Understanding the molecular structure of Datong coal by combining experimental and computational study

Abstract

Understanding the structure of coal is crucial to explain its chemical reactivity. In order to study the microstructure characteristics of coal in-depth, ultimate analysis, solid-state 13C nuclear magnetic resonance (13C-NMR), X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR) are used to analyze the Datong coal. The results show that the aromaticity of Datong coal is 62.60%, and the ratio of aromatic bridge carbon to aromatic peripheral carbon is 0.238, indicating that more naphthalene and anthracene are in the aromatic structure of coal. Hydroxyl (C–O), carbonyl (C=O) and carboxyl (COO–) are the main oxygen-containing groups in coal, and the nitrogen element mainly exists in the form of pyrrole and pyridine. The main substitution modes on the benzene ring are di- and tri-substituted. Based on the above analysis, the 2D and 3D macromolecular models are constructed and optimized by using computer-aided modeling. The model is verified by 13C-NMR and FTIR spectra with density functional theory calculations. The coal molecular formula is defined as C149H112O24N2. The reaction sites in coal structure are oxygen-containing functional groups and aliphatic structures (–CH, –CH2). Therefore, the molecular structure of Datong coal has been systematically described and understood at the molecular level based on experimental data and quantum chemical calculations.