Exhaust Purification Catalyst High-Aspect-Ratio Pores
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Solution Overview
Problem
Existing exhaust gas purification catalysts face challenges in maintaining high purification performance under high intake air mass conditions due to reduced gas diffusivity and active site efficiency, particularly in lower layers exposed to low-concentration gases, where the thicker upper layer reduces poison resistance and gas reachability.
Innovation Solution
A multi-layer catalyst structure with a lower catalyst coating layer featuring high-aspect-ratio pores and a specific composition, including noble metals and metal oxides, is used, where the lower layer has a porosity of 50-80% and high-aspect-ratio pores account for 0.5-50% of the volume, oriented at 0-45 degrees to the exhaust gas flow, enhancing gas diffusivity and resistance to poisons.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the amount of coating in the upper layer is increased to improve resistance to poison, then the gas diffusivity in the catalyst coating layer is reduced, but the purification performance under high Ga condition deteriorates
Solution Approach 1:
The patent applies local quality by creating distinct catalyst coating layers with different properties: the upper layer contains Rhodium for poison resistance, while the lower layer contains Platinum for high activity and includes high-aspect-ratio pores for enhanced gas diffusivity. This spatial differentiation allows each layer to optimize its function without compromising the other.
Solution Approach 2:
The catalyst coating is segmented into multiple layers with distinct compositions and structures. The upper layer focuses on durability and poison resistance, while the lower layer focuses on catalytic activity and gas transport. This segmentation resolves the contradiction by distributing functions across separate segments rather than requiring a single uniform layer.
2Productivity
If a void is provided in the catalyst layer to enhance gas diffusivity, then the thickness of the catalyst layer is increased, but the pressure loss of the catalyst is increased
Solution Approach 1:
The patent incorporates high-aspect-ratio pores (with aspect ratios of 5 or more) in the lower catalyst coating layer. These porous structures enhance gas diffusivity by providing direct transport pathways while maintaining a relatively thin overall layer thickness, thus avoiding significant pressure loss.
Solution Approach 2:
Instead of creating voids that increase layer thickness (one-dimensional approach), the patent uses high-aspect-ratio pores that extend vertically through the coating layer. This dimensional approach allows gas to bypass the thickening effect while still achieving enhanced diffusivity.
3Reliability
If the thickness of the upper layer is increased to improve resistance to poison, then the gas reachability to the lower layer is reduced, but the purification performance under high Ga condition deteriorates
Solution Approach 1:
The high-aspect-ratio pores in the lower layer create efficient gas transport channels that allow exhaust gas to reach the Platinum catalyst particles even when the upper layer is sufficiently thick to provide poison resistance. The porous structure decouples the relationship between layer thickness and gas reachability.
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 achieves improved purification performance under high gas flow conditions while maintaining resistance to poisons and high-temperature stress, ensuring efficient NOx conversion and catalyst durability.
Implementation Method 1
a lower catalyst coating layer that is present lower with respect to an uppermost catalyst coating layer has a high-aspect-ratio pore at a certain rate... enhancing gas diffusivity
Implementation Method 2
An exhaust gas purification catalyst for decomposition of such harmful gases... a catalyst coating layer formed thereon by wash coating of a slurry including a noble metal particle having catalyst activity
Implementation Method 3
an auxiliary catalyst having oxygen storage capacity (OSC)
Data Source
Figure 1(A)~1(C)
Figure 2
Figure 3
AI summary
The problem of the present invention is to provide an exhaust gas purification catalyst which can exhibit sufficient purification performance under a high Ga condition while having a resistance to stress such as high-temperature and poisonous substances. The present invention relates to an exhaust gas purification catalyst comprising two or more catalyst coating layers on a substrate, wherein a lower catalyst coating layer that is present lower with respect to an uppermost catalyst coating layer has a structure where a large number of voids are included and high-aspect-ratio pores having an aspect ratio of 5 or more account for a certain proportion or more of the whole volume of voids, thereby to improve gas diffusivity in the lower catalyst coating layer.