Effect of the Pyrrolic Nitrogen Functional Group in the Selective Adsorption of CO₂: GCMC, MD, and DFT Studies

Abstract

In this paper, the pyrrolic nitrogen functional group’s presence is investigated in the selective adsorption of CO2. The grand canonical Monte Carlo (GCMC), molecular dynamics (MD), and density functional theory (DFT) were used for this study’s goal. GCMC was used to calculate adsorption isotherms, selectivity, and isosteric heats. MD was used to calculate the radial distribution function (RDF) and diffusion. Reactivity parameters, electrostatic potential (ESP), reduced density gradient (RDG), and independent gradient model (IGM) were calculated using DFT. Adsorption isotherms, selectivity, and isosteric heats demonstrated that the NH group caused the selective adsorption of CO2 among CH4, CO, and N2 gases. The adsorption quantities for CO2, CH4, CO, and N2 are 4.77, 2.65, 2.38, and 2.09 average loading (per cell), respectively, at 10 MPa and 298 K. Furthermore, the thermodynamic parameters and Henry’s constant were calculated, indicating that CO2 adsorption is more dependent on temperature than that of other gases. RDF results showed an effective interaction between oxygen and carbon of CO2 and hydrogen and nitrogen of NH, respectively. Additionally, ESP results revealed that the NH group changed the electron’s density in the molecule surface, causing a more vital interaction between CO2 and NH, confirming the RDG and IGM results.

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