Layered Exhaust Catalyst Layout for Lean NOx Storage
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Solution Overview
Problem
Existing catalysts for exhaust gas purification from internal combustion engines face challenges in achieving effective NOx storage performance during lean start conditions due to the inhibition of NO oxidation by co-existing CO, leading to delayed NOx storage reactions and increased emissions.
Innovation Solution
A catalyst design with a lower layer containing higher Pd concentration on the upstream side and a downstream side with lower Pd concentration, promoting rapid CO purification and heat transfer to enhance NO oxidation and storage reactions, thereby improving NOx storage performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If a three-way catalyst is used to purify exhaust gas, then CO, HC, and NOx can be purified simultaneously, but the catalyst requires precise air-fuel ratio control and shows performance degradation over time
Solution Approach 1:
The patent introduces a dual-catalyst system where a first catalyst (e.g., Pt-Rh) and a second catalyst (e.g., Pd-Ba) work sequentially. The first catalyst performs primary purification of CO, HC, and NOx, while the second catalyst acts as an intermediary to further purify remaining pollutants and regenerate active components, thereby stabilizing overall catalyst performance over time.
Solution Approach 2:
The patent employs composite catalyst structures combining different metallic components (Pt, Rh, Pd, Ba) and support materials (alumina, ceria). These composite materials leverage the complementary strengths of each component: Pt and Rh for high-temperature NOx reduction, Pd for low-temperature CO oxidation, and Ba for oxygen storage, achieving both high purification efficiency and long-term stability.
2Productivity
If catalyst temperature is increased to improve purification efficiency, then reaction rate increases, but catalyst damage and performance degradation accelerate
Solution Approach 1:
The patent utilizes oxygen storage capacity (OSC) of ceria-based materials to dynamically adjust the local oxygen concentration around catalyst active sites. This parameter change allows the catalyst to maintain high purification efficiency without requiring excessive temperature increases, as the OSC buffer provides oxygen during fuel-rich conditions and absorbs excess oxygen during fuel-lean conditions, stabilizing reaction conditions.
Solution Approach 2:
The patent incorporates thermal barrier coatings and heat-resistant support materials (e.g., stabilized zirconia) that act as thermal buffers before heat reaches the active catalyst layers. This beforehand cushioning protects the catalyst from thermal shock and prevents rapid performance degradation during transient high-temperature events such as cold starts or rapid acceleration.
3Object-generated harmful factors
If noble metal loading is increased to enhance catalytic activity, then purification performance improves, but manufacturing cost increases significantly
Solution Approach 1:
The patent employs localized noble metal deposition where Pt, Rh, and Pd are selectively positioned in different zones or layers of the catalyst structure based on their specific functions. For example, Pt is concentrated in the washcoat layer for maximum surface area contact, while Rh is positioned in specific channels for NOx reduction, optimizing the distribution of expensive noble metals rather than uniform loading throughout the entire catalyst volume.
Solution Approach 2:
The patent utilizes highly porous support structures (ceramic honeycomb substrates with high surface area-to-volume ratio, mesoporous alumina washcoats) that dramatically increase the available surface area for catalytic reactions. This porous architecture allows much lower noble metal loadings to achieve the same purification efficiency, as the increased surface area provides more active sites per unit mass of expensive metal.
4Ease of manufacture
If catalyst structure is simplified to reduce manufacturing complexity, then production cost decreases, but catalyst effectiveness and selectivity are compromised
Solution Approach 1:
The patent divides the catalyst into functional segments or zones: a substrate layer for structural support, a washcoat layer for high surface area, and active metal dispersion layers for specific reactions. Each segment performs a specialized function, allowing the overall catalyst to achieve high purification effectiveness while each individual segment remains relatively simple to manufacture using standard industrial processes.
Solution Approach 2:
The patent designs the catalyst substrate and washcoat materials to perform multiple functions simultaneously: the ceramic honeycomb substrate provides both structural support and thermal management; the ceria-alumina washcoat provides oxygen storage, thermal stability, and additional catalytic activity. This multi-functionality reduces the need for separate components, simplifying manufacturing while maintaining or enhancing purification effectiveness.
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 enhanced NOx storage performance in lean atmospheres by quickly purifying CO and heating the catalyst to activation temperature, reducing NOx emissions across a wide range of air-fuel ratios.
Implementation Method 1
Catalyst for exhaust gas purification
Implementation Method 2
Catalyst for exhaust gas purification
Data Source
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AI summary
Provided is a catalyst for exhaust gas purification that has improved NOx storage performance in a lean atmosphere. A catalyst 100 for exhaust gas purification disclosed herein includes a substrate 10 and a catalyst layer 20. The catalyst layer 20 includes a lower layer 22, a middle layer 24, and an upper layer 26. The upper layer 26 contains Rh. The middle layer 24 contains at least Pt and a NOx storage material. The lower layer 22 has a lower-layer front portion 22a containing Pd and a lower-layer rear portion 22b containing Pd. The Pd content (CF) in the lower-layer front portion 22a per L of the substrate is greater than the Pd content (CR) in the lower-layer rear portion 22b per L of the substrate.