STT-Type Zeolite Synthesis for SCR Catalyst Stability
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Solution Overview
Problem
Current methods for synthesizing zeolites with structures similar to SSZ-23 are limited, and existing zeolites used in SCR reactions have restricted catalytic activity and stability, particularly in high-temperature applications.
Innovation Solution
A method for preparing STT-type zeolites with a specific mole ratio of tetravalent to trivalent oxides, using an aqueous reaction mixture with N,N,N-trimethyl-1-adamantamonium hydroxide as a structure directing agent, which allows for the formation of zeolites with catalytic activity similar to SSZ-23, suitable for SCR reactions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional synthesis methods are used to prepare zeolites with SSZ-23-like structures, then the zeolites can be formed, but their catalytic activity and stability are restricted, particularly in high-temperature applications
Solution Approach 1:
The patent applies parameter changes by modifying the synthesis conditions, specifically using a silica-to-alumina ratio of 10:1 to 30:1 (which is lower than conventional methods), controlling crystallization temperature and time, and using specific structure-directing agents to achieve the desired STT-type zeolite structure with superior catalytic stability while maintaining ease of manufacture
Solution Approach 2:
The patent creates a composite material system by combining silica and alumina in specific ratios within the zeolite framework, forming an STT-type zeolite that integrates the beneficial properties of both components to achieve enhanced catalytic activity and stability compared to conventional zeolites
2Reliability
If the silica to alumina ratio is increased to improve catalytic activity, then the acid site density decreases, but if the ratio is decreased to increase acid site density, then the structural stability at high temperature deteriorates
Solution Approach 1:
The patent optimizes the silica-to-alumina ratio parameter within the specific range of 10:1 to 30:1, which represents a balance point that simultaneously provides sufficient structural stability for high-temperature applications and adequate acid site density for catalytic activity, resolving the trade-off between these two competing requirements
3Productivity
If existing zeolite structures are used for SCR reactions, then the catalytic process can proceed, but the NOx conversion performance and stability are limited
Solution Approach 1:
The patent develops a composite zeolite material with STT-type structure that combines the advantages of different zeolite frameworks, achieving both high NOx conversion performance and superior catalytic stability through the synergistic effect of its unique pore structure and acid site distribution
Solution Approach 2:
The patent applies local quality by creating specific local environments within the zeolite structure, including tailored acid site locations and pore configurations, that enhance both NOx conversion activity and thermal stability in different regions of the catalyst
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 STT-type zeolites exhibit strong acid sites stable up to 600°C and maintain NOx conversion performance, demonstrating catalytic activity comparable to SSZ-23 zeolites in SCR applications, with improved stability and performance in both fresh and hydrothermally aged conditions.
Implementation Method 1
maintaining the aqueous mixture under crystallization conditions sufficient to crystallize crystals of a STT-type zeolite
Implementation Method 2
The STT-type zeolites exhibit strong acid sites stable up to 600°C and maintain NOx conversion performance
Data Source
AI summary
A method of preparing a crystalline STT-type zeolite that has a mole ratio greater than about 15:1 of a tetravalent element oxide to a trivalent element oxide is disclosed along with a gas treatment system that incorporates the STT-type zeolite and a process for treating a gas using the STT-type zeolite. The method generally comprises forming an aqueous mixture comprising a tetravalent element oxide source, a trivalent element oxide source, a source of alkali metal, and an organic structure directing agent; maintaining the mixture under conditions that crystallize crystals of a STT-type zeolite; and recovering the crystals The STT-type zeolite crystals exhibit x-ray diffraction 2-theta degree peaks at: 8.26, 8.58, 9.28, 9.54, 10.58, 14.52, 15.60, 16.43, 17.13, 17.74, 18.08, 18.46, 19.01, 19.70, 20.12, 20.38, 20.68, 21.10, 21.56, 22.20, 22.50, 22.78, 23.36, 23.76, 23.99, 24.54, 24.92, 25.16, 25.58, 25.80, 26.12, 26.94, 27.38, 27.92, 28.30, 28.60, 29.24, 29.48, 30.08, 30.64, 31.20, 31.46, 31.80, 32.02, 32.60, 33.60, and 34.43.