Zone-Coated Dual-Use Ammonia Oxidation Catalyst
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Solution Overview
Problem
Existing exhaust systems for heavy-duty diesel vehicles face challenges in controlling the delivery of nitrogenous reductant to SCR catalysts, leading to issues with NOx emission standards and ammonia slip, which results in inefficient use of reductant and potential formation of undesired by-products.
Innovation Solution
A composite, zone-coated, dual-use ammonia and nitric oxide oxidation catalyst is introduced, featuring a first washcoat layer with a higher platinum group metal loading and a second washcoat layer with a lower loading, along with a washcoat layer containing aluminosilicate zeolite with copper, iron, and/or manganese. This catalyst is designed to remove slipped nitrogenous reductant and oxidize nitric oxide to nitrogen dioxide, promoting downstream selective catalytic reduction reactions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a dual-SCR system with multiple catalysts is used to meet NOx emission standards, then NOx reduction efficiency is improved, but system complexity and manufacturing cost increase
Solution Approach 1:
The patent combines ammonia oxidation and nitric oxide oxidation functions into a single composite catalyst with multiple washcoat layers. The first washcoat layer contains ammonia oxidation catalyst and the second washcoat layer contains nitric oxide oxidation catalyst, allowing both SCR functions to be integrated in one device rather than requiring separate catalysts, thereby reducing system complexity while maintaining NOx reduction efficiency
Solution Approach 2:
The composite catalyst performs multiple functions simultaneously: it oxidizes ammonia to prevent ammonia slip, oxidizes nitric oxide to nitrogen dioxide to promote fast SCR reactions, and supports the overall SCR process. This multi-functional design replaces what would traditionally require multiple separate catalysts, simplifying the exhaust aftertreatment system
2Ease of manufacture
If uniform platinum group metal loading is used across the catalyst, then manufacturing process is simplified, but catalytic performance for both ammonia and nitric oxide oxidation is compromised
Solution Approach 1:
The patent applies different platinum group metal loadings to different zones of the catalyst. The first washcoat layer has a higher platinum group metal loading optimized for ammonia oxidation, while the second washcoat layer has a lower loading optimized for nitric oxide oxidation. This zoned approach ensures each region has the appropriate catalytic properties for its specific function, maintaining high overall 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 composite catalyst improves manufacturing simplicity, reduces the complexity of dual-SCR systems, and allows for more compact exhaust aftertreatment systems, while effectively oxidizing ammonia and nitric oxide, thus enhancing NOx reduction and reducing the formation of N2O and other harmful by-products.
Implementation Method 1
a first catalyst washcoat zone (1) comprised of a first catalyst washcoat layer and disposed at an inlet end (I) of a flow-through honeycomb substrate monolith (5)... comprising one or more platinum group metal components... for oxidising ammonia
Implementation Method 2
for oxidising ammonia in an exhaust gas flowing in an exhaust system... and for oxidising nitric oxide (NO) in the exhaust gas to nitrogen dioxide (NO2)
Implementation Method 3
a washcoat layer comprising an aluminosilicate zeolite including copper, iron and/or manganese, which is active for catalysing the reduction of oxides of nitrogen with a nitrogenous reductant
Data Source
AI summary
A composite, zone-coated, dual-use ammonia (AMOX) and nitric oxide oxidation catalyst (12) comprises: a substrate (5) having a total length L and a longitudinal axis and having a substrate surface extending axially between a first substrate end (I) and a second substrate end (O); two or more catalyst washcoat zones (1; 2) comprised of a first catalyst washcoat layer (9) comprising a refractory metal oxide support material and one or more platinum group metal components supported thereon and a second catalyst washcoat layer (11) different from the first catalyst washcoat layer (9) and comprising a refractory metal oxide support material and one or more platinum group metal components supported thereon, which two or more catalyst washcoat zones (1; 2) being arranged axially in series on and along the substrate surface, wherein a first catalyst washcoat zone (1) having a length L1, wherein L1<L, is defined at one end by the first substrate end (I) and at a second end (13) by a first end (15) of a second catalyst washcoat zone (2) having a length L2, wherein L2<L, wherein the first catalyst washcoat zone (1) comprises a first refractory metal oxide support material and one or more platinum group metal components supported thereon; and the second catalyst washcoat zone comprises a second refractory metal oxide support material and one or more platinum group metal components supported thereon; and a washcoat overlayer (G) extending axially from the first substrate end for up to 200% of the axial length of the underlying first catalyst washcoat layer, which washcoat overlayer comprising a particulate metal oxide loading of >48.8 g/l (>0.8 g/in3), wherein the particulate metal oxide is an aluminosilicate zeolite including at least one of copper, iron and manganese, wherein a total platinum group metal loading in the first catalyst washcoat zone (1) defined in grams of platinum group metal per litre of substrate volume (g/l) is different from the total platinum group metal loading in the second catalyst washcoat zone (2).