Layered Catalyst Composite for High-Temperature Exhaust Stability
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Solution Overview
Problem
Existing three-way conversion catalysts face challenges in maintaining activity and stability at high temperatures due to thermal degradation of alumina supports, which affects their ability to efficiently oxidize hydrocarbons and reduce nitrogen oxides in exhaust gases, especially under stringent emission standards like SULEV and LEV-II.
Innovation Solution
A layered catalyst composite structure comprising a carrier with three layers: a first layer of palladium on a support, a second layer of rhodium on a support, and a third layer of palladium on a support, each with specific loadings and oxygen storage components, including ceria-zirconia composites, to enhance stability and catalytic activity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If activated alumina support is used to provide high surface area, then catalytic activity is improved, but thermal stability deteriorates at high temperatures
Solution Approach 1:
The patent uses a composite support structure combining activated alumina with thermally stable materials such as zirconia, titania, or rare earth metal oxides. This composite approach allows the catalyst to maintain the high surface area benefits of activated alumina while gaining thermal stability from the refractory oxide components, thereby resolving the contradiction between catalytic activity and thermal stability.
Solution Approach 2:
The patent modifies the physical and chemical parameters of the support material by controlling the phase composition of alumina (gamma, delta, eta, kappa, theta phases) and incorporating stabilizing oxides. This parameter adjustment allows the support to maintain structural integrity at high temperatures while preserving sufficient surface area for catalytic activity.
2Stability of the object's composition
If alumina support undergoes thermal degradation, then volume shrinkage occurs, but catalytic metal becomes occluded with loss of surface area
Solution Approach 1:
The patent incorporates thermally stable refractory oxides (zirconia, titania, rare earth metal oxides) into the alumina support structure before thermal degradation can occur. These stabilizing components act as a cushion against thermal stress, preventing the phase transitions and volume shrinkage that would otherwise cause metal occlusion and surface area loss, thereby protecting catalytic activity in advance.
Solution Approach 2:
By creating a composite support system where refractory oxides are integrated with alumina, the patent ensures that the support structure maintains its volume and porosity at high temperatures. This composite structure prevents the metal particles from becoming occluded, thereby preserving the exposed catalyst surface area and maintaining reliability.
3Duration of action of stationary object
If stabilized alumina is used to prevent thermal degradation, then durability is improved, but initial surface area is reduced
Solution Approach 1:
The patent optimizes the phase composition and loading levels of stabilizing oxides to achieve a balance between durability and surface area. By carefully controlling the amount and type of stabilizers (e.g., 1-10 wt% zirconia, titania, or rare earth oxides), the support maintains sufficient surface area for catalytic activity while gaining the thermal stability needed for long-term durability.
Solution Approach 2:
The composite support structure is designed to maximize the synergistic effects between alumina and stabilizing oxides. The refractory oxide components provide structural framework that maintains surface area at high temperatures, while alumina provides the high surface area needed for catalysis. This composite approach achieves both durability and adequate surface area simultaneously.
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 layered catalyst composite provides improved stability and catalytic performance, effectively oxidizing hydrocarbons and reducing nitrogen oxides, even at high temperatures, while maintaining economic viability, as demonstrated by reduced emissions of NOx, HC, and CO.
Implementation Method 1
catalysts promote the oxidation by oxygen in the exhaust gas stream of unburned hydrocarbons and carbon monoxide
Implementation Method 2
oxidation by oxygen in the exhaust gas stream of unburned hydrocarbons and carbon monoxide
Implementation Method 3
reduction of nitrogen oxides to nitrogen
Implementation Method 4
reduction of nitrogen oxides to nitrogen
Implementation Method 5
oxygen storage components, including ceria-zirconia composites, to enhance stability and catalytic activity
Data Source
AI summary
A layered, three-way conversion catalyst having the capability of simultaneously catalyzing the oxidation of hydrocarbons and carbon monoxide and the reduction of nitrogen oxides is disclosed. In one or more embodiments, the catalyst comprises three layers in conjunction with a carrier: a first layer deposited on the carrier and comprising palladium deposited on a refractory metal oxide and an oxygen storage component; a second layer deposited on the first layer and comprising rhodium deposited on a refractory metal oxide and an oxygen storage component; and a third layer deposited on the second layer and comprising palladium deposited on a refractory metal oxide.