Theoretical insights into the catalytic mechanism of propylene hydroformylation over Co–N–C materials

Abstract

M–N–C was recently reported to be a high activity catalyst for hydroformylation compared with a metal nanocluster. However, the nature of M–N–C sites and the dominant path of propylene hydroformylation on M–N–C sites with different structures are poorly understood. In this work, five different Co–N–C models (Co–N₃–C, Co–N₄–C, 0N-bridged Co₂–N₆–C, 1N-bridged Co₂–N₇–C and 2N-bridged Co₂–N₆–C) were constructed to simulate the Co active sites with different coordination that may exist on the surface of MOF-derived Co-based carbon materials. DFT combined with kinetic Monte Carlo (kMC) methods were used to study the catalytic performance for hydroformylation of different Co–N–C models. The results of the DFT calculations show that the coordination number and mode of N atoms could regulate the electronic density of the Co sites. The electronic density of the Co sites further affects the catalytic activity. The higher the electronic density is, the lower the energy barrier for partial hydrogenation of propylene and CO insertion reactions. Besides, the catalytic activity is also affected by the strong interaction in closer neighboring Co atoms in some Co₂–N_x–C models. The strong interaction affects the adsorption state and energy of species, which also reduces the overall reaction energy barrier. The kMC simulation results further showed that the dominant path of propylene hydroformylation was the n-butylaldehyde path for the 0N-bridged model, and the isobutylaldehyde path for Co–N₃–C and 2N-bridged models.