TiO2/SiO2 mixed oxide catalysts prepared by sol-gel techniques. Characterization by solid state CP/MAS spectroscopy Article uri icon

abstract

  • The influence of synthesis parameters on the structural properties of mixed oxides derived from silicon tetraethoxide and titanium tetra-isopropoxide precursors has been studied by 29Si NMR speectroscopy. A first set of gels, prepared by complete hydrolysis of the individual precursors and subsequent mixing of the hydrosols, is characterized by comparatively narrow lines for the Q2, Q3, and Q4 silica sites. Both the chemical shift values and the time constants of 1H29Si magnetization transfer are similar to those found in pure silica gels. This indicates that these oxides consist of domains of the individual components. A different appearance of the CP/MAS spectra is noted for the second set of gels, which is prepared by addition of the titanium alkoxide component at a stage where the silicon alkoxide hydrolysis has only proceeded to about 50%25, on average. The spectra of these samples are characterized by broad lines for the three types of sites. Larger contributions observed for Q2 and Q3 sites in these samples are attributed to the presence of SiOTi bridges. The influence of preparation parameters such as hydrolysis pH, drying temperature, and pore ripening treatment by redispersion in base, is studied by monitoring the spectral and dynamic parameters derived from the CP/MAS spectra. © 1991.

publication date

  • 1991-01-01