Layered Catalyst Composite for High-Temperature Emissions Control
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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, leading to reduced catalytic performance and increased emissions of hydrocarbons, carbon monoxide, and nitrogen oxides, which are difficult to meet stringent emissions 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, where each layer includes an oxygen storage component and specific metal oxides, such as ceria and zirconia, to enhance stability and catalytic activity, particularly with higher palladium loading in the third layer to improve hydrocarbon conversion and reduce nitrogen oxide emissions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
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 alumina with stabilizing materials such as zirconia, titania, or rare earth metal oxides. This composite approach allows the support to maintain both high surface area (from alumina) and thermal stability (from the stabilizing materials) simultaneously, preventing phase transition and volume shrinkage at high temperatures while preserving catalytic activity.
2Productivity
If higher palladium loading is used to improve hydrocarbon conversion, then catalytic activity is improved, but cost increases
Solution Approach 1:
The patent implements a layered catalyst structure where different metal compositions are distributed at different locations. The third layer (outermost layer) contains higher palladium loading specifically positioned to maximize hydrocarbon conversion where it is most needed, while the first and second layers use lower palladium loading with rhodium for nitrogen oxide reduction, thereby optimizing overall performance while controlling total precious metal content.
3Temperature
If alumina support undergoes phase transition at high temperature, then volume shrinkage occurs, but catalytic metal becomes occluded with loss of surface area
Solution Approach 1:
The patent incorporates thermal stabilizing materials (zirconia, titania, rare earth metal oxides) into the alumina support structure before the phase transition occurs. These stabilizing materials prevent the gamma-to-alpha phase transition of alumina that would otherwise cause volume shrinkage and occlusion of catalytic metals, thereby maintaining exposed catalyst surface area and activity even at high operating temperatures exceeding 1000°C.
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 enhanced oxidation of hydrocarbons and carbon monoxide and effective reduction of nitrogen oxides, maintaining catalytic activity and stability at high temperatures, thus meeting stringent emissions standards with improved efficiency and durability.
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
each layer includes an oxygen storage component and specific metal oxides, such as ceria and zirconia
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.