Study on the reaction mechanism of CO 2 inhibiting active functional groups and O 2

To investigate the microscopic reaction mechanism of CO2 inhibits coal spontaneous combustion, Taking the coal molecule side chain active groups (-CHO, -OCH3, -C = O, -CH2OH) as the research object, Using Gaussview6.0 and Gaussian16W software to apply quantum chemistry research methods, simulations were conducted to calculate the electrostatic potential distributions, frontier molecular orbitals, and both microscopic and thermodynamic parameters of the reactions between these groups and O2, before and after the introduction of CO2. The results show that the hydrogen atoms on the side chains exhibit high reactivity and are readily abstracted by O2, facilitating the cleavage of the O = O bond and the formation of new oxygen-containing compounds. CO2 molecules are adsorbed on the coal surface and cover the high reactive sites (low electrostatic potential region) of the active groups. By occupying the active adsorption sites on the coal surface, CO2 molecules hinder the approach of O2 and reduce the probability of direct interaction between O2 and reactive functional groups. Analysis of the frontier molecular orbitals (HOMO and LUMO) reveals that CO2 alters the electron distribution of the functional group, shifts their orbital energy levels, and consequently decreases their reactivity toward. Furthermore, the presence of CO2 induces an elongation of the O = O bond in O2 and a distortion of the bond angles within active groups, thereby suppressing the oxidative propensity of O2 and reducing the probability of effective reactant collisions. Thermodynamic calculations show that the energy barriers for oxidation reactions follow the order: O2+CO2 > CO2 > O2 > active group alone. This trend indicates that CO2 significantly increases the reaction energy barrier and thus inhibits the oxidative activity of coal functional groups. Overall, CO2 suppresses the coal-oxygen reaction through three primary mechanisms: steric hindrance via competitive adsorption on reactive sites; electronic modulation by altering charge distribution and frontier orbital energies, and thermodynamic inhibition by increasing the energy barrier of oxidation reactions. These findings establish a theoretical foundation for utilizing CO2 as an effective inert gas in underground fire prevention and extinguishing strategies.