Exhaust Catalyst Layer Segmentation for Oxygen Storage
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Solution Overview
Problem
Conventional exhaust gas purification catalysts using two OSC materials with different oxygen storage/release rates face challenges in optimizing both exhaust gas purification performance and OSC performance, with ceria-zirconia based composite oxides reducing catalyst metal activity and limiting improvements in OSC performance.
Innovation Solution
An exhaust gas purification catalyst with an uppermost catalyst layer comprising an upstream and downstream layer, where the first OSC material has a pyrochlore structure and the second OSC material has a higher oxygen storage/release rate, optimized in proportions of 0.55 to 0.73 and 0.27 to 0.55 respectively, to enhance OSC performance while maintaining exhaust gas purification efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If the OSC material content is increased to improve OSC performance, then the oxygen storage capacity is improved, but the exhaust gas purification performance is reduced due to reduced catalyst metal activity
Solution Approach 1:
The catalyst layer is segmented into multiple layers with different OSC material compositions. The upper catalyst layer contains a higher proportion of OSC materials (first and second OSC materials) to enhance oxygen storage capacity, while the lower catalyst layer contains less OSC material to maintain catalyst metal activity for exhaust gas purification. This segmentation allows each layer to optimize its function without compromising the other.
Solution Approach 2:
Different regions of the catalyst layer are assigned different OSC material contents based on local functional requirements. The upstream portion (upper catalyst layer) requires high OSC performance for oxygen storage during lean conditions, while the downstream portion (lower catalyst layer) requires high catalytic activity for pollutant conversion. This local quality differentiation resolves the contradiction by tailoring material composition to spatial functional demands.
2Adaptability or versatility
If two OSC materials with different oxygen storage/release rates are used together, then the OSC performance can be adjusted, but it is difficult to provide both high exhaust gas purification performance and high OSC performance simultaneously
Solution Approach 1:
The patent employs a composite material system consisting of two distinct OSC materials (first OSC material and second OSC material) with different oxygen storage/release characteristics. These materials are combined in specific proportions within the upper catalyst layer to create a composite OSC system that balances oxygen storage capacity and release rate, achieving both high OSC performance and maintained exhaust gas purification performance through synergistic material interaction.
3Quantity of substance
If ceria-zirconia based composite oxide is used as OSC material, then the OSC performance is improved, but the catalyst metal activity is reduced
Solution Approach 1:
The catalyst layer is divided into upper and lower layers to spatially separate the functions of oxygen storage and catalytic conversion. The upper catalyst layer contains high proportions of ceria-zirconia based composite oxides (first and second OSC materials) to maximize OSC performance, while the lower catalyst layer contains reduced OSC material content to preserve catalyst metal activity for efficient exhaust gas purification.
Solution Approach 2:
The composition of ceria-zirconia based composite oxides is optimized locally within different catalyst layers. The upper layer maintains high OSC material content (5-50 mass% first OSC material and 5-50 mass% second OSC material) for superior oxygen storage, while the lower layer reduces OSC material content to prevent excessive suppression of catalyst metal activity, thereby achieving local optimization of both OSC performance and catalytic activity.
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
This configuration improves OSC performance while maintaining exhaust gas purification efficiency, as demonstrated by the optimized proportions of OSC materials in the upstream and downstream catalyst layers, leading to enhanced oxygen storage and release capabilities.
Implementation Method 1
The OSC material causes NOx in the exhaust gas to be easily reduced by storing oxygen when the air-fuel mixture is lean and the oxygen concentration in the exhaust gas is high (lean exhaust gas), and causes CO and HC in the exhaust gas to be easily oxidized by releasing oxygen when the air-fuel mixture is rich and the oxygen concentration in the exhaust gas is low.
Implementation Method 2
a three-way catalyst that simultaneously performs oxidation of CO and HC and reduction of NOx is used as the exhaust gas purification catalyst, and a catalyst that contains a noble metal, such as platinum (Pt), palladium (Pd), and rhodium (Rh), as a catalyst metal is widely employed.
Data Source
AI summary
The present disclosure provides an exhaust gas purification catalyst improved in OSC performance while maintaining an exhaust gas purification performance, which comprises a substrate and at least one catalyst layer formed on the substrate, wherein an uppermost catalyst layer contains a catalyst metal, a first OSC material having a pyrochlore structure, and a second OSC material having a higher oxygen storage/release rate than the first OSC material, wherein the uppermost catalyst layer consists of an upstream catalyst layer and a downstream catalyst layer, and wherein a proportion of a mass of the second OSC material based on a total mass of the first OSC material and the second OSC material is in a specific range in each of the upstream catalyst layer and the downstream catalyst layer.