Study on the Effect of the Electron Density-Characterized Groups on the Nitrogen Transformation during Coal Pyrolysis

This paper clarifies the effects of the functional groups on the nitrogen migration during coal pyrolysis by utilizing the density functional theory (DFT) calculations and the support vector regression (SVR) modeling. First, the study evidences the enhanced pyrolysis by electron-donating groups (EDGs) and inhibition by electron-withdrawing groups (EWGs). For example, for pyridine pyrolysis, the inclusion of -NH₂ (EDG) is found to decrease the endothermicity and the maximal barrier involved in the HCN generation from 612.6 to 292.3 kJ/mol and from 624.2 to 296.0 kJ/mol, respectively. Second, DFT and Rdkit descriptors are filtered to constrain the SVR model to predict the activation energy and reaction energy. The results highlight the importance of the S_type descriptor. Finally, the TG-FTIR experiments using 2-pyridinecarboxylic acid and 2-hydroxypyridine as test samples are performed to validate the accelerated pyrolysis by the EDG group and the decelerated pyrolysis by EWG, showing accordance with our DFT calculations and SVR modeling. All of these findings will offer valuable insights for understanding the pyrolysis of coal.