SCRoF Zone Coating Strategy for Soot Oxidation
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Solution Overview
Problem
Existing integrated catalyst systems for diesel engine exhaust, such as SCRoF, face challenges in maintaining independent functionality due to high NH3 oxidation rates by traditional platinum group metal catalysts, which interfere with NOx reduction processes.
Innovation Solution
Employing ceria-based mixed metal oxide catalysts, specifically Fe-doped CeZr and Fe-doped CePr, with optimized metal ratios to enhance NO oxidation while minimizing NH3 oxidation, and using a zone coating strategy with Cu-zeolite catalysts downstream to prioritize PM oxidation, ensuring efficient NO2 production for low-temperature soot oxidation without interfering with SCR NOx reduction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If traditional platinum group metal catalysts are used in SCRoF, then NOx reduction is achieved, but NH3 oxidation rate increases which interferes with SCR process
Solution Approach 1:
The filter substrate is divided into two distinct zones: an inner zone containing PGM catalyst for NOx reduction, and an outer zone containing Cu-zeolite catalyst for PM oxidation. This spatial segmentation prevents the PGM from oxidizing NH3 while allowing the Cu-zeolite to oxidize PM, thus resolving the contradiction between NOx reduction efficiency and NH3 oxidation interference.
Solution Approach 2:
Different catalyst materials are applied to different regions of the filter substrate. The inner zone uses PGM (Pt, Pd, or Rh) with high NOx reduction activity, while the outer zone uses Cu-zeolite with high PM oxidation activity. This local quality differentiation ensures that each catalyst performs its optimal function without interfering with the other, particularly preventing PGM-induced NH3 oxidation.
2Temperature
If PGM catalyst is used for PM oxidation, then soot oxidation temperature is reduced, but NH3 oxidation increases reducing NH3 availability for SCR
Solution Approach 1:
The catalyst system is segmented into two zones: the inner zone with PGM for NOx reduction, and the outer zone with Cu-zeolite for PM oxidation. This segmentation allows PM oxidation to occur at lower temperatures via the outer zone without the PGM in the inner zone consuming NH3, thus maintaining NH3 availability for the SCR process.
Solution Approach 2:
The Cu-zeolite catalyst in the outer zone acts as an intermediary that enables low-temperature PM oxidation without directly consuming NH3. This intermediary catalyst performs the PM oxidation function that would otherwise require PGM, thereby preserving NH3 for the SCR process while achieving the desired temperature reduction for soot oxidation.
3Reliability
If separate DPF and SCR systems are used, then independent functionality of each catalyst is maintained, but total catalyst volume and system complexity increase
Solution Approach 1:
The DPF and SCR functions are merged into a single integrated catalyst substrate with dual zones. The inner zone performs SCR (NOx reduction) while the outer zone performs DPF (PM oxidation) functions. This merging maintains independent catalyst functionality through zonal separation while reducing system complexity and total catalyst volume compared to separate DPF and SCR systems.
Solution Approach 2:
The integrated catalyst substrate performs multiple functions simultaneously: the inner zone handles NOx reduction via SCR, while the outer zone handles PM oxidation via catalyzed soot filtration. This multi-functionality in a single component reduces the need for separate DPF and SCR systems, thereby reducing overall system complexity while maintaining the independent functionality of each catalytic process through zonal differentiation.
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
This approach reduces fuel consumption in active regeneration events by maximizing PM oxidation at lower temperatures while maintaining effective NOx reduction, thereby enhancing overall exhaust aftertreatment performance without compromising SCR functionality.
Implementation Method 1
NO oxidation to NO2 is desired
Implementation Method 2
Catalyst selection for PM treatment is based on oxygen storage capacity, such as ceria-zirconia mixed metal oxides
Implementation Method 3
The PM (soot) is collected within the filter and the exhaust gas is filtered. Once the soot has been collected, it is oxidized to CO2 using O2 or NO2 as an oxidant
Implementation Method 4
An SCR functions by using injected ammonia (NH3) to reduce NOx
Implementation Method 5
An SCRoF typically uses a Cu-zeolite catalyst to reduce NOx by reacting it with NH3
Implementation Method 6
The direction of exhaust flow from one side of the filter wall to the other is indicated by the arrow
Data Source
AI summary
An improved SCRoF (selective catalytic reduction on filter) device for treating exhaust from an internal combustion engine. The filter has numerous entry and exit channels. Exhaust enters the entry channels and flows through side walls into the exit channels. Relative to the exhaust flow path, these side walls are coated on the downstream side with a ceria-based catalyst and on the upstream side with a Cu-zeolite catalyst. This allows the filter to optimally achieve both particulate matter oxidation and NOx reduction, respectively.