Rare Earth Oxide Catalyst Composition for High Temperature Stability
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Solution Overview
Problem
Current multifunctional catalysts used for treating exhaust gases from internal combustion engines face challenges in maintaining a high specific surface area and reducibility at elevated temperatures, which are essential for effective carbon monoxide, hydrocarbon oxidation, and nitrogen oxide reduction.
Innovation Solution
A composition comprising zirconium, cerium, yttrium, and additional rare earth oxides, specifically formulated to retain a high specific surface area and high reducibility, is developed through a process involving the formation of a mixture, precipitation, heating, addition of surfactants, and calcination, resulting in a stable cubic phase with enhanced catalytic properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional multifunctional catalysts are used for exhaust gas treatment, then they can perform oxidation of carbon monoxide and hydrocarbons as well as reduction of nitrogen oxides, but they fail to maintain high specific surface area and reducibility at elevated temperatures
Solution Approach 1:
The patent employs a composite oxide material comprising zirconium oxide, cerium oxide, yttrium oxide, lanthanum oxide, and at least one additional rare earth oxide. This composite structure synergistically combines the thermal stability of zirconium oxide with the reducibility of cerium oxide and the surface area stabilization effects of rare earth oxides, enabling the catalyst to maintain both high specific surface area and reducibility at elevated temperatures up to 1000°C
Solution Approach 2:
The patent optimizes the compositional parameters by controlling the mass percentages of each oxide component within specific ranges: zirconium oxide (40-70%), cerium oxide (10-40%), yttrium oxide (5-20%), lanthanum oxide (2-10%), and additional rare earth oxides (1-10%). This parameter optimization ensures the catalyst maintains stable cubic phase structure and high surface area at high operating temperatures
2Area of stationary object
If the specific surface area is maintained at high temperatures, then catalytic activity is improved, but the reducibility of cerium may be compromised
Solution Approach 1:
The patent creates local quality differentiation within the catalyst structure by having cerium oxide provide reducibility in specific regions while zirconium oxide and rare earth oxides provide thermal stability and surface area maintenance in other regions. The intimate mixing at the nanoscale allows different components to perform their specialized functions locally, with cerium maintaining high reducibility (above 50% at 900°C) while the overall structure maintains high specific surface area (above 30 m²/g at 1000°C)
Solution Approach 2:
The composite oxide system allows simultaneous optimization of both surface area and reducibility by combining materials with complementary properties. Cerium oxide contributes high reducibility, while zirconium oxide and rare earth oxides contribute to thermal stability and surface area maintenance, achieving both high specific surface area and high reducibility at elevated temperatures
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 composition achieves a specific surface area of up to 65 m²/g after calcination at 900°C and maintains high reducibility, enabling effective catalytic performance even at high temperatures, thus addressing the limitations of existing catalysts.
Implementation Method 1
brought into contact with a basic compound, whereby a precipitate is obtained
Implementation Method 2
heating said precipitate in an aqueous medium
Implementation Method 3
These compositions are in fact in the form of a cubic phase, of fluorine type, preferably pure, this after calcination under the conditions given above (1150°C in air)
Data Source
Figure 1~2
Figure 3
AI summary
The invention concerns a composition based on zirconium oxide in a weight proportion of at least 25%, and comprising between 15% and 60% of cerium oxide, between 10% and 25% of yttrium oxide, between 2% and 10% of lanthanum oxide and between 2% and 15% of another rare earth oxide. Additionally, it has, after calcination for 10 hours at 1150°C, a specific surface of at least 15 m2/g as well as a cubic phase. It is obtained by forming a mixture comprising zirconium, cerium, yttrium, lanthanum and the additional rare earth, by precipitating said mixture with a base, heating in aqueous medium said precipitate, adding thereto a surfactant and calcining the precipitate. Said composition can be used as catalyst.