Titania-Silica Mixed Oxides: I. Influence of Sol-Gel and Drying Conditions on Structural Properties
Titania-Silica Mixed Oxides: I. Influence of Sol-Gel and Drying Conditions on Structural Properties
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DOI：
10.1006/jcat.1995.1118
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发表时间：
1995-04
影响因子：
7.3
通讯作者：
D. Dutoit;M. Schneider;A. Baiker
中科院分区：
文献类型：
--
作者：
D. Dutoit;M. Schneider;A. Baiker
通过醇盐-溶胶-凝胶工艺制备了具有高度分散钛的介孔二氧化钛-二氧化硅气凝胶，随后使用超临界CO{sub 2}进行半连续萃取。将酸性水解剂添加到由乙酰丙酮化物改性的四异丙氧基钛(IV)和四甲氧基硅(IV)在异丙醇中的溶液中。所得二氧化钛-硅胶通过不同的方法干燥，包括常规干燥、高温超临界干燥和超临界CO{sub 2}萃取（低温气凝胶）。通过N{sub 2}-物理吸附、X射线衍射、热分析和振动光谱（FTIR、FTRaman）研究了制备参数（水解路线、Ti含量、干燥方法和煅烧温度）对气凝胶和干凝胶结构和化学性质的影响。硅醇盐的预水解通常会导致较低的孔隙率，但在高达 1073 K 的煅烧温度下不会影响 Si-O-Ti 的连通性。传统干燥的干凝胶含有良好分散在二氧化硅基质中的钛，并且主要是微孔的。高温超临界干燥提供了微孔率可忽略不计的介孔至大孔气凝胶，但出现了不希望的锐钛矿偏析。对于低温气凝胶，名义 TiO{sub 2} 含量从 2 wt% 增加到 20 wt% 导致微孔率降低、BET 表面积更高（高达约 700 m{sup 2}/g），并且 Si-O-Timore » 物质的贡献增加。与此同时，Ti-O-Ti 连接性增加，但 X 射线分析没有任何长程有序的迹象。含有 20 wt% TiO{sub 2} 的低温气凝胶结合了介孔性、高 Ti 分散性和空气中高达 873 K 的结构稳定性，这是烯烃环氧化所需的性能。 64 条参考文献，10 个图，2 个标签。« 更少
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