Small Pore Molecular Sieve Copper Catalyst for NOx Reduction
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Solution Overview
Problem
Existing Cu-based molecular sieve catalysts are less thermally durable and produce higher levels of N2O when exposed to reducing atmospheres, particularly during high temperature lean/rich cycle excursions in vehicular diesel applications.
Innovation Solution
The use of small pore molecular sieve-supported copper catalysts, with a maximum ring size of eight tetrahedral atoms, which maintains catalytic activity even after exposure to reducing atmospheres at high temperatures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If Cu-based molecular sieve catalysts are used for SCR of NOx, then low temperature NOx reduction activity is improved, but thermal durability and stability under reducing atmosphere deteriorate
Solution Approach 1:
The patent changes the pore size parameter of the molecular sieve from medium/large pore (ZSM-5, Beta) to small pore (CHA framework with 8-membered rings), which fundamentally alters the catalyst's interaction with copper species and its stability under reducing conditions while maintaining SCR activity
Solution Approach 2:
The patent creates a composite catalyst system combining copper ions with small pore molecular sieves (CHA framework), where the specific pore structure and acidity of the molecular sieve work synergistically with copper to provide both high activity and improved thermal durability under lean/rich cycling
2Productivity
If Cu-based molecular sieve catalysts are exposed to reducing atmosphere at high temperature, then catalytic activity is maintained, but copper species stability and catalyst durability deteriorate
Solution Approach 1:
The patent changes the pore size parameter of the molecular sieve from medium/large pore (ZSM-5, Beta) to small pore (CHA framework with 8-membered rings), which fundamentally alters the catalyst's interaction with copper species and its stability under reducing conditions while maintaining SCR activity
Solution Approach 2:
The patent creates localized environments within the small pore molecular sieve structure that stabilize copper species specifically at the active sites, where the confined pore space and specific acidity provide a protective microenvironment that prevents copper migration and reduction while maintaining catalytic functionality
3Productivity
If medium/large pore molecular sieves (ZSM-5, Beta) are used, then catalytic activity is achieved, but dealumination and loss of acidity occur during high temperature hydrothermal ageing
Solution Approach 1:
The patent changes the pore size parameter of the molecular sieve from medium/large pore (ZSM-5, Beta) to small pore (CHA framework with 8-membered rings), which fundamentally alters the catalyst's interaction with copper species and its stability under reducing conditions while maintaining SCR activity
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
These catalysts demonstrate improved thermal stability and activity retention, with NOx conversion efficiencies remaining within 30% of initial activity at temperatures between 200 and 500°C, and within 10% at 250-350°C.
Implementation Method 1
Selective catalytic reduction (SCR) of NOx by nitrogenous compounds, such as ammonia or urea
Implementation Method 2
small pore molecular sieve-supported copper catalysts
Data Source
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AI summary
A system for treating an exhaust gas from a lean burn internal combustion engine comprises a NOx adsorber catalyst (NAC) and a downstream selective catalytic reduction (SCR) catalyst, wherein the SCR catalyst comprises a copper promoted small pore molecular sieve having a maximum ring size of eight tetrahedral atoms, wherein the system meters nitrogenous reductant into a flowing exhaust gas only when it is determined that the SCR catalyst is at above 100 °C.