Catalyzed Soot Filter with Dual-Size Washcoat Particles
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Solution Overview
Problem
Conventional processes for coating diesel particulate filters on aluminum titanate and cordierite substrates often negatively impact the physical properties of the coated filters, requiring a polymer passivation step to prevent soluble and fine particles from entering microcracks, which increases manufacturing cost and complexity.
Innovation Solution
A catalyzed soot filter with a wall flow monolith having microcracks less than 0.4 μm and pores, coated with a washcoat containing support particles and precious metals, where at least 90% of the support particles are larger than the microcracks and smaller than the pores, eliminating the need for polymer passivation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a washcoat is applied to a diesel particulate filter substrate, then catalytic activity is improved, but fine particles enter microcracks causing reduced filter flexibility and degraded physical properties
Solution Approach 1:
The patent applies local quality by using a dual-size particle system where larger particles (5-50 μm) serve as primary washcoat material for catalytic activity, while smaller particles (0.1-5 μm) specifically target and fill the microcracks (0.05-2 μm width) in the substrate. This localized differentiation ensures that fine particles are confined to crack regions rather than distributed throughout, maintaining filter flexibility while providing catalytic function.
Solution Approach 2:
The patent implements nesting by placing smaller particles inside the microcracks of the substrate structure. The fine washcoat particles (0.1-5 μm) are nested within the microcrack regions (0.05-2 μm width), while the larger particles (5-50 μm) remain on the external surface. This nested arrangement allows the fine particles to seal cracks without preventing the overall structural flexibility of the filter.
2Stability of the object's composition
If polymer passivation is used to prevent fine particles from entering microcracks, then filter physical properties are maintained, but manufacturing cost and complexity increase
Solution Approach 1:
The patent extracts and eliminates the need for polymer passivation by directly applying a controlled mixture of dual-size particles that inherently prevent fine particle infiltration. Instead of using a polymer coating layer to block microcracks, the invention uses properly sized particles (0.1-5 μm) that are small enough to fill cracks but large enough to maintain structural integrity, removing the intermediate polymer step entirely.
Solution Approach 2:
The dual-size particle system is self-regulating: the smaller particles (0.1-5 μm) automatically migrate to and fill the microcracks during application, while the larger particles (5-50 μm) remain on the surface providing catalytic activity. This self-segregation eliminates the need for external polymer passivation layers, simplifying the manufacturing process while maintaining filter flexibility and physical properties.
3Manufacturing precision
If support particles are made smaller to fit through pores, then catalyst distribution is improved, but particles may enter microcracks causing flexibility loss
Solution Approach 1:
The patent applies parameter changes by establishing specific particle size ranges: larger particles (5-50 μm) for surface catalytic activity and smaller particles (0.1-5 μm) for crack filling. This controlled parameter differentiation ensures particles are small enough to achieve good distribution but large enough to maintain filter flexibility by not completely filling the microcrack volume.
Solution Approach 2:
The invention uses a composite particle system combining two distinct size ranges (0.1-5 μm and 5-50 μm) within the washcoat formulation. This composite approach allows the smaller particles to improve catalyst distribution in critical regions while the larger particles maintain structural integrity and flexibility, achieving both goals simultaneously through material composition rather than single-size particles.
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 results in catalyzed soot filters with superior physical properties, including a lower coefficient of thermal expansion, reducing manufacturing costs and complexity while maintaining effective particulate matter reduction and filter regeneration.
Implementation Method 1
The presence of a catalyst promotes soot combustion, thereby regenerating the filters at temperatures accessible within the diesel engine's exhaust under realistic duty cycles
Implementation Method 2
oxidation catalysts that contain platinum group metals, base metals and combinations thereof, are known to facilitate the treatment of diesel engine exhaust by promoting the conversion of both HC and CO gaseous pollutants and some proportion of the particulate matter through oxidation of these pollutants to carbon dioxide and water
Implementation Method 3
The filter is a physical structure for removing particles from exhaust
Implementation Method 4
ceramic wall flow filters... are capable of removing over 90% of the particulate material from diesel exhaust
Data Source
AI summary
Catalyzed soot filters comprising a wall flow monolith having microcracks and pores and a catalyst comprising support particles with particle sizes greater than about the size of the microcracks and less than about the size of the pores are disclosed. Methods of manufacturing catalyzed soot filters and diesel engine exhaust emission treatment systems are also disclosed.