NOx Storage Catalyst with Layered Rh Placement
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Solution Overview
Problem
Conventional nitrogen oxide storage catalysts are ineffective for lean-burn engines at lower temperatures and contain high amounts of costly platinum group metals, necessitating improved designs for efficient NOx abatement during cold-start periods.
Innovation Solution
A treatment system with a nitrogen oxide storage catalyst design featuring lower loadings of platinum group metals, specifically Rh, utilizing a substrate with multiple washcoat layers including metal oxide support particles and nitrogen oxide storage materials, and strategically placing Rh and Pd layers to enhance NOx reduction efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional TWC catalysts are used for lean-burn engines, then the catalyst structure is simple, but the NOx reduction efficiency is poor due to excessive oxygen in the exhaust
Solution Approach 1:
The catalyst is divided into distinct functional layers: a first washcoat layer containing NOx storage materials (barium, cerium compounds) on metal oxide support particles, and a second washcoat layer containing Rh catalyst. This segmentation allows each layer to perform its specific function - the first layer stores NOx during lean operation, while the second layer reduces stored NOx during rich operation - thereby improving overall NOx reduction efficiency without requiring complete redesign of the entire catalyst structure
Solution Approach 2:
The catalyst employs composite material composition by combining different functional materials in specific layers. The first washcoat layer uses composite materials including barium compounds, cerium compounds, and metal oxide support particles to create an effective NOx storage component. The second washcoat layer uses Rh-based composite catalyst materials. This composite approach enables the catalyst to handle both lean and rich exhaust conditions effectively, improving reliability while managing structural complexity through functional specialization
2Reliability
If high amounts of Rh are used in the catalyst, then the NOx storage and conversion efficiency is improved, but the cost of the catalyst increases significantly
Solution Approach 1:
The invention applies local quality by concentrating Rh catalyst material specifically in the second washcoat layer where it is most needed for NOx reduction reactions, while keeping Rh content minimal or absent in the first washcoat layer. The second washcoat layer is applied to only a portion (100-x%) of the first washcoat layer surface, creating localized catalytic activity zones. This strategic placement improves NOx conversion efficiency at the required locations while minimizing the total quantity of expensive Rh material used throughout the entire catalyst
3Reliability
If the catalyst is designed for high-temperature operation, then the NOx reduction performance is good, but the performance during cold-start periods is insufficient
Solution Approach 1:
The catalyst design incorporates parameter changes by using materials and structures that maintain effectiveness across a broad temperature range. The first washcoat layer materials (barium compounds, cerium compounds on metal oxide supports) are selected for their ability to store NOx effectively at lower temperatures during cold-start, while the second washcoat layer Rh catalyst is optimized to become highly active at elevated temperatures. This parameter optimization across the temperature spectrum ensures reliable NOx reduction performance whether the engine is cold-starting or operating at high temperature
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 system achieves improved NOx storage and conversion efficiency at lower temperatures, particularly during cold-start conditions, while reducing the necessary amount of platinum group metals, thus meeting emission standards effectively and economically.
Implementation Method 1
a nitrogen oxide storage catalyst which stores NOx during periods of lean (oxygen-rich) operation, and releases the stored NOx during the rich (fuel-rich) periods of operation
Implementation Method 2
During periods of rich (or stoichiometric) operation, the catalyst component of the catalyst/NOx sorbent promotes the reduction of NOx to nitrogen by reaction of NOx (including NOx released from the NOx sorbent) with HC, CO and/or hydrogen present in the exhaust gas
Data Source
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AI summary
The present invention relates to a nitrogen oxide storage catalyst comprising: a substrate; a first washcoat layer disposed on the substrate, the first washcoat layer comprising metal oxide support particles and a nitrogen oxide storage material comprising at least one metal compound selected from the group consisting of alkaline earth meta! compounds, alkali metal compounds, rare earth metal compounds, and mixtures thereof, at least a portion of said at least one metal compound being supported on the metal oxide support particles; and a second washcoat layer disposed over the first washcoat layer, said second washcoat layer comprising Rh, wherein the first washcoat layer contains substantially no Rh, and wherein the second washcoat layer is disposed on 100 - x % of the surface of the first washcoat layer, x ranging from 20 to 80.