Dual-Layer Catalyst for Diesel NOx Reduction
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Solution Overview
Problem
Existing exhaust gas aftertreatment systems are ineffective in reducing nitrogen oxides (NOx) emissions from diesel engines during cold-start conditions, as the catalytic converter requires high temperatures to activate, leading to premature NOx release and reduced conversion efficiency.
Innovation Solution
A dual-layer catalyst system is introduced, comprising a NOx storage catalyst layer and an ammonia Selective Catalytic Reduction (SCR) catalyst layer, where the NOx storage catalyst releases stored NOx when heated to the active temperature of the SCR catalyst, allowing for efficient NOx reduction using ammonia as a reductant.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single-layer catalyst is used in the catalytic converter, then the device complexity is reduced, but the NOx reduction efficiency during cold-start conditions deteriorates due to the temperature gap between NOx release and reduction
Solution Approach 1:
The catalyst is divided into two distinct layers: a first layer containing a first catalyst for NOx storage and release, and a second layer containing a second catalyst for ammonia SCR of released NOx. This segmentation allows each layer to perform its specific function optimally, with the first layer storing NOx at low temperatures and the second layer reducing NOx at higher temperatures, thereby eliminating the temperature gap issue while maintaining manageable device complexity.
2Productivity
If the catalytic converter operates at high temperatures to activate the catalyst, then the NOx reduction efficiency is improved, but the cold-start emissions treatment capability deteriorates because the catalyst remains inactive during the cold-start period
Solution Approach 1:
The first catalyst performs preliminary action by storing NOx during the cold-start period when temperatures are below the activation threshold of the second catalyst. This preliminary storage of NOx ensures that when the exhaust temperature eventually rises to activate the second catalyst, the stored NOx is immediately available for reduction, eliminating the need to wait for high temperatures during the cold-start phase.
3Productivity
If the NOx release temperature is lowered to capture cold-start emissions, then the cold-start emissions treatment is improved, but the temperature gap between NOx release and reduction increases, reducing overall efficiency
Solution Approach 1:
The solution transitions from a single-temperature-operation approach to a two-dimensional temperature approach by stacking catalysts with different temperature characteristics in vertical layers. The first catalyst operates at lower temperatures for NOx storage during cold-start, while the second catalyst operates at higher temperatures for NOx reduction. This dimensional arrangement in the catalyst structure allows both temperature regimes to coexist and function sequentially, eliminating the temperature gap problem.
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 dual-layer catalyst significantly reduces the temperature gap between NOx release and reduction, improving NOx emission control during cold-start conditions, enhancing the overall efficiency of NOx reduction and minimizing ammonia slip.
Implementation Method 1
The first layer includes a first catalyst to store NOx when the first catalyst has a temperature below an active temperature of a second catalyst, the first catalyst to release the stored NOx when the first catalyst is heated to the active temperature of the second catalyst
Implementation Method 2
The second layer includes the second catalyst for ammonia Selective Catalytic Reduction of the released NOx
Data Source
AI summary
A dual-layer catalyst includes a substrate, a first layer disposed on the substrate, and a second layer disposed on the first layer. The first layer includes a first catalyst for storing NOx when the first catalyst has a temperature below an active temperature of a second catalyst. The first catalyst is to release the stored NOx when the first catalyst is heated to the active temperature of the second catalyst. The second layer includes the second catalyst for ammonia Selective Catalytic Reduction of the released NOx. The dual-layer catalyst is to be included in a catalytic converter and a catalyst system for reducing NOx emissions from a diesel engine, the NOx emissions including NOx emitted during a predetermined cold-start time period.