Effect of Na on the migration and release of pyridine nitrogen during coal pyrolysis

Based on density functional theory (DFT) and transition state theory, the effect of alkali metal Na on the formation mechanism and path of NH₃ and HCN during coal pyrolysis was studied at the M06-2X/6-311G(d) level. The seven membered ring containing pyridine was selected as the coal model, and the adsorption structure of Na on the coal surface was used as the coal model containing Na. The results show that the presence of Na significantly strengthens the bonding between N and C atoms in pyridine ring, which makes the stripping of N atom from benzene ring requires higher activation energy, thus inhibiting the formation of HCN. However, Na can improve the surface activity of coal, and the energy barrier of NH₃ formation rate determination step in the presence of Na is 271.35 kJ/mol lower than that in the absence of Na, which significantly promotes the formation of NH₃.