Multilayer Exhaust Catalyst Pd Rh Ratio Optimization
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Solution Overview
Problem
Exhaust gas purification catalysts exhibit low purification performance at low temperatures immediately after engine start-up and require improved warm-up and high-space velocity (SV) performance.
Innovation Solution
A multilayer catalyst coat structure with Pd in both the first-stage and second-stage layers, where the mass ratio of Pd to Rh is optimized between 0.5 and 3, and the OSC material CeO2 or CeO2-ZrO2 complex oxide is used to enhance warm-up and high-SV performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional single-layer catalyst coat structure is used, then the device complexity is low, but the warm-up performance and high-SV performance are insufficient
Solution Approach 1:
The catalyst coat layer is divided into multiple layers (first catalyst coat layer and second catalyst coat layer) with different compositions and functions. The first layer contains Pd and Rh for high-SV performance, while the second layer contains Pt and Rh for warm-up performance, allowing each layer to be optimized for its specific function rather than requiring a single complex layer to perform all functions
Solution Approach 2:
Different noble metals are distributed to different layers based on their catalytic characteristics. Pd and Rh are concentrated in the first layer where they excel at high-SV conditions, while Pt and Rh are placed in the second layer where they provide better warm-up performance. This local optimization of catalyst composition resolves the contradiction by giving each region its specialized function
2Reliability
If Pd is disposed only in the lower layer, then the manufacturing process is simple, but the warm-up performance is insufficient
Solution Approach 1:
The catalyst distribution is segmented by layer, with Pd primarily in the first catalyst coat layer and Pt in the second layer. This segmentation allows Pd to be deposited using simpler methods suitable for the first layer, while Pt is introduced in the second layer through separate deposition processes, maintaining manufacturing simplicity while achieving the desired warm-up performance through the layered structure
Solution Approach 2:
Pd is concentrated in the first catalyst coat layer where it provides excellent high-SV performance, while Pt is placed in the second layer where it enhances warm-up performance. This local quality differentiation allows each metal to be optimized for its specific location and function, resolving the contradiction between manufacturing simplicity and performance requirements
3Reliability
If the catalyst coat layer has a multilayer structure with optimized Pd and Rh distribution, then the warm-up performance and high-SV performance are improved, but the manufacturing precision requirements increase
Solution Approach 1:
The multilayer structure segments the catalyst distribution, with the first catalyst coat layer containing Pd and Rh in a mass ratio of 0.5 to 3, and the second layer containing Pt and Rh. This segmentation simplifies the manufacturing process by allowing each layer to be deposited with less stringent ratio control requirements, while the overall system achieves the desired performance through the combined effect of both layers
Solution Approach 2:
Each layer is given a specific catalyst composition optimized for its function: the first layer has Pd and Rh in a controlled mass ratio for high-SV performance, while the second layer has Pt and Rh for warm-up performance. This local quality optimization allows each layer to tolerate broader manufacturing variations individually, while the system as a whole maintains high performance
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 warm-up performance and high-SV performance by shifting Pd from the lower layer to the upper layer, maintaining effective HC purification and OSC capacity at varying air-fuel ratios.
Implementation Method 1
Ce-containing oxides (for instance ceria-zirconia complex oxides) having oxygen storage capacity (OSC) have been widely used as a carrier of the noble metal, for the purpose of mitigating atmosphere variations in air-fuel ratio at which the catalyst works effectively
Implementation Method 2
Three-way catalysts containing at least one noble metal from among Pt (platinum), Pd (palladium) and Rh (rhodium) are often used in order to purify exhaust gas emitted by an internal combustion engine
Data Source
AI summary
An exhaust gas purification catalyst of the present invention is provided with a base 10 and a catalyst coat layer 30. The catalyst coat layer is provided with Rh and Pd as noble metal catalysts. Herein Rh is disposed in a first-stage upper layer A and a second-stage upper layer C, and Pd is disposed in the first-stage upper layer A and a first-stage lower layer B, and in a second-stage lower layer D. A mass ratio (APd/ARh) of Pd to Rh, disposed in first-stage upper layer A is 0.5≤(APd/ARh)≤3.