Layered Catalyzed Soot Filter for Diesel Exhaust
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Solution Overview
Problem
Current catalyzed soot filters for diesel engines face challenges in oxidizing soot via NO2 during normal operations while suppressing NO2 formation, especially during active regeneration, and require additional NOx reduction systems, which increase complexity and cost. They also struggle to maintain low unconverted NO2 emissions and efficient filtration of CO and unburned hydrocarbons.
Innovation Solution
A catalyzed soot filter with a wall flow substrate coated with a layered structure, where the first coating contains platinum and optionally palladium, and the second coating contains palladium with a lower platinum concentration, applied in a specific loading ratio to optimize NO2 consumption and reduce NO2 formation, integrated with a diesel oxidation catalyst and optionally a selective catalytic reduction system.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a catalyzed soot filter uses a single coating with platinum group metals to oxidize soot via NO2 during normal operations, then soot oxidation is improved, but NO2 formation increases during active regeneration and additional NOx reduction systems are required
Solution Approach 1:
The filter is divided into two functional zones: a first zone with a coating containing platinum group metals for soot oxidation, and a second zone with a coating containing base metals for NO2 suppression. This segmentation allows each zone to perform its specific function independently, resolving the contradiction between soot oxidation efficiency and NO2 formation control
Solution Approach 2:
Different coatings with distinct catalytic properties are applied to different axial positions of the filter. The first zone (inlet side) uses Pt/Pd for effective soot oxidation, while the second zone (outlet side) uses base metals like Cu, Zn, or Mn to suppress NO2 formation. This local differentiation of material properties enables simultaneous achievement of both objectives
2Object-generated harmful factors
If additional NOx reduction systems are integrated with the soot filter, then NO2 emissions are reduced, but device complexity and cost increase
Solution Approach 1:
The soot filter substrate serves multiple functions: particulate matter filtration, soot oxidation catalysis, and NO2 emission suppression. By integrating the NO2 suppression function directly into the filter structure through the second coating zone, the system eliminates the need for separate NOx reduction devices, thereby reducing complexity while maintaining effectiveness
Solution Approach 2:
The NO2 suppression coating is merged with the soot filter structure itself, creating an integrated multi-functional component. The second coating zone containing base metals is applied directly to the substrate, combining the filtration and NO2 control functions in a single device rather than requiring separate systems
3Reliability
If precious metal loading is increased to improve soot oxidation, then oxidation efficiency is improved, but manufacturing cost increases
Solution Approach 1:
Precious metals (Pt, Pd) are concentrated in the first zone where they are most needed for soot oxidation, while the second zone uses cheaper base metals for NO2 suppression. This localized distribution optimizes precious metal usage by placing them only where required for their primary function, reducing overall cost while maintaining oxidation efficiency
Solution Approach 2:
The coating composition changes along the axial direction of the filter, with Pt/Pd content optimized in the first zone and base metal content optimized in the second zone. This parameter variation allows efficient use of precious metals in the oxidation zone while using cost-effective base metals in the suppression zone
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 solution effectively oxidizes soot using NO2 during normal operations, suppresses NO2 formation, maintains low unconverted NO2 emissions, and supports the oxidation of CO and unburned hydrocarbons, thereby minimizing breakthrough and maintaining soot filtration efficiency without the need for additional NOx reduction systems, reducing costs by minimizing precious metal usage.
Implementation Method 1
the first coating contains an oxidation catalyst comprising Pt and optionally Pd
Implementation Method 2
effectively oxidizes soot using NO2 during normal operations
Implementation Method 3
the second coating contains an oxidation catalyst comprising Pd and optionally Pt wherein the Pt concentration in the second coating is lower than the Pt concentration in the first coating
Implementation Method 4
suppresses NO2 formation
Implementation Method 5
supports the oxidation of CO and unburned hydrocarbons
Implementation Method 6
facilitate the treatment of diesel engine exhaust by promoting the conversion of both unburned hydrocarbons (HC) and carbon monoxide (CO) gaseous pollutants
Data Source
Figure 1
AI summary
Disclosed is a catalyzed soot filter with layered design. The first coating of the filter comprises an oxidation catalyst comprising platinum (Pt) and optionally palladium (Pd). The second coating of the filter comprises an oxidation catalyst comprising Pd and optionally Pt, wherein the Pt concentration in the second coating is lower than the Pt concentration in the first coating and wherein the weight ratio of Pt:Pd in the second coating is in the range of from 1 : 1 to 0 : 1; and wherein the first coating and the second coating are present on the wall flow substrate at a coating loading ratio in the range of from 0.25 to 3, calculated as ratio of the loading of the first coating (in g/inch3 (g/(2.54cm)3)): loading of the second coating (in g/inch3 (g/(2.54cm)3)).