Layered Exhaust Gas Catalyst for Heat-Resistant NOx Storage
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Solution Overview
Problem
Existing exhaust gas purifying catalysts face challenges in maintaining high NOx storing performance due to the low heat resistance and sintering of platinum (Pt) catalysts, especially under varying temperature conditions, leading to decreased NOx storage and oxidation efficiency.
Innovation Solution
A layered catalyst structure is employed, with a second layer containing Pt and Pd in specific ratios to enhance heat resistance and NOx storage capacity, where the upstream side contains more Pd to protect Pt from high temperatures and the downstream side has higher Pt content for effective NO oxidation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If Pt is used as the catalyst metal to achieve high NO oxidizing performance, then the NOx storing performance is improved, but the heat resistance decreases and sintering occurs under high temperature conditions
Solution Approach 1:
The catalyst layer is divided into three distinct layers with different compositions and functions. The first layer contains Pd for initial catalysis, the second layer contains Pt and NOx storing material for NOx storage, and the third layer contains Rh for final purification. This segmentation allows each layer to optimize its specific function while protecting Pt from excessive heat exposure.
Solution Approach 2:
The catalyst layer combines multiple materials (Pd, Pt, Rh, and NOx storing material) in a composite structure. This composite approach leverages the high NO oxidizing performance of Pt while using Pd and Rh to provide thermal stability and protect against sintering under high temperature conditions.
2Reliability
If the catalyst layer is designed with multiple layers to improve NOx storing performance, then the purification efficiency is improved, but the device complexity increases
Solution Approach 1:
The catalyst layer is divided into three distinct layers with different compositions and functions. The first layer contains Pd for initial catalysis, the second layer contains Pt and NOx storing material for NOx storage, and the third layer contains Rh for final purification. This segmentation allows each layer to optimize its specific function while protecting Pt from excessive heat exposure.
Solution Approach 2:
The multi-layer structure performs multiple functions simultaneously: the first layer provides initial catalytic activity, the second layer stores NOx and provides thermal stability, and the third layer ensures complete purification. This multi-functionality is achieved within a single integrated catalyst component, avoiding the need for separate devices.
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 structure maintains excellent NOx storing performance even under varying temperatures, ensuring effective NOx removal by optimizing Pt's heat resistance and oxidation performance, thereby improving the catalyst's durability and efficiency.
Implementation Method 1
Pt has high NO oxidizing performance in the lean atmosphere
Implementation Method 2
a second layer disposed on the first layer and containing a catalyst metal and a NOx storing material
Implementation Method 3
The NOx storing material is a component with functions of temporarily storing NOx as a nitrate when the air-fuel ratio of the mixed gas is in an oxygen-excess (lean) state
Data Source
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AI summary
An exhaust gas purifying catalyst with excellent NOx storing performance is provided. The exhaust gas purifying catalyst disclosed herein includes a base material 10 and a catalyst layer 20. The catalyst layer 20 includes a first layer 21 containing Pd, a second layer 22 containing a catalyst metal and a NOx storing material, and a third layer 23 containing Rh. The second layer 22 includes a second layer upstream side part 22a containing Pt and Pd and a second layer downstream side part 22b containing Pt. When the ratio of the Pd content to the content of the catalyst metal in the second layer upstream side part 22a is a Pd content ratio A and the ratio of the Pd content to the content of the catalyst metal in the second layer downstream side part 22b is a Pd content ratio B, the Pd content ratio A is less than 0.5 and the Pd content ratio A is higher than the Pd content ratio B.