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

Abstract

Hollow ZSM‐5 zeolites of size below one micrometer can be produced by desilication of crystals with aluminium zoning. The parent crystals have a core–shell structure: the core part has nearly no aluminium, whereas the aluminium content in the shell increases when extending to exterior surface. Transmission electron microscopy confirmed the preservation of the crystalline shell after base leaching, but could not identify its subtle change. An increase of the Si/Al ratio of the surface was detected upon leaching the parent material to form the hollow zeolite by using ambient pressure X‐ray photoelectron spectroscopy and infrared spectroscopy of substituted alkylpyridines. 27Al MAS NMR showed that base leaching results in a reduced percentage of distorted tetrahedrally coordinated aluminium. The reprecipitation of dissolved species occurs and tetrahedrally coordinated tin atoms can thus be introduced to the shell framework. Overall, the formation of hollow ZSM‐5 zeolites by desilication involves not only the removal of silicon‐rich core, but also a reduced percentage of exterior aluminium‐related acid sites, which should be considered while using hollow zeolites in acid‐catalyzed reactions.

Stable Palladium Oxide Clusters Encapsulated in Silicalite-1 for Complete Methane Oxidation

“…337 and 342.2 eV, respectively, can be assigned to PdO (Figure i). The line width of the Pd 3d peak increased by increasing the photon kinetic energy due to a decrease in resolving power of the beamline monochromator . Despite that, the Pd 3d peak intensity did not change significantly in the whole photoelectron kinetic energy range, suggesting that the palladium oxide particles were relatively homogeneously distributed.…”

Aromatics Production via Methanol-Mediated Transformation Routes

“…For example, para -xylene selectivity can be enhanced by depositing amorphous or crystalline silica composition on the individual ZSM-5 crystals. , In fact, aluminum zoning is well-known for ZSM-5 crystals synthesized with tetrapropylammonium ions (TPA + ) as a template . Over micrometer-sized ZSM-5 crystals, aluminum zoning was visualized by synchrotron-based micro-X-ray diffraction and atomic probe tomography (APT). , Over nanosized crystals, aluminum zoning still exists, , and van Bokhoven et al recently observed that the nanosized ZSM-5 crystals had a core–shell structure, in terms of aluminum distribution . The core part had nearly no aluminum, whereas the aluminum content in the shell gradually increased when extending to the exterior surface.…”

“…392,393 Over nanosized crystals, aluminum zoning still exists, 308,394 and van Bokhoven et al recently observed that the nanosized ZSM-5 crystals had a core−shell structure, in terms of aluminum distribution. 395 The core part had nearly no aluminum, whereas the aluminum content in the shell gradually increased when extending to the exterior surface. One could think that such an uneven distribution of aluminum might promote the location of Zn species close to the Brønsted acid sites in the shell, which could have an effect on the catalytic process.…”

Role of Zirconia in Oxide-Zeolite Composite for Thiolation of Methanol with Hydrogen Sulfide to Methanethiol

“…While the NaZSM-5 molecular sieve has been widely applied because of its various and adjustable active centers and characteristic microporous structure, adjusting the Si/Al ratio of the NaZSM-5 framework and constructing hierarchical porous structures has been pursued to create suitable active centers, strengthen molecular diffusion, and enhance the reactivity and selectivity while simultaneously inhibiting catalyst deactivation. Among the previous modification strategies, the common route involves impregnation and desiliconization/dealumination in acidic or basic environments [ 39 , 40 , 41 , 42 , 43 , 44 ]. ZrO 2 is a transition metal oxide with both acidic and basic properties [ 45 , 46 , 47 , 48 , 49 ], in which its monoclinic (m) and tetragonal (t) crystalline phases can be used as catalysts or carriers.…”