Layered Ammonia Slip Catalyst for Low-NOx CO and HC Oxidation
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Solution Overview
Problem
Existing ammonia slip catalysts (ASCs) face challenges in reducing ammonia slip without generating significant secondary NOx in lean burn exhaust gas treatment, and they often require additional components like diesel oxidation catalysts (DOC) for complete CO and HC conversion, increasing system complexity and cost.
Innovation Solution
A bi-layer or tri-layer ASC with palladium in the top layer, which enhances CO and HC oxidative potential while minimizing secondary NOx formation, allowing for a single-unit after-treatment system that eliminates the need for upstream DOCs and reduces system footprint and cost.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If a conventional ASC with segregated top and bottom layers is used, then ammonia slip is reduced, but secondary NOx is formed and system complexity increases due to requiring additional DOC components
Solution Approach 1:
The patent combines the DOC and ASC functions into a single integrated catalyst unit. The top layer contains Pd-based oxidation catalyst for oxidizing CO and HC, while the bottom layer contains the SCR catalyst for reducing NOx. This merging eliminates the need for separate DOC and ASC components, reducing system complexity while maintaining the ability to reduce ammonia slip and oxidize CO/HC simultaneously.
Solution Approach 2:
The integrated catalyst performs multiple functions within a single device: it oxidizes CO and HC in the top layer, reduces NOx in the bottom layer, and prevents ammonia slip by oxidizing any unreacted ammonia that passes through the SCR catalyst. This multi-functionality replaces what previously required separate DOC and ASC units.
2Use of energy by moving object
If Pd is added to the top layer to enhance CO and HC oxidation, then oxidative potential increases, but NH3 oxidation to secondary NOx may increase
Solution Approach 1:
The patent applies local quality by having different catalyst compositions in different layers. The top layer contains Pd-based oxidation catalyst specifically for CO and HC oxidation, while the bottom layer contains SCR catalyst for NOx reduction. The segregated layer structure ensures that Pd is localized where CO/HC oxidation is needed, minimizing its contact with ammonia and reducing secondary NOx formation while maintaining high oxidative potential.
3Productivity
If high-temperature operations are performed upstream, then regeneration efficiency improves, but thermal durability of sensitive catalysts deteriorates
Solution Approach 1:
The patent segments the after-treatment system into distinct functional zones with different temperature requirements. The integrated catalyst unit (with Pd top layer and SCR bottom layer) operates at lower temperatures upstream, while the DPF regeneration occurs downstream where high temperatures are needed. This segmentation allows high-temperature regeneration to occur away from temperature-sensitive catalysts, protecting their thermal durability while maintaining regeneration efficiency.
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 ASC effectively reduces ammonia slip and oxidizes CO and HC, generating heat for diesel particulate filter regeneration, thus simplifying the after-treatment system and improving thermal durability by positioning high-temperature operations downstream of sensitive catalysts.
Implementation Method 1
oxidizes CO and HC
Implementation Method 2
Selective Catalytic Reduction (SCR)... The reductant is absorbed onto the catalyst and the NOx reduction reaction takes place
Implementation Method 3
oxidize NH3 to yield N2 and/or secondary NOx + H2O
Implementation Method 4
generating heat for diesel particulate filter regeneration
Data Source
Figure 1A~1D
Figure 1E~2A
Figure 2B
AI summary
Provided is an ammonia slip catalyst article having supported palladium in a top or upstream layer for oxidation of carbon monoxide and/or hydrocarbons, an SCR catalyst either in the top layer or in a separate lower or downstream layer, and an ammonia oxidation catalyst in a bottom layer. Also provided are methods for treating an exhaust gas using the catalyst article, wherein the treatment involves reducing the concentrations of ammonia and optionally carbon monoxide and/or hydrocarbons in the exhaust gas.