SAPO-18 Synthesis via Cyclic OSDA for Hydrothermal Stability
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Solution Overview
Problem
Conventional methods for synthesizing SAPO-18 and Me-SAPO-18 require multiple stages, leading to increased costs and reduced hydrothermal stability of the resulting catalysts, particularly Cu-SAPO-18, which is less stable due to poor silicon distribution and extra-framework cation stabilization.
Innovation Solution
A direct synthesis method using a mixture of silicon, aluminum, phosphorus sources, and cyclic quaternary ammonium compounds, allowing for isolated silicon distribution and single-stage incorporation of metal cations like copper, enhancing Bronsted acidity and hydrothermal stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional multi-stage synthesis methods are used for SAPO-18 and Me-SAPO-18, then the synthesis process can be completed, but the synthesis costs increase and hydrothermal stability decreases
Solution Approach 1:
The patent combines multiple synthesis stages into a single hydrothermal treatment step. The synthesis mixture containing silicon source, aluminum source, phosphorus source, and cyclic quaternary ammonium compound is subjected to one-step hydrothermal treatment to directly produce Me-SAPO-18 with metal cations incorporated during crystallization, eliminating separate cation exchange and calcination steps while improving hydrothermal stability
Solution Approach 2:
The hydrothermal treatment step serves multiple functions simultaneously: it crystallizes the SAPO-18 structure, incorporates metal cations into the framework, and achieves the desired silicon distribution pattern. This multi-functional approach reduces the number of process steps while improving product quality and stability
2Manufacturing precision
If conventional synthesis methods are used, then SAPO-18 can be produced, but silicon distribution is poor and Bronsted acidity is reduced
Solution Approach 1:
The patent uses cyclic quaternary ammonium compounds as structure-directing agents that specifically guide silicon atoms to occupy isolated tetrahedral sites within the SAPO-18 framework. This local structural control ensures uniform silicon distribution and maximizes Bronsted acidity without complicating the overall synthesis procedure
Solution Approach 2:
The cyclic quaternary ammonium compound acts as an intermediary during the hydrothermal treatment, mediating the incorporation of silicon atoms into specific framework positions. The OSDA directs silicon placement to achieve isolated silicon distribution, and is subsequently removed after crystallization, leaving the desired structural configuration
3Reliability
If multi-stage synthesis is used for Cu-SAPO-18, then copper can be incorporated, but hydrothermal stability of the catalyst decreases
Solution Approach 1:
The patent incorporates copper cations into the SAPO-18 framework during the initial hydrothermal crystallization step, before any potential degradation can occur. This preliminary incorporation ensures copper is properly integrated into the structure with optimal stability from the outset, rather than attempting post-synthesis modification
Solution Approach 2:
The synthesis method merges crystal growth and metal cation incorporation into a single hydrothermal treatment step. Copper salts are added to the synthesis mixture before hydrothermal treatment, allowing simultaneous crystallization and metal incorporation, which enhances catalyst stability while maintaining synthesis efficiency
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 reduces synthesis steps, improves silicon distribution, and increases the hydrothermal stability of Me-SAPO-18, particularly Cu-SAPO-18, making it more effective as a catalyst for NOx reduction in SCR reactions.
Implementation Method 1
The synthesis mixture is then heated to a crystallization temperature of between about 100°C and about 350°C and retained at the crystallization temperature until crystals of the molecular sieve are produced
Implementation Method 2
The synthesis mixture is then heated to a crystallization temperature of between about 100°C and about 350°C and retained at the crystallization temperature until crystals of the molecular sieve are produced
Data Source
Figure 1~2
Figure 3
AI summary
The invention relates to the synthesis of silicoaluminophosphate and metal silicoaluminophosphate polymorphs of the molecular sieve SAPO-18 using cyclic quaternary ammoniums as organic structure-directing agents (OSDA), and to the use thereof as a catalyst.