Abstract

The thesis presents the work constituted by two major parts: (1) – synthesis of new mono-, bi- and trimetallic complexes based on Re, Nb and Ta and their physical-chemical characterization, and (2) – preparation of nanostructural functional materials derived from these complexes. The precursors and materials were characterized by FTIR, NMR, MS, SEM–EDS, TEM and X-ray diffraction. The electrochemical method and the interaction of Re₂O7 with M₂(OR)10 (M = Nb or/and Ta) were used to obtain Re₄O₄(OEt)₁₂ and (M1-xM'x)₄O₂(OR)₁₄(ReO₄)₂ (M = Nb; M' = Ta; R = Me, Et, nPr), where x = 0–1, respectively. The structures of these complexes were determined by single-crystal X-ray diffraction. The influence of the increasing ligand size on the solubility and stability of the complexes Re₄O₄(OEt)₁₂ and (M1-xM'x)₄O₂(OR)₁₄(ReO₄)₂ (M = Nb, M' = Ta; R = Me, Et, nPr) has been established. Nanosized Re metal particles (approximately 3 nm in diameter) were obtained from Re₄O₄(OEt)₁₂ by thermal decomposition in inert atmosphere at as low temperature as 380°C. Semi-ordered macro porous monoliths with the pore size in the range 100–250 nm, with the crystal structure related to the γ-Ta₂O₅, were produced from (Nb1-xTax)₄O₂(OMe)₁₄(ReO₄)₂ (x = 0.3, 0.5, 0.7) via thermal decomposition in air at the temperatures ≤ 1000°C, while in dry nitrogen the α-Nb₂O₅ for the Nb-rich precursors and γ-Ta₂O₅ for Ta:Nb ≥ 1:1 at the temperatures ≤ 1000°C were formed. The Re₄O₄(OEt)₁₂ and Ta₄O₂(OEt)₁₄(ReO₄)₂ alkoxide complexes have been used as precursors for Re oxide based catalysts. The simultaneous presence of the chemically connected oxidative (perrhenate) and acidic (tantalum oxide) components in the catalyst permit one-step production of DMM. The hydrolysis of (M1-xM'x)₄O₂(OEt)₁₄(ReO₄)₂ (M = Nb; M' = Ta; x=0–1) leads to formation of nanostaructural materials (nanobeads). The particles remain amorphous and retain Re until rather high temperatures (700°C). The Re content is lost at 1000°C with formation of porous nanobeads with crystal structure related to the γ-Ta₂O₅ and α-Nb₂O₅ for the corresponding precursors.

Keywords

catalysts; chemical synthesis; oxides; x rays; microscopy

Published in

Acta Universitatis Agriculturae Sueciae
2011, number: 2011:22
ISBN: 978-91-576-7557-6
Publisher: Department of Chemistry, Swedish University of Agricultural Sciences

SLU Authors

• Nikonova, Olesya

  • Department of Molecular Sciences, Swedish University of Agricultural Sciences
    

UKÄ Subject classification

Inorganic Chemistry


Permanent link to this page (URI)

https://res.slu.se/id/publ/33458