Eloy Nouel Rodríguez-Arias

Pyridine adsorption on a MoS2 modelled surface (Mo3S8). A CNDO molecular orbital study

Abstract Qualitative molecular orbital calculations (CNDO) were carried out for the interaction of a pyridine molecule on a modelled MoS 2 surface by a Mo 3 S 8 cluster. Different adsorption modes and adsorption sites were explored. The results show that π-aclsorption is more energetically favored than σ-one. Parallel adsorption produces the activation of Cue5f8C and Cue5f8N bonds suggesting an irreversible chemisorption with a subsequent fragmentation of the pyridine molecule. A charge transfer from the pyridine to the MoS 2 system occurs after chemisorption mainly in the π-adsorption. It is proposed that the σ-adsorption, which is responsible for hydrogenation of the pyridine molecule, results favored after the formation of molecular fragments from σ-adsorption.

Model parametric Hamiltonians and bonding theoretical tools in simulation of catalytic reaction steps. Hydrotreatment of oil components

Quantum chemistry calculations of hydrocarbons components and hydrogen have been carried out using model surface adsorption sites on aggregates and model parametric Hamiltonians. Baders topological analysis of the charge density in the valence region is used to describe the adsorption site on which reactions may occur. A description of the adsorbate and surface bindings with diatomic binding energies (DBE) and orbital interactions are presented. Chemisorption and hydrogenation reactions of molecular fragments that are intermediates in hydrocarbon formation on a nickel aggregate were calculated. Also, the growing of hydrocarbon chains and the building of carbonaceous filaments were studied. The modeling of hydrogen dissociation on HDS catalyst was analyzed. In addition, the hydrogenation step of the HDN reaction on a modeled MoS 2 catalyst, employing pyridine as model molecule, is presented.

Pyridine interaction with a partially hydrogenated MoS2 modelled surface. A molecular orbital study

Chemisorption of pyridine on a partially hydrogenated surface of MoS2 was modelled by the interaction of a pyridine molecule with a Mo3S8H2 cluster. Calculation of total energies, bond orders, diatomic energies, charge transferences and interatomic orbital overlaps was performed by the CNDO/UHF method. Results show a net charge transfer from the pyridine molecule to the Mo adsorption center. The interaction of π-adsorbed pyridine with chemisorbed hydrogen bridged on Moue5f8Mo positions leads to a partial hydrogenation of the nitrogen compound. A mechanism of pyridine hydrogenation is proposed based on the fact that Mo adsorption centers (vacancies) are pivotal for hydrogen atoms transfer. These results suggest a regioselective hydrogenation.

Modeling MoS2 catalytic surface with simple clusters

Abstract Theoretical calculations using a modified version of CNDO/UHF method to correct binding energies were carried out on a series of linear Mo x S y ( x =3; y =6, 8, 10, 12, 14 and x =5; y =12, 14) and non-linear ( x =3, y =6, 8, and x =5, y =6, 8, 10, 12, 14, 16, 18, 20) clusters. Results show the formation of S 2 − species on the surface and the existence of a Moue5f8Mo interaction. The HOMO orbitals are localized on mono-coordinate S atoms which shows that these atoms have electron-donating properties while the LUMO orbital is delocalized over all coordinatively unsaturated Mo atoms which presents electron-acceptor properties. It is shown that the non-linear clusters are better models for representation of MoS 2 catalysts, because they of their stability respect to the linear clusters.