Rafael Añez

Interaction of CO molecule with Au/MOR catalyst: ONIOM-PM6 study, active sites, thermodynamic and vibrational frequencies.

ONIOM calculations have been carried out to determine geometries, adsorption energies, and vibrational frequencies of CO on a model for Au-exchanged mordenite catalysts, Au/MOR. The CO-calculated vibrational frequencies (upsilon(CO)) are in good agreement with the reported experimental values. We proposed to interpret the frequency results. CH(3)COCH(3) and CH(3)SH adsorption enthalpy calculations on Au/MOR model show that the Au/MOR catalyst behaves like a soft acid according to Pearsons rule. A higher structural deformation degree of the mordenite was found in the calculations with PM6 than with universal force field approach approach. A new pseudopotential (ACEP-121) was developed to improve the Au-Au distance, and Au ionization potential.

Transition structure for the retroene-type elimination reaction of propene from allylmethylsulfide

Abstract The activation energy for the retroene elimination of propene from allylmethylsulfide was calculated at three different levels of ab initio molecular orbital theory (HF, DFT(B3LYP) and MP2) combined with three different basis sets (3-21G ∗ , 6-31G ∗ and 6-31+G ∗∗ ). The activation energies were determined at room temperature and at 375°C. Our calculations lead to transition states that consist of a non-planar six center cyclic structure with a distorted chair-like geometry. Moreover, the transition states geometry has a marked “product-like” character. We found that the combination B3LYP/6-31+G ∗∗ produces activation energy values closer to the experimental ones, but the simpler combination B3LYP/6-31G ∗ produces excellent values too in less time. In all cases studied, the activation energies obtained from both the density functional and MP2 are better than those obtained using the Hartree–Fock method, which overestimates the barrier height. Regardless of the theory level used (HF, DFT or MP2), the basis sets 6-31G ∗ and 6-31+G ∗∗ produce practically the same values of activation energy; however, the first set is about twice as fast as the second one. The transition structures geometry obtained by different combination methods/basis sets present only slight structural differences.

Theoretical study of substituted methyl mercury in gas phase and in solution

Quantum chemistry calculations were carried out, using density functional theory, in order to investigate the thermodynamic properties, enthalpy (ΔH), Gibbs free energy (ΔG) and equilibrium constant (K

Theoretical study of NO2 adsorption on a transition-metal zeolite model

_{eq}

CATIVIC: Parametric quantum chemistry package for catalytic reactions: I

), for the dissociation of a series of methylmercury series compounds. Two kind of pseudopotentials were studied, the relativistic compact effective potentials and the Stuttgart pseudopotential. The B3LYP, BLYP, BP86 and BMK functionals were employed. The calculations were performed in gas phase and in presence of solvent. The results reveal that, none of the studied functionals was able to reproduce the experimental C-Hg and Hg-X, X=Cl, Br and I bond distances. The presence of solvent, water, acetonitrile and dimethylsulfoxide, has a strong influence on the ΔH and ΔG values. On the other hand, the results show that there is a lineal correlation between the logarithm of the experimental K

Diatomic molecule data for parametric methods. I

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Stabilization of the (1 1 0) tetragonal zirconia surface by hydroxyl chemical transformation

(exp) and the calculated K

Application of computational methods to catalytic systems

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Improvement of scale factors for harmonic vibrational frequency calculations using new polarization functions

(theo). This type of correlation could be useful in the resolution of problems related with the contamination by methylmercury compounds.