ELECTRONIC STATES OF NICKEL(II) IN SPINEL-TYPE STRUCTURES

The electronic spectra of Ni-II as the promoter of a hydrodesulfurizat ion catalyst (NiO-MoO3/gamma-Al2O3) has been studied. On the basis of the positions and intensities of the maxima in electronic d-d transiti ons the presence of an octahedral point group symmetry (O-h) of Ni-II was established for the untreated sample and samples taken from the re generated catalyst layers. In other cases, the distribution of d-d tra nsition maxima indicated that in addition to the octahedral (O-h) a te trahedral (T-d) coordination of Ni-II was also present, suggesting the occurrence of a spinel-type structure. The experimental values obtain ed for the crystal field splitting parameter (10D(q)) enabled calculat ion of the electronic state energies, as well as the values of paramet ers of partially populated d-orbitals of Ni-II. On the basis of these data, the effective values of ionization potential H-dd were calculate d and a most probable MO scheme was proposed. Copyright (C) 1996 Elsev ier Science Ltd