NOx Storage Catalyst Layered Washcoat Structure
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Solution Overview
Problem
Current nitrogen oxide storage catalysts face challenges in achieving efficient NOx storage and conversion, especially at low exhaust gas temperatures, and in coordinating NOx storage, NO2 formation, and reduction capacity, which is critical for meeting stringent emissions regulations like Euro 6d.
Innovation Solution
A nitrogen oxide storage catalyst with a specific layered structure comprising washcoat layers A, B, C, and D, where layer A contains cerium oxide and alkaline earth or alkali compounds with platinum or palladium, layer B is free of alkali and alkaline earth compounds, layer C includes palladium and rhodium on cerium oxide, and layer D comprises platinum or palladium, optimized for improved NOx conversion across a wide temperature range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a nitrogen oxide storage catalyst is used to remove NOx from lean-burn engine exhaust, then NOx conversion is improved, but efficient NOx storage and conversion at low exhaust gas temperatures remains challenging
Solution Approach 1:
The catalyst is divided into multiple functional layers (washcoat layers A, B, C, and D) with distinct compositions and functions. Layer A contains alkaline earth/alkali compounds for NOx storage, layer B provides oxidation function without alkali compounds, layer C contains Pd-Rh for reduction, and layer D provides additional reduction capacity. This segmentation allows each layer to optimize its function independently, particularly improving low-temperature performance.
Solution Approach 2:
Different regions of the catalyst have different chemical compositions tailored to specific functions. The alkaline earth/alkali compounds are localized in layer A for optimal NOx storage, while Pd and Rh are concentrated in layers C and D for reduction. This local quality optimization ensures that each functional component operates most effectively at its designated location, addressing the temperature-dependent performance issues.
2Reliability
If multiple functional components are combined in a nitrogen oxide storage catalyst to improve NOx storage and conversion, then conversion efficiency is improved, but coordinating NOx storage, NO2 formation, and reduction capacity becomes more difficult
Solution Approach 1:
The catalyst structure is segmented into four distinct washcoat layers, each with a specific function: layer A (NOx storage with alkaline earth/alkali compounds), layer B (oxidation without alkali interference), layer C (reduction with Pd-Rh), and layer D (additional reduction). This segmentation simplifies the coordination of multiple functions by assigning them to separate zones, reducing the complexity of optimizing interactions between components.
Solution Approach 2:
The patent combines multiple functional components (alkaline earth compounds, alkali compounds, cerium oxide, Pd, Pt, Rh) into a unified multi-layer catalyst structure where they work synergistically. The merging of these components in a coordinated layered architecture allows simultaneous optimization of NOx storage, NO2 formation, and reduction capacity, rather than treating them as separate problems.
3Quantity of substance
If alkaline earth and alkali compounds are used together in the catalyst to enhance NOx storage capacity, then storage capacity is improved, but undesired interactions between components may occur
Solution Approach 1:
Alkaline earth compounds and alkali compounds are segregated into different layers (layer A contains alkaline earth/alkali, layer B is free of alkali compounds). This spatial segmentation prevents undesired chemical interactions between these components while maintaining their individual NOx storage contributions, thereby preserving high storage capacity without the harmful side effects of their direct interaction.
Solution Approach 2:
Cerium oxide is used as an intermediary component between the alkaline earth/alkali compounds and the precious metals. It facilitates the functional separation and reduces direct interactions between the alkaline components and other catalyst materials, thereby preventing undesired interactions while maintaining overall catalyst 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 catalyst achieves effective NOx conversion at temperatures from 200 to 450°C, meeting Euro 6 emissions standards by enhancing NOx storage and reduction capacity, particularly in urban driving conditions where temperatures are low.
Implementation Method 1
in a lean operating phase of the engine, the nitrogen oxides from the storage material of the storage catalytic converter are stored primarily in the form of nitrates
Implementation Method 2
to oxidize NO to NO2 and CO and HC to CO2 under lean conditions
Implementation Method 3
to reduce released NO2 to nitrogen during the rich operating phases in which the nitrogen oxide storage catalyst is regenerated
Implementation Method 4
The ammonia used as a reducing agent can be made available by metering an ammonia precursor compound, such as urea, ammonium carbamate or ammonium formate, into the exhaust system and subsequent hydrolysis
Data Source
Figure 1
AI summary
The present invention relates to a nitrogen oxide storage catalyst comprising a support body and washcoat layers A, B, C and D, wherein: - washcoat layer A is arranged on the support body and contains cerium oxide, an alkaline earth compound and/or an alkali compound, as well as platinum or platinum and palladium in a weight ratio > 5:1; - washcoat layer B is arranged on washcoat layer A and contains cerium oxide, as well as platinum or platinum and palladium in a weight ratio > 5:1 and is free of alkali compounds and compounds of calcium, strontium and barium; - washcoat layer C is arranged on washcoat layer B and comprises palladium or palladium and platinum supported on cerium oxide in a weight ratio > 2:1, as well as rhodium; and - washcoat layer D is arranged on washcoat layer C and comprises platinum or platinum and palladium, as well as a method for converting NOx in exhaust gases from motor vehicles operated with lean-burn engines.