Unveiling the mechanism of controllable CO2 hydrogenation by group VIB metal single atom anchored on N-doped graphite: A density functional theory study

Abstract

CO2 hydrogenation has raised considerable interest due to concerns about climate change. Realizing low-temperature reverse water gas shift (rWGS) reaction remains a significant challenge in the context of coupling it with the C–C growth reactions to convert CO2 to C2+ fuels. We carried out systematic DFT simulations to unveil the underlying low-temperature mechanism for the selective hydrogenation of CO2 to produce CO, over a variety of metal-based single atom catalysts (SACs) supported on the nitrogen-doped graphite. Group VIB metal-based SACs outperformed other 15 metal candidates in terms of versatile capacities in both selective activation of CO2 molecule and facilitating escaping of CO and H2O. Mo1/N3-Gt was especially outstanding by giving rise to spontaneous production of CO and O∗ through an effective electron injection into the CO2 molecule. Water formation has been identified as the potential rate-controlling step in such a catalytic reaction over Mo1/N3-Gt with an energy barrier of 1.10 eV. Herein, the H migration played a pivotal role and had tight affinity to the charge of H∗ on the active site of catalyst. The dynamic coordination environment of Moδ+ was revealed to be the dominant factor affecting the surface H∗ charge, leading to a variety of hydrogenation behaviors. The electron-deficient ligands of CO2 and O∗ on Mo1/N3-Gt, as well as additional adsorbed H2, were effective in adjusting the 4d and 5s electronic structure of central Mo and consequently resulted in nearly electric neutral surface H∗s, thus most benefiting the hydrogenation process. The optimal charge of the coordinated Mo for an outstanding selective hydrogenation performance in this scenario was found to be no less than +1.7e.