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Defining aluminum-zoning during synthesis of ZSM-5 zeolites

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Abstract

ZSM-5 zeolites attract considerable attention owing to their wide range of applications in catalysis and separation. The crystals that are synthesized with tetrapropylammonium ions (TPA+) as the template show aluminum-zoning, i.e. aluminum being concentrated in the rim part of the crystal. Here, we study the aluminum distribution within individual crystals as a function of synthesis time and find that the degree of aluminum-zoning evolves. Crystals with inhomogeneous aluminum distribution persist since their emergence from the early stages of hydrothermal treatment. The degree of aluminum-zoning in the crystals increases with the synthesis time, accompanied by an increase in the crystal size and subsequently the formation of a well-defined crystal morphology. This indicates a gradual aluminum migration toward the crystal surface during the course of crystallization. Moreover, the addition of high-aluminum-containing species to the existing crystals preferentially takes place at the late stages of synthesis, which contributes to the inhomogeneous aluminum distribution within a crystal. As a result, the finally formed crystals have not only the largest crystal size but also the highest degree of aluminum-zoning. The insight into the origin of aluminum-zoning that our work provides advances our understanding of the relationship between aluminum distribution in zeolites and the synthesis time to design better catalysts.

Graphical abstract: Defining aluminum-zoning during synthesis of ZSM-5 zeolites

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Publication details

The article was received on 03 Oct 2019, accepted on 02 Dec 2019 and first published on 02 Dec 2019


Article type: Paper
DOI: 10.1039/C9CP05423E
Phys. Chem. Chem. Phys., 2020, Advance Article
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    Defining aluminum-zoning during synthesis of ZSM-5 zeolites

    T. Li, F. Krumeich, M. Chen, Z. Ma and J. A. van Bokhoven, Phys. Chem. Chem. Phys., 2020, Advance Article , DOI: 10.1039/C9CP05423E

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