Supported and inserted monomeric niobium oxide species on/in silica: a molecular picture
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 Bronsted 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.
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This work was performed using HPC resources from GENCI-[CCRT/CINES/IDRIS] (Grant 2010-[x2010082022]) and the CCRE of Universite´ Pierre et Marie Curie. COST action D36, WG No D36/0006/06 and the Polish National Science Centre (project No 2014/15/B/ST5/00167) are acknowledged for the financial support.