Complex Oxide Exhaust Catalyst Redox Heat Resistance
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Solution Overview
Problem
Current complex oxides used in exhaust gas purification catalysts for automobiles lack high redox ability and heat resistance, especially at low temperatures, and suffer from degradation due to vaporization of bismuth components under high-temperature reducing conditions.
Innovation Solution
A complex oxide comprising cerium, silicon, and optionally rare earth metals, produced through specific steps involving temperature-programmed reduction and oxidation, which forms Si-rich domains with CeO2 and SiO2 at the nanometer level, enhancing heat resistance and maintaining high redox ability even at low temperatures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If CeZrBi complex oxide is used to achieve high redox ability at low temperatures, then redox ability is improved, but heat resistance deteriorates due to bismuth vaporization at high temperatures
Solution Approach 1:
The invention removes the problematic bismuth component from the complex oxide composition while retaining cerium and silicon. This extraction eliminates the vaporization issue at high temperatures while preserving the redox functionality through cerium-based mechanisms, resolving the contradiction between low-temperature redox ability and high-temperature stability
Solution Approach 2:
The invention creates a composite oxide material comprising cerium oxide and silicon oxide in specific ratios (SiO2: 1-20 parts by mass per 100 parts by mass of rare earth metal elements). This composite structure provides both the redox ability of cerium and the thermal stability of silicon, eliminating bismuth vaporization while maintaining catalytic performance
2Stability of the object's composition
If fourth component (Ba, Ag, Pt) is added to improve heat resistance, then heat resistance is improved, but bismuth vaporization risk remains under reducing atmosphere
Solution Approach 1:
The invention removes the problematic bismuth component entirely from the composition, eliminating the need for additional stabilizing elements like Ba, Ag, or Pt. By extracting the vaporization-prone element and replacing it with thermally stable silicon, the patent achieves heat resistance without compromising redox ability or requiring additional additives
Solution Approach 2:
The invention changes the compositional parameters by eliminating bismuth and optimizing the SiO2 content to 1-20 parts by mass per 100 parts by mass of rare earth metal elements. This parameter optimization provides inherent thermal stability while maintaining redox functionality, making additional heat-resistant additives unnecessary
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 resulting complex oxide exhibits excellent reducing properties and heat resistance, retaining high redox ability and specific surface area even after repeated oxidation and reduction cycles, making it suitable for efficient exhaust gas purification.
Implementation Method 1
when it is subjected to temperature-programmed reduction (TPR) measurement in a 10% hydrogen-90% argon atmosphere at from 50° C. to 900° C.
Implementation Method 2
followed by oxidation treatment at 500° C. for 0.5 hours
Implementation Method 3
A characteristic of said auxiliary catalyst material is that it absorbs oxygen in an oxidizing atmosphere and releases oxygen in a reducing atmosphere
Implementation Method 4
Auxiliary catalyst materials having such a characteristic efficiently purify harmful components in exhaust gas
Data Source
AI summary
Provided are: a complex oxide that exhibits high redox ability even at low temperatures, has excellent heat resistance, and stably retains these characteristics even on repeated oxidation and reduction at high temperature; a method for producing the same; and an exhaust gas purification catalyst. The inventive complex oxide contains more than 0 but no more than 20 parts by mass of Si, calculated as SiO2, per total 100 parts by mass of rare earth metal elements including Ce, calculated as oxides; and has a characteristic such that when it is subjected to temperature-programmed reduction (TPR) measurement in a 10% hydrogen-90% argon atmosphere at from 50° C. to 900° C. with the temperature increasing at a rate of 10° C./min, followed by oxidation treatment at 500° C. for 0.5 hours, and then temperature-programmed reduction measurement is performed again, its calculated reduction rate at and below 400° C. is at least 1.5%.