Engineering Mesopore Formation in Hierarchical Zeolites under High Hydrostatic Pressure

Abstract

Tailoring the textural properties of porous materials is of paramount importance to optimize their performance in a variety of applications. To this end, critical synthesis parameters influencing crystallization and reorganization of porous materials need to be identified and judiciously controlled. Although the effect of pressure on chemical transformations is ubiquitously present, its impact on fabricating porous materials with tailored physicochemical properties remains unexplored and its potential untapped. In this work, we disclose a detailed study on the effects of high hydrostatic pressure on the formation of well-controlled intracrystalline mesopores in ultrastable Y (USY) zeolite by the so-called surfactant-templating method. The rate of mesopore formation significantly increases upon elevating the pressure, whereas the average size of the mesopores—directed by the self-assembly of the surfactant—decreases. By simultaneously adjusting the external pressure and selecting surfactants of different lengths, we have been able to precisely control the mesopore size in the USY zeolite. Our findings clearly show that external hydrostatic pressure can be used to both accelerate mesopore formation and engineer their size with subnanometer precision. As a second example, we investigated the effect of external pressure on the synthesis of MCM-41. The results on MCM-41, consistent with our observations on the USY zeolite, further confirm that the use of high external pressure greatly affects the self-assembly behaviors of the amphiphilic molecules involved in the synthesis/modification of the porous materials. Our results show that the high-pressure approach represents an untapped opportunity for synthesis/modification of functional porous materials that will likely yield new discoveries in this field.