Two-Layer NOx Storage Catalyst for Lean-Burn Engines
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Solution Overview
Problem
Existing nitrogen oxide storage catalytic converters for lean-burn internal combustion engines, such as diesel engines, fail to achieve greater than 60% NOx conversion at temperatures between 200 to 450°C, which is necessary to comply with future emissions legislation, especially at cold and high temperatures.
Innovation Solution
A nitrogen oxide storage catalyst with at least two catalytically active coatings on a support body, where the lower coating contains cerium oxide, platinum, and/or palladium without alkaline earth compounds, and the upper coating includes a basic magnesium-aluminum mixed oxide with barium or strontium oxide, ensuring effective NOx conversion across a wide temperature range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional nitrogen oxide storage catalytic converters are used, then NOx storage is achieved at low or high temperatures, but NOx conversion greater than 60% at temperatures of 200 to 450°C is not achieved
Solution Approach 1:
The catalyst is divided into two distinct layers: a lower layer containing basic magnesium-aluminum mixed oxide with alkaline earth metal compounds for NOx storage, and an upper layer containing cerium oxide and platinum group metals for oxidation and reduction reactions. This segmentation allows each layer to specialize in specific functions, achieving >60% NOx conversion at 200-450°C while maintaining performance across wide temperature ranges.
Solution Approach 2:
The invention uses composite materials in both layers: the lower layer combines basic magnesium-aluminum mixed oxide with alkaline earth metal compounds (barium oxide or strontium oxide), while the upper layer combines cerium oxide with platinum and/or palladium. These composite materials provide synergistic effects that enable high NOx conversion efficiency across the 200-450°C temperature range.
2Reliability
If single-layer catalytic converters are used, then manufacturing is simpler, but NOx conversion performance at both cold and high temperatures is insufficient
Solution Approach 1:
The catalyst is divided into two distinct layers: a lower layer containing basic magnesium-aluminum mixed oxide with alkaline earth metal compounds for NOx storage, and an upper layer containing cerium oxide and platinum group metals for oxidation and reduction reactions. This segmentation allows each layer to specialize in specific functions, achieving >60% NOx conversion at 200-450°C while maintaining performance across wide temperature ranges.
Solution Approach 2:
The two-layer structure provides multi-functionality: the lower layer performs NOx storage and release, while the upper layer performs oxidation of CO and HC under lean conditions and reduction of NOx under rich conditions. This multi-functional design achieves Euro 6 compliance across both cold and high temperature operations without requiring multiple separate devices.
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 described catalyst achieves NOx conversion greater than 60% at temperatures from 200 to 500°C, making it suitable for Euro 6 emissions compliance by optimizing NOx reduction both at cold and high temperatures.
Implementation Method 1
in a lean operating phase of the engine the nitrogen oxides are stored by the storage material of the storage catalytic converter mainly in the form of nitrates
Implementation Method 2
Due to their basic properties, these compounds are able to form nitrates with the acidic nitrogen oxides in the exhaust gas and store them in this way
Implementation Method 3
to oxidize NO to NO2 and CO and HC to CO2 under lean conditions
Implementation Method 4
to reduce released NO2 to nitrogen during the rich operating phases
Implementation Method 5
at least one finely divided, oxygen-storing material
Data Source
Figure 1
Figure 2a~2b
Figure 3
AI summary
The invention relates to a nitrogen oxide storage catalyst consisting of at least two catalytically active coatings on a supporting body, a lower coating (A) containing cerium oxide in addition to platinum and/or palladium and no alkaline earth compound and an upper coating (B), which is arranged above coating (A), containing an alkaline earth compound and a basic magnesium-aluminium mixed oxide in addition to platinum and palladium. The invention also relates to a method for converting NOx in the exhaust gases of motor vehicles operated using lean-burn engines.