RESUMEN
Reactions of PtX+ (X = F, Cl, Br, I) with methane have been investigated at the density functional theory (DFT) level. These reactions take place more easily along the low-spin potential energy surface. For HX (X = F, Cl, Br, I) elimination, the formal oxidation state of the metal ion appears to be conserved, and the importance of this reaction channel decreases in going as the sequence: X = F, Cl, Br, I. A reversed trend is observed in the loss of H2 for X = F, Cl, Br, while it is not favorable for PtI+ in the loss of either HI or H2. For HX eliminations, the transfer form of H is from proton to atom, last to hydride, and the mechanisms are from PCET to HAT, last to HT for the sequence of X = F, Cl, Br, I. One reason is mainly due to the electronegativity of halogens. Otherwise, the mechanisms of HX eliminations also can be explained by the analysis of Frontier Molecular Orbitals. While for the loss of H2, the transfer of H is in the form of hydride for all the X ligands. Noncovalent interactions analysis also can be explained the reaction mechanisms.
RESUMEN
We calculated the adsorption of H, O, OH, and H2O and the dissociation of H2O molecule on the Cu(111), Cu(100), and Cu(110) surfaces using density functional theory. H, O, and OH tend to adsorb stably at the highly coordinated dh and h sites on the Cu(111) and Cu(100) surfaces. OH and H tend to adsorb on sb site on the Cu(110) surface. The more charge transfer of the adsorbed substance, the more stable the adsorption. The dissociation product is O+H on the Cu(111) surface, while the dissociation product is OH+H on the Cu(100) and Cu(110) surfaces. Due to the different geometric structures of initial state (IS), transition state (TS), and final state (FS) in the dissociation reaction, the dissociation of water on the copper surface does not establish a linear Brønsted-Evans-Polanyi (BEP) relationship. These results provide theoretical support for the understanding of the interaction between water and metals as well as the behavior of water molecules.
RESUMEN
Using density functional theory methods, H2O dissociation was investigated on the Ni(111), Ni(100), and Ni(110) surfaces. H and O atom as well as OH species adsorb stably at the high coordination sites. While on the Ni(110) surface, the OH species prefers at the twofold short bridge site because the adsorption on the fourfold hollow site is less feasible due to the increased distances between the nickel atoms. The amount of charge transfer is related to the adsorption stability. The more charge transfer, the more stable the adsorption. The charge transfer decreases in the order of O > OH > H. H2O molecule adsorbs at the top site in a configuration parallel to the surface. The final products are different for H2O dissociation due to the different mechanisms. On the Ni(111) surface, the final product is the O atom. On the Ni(100) and Ni(110) surfaces, the most abundant species are OH and H, but the reaction mechanisms were different. It is not necessary to linear BEP relationship for a given reaction on different surfaces. These results could provide fundamental insights into water behaviors and a favorable theoretical basis for further understanding and research on the interaction between water and metal surfaces.
RESUMEN
The effect of potassium on carbon adsorption and deposition on the Co(0001) surface was studied on the basis of theoretical calculations. Thermodynamically, the surface Cn species is expected, and C2 dimer may be a critical elementary unit. With the increase of carbon coverage, a fraction of the carbon atoms may diffuse into the subsurface. But kinetically, the formation of Cn species is more favorable, and there is no driving force for carbon to migrate into the subsurface. As the surface carbon concentration increases, the adsorbed carbon atoms turn into carbon chains and then into graphene sheets parallel to the surface. Potassium promoter has little effect on the most stable adsorption configurations of carbon atoms but increases the adsorption energy of carbon species, which can be explained by the decreasing of the surface work function resulting from the electron effect of potassium promoter. The potassium promotes carbon deposition and carbonization of the cobalt surface to a certain extent. These results could support some useful information for the carbon deposition and cobalt carbide formation.