Two-Stage Base Metal Catalyst for Exhaust Purification
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Solution Overview
Problem
Existing exhaust gas purification systems using base metals face challenges such as easy oxidation, impaired fuel efficiency, and poor catalyst utilization efficiency due to the need for enrichment control and the generation of N2O, which affects the purification of NOx, HC, and CO.
Innovation Solution
A catalyst system that actively generates NH3 as the first-stage catalyst and uses a second-stage catalyst to adsorb NH3, allowing for effective purification of NOx, HC, and CO, even under slightly enriched conditions, while minimizing fuel efficiency reduction and enhancing oxidation performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of substance
If base metals are used as catalyst components instead of precious metals, then resource depletion problems are addressed and cost is reduced, but the catalysts are more easily oxidized and require enrichment control which impairs fuel efficiency
Solution Approach 1:
The catalyst system is divided into multiple stages: a first-stage base metal catalyst (Cu, Fe, or Co) for initial purification and NH3 generation, and a second-stage Pt catalyst for final purification. This segmentation allows base metals to perform their function without requiring continuous enrichment control, as the two-stage system handles different purification tasks separately, reducing overall fuel efficiency impairment while maintaining low precious metal usage.
Solution Approach 2:
NH3 acts as an intermediary substance generated by the first-stage base metal catalyst and utilized by the second-stage Pt catalyst for selective catalytic reduction of NOx. This intermediary mechanism enables efficient NOx purification without requiring continuous enrichment control of the entire system, thereby improving fuel efficiency while maintaining base metal catalyst performance.
2Reliability
If enrichment control is implemented to prevent oxidation of base metal catalysts, then catalyst stability is improved, but fuel efficiency deteriorates
Solution Approach 1:
The catalyst system divides purification functions across two stages, allowing the first-stage base metal catalyst to operate without continuous enrichment control since the second-stage Pt catalyst handles final purification. This segmentation maintains catalyst stability during normal operation while minimizing fuel efficiency impairment.
Solution Approach 2:
Enrichment control is applied periodically or intermittently rather than continuously, specifically activated when NOx purification is required or when base metal catalyst oxidation prevention is needed. This periodic application maintains catalyst stability while minimizing overall fuel efficiency deterioration during normal operation.
3Device complexity
If a single-stage catalyst system is used, then device complexity is reduced, but purification performance for all components (NOx, HC, CO) cannot be achieved efficiently
Solution Approach 1:
The purification system is segmented into two functional stages: the first-stage base metal catalyst handles HC and CO oxidation and NH3 generation, while the second-stage Pt catalyst performs selective NOx reduction using the generated NH3. This segmentation achieves comprehensive purification performance while maintaining relatively simple device structure through functional division rather than multiple independent systems.
Solution Approach 2:
The first-stage base metal catalyst performs multiple functions simultaneously: oxidizing HC and CO, generating NH3 for subsequent NOx reduction, and operating under various air/fuel ratio conditions. This multi-functionality reduces the need for additional separate components, maintaining device simplicity while achieving comprehensive purification performance.
4Use of energy by moving object
If base metal catalysts operate under lean conditions, then fuel efficiency is improved, but oxidation performance and HC purification rate deteriorate
Solution Approach 1:
The two-stage catalyst system segments oxidation and reduction functions: the first-stage base metal catalyst performs HC and CO oxidation effectively under lean or stoichiometric conditions, while the second-stage Pt catalyst handles NOx reduction. This segmentation allows the system to maintain high HC purification rates under lean operating conditions that improve fuel efficiency, as each stage is optimized for its specific 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
This approach enables high-efficiency NOx purification, increased HC purification rates, and reduced fuel consumption by optimizing the generation and utilization of NH3, achieving selective reduction of N2O and NOx, and improving overall catalyst performance.
Implementation Method 1
a first-stage catalyst that actively generates NH3
Implementation Method 2
a second-stage catalyst that can adsorb NH3 generated by the first-stage catalyst
Implementation Method 3
exhaust gas purification catalysts employ a variety of catalysts, including platinum-group elements such as Pt, Pd and Rh, etc., as catalyst components
Implementation Method 4
oxidation performance is drastically increased
Implementation Method 5
achieving selective reduction of N2O and NOx
Data Source
Figure 1~2
Figure 3
Figure 4~5
AI summary
A catalyst system for exhaust gas purification which comprises a first-stage base metal catalyst located upstream and a second-stage base metal catalyst located downstream, wherein the first-stage base metal catalyst comprises at least one oxide support selected from the group consisting of alumina, ceria, zirconia, yttria, and titania and Cu metal and/or a Cu oxide supported thereon, and in cases where the amount of NOx in the exhaust gas has become or exceeded an NOx criterion, the state of the exhaust gas is switched from slightly rich to rich.