Microporous Crystalline Catalyst for SCR NOx Reduction
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Solution Overview
Problem
There is a need for microporous crystalline materials with enhanced performance and hydrothermal stability to effectively catalyze the selective reduction of nitrogen oxides (NOx) in exhaust gases, especially under extreme temperature and humidity conditions, as existing zeolitic catalysts are inadequate.
Innovation Solution
A microporous crystalline material with building units of double-6-rings (d6r) and pore openings of 8-rings, comprising alkali-earth, rare-earth, or alkali metals, along with iron or copper, and a molar silica to alumina ratio (SAR) of 3 to 12, is developed, which is synthesized using a method involving gel formation, metal introduction, and steaming to enhance stability and NH3 adsorption capacity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional zeolitic catalysts are used for SCR of NOx, then the catalytic function is provided, but the hydrothermal stability is insufficient under extreme temperature and humidity conditions
Solution Approach 1:
The patent applies parameter changes by optimizing the silica-to-alumina ratio (SAR) to specific ranges (3-12, preferably 4-8) and controlling the crystalline structure parameters (unit cell angle, peak positions) to achieve enhanced hydrothermal stability. The steaming treatment at 400-800°C for 0.1-16 hours further modifies structural parameters to improve stability under extreme conditions while maintaining catalytic activity.
Solution Approach 2:
The invention creates a composite crystalline material with specific building units (double-6-rings, 8-rings, and/or 5-rings) and controlled metal content (0.01-10 wt% metal oxides). This composite structure combining specific framework types with controlled composition achieves both hydrothermal stability and catalytic function under extreme temperature and humidity conditions.
2Reliability
If the microporous crystalline material is designed with specific structure and composition for enhanced stability, then the hydrothermal stability is improved, but the manufacturing complexity increases
Solution Approach 1:
The patent applies preliminary action by performing steaming treatment during the manufacturing process (at 400-800°C for 0.1-16 hours) to pre-stabilize the crystalline structure before deployment. This preliminary stabilization step ensures hydrothermal stability is built into the material during production, avoiding the need for complex post-processing or operation-specific adjustments.
Solution Approach 2:
The invention controls key parameters within specific ranges (SAR: 3-12, unit cell angle: 94.0-95.0°, peak positions at specific 2θ values) to achieve hydrothermal stability. By defining explicit parameter ranges rather than requiring precise single-point values, the manufacturing process becomes more robust and less complex while still ensuring the desired stability performance.
3Quantity of substance
If the material composition is optimized for high NH3 adsorption capacity, then the SCR performance is improved, but the structural stability may be compromised
Solution Approach 1:
The patent optimizes the NH3 adsorption capacity by controlling the molar NH3/Al ratio within specific ranges (0.6-1.0, preferably 0.7-0.9) while simultaneously maintaining the silica-to-alumina ratio within 3-12. This balanced parameter optimization ensures both high NH3 adsorption capacity for SCR performance and structural stability through the controlled framework composition.
Solution Approach 2:
The invention introduces metal oxides (0.01-10 wt%) as local modifications to enhance NH3 adsorption capacity at specific sites within the crystalline structure. This localized enhancement through metal incorporation improves SCR performance without compromising the overall structural stability of the bulk material, as the metals are incorporated in controlled amounts within the stable framework.
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 material exhibits improved stability and NOx reduction performance, retaining surface area and micropore volume after exposure to water immersion, and maintains high NO conversion efficiency even at elevated temperatures, making it suitable for SCR applications.
Implementation Method 1
exhibits an NH3 adsorption capacity expressed as the molar NH3/Al ratio of 0.7 to 0.9
Implementation Method 2
steaming said material at 400 to 800° C. in 1 to 100% steam for at least 0.1 hour
Implementation Method 3
selective catalytic reduction (SCR) of nitrogen oxides (NOx) in exhaust gases
Data Source
AI summary
There is disclosed a microporous crystalline material comprising a crystal structure having building units of double-6-rings (d6r) and pore opening of 8-rings, wherein the material comprises a first metal chosen from alkali-earth group, rare-earth group, alkali group or mixtures thereof, and a second metal chosen from copper, iron or mixtures thereof, wherein the material has molar silica to alumina ratio (SAR) from 3 to 12, and is further steamed to enhance stability. Methods of making the crystalline material are also disclosed. There is also disclosed a method of selective catalytic reduction of nitrogen oxides in exhaust gas, comprising at least partially contacting the exhaust gases with an article comprising the disclosed microporous crystalline material.