Electronic states of nickel(ii) in spinel-type structures

Abstract

—The electronic spectra of Ni II as the promoter of a hydrodesulfurization catalyst (NiO-MoO 3/γ-Al 2O 3) has been studied. On the basis of the positions and intensities of the maxima in electronic d-d transitions the presence of an octahedral point group symmetry (O h) of Ni II was established for the untreated sample and samples taken from the regenerated catalyst layers. In other cases, the distribution of d-d transition maxima indicated that in addition to the octahedral (O h) a tetrahedral (T d) coordination of Ni II was also present, suggesting the occurrence of a spinel-type structure. The experimental values obtained for the crystal field splitting parameter (10D q) enabled calculation of the electronic state energies, as well as the values of parameters of partially populated d-orbitals of Ni II. On the basis of these data, the effective values of ionization potential H dd were calculated and a most probable MO scheme was proposed.