Tunable Reactivity of MNi12 (M = Fe, Co, Cu, Zn) Nanoparticles Supported on Graphitic Carbon Nitride in Methanation

As a unique two-dimensional material, graphitic carbon nitride (g-C3N4) has received significant attention for its particular electronic structure and chemical performance. Its instinctive defect can provide a stable anchoring site for metals, potentially improving the surface reactivity. Ni-based catalysts are economical but their activity for CO2 methanation is lower than that of noble metal catalysts. Ni nanoparticles (NPs) supported on a substrate can further enhance the stability and activity of catalysts. Based on the principles of strong metalsupport interaction (SMSI) and the synergistic effect on an alloy, MNi12/g-C3N4 composites as novel catalysts are expected to improve stability and catalytic performance of Ni-based catalysts. The configurations are established with core-shell structures of MNi12 (M = Fe, Co, Cu, Zn) nanoparticles (NPs) supported on g-C3N4 in this work. In the CO2 methanation reaction, the reactivity of CO on slab (Eco) is a critical factor, which is relative to the catalytic activity. Thus, the catalytic reactivity of these complexes via CO adsorption were explored using density functional theory (DFT). The values of cohesive energy (E-coh) for MNi12 NPs range from -39.90 eV to -34.82 eV, suggesting that the formation of these NPs is favored as per thermodynamics, and E(coh )and partial density of state (PDOS) reveal that the central M atom with the less filled d-shell interacts more strongly with surface Ni atoms. Therefore, ZnNi12 is the most unstable structure among all the studied alloy, and the synergistic effect is also the weakest among them. When MNi12 NPs are supported on the g-C3N4 substrate, the binding energies (E-b) vary from -9.40 eV to -8.39 eV, indicating that g-C3N4 is indeed a good material for stabilizing these NPs. The PDOS analysis of pure g-C3N4 suggests the sp(2) dangling bonds of N atoms in g-C3N4 can stabilize these transition metal NPs. Furthermore, the results of CO adsorbed on MNi12 NPs and MNi12/g-C3N4 composites show that Eco and dco reduced with the introduction of g-C3N4. According to the results of the analysis of the Hirshfeld charges and electrostatic potential (ESP), the reason is that CO obtains less electrons from MNi12 NPs after deposition on the g-C3N4 substrate, which lowers the reactivity of CO on catalysts. Additionally, the deformation charge density is analyzed to investigate the interaction between the NPs and g-C3N4. With the introduction of g-C3N4, charge redistribution indicates the strong metal-support interaction, which further reduces the CO adsorption energy. In summary, MNi12 supported on g-C3N4 exhibit not only high stability but also tunable reactivity in CO2 methanation. These changes are beneficial for CO2 methanation reaction.