Zoned SCR Catalyst System for Broad Temperature NOx Control
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Solution Overview
Problem
Current selective catalytic reduction (SCR) catalyst systems for lean-burn gasoline and diesel engines are limited by their narrow temperature windows and sensitivity to NOx concentrations, failing to provide effective NOx control across a broad range of temperatures and NO concentrations, especially during low load and high load operations and cold start conditions.
Innovation Solution
A dual or triple zoned SCR system is implemented, where the first zone is composed of iron and the subsequent zones are composed of copper, with specific volume ratios optimized to enhance NOx conversion across a broader temperature range and NO concentrations, and a diverter valve is used to manage NH3 oxidation at high temperatures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If a single-material SCR catalyst (either Fe-based or Cu-based) is used, then the catalyst can provide good NOx conversion in a specific temperature range, but the temperature window is narrow and cannot cover both low-temperature and high-temperature operations
Solution Approach 1:
The SCR catalyst is divided into multiple zones with different materials: a first zone containing Fe-based catalyst and a second zone containing Cu-based catalyst. The Fe-based zone handles high-temperature NOx conversion while the Cu-based zone handles low-temperature conversion, collectively providing a broad temperature window covering both low-load and high-load engine operations.
Solution Approach 2:
Different zones of the catalyst are assigned different material compositions tailored to specific temperature ranges. The Fe-based zone is optimized for high-temperature performance while the Cu-based zone is optimized for low-temperature performance, allowing each local region to excel at its designated temperature range.
2Temperature
If Cu-based SCR catalyst is used to improve low-temperature NOx conversion, then cold start performance is enhanced, but NH3 oxidation occurs at high temperatures reducing overall efficiency
Solution Approach 1:
The catalyst is segmented into a Fe-based zone positioned to handle high-temperature conditions where it prevents NH3 oxidation, and a Cu-based zone positioned to handle low-temperature conditions where it provides efficient NOx conversion. This spatial segmentation allows each material to operate in its optimal temperature range without suffering from its drawbacks.
3Stability of the object's composition
If Fe-based SCR catalyst is used to maintain stability at high temperatures, then thermal stability is improved, but low-temperature NOx conversion efficiency decreases
Solution Approach 1:
The catalyst system is segmented into Fe-based and Cu-based zones, where the Fe-based zone provides thermal stability for high-temperature operations and the Cu-based zone provides high activity for low-temperature NOx conversion, allowing the system to maintain both stability and productivity across the full temperature range.
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 system achieves significant NOx conversion improvements across various temperatures and NO concentrations, with optimal performance achieved by adjusting the volume ratios of iron and copper zones and using a diverter valve to mitigate NH3 oxidation penalties, resulting in robust NOx control from low to high temperatures.
Implementation Method 1
Selective Catalytic Reduction (SCR) with NH3 is a leading candidate for NOx control on lean-burn gasoline engines and diesel engines. The SCR catalyst uses base metals to promote the reaction between NOx and NH3 to produce N2 under lean conditions.
Data Source
AI summary
According to one embodiment of the present invention a selective reduction catalyst system with a broad temperature window for lean-burn gasoline and diesel engines is disclosed. The system includes a first and second zone, wherein the first zone is composed of an iron SCR catalyst and a second zone is composed of a copper SCR catalyst, and wherein the second zone is positioned downstream of the first zone. In another embodiment, a small copper SCR catalyst is placed in front of a second zone composed of an iron SCR catalyst and a third zone composed of a copper SCR catalyst, wherein the volume of the first copper SCR catalyst is a fraction of the volume of the second copper SCR catalyst. In yet another embodiment, a diverter valve would be included in the system to eliminate any NOx penalty produced by the front Cu SCR catalyst.