Layered Pt-Pd Soot Filter for NO2 and Back Pressure Control
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Solution Overview
Problem
Current catalyzed soot filters for diesel engines face challenges in efficiently oxidizing soot during normal operation while minimizing NO2 emissions, especially during active regeneration, and often require additional precious metals that increase complexity and cost, and may not fully oxidize CO and HC, leading to higher emissions and increased back pressure.
Innovation Solution
A catalyzed soot filter with a wall flow substrate coated with a combination of platinum (Pt) and palladium (Pd) oxidation catalysts, where the Pt concentration is higher in the first coating and lower in the second, with overlapping coating lengths to optimize NO2 consumption and reduce unconverted NO2 emissions, integrated with a diesel oxidation catalyst (DOC) and optionally a selective catalytic reduction (SCR) article for enhanced emission control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a catalyzed soot filter uses traditional single-coating design with high Pt loading to oxidize soot, then soot oxidation efficiency is improved, but NO2 emissions increase and precious metal cost increases
Solution Approach 1:
The filter substrate is divided into multiple coating zones along the flow direction: a first coating zone with high Pt concentration for efficient soot oxidation, and a second coating zone with low or no Pt for NO2 reduction. This segmentation allows different sections to perform specialized functions, resolving the contradiction between oxidation efficiency and NO2 emission control.
Solution Approach 2:
Different regions of the catalyst coating have different compositions optimized for their specific location: the upstream region uses Pt-rich composition for rapid soot oxidation activation, while the downstream region uses Pt-poor or Pt-free composition to reduce NO2 formation. This local quality variation enables simultaneous achievement of high oxidation efficiency and low NO2 emissions.
2Productivity
If additional precious metals are added to enhance oxidation catalyst performance, then CO and HC oxidation is improved, but system complexity and manufacturing cost increase
Solution Approach 1:
Platinum is used to perform multiple functions: it catalyzes soot oxidation, CO oxidation, and HC oxidation. By utilizing Pt's multi-functionality, the need for additional precious metals is reduced, simplifying the catalyst composition while maintaining high oxidation efficiency for all pollutants.
Solution Approach 2:
The Pt concentration is varied spatially along the filter substrate, creating a gradient from high Pt loading in the first coating zone to low or zero Pt loading in the second coating zone. This parameter change optimizes catalytic activity for different reactions at different locations without requiring additional metal elements.
3Productivity
If wall flow filter accumulates soot particles to achieve high filtration efficiency, then particulate matter removal is improved, but back pressure increases
Solution Approach 1:
The catalytic coating enables continuous passive regeneration by oxidizing accumulated soot particles at low temperatures using available oxygen in the exhaust stream. This continuous oxidation process prevents excessive soot accumulation, maintaining low back pressure while preserving high filtration efficiency.
Solution Approach 2:
The Pt catalyst acts as a strong oxidant promoter, enabling soot oxidation to proceed at much lower temperatures than would be required without catalysis. This accelerated oxidation during normal operation continuously burns off accumulated particles, preventing back pressure buildup while maintaining filtration 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 solution effectively oxidizes soot and reduces NO2 emissions, maintaining low unconverted NO2 concentrations, optimizing CO and HC oxidation, and minimizing back pressure, thus meeting regulatory standards without the need for additional NOx reduction systems, while reducing the use of precious metals and system complexity.
Implementation Method 1
oxidation catalysts that contain platinum group metals, base metals and combinations thereof facilitate the treatment of diesel engine exhaust by promoting the conversion of both unburned hydrocarbons (HC) and carbon monoxide (CO) gaseous pollutants, and some proportion of the particulate matter through oxidation of these pollutants to carbon dioxide and water
Implementation Method 2
Certain oxidation catalysts also promote the oxidation of NO to NO2
Implementation Method 3
Known filter structures that remove particulate matter from diesel exhaust include honeycomb wall flow filters, wound or packed fiber filters, open cell foams, sintered metal filters, etc.
Implementation Method 4
The accumulating particles will increase the back pressure from the filter on the engine. Thus, the accumulating particles have to be continuously or periodically burned out of the filter to maintain an acceptable back pressure
Data Source
AI summary
Disclosed is a catalyzed soot filter with layered design wherein the first coating of the filter comprises an oxidation catalyst comprising platinum (Pt) and optionally palladium (Pd), wherein 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/(2.54 cm)3)): loading of the second coating (in g/inch3 (g/(2.54 cm)3)).