Quantum chemical study on inhibition effect of oxygen-containing groups in coal by metal ions （Na+, Ba2+, Ca2+）

In order to explore the mechanism of inhibitor on coal spontaneous combustion, the oxygen-containing groups aldehyde （-CHO） and methoxy（-OCH3） in coal molecular side chain were selected as the subjects of the study. The geometric configuration, electrostatic potential, reaction tendency, frontier orbitals, natural bond orbitals and charge transfer of the oxygen-containing groups（-CHO and -OCH3） and their complexes with Na+, Ba2+ and Ca2+ were deeply studied by using Gaussian 16W simulation software. The results show that Na+, Ba2+ and Ca2+ tend to cooperate with the oxygen-containing groups to form complexes, which weakens the electrophilic reaction ability and disables the nucleophilic reaction ability of -CHO and -OCH3 oxygen-containing groups, thus reducing the chemical activity of oxygen-containing groups. Metal ions increase the energy level difference（ELOMO-EHOMO） and the absolute value of the highest occupied molecular orbital（HOMO） energy of oxygen-containing groups, and thereby increases the stability of oxygen-containing group. The results of natural bond orbital theory analysis（NBO） shows that -CHO and -OCH3 oxygen-containing groups can coordinate steadily with Na+, Ca2+ and Ba2+, and the electrons of O in the two the groups transfer to Na+, Ca2+ and Ba2+ to form coordinate bonds. The combination of oxygen-containing groups with metal ions reduces the chance of contact between oxygen-containing groups and oxygen, which inhibits coal spontaneous combustion.