Layered Diesel Oxidation Catalyst Composite for NO2 Formation
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Solution Overview
Problem
Diesel oxidation catalysts face deactivation due to thermal sintering, leading to reduced catalytic performance and emissions of NOx, HC, and CO in lean burn engines, necessitating improved catalyst systems for stringent emissions regulations.
Innovation Solution
A layered catalyst composite with a bottom washcoat layer containing platinum and palladium in a specific weight ratio and a top washcoat layer comprising zeolite and platinum, with minimal palladium, to enhance NO2 formation while maintaining CO and HC oxidation efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single-layer catalyst is used, then the structure is simple, but the NO2 formation efficiency is insufficient
Solution Approach 1:
The catalyst is divided into two distinct layers: a first layer in direct contact with the support material having a nitrogen oxide storing function, and a second layer in contact with the exhaust gas having a catalytic function. This segmentation allows each layer to be optimized for its specific function, thereby improving overall NO2 formation efficiency while maintaining structural simplicity.
Solution Approach 2:
Each layer is given different compositional characteristics tailored to its specific function. The first layer contains materials optimized for NOx storage, while the second layer contains materials optimized for catalytic oxidation. This local quality differentiation enables each region of the catalyst to perform its designated function at maximum efficiency.
2Productivity
If high temperature exposure occurs, then the catalyst converts pollutants effectively, but thermal sintering deactivates the catalyst
Solution Approach 1:
The first layer acts as a protective barrier that stores nitrogen oxides before they reach the catalytic layer. This beforehand cushioning prevents direct high-temperature exposure of the catalytic components, reducing thermal sintering and maintaining catalyst stability during high-temperature operation.
Solution Approach 2:
The catalyst uses a composite structure with two different material compositions. The first layer uses materials with high thermal stability for NOx storage, while the second layer uses materials optimized for catalytic activity. This composite approach allows the system to maintain both high pollutant conversion efficiency and catalyst stability under high-temperature 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 layered catalyst composite effectively converts NOx to NO2, maintains CO and HC oxidation efficiency, and improves sulfur tolerance, even in aged catalysts, thereby enhancing overall emissions treatment performance.
Implementation Method 1
oxidation catalysts... are known for use in treating the exhaust of diesel engines to convert both hydrocarbon and carbon monoxide gaseous pollutants by catalyzing the oxidation of these pollutants to carbon dioxide and water
Implementation Method 2
oxidation catalysts that contain platinum group metals... promote the oxidation of nitric oxide (NO) to NO2
Data Source
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AI summary
Oxidation catalyst composites for the treatment of exhaust gas emissions, such as the abatement of unburned hydrocarbons (HC), and carbon monoxide (CO) and the oxidation of NO to NO2 are disclosed. The catalyst composites comprise two washcoat layers containing two different compositions of platinum group metals to optimize the NO2 exiting the catalyst composite. The key to improvement in NO oxidation is to have one catalyst layer that contains Pt while being substantially free of Pd. Methods and systems utilizing the catalyst composites are also disclosed.