Energetics of chemisorption and conversion of methane on transition metal surfaces
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The chemisorption and conversion of methane on Pt(111), Rh(111), Ru(0001), Ir(111), Cu(111) and NTi(111) were investigated using the unity bond index-quadratic exponential (UBI-QEP) method. Following conclusions were found from the analyses. (1) The main dissociate species of methane on the metal surfaces is CH3. The dissociation of CH. species on Ru(0001) is the easiest but the dissociation on Cu(111) is very difficult. (2) Coupling of CH3 may produce ethane, and then dehydrogenation of ethane may produce ethylene. The coupling of CH3 is the easiest on Pt(111) and Cu(111), but it is very difficult on Ru(0001). It indicated that copper was favorable to the C-2 selectivity. Non-oxidative reactions of methane coupling may produce ethane but it is difficult to get ethylene. (3) There are two competitive reaction pathways for part oxidation of methane to CO, directly heat-cracking pathway on Ni(111) and burning-reforming pathway on other metal surfaces. The selectivity of CO can be increased at elevated temperatures. (4) Carbon-deposit is the cause of the dissociation of CH. It can easily take place on Ni(111) and Ru(0001), but it is weak on other metal surfaces because that CH can fast produce CO without passing the surface carbon. (C) 2002 Elsevier Science B.V. All rights reserved.
出处JOURNAL OF MOLECULAR STRUCTURE-THEOCHEM，2002,587:63-71