Characterization of VOx-TiO2 catalysts and their activity in the partial oxidation of methyl ethyl ketone

The present work focuses on the partial oxidation of methyl ethyl ketone to acetic acid over TiO₂ supported vanadia catalysts with V loadings from 1 to 13.5 wt.%. In order to elucidate the relation between catalytic activity and the structure of the catalysts, the catalysts were also characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), temperature programmed reduction with hydrogen (TPR), and temperature programmed desorption of lattice oxygen (TPD-O₂). The investigations show that with increasing V loading the MEK conversion increased whereas the turn-over frequency decreased. At lower V loading (1–4 wt.%) the total oxidation to CO_x was favoured and the selectivities to acetic acid and other oxygenated products were low. The highest selectivities to acetic acid were achieved at V loadings of 4–6 wt.%. Based on literature data and our results, a scheme of the reaction pathways for the partial oxidation of MEK to AcOH and other by-products was developed.     

Positron annihilation studies of binary Ni-based alloys

Positron annihilation studies of Ni–1 at. % X (X = Pb, In and Zn) alloys have been performed. The experimentally observed changes in the parameters connecting the shape of angular correlation curve with the kind and concentration of crystal lattice defects are correlated with the values of the vacancy-solute binding energy calculated from the vacancy model of melting.