Cerium-Zirconium Core-Shell Oxide for High-Temp Stability
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Solution Overview
Problem
Cerium-zirconium oxygen storage materials used in vehicle exhaust purification lack sufficient thermal stability and specific surface area at high temperatures, limiting their durability and effectiveness in high-temperature environments.
Innovation Solution
A cerium-zirconium-based composite oxide with a core-shell structure is developed, where a yttrium oxide-enriched shell is constructed on the outer layer, with a higher yttrium oxide content in the shell layer than in the overall composite oxide, and a higher zirconium oxide content in the core layer, enhancing thermal stability and maintaining a large specific surface area even at high temperatures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If coprecipitation method is used to prepare cerium-zirconium composite oxide, then oxygen storage capacity is improved, but thermal stability deteriorates at high temperature
Solution Approach 1:
The composite oxide is divided into core and shell layers with different compositions. The core layer contains cerium-zirconium composite oxide for oxygen storage, while the shell layer contains yttrium oxide and zirconium oxide for thermal stability, allowing each layer to perform its specific function optimally
Solution Approach 2:
The patent creates a composite oxide combining cerium oxide, zirconium oxide, and yttrium oxide in a core-shell structure. This composite material integrates the oxygen storage capability of cerium-zirconium oxide with the thermal stability of yttrium oxide, resolving the contradiction between oxygen storage capacity and thermal stability
2Area of stationary object
If step-by-step precipitation is used to improve sintering resistance, then specific surface area is improved, but thermal stability still deteriorates due to cerium sintering on outer layer
Solution Approach 1:
Different regions of the composite oxide particles have different compositions and properties. The shell layer is enriched with yttrium oxide which has high sintering resistance, while the core layer contains the cerium-zirconium composite. This local differentiation allows the outer shell to protect against sintering while the inner core provides oxygen storage capacity
Solution Approach 2:
Yttrium oxide acts as an intermediary substance in the shell layer that prevents direct contact and interaction between cerium oxide particles at high temperature. This intermediary layer with high sintering resistance protects the cerium oxide core from sintering, maintaining specific surface area while preserving thermal stability
3Stability of the object's composition
If rare earth metal salts are used on surface to improve heat resistance, then thermal stability is improved, but specific surface heat resistance deteriorates without stable core-shell structure
Solution Approach 1:
The core-shell structure is pre-formed during the precipitation process before heat treatment. The shell layer is deliberately designed with appropriate thickness and composition (enriched with yttrium oxide) to provide protective function. This preliminary structural preparation ensures that when heat treatment is applied, the core-shell structure remains stable and protects the specific surface area from deterioration
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 composite oxide exhibits high heat resistance and maintains a specific surface area of over 50 m2/g and oxygen storage capacity of at least 500 μmol O2/g after calcination at 1100°C for 4 hours, significantly improving thermal stability and oxygen storage performance.
Implementation Method 1
yttrium ions converge on the grain surface, inhibit the high temperature sintering of cerium zirconium compound oxide
Implementation Method 2
high oxygen storage and release capabilities in high temperature environments
Data Source
AI summary
The present disclosure provides a cerium-zirconium-based composite oxide with a core-shell structure and a preparation method thereof, a catalyst system using the cerium-zirconium-based composite oxide, a catalytic converter for purifying tail gas by using the catalyst system, and application of the catalyst system or the catalytic converter in motor vehicle exhaust purification, industrial waste gas treatment or catalytic combustion. In the present invention, the cerium-zirconium-based composite oxide with a core-shell structure oxygen storage material is prepared by a step-by-step precipitation method. On the one hand, yttrium and a part of zirconium and cerium are precipitated on a cerium-zirconium surface, where the post-precipitation of yttrium is to segregate yttrium ions (Y3+) on a grain boundary surface, thus reducing lattice surface energy, pinning the grain boundary surface, making the migration of the grain boundary surface difficult, controlling the growth of grains.