A Stable and Highly Active Hybrid Mesoporous Solid Acid Catalyst
A Stable and Highly Active Hybrid Mesoporous Solid Acid Catalyst
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DOI：
10.1002/adma.200500426
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发表时间：
2005-08
影响因子：
29.4
通讯作者：
K. Nakajima;I. Tomita;M. Hara;S. Hayashi;K. Domen;J. Kondo
中科院分区：
文献类型：
--
作者：
K. Nakajima;I. Tomita;M. Hara;S. Hayashi;K. Domen;J. Kondo
介孔二氧化硅[1ą10]内表面的有机修饰由于在催化、[11，12]吸附和分离等方面的潜在应用而受到广泛关注。[13]烷基磺酸通过合成后接枝或一锅合成法共价连接到二氧化硅表面，用于在介孔二氧化硅和周期性介孔有机二氧化硅(PMO)中制备强酸中心。迄今为止，[14ą24]磺酸基团是通过丙硫醇基团[15ą20，24]氧化得到的，这会导致介观有序性的丧失和织构性质的退化。此外，硫醇基团[19，24]的不完全氧化导致了催化反应中硫物种的严重浸出。为了构建新型介孔固体酸催化剂，我们团队开发了一种化学修饰技术，在PMO材料的表面创建催化活性中心。由此产生的有机基团在硅酸盐基质中的均匀分布为表面结合的有机基团提供了顺利的可访问性，具有进一步修饰的空间。在这里，通过两步化学修饰，成功地将PMO表面的乙烯中心(ą、CHCH、ą)转化为苯磺酸基团(Ph、ą、SO3H)。该过程包括与苯环丁烯[25]的DielsąAlder反应，然后在浓硫酸中进行磺化。这是通过化学修饰在PMO中创建催化活性中心以构建杂化介孔固体酸催化剂的第一个例子。这一方法代表着在开发实用的周期性介孔有机二氧化硅材料方面的重大突破。图1显示了杂化介孔固体酸催化剂的合成路线和每种杂化材料的结构性质的变化。以乙烯桥联有机硅烷化合物(C2H5O)3SiąCHCHąSi(OC2H5)3为起始原料，在嵌段共聚表面活性剂的存在下，在酸性溶液中水解和缩合，制备了杂化介孔乙烯-二氧化硅(HME)。得到的材料具有p6 mm对称性的六方有序介孔结构，桥联的乙烯基团均匀地结合到骨架中，没有SiąC键断裂。通过与苯环丁烯的DielsąAlder反应，在表面的乙烯位引入了侧基亚苯基。所结合的苯撑在1，2-取代位上通过两个烷基链固定在骨架上(图1C)。在此过程中，虽然比表面积从652m2·g·ą-1略降至506m2·g-1，但仍完全保持了原有的六方介孔结构。介孔直径从6.8 nm到6.0 nm的变化，同时保持了原来狭窄的孔径分布，这表明表面上的乙烯中心发生了均匀的修饰。然后，通过在浓硫酸中进行简单处理，可以很容易地实现侧基苯基的磺化。该材料保留了原有的有机ą无机网络和介孔结构，其孔径为6.0 nm，比表面积为565m2 gą1，中孔体积为0.78mL gą1。因此，可以合理地假设，在不破坏原始介孔结构和介观有序性的情况下，乙烯基苯磺酸基团(PhąSO3 H)的演化是可以实现的(见支持信息).核磁共振分析证实了骨架中有机基团的变化。13C交叉…
The organic tailoring of internal surfaces of mesoporous silica [1ą10] has recently received much attention owing to a range of potential applications in catalysis,[11, 12] adsorption, and separation.[13] The covalent attachment of alkylsulfonic acid groups to silica surfaces by post-synthesis grafting or one-pot synthesis has been proposed for the fabrication of strong acid sites in mesoporous silica and periodic mesoporous organosilica (PMO).[14ą24] Sulfonic groups have to date been obtained via the oxidation of propanethiol groups,[15ą20, 24] which results in a loss of mesoscopic ordering and degradation of textural properties. In addition, incomplete oxidation of the thiol groups [19, 24] leads to serious leaching of the sulfur species during catalytic reactions. For the construction of new types of mesoporous solid acid catalysts, our group has developed a chemical modification technique that creates catalytically active sites on the surface of PMO material. The resultant homogeneous distribution of organic groups in the silicate matrix provides smooth accessibility to the incorporated organic groups at the surface, with scope for further modification. Here, ethenylene sites (ąCHCHą) on the surface of PMO are successfully converted to phenylene sulfonic acid groups (PhąSO3H) by a two-step chemical modification. The procedure involves the DielsąAlder reaction with benzocyclobutene [25] followed by sulfonation in concentrated H2SO4. This is the first example of the creation of catalytically active sites in PMO by chemical modification for the construction of a hybrid mesoporous solid acid catalyst. This methodology represents a significant breakthrough in the development of practical periodic mesoporous organosilica materials. A schematic illustration of the synthetic pathway to the hybrid mesoporous solid acid catalyst and the change in the structural properties of each hybrid material is shown in Figure 1. The starting material, the ethenylene-bridged organosilane compound (C2H5O) 3SiąCHCHąSi (OC2H5) 3, is hydrolyzed and condensed in acidic solution in the presence of a block copolymer surfactant to prepare the hybrid mesoporous ethenylene-silica (HME). The resulting material exhibits a hexagonally ordered mesoporous structure with p6mm symmetry, and the bridged ethenylene groups are homogeneously incorporated into the framework without SiąC bond cleavage. The pendant phenylene groups are introduced at the ethenylene sites on the surface by the DielsąAlder reaction with benzocyclobutene. The incorporated phenylene is anchored to the framework by two alkyl chains at the 1, 2-substitution (Fig. 1C). Although the surface area decreases slightly from 652 to 506 m2 gą1 during this procedure, the original hexagonal mesoporous structure is completely preserved. The change in mesopore diameter from 6.8 to 6.0 nm while maintaining the original narrow pore size distribution is indicative of the homogeneous modification of ethenylene sites on the surface. The sulfonation of pendant phenylene groups can then be readily achieved by simple treatment in concentrated H2SO4. The original organicąinorganic network and mesoporous structure is retained, and the resulting material exhibits a uniform pore size of 6.0 nm, a relatively high surface area of 565 m2 gą1, and a mesopore volume of 0.78 mL gą1. Therefore, it is reasonable to suppose that the evolution of phenylenesulfonic acid groups (PhąSO3H) at ethenylene sites is achieved without degradation of the original mesoporosity and mesoscopic ordering (see Supporting Information). The change in organic groups in the framework was confirmed by NMR analysis. 13C cross …