Core–Shell Zeolite Microcomposites

Abstract

Core–shell zeolite composites possessing a core and a shell of different zeolite structure types have been synthesized. A characteristic feature of the obtained composites is the relatively large single‐crystal core and the very thin polycrystalline shell. The incompatibility between the core crystals and the zeolite precursor mixture yielding the shell layer has been circumvented by the adsorption of nanoseeds on the core surface, which induced the crystallization of the shell. The pretreated core crystals are subsequently subjected to a continuous growth in a zeolite precursor mixture. The feasibility of this synthetic approach has been exemplified by the preparation of core–shell β‐zeolite–silicalite‐1 composites. The synthesized composites have been characterized using X‐ray diffraction, high‐resolution transmission electron microscopy, and scanning electron microscopy. The integrity of the shell layer has been tested via N2‐adsorption measurements on materials comprising a calcined core (β‐zeolite) and a non‐calcined tetrapropylammonium (TPA)‐containing shell, the latter being non‐permeable for the N2 molecules. These measurements have shown that 86 % of the β‐zeolite crystals are covered with a defect‐free TPA–silicalite‐1 shell after a single hydrothermal treatment, while after three consecutive crystallization steps this value reaches 99 %. The shell integrity of the calcined composite has been studied by the adsorption of butane, toluene, and 1,3,5‐trimethylbenzene, which confirmed the superior performance of the triple‐shell composites.

Fixed-Bed Adsorption Separation Of Xylene Isomers over SiO2/Silicallite-1 Core-Shell Adsorbents

“…A similar report has been found in literature by Bouizi et al where they studied the adsorption capacity of hydrocarbon molecules using β-zeolite/silicalite-1 coreshell adsorbents. They found that the core has higher adsorption capacity than shell while the core-shell adsorbent shows the intermediate capacity of core and shell [15].…”

“…Zeolite core-shell composites are novel class of materials for their potential application in the field of catalysis, adsorption, and storage and controlled release [11][12][13][14][15]. The application of these materials in adsorption based separation process has not been fully explored.…”

“…This is because of that the pore size of silicalite-1 is smaller than the kinetic diameter of trimethylbezene. They have shown that silicalite-1 particles (~1µm) have less capacity of adsorption of trimethylbezene in comparison with β-zeolite core and the capacity of adsorption was even much lower when core-shell particles used as adsorbent [15]. Casado et al reported the gas adsorption properties of hollow zeolite sphere [13].…”

Silicalite-1 Shell Synthesized onto Cylinder-Shaped ZSM-5 Extrudate for Disproportionation of Toluene into Para-Xylene

“…A number of core/shell zeolite composites have been reported, including ZSM-5/silicalite-1 [14][15][16], LTA/FAU [17], EMT/FAU [18], CHA/SOD [19], BEA/MFI [20], MFI/AFI [2,21], etc. Zheng et al [22] obtained the Y/Beta composite with a core/shell structure through adding NaY zeolite into the precursor solution for synthesizing Beta zeolite; the composite showed an increased conversion in catalytic cracking of noctane.…”

Spheres of Microporous Titanosilicate Umbite with Hierarchical Pore Systems

“…[11] Core-shell zeolite composites possessing a core and a shell of different zeolites would be analogous materials. [12] Also, macroporous silicates with zeolite (silicalite-1) frameworks have been prepared by hydrothermal synthesis by using arrays of monodisperse polystyrene spheres as templates [6] or by alternating layers of silicalite-1 nanoparticles and oppositely charged polyonic macromolecules which are sequentially adsorbed onto micrometric latex spheres and then assembled into ordered macroporous monoliths, [13] micro/meso/macroporous organized silicalite-1 monoliths and mesoporous films by starch gel templating, [4] and self-supporting porous zeolite membranes with spongelike architectures and zeolitic microtubes from cellulose acetate filter membrane. [14] Inexpensive and environmentally benign biological species are excellent for serving as macrotemplates for the synthesis of hierarchical structures, [15] while the cellular tissue of wood [16] and pinewood char [17] have been used to fabricate ordered macro and micropore structures.…”