Quantum chemical SINDO1 study of vanadium pentoxide

An improved set of parameters for vanadium in the semiempirical quantum chemical SCF MO method SINDO1 is presented. It is shown that both the geometries and heats of formation of a number of vanadium-containing compounds calculated by this method are in good agreement with available experimental data. Model clusters of increasing size are used for the study of geometric and energetic properties of vanadium pentoxide. Both hydrogen atom and proton adsorption on the (010) surface of vanadium pentoxide and a subsequent formation of different oxygen vacancies have been investigated. Based on these computational results the reactivities of V₂O₅-surface oxygen atoms for adsorption are discussed.     

The effect of the framework structure on the chemical properties of the vanadium oxide species incorporated within zeolites

V-silicalite catalysts (VS-1 and VS-2) prepared by hydrothermal synthesis have been studied by ESR, XAFS (XANES and EXAFS) and photoluminescence spectroscopy. The in situ characterization of these V-silicalites shows that vanadium is present within the zeolitic framework as a highly dispersed tetrahedrally coordinated V-oxides, VO₄ unit, having a short V=O bond length. Photoluminescence spectroscopy in static and dynamic mode, as well as XAFS studies allow to detect in the V-silicalites different V species than that present in V-HMS or V/SiO₂, in terms of V=O bond length, vibrational energy, bond angle and lifetime of the excited triplet state. It is suggested that the combined contribution of the neighboring Si---OH group attached to the VO₄ unit and the zeolitic rigid framework structure of V-silicalites cause a more significant and pronounced effect on the chemical properties of the VO₄ unit than the flexible structure of V-HMS or V/SiO₂. Moreover, the dynamic quenching of the phosphorescence by the addition of reactant molecules such as NO or propane indicates that the V species in the excited triplet state can be expected to be the active sites for the photocatalytic reactions.     

Active centres of magnesium oxide surface and calculations of dissociative chemisorption of methane on modified MgO

In the framework of supermolecular approach using MINDO/3 method the various channels of dissociative chemisorption of methane molecule on pure and lithium doped magnesium oxide surfaces are considered. On the basis of the obtained calculation results the possible ways of methane activation on MgO and Li/MgO are discussed.     

CO and NO adsorption on copper-containing zeolite. A theoretical ab initio study

Ab initio calculations were performed to simulate the interaction between CO or NO and copper-containing zeolite at the SCF level. The zeolite catalysts were modelled by a molecular cluster of composition H₈Si₃AlO₄Cu⁺ with = 0, 1. For = 0 the oxidation state of the Cu atom corresponds to 1+ in Cu⁺/zeolite, while for° = 1 it is equal to 2+ in Cu²⁺/zeolite. It was found that only Cu⁺/zeolite should be responsible for CO and NO adsorption from the gas phase. The calculated heats of adsorption compare well with available experimental data and together with adsorption geometries allow us to interpret the observed IR data.