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

Abstract

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-Timore » 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.« less

Authors:
; ;  [1]
  1. Swiss Federal Institute of Technology, Zurich (Switzerland)
Publication Date:
OSTI Identifier:
98954
Resource Type:
Journal Article
Journal Name:
Journal of Catalysis
Additional Journal Information:
Journal Volume: 153; Journal Issue: 1; Other Information: PBD: 15 Apr 1995
Country of Publication:
United States
Language:
English
Subject:
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

Citation Formats

Dutoit, D C.M., Schneider, M, and Baiker, A. Titania-silica mixed oxides: I. Influence of sol-gel and drying conditions on structural properties. United States: N. p., 1995. Web. doi:10.1006/jcat.1995.1118.
Dutoit, D C.M., Schneider, M, & Baiker, A. Titania-silica mixed oxides: I. Influence of sol-gel and drying conditions on structural properties. United States. https://doi.org/10.1006/jcat.1995.1118
Dutoit, D C.M., Schneider, M, and Baiker, A. Sat . "Titania-silica mixed oxides: I. Influence of sol-gel and drying conditions on structural properties". United States. https://doi.org/10.1006/jcat.1995.1118.
@article{osti_98954,
title = {Titania-silica mixed oxides: I. Influence of sol-gel and drying conditions on structural properties},
author = {Dutoit, D C.M. and Schneider, M and Baiker, A},
abstractNote = {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.},
doi = {10.1006/jcat.1995.1118},
url = {https://www.osti.gov/biblio/98954}, journal = {Journal of Catalysis},
number = 1,
volume = 153,
place = {United States},
year = {1995},
month = {4}
}