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Abstract: First-principles calculations based on density functional theory and the generalized gradient approximation have been used to study the adsorption and dissociation of CH4 on Ni(100) surface. The favored adsorption sites of H, CH3, and CH4 are identified by considering the energy and stability of various binding sites. H atoms prefer the fourfold Hollow sites, while CH3 species favors the Bridge site with one of the C–H bonds pointing towards the neighbor Ni atom. When H and CH3 are coadsorbed on Ni(100) surface, several stable configurations are found, in which the atomic H and CH3 species are adsorbed at the Hollow and Bridge site, respectively, because of their little energetic difference. Through the electronic and vibrational calculations, the C–H–Ni three-center bond is regarded as the key factor determining the CH3 adsorption. The CH4 dissociation on Ni(100) surface is investigated with three different CH4 orientations considered. The energy barriers are calculated to be 0.61, 0.61 and 0.62eV, corresponding to the CH4 molecules orientated with one, two and three C–H bonds pointing towards the surface, respectively. All calculated activation energies have been corrected by including zero-point energy and dispersion energy, and are in good agreement with the experimental result (0.61±0.02eV). Because the energy barriers for the different reaction pathways take similar values, the CH4 orientation has a minor effect on the reactivity. [Copyright &y& Elsevier]

Abstract: DFT–GGA calculations have been used to study the chemisorption of CH x (x =0–3), C2H y (y =3–5) and C3H z (z =3–8) on Pt(111) at the coverage of 1/9 ML. The adsorption energies, favored binding sites and geometric parameters of adsorption configurations are determined. All the carbonaceous species are found to be adsorbed on Pt(111) with C atoms sp3-hybridized. The geometries of adsorption configurations have been compared with published experimental data to evaluate the reliability of our calculation method. The calculated adsorption energies of C1 species, ranked in descending order, are as follows, C>CH>CH2 >CH3, and the similar trend has been observed with respect to the chemisorption of C2 species. As for the C3 species, propylene prefers binding to the surface in the di-σ mode and the adsorption energy is calculated to be −0.93eV. The stepwise dehydrogenation of propane to propynyl (CCCH3) is investigated by calculating the change of reaction heat, which suggests that propylidyne (CCH2CH3) is the most stable species on Pt(111). Based on the adsorption energies and Brønsted–Evans–Polanyi (BEP) analysis, propyne is predicted to be the most likely starting point for the C–C scission. [Copyright &y& Elsevier]