Multi-Layer Exhaust Catalyst Segmentation for HC Poisoning
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Solution Overview
Problem
Existing catalyst systems for exhaust gas purification from internal combustion engines face challenges in achieving high oxidation efficiency for hydrocarbons (HC), carbon monoxide (CO), and nitrogen oxides (NO) simultaneously, as the optimal weight ratios of platinum to palladium in single catalyst layers are difficult to determine and palladium is prone to poisoning by HC.
Innovation Solution
A catalyst device with multiple layers, where the first layer is optimized for HC oxidation with a specific Pt/Pd ratio on the upstream side, the second layer for NO oxidation with a higher Pt content on the downstream side, and the third layer for CO oxidation with a high Pd content in a lower layer, reducing HC poisoning and enhancing overall oxidation efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a single catalyst layer with uniform Pt/Pd ratio is used, then the structure is simple, but high oxidation efficiency for HC, CO, and NO cannot be achieved simultaneously
Solution Approach 1:
The catalyst is divided into three distinct coating layers (first, second, and third layers) with different Pt/Pd weight ratios. The first layer has a ratio of 0.50 to 2.00, the second layer has a ratio of 2.00 to 5.00, and the third layer has a ratio of 5.00 to 20.00. This segmentation allows each layer to optimize for different oxidation reactions, achieving high efficiency for HC, CO, and NO simultaneously while managing the complexity through a systematic multi-layer structure.
Solution Approach 2:
Different regions of the catalyst (different coating layers) are assigned different Pt/Pd ratios tailored to specific functions. The first layer with lower Pt/Pd ratio is optimized for HC oxidation, the second layer with intermediate ratio for CO oxidation, and the third layer with highest ratio for NO oxidation. This local quality differentiation enables each region to perform its specific oxidation function optimally.
2Productivity
If palladium content is increased to improve CO oxidation, then CO purification efficiency improves, but palladium poisoning by HC increases
Solution Approach 1:
The catalyst is segmented into three layers with progressively increasing Pt/Pd ratios. The first layer contains the highest Pd content (lowest Pt/Pd ratio of 0.50 to 2.00) and is positioned to handle HC oxidation first, protecting the Pd in subsequent layers from HC poisoning. The second layer (Pt/Pd ratio of 2.00 to 5.00) and third layer (Pt/Pd ratio of 5.00 to 20.00) contain progressively less Pd, which remains available for CO oxidation without being poisoned by HC.
Solution Approach 2:
The first catalyst layer with high Pd content is positioned upstream to perform HC oxidation first, before the exhaust gas reaches the subsequent layers. This preliminary action removes or reduces HC concentration before it can poison the Pd in the second and third layers, thereby protecting the CO oxidation function while maintaining high Pd utilization in the first layer.
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 multi-layer catalyst device achieves high oxidation efficiency for HC, CO, and NO, inhibiting palladium poisoning and maintaining high catalyst activity across all layers, thereby improving exhaust gas purification performance.
Implementation Method 1
the first catalyst coating layer contains platinum and palladium, and the ratio (WPt1/WPd1) of the weight of the platinum (WPt1) to the weight of the palladium (WPd1) is 0.75 to 4.50
Implementation Method 2
HC are purified by being oxidized to water (H2O) and carbon dioxide (CO2) by the DOC
Implementation Method 3
the second catalyst coating layer contains platinum and palladium, and the ratio (WPt2/WPd2) of the weight of the platinum (WPt2) to the weight of the palladium (WPd2) is greater than 4.50 to 25.0
Implementation Method 4
CO is purified by being oxidized to carbon dioxide (CO2) by the DOC
Implementation Method 5
the third catalyst coating layer at least contains palladium, and the ratio (WPt3/WPd3) of the weight of the platinum (WPt3) to the weight of the palladium (WPd3) is 0.12 or less
Implementation Method 6
a portion of the NO is first oxidized to NO2 by the DOC
Data Source
AI summary
An oxidation catalyst device for exhaust gas purification, having a first catalyst coating layer on the exhaust gas flow's upstream side, second catalyst coating layer of an upper layer on exhaust gas flow's downstream side, and third catalyst coating layer of a lower layer on exhaust gas flow's downstream side, on a substrate, wherein the weight ratio of platinum to palladium in the first catalyst coating layer is 0.75 to 4.50, weight ratio of platinum to palladium in second catalyst coating layer is greater than 4.50 to 25.0, weight ratio of platinum to palladium in third catalyst coating layer is 0.12 or less, the length of first catalyst coating layer is 8% to 55% of the substrate's length, length of second catalyst coating layer is 45% to 95% of the substrate's length, and length of third catalyst coating layer is 45% to 95% of the substrate's length.