Epitaxial Growth of ZSM-5@Silicalite-1: A Core–Shell Zeolite Designed with Passivated Surface Acidity

Abstract

The design of materials with spatially controlled chemical composition has potential advantages for wide-reaching applications that span energy to medicine. Here, we present a method for preparing a core-shell aluminosilicate zeolite with continuous translational symmetry of nanopores and an epitaxial shell of tunable thickness that passivates Brønsted acid sites associated with framework Al on exterior surfaces. For this study, we selected the commercially relevant MFI framework type and prepared core-shell particles consisting of an aluminosilicate core (ZSM-5) and a siliceous shell (silicalite-1). Transmission electron microscopy and gas adsorption studies confirmed that silicalite-1 forms an epitaxial layer on ZSM-5 crystals without blocking pore openings. Scanning electron microscopy and dynamic light scattering were used in combination to confirm that the shell thickness can be tailored with nanometer resolution (e.g., 5-20 nm). X-ray photoelectron spectroscopy and temperature-programmed desorption measurements revealed the presence of a siliceous shell, while probe reactions using molecules that were either too large or adequately sized to access MFI pores confirmed the uniform shell coverage. The synthesis of ZSM-5@silicalite-1 offers a pathway for tailoring the physicochemical properties of MFI-type materials, notably in the area of catalysis, where surface passivation can enhance product selectivity without sacrificing catalyst activity. The method described herein may prove to be a general platform for zeolite core-shell design with potentially broader applicability to other porous materials.

Surface‐Passivated Hierarchically Structured ZSM5 Zeolites: High‐Performance Shape‐Selective Catalysts for para‐Xylene Production

“…According to previous reports, the passivation of the external surface of ZSM‐5 zeolites has been adopted by various post‐treatments, such as impregnating with B, Mg, and P elements, coating of inert silicalite‐1 layers, chemical liquid deposition (CLD) of tetraethoxysilane (TEOS), and mechanochemical approaches . However, in most cases, these passivation treatments always lead to a decrease of zeolite catalyst activity because of the pore blockage and/or loss of acid sites.…”

Strategies to Enhance the Catalytic Performance of ZSM-5 Zeolite in Hydrocarbon Cracking: A Review

“…It restrained the carbon depositing on the external surface, which avoided the decreasing accessibility of acid site in the pore channel. Overall, ZSM-5@silicalite-1 with passivated surface acid sites could enhance the catalytic stability and product selectivity without sacrificing its catalyst activity [38,39].…”

“…For zeolite prepared with the assistance of OSDA, not only the external surface Al but also large framework Al would be dissolved by HNO3 treatment. Rimer et al [38] designed ZSM-5 zeolite with passivated surface acidity by adding silicalite-1 shell on the external surface. Few acid sites exist on the external surface of ZSM-5 zeolite after Rimer et al [38] designed ZSM-5 zeolite with passivated surface acidity by adding silicalite-1 shell on the external surface.…”

“…Rimer et al [38] designed ZSM-5 zeolite with passivated surface acidity by adding silicalite-1 shell on the external surface. Few acid sites exist on the external surface of ZSM-5 zeolite after Rimer et al [38] designed ZSM-5 zeolite with passivated surface acidity by adding silicalite-1 shell on the external surface. Few acid sites exist on the external surface of ZSM-5 zeolite after adding silicalite-1 shell.…”

Structural features of core–shell zeolite–zeolite composite and its performance for methanol conversion into gasoline and diesel

“…[1][2][3][4][5][6][7] The high acid density of zeolite catalysts can be alleviated by processes such as hydrothermal treatment in the presence of steam, [8][9][10][11][12][13] acid leaching, 14,15 and extraction of aluminum from the framework of zeolite by reacting with SiCl 4 , [16][17][18] EDTA,17 or (NH 4 ) 2 SiF 6 . [16][17][18] The disadvantage of steaming is the partial amorphization of the zeolite framework.…”