DOC and CSF Catalyst Configuration for NOx Ratio Control
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing diesel engine exhaust treatment systems face challenges in optimally controlling the NO to NO2 ratio entering the Selective Catalytic Reduction (SCR) catalyst, which affects the efficiency of NOx reduction, particularly due to the large volume of oxidation catalysts in Diesel Oxidation Catalysts (DOC) and Catalyzed Soot Filters (CSF) upstream of the SCR.
Innovation Solution
A method involving a DOC with platinum and palladium dispersed on a refractory metal oxide mixed with zeolite, combined with a CSF having platinum group metals and specific passage designs, optimizes the NO to NO2 ratio by producing no NO2 in the DOC and controlling the ratio between 0.6 and 1.4, ensuring effective NOx reduction in the SCR system.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a large volume of oxidation catalyst is used in DOC and CSF upstream of SCR, then particulate matter removal and soot combustion are improved, but the NO to NO2 ratio control deteriorates
Solution Approach 1:
The patent applies local quality by creating distinct functional zones within the catalytic system: the DOC is optimized for oxidation functions (HC and CO conversion, some particulate oxidation) while the CSF is optimized for particulate filtration and controlled NO to NO2 conversion. This spatial differentiation of catalytic functions allows each component to perform its specialized role without interfering with the overall NOx ratio control.
Solution Approach 2:
The patent segments the exhaust treatment function into separate catalytic components (DOC and CSF) with distinct roles. The DOC handles gaseous oxidation while the CSF handles particulate filtration and controlled NO2 generation. This segmentation allows independent optimization of each component's catalytic composition and structure, resolving the contradiction between high particulate removal and precise NOx ratio control.
2Productivity
If oxidation catalysts are placed upstream of SCR catalyst, then HC and CO conversion are improved, but NO2 production increases which affects SCR efficiency
Solution Approach 1:
The patent changes the catalytic parameters (metal composition, surface area, activity) of the DOC and CSF to control the extent of NO to NO2 conversion. By adjusting these parameters, the system produces an optimized NOx mixture that is specifically suited for SCR reduction, rather than maximizing NO2 production. This parameter optimization ensures high SCR efficiency while maintaining effective gaseous pollutant conversion.
Solution Approach 2:
The patent implements a feedback mechanism where the NOx composition downstream of the CSF is monitored and used to adjust upstream catalytic conditions. This feedback loop ensures that the DOC and CSF operate at optimal conversion rates that produce the desired NOx ratio for maximum SCR efficiency, dynamically balancing gaseous conversion and NOx composition control.
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 enhances the control of the NO to NO2 ratio, improving the NOx reduction efficiency in the SCR system, allowing for simultaneous treatment of particulate matter and gaseous components in diesel engine exhaust, meeting stringent emission regulations by optimizing the catalyst composition and configuration.
Implementation Method 1
Oxidation catalysts that contain platinum group metals, base metals and combinations thereof are known to facilitate the treatment of diesel engine exhaust by promoting the conversion of both HC and CO gaseous pollutants and some proportion of the particulate matter through oxidation of these pollutants to carbon dioxide and water
Implementation Method 2
oxidation catalysts that contain platinum group metals (which are typically dispersed on a refractory oxide support) also promote the oxidation of nitric oxide (NO) to NO2
Implementation Method 3
There are many known filter structures that are effective in removing particulate matter from diesel exhaust, such as honeycomb wall flow filters, wound or packed fiber filters, open cell foams, sintered metal filters, etc
Implementation Method 4
The presence of a catalyst promotes soot combustion, thereby regenerating the filters at temperatures accessible within the diesel engine's exhaust under realistic duty cycles
Implementation Method 5
A proven NOx abatement technology applied to stationary sources with lean exhaust conditions is Selective Catalytic Reduction (SCR). In this process, NOx is reduced with ammonia (NH3) to nitrogen (N2) over a catalyst typically composed of base metals
Implementation Method 6
Selective Catalytic Reduction (SCR)... NOx is reduced with ammonia (NH3) to nitrogen (N2)
Data Source
Figure 1
Figure 2
Figure 3
AI summary
An emission treatment system and method for remediating the nitrogen oxides (NOx), particulate matter, and gaseous hydrocarbons present in diesel engine exhaust streams are described. The emission treatment system has an oxidation catalyst upstream of a soot filter upstream from a NOx reducing catalyst.