Exhaust Gas Purifying Catalyst Layered Palladium Structure
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Solution Overview
Problem
Current three-way catalyst systems used in automobiles are inadequate in reducing hydrocarbon (HC) emissions, as the concentration of palladium in the catalytic layer is too low to efficiently oxidize HC desorbed from hydrocarbon-adsorbing materials, leading to significant HC release into the atmosphere.
Innovation Solution
A layered structure of catalytic layers is introduced, with a second catalytic layer having a higher concentration of palladium and rhodium interposed between the substrate and the first catalytic layer, enhancing the oxidation efficiency of HC desorbed from the hydrocarbon-adsorbing layer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a three-way catalyst with low palladium concentration is used, then the catalyst structure is simpler and cost is lower, but the oxidation efficiency of hydrocarbon emissions is insufficient
Solution Approach 1:
The catalytic layer is divided into two distinct layers: a first catalytic layer with lower palladium concentration for general catalysis, and a second catalytic layer with higher palladium concentration specifically for oxidizing hydrocarbons. This segmentation allows each layer to be optimized for its specific function, improving overall HC oxidation efficiency while maintaining reasonable structural complexity.
Solution Approach 2:
Different regions of the catalytic layer are given different palladium concentrations according to their specific functions. The second catalytic layer, which directly contacts hydrocarbon-rich exhaust gas, is enriched with palladium to provide high oxidation efficiency, while the first catalytic layer maintains lower palladium concentration for cost-effectiveness and general catalytic activity.
2Productivity
If a single catalytic layer with uniform palladium concentration is used, then the manufacturing process is simpler, but the oxidation efficiency of desorbed hydrocarbons is insufficient
Solution Approach 1:
The single catalytic layer is segmented into two functional layers with different palladium concentrations. The first catalytic layer serves as a base layer with lower palladium content, while the second catalytic layer is an enriched layer with higher palladium content positioned to receive desorbed hydrocarbons. This segmentation improves HC oxidation efficiency while the layered structure can be manufactured using sequential deposition processes.
Solution Approach 2:
The first catalytic layer is formed first as a preliminary structure, followed by the deposition of the second catalytic layer with higher palladium concentration. This preliminary action allows the catalyst to be manufactured in a controlled sequence, building up the functional gradient from bottom to top, which facilitates the oxidation of desorbed hydrocarbons.
3Productivity
If hydrocarbon-adsorbing material is added to the catalyst, then HC emission can be reduced by adsorbing and desorbing HC, but the oxidation efficiency of desorbed HC becomes insufficient
Solution Approach 1:
The second catalytic layer is locally enriched with palladium specifically at the region where hydrocarbons desorb from the hydrocarbon-adsorbing material. This local quality enhancement ensures that the oxidation activity is concentrated exactly where it is most needed - at the interface with the desorbing hydrocarbons - thereby improving oxidation efficiency without requiring complex modifications to the entire catalytic structure.
Solution Approach 2:
The second catalytic layer acts as an intermediary between the hydrocarbon-adsorbing material and the exhaust gas stream. It receives desorbed hydrocarbons from the adsorbing material and provides the catalytic oxidation function, effectively mediating the conversion of adsorbed HC into oxidized products. This intermediary role highlights the need for high palladium concentration in this specific zone.
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
This configuration significantly decreases HC emissions by improving the oxidation efficiency of the catalytic system, as demonstrated by reduced THC emissions in endurance tests compared to traditional catalyst systems.
Implementation Method 1
a hydrocarbon-adsorbing layer covering the substrate... it is possible to allow HC adsorb on the hydrocarbon-adsorbing material when the temperature of the catalyst is low
Implementation Method 2
the precious metal plays the role in promoting the reduction of nitrogen oxides (NO x ) and the oxidations of carbon monoxide (CO) and hydrocarbons (HC)
Implementation Method 3
the refractory carrier plays the roles in increasing the specific surface area of the precious metal and supressing the sintering of the precious metal by dissipating heat generated by the reactions
Data Source
Figure 1~2
Figure 3~4
AI summary
Decreasing HC emission is made possible. An exhaust gas-purifying catalyst (1) includes a substrate (2), a hydrocarbon-adsorbing layer (3) covering the substrate (2), and a catalytic layer (4) covering the hydrocarbon-adsorbing layer (3). The catalytic layer (4) includes a layered structure of a first catalytic layer (4a) including a precious metal and a carrier supporting it, and a second catalytic layer (4b) including the same precious metal as the precious metal of the first catalytic layer (4a) and a carrier supporting it and having a concentration of the precious metal higher than that in the first catalytic layer (4a).