Three-Zone Exhaust Catalyst for Ammonia Slip Abatement
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Solution Overview
Problem
Existing ammonia emissions from gasoline engines cannot be effectively managed by conventional ammonia slip catalysts due to limited ammonia storage capacity and desorption risks during temperature fluctuations, especially after catalyst aging.
Innovation Solution
A catalyst comprising a carrier body with distinct material zones: A (rhodium, nickel, or cerium), B (platinum), and C (zeolite) that facilitates ammonia decomposition, oxidation, and storage/reduction under varying operating conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If an SCR layer is used to store ammonia during rich phase operation, then ammonia storage capacity is improved, but ammonia emissions occur once the storage capacity is reached or after catalyst aging
Solution Approach 1:
The catalyst is divided into three distinct material zones: Zone A (rhodium/nickel/cerium) for ammonia decomposition under rich conditions, Zone B (platinum) for oxidation under lean conditions, and Zone C (zeolite) for ammonia storage and reduction. This segmentation allows each zone to specialize in a specific function, preventing ammonia emissions by providing multiple pathways for ammonia handling rather than relying on a single storage layer with limited capacity.
Solution Approach 2:
The catalyst utilizes temperature-dependent changes in reaction pathways. Under rich conditions (lower temperature), Zone A decomposes ammonia to nitrogen and hydrogen. Under lean conditions (higher temperature with oxygen present), Zone B oxidizes ammonia to nitrogen. This parameter change approach allows the catalyst to adapt its behavior based on operating conditions, preventing ammonia emissions across different phases without relying solely on storage capacity.
2Productivity
If ammonia is stored on the SCR layer, then ammonia conversion is improved during rich operation, but ammonia desorption occurs at temperature increases resulting in emissions
Solution Approach 1:
Zone A (rhodium/nickel/cerium) is positioned to act as a preliminary decomposition zone for ammonia under rich conditions, converting ammonia to nitrogen and hydrogen before the gas reaches the storage and oxidation zones. This preliminary action prevents ammonia accumulation on the SCR layer, reducing the risk of subsequent desorption and emissions when temperature increases occur.
Solution Approach 2:
Zone A serves as an intermediary decomposition zone between the exhaust inlet and the SCR layer. By decomposing ammonia in this intermediate zone before it reaches the storage layer, the system prevents direct loading of the SCR layer with ammonia, thereby reducing desorption risks during temperature fluctuations while maintaining high ammonia conversion efficiency.
3Productivity
If PGM based materials are used for ammonia oxidation, then oxidation activity is improved, but nitrogen oxides are formed as byproducts
Solution Approach 1:
Zone B (platinum) is specifically designed for ammonia oxidation under lean conditions, while Zone C (zeolite) is specifically designed for selective catalytic reduction of nitrogen oxides. This local quality differentiation ensures that oxidation and reduction functions are spatially separated, allowing ammonia oxidation to occur without excessive nitrogen oxide formation, as the zeolite zone can subsequently reduce any formed oxides.
Solution Approach 2:
The catalyst employs a composite structure combining different material zones: PGM-based platinum for oxidation, rhodium/nickel/cerium for decomposition, and zeolite for reduction and storage. This composite approach allows the system to perform multiple functions simultaneously - oxidizing ammonia while the zeolite component manages nitrogen oxide reduction - thereby improving overall productivity while minimizing harmful byproduct formation.
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 effectively reduces ammonia emissions by decomposing ammonia under rich conditions and oxidizing it under lean conditions, while storing and releasing ammonia as needed, thus overcoming storage limitations and desorption issues.
Implementation Method 1
material zone A comprises rhodium and/or nickel and/or cerium
Implementation Method 2
catalysts which decompose ammonia to nitrogen and hydrogen
Implementation Method 3
ammonia can be oxidized by the PGM layer
Implementation Method 4
platinum group metal (PGM) component, in particular platinum, to carry out the oxidation of ammonia
Implementation Method 5
a zeolite which is able to store ammonia
Implementation Method 6
to catalyze the selective catalytic reduction of NOx
Data Source
Figure 1~2
AI summary
The present invention relates to a catalyst comprising a carrier body having a length L extending between a first end face and a second end face, and differently composed material zones A, B and C arranged on the carrier body, wherein material zone A comprises rhodium and/or nickel and/or cerium; material zone B comprises platinum; and material zone C comprises a zeolite which is able to store ammonia and to catalyze the selective catalytic reduction of NOx.