Exhaust Gas Catalyst Dual-Layer Structure for NOx Purification
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Solution Overview
Problem
Existing exhaust gas purification catalysts face challenges in maintaining efficient NOX purification performance under varying exhaust gas atmospheres, particularly when transitioning from lean to rich conditions, due to fluctuations in air-fuel ratios and road conditions, which current technologies struggle to adapt to effectively.
Innovation Solution
The development of an exhaust gas purification catalyst with a lower layer of ceria-based oxide particles having a specific particle size distribution and an upper layer with a precious metal supported on metal oxide particles, where the lower layer is designed to provide sustained oxygen release and the upper layer enhances purification performance under stoichiometric conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single-layer catalyst structure is used, then the device complexity is reduced, but the adaptability to varying exhaust gas atmospheres deteriorates
Solution Approach 1:
The catalyst is divided into two functional layers: a lower layer containing ceria-based oxide particles for oxygen storage and release, and an upper layer containing precious metal supported on metal oxide particles for catalytic purification. This segmentation allows each layer to specialize in specific functions, improving adaptability to varying exhaust gas atmospheres while maintaining manageable device complexity.
Solution Approach 2:
The invention transitions from a single-layer homogeneous structure to a multi-layer heterogeneous structure with distinct functional zones. The vertical dimension is utilized to create a gradient of functionality, with the lower layer providing oxygen buffer capacity and the upper layer providing catalytic activity, thereby enhancing adaptability without excessive complexity.
2Reliability
If the Rh content in the lower layer is increased, then the NOX purification performance is improved, but the cost and precious metal consumption increase
Solution Approach 1:
Rhodium is distributed non-uniformly across the catalyst structure, with limited amounts in the lower layer (not more than 0.25 g/L) and concentrated in the upper layer where it is most needed for catalytic activity. This local quality approach ensures adequate NOX purification performance while minimizing overall precious metal consumption.
Solution Approach 2:
The ceria-based oxide particles in the lower layer act as an intermediary for oxygen storage and release, reducing the direct dependency on rhodium for all purification functions. This intermediary mechanism allows the system to maintain NOX purification performance with reduced rhodium content by providing oxygen buffer capacity that supports the precious metal in the upper layer.
3Manufacturing precision
If the ceria-based oxide particles have a narrow particle size distribution, then the manufacturing precision is improved, but the oxygen release characteristics and adaptability to different atmospheres deteriorate
Solution Approach 1:
The invention specifies a controlled particle size distribution for ceria-based oxide particles with a peak in the range of 0.90 to 6.50 μm. This parameter optimization balances manufacturing feasibility with functional performance, ensuring adequate oxygen storage and release characteristics while maintaining reasonable manufacturing precision through defined particle size specifications.
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 enables the catalyst to maintain excellent NOX purification performance and adapt to various exhaust gas atmosphere changes, ensuring effective purification even under high load and temperature conditions, thereby meeting stringent regulatory standards.
Implementation Method 1
it is common to include a ceria component, which has a function of occluding and releasing oxygen, in the exhaust gas purification catalyst
Implementation Method 2
three-way catalysts in which a precious metal is supported on an inorganic oxide are known. Three-way catalysts which can efficiently remove hydrocarbons (HC), nitrogen oxides (NOX), and carbon monoxide (CO) at the same time are widely used.
Data Source
AI summary
An exhaust-gas purifying catalyst includes a lower layer containing ceria-based oxide particles and an upper layer containing metal oxide particles and a precious metal supported on the metal oxide particles, wherein the exhaust-gas purifying catalyst is characterized in that the Rh content of the lower layer is equal to or less than 0.25 g/L, and also that the particle-size distribution of the ceria-based oxide particles in the lower layer, which is obtained by scanning electron microscopy, has a first peak in which the peak top thereof is in a region of 0.90-6.50 μm and a second peak in which the peak top thereof is in a region of 9.50-34.0 μm.