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Title: Single Source Molecular Precursors to Niobia-Silica and NiobiumPhosphate Materials

Abstract

The molecular precursors Nb(OiPr)2[OSi(OtBu)3]3 and {l_brace}Nb(OiPr)4[O2P(OtBu)2]{r_brace}2 have been prepared. The first compound undergoes facile thermal conversion to high surface area, acidic niobia silica, whereas the second one thermally decomposes to a low surface area niobium phosphate.

Authors:
;
Publication Date:
Research Org.:
Ernest Orlando Lawrence Berkeley NationalLaboratory, Berkeley, CA (US)
Sponsoring Org.:
USDOE Director. Office of Science. Basic EnergySciences
OSTI Identifier:
919833
Report Number(s):
LBNL-59614
Journal ID: ISSN 0026-9247; MOCHAP; R&D Project: 401701; BnR: KC0302010; TRN: US200822%%583
DOE Contract Number:
DE-AC02-05CH11231
Resource Type:
Journal Article
Resource Relation:
Journal Name: Monatshefte fur Chemie; Journal Volume: 137; Related Information: Journal Publication Date: 2006
Country of Publication:
United States
Language:
English
Subject:
37; NIOBIUM PHOSPHATES; SILICA; SURFACE AREA

Citation Formats

Lugmair, Claus G., and Tilley, T. Don. Single Source Molecular Precursors to Niobia-Silica and NiobiumPhosphate Materials. United States: N. p., 2006. Web. doi:10.1007/s00706-006-0445-9.
Lugmair, Claus G., & Tilley, T. Don. Single Source Molecular Precursors to Niobia-Silica and NiobiumPhosphate Materials. United States. doi:10.1007/s00706-006-0445-9.
Lugmair, Claus G., and Tilley, T. Don. Fri . "Single Source Molecular Precursors to Niobia-Silica and NiobiumPhosphate Materials". United States. doi:10.1007/s00706-006-0445-9.
@article{osti_919833,
title = {Single Source Molecular Precursors to Niobia-Silica and NiobiumPhosphate Materials},
author = {Lugmair, Claus G. and Tilley, T. Don},
abstractNote = {The molecular precursors Nb(OiPr)2[OSi(OtBu)3]3 and {l_brace}Nb(OiPr)4[O2P(OtBu)2]{r_brace}2 have been prepared. The first compound undergoes facile thermal conversion to high surface area, acidic niobia silica, whereas the second one thermally decomposes to a low surface area niobium phosphate.},
doi = {10.1007/s00706-006-0445-9},
journal = {Monatshefte fur Chemie},
number = ,
volume = 137,
place = {United States},
year = {Fri Jan 13 00:00:00 EST 2006},
month = {Fri Jan 13 00:00:00 EST 2006}
}
  • No abstract prepared.
  • The following dimolybdenum complexes containing -OSi(O{sup t}Bu){sub 3}, -O{sub 2}P(O{sup t}Bu){sub 2}, and -OB[OSi(O{sup t}Bu){sub 3}]{sub 2} ligands have been synthesized and structurally characterized: Mo{sub 2}(NMe{sub 2}){sub 4}[OSi(O{sup t}Bu){sub 3}]{sub 2} (1), Mo{sub 2}(O{sup t}Bu)4[OSi(O{sup t}Bu){sub 3}]{sub 2} (2), Mo{sub 2}(NMe){sub 4}(OB[OSi(O{sup t}Bu){sub 3}]{sub 2}){sub 2} (3), Mo{sub 2}(NMe{sub 2}){sub 2}[-O{sub 2}P(O{sup t}Bu){sub 2}]{sub 2}[O{sub 2}P(O{sup t}Bu){sub 2}]{sub 2} (4), Mo{sub 2}(NMe{sub 2}){sub 2}[OSi(O{sup t}Bu){sub 3}]{sub 2}[-O{sub 2}P(O{sup t}Bu){sub 2}]{sub 2} (5), and Mo{sub 2}(NMe{sub 2}){sub 2}[-O{sub 2}P(O{sup t}Bu){sub 2}]{sub 2}OB[OSi(O{sup t}Bu){sub 3}]{sub 2} (6). The isolation and structural characterization of trans- and cis-isomers of complexes 4 and 5 (4amore » and 4b, 5a and 5b, respectively) are also reported. Studies of the thermal decompositions of the complexes (by thermogravimetric analysis and solution 1H NMR spectroscopy) were performed. Xerogels with approximate compositions of 2MoO{sub 1.5}{center_dot}2P{sub 2}O{sub 5} and 2MoO{sub 1.5}{center_dot}2P{sub 2}O{sub 5}{center_dot}2SiO{sub 2} were derived from 4a and 5a or 5b, respectively, via solution thermolyses (toluene). The as-synthesized (and dried) xerogels contain one equiv of HNMe{sub 2} per molybdenum center (by combustion analysis, IR spectroscopy, and thermogravimetric analysis), and these materials have high surface areas (up to 270 m{sup 2} g{sup -1}). Upon calcination at 300 C, the coordinated amines are lost and the surface areas are significantly reduced (to 40 m{sup 2} g{sup -1} and <5 m{sup 2} g{sup -1} for the materials derived from 4 and 5a or 5b, respectively). Solid-state {sup 31}P MAS NMR spectroscopy suggests that the as-synthesized xerogels retain structural features of the starting molecular precursors, as indicated by the presence of resonances that correspond to both bridging and terminal -O{sub 2}P(O{sup t}Bu){sub 2} ligands. Upon calcination at 300 C, the resonances for bridging -O{sub 2}P(O{sup t}Bu){sub 2} groups are replaced by those for PO{sub 4}{sup 3-}. The material derived from 4 exhibits low activity and poor selectivity for the oxidative dehydrogenation (ODH) of propane to propylene. Cothermolyses of 4 and Bi[OSi(O{sup t}Bu){sub 3}]{sub 3} resulted in formation of Bi/Mo/P/Si/O materials with improved performance for the ODH of propane.« less
  • A series of composite oxides containing niobia (Nb{sub 2}O{sub 5}) and silica (SiO{sub 2}) was prepared by either incipient wetness impregnation to form surface phase oxides or by coprecipitation to form mixed oxides. At low Nb{sub 2}O{sub 5} concentrations, both the surface phase and mixed oxides showed strong Lewis acidity as determined by thermogravimetric and infrared studies of adsorbed pyridine. A surface phase oxide containing 0.25 monolayer of Nb{sub 2}O{sub 5} on SiO{sub 2} further showed strong Broensted acidity. With increasing Nb{sub 2}O{sub 5} concentration and/or treatment temperature, Nb{sub 2}O{sub 5} in these composite oxides became more bulk-like and showedmore » a corresponding decrease in acid strength. These acidic properties are discussed in terms of proposed structural models which contain tetrahedral niobia, octahedral niobia, and Nb=O bonds as basic building blocks.« less
  • The synthesis and characterization of ultrafine CuInS2 nanoparticles are described. Ultraviolet irradiation was used to decompose a molecular single source precursor, yielding organic soluble {approx}2 nm sized nanoparticles with a narrow size distribution. UV-vis absorption, 1H and 31P(1H) NMR, and fluorescence spectroscopies and mass spectrometry were used to characterize decomposition of the precursors and nanoparticle formation. The nanoparticles were characterized by high-resolution transmission electron microscopy (HRTEM), scanning electron microscopy energy dispersive X-ray spectroscopy, powder X-ray diffraction (XRD), electron diffraction, inductively coupled plasma analysis, UV-vis absorption spectroscopy, and fluorescence spectroscopy. They have a wurzite-type crystal structure with a copper-rich composition. Themore » hypsochromic shift in their emission band due to quantum confinement effects is consistent with the size of the nanocrystals indicated in the HRTEM and XRD analyses.« less
  • ZrO{sub 2}-SiO{sub 2} and Nb{sub 2}O{sub 5}-SiO{sub 2} mixture coatings as well as those of pure zirconia (ZrO{sub 2}), niobia (Nb{sub 2}O{sub 5}), and silica (SiO{sub 2}) deposited by ion-beam sputtering were investigated. Refractive-index dispersions, bandgaps, and volumetric fractions of materials in mixed coatings were analyzed from spectrophotometric data. Optical scattering, surface roughness, nanostructure, and optical resistance were also studied. Zirconia-silica mixtures experience the transition from crystalline to amorphous phase by increasing the content of SiO{sub 2}. This also results in reduced surface roughness. All niobia and silica coatings and their mixtures were amorphous. The obtained laser-induced damage thresholds inmore » the subpicosecond range also correlates with respect to the silica content in both zirconia- and niobia-silica mixtures.« less