Segmented SCR Catalyst for Low Ammonia NOx Removal
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Solution Overview
Problem
Conventional SCR catalysts using transition metal ion-exchange zeolite exhibit insufficient NOx removal performance at low ammonia adsorption levels, requiring excessive ammonia supply, which leads to ammonia slip and system redesign issues, failing to meet emissions standards like EU Stage V and IV.
Innovation Solution
An exhaust gas purification apparatus with two catalyst regions: a non-zeolite-based catalyst region containing oxygen storage and release materials and transition metal elements, and a zeolite-based catalyst region with supported transition metals, arranged in a specific sequence to enhance NOx removal performance even at low ammonia adsorption levels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If conventional transition metal ion-exchange zeolite SCR catalyst is used, then maximum ammonia adsorption capacity is improved, but NOx removal performance at low ammonia adsorption levels deteriorates
Solution Approach 1:
The SCR catalyst is divided into two distinct regions: a first catalyst region containing non-zeolite-based catalyst material (such as metal oxides like ceria, zirconia, or perovskite structures) and a second catalyst region containing zeolite-based catalyst material. This segmentation allows each region to perform different functions - the first region provides high NOx removal performance at low ammonia adsorption levels, while the second region provides high ammonia adsorption capacity.
Solution Approach 2:
Different catalyst materials are used in different spatial regions of the catalyst structure. The first catalyst region uses non-zeolite materials with specific local properties optimized for low-ammonia conditions, while the second catalyst region uses zeolite materials with properties optimized for high ammonia adsorption. This local quality differentiation resolves the contradiction between performance at low ammonia levels and maximum adsorption capacity.
2Reliability
If excessive ammonia is supplied to improve NOx removal performance, then NOx removal performance is improved, but ammonia slip increases
Solution Approach 1:
The segmented catalyst structure with two distinct regions enables efficient ammonia utilization. The first catalyst region efficiently converts ammonia to nitrogen at low adsorption levels, reducing the need for excessive ammonia supply. The second catalyst region adsorbs and stores ammonia when available, preventing ammonia slip by capturing excess ammonia that would otherwise be released into the exhaust stream.
Solution Approach 2:
The dual-region catalyst changes the operational parameters of the SCR system by providing high NOx removal performance across a broader range of ammonia concentrations. This eliminates the need to operate at high ammonia supply levels, thereby reducing ammonia slip while maintaining effective NOx removal.
3Reliability
If ammonia supply is increased to compensate for low adsorption performance, then NOx removal performance is improved, but system complexity increases due to need for ammonia oxidation catalyst
Solution Approach 1:
The dual-region catalyst structure combines multiple functions within a single catalyst component. The first catalyst region provides high NOx removal performance at low ammonia levels, the second catalyst region provides ammonia adsorption capacity, and together they eliminate ammonia slip. This multi-functional integration replaces the need for separate ammonia oxidation catalysts and complex control systems, simplifying the overall system while maintaining high NOx removal performance.
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 apparatus achieves high NOx removal performance across a wide range of ammonia adsorption levels, reducing the need for excessive ammonia supply and minimizing ammonia slip, thus meeting stringent emissions standards.
Implementation Method 1
one or more selective reducing catalysts which adsorb ammonia and bring the ammonia into contact with NOx to perform reduction
Implementation Method 2
NOx is chemically reacted with ammonia on the SCR catalyst to purify NOx to nitrogen and water
Implementation Method 3
one or more oxidation catalysts which oxidize at least one selected from the group consisting of CO, HC, NO and NH3 in an exhaust gas
Data Source
Figure 1~3
Figure 4~6
AI summary
Provided is an exhaust gas purification apparatus for lean combustion engines with excellent NOx removal performance, which can exhibit relatively high NOx removal performance even under a condition of a relatively low amount of ammonia adsorbed. The exhaust gas purification apparatus 100 for lean combustion engines comprises a selective reducing catalyst SCR which has at least a first catalyst region SCR1 containing at least an oxygen storage and release material and a transition metal element and a second catalyst region SCR2 containing at least zeolite and a transition metal element supported on the zeolite, wherein the maximum amount of NH3 adsorbed per unit volume of the first catalyst region SCR1 is smaller than the maximum amount of NH3 adsorbed per unit volume of the second catalyst region SCR2 under a condition of NH3 adsorption at 33% of the saturated adsorption amount, and the first catalyst region SCR1 is arranged on the upstream side of an exhaust gas flow channel for an exhaust gas with respect to the second catalyst region SCR2 so that the exhaust gas contacts the first catalyst region SCR1 and the second catalyst region SCR2 in this order.