Double-Layer Three-Way Catalytic Converter Aging Resistance
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Solution Overview
Problem
Current three-way catalytic converters face challenges in maintaining high temperature stability and dynamic conversion capacity after aging, particularly under stringent emissions regulations such as Euro 6c, which demands improved light-off temperatures and pollutant conversion efficiency.
Innovation Solution
A double-layer three-way catalytic converter design is implemented, where the proportion of rare earth metal oxides in the cerium/zirconium/rare earth metal mixed oxides is strategically distributed between two layers, with layer A containing palladium and layer B containing rhodium or palladium, and both layers supported on active aluminum oxide, enhancing the catalyst's temperature stability and dynamic conversion capabilities.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a single-layer three-way catalyst is used, then the structure is simple, but the temperature stability and dynamic conversion capacity after aging are insufficient
Solution Approach 1:
The catalyst is divided into two functional layers: a first layer containing a temperature-stable metal oxide (e.g., zirconium oxide, hafnium oxide) providing structural stability and resistance to thermal aging, and a second layer containing oxygen storage materials (e.g., cerium oxide) and active components for pollutant conversion. This segmentation allows each layer to specialize in its function, improving overall reliability after aging while maintaining reasonable structural complexity.
Solution Approach 2:
The patent employs composite material structures in both layers. The first layer uses composite metal oxides (e.g., ZrO2-HfO2, ZrO2-CeO2) to achieve temperature stability. The second layer combines oxygen storage materials with platinum group metals to enhance dynamic conversion capacity. These composite materials provide synergistic effects that improve aging resistance without excessive complexity.
2Productivity
If the catalyst is positioned close to the engine, then exhaust gas purification after cold start is improved, but the catalyst must withstand higher temperatures which accelerates aging
Solution Approach 1:
The first layer is designed with temperature-stable metal oxides that pre-establish thermal resistance before the catalyst is exposed to high-temperature exhaust gases. This preliminary structural preparation allows the catalyst to be positioned close to the engine for improved cold-start purification while the first layer already provides protection against thermal degradation and aging.
Solution Approach 2:
The temperature-stable metal oxide layer acts as a protective cushion that absorbs and dissipates thermal stress before it reaches the sensitive active components in the second layer. This beforehand cushioning effect enables the catalyst to withstand high temperatures near the engine without accelerated aging, maintaining both productivity and reliability.
3Stability of the object's composition
If high zirconium content is used in the mixed oxide, then temperature stability is improved, but the oxygen storage capacity may be reduced
Solution Approach 1:
The patent applies local quality by concentrating temperature-stable metal oxides (high zirconium content) in the first layer where thermal stability is most needed, while the second layer contains oxygen storage materials with appropriate composition for maximum oxygen storage capacity. This spatial differentiation of material properties allows each layer to optimize its function without compromising the other, achieving both temperature stability and oxygen storage capacity.
Solution Approach 2:
The use of composite metal oxides in the first layer (e.g., ZrO2-HfO2, ZrO2-CeO2) provides synergistic effects where the combination of materials delivers both high temperature stability and retained oxygen storage capacity. The composite structure allows zirconium to provide thermal stability while other components contribute to oxygen storage, resolving the trade-off between these two properties.
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 significantly reduces light-off temperatures and improves dynamic conversion capacity after aging, ensuring effective pollutant conversion even under demanding conditions, as demonstrated by improved T50 temperatures and conversion rates in engine test bench results.
Implementation Method 1
Oxygen storage materials, such as cerium/zirconium mixed oxides. In the latter, cerium oxide, a rare-earth metal oxide, is the key component for oxygen storage.
Implementation Method 2
The catalytically active materials used are typically platinum group metals, especially platinum, palladium, and rhodium, which are present, for example, on γ-aluminum oxide as a support material. Three-way catalytic converters, operating near λ = 1, are able to simultaneously convert hydrocarbons, carbon monoxide, and nitrogen oxides into harmless components.
Implementation Method 3
double-layer catalysts are frequently used, which allow for the separation of different catalytic processes and thus an optimal coordination of the catalytic effects in the two layers.
Data Source
AI summary
The present invention relates to a catalyst comprising two layers on an inert catalyst support, wherein a layer A lying directly on the catalyst support contains at least one platinum group metal and a cerium/zirconium/rare earth metal mixed oxide, and a layer B applied to layer A and in direct contact with the exhaust gas stream contains at least one platinum group metal and a cerium/zirconium/rare earth metal mixed oxide, characterized in that the proportion of the rare earth metal oxide in the cerium/zirconium/rare earth metal mixed oxide of layer A is smaller than the proportion of the rare earth metal oxide in the cerium/zirconium/rare earth metal mixed oxide of layer B.