Interzeolite Transformation for Metal Encapsulation Without SDA
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Solution Overview
Problem
Encapsulating metal clusters within silica-rich zeolites like ZSM-5 is challenging due to high crystallization temperatures and pH requirements, making direct hydrothermal synthesis with ligand-stabilized metal precursors and post-synthesis exchange methods impractical for medium-pore zeolites.
Innovation Solution
A method involving interzeolite transformation of lower framework density zeolites into higher framework density zeolites without organic structure directing agents (SDA), using a basic solution with specific NaOH/SiO2 and H2O/SiO2 ratios, and temperatures above the crystallization temperature of the parent zeolite, allowing for the encapsulation of metals like Pt, Rh, and Ru within zeolites such as ZSM-5, SSZ-35, and chabazite.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If direct hydrothermal synthesis is used to encapsulate metal clusters in silica-rich zeolites like ZSM-5, then metal encapsulation can be achieved, but the high crystallization temperatures and pH requirements make the process impractical
Solution Approach 1:
The patent applies preliminary action by first forming a parent zeolite structure with lower framework density that can accommodate metal precursors at milder conditions, then subsequently transforming this parent structure into the desired daughter zeolite with higher framework density. This two-step approach allows metal encapsulation to occur before the high-temperature crystallization phase, avoiding the impracticality of direct high-temperature synthesis while still achieving the target zeolite structure with encapsulated metals.
2Reliability
If post-synthesis exchange methods are used to encapsulate metals in zeolites, then metal encapsulation is possible, but the small apertures in small and medium-pore zeolites preclude this approach
Solution Approach 1:
The patent overcomes the aperture limitation by performing metal precursor incorporation during the formation of the parent zeolite structure before the transformation to the final daughter structure. This preliminary action allows metal species to be introduced when the framework density is lower and apertures are larger, enabling successful encapsulation that would be impossible through post-synthesis exchange in the final high-density zeolite structure.
Solution Approach 2:
The patent uses the parent zeolite structure as an intermediary phase that facilitates metal encapsulation. The parent zeolite with lower framework density acts as a temporary container that accommodates metal precursors, then transforms into the desired daughter zeolite structure. This intermediary approach bypasses the aperture restriction problem by occurring in a structural phase that is more accessible to metal species.
3Ease of manufacture
If organic structure directing agents (SDA) are used in zeolite synthesis, then specific zeolite structures can be formed, but the patent aims to eliminate SDA use for more efficient and facile metal encapsulation
Solution Approach 1:
The patent extracts and eliminates the need for organic structure directing agents from the synthesis process. By using interzeolite transformation of parent structures, the method achieves specific zeolite structure formation without requiring SDA templates, thereby simplifying the synthesis process, reducing costs, and improving ease of manufacture while maintaining the desired zeolite structure and metal encapsulation.
4Reliability
If high pH and temperature conditions are used for zeolite crystallization, then silica-rich zeolites like ZSM-5 can be formed, but these conditions decompose ligand-stabilized metal precursors
Solution Approach 1:
The patent applies preliminary action by incorporating metal precursors into the parent zeolite structure before subjecting the material to the high pH and temperature conditions required for crystallization. The metal precursors are introduced during the formation of the parent structure at milder conditions where they remain stable, then the entire structure is subsequently transformed under harsh conditions. This timing ensures metal precursor stability during incorporation while still achieving the desired crystallization.
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
This method provides a general and efficient route for metal cluster encapsulation in silica-rich zeolites, preserving the metal clusters during transformation and avoiding the use of SDAs, which is not feasible with conventional methods, resulting in stable and catalytically active zeolite structures.
Implementation Method 1
converting the lower framework density (FD) zeolite to a zeolite having higher framework density values through direct hydrothermal synthesis
Implementation Method 2
the conversion is conducted by direct hydrothermal synthesis in a basic solution having a NaOH/SiO2 ratio in the range of from 0.25 to 1.0 and a H2O/SiO2 ratio greater than 50, and at a temperature above the crystallization temperature of the parent zeolite
Implementation Method 3
the methods include ion exchange, incipient wetness and incorporation of metal precursors during synthesis
Implementation Method 4
inserting a metal precursor into a lower framework density (FD) zeolite
Implementation Method 5
direct hydrothermal synthesis in a basic solution having a NaOH/SiO2 ratio in the range of from 0.25 to 1.0
Data Source
Figure 1A~1B
Figure 2A~2B
Figure 3A~3D
AI summary
Provided is a method of encapsulating a metal in a zeolite. The method comprises inserting a metal precursor into a parent zeolite, and then converting the parent zeolite to a zeolite having a higher framework density than the parent zeolite. The conversion is achieved without the need of an organic structure directing agent.