Cooperative electronic effects of Na+ and Ca2+ on an oxygenated aromatic model

Abstract

This study uses molecular modeling to investigate the individual and combined effects of sodium (Na⁺) and calcium (Ca²⁺) ions on a representative molecular model of Yallourn lignite. Lignite, a geologically young and chemically reactive coal rich in oxygen-containing functional groups, can be chemically modified through ion exchange with metal cations. Experimental studies have suggested that Na⁺ and Ca²⁺ ions alter the thermal behavior and gasification reactivity of lignite, particularly when co-added. To provide molecular-level insights into these effects, we performed density functional theory calculations at the B3LYP/6-31G* level, including full geometry optimization, electrostatic potential distributions, and Löwdin bond-order analysis. The results reveal that Na⁺ and Ca²⁺ exert distinct effects on molecular geometry and electron localization, while their co-addition induces cooperative stabilization and polarization. These findings deepen our understanding of ion-induced structural and electronic modifications and present a reproducible computational framework for designing catalytic upgrading strategies for low-grade carbonaceous materials.