Core-Shell Cu-Fe SSZ-13 Catalyst for Low-Temperature NOx Conversion
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Solution Overview
Problem
Current SCR catalysts, such as Cu-SSZ13, face challenges in achieving optimal NOx conversion at low NH3 storage levels and maintaining catalytic activity under harsh hydrothermal conditions, particularly in light duty diesel applications where fast transient NOx conversion is required.
Innovation Solution
A copper-promoted and iron-promoted 8-ring small pore molecular sieve with a CHA crystal structure, either alone or in combination, is used in a specific ratio, often with a barium component, to enhance NOx conversion efficiency across a wide temperature range, including low temperatures and after hydrothermal aging.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If traditional Cu-SSZ13 catalysts are used, then NOx conversion is achieved at high NH3 storage levels, but NOx conversion efficiency is insufficient at low NH3 storage levels
Solution Approach 1:
The patent applies local quality by creating distinct functional zones within the catalyst structure. The core contains Cu-SSZ13 for NH3 storage, while the shell contains Fe-SSZ13 for NOx conversion. This spatial differentiation allows the catalyst to maintain high NOx conversion efficiency at low NH3 storage levels by concentrating the conversion function in the Fe-containing shell region.
Solution Approach 2:
The patent employs composite materials by combining Cu-SSZ13 and Fe-SSZ13 in a core-shell structured catalytic article. This composite structure integrates the NH3 storage capability of Cu-SSZ13 with the NOx conversion efficiency of Fe-SSZ13, achieving superior performance at low NH3 storage levels compared to traditional single-material catalysts.
2Reliability
If metal-promoted zeolites are used for SCR catalysis, then catalytic activity is maintained under normal conditions, but activity declines under harsh hydrothermal conditions exceeding 700°C
Solution Approach 1:
The patent applies parameter changes by carefully controlling the silica-to-alumina ratio (greater than 1, preferably greater than 5 or 10) and the metal loading amounts (Cu: 0.1-10 wt%, Fe: 0.1-10 wt%). These parameter optimizations enhance the zeolite framework's resistance to dealumination under hydrothermal conditions, maintaining catalytic activity even at temperatures exceeding 700°C.
Solution Approach 2:
The composite structure of Cu-SSZ13 and Fe-SSZ13 provides synergistic effects that improve hydrothermal stability. The Fe-SSZ13 component contributes to structural stability under harsh conditions, while the Cu-SSZ13 maintains NH3 storage capability, together preserving catalytic activity at high temperatures where traditional single-metal catalysts would degrade.
3Reliability
If zeolites with 8-ring pore openings and cage-like structures are used, then wide temperature window and excellent hydrothermal durability are achieved, but low temperature NOx conversion performance is insufficient
Solution Approach 1:
The patent applies local quality by assigning different functional roles to different regions and components. The Cu-SSZ13 core provides excellent hydrothermal durability and NH3 storage, while the Fe-SSZ13 shell specifically enhances low-temperature NOx conversion. This functional differentiation resolves the contradiction between durability and low-temperature activity.
Solution Approach 2:
The patent merges the advantages of Cu-SSZ13 (hydrothermal stability and NH3 storage) with Fe-SSZ13 (low-temperature NOx conversion) in a core-shell structure. This combination allows the catalyst to simultaneously achieve wide temperature window operation, hydrothermal durability, and improved low-temperature conversion performance.
4Speed
If light duty diesel applications require fast transient NOx conversion, then response time is reduced, but catalytic activity under transient conditions is insufficient
Solution Approach 1:
The patent applies parameter changes by optimizing the metal loading ratios and particle size distribution to enhance mass transfer rates and active site accessibility. The Fe-SSZ13 shell with its specific surface area and pore structure facilitates rapid NOx uptake and conversion during transient conditions, improving both response speed and conversion reliability.
Solution Approach 2:
The Cu-SSZ13/Fe-SSZ13 composite structure provides fast transient response through the Fe-SSZ13 shell's high surface area and catalytic activity. The core-shell architecture enables rapid NH3 release from the Cu-core and immediate NOx conversion in the Fe-shell, achieving fast transient response required for light duty diesel applications.
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 proposed solution demonstrates improved NOx conversion efficiency at low NH3 storage levels and maintains high activity even after hydrothermal aging, outperforming traditional Cu-SSZ13 catalysts in both fresh and aged conditions, particularly in light duty diesel engines.
Implementation Method 1
copper-promoted and iron-promoted 8-ring small pore molecular sieve with a CHA crystal structure... to enhance NOx conversion efficiency... improved NOx conversion efficiency at low NH3 storage levels and maintains high activity even after hydrothermal aging
Implementation Method 2
8-ring small pore molecular sieve with a CHA crystal structure... cage like structure results from the connection of double six-ring building units by 4 rings... wide temperature window coupled with the excellent hydrothermal durability
Data Source
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AI summary
Described are compositions and catalytic articles comprising a copper-promoted 8-ring small pore molecular sieve and an iron-promoted 8-ring small pore molecular sieve. The catalytic articles are useful in methods and systems to catalyze the reduction of nitrogen oxides in the presence of a reductant.