Lean NOx Trap Catalyst Layered Design for Emission Stability
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Solution Overview
Problem
Conventional lean NOx trap catalysts exhibit inconsistent performance between activated and deactivated states, leading to challenges in engine calibration and poorer emissions profiles due to varying activity levels over the catalyst's lifetime and in response to short-term changes in exhaust gas composition.
Innovation Solution
A lean NOx trap catalyst comprising three layers: a first layer with platinum group metals and ceria-containing material, a second layer with noble metals and ceria-containing material, and a third layer with noble metals having reducing activity, where the ceria-containing material in the first layer includes a rare earth dopant, enhancing NOx storage and conversion characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional lean NOx trap catalyst is used, then the catalyst can store and convert NOx, but the performance varies significantly between activated and deactivated states leading to inconsistent emissions control
Solution Approach 1:
The patent applies local quality by creating distinct functional layers with specific compositions: a first layer with barium oxide and platinum group metals for NOx storage, a second layer with ceria and noble metals for oxidation, and a third layer with rhodium for reduction. Each layer has optimized local properties to perform its specific function, ensuring consistent overall performance regardless of catalyst state.
Solution Approach 2:
The patent uses composite materials by combining multiple metal oxides (barium oxide, ceria, alumina, zirconia) with platinum group metals in a structured layered configuration. This composite structure provides both NOx storage capacity and catalytic activity with stable performance across different operating conditions.
2Productivity
If the catalyst operates below its operating temperature during cold start, then the emission control system is relatively inefficient, but increasing temperature quickly may cause thermal damage
Solution Approach 1:
The patent employs parameter changes by incorporating ceria which can store and release oxygen, enabling the catalyst to maintain activity at lower temperatures. The ceria undergoes reversible reduction and oxidation cycles, providing oxygen during cold start conditions without requiring high temperatures, thus improving cold start efficiency while avoiding thermal damage.
Solution Approach 2:
The patent applies preliminary action through the ceria component that pre-stores oxygen in its lattice structure during lean conditions. This stored oxygen is available immediately during cold start or rich conditions, enabling NOx reduction reactions to proceed at lower temperatures without waiting for thermal activation, thereby improving cold start performance safely.
3Quantity of substance
If the NOx adsorbent uses alkaline earth metals in the form of oxides, then the NOx can be adsorbed under lean conditions, but the adsorption capacity and stability may be limited
Solution Approach 1:
The patent enhances adsorbent performance by creating a composite system where barium oxide provides NOx storage capacity while ceria and alumina provide structural stability and thermal resistance. The synergistic combination of these materials increases both the quantity of NOx that can be stored and the long-term stability of the adsorbent composition.
Solution Approach 2:
The patent applies multi-functionality by designing the barium oxide-ceria-alumina composite to simultaneously perform NOx adsorption, oxygen storage, and structural support functions. This multi-functional design increases NOx storage capacity while maintaining stability under varying exhaust conditions without requiring separate components for each function.
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 described catalyst configuration improves NOx storage efficiency and CO conversion performance consistently across both active and deactivated states, providing better emissions control and stability.
Implementation Method 1
a first layer, said first layer comprising one or more platinum group metals, a first ceria-containing material, and a first inorganic oxide; wherein the first ceria-containing material or the first inorganic oxide comprises a rare earth dopant
Implementation Method 2
The oxidation/reduction catalyst is typically one or more noble metals, preferably platinum, palladium, and/or rhodium. Typically, platinum is included to perform the oxidation function and rhodium is included to perform the reduction function
Implementation Method 3
NOx adsorber catalysts are devices that adsorb NOx under lean exhaust conditions, release the adsorbed NOx under rich conditions, and reduce the released NOx to form N2
Data Source
AI summary
A lean NOx trap catalyst and its use in an emission treatment system for internal combustion engines is disclosed. The lean NOx trap catalyst comprises a first layer, a second layer, and a third layer.