Amorphous Microporous Titania–Silica Mixed Oxides: Preparation, Characterization, and Catalytic Redox Properties
Amorphous Microporous Titania–Silica Mixed Oxides: Preparation, Characterization, and Catalytic Redox Properties
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DOI：
10.1006/jcat.1996.0349
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发表时间：
1996-10
影响因子：
7.3
通讯作者：
S. Klein;Serge Thorimbert;W. Maier
中科院分区：
文献类型：
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作者：
S. Klein;Serge Thorimbert;W. Maier
在没有螯合剂或预水解技术的情况下，通过简单的酸催化溶胶-凝胶过程，获得了微孔二氧化钛-二氧化硅混合氧化物，其孔径为0.7 nm，钛在二氧化硅基体中高度分散，具有窄单峰孔径分布。醇钛 (IV) 和四乙氧基硅烷 (TEOS) 的混合物在醇溶液中用盐酸水溶液水解，然后煅烧，产生无定形微孔混合氧化物。化学成分没有限制，涵盖了从微孔二氧化硅到微孔二氧化钛的整个范围。通过物理吸附（Ar和N2）、X射线粉末衍射、光谱技术、高分辨率TEM（结合EDX和电子衍射）和催化测试反应（烯烃的环氧化、饱和烃的选择性氧化），研究了材料的结构和化学性质作为制备参数（例如酸、二氧化钛或水含量、醇的性质、凝胶化温度、干燥条件和钛源）的函数。高钛分散度受到钛源和/或溶胶-凝胶过程中使用的醇的变化的负面影响。在最佳酸浓度下，检测到随着 Si/Ti 比率的变化，BET 表面积的增加。硅过量的材料在高达 1173 K 的 X 射线下保持非晶态。吡啶处理后的 FTIR 研究表明该材料仅具有弱酸性。通过 DRIFT 光谱观察到，随着 Ti 含量的增加，Ti-O-Ti 连接性增加，导致环氧化活性降低。该玻璃不仅表现出与其他含二氧化钛材料相当的 TBHP 选择性氧化反应催化活性，而且烯烃的尺寸选择性环氧化被解释为由于其独特的微孔性而产生的形状选择性。水和辛烷的竞争性吸附实验表明，无定形氧化物的亲水性是与其沸石类似物相比的主要区别。
Microporous titania–silica mixed oxides with a narrow monomodal pore size distribution at pore diameters of 0.7 nm with highly dispersed titanium in the silica matrix have been obtained by a simple acid-catalyzed sol–gel process in the absence of chelating agents or the prehydrolysis techniques. A mixture of titanium(IV)alkoxide and tetraethoxysilane (TEOS) has been hydrolysed in alcoholic solution with aqueous hydrochloric acid followed by calcination, resulting in amorphous, microporous mixed oxides. There is no limitation on the chemical composition, which covers the whole range from microporous silica to microporous titania. The structural and chemical properties of the materials as a function of preparation parameters (such as acid, titania, or water content, respectively, nature of alcohol, gelation temperature, drying conditions, and titanium source) have been studied by means of physisorption (Ar and N2), X-ray powder diffraction, spectroscopic techniques, high resolution TEM (in combination with EDX and electron diffraction) and catalytic test reactions (epoxidation of olefins, selective oxidations of saturated hydrocarbons). The high Ti dispersion was negatively affected by changes in the Ti source and/or the alcohol used for the sol–gel process. Increasing BET surface areas were detected as function of the Si/Ti ratio at an optimum in acid concentration. The Si-excess materials stayed X-ray amorphous up to 1173 K. FTIR studies after pyridine treatment showed the materials having weak acidity only. With increasing Ti content an increase in Ti–O–Ti connectivity is observed by DRIFT spectroscopy, resulting in a decrease in epoxidation activity. The glasses show not only catalytic activity for selective oxidation reactions with TBHP comparable with that of other titania containing materials, but size selective epoxidations of olefins are interpreted as shape selectivity resulting from their distinct microporosity. Competitive adsorption experiments of water and octane suggest the hydrophilicity of the amorphous oxides to be the major difference in comparison to their zeolitic analogues.