Mechanisms for methane and ethane formation in the reaction of hydrogen with carbonaceous materials

A systematic density functional theory (DFT) study of the hydrogen reactions with carbonaceous surfaces was carried out in order to provide molecular-level understanding on the mechanisms of chemical processes involved in carbon hydrogasification. It was found that hydrogen is dissociatively chemisorbed on the active sites of zigzag and armchair configurations of carbonaceous models. In addition, mechanisms for methane and ethane production during the carbon-H, reaction were proposed suggesting that methane formation is exothermic and ethane formation is also possible but with a much lesser extent. These results agree with available experimental observations. Rate constants of the rate limiting steps were also calculated using the transition state theory. From both the thermodynamic and kinetic points of view, methane formation is much easier from zigzag edges rather than from armchair edges. The large activation energies for both pathways suggest that these reactions are favored at high temperatures. (C) 2005 Elsevier Ltd. All rights reserved.