Multilayer NOx Storage Catalyst for Cold-Start Rear-Zone Purification
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Solution Overview
Problem
Conventional exhaust gas purification catalysts face challenges in achieving high NOx purification performance due to temperature distribution in the catalyst layer, leading to incomplete NOx removal at the rear portion of the catalyst layer during engine startup.
Innovation Solution
The catalyst layer is configured with a multilayer structure, featuring a higher concentration of NOx storage material in the rear portion compared to the front portion, and includes Rh in the upper layer to enhance NOx storage and purification efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional catalyst layer structure is used, then the catalyst can be manufactured with uniform composition, but NOx purification performance deteriorates due to temperature distribution causing incomplete NOx removal at the rear portion during engine startup
Solution Approach 1:
The catalyst layer is divided into a front portion and a rear portion with different NOx storage material concentrations. The rear portion has a higher concentration to compensate for lower temperature during engine startup, while the front portion has lower concentration. This local differentiation ensures both portions can effectively purify NOx under their respective temperature conditions.
Solution Approach 2:
The catalyst layer is segmented into distinct functional zones (front portion and rear portion) with different compositions optimized for their specific operational conditions. This segmentation allows each zone to be optimized independently for its temperature and NOx purification requirements.
2Reliability
If the catalyst layer is warmed uniformly, then complete NOx removal can be achieved, but during engine startup the rear portion remains insufficiently warmed leading to NOx emission
Solution Approach 1:
The rear portion is pre-configured with a higher concentration of NOx storage material before engine operation. This preliminary preparation ensures that when the rear portion is warmed during engine startup, it has sufficient capacity to store and purify NOx immediately, eliminating the delay in NOx removal that would occur with uniform composition.
3Quantity of substance
If higher concentration of NOx storage material is used throughout the catalyst layer, then NOx storage capacity increases, but the front portion becomes inefficient due to excessive storage material at lower temperatures
Solution Approach 1:
The NOx storage material concentration is locally optimized: higher concentration in the rear portion where temperature is sufficient for effective purification, and lower concentration in the front portion where temperature is lower. This prevents waste of storage material capacity in the front portion while maximizing overall NOx storage and purification 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 multilayer structure ensures efficient NOx storage and purification even when the rear portion of the catalyst layer is insufficiently warmed, reducing NOx emissions at engine startup and enhancing overall NOx purification performance.
Implementation Method 1
NO is oxidized to NO2 by a catalytic metal and this NO2 reacts with the alkali metal component or the alkali earth metal component
Implementation Method 2
this NO2 reacts with the alkali metal component or the alkali earth metal component
Implementation Method 3
the catalyst activated by heating purifies released NO2
Implementation Method 4
the catalyst layer is gradually warmed by an exhaust gas from a front portion thereof
Data Source
Figure 1~2
AI summary
The present invention provides an exhaust gas purification catalyst including a NOx storage layer and has high NOx purification performance. The exhaust gas purification catalyst disclosed here includes a base material and a catalyst layer. The catalyst layer includes a lower layer, an intermediate layer, and an upper layer. The lower layer contains a catalytic metal. The upper layer contains Rh. The intermediate layer includes a front portion located on an upstream side in an exhaust gas flow direction and a rear portion located on a downstream side. Each of the front portion and the rear portion contains Pt and a NOx storage material. The NOx storage material includes at least one NOx storage element selected from the group consisting of an alkali metal element and an alkali earth metal element. A ratio (CA/CB) of a concentration (CA) of the NOx storage element included in the front portion per 1 L of the base material to a concentration (CB) of the NOx storage element included in the rear portion per 1 L of the base material satisfies 0 < CA/CB < 1.