Double-Layer Three-Way Catalyst for Oscillating Lambda Conditions
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Solution Overview
Problem
Gasoline engines operating under oscillating lean and rich conditions pose challenges for three-way catalyst systems in achieving optimal pollutant conversion, particularly in maintaining efficient hydrocarbon reduction under rich conditions, necessitating the development of catalyst formulations and systems that can operate effectively across a broader lambda range without compromising emission performance.
Innovation Solution
A double-layer three-way catalyst system is introduced, comprising a first layer with active alumina, cerium/zirconium mixed oxide, and palladium, and a second layer with active alumina, rhodium, and neodymium/zirconium mixed oxide, where the second layer is free of cerium and cerium-containing materials, optimized for improved NOx reduction and hydrocarbon conversion across varying lambda conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If oxygen storage material (OSM) in the form of Ce-mixed oxides is included in the TWC formulation to broaden optimal operation, then the catalyst can operate under a broader lambda range, but the hydrocarbon conversion drops rapidly under purely rich conditions
Solution Approach 1:
The catalyst is divided into two distinct layers: a first layer containing Ce-mixed oxides for oxygen storage and lean-condition operation, and a second layer free of cerium for rich-condition hydrocarbon conversion. This segmentation allows each layer to be optimized for its specific function without the negative interactions that occur when cerium is present during rich conditions.
Solution Approach 2:
Different regions of the catalyst (layers) have different compositions tailored to local requirements: the first layer has high oxygen storage capacity for lean conditions, while the second layer has enhanced hydrocarbon conversion capability for rich conditions. This local quality differentiation resolves the contradiction by providing the right properties in the right location.
2Reliability
If multiple catalyst bricks with different formulations are used to optimize emission performance, then emission conversion is improved, but the application complexity increases
Solution Approach 1:
The patent combines the functions of multiple catalyst bricks into a single integrated catalyst unit with two layers. The first layer provides oxygen storage and lean-condition conversion, while the second layer provides rich-condition conversion. This merging maintains the emission performance benefits of multiple catalysts while reducing the complexity of having multiple separate components.
Solution Approach 2:
The two-layer catalyst structure provides multi-functionality within a single device: it can effectively treat both lean and rich exhaust conditions, covering the full range of engine operating conditions. This universal capability replaces the need for multiple specialized catalyst bricks.
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 system demonstrates enhanced NOx reduction and hydrocarbon conversion efficiency compared to conventional systems, as evident in the comparative testing, showcasing improved performance under dynamic driving conditions without increasing application complexity.
Implementation Method 1
oxygen storage material (OSM) in the form of Ce-mixed oxides were included in the formulation of the TWC
Implementation Method 2
a second layer applied to the first layer and in direct contact with the exhaust gas to be purified, comprising active alumina and rhodium as a catalytically active noble metal
Implementation Method 3
mainly NO x are reduced to nitrogen N2 using e.g. CO as reducing agent
Implementation Method 4
CO and HC are catalytically oxidized to carbon dioxide and water
Data Source
AI summary
The present invention describes a three-way-catalyst system comprising a first three-way catalyst on an inert catalyst support which is a double-layer catalyst comprising a first layer on the inert catalyst support, comprising active alumina, a cerium/zirconium mixed oxide and palladium and a second layer applied to the first layer and in direct contact with the exhaust gas to be purified, comprising active alumina and rhodium and being free of cerium and cerium containing materials and a second three-way-catalyst located upstream of the first three-way catalyst.