Supramolecular self-assembled molecules as organic directing agent for synthesis of zeolites
Supramolecular self-assembled molecules as organic directing agent for synthesis of zeolites
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DOI：
10.1038/nature02909
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发表时间：
2004-09-16
期刊：
影响因子：
64.8
通讯作者：
Valencia, S
中科院分区：
文献类型：
--
作者：
Corma, A;Rey, F;Valencia, S
具有均匀微孔的固体材料，如沸石，可以作为分子混合物的选择性催化剂和吸附剂，通过分离那些足够小的分子进入它们的孔，同时留下较大的分子（1，2）。沸石A是具有高空隙体积的微孔材料。尽管其在工业上广泛使用，例如在分子分离和洗涤（3，4）中，但由于其差的酸催化活性和水热稳定性以及其低疏水性，其作为石油精炼材料的能力是有限的。这些特征最终是低骨架Si/Al比（通常约为1）和在孔和腔中产生的高阳离子分数的结果（1，2）。研究人员已经通过将Si/Al组合物增加到高达3（5-9）的比率来改变A型沸石的性质。在这里，我们描述了沸石A结构的合成表现出高Si/Al比高达无穷大（纯二氧化硅）。我们合成这些材料，命名为ITQ-29，使用超分子有机结构导向剂获得的自组装，通过π-π型相互作用，两个相同的有机阳离子部分。高度疏水的纯二氧化硅沸石A可用于烃分离，避免低聚反应，而具有高Si/Al比的材料提供优异的形状选择性裂化添加剂，用于提高流化催化裂化操作中的丙烯产率。我们还将我们的超分子结构导向剂的使用扩展到一系列其他沸石的合成。
Solid materials with uniform micropores, such as zeolites, can act as selective catalysts and adsorbents for molecular mixtures by separating those molecules small enough to enter their pores while leaving the larger molecules behind(1,2). Zeolite A is a microporous material with a high void volume. Despite its widespread industrial use in, for example, molecular separations and in detergency(3,4), its capability as a petroleum-refining material is limited owing to its poor acid-catalytic activity and hydrothermal stability, and its low hydrophobicity. These characteristics are ultimately a consequence of the low framework Si/Al ratio (normally around one) and the resulting high cationic fraction within the pores and cavities(1,2). Researchers have modified the properties of type-A zeolites by increasing the Si/Al compositions up to a ratio of three(5-9). Here we describe the synthesis of zeolite A structures exhibiting high Si/Al ratios up to infinity ( pure silica). We synthesize these materials, named ITQ-29, using a supramolecular organic structure-directing agent obtained by the self-assembly, through pi-pi type interactions, of two identical organic cationic moieties. The highly hydrophobic pure-silica zeolite A can be used for hydrocarbon separations that avoid oligomerization reactions, whereas materials with high Si/Al ratios give excellent shape-selective cracking additives for increasing propylene yield in fluid catalytic cracking operations. We have also extended the use of our supramolecular structure-directing agents to the synthesis of a range of other zeolites.