CO Clean-Up Catalyst for Exhaust Purification
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Solution Overview
Problem
Three-way catalysts (TWCs) in vehicles often fail to purify carbon monoxide (CO) when the air/fuel ratio is rich, leading to CO being discharged into the environment, necessitating an additional catalytic converter for CO clean-up.
Innovation Solution
A CO clean-up catalyst (CUC) system comprising 0.2-1.5 wt% Pt, 0-0.4 wt% Pd, 0-0.4 wt% Rh, 0-5.0 wt% Ba, 40-90 wt% CeO2, and 9.8-59.8 wt% Al2O3, with optional additives like La, Zr, or Mg, is integrated into the exhaust pipe downstream of the TWC and SCR catalyst to purify CO slipped at a rich air/fuel ratio.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If the air/fuel ratio is adjusted to rich for generating NH3 in the TWC, then NH3 generation is improved, but CO purification deteriorates because the TWC slips CO at rich air/fuel ratio
Solution Approach 1:
The aftertreatment system is divided into functionally distinct segments: the TWC (upstream) focuses on NH3 generation through rich air/fuel ratio operation, while the CUC (downstream) is dedicated to CO purification. This segmentation allows each component to optimize its specific function without interfering with the other, resolving the contradiction between NH3 generation and CO purification.
Solution Approach 2:
The CUC acts as an intermediary component between the TWC and the exhaust outlet. It receives the exhaust gas containing slipped CO from the TWC and performs the clean-up function, mediating the harmful effect of CO slip while allowing the TWC to continue its NH3 generation function uninterrupted.
2Object-generated harmful factors
If an additional catalytic converter is added to purify CO slipped from the TWC, then CO purification is improved, but device complexity increases
Solution Approach 1:
The CUC is designed with multi-functionality, incorporating both CO purification capability and NH3 generation capability within a single catalyst component. This allows the downstream catalyst to handle multiple functions that would otherwise require separate devices, reducing system complexity while maintaining effective CO purification.
Solution Approach 2:
The CUC merges the functions of CO oxidation and NH3 generation into a single catalytic converter located downstream of the TWC. This consolidation reduces the number of separate components needed in the aftertreatment system, simplifying the overall device architecture while achieving the desired CO purification performance.
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 CUC effectively reduces CO discharge to the outside by optimizing the air/fuel ratio and temperature control, enhancing NH3 generation while maintaining efficient NOx purification.
Implementation Method 1
a CO clean-up catalyst (CUC) mounted on the exhaust pipe at a downstream of the SCR catalyst and purifying the CO slipped from the TWC or contained in the exhaust gas at the rich air/fuel ratio
Implementation Method 2
The TWCs are mainly installed in gasoline vehicles, and Pt/Rh, Pd/Rh or Pt/Pd/Rh systems are used as the TWCs
Implementation Method 3
a selective catalytic reduction (SCR) catalyst for purifying the NOx slipped from the TWC
Data Source
AI summary
An after treatment method is disclosed. The after treatment method may include: operating an engine at a lean air/fuel ratio; calculating an amount of NH3 stored in an SCR catalyst; calculating an amount of NOx which will flow into the SCR catalyst; determining whether conversion to a rich air/fuel ratio is desired; calculating, when the conversion to the rich air/fuel ratio is desired, a rich duration for which the rich air/fuel ratio is maintained and a target air/fuel ratio; and operating the engine at the target air/fuel ratio for the rich duration.