Zeolite Catalyst with Cerium Promoter for SCR Stability
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Solution Overview
Problem
Existing SCR catalysts face challenges in maintaining high catalytic activity at low temperatures and hydrothermal stability, especially when exposed to high temperatures, which affects their performance and consistency in reducing NOx emissions from diesel engines.
Innovation Solution
A catalyst composition featuring zeolites with a CHA framework, low silica-to-alumina ratio, and low copper loading, combined with high concentrations of cerium, which enhances hydrothermal stability and catalytic performance across a broad temperature range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If high copper loading is used to improve low-temperature catalytic activity, then low-temperature activity is improved, but hydrothermal stability deteriorates at high temperatures
Solution Approach 1:
The patent changes the copper loading parameter from high to low levels, and compensates by optimizing the zeolite framework composition (silica-to-alumina ratio) and crystal size parameters to maintain catalytic activity while improving hydrothermal stability at high temperatures
Solution Approach 2:
The patent creates a composite catalyst system combining low-copper loading with specific zeolite framework structures (CHA topology) and controlled silica-to-alumina ratios, where the composite material properties provide both low-temperature activity and high-temperature stability that neither component alone could achieve
2Reliability
If high silica-to-alumina ratio is used to improve hydrothermal stability, then hydrothermal stability is improved, but catalytic activity deteriorates
Solution Approach 1:
The patent optimizes the silica-to-alumina ratio to a specific range that balances hydrothermal stability and catalytic activity, rather than using extremely high ratios that would compromise activity. This parameter optimization is combined with low copper loading and controlled crystal size to achieve both stability and activity
Solution Approach 2:
The patent creates local active sites with high copper concentration at specific locations within the zeolite structure (exchanged copper cations in framework positions), while maintaining overall low copper loading. This local quality approach allows high activity at active sites without compromising overall hydrothermal stability
3Productivity
If small crystal size is used to improve mass transfer, then mass transfer is improved, but hydrothermal stability deteriorates
Solution Approach 1:
The patent changes the crystal size parameter to a moderate range that balances mass transfer and hydrothermal stability. This is compensated by optimizing copper loading and framework composition to ensure sufficient catalytic activity and stability without requiring extremely small crystal sizes
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 catalyst composition achieves improved NOx conversion and selectivity to N2 at high temperatures while maintaining performance consistency between fresh and aged states, outperforming traditional catalysts in terms of hydrothermal durability and low-temperature activity.
Implementation Method 1
The reduction of NO x to N 2 in a lean burn exhaust gas, such as that created by diesel engines, is particularly problematic because the exhaust gas contains enough oxygen to favor oxidative reactions instead of reduction. NO x can be reduced in a diesel exhaust gas, however, by a process commonly known as Selective Catalytic Reduction (SCR).
Implementation Method 2
While zeolites per se often have catalytic properties, their SCR catalytic performance may be improved in certain environments by a cationic exchange wherein a portion of ionic species existing on the surface or within the framework is replaced by metal cations, such Cu 2+
Implementation Method 3
High concentrations of cerium can be incorporated into such metal promoted zeolites to improve the material's hydrothermal stability, low temperature catalytic performance, and/or consistency in catalytic performance between the fresh and aged states of the catalyst.
Data Source
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AI summary
Provided is a catalyst comprising (a) a zeolite material having a mean crystal size of at least about 0.5 µm, having a CHA framework that contains silicon and aluminum, and having a silica-to-alumina mole ratio (SAR) of about 10 to about 25; and (b) an extra-framework promoter metal (M) disposed in said zeolite material as free and/or exchanged metal, wherein the extra-framework promoter metal is copper, iron, and mixtures thereof, and is present in a promoter metal-to-aluminum atomic ratio (M :AI) of about 0.10 to about 0.24 based on the framework aluminum; and optionally comprising (c) at least about 1 weight percent of cerium in said zeolite material, based on the total weight of the zeolite, wherein said cerium is present in a form selected from exchanged cerium ions, monomeric ceria, oligomeric ceria, and combinations thereof, provided that said oligomeric ceria has a particle size of less than 5 µm.