 13-fold higher than that of conventional Wilkinson's catalyst (508 h-1). Density functional theory calculations reveal that PPh3-coordinated Rh clusters can facilitate the adsorption and activation of olefins and H2. The adjacent Rh-N4 provides a more favorable adsorption site for CO, enabling the easy addition of CO to carbon chain. The incorporated PPh3 increases the electron cloud density of Rh clusters, reduces the energy barriers of hydrogenation step on Rh clusters, and thereby enhancing the activity of catalyst for hydroformylation. Furthermore, PPh3-RhAC-SA/N-C can be applied as a recyclable catalyst without obvious deactivation. This work provides a novel design concept for the construction of dual sites coupling catalyst from the atomic scale for synergistic heterogeneous hydroformylation.