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Abstract

Catalysis often requires spatial separation of active centres. In material science this translates to a challenge in the synthesis of such materials, namely core-shells. Yolk-shell materials, a type of core-shell materials, possess a void between the core and shell that can be advantageous in catalysis. Yolk-shell materials with zeolitic core have not been reported extensively, despite their potential applicability in catalysis. This stems from the non-spherical morphology and surface properties of the zeolites, which makes controlled coating without defects difficult. Herein, we report a strategy for the encapsulation of beta zeolite (HBEA) with disordered mesoporous silica shell (HBEA@void@mSiO₂). HBEA is chosen as the centre (yolk) due to its cuboidal shape. The process involves creation of two shells, (a) sacrificial shell composed of resorcinol and formaldehyde, and (b) mesoporous silica shell. The result is an organic@inorganic hybrid that is thermally treated to obtain the corresponding hybrid. Polyvinylpyrrolidone (PVP) is an important component of the synthesis which assists in obtaining a uniform coating around the core. Thorough morphological, structural, fractal and textural characterization of this material was performed by electron microscopy, XRD, SAXS and sorption techniques. The hybrid possesses a hierarchical structure with an increasing porosity and spatial isolation of the core by the presence of a void. The siliceous nature of HBEA@void@mSiO₂ also enables a post-synthesis treatment for functional modification with mercaptosilane groups. The synthesis process shown here is highly controllable and has laid a solid foundation for a generalized synthesis strategy to build functional yolk-shell materials based on zeolites.