Multilayer Exhaust Catalyst with Ce-Free Middle Layer
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Solution Overview
Problem
Exhaust gas purification catalysts face challenges in achieving high cold hydrocarbon (HC) purification performance at low temperatures and hot nitrogen oxide (NOx) purification performance at high load conditions, requiring a catalyst that balances both effectively.
Innovation Solution
A multilayer catalyst structure is employed, with a Ce-free layer between layers containing Pd and Rh, and a specific cerium content ratio in the Ce-containing oxide layers to optimize both cold HC and hot NOx purification performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a Ce-containing oxide carrier is used to store and release oxygen for stabilizing catalyst performance, then hot NOx purification performance is improved, but cold HC purification performance at low temperature deteriorates
Solution Approach 1:
The catalyst coat layer is divided into multiple layers with different compositions and functions. The lower layer contains Pd and Ce-containing oxide for hot NOx purification, while the upper layer contains Rh and alumina for cold HC purification. This segmentation allows each layer to optimize its performance for specific temperature ranges and pollutant types, resolving the contradiction between hot and cold performance.
Solution Approach 2:
Different regions of the catalyst coat layer are assigned different material compositions tailored to local functional requirements. The lower layer near the substrate uses Ce-containing oxide for oxygen storage and release at high temperatures, while the upper layer uses alumina with Rh for low-temperature HC oxidation. This local quality differentiation enables simultaneous optimization of both hot and cold purification performance.
2Device complexity
If Pd and Rh are supported in the same carrier layer, then device complexity is reduced, but purification performance for both cold HC and hot NOx deteriorates
Solution Approach 1:
The catalyst coat layer is segmented into at least two distinct layers: a lower layer containing Pd supported on Ce-containing oxide, and an upper layer containing Rh supported on alumina. This segmentation allows each noble metal to function in its optimal environment, with Pd handling NOx reduction at high temperatures and Rh handling HC oxidation at low temperatures, thereby improving overall purification performance despite increased structural complexity.
3Reliability
If the catalyst coat layer is made into a multilayer structure with separate Pd and Rh layers, then cold HC and hot NOx purification performance are improved, but device complexity increases
Solution Approach 1:
The multilayer structure implements local quality by assigning specific material compositions to specific layers based on their functional requirements. The lower layer uses Pd/Ce-containing oxide for high-temperature NOx purification, while the upper layer uses Rh/alumina for low-temperature HC purification. This localized optimization of material properties enables simultaneous improvement of both cold and hot performance.
Solution Approach 2:
The catalyst employs composite material structures in each layer: Pd combined with Ce-containing oxide in the lower layer, and Rh combined with alumina in the upper layer. These composite materials provide synergistic effects where the support materials enhance the catalytic activity and stability of the noble metals, enabling improved performance across different temperature ranges.
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 multilayer structure with a Ce-free layer and optimized cerium content ratio enhances cold HC and hot NOx purification performance, achieving better emission control across varying engine conditions.
Implementation Method 1
Ce-containing oxides (for instance, ceria-zirconia complex oxides) having oxygen storage capacity (OSC) have been widely used as a carrier of the noble metal, for the purpose of mitigating atmosphere variations in the air-fuel ratio at which the catalyst works effectively
Implementation Method 2
Three-way catalysts containing at least one noble metal from among Pt (platinum), Pd (palladium) and Rh (rhodium) are often used in order to purify exhaust gas emitted from an internal combustion engines
Data Source
Figure 1~2
AI summary
The exhaust gas purification catalyst according to the present invention includes a substrate 10 and a catalyst coat layer 30. The catalyst coat layer 30 is formed into a multilayer structure having a lower layer 32, a middle layer 34 and an upper layer 36. The upper layer 36 contains Rh and a Ce-containing oxide. The lower layer 32 contains Pd and a Ce-containing oxide. The middle layer 34 is a Ce-free layer that contains Pd but does not contain a Ce-containing oxide. A ratio (B/A) of the content B of Ce in the lower layer 32 to the content A of Ce in the upper layer 36 satisfies 2≤(B/A).