title: Supported and inserted monomeric niobium oxide species on/in silica: a molecular picture.
abstract: The geometry, energetic, and spectroscopic properties of molecular structures of silica-supported niobium oxide catalysts are studied using periodic density functional calculations (DFT) and compared with experimental data. The calculations are done for Nb oxide species inserted or grafted in/on an amorphous hydroxylated silica surface. Different positions of the Nb atom/atoms in the silica structure have been investigated. By means of DFT calculations the geometry and the degree of hydration of Nb oxide species with oxidation state +5 have been studied. The local Nb geometry depends on different parameters such as the number of Nb-O-Si groups vs. Nb-O-H groups, the formation of H bonds and the distance between Nb atoms. The interaction between the oxide and silanol groups occurs by formation of Si-O-Nb bonds with chemically and thermally stable Brønsted and Lewis acid sites. UV-Vis, reflection absorption infrared vibrational spectra (RAIRS) as well as various thermodynamic properties have also been investigated in order to get a better insight into the system studied and to provide support to possible experimental studies.
authors.affiliation: Technische Universität Hamburg, Harburg, Chemische Reaktionstechnik, Eißendorfer Straße 38, 21073 Hamburg, Germany.
authors.forename: Diana C
authors.initials: DC
authors.lastname: Tranca
authors.forename: Anna
authors.initials: A
authors.lastname: Wojtaszek-Gurdak
authors.forename: Maria
authors.initials: M
authors.lastname: Ziolek
authors.forename: Frederik
authors.initials: F
authors.lastname: Tielens