Electronic structure of MoO sub(2). DFT periodic and cluster model studies

• Published in: Applied catalysis. A, General General, 2011-01, Vol.391 (1-2), p.137-143
• Main Authors: Tokarz-Sobieraj, Renata, Grybos, Robert, Witko, Malgorzata
• Format: Article
• Language: English
• Subjects: Bands; Covalence; Electronic structure; Fermi level; Fermi surfaces; Mathematical models; Molybdenum; Slabs; Surface chemistry
• ISSN: 0926-860X
• DOI: 10.1016/j.apcata.2010.07.041

Electronic properties of MoO sub(2) bulk and (0 1 1) surface are discussed. It is found that Fermi level is located within the band dominated by d molybdenum orbitals, thereby reflecting the metallic character of the system. Results for (0 1 1)MoO sub(2) surface indicate that the surface retains the metallic character of the bulk. Depending on the thickness of the slab used to model the surface (1-layer or 2-layers) the electronic structure and properties change. In the 2-layer slab, bands close to the Fermi level originate both from regular six-fold coordinated Mo(6) centers as well as from five-fold coordinated Mo(5) centers occurring due to surface formation. In the 1-layer slab, peaks right below the Fermi level are dominated by the surface centers that are six-fold coordinated Mo(6) but also centers which are effectively four-fold coordinated Mo(4). This has a profound effect on the reactivity as was tested by a probe reaction of H sub(2) adsorption, which did not interact with the surface described by the 2-layer slab, but underwent dissociation on the 1-layer slab. The Mo-Mo pairs with bonds of approximately single character, characteristic for the bulk structure, are also present on the surface, both on 1-layer and 2-layer slabs. The local properties of (0 1 1)MoO sub(2) surface are very similar to other transition metal oxides. Metal-oxygen bonds are of a mixed ionic and covalent nature and the nucleophilicity of oxygen increases with the increase of coordination numbers of the corresponding oxygen atoms.