Hollow Zeolite Structures: An Overview of Synthesis Methods

Abstract

SSCI-VIDE+ING+CPG:DFA:ATUInternational audienceHollow capsules with dimensions below 1 mu m have recently attracted much attention due to their potential applications as catalysts as well as biomedical and pharmaceutical vectors for controlled drug delivery. Among them, hollow zeolites are particularly interesting because they possess (0 a crystalline structure, which greatly improves their hydrothermal and chemical stability as compared to amorphous silica analogs and (ii) a microporous network that acts as a shape-selective membrane. Moreover, their properties can be continuously tuned by changing their composition, in particular the framework aluminum content. In this perspective review, we examine the recent progress in the development of synthetic methods for the preparation of hollow zeolite and zeotype structures, from templating routes providing large polycrystalline capsules to controlled dissolution methods leading to nanometer-sized hollow single crystals. The applications of these materials will be illustrated and discussed, namely their main potential as catalytic nanoreactors, these being materials particularly adapted for the encapsulation and the confinement of metal nanoparticles. Critical perspectives on future materials with specific properties are also addressed, particularly those with less common zeolite structures and/or compositions

Gemini‐type cationic surfactant‐directed synthesis of hollow ZSM‐5 zeolite with intracrystalline mesopores and its application in the hydroxylation of phenol

“…When the temperature is increased to 150 °C, the effect of phase‐separation can be alleviated by the higher autogentic pressure in the hydrothermal reactor and the nuclei of MFI structure will grow faster on the surface and interior of GQHAC agglomerates by consuming the nearby aluminosilicate domain . According to the theory of Ostwald Ripening, the internal nuclei of ZSM‐5 zeolite will be easily dissolved in the process of crystallization, resulting in the formation of hollow morphology with MFI structure and intracrystalline mesopores in the shell . As a result, the newly created mesopores go through a transformation of core‐shell structure with amorphous mesopores to hollow structure with intracrystalline mesopores by increasing the crystallization temperature.…”

Demonstration of Improved Effectiveness Factor of Catalysts Based on Hollow Single Crystal Zeolites

“…The “hollowing” zeolite process has been widely reported for zeolites with MFI framework type, leading to nanoboxes with regular zeolitic walls whose thickness can be controlled down to a few nanometers . More recently, we succeeded in preparing hollow Beta and Y zeolite crystals, with *BEA and FAU framework types, respectively …”

Variation of Aluminium Distribution in Small‐Sized ZSM‐5 Crystals during Desilication

“…If hollow crystals possess zeolite shells, encapsulated nanoparticles can be protected from external poisoning due to the molecular sieving effect . Recently, typical strategies of making hollow zeolite crystals have been reviewed . Hollow crystals produced by template‐based methods are usually large, in the micrometer range with polycrystalline walls.…”