Layered Exhaust Gas Catalyst to Limit PGM Sintering and Migration
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Solution Overview
Problem
Existing exhaust gas purification catalysts face degradation in performance due to sintering and migration of platinum group elements under high-temperature conditions, leading to reduced efficiency in purifying harmful components from engine exhaust.
Innovation Solution
A catalyst layer comprising a first layer with a specific composition of zirconium-cerium complex oxide and a second layer with aluminum oxide, each containing platinum group elements, is designed to maintain optimal performance by limiting sintering and migration, enhancing purification efficiency at low to medium temperatures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If alumina and Zr-Ce-based complex oxide are contained in one layer, then alloying of platinum group elements can be suppressed, but sintering and migration of platinum group elements occur under high-temperature environment, leading to decreased exhaust gas purification performance
Solution Approach 1:
The catalyst layer is divided into multiple sub-layers with distinct compositions. The first sub-layer contains alumina and Zr-Ce-based complex oxide with Pd, while the second sub-layer contains Rh supported on alumina. This segmentation prevents mixing of different platinum group elements and their supports, thereby suppressing sintering and migration that would occur if all components were in a single layer, while maintaining effective exhaust gas purification performance.
2Adaptability or versatility
If Zr-Ce-based complex oxide is used as support, then oxygen storage capacity is enhanced and operating window is expanded, but sintering of support materials occurs under high-temperature conditions, reducing catalyst durability
Solution Approach 1:
The catalyst layer is segmented into sub-layers where Zr-Ce-based complex oxide is specifically placed in the first sub-layer with Pd, separate from the Rh-containing second sub-layer. This segmentation prevents high-temperature sintering interactions between different supports and platinum group elements, maintaining the oxygen storage capacity and extended operating window while ensuring long-term catalyst durability through reduced thermal degradation.
Solution Approach 2:
Different regions (sub-layers) of the catalyst layer are assigned different compositions optimized for specific functions. The first sub-layer with Zr-Ce-based complex oxide and Pd is optimized for oxygen storage and low-temperature activity, while the second sub-layer with Rh on alumina is optimized for NOx reduction. This local quality differentiation prevents unwanted sintering interactions while maintaining overall catalyst 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
The catalyst layer configuration improves exhaust gas purification performance, particularly at low to medium temperatures, by suppressing sintering and migration of platinum group elements, thereby maintaining effective purification even after exposure to high temperatures.
Implementation Method 1
a three-way catalyst having a catalytic activity to oxidize HC and convert it to water and carbon dioxide, to oxidize CO and convert it to carbon dioxide as well as to reduce NOx and convert it to nitrogen
Implementation Method 2
A Zr-Ce-based complex oxide has an oxygen storage capacity (OSC), and is advantageous in mitigating fluctuations in the oxygen concentration in the exhaust gas
Data Source
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AI summary
An object of the present invention is to provide an exhaust gas purification catalyst with improved exhaust gas purification performance, and in order to achieve such an object, the present invention provides an exhaust gas purification catalyst (1A) including a substrate (10) and a catalyst layer (20) provided on the substrate (10), wherein the catalyst layer (20) includes a first layer (21) containing Rh, and Pd and/or Pt, and a second layer (22) containing Rh, and Pd and/or Pt, wherein a total content of Zr and Ce in terms of oxide and a content of aluminum element in terms of oxide in the first layer (21) are 70% by mass or more and 15% by mass or less, respectively, based on a mass of the first layer (21), and wherein a content of aluminum element in terms of oxide and a total content of Zr and Ce in terms of oxide in the second layer (22) are 75% by mass or more and 15% by mass or less, respectively, based on a mass of the second layer (22).