Metal oxide (TiO{sub 2}, MoO{sub 3}, WO{sub 3}) substituted silicate xerogels as catalysts for the oxidation of hydrocarbons with hydrogen peroxide
- Hebrew Univ. of Jerusalem (Israel)
TiO{sub 2}, MoO{sub 3}, and WO{sub 3} have been dispersed in amorphous silica using the low temperature sol-gel procedure for xerogel preparation. These simply prepared amorphous compounds are proposed as possible alternatives to metal-substituted crystalline molecular sieves in H{sub 2}O{sub 2} oxidations. The metallosilicate compounds are catalytically active in the 30% aqueous H{sub 2}O{sub 2} oxidation of alkenes and alcohols provided the metal oxide precursor in the xerogel synthesis is a metal-dichlorodialkoxy compound yielding MO{sub x}(Cl)-SiO{sub 2}, and not the tetraalkoxy derivative yielding MO{sub x}-SiO{sub 2}. Catalyst efficiency is increased by using low loading of metal oxide in the silica framework. Excess H{sub 2}O{sub 2} reduces yield due to the detrimental effect of water, so more hydrophobic silicates with phenyl-silicon units increases catalyst efficiency. IR studies show that in the xerogels, the absorption at {approximately}950 cm{sup -1} is mainly due to the Si-OH vibrations in (SiO){sub 3}Si-PH units and not (SiO){sub 3}Si-OM as has often been reported in studies of titanium-substituted zeolites. {sup 29}Si MAS NMR spectra, sensitive to second neighbor atoms, of catalytically active MO{sub x}(Cl)-SiO{sub 2} versus inactive MO{sub x}-SiO{sub 2} reveals that the former have larger Q{sub 3} peaks and therefore more (SiO){sub 3}Si-OM units, indicating higher molecular dispersion of the metal oxide in the xerogels. Diffuse reflectance UV-vis measurements indicate, however, that this molecular dispersion is not complete as absorptions attributable to polymeric forms of metal oxide are observable. The catalytic xerogels are microporous with an average pore diameter of 15 {Angstrom} and a surface area of 750 m{sup 2}/g. 46 refs., 12 figs., 2 tabs.
- OSTI ID:
- 478760
- Journal Information:
- Journal of Catalysis, Vol. 166, Issue 2; Other Information: PBD: Mar 1997
- Country of Publication:
- United States
- Language:
- English
Similar Records
Ionic conductivity and structure of (LiCl)[sub 2]-Al[sub 2]O[sub 3]-SiO[sub 2] xerogels
Synthesis of mesoporous TS-1 using a hybrid SiO{sub 2}–TiO{sub 2} xerogel for catalytic oxidative desulfurization