Abstract
This paper deals with the synthesis conditions–defect formation relationship in zeolites. Silicalite‐1 (MFI‐type) is used as a model material. Samples synthesized from a system with high basicity (at 100 °C), a system with moderate basicity (at 150 °C), and a fluoride‐containing system in neutral medium (at 170 °C) are compared. Well‐crystallized materials with sizes ≈0.1, 1–10, and 30–40 µm are obtained. The samples are analyzed by complementary methods providing information on the short‐ and long‐range order in the zeolite framework. A strong correlation between the number of point defects in the zeolite framework and preparation conditions is established. Silicalite‐1 synthesized under mild synthesis conditions from a highly basic system exhibits a larger number of framework defects and thus low hydrophobicity. Further, the calcined samples are subjected to aluminum and silicon incorporation by postsynthesis treatment. The Al/Si incorporation in the zeolite framework and its impact on the physicochemical properties is studied by XRD, TEM/SEM, solid‐state NMR, FTIR, and thermogravimetric analyses. The defects healing as a function of the number of point defects in the initial material and zeolite crystal size is evaluated. The results of this study will serve for fine‐tuning zeolite properties by in situ and postsynthesis methods.
Highlights
The most commonly utilized molecular sieve materials at large scales are the microporous alumosilicate zeolites
We studied the number of framework defects in silicalite-1 crystals as a function of synthesis conditions
It was found that the basicity of the system and the crystallization temperature have a pronounced effect on the number of framework defects and, hydrophobicity/hydrophilicity of the zeolite
Summary
The most commonly utilized molecular sieve materials at large scales are the microporous alumosilicate zeolites These crystalline solids possess an ordered system of voids and/or channels.[1] Their structure consists of tetrahedra involving a central T atom (T = Si, Al, Ge, B, ...) surrounded by oxygen atoms at vertices. The study demonstrates how the drawback of a large number of structural defects could be turned into an advantage that facilitates the engineering of zeolite properties by post-synthesis treatment
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