Atomistic mechanistic insights into CO2 capture and hydrogenation on Ni-Sn co-doped graphene: A DFT-MD approach for environmental management.

The mitigation of CO2 emissions in petroleum processing requires advanced materials capable of both efficient capture and catalytic conversion to value-added chemicals. In this study, Ni-Sn co-doped graphene (N-Gr@Ni@Sn) was theoretically designed and evaluated as a bifunctional platform for CO2 adsorption and hydrogenation to formic acid (HCOOH). Density functional theory (DFT) calculations, combined with molecular dynamics (MD) simulations, were employed to investigate adsorption geometries, electronic structure modifications, reaction energetics, and stability. Frontier molecular orbital (FMO) and density of states (DOS) analyses revealed a drastically reduced HOMO-LUMO gap (0.189 eV), enhanced electronic conductivity, and the creation of complementary electron-rich and electron-deficient sites around the dopants. Quantum Theory of Atoms in Molecules (QTAIM) and Non-Covalent Interaction (NCI) analyses confirmed a cooperative network of covalent and dispersive interactions stabilizing CO2 at the active sites. The calculated adsorption energy was -225.71 kcal mol-1, with a forward activation barrier of 17.51 kcal mol-1 for desorption and 20.04 kcal mol-1 for CO2-to-HCOOH conversion, indicating favorable thermodynamics and kinetics. MD simulations demonstrated exceptional thermal stability over 1000 ps, with persistent Ni-O(CO2) coordination and Sn-Ni coupling. These findings suggest that Ni-Sn co-doped graphene offers a promising route for integrating CO2 capture with catalytic valorization in petroleum gas treatment, though experimental validation is required to confirm synthesis feasibility, dopant stability, and performance under realistic process conditions.