Rh Catalyst Layer Composition for Oxygen Storage and Heat Resistance
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Solution Overview
Problem
Existing exhaust gas purification catalysts using Ce-Zr-Al-based complex oxides face challenges in maintaining both oxygen storage capacity and exhaust gas purification performance, particularly under high-temperature conditions, due to excessive Ce content promoting Rh oxidation and thermal expansion differences leading to Rh burial and sintering.
Innovation Solution
Adjusting the content of Ce-Zr-Al-based complex oxide to 70% by mass and the Ce to Zr mass ratio to 0.03 to 0.50, with additional Al content and optional inclusion of rare earth elements, enhances oxygen storage capacity while suppressing Rh degradation under high temperatures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If the content of Ce in the Ce-Zr-Al-based complex oxide is increased to improve oxygen storage capacity, then the exhaust gas purification performance of Rh is improved, but Rh oxidation is promoted and exhaust gas purification performance decreases
Solution Approach 1:
The patent optimizes the Ce/Zr molar ratio parameter within a specific range (1/3 to 3/1) and the Al/(Ce+Zr) molar ratio parameter within a specific range (2 to 10). By controlling these compositional parameters, the catalyst achieves both sufficient oxygen storage capacity and prevention of Rh oxidation, resolving the contradiction between these two requirements.
Solution Approach 2:
The patent uses a composite Ce-Zr-Al-based complex oxide material that combines multiple metal oxides. This composite structure allows the material to exhibit both oxygen storage capacity (from Ce) and thermal stability with controlled Rh oxidation (from Zr and Al), thereby resolving the contradiction between oxygen storage and Rh protection.
2Quantity of substance
If the content of Ce in the Ce-Zr-Al-based complex oxide is increased to improve oxygen storage capacity, then the exhaust gas purification performance is improved, but the heat resistance becomes insufficient leading to aggregation and pore disappearance
Solution Approach 1:
The patent employs a composite Ce-Zr-Al complex oxide where ZrO2 and Al2O3 components provide high-temperature structural stability. This composite material prevents aggregation and pore collapse at high temperatures while maintaining oxygen storage capacity through the Ce component, thus resolving the contradiction between oxygen storage and heat resistance.
Solution Approach 2:
The patent specifies optimal ranges for compositional parameters (Ce/Zr ratio and Al/(Ce+Zr) ratio) that balance oxygen storage capacity with heat resistance. By controlling these parameters, the material achieves both high oxygen storage and sufficient thermal stability up to 900°C or higher.
3Reliability
If the proportion of components other than Ce-Zr-Al-based complex oxide is increased to suppress thermal expansion differences, then Rh burial and sintering are suppressed, but oxygen storage capacity decreases
Solution Approach 1:
The patent optimizes the proportion of Ce-Zr-Al complex oxide within the catalyst layer by controlling the Ce/Zr and Al/(Ce+Zr) molar ratios. This parameter optimization ensures sufficient oxygen storage capacity while the specific composition provides matched thermal expansion characteristics that prevent Rh burial and sintering, resolving the contradiction between these two requirements.
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 oxygen storage capacity and maintains exhaust gas purification performance of Rh, even under high-temperature exposure, by optimizing the composition of the catalyst layer.
Implementation Method 1
A Ce-Zr-Al-based complex oxide has oxygen storage capacity (OSC). Therefore, use of a Ce-Zr-Al-based complex oxide can mitigate fluctuations in the oxygen concentration of exhaust gas
Implementation Method 2
Ce promotes the oxidation of Rh. Pt and Pd tend to exhibit enhanced exhaust gas purification performance when moderately oxidized, whereas Rh tends to exhibit decreased exhaust gas purification performance when oxidized
Implementation Method 3
A catalyst containing a noble metal element such as Pt, Pd, or Rh is used to purify and detoxify those harmful components. Pt and Pd are mainly involved in oxidative purification of HC and CO, and Rh is mainly involved in reductive purification of NOx
Data Source
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AI summary
An object of the present invention is to provide an exhaust gas purification catalyst including a catalyst layer containing Rh and a Ce-Zr-Al-based complex oxide, the exhaust gas purification catalyst being capable of achieving both improvement of the oxygen storage capacity of the Ce-Zr-Al-based complex oxide and prevention of the decrease in the exhaust gas purification performance of Rh, and the present invention provides an exhaust gas purification catalyst (1) including a substrate (10) and a first catalyst layer (20) provided on the substrate (10), wherein the first catalyst layer (20) contains Rh and a complex oxide containing Ce, Zr, and Al, wherein the content of the complex oxide is 70% by mass or more, based on a total mass of all components other than Rh in the first catalyst layer (20), and wherein a mass ratio of a content of Ce in terms of metal in the complex oxide to a content of Zr in terms of metal in the complex oxide is 0.03 or more and 0.50 or less.