LT-LNT Catalyst Alumina Support for Lean NOx Storage
Solution Overview
Problem
Lean burn engines, particularly diesel engines, face challenges in reducing NOx emissions due to excessive oxygen in exhaust gases, as conventional three-way catalytic converters are ineffective, and existing NOx traps struggle with efficient NOx conversion and storage under lean conditions, requiring frequent and short rich cycles for regeneration.
Innovation Solution
A low temperature lean NOx trap (LT-LNT) composition with a washcoat layer on a carrier substrate, including a platinum group metal component impregnated on a support material with at least 50% alumina, and a low temperature NOx storage material comprising a bulk particulate reducible metal oxide, which enhances NOx conversion and storage capabilities, allowing for efficient NOx reduction and hydrocarbon/carbon monoxide oxidation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional three-way catalytic converters are used in lean burn engines, then the exhaust treatment is simple, but NOx reduction is ineffective due to excessive oxygen in exhaust gases
Solution Approach 1:
The patent changes the operational parameters by introducing periodic rich conditions to switch the oxygen concentration in exhaust gases, enabling the catalytic converter to effectively reduce NOx during rich periods when oxygen levels are reduced, while maintaining lean operation during normal combustion for fuel economy
Solution Approach 2:
The patent implements periodic switching between lean and rich operating modes, where the catalyst alternates between storing NOx during lean periods and reducing stored NOx during rich periods, creating a cyclic operation that overcomes the limitation of conventional continuous lean operation
2Productivity
If lean operating cycle is extended to enhance NOx conversion efficiency, then fuel economy improves, but the frequency and duration of rich cycles must be increased for regeneration
Solution Approach 1:
The patent extracts the oxygen from exhaust gases during rich periods through the reduction reactions, removing the limiting factor (excessive oxygen) that prevents effective NOx reduction, thereby allowing longer lean operating cycles for improved fuel economy without compromising regeneration effectiveness
3Reliability
If NOx is stored during lean operation and released during rich periods, then NOx conversion is achieved, but frequent short rich cycles are required for effective regeneration
Solution Approach 1:
The patent merges the NOx storage function during lean periods with the NOx reduction function during rich periods into a single integrated catalytic system, allowing the catalyst to perform both functions sequentially without requiring separate devices, thereby reducing the overall regeneration frequency needed
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 LT-LNT composition achieves high NOx conversion efficiency, low CO and HC light-off temperatures, and improved SCR performance, enabling effective NOx reduction and oxidation of hydrocarbons and carbon monoxide, while also providing on-board diagnostic capabilities for monitoring catalyst aging.
Implementation Method 1
a platinum group metal component impregnated on a first support material comprising at least 50% alumina
Implementation Method 2
a low temperature NOx storage material comprising a bulk particulate reducible metal oxide
Implementation Method 3
a lean NOx trap (LNT) activates reactions by promoting a steam reforming reaction of hydrocarbons and a water gas shift (WGS) reaction to provide H2 as a reductant to abate NOx
Implementation Method 4
The water gas shift reaction is a chemical reaction in which carbon monoxide reacts with water vapor to form carbon dioxide and hydrogen
Implementation Method 5
The presence of ceria in an LNT catalyzes the WGS reaction, improving the LNT's resistance to SO2 deactivation and stabilizing the PGM
Data Source
AI summary
A lean burn engine exhaust treatment articles comprising a low temperature lean NOx trap (LT-LNT) composition and methods for their use is disclosed. A lean burn engine exhaust gas treatment system including the lean burn engine exhaust treatment articles is also disclosed. The low temperature lean NOx trap (LT-LNT) compositions can comprise a washcoat layer on a carrier substrate, the washcoat layer including a platinum group metal component impregnated on a first support material comprising at least 50% alumina. The washcoat layer may further include a low temperature NOx storage material comprising a bulk particulate reducible metal oxide. Methods of monitoring the aging state of a lean burn oxidation catalyst in a lean burn engine catalyst system are also disclosed.