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Synthesis of Zeolites Using the ADOR (Assembly-Disassembly-Organization-Reassembly) Route
Published on: April 3, 2016
Do zeolite precursor species really exist in aqueous synthesis media?
Christopher T G Knight1, Jingpeng Wang, Stephen D Kinrade
1School of Chemical Sciences, University of Illinois at Urbana-Champaign, 600 South Mathews Avenue, Urbana, IL 61801, USA.
Physical Chemistry Chemical Physics : PCCP
|June 29, 2006
Summary
This study challenges previous findings on tetrapropylammonium silicate mixtures, showing that proposed silicate oligomers are misidentified. Silicalite-1 formation likely involves simpler precursors than previously suggested.
Area of Science:
- Materials Chemistry
- Solid-State Chemistry
- Zeolite Synthesis
Background:
- A previous study proposed specific silicate oligomers, including a pentacyclic dodecamer, as nanoprecursors for silicalite-1 zeolite formation.
- These proposed precursors were identified in tetrapropylammonium (TPA) silicate mixtures with a specific molar composition.
Purpose of the Study:
- To re-examine the silicate oligomer speciation in TPA silicate mixtures using advanced NMR techniques.
- To verify or refute the existence and proposed roles of the previously identified prismatic double five-ring and pentacyclic dodecamer species.
- To clarify the precursor species involved in the synthesis of silicalite-1.
Main Methods:
- Utilized two-dimensional (29)Si COSY NMR spectroscopy.
- Analyzed a tetrapropylammonium silicate mixture enriched in the (29)Si isotope.
Main Results:
- Demonstrated that previously assigned NMR signals were erroneous.
- Showed the signal attributed to the double five-ring actually corresponds to the pentacyclic octamer.
- Revealed that signals assigned to the pentacyclic dodecamer originated from three distinct, separate species.
Conclusions:
- The existence of the proposed complex silicate oligomers (double five-ring and pentacyclic dodecamer) as precursors for silicalite-1 is not supported by this study.
- Silicalite-1 formation likely proceeds through simpler precursor species, such as the orthosilicate anion, rather than complex sequential condensation.
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