科研之友
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摘要
A previous set of investigations related to adsorption, diffusion, and dissociation properties of CO [D. C. Sorescu, D. L. Thompson, M. M. Hurley, and C. F. Chabalowski, Phys. Rev. B 66, 035416 (2002)] and H-2 [D. C. Sorescu, Catal. Today 105, 44 (2005)] on Fe(100) surface have been extended to the case of chemisorption properties of CHx (x=0,4) species on the same surface. Similar to our previous studies, the current work is based on first-principles plane-wave calculations using spin-polarized density functional theory (DFT) and the generalized gradient approximation (GGA). The calculations employ slab geometry and periodic boundary conditions. It was determined that CHx (x=0,2) species preferentially adsorb at the four-folded sites while the CH3 species prefer the binding at the bridge site. In contradistinction, the CH4 molecule is only weakly physisorbed on the surface, independent of surface site or molecular orientation. In the case of the C atom, the adsorption investigations have been extended to include both the coverage effects as well as the possibility for absorption at subsurface sites. The presence of the C atom at either hollow or subsurface sites was found to increase the stability of the other atomic (C, H, O) and molecular or radical species [CO, CHx (x=1,4)] adsorbed on the surface. Beside chemisorption properties, the activation energies for surface diffusion have been determined for all individual CHx (x=0,3)species while in the case of C atom diffusion to subsurface sites have also been considered. Finally, we have determined the minimum energy path for the elementary hydrogenation reactions of CHx (x=0,3) species. We found that for the ensemble of surface processes involving dissociation of CO and H-2 on Fe(100) surface followed by hydrogenation of CHx (x=0,3) species with formation of CH4, the CO dissociation is the rate determining step with an activation energy of 24.5 kcal/mol.
- 出版日期2006-4
