Exhaust Catalyst Pt-Pd Ratio Sintering
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Solution Overview
Problem
Existing exhaust gas purifying catalysts face a decline in NOx purification performance due to platinum sintering, which reduces catalyst activity, and are inadequate for lean-burn engines where NOx emissions are high.
Innovation Solution
Supporting platinum and palladium together on the same carrier at specific ratios, along with rhodium in separate layers, inhibits platinum sintering and enhances NOx purification performance, particularly in lean atmospheres.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If platinum is used as catalyst metal for NOx purification, then catalyst activity is initially high, but sintering occurs during long-term use causing particle size increase and activity decrease
Solution Approach 1:
Palladium acts as an intermediary substance that physically interacts with platinum atoms during thermal exposure. The palladium atoms form a protective interface around platinum particles, preventing direct contact and coalescence between platinum atoms that would otherwise lead to sintering. This intermediary mechanism allows the catalyst to maintain high activity over extended periods without requiring changes to the platinum itself.
Solution Approach 2:
The catalyst employs a composite material structure combining platinum and palladium in specific ratios (0.03 to 0.15 mass ratio of Pd to Pt). This composite approach leverages the high catalytic activity of platinum for NOx purification while utilizing palladium's resistance to sintering to stabilize the overall structure. The synergistic combination creates a material that exhibits both high initial activity and long-term stability, overcoming the limitations of pure platinum.
2Reliability
If platinum particle size increases due to sintering, then catalyst activity decreases, but increasing platinum loading to compensate increases cost
Solution Approach 1:
Palladium serves as a protective intermediary that prevents platinum particle growth. By forming a mixed metal oxide structure where Pd and Pt coexist in specific ratios, the system creates physical and chemical barriers that inhibit sintering. This allows maintenance of small, highly active platinum particles without requiring excess platinum loading, thus preserving catalyst activity while controlling material quantities.
Solution Approach 2:
The invention optimizes the compositional parameters by controlling the mass ratio of Pd to Pt within 0.03 to 0.15. This parameter optimization ensures sufficient palladium is present to prevent sintering while minimizing unnecessary material usage. Additionally, the reduction in Pt particle size (maintained below 5 nm) represents a critical parameter change that maximizes surface area and catalytic activity per unit mass of platinum.
3Reliability
If conventional single-layer catalyst structure is used, then manufacturing is simple, but NOx purification performance is insufficient for lean-burn engines
Solution Approach 1:
The catalyst is divided into distinct functional layers: a first catalyst layer containing Pt and Pd for primary NOx purification, and a second catalyst layer containing Rh for enhancement. This segmentation allows each layer to be optimized for specific functions - the Pt-Pd layer for base activity and sintering prevention, and the Rh layer for boosted performance in lean-burn conditions. The layered structure achieves superior purification without requiring complex internal architectures within each layer.
Solution Approach 2:
The Pt-Pd composite layer serves multiple functions simultaneously: it provides high catalytic activity for NOx purification, prevents sintering of platinum particles, and maintains structural stability under varying exhaust conditions. This multi-functionality is achieved through the synergistic interaction between Pt and Pd atoms in the mixed metal oxide, eliminating the need for separate components for each function and keeping the overall structure relatively simple.
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 solution significantly improves NOx purification efficiency while maintaining catalyst activity, effectively purifying NOx emissions from lean-burn engines and reducing platinum particle size, thus maintaining performance over time.
Implementation Method 1
sintering of platinum takes place, which results in an increase in platinum particle size
Implementation Method 2
exhaust gas purifying catalysts are composed of a substrate and a catalyst layer disposed on the substrate
Data Source
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AI summary
The object of the present invention is to provide a novel exhaust gas purifying catalyst having excellent NOx purification performance. The object can be achieved by an exhaust gas purifying catalyst comprising: a substrate; and a catalyst layer disposed on the substrate which comprises a first carrier, and platinum and a first palladium supported on the first carrier; in which the weight ratio of the platinum to the first palladium is 3:1 to 8:1.