Unveiling molecular mechanisms of enhanced N2 solvation and diffusion in ionic liquid mixtures

Abstract

Ammonia synthesis depends on N₂ critically, a principal raw material whose solubility influences the reaction kinetics and product selectivity. Ionic liquids (ILs) possess the advantage of structure tunability to modulate N₂ solubility. In practical applications, ILs are commonly mixed with other solvents to achieve a balance between reaction and transport processes. Herein, the dissolution and diffusion behaviors of N₂ in mixed systems are analyzed microscopically through molecular dynamics simulations. It reveals that introducing a small quantity of trihexyl(tetradecyl)phosphonium tris(pentafluoroethyl)-trifluorophosphate into tetrahydrofuran enhances the solubility and diffusion coefficients of N₂ significantly. The transition point is governed by the fraction of nanocavity, which exhibits distinct expansion, saturation, and compression zones. Furthermore, the response trend of N₂ solubility in mixed systems to temperature changes varies with molar concentrations, reflecting differences in solvation enthalpy changes. These findings provide theoretical insights for the design of mixed solvents with high N₂ dissolution and diffusion capabilities.