Exploring silanols on the surface of mesopores in hierarchical NaX zeolites: synthesis of amphiphilic catalysts for condensation reactions

Abstract

The Knoevenagel condensation reaction is an important route for C-C bonds formation and can be catalyzed by zeolites with high aluminum content, such as the NaX zeolite, with FAU topology. Recent results have demonstrated that the hierarchical NaX zeolite exhibits significantly higher catalytic performance in this reaction due to the improved mass transport in mesopores. Silanols are created when mesopores are introduced in zeolite crystals and can be used to modify the properties of the catalyst. During the condensation reaction, formed water can impair the catalytic activity by chemisorbing on hydrophilic sites. The hydrophobization of the surface to aid in the expulsion of water could overcome this problem. This project intends to simultaneously improve the accessibility to the catalytic sites of NaX zeolites, synthesizing hierarchical mesoporous structures, and to use the silanols on the surface of the mesopores to anchor hydrophobic groups, in order to increase the catalytic activity by moving water during the Knoevenagel condensation reaction. Our novel approach can extend the application of hierarchical zeolites in catalysis beyond the diffusional aspect.