Wall-Flow Filter with Dual Coatings for Back Pressure Management
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Solution Overview
Problem
Current particulate filters face a trade-off between catalytic activity and filtration efficiency, often resulting in increased exhaust-gas back pressure, which limits their effectiveness in reducing harmful emissions from internal combustion engines.
Innovation Solution
A wall-flow filter design featuring a catalytically active coating (Z) in the porous walls and a membrane coating (F) on the surfaces, with palladium and/or rhodium, and a cerium/zirconium mixed oxide, optimized to balance catalytic activity and filtration efficiency while minimizing back pressure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a catalytically active coating is applied to the channel walls of a wall-flow filter, then catalytic effectiveness is improved, but exhaust-gas back pressure increases
Solution Approach 1:
The patent applies different coatings to different locations: coating Z (catalytically active with Pd/Rh and cerium/zirconium mixed oxide) is applied to the porous walls and/or outlet channel surfaces, while coating F (filtration membrane without noble metal) is applied mainly to inlet channel surfaces. This local differentiation optimizes catalytic activity where needed while minimizing back pressure increase at the inlet.
2Stress or pressure
If the amount of oxidic support materials for catalytic noble metals is reduced in a filter, then exhaust-gas back pressure is minimized, but catalytic effectiveness deteriorates
Solution Approach 1:
The patent uses a composite coating system combining coating Z (containing Pd/Rh noble metals with cerium/zirconium mixed oxide support) and coating F (filtration membrane without noble metal). This composite approach provides catalytic functionality with reduced oxidic support material quantities while maintaining effectiveness.
3Stress or pressure
If catalytically active material is dispersed in the porous walls (in-wall coating), then exhaust-gas back pressure is reduced, but the amount of catalytic substance is limited by absorption capacity
Solution Approach 1:
The patent transitions from purely in-wall coating to on-wall coating by applying coating Z to the surfaces of the channel walls (particularly outlet channels) and coating F to inlet channel surfaces. This surface-based approach provides additional dimension for catalytic material placement beyond pore absorption, increasing the quantity of catalytic substance while maintaining low back pressure.
4Reliability
If a filtration layer is created on inlet channel walls, then filtration efficiency is improved, but device complexity increases
Solution Approach 1:
The patent merges filtration and catalysis functions into a single integrated coating system. Coating F provides filtration membrane functionality on inlet surfaces, while coating Z provides catalytic activity on outlet surfaces and porous walls. This merging eliminates the need for separate filtration and catalysis components, reducing overall device complexity.
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 filter achieves enhanced filtration efficiency and catalytic activity with a moderate increase in exhaust-gas back pressure, improving soot particle deposition and burn-off, and maintaining stability even when exposed to condensation water.
Implementation Method 1
The catalytically active coating Z... comprises palladium and/or rhodium and a cerium/zirconium mixed oxide
Implementation Method 2
The wall-flow filter substrate has... coatings Z and F that differ from one another... the coating F is located mainly on the surfaces OE
Implementation Method 3
the wall-flow filter substrate has channels E and A, which extend in parallel between a first and a second end of the wall-flow filter substrate, are separated by porous walls
Data Source
AI summary
The invention relates to a wall flow filter for removing particulate matter from the exhaust of internal combustion engines, comprising a wall flow filter substrate having a length L, and different coatings Z and F, the wall flow filter substrate being provided with channels E and A which run parallel between a first end and a second end of the wall flow filter substrate, are separated by porous walls, and form surfaces OE and OA, respectively; channels E are closed at the second end, and channels A are closed at the first end; coating Z is disposed in the porous walls and/or on surfaces OA, but not on surfaces OE, and contains palladium and/or rhodium and a cerium/zirconium mixed oxide; coating F is disposed mainly on surfaces OE, but not on surfaces OA, and comprises a membrane and no precious metal. The wall flow filter is characterized in that the mass ratio of coating Z to coating F ranges from 0.1 to 25.