José-Manuel Martínez-Magadán

Mcscf+mrci study of the interaction of zn, zn+ and zn2+ with the hydrogen molecule

Abstract The C 2v potential energy curves for the interaction of Zn, Zn + and Zn 2+ with the hydrogen molecule were calculated at the MRCI+MP2 level using the pseudopotential method of Durand and double-ζ Gaussian basis sets. The 1 A 1 , 3 B 2 and 1 B 2 curves for Zn+H 2 , the 2 A 1 , 2 B 2 (p) and 2 B 2 (d) curves for Zn + +H 2 and the 1 A 1 , 3 B 2 and 1 B 2 curves for Zn 2+ +H 2 were studied. We first analysed the unrelaxed H 2 approach to the metallic center, followed by the angle relaxation for all the complexes. We propose a model consisting of two alternative mechanisms leading to attractive interactions. All nine reactions studied are explained in the light of our model.

DFT Study of the Interaction of the HZSM-5 Zeolite with the Benzene Molecule

We have performed density functional theory (DFT) calculations to describe the interaction of an active site of the HZSM-5 zeolite with a benzene molecule. We used a ring of ten SiO4 tetrahedral (10T) units to represent the structure of the HZSM-5 zeolite. The calculations were of the all-electron type, the exchange-correlation contributions were taken into account by means of the BLYP density functional, and orbital basis sets of double numerical polarization quality were employed for all atoms. Starting from the silicalite 10T ring, with silicon atoms at each site, we found the most energetically favored site for the substitution of an aluminum atom by a silicon atom to produce an HZSM-5 ring model, with a Si/Al ratio of 9. In order to simulate the adsorbed state of benzene onto the zeolite, the geometry of the aromatic molecule was fully optimized in its interaction with the zeolite model, while keeping the ring frozen. The electronic structure of the benzene-HZSM-5 complex was then analyzed and discussed. Our results account for a significant interaction between the acid proton from the HZSM-5 cavity with benzene, shown by changes of the-bond cloud of benzene, which would lead to an active carbocationic moiety. c 2000 John Wiley & Sons, Inc. Int J Quantum Chem 80: 125-132, 2000

Role of excited states of maximal d-shell occupancy in the Ru + H2 reaction

Abstract Pseudopotential-CI calculations including relativistic effects have been performed to study the Ru + H2 reaction, for all the channels of C2v symmetry which correlate with the ground state and the first excited triplet state of the reactants: Ru(5F; d7s1) + H2, and Ru(3F; d7s1) + H2, respectively. The most interesting results are obtained for the low-multiplicity channels, for which the potential-energy surfaces are explained in terms of avoided crossings, showing that for the capture and activation of the H2 molecule by the lowest triplet state Ru(3F; 4d75s1), the higher-lying state Ru(3F; 4d85s0) is partly responsible for the reactivity of the metallic center.

Promotional effect of Co or Ni impurity in the catalytic activity of MoS2: An electronic structure study

It has been observed that the catalytic activity of MoS2 crystals is enhanced when either Co or Ni atoms are added. The presence of these atoms leads to electronic rearrangements, which are considered the source of catalytic improvement. However, the relation between the electronic properties and the enhancement of the catalytic activity is not yet fully understood. In order to get insight into the electronic-level changes that affect the catalyst performance, a solid-state density functional study has been carried out for Mo, Co/Mo, and Ni/Mo sulfides, using bulk and surface models. The MoS2 crystallize in a well-known layered structure, which has been used together with the supercell model to simulate the (10N 10 ) edge surface of MoS 2. The binary sulfides were obtained substituting Co or Ni by Mo from the original MoS2 bulk model. The electronic structure in a nonmagnetic state is analyzed and, in particular, the density of states of metal and sulfur atoms for the surface and bulk are compared. Finally, we discuss the important role that these properties play in the hydrodesulfurization reaction and concluded that Mo at the surface remains the relevant reactive atomic center in the bimetallic systems, whereas Co and Ni are responsible for increasing the Mo reactivity at the surface. c 2000 John Wiley & Sons, Inc. Int J Quantum Chem 80: 406-415, 2000

Molecular design of high performance zwitterionic liquids for enhanced heavy-oil recovery processes

Branched gemini zwitterionic liquids, which contain two zwitterionic moieties of linked quaternary-ammonium and carboxylate groups, are proposed as chemicals to be applied in the Enhanced Oil Recovery (EOR) from fractured carbonate reservoirs. The zwitterionic moieties are bridged between them through an alkyl chain containing 12 ether groups, and each zwitterionic moiety has attached a long alkyl tail including a CC double bond. A theoretical molecular mechanism over which EOR could rest, consisting on both the disaggregation of heavy oil and the reservoir-rock wettability alteration, was suggested. Results show that chemicals can both reduce the viscosity and remove heavy-oil molecules from the rock surface.