Beatriz Irigoyen

Oxidation of toluene to benzaldehyde over VSb0.8Ti0.2O4. Effect of the operating conditions

Abstract In the present work, the kinetic toluene oxidation on VSb0.8Ti0.2O4 based catalyst was studied. A reaction network, which involves three steps: the partial oxidation of toluene to benzaldehyde, a consecutive oxidation of benzaldehyde to carbon oxides and a parallel oxidation of toluene to carbon oxides, was proposed. The kinetic parameters were estimated assuming the redox mechanism proposed by Mars and van Krevelen. The products distribution was strongly affected by the reaction temperature. The adjustment of activation energies for total and partial oxidation of toluene led to the same values. The activation energy for the benzaldehyde oxidation was lower than the one for its formation.

Vanadium antimonate as a partial oxidation catalyst

Abstract The catalytic selective oxidation on vanadium antimonate oxides partially doped with titanium was studied. Solids with nominal composition VSbO 4 , V 0.8 SbTi 0.2 O 4 and VSb 0.8 Ti 0.2 O 4 were prepared by solid-state reaction. The solids were characterised by sorptometry, X-ray diffraction (XRD), temperature programmed reduction (TPR) and X-ray photoelectron spectroscopy (XPS). Catalytic tests were carried out in a fixed-bed reactor using toluene and air as reactants. It was found that partial substitution of V or Sb by Ti produces changes in the unit-cell composition and the redox properties of the solids. A possible role for V and Sb in the reaction mechanism of partial oxidation was established. Vanadium sites (V 4+ ) are involved in the incorporation of gaseous oxygen as lattice oxygen and hold the Sb sites in an oxidation state (Sb 5+ ) high enough to insert the lattice oxygen in the hydrocarbon molecule. A relationship between activity and V 4+ /Sb 5+ ratio of the unit-cell was found. The selectivity to benzaldehyde is correlated with the redox properties of the solids while the selectivity to total oxidation products could be interpreted by the site isolation theory.

Electronic structure and bonding of hydrogen in a screw dislocated bcc Fe

Abstract The bonding of HFe is analyzed using qualitative electronic calculations in the framework of the atom superposition and electron delocalization orbital cluster method (ASED-MO). The changes in the electronic structure of bcc Fe upon introduction, a screw dislocation are compared with Fe surfaces. A comparison is drawn with H adsorption at Fe ( 1 1 2) surface and H absorption in the bulk Fe with a dislocation. The results suggest that the detrimental effect of H on the FeFe bonds in a screw dislocation is almost half-severe than in other defects, such as an edge dislocation or vacancy and it is limited to its first neighbor. An analysis of the orbital interaction reveals that FeH bonding involves mainly the Fe 4s and H 1s orbitals. When H is in the bulk, the region near screw dislocation core is much more repulsive than in a normal Fe lattice. These results allow us consider that H accumulation could be less favorable near a screw dislocation than an edge dislocation.

An experiment on the liquid–vapor equilibrium for water

In the present paper we propose a simple and easy method to determine the latent heat of vaporization of pure water, using the Clausius–Clapeyron equation. The vapor pressure of water was calculated from measurements of temperature and volume, assuming an ideal gas behavior for the vapor. The calculated heat of phase change is in a good agreement with the latent heat of vaporization, obtained from the empirical Antoine equation and from the literature.