Two-Layer Exhaust Catalyst for Saddle Vehicles
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Solution Overview
Problem
Exhaust gas cleaning catalysts for saddle-type vehicles face challenges in maintaining catalytic activity due to metallization of PdO, which leads to sintering of Pd fine particles, especially under varying oxygen, HC, and CO concentrations and wide A/F windows, resulting in reduced durability and performance.
Innovation Solution
A two-layer catalyst structure is employed, with a lower layer composed of a cerium-zirconium composite oxide supporting metallic Pd or Pd oxide and an upper layer composed of zirconium composite oxide supporting Rh or Rh+Pt, incorporating Nd and La to enhance thermal stability and OSC performance, thereby suppressing PdO reduction and maintaining catalytic activity across varying conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If Pd is used as the main catalyst component to reduce cost, then manufacturing cost is reduced, but catalytic activity is reduced due to sintering of Pd particles via reduction of PdO
Solution Approach 1:
A Rh-containing upper layer is introduced as an intermediary between the Pd-containing lower layer and the exhaust gas. This Rh layer acts as a protective barrier that prevents reducing exhaust gas components from reaching the PdO, thereby preventing PdO reduction and subsequent Pd particle sintering while allowing the Pd layer to maintain its catalytic function
Solution Approach 2:
The catalyst employs a composite two-layer structure combining Rh (or Rh+Pt) in the upper layer with Pd in the lower layer. This composite structure leverages the superior stability and resistance to reduction of Rh/Pt to protect the cost-effective Pd catalyst, achieving both cost reduction and maintained catalytic activity
2Reliability
If a two-layer catalyst with Pd in lower layer and Rh/Pt in upper layer is used, then durability is improved, but device complexity increases
Solution Approach 1:
The catalyst is segmented into two distinct functional layers: a lower layer containing Pd for cost-effective catalysis and an upper layer containing Rh or Rh+Pt for protection against reduction. This segmentation allows each layer to perform its specific function optimally while maintaining overall system durability
Solution Approach 2:
The upper Rh-containing layer serves multiple functions simultaneously: it acts as a protective barrier against PdO reduction, maintains catalytic activity under varying A/F conditions, and provides NOx reduction capability. This multi-functionality justifies the added structural complexity by delivering multiple benefits from a single component
3Adaptability or versatility
If the catalyst is used in saddle-type vehicle exhaust with wide A/F window, then adaptability is improved, but catalytic activity is reduced due to drastic changes in oxygen, HC, and CO concentrations
Solution Approach 1:
The catalyst structure is designed to dynamically respond to varying exhaust conditions. The Rh-containing upper layer dynamically adjusts to changing A/F ratios and exhaust compositions, maintaining its protective function across the wide A/F window typical of saddle-type vehicles while allowing the Pd layer to adapt its catalytic activity to the specific operating conditions
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 exhibits improved durability and exhaust gas cleaning performance, maintaining effectiveness even under rich conditions with a wide A/F window, ensuring sustained catalytic activity and NOx removal performance.
Implementation Method 1
a lower layer prepared by distributing metallic Pd or Pd oxide on a specific cerium-zirconium composite oxide material having high OSC performance
Implementation Method 2
a catalyst component which is supported on the carrier and contains metallic Pd or Pd oxide
Implementation Method 3
the second catalyst layer includes a carrier formed of a zirconium composite oxide... and a catalyst component which is supported on the carrier and contains metallic Rh or Rh oxide, or both metallic Rh or Rh oxide and metallic Pt or Pt oxide
Data Source
Figure 1(a)~1(b)
Figure 2
Figure 3
AI summary
An exhaust gas cleaning catalyst for a saddle-type vehicle, the catalyst including a support; a first catalyst layer formed on a surface of the support; and a second catalyst layer formed on the first catalyst layer, wherein the first catalyst layer includes a carrier formed of a composite oxide having a CeO2 content of 45 to 70 mass%, a ZrO2 content of 20 to 45 mass%, an Nd2O3 content of 2 to 20 mass%, and an La2O3 content of 1 to 10 mass%, and a catalyst component which is supported on the carrier and contains metallic Pd or Pd oxide; and the second catalyst layer includes a carrier formed of a composite oxide having a zrO2 content of 50 to 95 mass%, a CeO2 content of 0 to 40 mass%, an Nd2O3 content of 2 to 20 mass%, and an La2O3 content of 1 to 10 mass%, and a catalyst component which is supported on the carrier and contains metallic Rh or Rh oxide, or both metallic Rh or Rh oxide and metallic Pt or Pt oxide.