Quantum Chemistry Calculation Of Effect Of Gases On Coal Surfaces And Carbon Nanotubes

The interaction of gas and coal surface is the foundation for investigating reaction mechanism of coal and gas. We chose five kinds of structural models and six kinds of gases as investigated object in this dissertation. The five kinds of models were corresponding to lignite, subbituminous coal, high volatile bituminous coal, low volatile bituminous coal and anthracite; the six kinds of gases were CH₄, CO, CO₂, O₂, H₂O and H₂. The microcosmic parameters corresponding to the interaction of the five kinds of models and six kinds of gases, such as adsorption energy, adsorption distance, bond order and change of net charge, were calculated respectively using semi-empirical quantum chemical method. We used the method of "multipoint calculationand whole average" in the dissertation. By analysis of adsorption energies, we found that the adsorption order of gases on coal surfaces was: O₂>CO>H₂O>CO₂>CH₄≈H₂, which accorded with experiments and literatures. The data of adsorption energy of CH4 and coal surfaces was almost in agreement with earlier reports. The curves of bonding energies calculated by quantum chemistry were fitted well using Morse function, the quantitative parameters of adsorption action were obtained. By analysis of adsorption distances and bond orders of gases on coal surfaces, we concluded that the adsorption action of CO on coal surfaces was the strongest among the six gases, even some adsorption on some spots reached the intensity of chemical action; the adsorption actions of H₂ and CH4 on coal surfaces were the weakest, which were considered physical action; the interactions of CO₂, H₂O and O₂ on coal surfaces were similar, which were between the adsorption action of CO and the adsorption actions of H₂ and CH₄. The net charges of each carbon atoms on coal surfaces slightly became negative after adsorpting CH₄. The positive charges of aromatic carbon atoms became obviously strong, however, the changes of the net chargesof nonaromatic carbon atoms out of the benzene were unconspicuous after adsorpting CO, CO2, O2, H2O and H2.The interaction of H2 and two kinds of defects on carbon nanotubes chair (5,5), chair (6,6) and zigzag (10,0) were calculated using the semi-empirical quantum chemical method. We calculated the movement of hydrogen along the axes of carbon nanotubes with defects by the same method. The results showed that the actions of H2 and defects of carbon nanotubes were physical adsorption; the tendency of H2 entering the carbon nanotubes was relevant to the type and position of the defects. According to the adsorption energies, we found that the shortcut of H2 into carbon nanotubes through the center of defects was, firstly, H2 entered into carbon nanotubes along with the direction perpendicular to tube axes, and then H2 moved along the tube axes. The carbon atoms close to H2 decided the interaction of hydrogen and the defects, and the microcosmic property of the whole defects would be changed through the carbon atoms. The action of H2 made the symmetry of defects reduced and made negative charge enriched obviously on the carbon atoms lying on the defects. In addition, thesize and position of defects had no influence on the H2 movement along the axes of carbon nanotubes.