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Abstract: The electronic structures, stabilities and magnetic properties of the Fe3O4(111), (110) and (001) surfaces have been computed at the level of density functional theory by including the Hubbard parameter (U) for describing the on-site Coulomb interaction of iron 3d electrons. Among the six Fe3O4(111) terminations, the Fetet1 (exposing tetrahedral coordinated iron) and Feoct2 (exposing octahedral coordinated iron) terminations are more stable and have metallic character. For the Fe3O4(110) surface, strong surface distortion has been found; the A-layer termination (exposing tetrahedral coordinated iron) has metallic character, while the B-layer termination (exposing tetrahedral and octahedral coordinated iron) has half-metal character. For the Fe3O4(001) surface, both A-layer (exposing tetrahedral coordinated iron) and B-layer (exposing octahedral coordinated iron) terminations have half-metal character. The surface stability of (111)>(001)>(110) on the basis of the computed surface energies agrees well with the experimental findings, and explains reasonably the observed diversity and complexity of the experiments. [Copyright &y& Elsevier]

Abstract: The structures and energetics of the chemisorbed CO2, CH x species and H as well as C2H4 on the α-Mo2C(0001) surface have been computed at the GGA-RPBE level of density functional theory. It is found that CO2 adsorbs dissociately into CO and O, in agreement with the experimental finding. The adsorbed O, CH x and H species prefer the site of three surface molybdenum atoms over a second layer carbon atom (V C site). On the basis of the calculated adsorption energies of CH x and H, the sequential dehydrogenation of CH4 and the C/C coupling reaction of CH x have been discussed. [Copyright &y& Elsevier]

Abstract: Adsorption of oxygen and CO on Mo- and C-terminated α-Mo2C(0001) has been investigated at the density functional level of theory. On the Mo-terminated surface, the most stable adsorption configuration (1) has atomic oxygen capping the threefold Mo hollow position over a second layer carbon atom (V C, C vacancy site). On the C-terminated surface, the most stable adsorption configuration (8) has atomic oxygen capping the threefold Mo hollow site over a first layer carbon atom (H C, C hollow site). For CO adsorption, the most stable configuration (17) has CO capping structure over carbon vacancy (V C) on the Mo-terminated surface, but atop of the surface carbon with the formation of ketenylidene (Ch name="dbnd" />O) species on the C-terminated surface (21). Analysis of density of states reveals the metallic character of the clean and oxygen doped surfaces and the activation of the surfaces by oxygen adsorption. [Copyright &y& Elsevier]

Abstract: Density functional theory computations have been carried out on the adsorption of NO, NO2, pyridine and pyrrole on the α-Mo2C(0001) surface for understanding the hydrodenitrogenation processes. On the Mo-terminated surface, NO decomposes into surface N and O, and NO2 dissociates into surface O and NO without any barriers, while the most stable adsorption modes of pyridine and pyrrole have π-face coordination over the three-fold molybdenum hollow sites with strongly destroyed aromatic systems. On the C-terminated surface, adsorbed surface species have been found for NO and NO2, while destroyed ring systems are found for pyridine and pyrrole. It is found that adsorption on the Mo-terminated surface is much stronger than that on the C-terminated surface. [Copyright &y& Elsevier]