Hydrogen adsorption on a Mo27S54 cluster: A density functional theory study

Theoretical study of the catalytic hydrodeoxygenation of furan, methylfuran and benzofurane on MoS2

Herein, we have studied the direct deoxygenation (DDO) (without prior hydrogenation) of furan, 2-methylfuran and benzofuran on the metal edge of MoS2 with a vacancy created under pressure of dihydrogen. For the three molecules, we found that the desorption of the water molecule for the regeneration of the vacancy is the most endothermic. Based on the thermodynamic and kinetic aspects, the reactivity order of the oxygenated compounds is furan ≈ 2-methylfuran > benzofuran, which is in agreement with literature. We present the key stages of the mechanisms and highlight the effects of substituents.

A density functional theory study of the hydrogenation and reduction of the thio-spinel Fe3S4{111} surface

The mineral greigite, Fe3S4, shows promising electro-reduction activity, especially towards carbon dioxide conversion to small organic molecules. We have employed density functional theory calculations with correction for the long-range dispersion forces to investigate the behavior of hydrogen on the greigite{111} surface. We have studied the adsorption, diffusion, surface reduction and associative (i.e. Volmer-Tafel mechanism) and molecular desorption of hydrogen as a function of its coverage. We found that (i) the H ad-atoms adsorb on S sites far from metallic centres in the topmost surface layer; (ii) the reduction of greigite by hydrogen is energetically unfavorable at any surface coverage; and (iii) molecular hydrogen evolution has a transition state at ∼0.5 eV above the energy of the reactants on Fe3S4{111}, which is very similar to the barrier found experimentally on Pt{111}. We have also determined the electrode potential under room conditions at which the H2 evolution reaction becomes energetically barrierless.

Small stoichiometric (MoS2)n clusters with the 1T phase

Stoichiometric (MoS₂)_n clusters (n = 1–6) were systematically studied by density functional theory calculations with hybrid B3LYP and pure GGA PW91 functionals.

How to find an optimum cluster size through topological site properties: MoSx model clusters

Computational investigations in catalysis frequently use model clusters to represent realistically the catalyst and its reaction sites. Detailed knowledge of the molecular charge, thus electronic density, of a cluster would then allow physical and chemical insights of properties and can provide a procedure to establish their optimum size for catalyst studies. For this purpose, an approach is suggested to study model clusters based on the distributed multipole analysis (DMA) of molecular charge properties. After full density functional theory (DFT) geometry optimization of each cluster, DMA computed from the converged DFT one-electron density matrix allowed the partition of the corresponding cluster charge distribution into monopole, dipole, and quadrupole moments on the atomic sites. The procedure was applied to MoS2 model clusters Mo10S18, Mo12S26, Mo16S32, Mo23S48, and Mo27S54. This analysis provided detailed features of the charge distribution of each cluster, focused on the 1010 (Mo or metallic edge) and 1010 (sulfur edge) active planes. Properties of the Mo27S54 cluster, including the formation of HDS active surfaces, were extensively discussed. The effect of cluster size on the site charge distribution properties of both planes was evaluated. The results showed that the Mo16S32 cluster can adequately model both active planes of real size Mo27S54. These results can guide future computational studies of MoS2 catalytic processes. Furthermore, this approach is of general applicability.