Exhaust Gas Purification Catalyst with Layered CeO2 Distribution
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Solution Overview
Problem
Exhaust gas purification catalysts designed for specific operation states of internal combustion engines fail to maintain effective purification performance when the engine's operating conditions change, leading to increased emissions of harmful components.
Innovation Solution
An exhaust gas purification catalyst with a stacked structure of four catalyst layers, each with varying compositions of CeO2 and catalytic metals (Pd, Pt, Rh) to adapt to different engine operation states, including warm-up, fluctuations in air-fuel ratio, and high-speed operations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the catalyst is designed with fixed composition for specific operation state, then purification performance is improved for that state, but purification performance deteriorates when operation state changes
Solution Approach 1:
The catalyst layer is divided into multiple regions with different CeO2 content and catalytic metal compositions. The upstream side has lower CeO2 content (0-15 g/L) suitable for warm-up operation, while the downstream side has higher CeO2 content (20-63 g/L) suitable for fluctuating air-fuel ratio conditions. This spatial variation in composition allows the catalyst to adapt to different operation states without requiring multiple catalysts.
Solution Approach 2:
The catalyst layer is segmented into at least two layers stacked in the thickness direction, with each layer having different CeO2 content and catalytic metal compositions. This segmentation allows independent optimization of each layer for specific operation conditions, enabling the overall catalyst to handle multiple operation states effectively.
2Reliability
If CeO2 content is increased to improve oxygen storage capacity, then air-fuel ratio compensation ability is improved, but catalytic activity during warm-up operation deteriorates
Solution Approach 1:
Different CeO2 content is assigned to different spatial regions of the catalyst layer. The upstream region (closer to exhaust inlet) has lower CeO2 content (0-15 g/L) to maintain catalytic activity during warm-up, while the downstream region has higher CeO2 content (20-63 g/L) to provide oxygen storage capacity for air-fuel ratio compensation. This resolves the contradiction by localizing the oxygen storage function away from the warm-up critical zone.
Solution Approach 2:
The solution moves from a single uniform CeO2 content to a gradient distribution in the thickness direction of the catalyst layer. By utilizing the thickness dimension, the catalyst achieves both low CeO2 content (for warm-up) and high CeO2 content (for air-fuel ratio compensation) simultaneously in different spatial locations.
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 stable and efficient purification of harmful components across varying engine conditions by optimizing CeO2 and catalytic metal distributions to suit the various engine states, reducing emissions of harmful components like hydrocarbons and nitrogen oxides.
Implementation Method 1
CeO2 stores oxygen while exhaust gas in a lean state (excessive oxygen) is being supplied, and releases oxygen when exhaust gas in a rich state (insufficient oxygen) is being supplied
Implementation Method 2
The catalytic metal is a precious metal material that promotes the oxidation (or reduction) of the harmful components
Implementation Method 3
promotes the oxidation (or reduction) of the harmful components
Implementation Method 4
promotes the oxidation (or reduction) of the harmful components
Data Source
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AI summary
An exhaust gas purification catalyst disclosed herein includes: a substrate 10 that has a plurality of cells 12 and a partition wall 14 separating the plurality of cells 12; and a catalyst layer 20 provided on the surface of the partition wall 14. The catalyst layer 20 includes a lower catalyst layer 22 and an upper catalyst layer 24. A lower-layer front portion A containing Pd is provided on the upstream side of the lower catalyst layer 22, and a lower-layer rear portion B containing at least one among Pd and Pt is provided on the downstream side. Further, an upper-layer front portion C containing Rh is provided on the upstream side of the upper catalyst layer 24, and an upper-layer rear portion D containing Rh is provided on the downstream side. The lower-layer front portion A, the lower-layer rear portion B, the upper-layer front portion C, and the upper-layer rear portion D each have CeO2 content individually set. As a result, it is possible to provide an exhaust gas purification catalyst that can exhibit adequate purification performance according to an operation state of an internal combustion engine.