![]() The inert Silicalite‐1 shell covered the external acidic sites of the Beta zeolite core, suppressing dehydration and non‐enantioselective transesterification of the alcohol. In the present review, besides on the hierarchically porous all-zeolite material, special focus is laid on the preparation of zeolitic composite materials with hierarchical porosity capable to face the demands of industrial application.īeta–Silicalite‐1 core–shell microcomposites with controllable shell thickness were synthesized and used as racemization catalysts in the one‐pot dynamic kinetic resolution (DKR) of secondary alcohols by using lipase‐catalyzed transesterification. ![]() Very often, such strategies with their underlying principles were developed for improving the performance of the final materials in different technical applications like adsorptive or catalytic processes. In addition, this review might serve as a toolbox providing several synthetic and post-synthetic strategies to prepare zeolitic or zeolite containing material with tailored hierarchical porosity. A classification of hierarchical porosity is proposed based on the flow distribution pattern within the respective pore systems. This review is a survey into the world of hierarchical systems with special focus on hierarchically porous zeolite materials. Especially mass-flow related systems in the natural environment feature special hierarchically branched patterns. The property 'hierarchy' is mainly characterised by a certain ordering of individual elements relative to each other, often in combination with a certain degree of branching. 'Hierarchy' is a property which can be attributed to a manifold of different immaterial systems, such as ideas, items and organisations or material ones like biological systems within living organisms or artificial, man-made constructions. As compared with the commercial ZSM-5 zeolite, the composite catalyst exhibits excellent catalytic performances with a longer catalytic life as well as a higher conversion and a slightly higher yield of diesel oil. The adjustable thickness and SiO2/Al2O3 ratio of the shell offer the as-synthesized composite a potential and high-efficiency catalyst for methanol conversion into gasoline and diesel. Aluminum species were observed to transfer from the alumina-rich cores to the high-silica shells. The structural, crystalline, and textural properties of the as-synthesized samples were characterized by x-ray powder diffraction (XRD), energy-dispersive x-ray spectroscopy, X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), transmission electron microscopy (TEM), selected area electron diffraction (SAED), N2 adsorption-desorption, in situ IR spectra of pyridine and NH3-TPD. Acid sites associated with framework Al on exterior surfaces of ZSM-5 zeolite cores are therefore passivated in different degrees by the epitaxial MFI zeolite shell. Zeolite–zeolite composite composed of alumina-rich hierarchically porous ZSM-5 cores and high-silicon MFI shells was prepared by a hydrothermal synthesis procedure, in which a commercial ZSM-5 zeolite with a SiO2/Al2O3 of 36 was treated by an alkaline solution and then used as a supporter for epitaxial growth of a polycrystalline Silicalite-1 zeolite shell (denoted as MMZsa). The method described herein may prove to be a general platform for zeolite core-shell design with potentially broader applicability to other porous materials. The synthesis of 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. 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. 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). Transmission electron microscopy and gas adsorption studies confirmed that silicalite-1 forms an epitaxial layer on ZSM-5 crystals without blocking pore openings. 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). 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. The design of materials with spatially-controlled chemical composition has potential advantages for wide-reaching applications that span energy to medicine.
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