Enhanced Reaction in Supercritical Inhomogeneous Microaggregation

Supercritical fluids (SCFs) play a crucial role in various environmental, geological, and celestial processes primarily due to their unique thermodynamic properties and ability to influence chemical reactions. SCFs are generally thought to modulate reactions through their inhomogeneous microscopic behavior. However, how these microscopic behaviors influence reactions within SCFs remains insufficiently clarified. To solve this, metadynamics is employed to describe the reaction events under actual supercritical conditions (800-1000 K). Through the calculations of the free energy surface of probe reactions, we demonstrate that liquid-like atoms and corresponding high-density clusters, specially forming in supercritical fluids, enhance reactant collisions and thermodynamically stabilize the transition state, while this enhancement mechanism shifts near the Widom line, where further crossings of this line result in excess liquid-like atoms and then limited kinetic diffusion. These findings underscore the connection between the fluid microstructure and chemical reactivity, providing a foundation for advancing the industrial applications of SCFs.