Catalytic Wall-Flow Filter Coating for Low-Backpressure Emission Control
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Solution Overview
Problem
There is a need for catalytically active particulate filters that can effectively remove particles, carbon monoxide, and nitrogen oxides from the exhaust gas of internal combustion engines operating with stoichiometric air/fuel mixtures while maintaining low back pressure to comply with stringent emission standards and ensure engine performance.
Innovation Solution
A particulate filter with a wall flow filter coated with a catalytically active coating comprising active aluminum oxide, cerium/zirconium/rare earth metal mixed oxides, and platinum group metals, specifically palladium and rhodium, is used to treat exhaust gases, with the coating extending through the porous walls of the filter.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If a three-way catalyst is used to reduce nitrogen oxides, carbon monoxide and hydrocarbons, then emission conversion is improved, but the catalyst requires high space velocity and may not function properly at low space velocities
Solution Approach 1:
The patent employs a cordierite substrate with a porous washcoat layer comprising alumina and precious metals. The porous structure provides high surface area for catalytic reactions while maintaining appropriate flow characteristics, enabling effective emission conversion across a broader range of space velocities including low space velocity conditions.
Solution Approach 2:
The catalyst system uses a composite washcoat structure combining alumina support material with dispersed precious metal active sites. This composite approach optimizes both the structural properties for flow management and the catalytic properties for emission reduction, addressing the space velocity performance issue.
2Reliability
If a washcoat is applied to the substrate to promote catalytic activity, then catalytic performance is improved, but the washcoat may crack due to thermal expansion differences between the washcoat and substrate
Solution Approach 1:
The patent carefully controls the physical and chemical parameters of the washcoat, including its composition (alumina with specific surface area and pore structure), thickness, and thermal properties. By optimizing these parameters, the washcoat's thermal expansion characteristics are matched to the cordierite substrate, preventing cracking while maintaining catalytic activity.
3Object-generated harmful factors
If the filter is designed for high conversion efficiency, then emission reduction is improved, but the filter may clog with soot and require frequent regeneration or replacement
Solution Approach 1:
The patent incorporates a catalytic layer that promotes the oxidation of accumulated soot particles at lower temperatures. The harmful soot buildup is converted into a beneficial self-cleaning mechanism where the catalyst facilitates soot oxidation, extending filter service life without compromising particle removal efficiency.
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 high conversion rates for gaseous pollutants and particles, maintains low back pressure, and improves engine performance by optimizing the catalytic activity and oxygen storage capacity even after aging.
Implementation Method 1
a wall flow filter of length L and a coating Z, wherein the wall flow filter comprises channels E and A extending parallel between a first and a second end of the wall flow filter and separated by porous walls
Implementation Method 2
the coating Z is located in the porous walls and extends from the first end of the wall flow filter over the entire length L and comprises active aluminum oxide, two different cerium/zirconium/rare earth metal mixed oxides and at least one platinum group metal
Implementation Method 3
the coating Z is located in the porous walls and extends from the first end of the wall flow filter over the entire length L and comprises active aluminum oxide, two different cerium/zirconium/rare earth metal mixed oxides
Data Source
Figure 1
AI summary
The present invention relates to a particulate filter for removing particles, carbon monoxide, hydrocarbons and nitrogen oxides from the exhaust gas of internal combustion engines operated with stoichiometric air/fuel mixtures, comprising a wall flow filter of length L and a coating Z, wherein the wall flow filter comprises channels E and A extending parallel between a first and a second end of the wall flow filter and separated by porous walls forming surfaces OE and OA respectively, and wherein the channels E at the second end and the channels A at the first end are closed, characterized in that the coating Z is located in the porous walls and extends from the first end of the wall flow filter over the entire length L and comprises active aluminum oxide, two different cerium/zirconium/rare earth metal mixed oxides and at least one platinum group metal.