LTL Zeolite Spherical Crystallites via FAU Conversion
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Solution Overview
Problem
Conventional synthesis methods for LTL framework type zeolites often result in cylindrical crystals with one-dimensional channels, limiting catalyst activity and stability due to diffusion limitations, and there is a need for novel compositions with small crystal size and non-cylindrical morphology.
Innovation Solution
A method involving a reaction mixture of FAU framework type zeolite, hydroxide ions, a source of alkali metal, and water, with specific mole ratios, subjected to crystallization conditions to form polycrystalline aggregates of spherical or cube-like crystallites with average sizes between 10 to 50 nm, allowing for the production of LTL framework type zeolites with tunable morphology.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If conventional synthesis methods are used to produce LTL framework type zeolites, then cylindrical crystals with one-dimensional channels are formed, but mass transportation rates are limited due to diffusion limitations
Solution Approach 1:
The patent applies spheroidality by transforming the conventional cylindrical crystal morphology into spherical or cube-like crystallites. This curvature change eliminates the one-dimensional channel structure and creates isotropic diffusion pathways in all directions, thereby improving mass transportation rates and reducing diffusion limitations while maintaining the LTL framework type zeolite structure.
2Productivity
If conventional synthesis methods are used, then LTL framework type zeolites are produced, but crystal size is large causing diffusion limitations
Solution Approach 1:
The patent applies segmentation by dividing large crystals into smaller crystallites with average sizes of 10 to 50 nm. This segmentation increases the total surface area and creates multiple active sites, thereby improving catalyst activity while reducing the diffusion path lengths within each crystallite, which addresses the diffusion limitations associated with large crystal sizes.
3Shape
If surfactants or molecular modifiers are used to tune morphology, then crystal shape can be controlled, but the synthesis process becomes more complex
Solution Approach 1:
The patent applies the taking out principle by removing surfactants and molecular modifiers from the synthesis process. Instead of using these additional agents to control morphology, the patent achieves shape control through modified synthesis conditions and precursor ratios, thereby simplifying the synthesis process while still achieving the desired spherical or cube-like crystallite morphology.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The method effectively produces LTL framework type zeolites with small, non-cylindrical crystallites, enhancing mass transportation rates and catalyst performance by reducing diffusion limitations, and maintaining the basic crystal structure while allowing for calcination and post-synthesis modifications.
Implementation Method 1
K. Honda et al. (J. Nanosci. Nanotechnol. 2013, 13, 3020-3026) disclose the preparation of a LTL framework type zeolite in the absence of an organic structure directing agent by the hydrothermal conversion of a FAU framework type zeolite
Implementation Method 2
subjecting the reaction mixture to crystallization conditions sufficient to form crystals of the LTL framework type zeolite
Data Source
AI summary
Small crystal LTL framework type zeolites, characterized as polycrystalline aggregates, each of the aggregates comprising a plurality of spherical or cube-like crystallites and wherein each crystallite has an average crystallite size of from 10 to 50 nm, are disclosed. Such zeolites can be prepared by hydrothermal conversion of FAU framework type zeolites at low H2O/SiO2 mole ratios.