Titania-silica mixed oxides: I. Influence of sol-gel and drying conditions on structural properties

Journal Article · Sat Apr 15 00:00:00 EDT 1995 · Journal of Catalysis

DOI:https://doi.org/10.1006/jcat.1995.1118· OSTI ID:98954

Dutoit, D C.M.; Schneider, M; Baiker, A ^[1]

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1. Swiss Federal Institute of Technology, Zurich (Switzerland)

Mesoporous titania-silica aerogels with highly dispersed titanium have been prepared by an alkoxide-sol-gel process with ensuing semicontinuous extraction using supercritical CO{sub 2}. An acidic hydrolysant was added to a solution of tetraisopropoxytitanium (IV) modified by acetylacetonate and tetramethoxysilicon (IV) in isopropanol. The resulting titania-silica gels were dried by different methods, including conventional drying, high-temperature supercritical drying, and extraction with supercritical CO{sub 2} (low-temperature aerogel). The influence of preparation parameters (the hydrolysis route, Ti-content, drying method, and calcination temperature) on the structural and chemical properties of the aero- and xerogels was studied by means of N{sub 2}-physisorption, X-ray diffraction, thermal analysis, and vibrational spectroscopy (FTIR, FTRaman). Prehydrolysis of the silicon alkoxide generally led to lower porosity, but did not influence the Si-O-Ti connectivity up to a calcination temperature of 1073 K. The conventionally dried xerogels contained titanium well-dispersed in the silica matrix and were predominantly microporous. High-temperature supercritical drying afforded meso- to macroporous aerogels with negligible microporosity, but undesired segregation of anatase. With the low-temperature aerogels, an increase in the nominal TiO{sub 2} content from 2 to 20 wt% resulted in lower microporosity, higher BET surface area (up to ca. 700 m{sup 2}/g), and a rise in the contribution of Si-O-Ti species. Concomitantly the Ti-O-Ti connectivity increased without any indication of long-range ordering from X-ray analysis. The low-temperature aerogel with 20 wt% TiO{sub 2} combined mesoporosity with high Ti dispersion and structural stability up to 873 K in air, properties desirable for epoxidation of olefins. 64 refs., 10 figs., 2 tabs.

• OSTI ID: 98954
• Journal Information: Journal of Catalysis, Vol. 153, Issue 1; Other Information: PBD: 15 Apr 1995
• Country of Publication: United States
• Language: English

Related Subjects

40 CHEMISTRY
10 SYNTHETIC FUELS
TITANIUM OXIDES
STRUCTURAL CHEMICAL ANALYSIS
SILICA
SOL-GEL PROCESS
CHEMICAL PREPARATION
SUPERCRITICAL GAS EXTRACTION
SORPTIVE PROPERTIES
X-RAY DIFFRACTION
THERMAL ANALYSIS
ABSORPTION SPECTROSCOPY
RAMAN SPECTROSCOPY
SURFACE AREA
POROSITY
PHASE STUDIES
X-RAY SPECTROSCOPY