Decomposition of Methylamine on the Clean and P Modified Mo(100) Surfaces

作者：Lue Cun Qin; Ling Kai Cheng^*; Wang Gui Chang

来源：Acta Physico - Chimica Sinica, 2009, 25(11): 2336-2342.

• Density functional theory
• Methylamine
• Decomposition
• Mo(100)
• Phosphorus modified Mo(100)
• Generalized gradient approximation
• Slab model

The reaction pathways for methylamine decomposition (CH(3)NH(2)-> CH(3)+NH(2)) on a clean Mo(100) surface and on a phosphorus (P) modified Mo(100) surface (P-Mo(100)) were invesfigated using first-principles (density functional theory based on generalized gradient approximation (DFT-GGA)) calculations with the slab model. Geometries of reactants, transition states, and products were calculated. Adsorption energies of possible species and activation energy barriers of the reaction were obtained. Calculated results show that methylamine is adsorbed in the top site while the methyl and amino groups are adsorbed in the bridge site on the clean and phosphorus modified Mo(100) surfaces. The activation energy of methylamine C-N cleavage was found to be 2.39 eV on the phosphorus modified Mo(100) surface, which is higher than that on the clean Mo(100) surface (1.99 eV). This indicates that the Mo(100) surface is passivated by phosphorus atoms. An electronic structure analysis shows that a modified phosphorus atom reduces the electron donation ability of the molybdenum which results in a downshift of the surface metal atom d-band center. Thus, the reactivity of the Mo(100) surface decreases and the activation energy for methylamine C-N cleavage increases. The decomposition of activation energy indicates that the difference in methylamine C-N cleavage activation energy for the two surfaces is caused by the structural deformation of methylamine from the initial state to the transition state, the adsorption energy of the methyl (without an amino group) in the transition state configuration (E(CH3)(TS)) and the interaction energy between methyl group and amino group in the transition state Compared with Mo(100), the increase in activation energy induced by Delta E(CH3NH2)(def), and E(CH2)(TS), is higher than the decrease in activation energy induced by E(CH3) ... NH(2)(int), on the phosphorus modified Mo(100) surface, which results in the methylamine C-N cleavage activation energy on the phosphorus modified Mo(100) surface being higher than the that on clean Mo(100) surface.

• 出版日期2009-11
• 单位太原理工大学; 南开大学; 山西大同大学