A semiempirical quantum-chemical method of calculation: From physical adsorption to catalytic transformations

The main equations for semi-empirical quantum-chemical calculations taking into account the electrostatic field of the ionic crystal at the stage of construction of the Fockian in the CNDO/INDO approximations are presented. The possibility of accounting for electrostatic and dispersion interactions was discussed. A new method for modeling bulk and surface F-centers was proposed. Models for the adsorption of molecular (H2O, NH3, and O-2), radical (NO2.), and ion-radical (O-n(-), n = 1-3)species on a number of face-centered cubic crystals (NaCl, KCl, KBr, and MgO) were developed. The effect of the polarity of the solvent on the Menshutkin reaction (for the NH3 + HF system) is discussed. The possibility for the O-2 molecule to experience a transition from the triplet to the singlet state under the action of the crystal field was discussed. The results were compared with the available experimental data (heat phase adsorption, g-tensor, hyperfine coupling, etc.). Based on experimental values of the g-tensor, a model for an active center of composition Li+O47-, which catalyzes the oxidative dimerization of methane over the Li-MgO system, was developed. The activation of the methane molecule was shown to be accompanied by the desorption of a methyl radical into the gas phase, a process that occurs at one of the oxygen anion-radicals of the proposed active center. Possible method for governing the reaction were considered.