Wall-Flow Catalyst Layer Layout for High-Speed NOx Purification
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Solution Overview
Problem
Existing exhaust gas purification catalysts face challenges in achieving sufficient NOx purification performance, particularly during high-speed operation, due to the generation of significant NOx at elevated temperatures in combustion chambers.
Innovation Solution
The catalyst design includes first and second catalyst layers on a wall-flow substrate, where the first layers extend along the exhaust gas flow direction on the inflow-side cells and the second layers extend opposite to the flow direction on the outflow-side cells, with specific length, thickness, and mass ratios that enhance purification performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a single catalyst layer is formed in the wall-flow substrate, then the structure is simple and manufacturing is easier, but the exhaust gas purification performance is insufficient
Solution Approach 1:
The catalyst system is segmented into multiple independent catalyst layers (first catalyst layer with Pt/Pd, second catalyst layer with Rh) positioned at different locations within the wall-flow substrate. Each layer performs specific purification functions, with the first layer handling HC and CO oxidation and the second layer handling NOx reduction, thereby improving overall purification performance while maintaining manageable structural complexity
Solution Approach 2:
Different catalyst layers are applied to different regions of the wall-flow substrate with specific compositions and functions. The first catalyst layer is formed in inflow-side cells for oxidative purification, while the second catalyst layer is formed in outflow-side cells for reductive purification, optimizing the catalytic function at each location according to the local exhaust gas composition and flow conditions
2Reliability
If catalyst layers are optimized for low-speed operation, then low-speed purification performance is good, but high-speed NOx purification performance is insufficient
Solution Approach 1:
The catalyst system incorporates different noble metal compositions and layer configurations that respond differently to operating conditions. The first catalyst layer with Pt and Pd provides robust low-speed performance through oxidative purification, while the second catalyst layer with Rh becomes more effective at high speeds for NOx reduction, allowing the system to adapt to varying operating conditions through inherent parameter differences in the catalyst layers
3Reliability
If more noble metal catalysts are used to improve purification performance, then exhaust gas purification performance improves, but manufacturing cost increases
Solution Approach 1:
The noble metal catalysts are segmented into different layers with different compositions and quantities. The first catalyst layer uses Pt and Pd at specific loadings for oxidative purification, while the second catalyst layer uses Rh for reductive purification. This segmentation allows optimization of noble metal distribution, reducing overall cost while maintaining high purification performance through specialized function allocation
Solution Approach 2:
Different noble metal compositions are applied locally to different regions of the substrate based on specific purification needs. The inflow-side cells receive Pt/Pd for oxidation, while outflow-side cells receive Rh for reduction, optimizing catalyst effectiveness in each region while minimizing total noble metal usage through targeted application
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 design achieves improved PM collection and exhaust gas purification performance, including enhanced NOx purification, particularly under high-speed conditions.
Implementation Method 1
a substrate having a structure called a wall-flow structure is used as a GPF. In the wall-flow substrate, when exhaust gas flows in from a cell inlet, passes through a porous partition wall dividing cells, and flows out from a cell outlet, PM in the exhaust gas is collected in a pore inside the partition wall.
Implementation Method 2
Noble metal catalysts such as platinum (Pt), palladium (Pd) and rhodium (Rh) are used as a three-way catalyst. Pt and Pd are mainly involved in oxidative purification of HC and CO and Rh is mainly involved in reductive purification of NOx.
Data Source
AI summary
An object of the present invention is to provide an exhaust gas purification catalyst including a wall-flow substrate and a catalyst layer, and having an improved exhaust gas purification performance, and, in order to achieve such an object, the present invention provides an exhaust gas purification catalyst including: a wall-flow substrate, first catalyst layers; and second catalyst layers; wherein the first catalyst layers and the second catalyst layers satisfy the following expressions (1) to (3):L1<L2 (1)T1<T2 (2)WC1>WC2 (3)wherein L1 represents the length of the first catalyst layers, L2 represents the length of the second catalyst layers, T1 represents the thickness of the rising portions of the first catalyst layers, T2 represents the thickness of the rising portions of the second catalyst layers, WC1 represents the mass of the first catalyst layers per unit volume of the portion of the substrate provided with the first catalyst layers, and WC2 represents the mass of the second catalyst layers per unit volume of the portion of the substrate provided with the second catalyst layers.