Exhaust Purification Device with Segmented Noble Metal Catalyst Layers
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Solution Overview
Problem
Conventional exhaust gas purification devices with wall-flow particulate filters face challenges in achieving enhanced purification performance while minimizing pressure loss, particularly due to sintering issues between noble metal catalysts like platinum and rhodium at high temperatures and uneven pressure distribution.
Innovation Solution
The device employs a substrate with a wall-flow structure, featuring an upstream and downstream catalyst layer with different noble metals (platinum, palladium, and rhodium) supported on carriers, where the upstream catalyst layer has a smaller coating amount and is unevenly distributed to avoid contact with outlet cells, and the downstream layer is similarly configured but with a larger coating amount, ensuring efficient gas flow and reduced sintering.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If Pt and Rh are supported separately inside a partition wall, then purification performance is enhanced, but sintering occurs at high temperature causing performance degradation
Solution Approach 1:
The catalyst structure is segmented into multiple independent layers: a first catalyst layer containing Pt and a second catalyst layer containing Rh, with each layer separated by a porous coating layer. This segmentation prevents direct contact between Pt and Rh, thereby preventing sintering while maintaining purification performance.
Solution Approach 2:
A porous coating layer acts as an intermediary between the Pt-containing first catalyst layer and the Rh-containing second catalyst layer. This intermediary layer physically separates the two noble metals, preventing their direct interaction and sintering at high temperatures while still allowing exhaust gas to pass through for catalytic action.
2Stability of the object's composition
If Rh layer is disposed outside the partition wall, then sintering between Pd and Rh is suppressed, but pressure loss increases
Solution Approach 1:
Instead of placing the Rh layer outside the partition wall (one-dimensional surface placement), the invention positions the Rh-containing second catalyst layer inside the partition wall but in a separate dimension from the Pt-containing first catalyst layer, with the porous coating layer providing spatial separation. This internal layered arrangement maintains gas flow paths while preventing sintering.
Solution Approach 2:
A porous coating layer is used to separate the Pt and Rh catalyst layers while maintaining permeability to exhaust gas. The porous structure allows gas molecules to pass through freely, minimizing pressure loss, while the physical separation prevents direct contact between the noble metal particles, suppressing sintering.
3Loss of energy
If coating amount of upstream catalyst layer is reduced, then pressure loss is reduced, but purification performance may be compromised
Solution Approach 1:
The catalyst layers are designed with different local qualities: the first catalyst layer (Pt) and second catalyst layer (Rh) have different coating amounts optimized for their respective positions and functions. The upstream first catalyst layer has a coating amount optimized to balance pressure loss reduction while maintaining sufficient purification capability for the specific exhaust conditions at that location.
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
This configuration significantly enhances exhaust gas purification performance while reducing pressure loss, maintaining catalyst effectiveness at high temperatures and preventing sintering, thus offering improved emissions control.
Implementation Method 1
exhaust gas that flows in through cell inlets passes through partitioning porous cell partition walls, and is discharged out through the cell outlets. As the exhaust gas passes through a porous cell partition wall, the particulate matter is trapped within the pores inside the partition wall.
Implementation Method 2
Approaches involving supporting a noble metal catalyst on the above particulate filters have been studied in recent years with a view to further increasing purification performance.
Implementation Method 3
Pt and Rh co-exist inside the partition wall, and hence sintering (grain bonding) between Pt and Rh occurs when the catalyst is exposed to high temperature. The purification performance on exhaust gas may drop as a result.
Data Source
AI summary
An exhaust gas purification device of the present invention is provided with: a substrate of wall flow structure having an inlet cell, an outlet cell and a porous partition wall; an upstream catalyst layer, provided inside the partition wall and disposed in an upstream portion of the substrate including an exhaust gas inflow end section; and a downstream catalyst layer, provided inside the partition wall and disposed in a downstream portion of the substrate including an exhaust gas outflow end section. The upstream catalyst layer and the downstream catalyst layer each contain a carrier and at least one noble metal from among Pt, Pd and Rh, supported on the carrier. The noble metal in the upstream catalyst layer and the noble metal in the downstream catalyst layer are different from each other.