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Open Access Publications from the University of California

Ga[OSi(OtBu)3]3·THF, a thermolytic molecular precursor for high surface area gallium-containing silica materials of controlled dispersion and stoichiometry

  • Author(s): Dombrowski, JP
  • Johnson, GR
  • Bell, AT
  • Tilley, TD
  • et al.

© 2016 The Royal Society of Chemistry. The molecular precursor tris[(tri-tert-butoxy)siloxy]gallium, as the tetrahydrofuran adduct Ga[OSi(OtBu)3]3·THF (1), was synthesized via the salt metathesis reaction of gallium trichloride with NaOSi(OtBu)3. This complex serves as a model for isolated gallium in a silica framework. Complex 1 decomposes thermally in hydrocarbon solvent, eliminating isobutylene, water, and tert-butanol to generate high surface area gallium-containing silica at low temperatures. When thermal decomposition was performed in the presence of P-123 Pluronic as a templating agent the generated material displayed uniform vermicular pores. Textural mesoporosity was evident in untemplated material. Co-thermolysis of 1 with HOSi(OtBu)3in the presence of P-123 Pluronic led to materials with Ga : Si ratios ranging from 1 : 3 to 1 : 50, denoted UCB1-GaSi3, UCB1-GaSi10, UCB1-GaSi20and UCB1-GaSi50. After calcination at 500 °C these materials exhibited decreasing surface areas and broadening pore distributions with increasing silicon content, indicating a loss of template effects. The position and dispersion of the gallium in UCB1-GaSi materials was investigated using71Ga MAS-NMR, powder XRD, and STEM/EDS elemental mapping. The results indicate a high degree of gallium dispersion in all samples, with gallium oxide clusters or oligomers present at higher gallium content.

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