Supramolecular approaches for pore expansion in mesoporous Y zeolites

With a motivation of improving accessibility for mass transport of sterically bulky molecules, we demonstrate the synthesis of mesoporous Y zeolite catalysts with increased pore size. Our supramolecular approach relies on the swelling of surfactant assemblies with organic molecules, such as 1,3,5-trimethylbenzene (TMB), para-xylene (p-xylene), and 1,4-diisopropylbenzene (DIPB), as well as cosolvents consisting of ethanol and tert-butyl alcohol (TBA). With both trimethylalkylammonium bromide (CnTAB, n = 16 and 18) surfactants investigated, TMB exhibits a stronger swelling effect compared with both p-xylene and DIPB, which suggests an optimum in the hydrophobicity of the swelling agent. Cosolvents such as TBA and ethanol act as pore-size and porosity property modulators, with TBA exhibiting a greater degree of mesopore expansion than ethanol. Our optimized material consisted of a mesopore size of 6.8 nm and a mesopore volume of 0.41 cm3/g, which was synthesized with a TMB/C18TAB ratio of 12. The catalytic results of Friedel Crafts Acylation (FCA) of 2-methoxynaphthalene (2-MN) reaction prove that the synthesis of the larger mesopores via swelling in this material preserves accessibility of catalytic sites. The addition of swelling agents and cosolvents decreases the mesopore volume as a result of a lower NaOH activity, and conducting syntheses with a higher NaOH concentration compensates for this. The effects of mesopore expansion could not be achieved postsynthetically, by treating an as-made conventional mesoporous Y material with TMB swelling agent. This emphasizes the importance of retaining flexibility in the surfactant assembly when performing mesopore expansion via swelling that is driven by non-covalent interactions.