Metal-Substituted Beta Zeolite Ion Exchange for Catalytic Activity
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Solution Overview
Problem
Conventional beta zeolites with high Si/Al ratios exhibit reduced ion exchange capacity and catalytic activity for exhaust gas purification due to low metal loading, which decreases their effectiveness under high-temperature hydrothermal conditions.
Innovation Solution
A method involving ion exchange of alkali metal-type beta zeolites without organic structure-directing agents (OSDA) with ammonium ions followed by copper or iron(II) ion exchange using a filter cake process, resulting in a metal-substituted beta zeolite with a higher Lewis acid site amount than Bronsted acid sites, enhancing catalytic performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the Si/Al ratio of beta zeolite is increased to enhance resistance to water and heat, then hydrothermal stability is improved, but the number of ion exchange sites decreases resulting in low catalytic activity
Solution Approach 1:
The invention changes the Si/Al ratio parameter to a low range (3-8), which is lower than conventional beta zeolites, to increase the number of ion exchange sites and enable higher metal loading while maintaining acceptable hydrothermal stability through the specific synthesis method and metal substitution approach
2Reliability
If the Si/Al ratio is increased to reduce ion exchange sites, then hydrothermal durability is improved, but the amount of transition metal that can be loaded decreases resulting in low catalytic activity
Solution Approach 1:
The invention uses a low Si/Al ratio (3-8) to increase the number of available ion exchange sites, enabling higher transition metal loading amounts while achieving the desired catalytic activity for exhaust gas purification
Solution Approach 2:
The invention employs ammonium ions as an intermediary substance in the ion exchange process, first exchanging alkali metal ions with ammonium ions, then exchanging ammonium ions with transition metal ions, which facilitates controlled metal loading and distribution within the zeolite structure
3Quantity of substance
If transition metal is fixed by deposition method other than ion exchange, then metal loading can be increased, but metal atoms aggregate under high-temperature conditions hindering gas molecule contact and reducing catalytic activity
Solution Approach 1:
The invention uses ammonium ions as a mediator in a two-step ion exchange process, first replacing alkali metal ions with ammonium ions, then replacing ammonium ions with transition metal ions. This intermediary approach ensures uniform metal distribution and strong metal-zeolite interaction, preventing metal aggregation under high-temperature conditions and maintaining catalytic activity stability
Solution Approach 2:
The invention replaces the deposition method with an ion exchange mechanism, where transition metal ions are introduced through ionic substitution rather than physical deposition. This chemical substitution method creates stronger bonding between metal ions and the zeolite framework, preventing aggregation and maintaining catalytic performance under high-temperature conditions
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 resulting metal-substituted beta zeolite demonstrates superior catalytic performance and hydrothermal durability, particularly in SCR catalyst activity under high-temperature conditions, with increased copper or iron ion loading and reduced hexacoordinated aluminum, leading to improved catalytic activity and stability.
Implementation Method 1
exchanging, for ammonium ions, alkali metal ions in a beta zeolite of an alkali metal type produced without using any OSDA
Implementation Method 2
allowing a copper ion- or iron(II) ion-containing aqueous solution to pass through a cake of the ammonium-substituted beta zeolite to exchange ammonium ions in the ammonium-substituted beta zeolite for copper or iron(II) ions
Data Source
AI summary
The purpose of the present invention is to provide a metal-substituted beta zeolite that exhibits a more excellent catalytic performance than conventional one, and a method for producing the same. The present invention provides a metal-substituted beta zeolite by subjecting an alkali metal-form beta zeolite produced without using an organic structure-directing agent to ion exchange with ammonium ion and then, using a filter cake procedure, to ion exchange with copper ion or iron(II) ion. The present invention also provides a metal-substituted beta zeolite which has been ion exchanged with copper ion or iron(II) ion and in which the amount of Lewis acid sites is greater than the amount of Bronsted acid sites when the amount of Bronsted acid sites and the amount of Lewis acid sites are measured by ammonia infrared-mass spectroscopy temperature-programmed desorption on the as-produced state.