We have constructed hydrogen saturated carbon and silicon clusters with only 5-atom rings to study their effect on the electronic properties of the corresponding amorphous materials. Using density functional theory and the local density approximation we calculate the electronic structure of pure and contaminated clusters, symmetric and nonsymmetric, with the impurity in the center or in the nearest neighbor position. For the pure cluster we find, by comparison to reference clusters with 6-atom boat-type rings, that the pentagonal clusters have a narrower valence band and that the top of the valence band moves to lower energies. Without the hydrogen contribution the energy gap for the pentagonal carbon cluster is larger than that for the hexagonal one and the gap for both silicon clusters is practically the same, contrary to expectations due only to size. For the impure clusters the carbon gap values decrease as the atomic number of the impurity increases, whereas the effect is opposite for silicon; also, the width of the valence band is larger in all cases than that for the pure clusters.
The study of the interaction between vanadium oxide and the HY-zeolite using molecular dynamics interaction was carried out for two systems: i) when vanadium oxide penetrates a zeolite ring at its center, and ii) when vanadium oxide impacts the zeolite surface model. The dynamical effects are used to investigate the reduced activity and eventual degradation of the catalyst for the vanadium oxide presence. In the first case, we observe the breaking of an OH-bond that belongs to the acid site. This is related to an initial loss activity stage of the catalyst. In the second case, vanadium oxide is weakly adsorbed onto the zeolite surface velocity depending. Density functional theory, with nonlocal exchange and correlation functional and the basis set of double numerical accuracy, is used to analyze the electronic structure. It was used in combination with Born-Oppenheimer dynamics to perform calculations.
A current problem about oils and feedstock in fluid catalytic cracking (FCC) is the continuous cumulative deposition of metal contaminants on the catalyst, resulting in important modifications of its properties. Vanadium plays a detrimental role on the catalyst components because enhances
the destruction of the Y-zeolite structure during regeneration stage when it is exposed by steam and oxygen at high temperatures. Knowledge of the mechanism interaction of vanadium with the catalyst is important to improve FCC performance. Quantum Molecular Dynamics calculations were done
introducing the VO, V2O3, VO2 or V2O5 molecules at the center of a Y-zeolite ring simulating regeneration conditions. The results indicate that the principal reaction is carried out among the zeolite and the vanadium atoms of molecules.
This happens, when interaction is presented, since the loss of a hydrogen atom of the active place causes high degree of oxygen reactivity.
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