Layered Exhaust Catalyst Coating for Hot Range Purification
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Solution Overview
Problem
Conventional exhaust gas purifying catalysts fail to meet the stringent emission reduction demands in the Hot range (400-600°C) due to inadequate high-temperature performance.
Innovation Solution
The catalyst features a layered structure with specific noble metal and ceria-zirconia compound oxides in the inside and outside layers, optimized with weight ratios and additional components like rare earth and alkaline earth elements, enhancing purification performance by improving heat resistance and catalytic activity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional single-layer catalyst coating is used, then the structure is simple and manufacturing is easy, but the purification performance in the Hot range (400-600°C) is insufficient
Solution Approach 1:
The catalyst coating is divided into multiple layers (first catalyst coating layer and second catalyst coating layer) with different ceria-zirconia compositions. The first layer contains ceria-zirconia with a specific ratio optimized for Hot range performance, while the second layer has a different ratio for complementary function. This segmentation allows each layer to perform its specialized function, resolving the contradiction between performance and complexity.
Solution Approach 2:
Different regions of the catalyst coating are assigned different ceria-zirconia compositions tailored to local requirements. The first catalyst coating layer uses ceria-zirconia with one specific ratio for Hot range optimization, while the second layer uses a different ratio. This local differentiation of material properties enables the system to achieve high purification performance across different operating conditions without requiring a completely complex redesign.
2Duration of action of stationary object
If the ceria-zirconia ratio is optimized for high temperature heat resistance, then durability improves, but low temperature ignitability deteriorates
Solution Approach 1:
The catalyst coating is segmented into two layers, each with different ceria-zirconia ratios optimized for different temperature ranges. The first layer contains ceria-zirconia with a ratio optimized for high-temperature stability and heat resistance, while the second layer has a different ratio that maintains low-temperature ignitability. This segmentation allows the system to simultaneously achieve both high-temperature durability and low-temperature activation without compromise.
Solution Approach 2:
The ceria-zirconia ratio parameter is changed between layers to optimize performance for different temperature conditions. By varying this critical compositional parameter across layers, the system achieves high-temperature heat resistance in one layer while maintaining low-temperature ignitability in another, resolving the contradiction between these opposing requirements.
3Reliability
If emission reduction in Hot range is prioritized, then purification performance improves, but catalyst complexity and manufacturing difficulty increase
Solution Approach 1:
The catalyst is segmented into two coating layers applied in sequence, with each layer containing ceria-zirconia at different ratios. This segmentation enables optimization for Hot range emission reduction while maintaining a relatively straightforward manufacturing process using conventional coating techniques applied in multiple stages.
Solution Approach 2:
The catalyst uses composite ceria-zirconia materials with different compositional ratios in different layers. These composite materials provide enhanced purification performance in the Hot range while the layered composite structure can be manufactured using established catalyst coating technologies, balancing performance improvement with manufacturing feasibility.
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 exhibits significantly improved NOx purification efficiency and durability in the Hot range, outperforming conventional systems in emission reduction tests.
Implementation Method 1
a catalyst containing a refractory inorganic oxide such as cerium-zirconium compound oxide (CeZr compound oxide) and others and a noble metal such as Pd, Pt, Rh and others
Implementation Method 2
removes toxic substances, such as CO, HC, NOx and others, contained in exhaust gas
Implementation Method 3
removes toxic substances, such as CO, HC, NOx and others, contained in exhaust gas
Implementation Method 4
a compound oxide of (i) Ce, (ii) Zr, and (iii) an element selected from a group consisting of rare earth elements, alkaline earth elements and Y
Data Source
Figure 1
Figure 2
AI summary
An exhaust gas purifying catalyst exhibiting high purification performance in the Hot range is provided. The exhaust gas purifying catalyst has a catalyst substrate and a catalyst coating layer formed on the catalyst substrate. The catalyst coating layer has a layered structure including an inside layer a containing the component (a-1) and the component (a-2) described below, and an outside layer b containing the component (b-1) and the component (b-2) described below. Component (a-1) and component (b-1): noble metals. Component (a-2): a compound oxide of (i) Ce, (ii) Zr and (iii) an element selected from the group consisting of rare earth elements, alkaline earth elements and Y, having a ratio of (ii) to (i) within the range of more than 40/100 but not more than 100/2 in terms of the weight ratio between CeO2 and ZrO2. Component (b-2): a compound oxide of elements including at least (v) and (vi) selected among (iv) Ce, (v) Zr and (vi) an element selected from the group consisting of rare earth elements, alkaline earth elements and Y, having a ratio of (v) to (iv) of not more than 40/100 in terms of the weight ratio between CeO2 and ZrO2.