Four-Way Catalyst In-Wall On-Wall Coating Back-Pressure
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Solution Overview
Problem
Current four-way conversion catalysts face challenges in achieving high particle filtration efficiency while minimizing back-pressure increase in exhaust gas treatment systems for gasoline engines, as higher catalyst loadings required for efficiency lead to increased back-pressure and steeper pressure gradients over the catalyst's lifetime.
Innovation Solution
A four-way conversion catalyst design featuring a porous wall flow filter substrate with both in-wall and on-wall coatings, where the in-wall coating comprises an oxygen storage compound and platinum group metals supported on a refractory metal oxide, and the on-wall coating includes a porous oxidic compound with minimal platinum group metal content, optimizing filtration efficiency without significant back-pressure rise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If higher catalyst loading is applied to achieve higher particle filtration efficiency, then filtration efficiency is improved, but back-pressure increases
Solution Approach 1:
The catalytic washcoat is segmented into two distinct locations: in-wall coating within the substrate pores and on-wall coating on the substrate surface. This segmentation allows particle filtration to occur primarily in the in-wall coating region while the on-wall coating handles catalytic conversions, reducing the catalyst loading required in the filtration path and thereby minimizing back-pressure increase.
Solution Approach 2:
Different regions of the substrate are assigned different functions with different coating compositions. The in-wall coating region is optimized for particle filtration with appropriate porosity and catalyst loading, while the on-wall coating region is optimized for catalytic reactions. This local differentiation allows each region to be optimized for its specific function without compromising the other.
2Reliability
If higher catalyst loading is applied to achieve desired filtration efficiency in fresh state, then filtration efficiency is improved, but back-pressure increase becomes steeper during catalyst lifetime
Solution Approach 1:
By segmenting the catalytic washcoat into in-wall and on-wall coatings, the system achieves the desired filtration efficiency in the fresh state without requiring excessively high catalyst loading. The on-wall coating compensates for catalyst deactivation over time by providing additional active sites, thereby maintaining stable back-pressure throughout the catalyst's operational lifetime.
Solution Approach 2:
The invention changes the distribution parameter of catalyst loading from uniform high loading to differentiated loading between in-wall and on-wall regions. This parameter change allows the system to maintain filtration efficiency while preventing excessive back-pressure increase during the catalyst's service life.
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 catalyst achieves improved particle filtration efficiency with a moderate increase in back-pressure, maintaining vehicle performance and fuel economy by distributing the catalyst loading effectively between in-wall and on-wall coatings.
Implementation Method 1
the catalyst comprises a porous wall flow filter substrate... the catalyst achieves improved particle filtration efficiency
Implementation Method 2
three-way conversion catalytic in-wall coating which comprises an oxygen storage compound and a platinum group metal supported on a refractory metal oxide
Implementation Method 3
oxygen storage compound... four-way conversion catalyst for the treatment of an exhaust gas stream
Data Source
AI summary
A four-way conversion catalyst for treating a gasoline engine exhaust gas has a porous wall flow filter substrate with an inlet end, outlet end, substrate axial length extending between the inlet and outlet end, and passages defined by porous internal walls of the substrate, the passages having inlet passages with an open inlet and closed outlet, and outlet passages having a closed inlet and open outlet. The internal wall pores have a three-way conversion catalytic in-wall coating with an oxygen storage compound and a platinum group metal supported on a refractory metal oxide. On at least a portion of the internal wall surface defining the interface between the internal walls and the passages, the catalyst has a porous on-wall coating from the internal wall surface to the passage. The coating has porous oxidic compound and platinum group metal content of 0 to 0.001 wt. %, of the total coating weight.