Lean NOx Adsorber Catalyst Low-Temperature Performance
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Solution Overview
Problem
Current exhaust gas treatment systems for internal combustion engines, particularly NOx adsorber catalysts, are inefficient at low temperatures and require improvements in NOx storage and conversion characteristics, as well as CO and HC conversions.
Innovation Solution
A lean NOx trap catalyst comprising a first layer with a mixture of platinum and palladium supported on high surface area inorganic oxides, combined with a second layer containing ceria and an alkali or alkaline earth metal, enhances NOx storage and conversion capabilities, especially at low temperatures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If conventional NOx adsorber catalysts are used, then high temperature NOx conversion is achieved, but low temperature performance is poor
Solution Approach 1:
The catalyst is divided into multiple functional layers with distinct compositions and roles. The first layer contains Pt-Pd-OSC for oxidation and low-temperature activity, while the second layer contains alkaline earth metals for NOx storage, enabling each layer to optimize performance for its specific function and temperature range
Solution Approach 2:
The invention uses composite material structures combining different metal oxides (ceria, zirconia, magnesia) with platinum group metals (Pt, Pd) and alkaline earth metals (Ba, Sr, Ca). These composites create synergistic effects where OSC materials enhance low-temperature oxidation while alkaline earth metals provide high-capacity NOx storage
2Reliability
If single-layer catalyst structures are used, then manufacturing is simple, but NOx storage and conversion characteristics are insufficient
Solution Approach 1:
The catalyst structure is segmented into multiple layers, each with specific functions: the first layer handles oxidation and low-temperature activation, while the second layer provides high-capacity NOx storage. This segmentation allows optimization of each layer's composition for its specific function
Solution Approach 2:
The catalyst system is designed to perform multiple functions within a single device: oxidation of CO and HC, activation of oxygen, storage of NOx, and conversion of stored NOx. The multi-layer structure enables these diverse functions to coexist and work synergistically
3Temperature
If conventional oxidation/reduction catalyst compositions are used, then high temperature conversion works, but CO and HC conversion at low temperature is insufficient
Solution Approach 1:
The invention changes the compositional parameters of the catalyst by incorporating OSC materials (ceria, zirconia, magnesia) and specific Pt-Pd ratios. These parameter changes enable the catalyst to maintain high activity at low temperatures by enhancing oxygen storage capacity and improving low-temperature oxidation kinetics
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 catalyst system demonstrates improved NOx storage and conversion efficiency, along with enhanced CO and HC conversion performance, even at low temperatures, effectively addressing the inefficiencies of existing systems.
Implementation Method 1
nitric oxide reacts with oxygen to produce NO2 in the presence of the oxidation catalyst
Implementation Method 2
the NO2 is adsorbed by the NOx adsorbent in the form of an inorganic nitrate
Implementation Method 3
the stored inorganic nitrates decompose to form NO or NO2
Implementation Method 4
the nitrogen oxides are converted to nitrogen, carbon dioxide and water in the presence of heat, carbon monoxide and hydrocarbons in the exhaust stream
Data Source
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AI summary
A lean NOxtrap catalyst and its use in an emission treatment system for internal combustion engines is disclosed. The lean NOx trap catalyst comprises a first layer and a second layer.