Exhaust Gas Catalyst Layer Segmentation for Low-Temperature Ignition
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Solution Overview
Problem
Current exhaust gas purifying catalysts face challenges in achieving high ignition performance, particularly at low temperatures, due to tightening regulations on automobile exhaust gas emissions.
Innovation Solution
The catalyst features a layered structure with an upstream portion containing cerium-zirconium composite oxide in a Ce-rich state and a downstream portion with a Zr-rich state, along with specific noble metal distributions and refractory inorganic oxides, to enhance adsorption and degradation of exhaust gases.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional catalyst layer structure is used, then the catalyst can maintain basic exhaust gas purification function, but the ignition performance at low temperature is insufficient
Solution Approach 1:
The catalyst layer is divided into an inside layer and an outside layer with different compositions. The inside layer contains cerium-zirconium composite oxide with high CeO2 proportion (50-95 wt%) for low-temperature activation, while the outside layer contains cerium-zirconium composite oxide with high ZrO2 proportion (50-95 wt%) for thermal stability and NOx purification. This segmentation allows each layer to perform its specialized function optimally.
Solution Approach 2:
Different regions of the catalyst layer are assigned different material compositions tailored to their specific functions. The inside layer near the substrate uses Ce-rich composite oxide for rapid heating and activation, while the outside layer exposed to exhaust gas uses Zr-rich composite oxide for durability and catalytic activity. This local differentiation resolves the contradiction between low-temperature activation and thermal stability.
2Productivity
If the catalyst operates at low temperature, then energy consumption is reduced, but the purification efficiency of exhaust gases decreases
Solution Approach 1:
The inside layer with high CeO2 content performs preliminary heating and activation of the catalyst during cold start conditions. Cerium oxide facilitates oxygen storage and release, creating favorable conditions for catalytic reactions at lower temperatures. This preliminary thermal preparation enables the catalyst to achieve effective purification efficiency even when the engine operates at low temperature.
Solution Approach 2:
The catalyst composition parameters are optimized to function effectively across a range of temperatures. By controlling the Ce/Zr ratio in different layers, the catalyst maintains high activity at low temperatures through CeO2-driven oxygen exchange reactions, while transitioning to ZrO2-dominated chemistry at higher temperatures for sustained purification efficiency. This parameter optimization decouples purification efficiency from operating temperature.
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 results in improved exhaust gas purifying performance and ignition performance, achieving low emissions of HC, CO, and NOx, as demonstrated by the Embodiments and comparative examples.
Implementation Method 1
the cerium-zirconium composite oxide in which a relative proportion of CeO2 is 50 to 95 wt % in the upstream inside layer of the upstream portion in the catalyst coating layer adsorbs exhaust gas components in an exhaust gas
Implementation Method 2
The noble metal contained in the catalyst coating layer degrades the adsorbed exhaust gas components
Data Source
AI summary
An exhaust gas purifying catalyst having a good ignition performance is provided. The exhaust gas purifying catalyst 1 includes a catalyst substrate 3 and a catalyst coating layer 5 which contains a noble metal and a refractory inorganic oxide and is formed on the catalyst substrate. The exhaust gas purifying catalyst is characterized in that the catalyst coating layer 5 includes an upstream portion 11 located upstream and a downstream portion 13 located downstream in a flow direction of an exhaust gas. The upstream portion 11 has a layered structure including an upstream portion inside layer 17 and an upstream portion outside layer 15. The upstream portion inside layer contains a cerium-zirconium composite oxide in which a relative proportion of CeO2 is 50 to 95 wt %, as the refractory inorganic oxide, and the upstream portion outside layer 15 and the downstream portion 13 contain a cerium-zirconium composite oxide in which a relative proportion of ZrO2 is 50 to 95 wt %, as the refractory inorganic oxide.