Three-Way Diesel Catalyst Coatings for Cold-Start Emission Control
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Solution Overview
Problem
Current diesel exhaust catalysts are ineffective in reducing NOx emissions, particularly during the cold-start period when temperatures are low, and cannot efficiently convert CO and total hydrocarbons under Lambda=1 conditions, which are necessary to meet stringent emission regulations like Euro7.
Innovation Solution
A three-way diesel catalyst with a substrate coated with two specific layers: a first layer containing platinum group metals and cerium oxide as an oxygen storage compound, and a second layer with additional platinum group metals, designed to enhance NOx, CO, and THC conversion efficiency across a wide temperature range, including cold-start conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a typical diesel catalyst is used, then the catalyst structure is simple and easy to manufacture, but the NOx conversion efficiency is poor during cold-start period
Solution Approach 1:
The catalyst is divided into two distinct coatings: a first coating containing a diesel oxidation catalyst component and an oxygen storage component, and a second coating containing a three-way catalyst component. This segmentation allows each coating to perform its specialized function optimally, with the first coating handling diesel oxidation and oxygen storage at lower temperatures, and the second coating handling NOx conversion at higher temperatures.
Solution Approach 2:
Different regions of the catalyst substrate are assigned different functional properties through the two-coating structure. The first coating is applied to cover at least 50% of the substrate axial length from the inlet end, providing diesel oxidation and oxygen storage capabilities where they are most needed during cold-start. The second coating is applied to cover at least 50% of the substrate axial length from the outlet end, providing three-way catalyst functionality where higher temperatures enable effective NOx conversion.
2Loss of energy
If Lambda=1 conditions are applied to achieve early SCR light-off, then CO2 emissions are reduced, but CO and THC emissions increase significantly
Solution Approach 1:
The catalyst is designed to convert the harmful CO and THC emissions that are generated under Lambda=1 conditions into beneficial products. The first coating with diesel oxidation catalyst component oxidizes CO and THC, while the second coating with three-way catalyst component further converts these emissions, transforming the harmful byproducts of Lambda=1 operation into harmless CO2 and H2O.
Solution Approach 2:
The catalyst combines two different catalyst systems in a single device: a diesel oxidation catalyst (DOC) component in the first coating and a three-way catalyst (TWC) component in the second coating. This composite structure enables the catalyst to handle both the oxidation of CO/THC and the conversion of NOx, allowing Lambda=1 conditions to be used for early SCR light-off without sacrificing emission control performance.
3Adaptability or versatility
If a single coating catalyst is used, then the manufacturing process is simple, but the catalyst cannot effectively handle both cold-start and high-temperature conditions
Solution Approach 1:
The catalyst is divided into two distinct coatings: a first coating containing a diesel oxidation catalyst component and an oxygen storage component, and a second coating containing a three-way catalyst component. This segmentation allows each coating to perform its specialized function optimally, with the first coating handling diesel oxidation and oxygen storage at lower temperatures, and the second coating handling NOx conversion at higher temperatures.
Solution Approach 2:
The first coating is applied to prepare the substrate for cold-start conditions by providing diesel oxidation and oxygen storage capabilities. This preliminary action ensures that the catalyst is ready to handle CO and THC emissions from the outset, while the second coating is positioned to handle NOx conversion once temperatures rise, creating a staged response to different operating conditions.
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 significantly improves NOx, CO, and THC conversion efficiency during cold-start periods and under Lambda=1 conditions, ensuring compliance with stringent emission regulations by combining diesel oxidation and three-way catalyst functions.
Implementation Method 1
a specific oxygen storage compound, wherein at least 30 weight-% of said oxygen storage compound consist of cerium oxide
Implementation Method 2
the first coating particularly comprises two platinum group metal components each supported on an oxidic support material
Data Source
AI summary
The present invention relates to a catalyst, in particular to a three-way diesel catalyst, for the treatment of a diesel exhaust gas, the catalyst comprising a substrate and two specific coatings disposed thereon, wherein the first coating particularly comprises a first platinum group metal component supported on a first oxidic support material, a second platinum group metal component supported on a second oxidic support material, and a first oxygen storage component, wherein at least 30 weight-% of the first oxygen storage component consist of cerium oxide, calculated as CeOa, and wherein the second coating particularly comprises a third platinum group metal component and a fourth platinum group metal component, wherein the third platinum group metal component and the fourth platinum group metal component are supported on a third oxidic support material. Further, a process for the preparation of such a catalyst is disclosed as well as a use thereof.