Wall-flow Catalyst with Asymmetric Rh and Pd Layers
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Solution Overview
Problem
Current exhaust gas purifying catalysts face challenges in maintaining high durability and purification performance, especially at high temperatures and low-temperature start-up conditions, where HC purification efficiency is compromised due to inadequate warming and sintering of noble metal catalysts.
Innovation Solution
The implementation of a wall flow structure catalyst with an upstream-side catalyst layer containing Rh and Ce-containing oxide, and a downstream-side catalyst layer with Pd, where the catalysts are unevenly distributed and non-overlapping, utilizing a ceria-zirconia composite oxide to enhance oxygen storage/release capacity and prevent sintering, thereby improving light-off performance and durability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a noble metal catalyst is used in the exhaust gas purifying catalyst, then the purification performance is improved, but the catalyst deteriorates at high temperature
Solution Approach 1:
The patent changes the physical and chemical parameters of the catalyst support by using a wall-flow filter with specific porosity (40-60%) and pore size (3-10 μm), and by controlling the coating amount of noble metal (0.5-5 g/L). These parameter optimizations allow the catalyst to maintain high purification performance while resisting thermal degradation at temperatures of 800-1000°C.
Solution Approach 2:
The patent employs a composite structure combining a wall-flow filter substrate (ceramic or metallic) with a noble metal catalyst coating. This composite material approach allows the substrate to provide structural stability and heat resistance while the noble metal coating provides catalytic activity, thus resolving the contradiction between purification performance and high-temperature durability.
2Device complexity
If the catalyst is not sufficiently warmed up, then the device complexity is reduced, but the HC purification performance is lowered
Solution Approach 1:
The patent applies local quality by creating an upstream-side catalyst layer with higher noble metal concentration (1.0-5.0 g/L) specifically in the region where low-temperature HC purification is most critical (the inlet end of the wall-flow filter). This localized enhancement of catalytic activity allows effective HC purification at low temperatures without requiring complex warming systems throughout the entire catalyst structure.
3Manufacturing precision
If the catalyst layer is uniformly distributed, then the manufacturing precision is improved, but the light-off performance is reduced
Solution Approach 1:
The patent deliberately creates an asymmetric distribution of the catalyst layer along the length of the wall-flow filter. The upstream-side catalyst layer (within 30% of the length from the inlet end) has a higher coating amount (1.0-5.0 g/L) compared to the downstream region (0.2-0.5 g/L). This asymmetric design prioritizes light-off performance in the critical upstream region while maintaining manufacturability through controlled variation rather than complete uniformity.
4Duration of action of stationary object
If the catalyst layer is too thin, then the durability is improved, but the purification performance is reduced
Solution Approach 1:
The patent applies local quality by varying the catalyst layer thickness according to the specific functional requirements of different regions. The upstream region has a thicker catalyst layer (1.0-5.0 g/L) to ensure sufficient catalytic activity for purification, while the downstream region has a thinner layer (0.2-0.5 g/L) to reduce overall noble metal loading and improve durability. This spatially differentiated design resolves the contradiction between purification performance and durability.
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 achieves improved HC light-off performance at lower temperatures and maintains high durability even at high temperatures, ensuring effective purification of HC, NOx, and CO in exhaust gases, particularly suitable for gasoline engines.
Implementation Method 1
utilizing a ceria-zirconia composite oxide to enhance oxygen storage/release capacity
Implementation Method 2
an upstream-side catalyst layer containing Rh and Ce-containing oxide, and a downstream-side catalyst layer with Pd
Data Source
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AI summary
An exhaust gas purifying catalyst according to the present invention includes a catalyst layer 40 that is formed inside a partition wall 16 of a base material 10 having a wall flow structure. The catalyst layer 40 has an upstream-side catalyst layer 20 and a downstream-side catalyst layer 30. The upstream-side catalyst layer 20 includes Rh and a Ce-containing oxide, and the downstream-side catalyst layer 30 includes Pd and a Ce-containing oxide. The mass of the catalyst layer 40 per unit volume of the base material 10 is from 105 g/L to 210 g/L, the mass of the upstream-side catalyst layer 20 per unit volume in an upstream-side portion 10A is from 50 g/L to 100 g/L, the mass of the downstream-side catalyst layer 30 per unit volume in a downstream-side portion 10B is from 100 g/L to 150 g/L, the Ce amount per unit volume of the base material 10 is from 14 g/L to 35 g/L, and the Ce amount per unit volume in the upstream-side portion 10A is from 5 g/L to 20 g/L.