Supramolecular self-assembled molecules as organic directing agent for synthesis of zeolites

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Abstract
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 behind1,2. Zeolite A is a microporous material with a high void volume. Despite its widespread industrial use in, for example, molecular separations and in detergency3,4, 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 cavities1,2. Researchers have modified the properties of type-A zeolites by increasing the Si/Al compositions up to a ratio of three5,6,7,8,9. 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 π–π 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.

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