Exploring the Conformational Space of a Sulfonyl-Based Ionic Liquid on Platinum-Based Mono and Bimetallic Surfaces

Understanding the arrangement of ionic liquids at the interface and their interactions with the surface is crucial for enhancing selectivity in heterogeneous reactions for practical applications. In this study, we investigate the nature of the adsorption and structural orientations of a sulfonyl-based ionic liquid on platinum-based mono- and bimetallic (111) surfaces employing replica exchange molecular dynamics and first-principles density functional theory calculations. More than 30 confirmations of the ionic liquid are identified on both monometallic and bimetallic surfaces. In addition to adsorption energies, factors such as dynamics of ionic liquids, molecule-surface distances, and charge transfer analyses are found to be important indicators for understanding adsorption phenomena. The sulfonyl anion exhibits contrasting behavior on the two surfaces, showing a preference for chemisorption on the monometallic surface, while the pyrrolidinium cation is physisorbed on both metal surfaces. Both metal surfaces are negatively charged primarily because of charge transfer from the sulfonyl anion. The analysis of the orientational preference reveals a nearly flat orientation of the cation on the monometallic surface, while a tilted orientation is observed on the bimetallic surface.