Sequential Fe-FER and Vanadium SCR Catalysts for Low-N2O NOx Control
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing SCR catalysts face inefficiencies in reducing nitrogen oxides (NOx) in exhaust gases from lean-burn engines due to high oxygen content, leading to ammonia oxidation to nitrous oxide (N2O) and reduced reducing agent availability, particularly at high temperatures.
Innovation Solution
A catalyst system comprising an iron (Fe)-loaded ferrierite (FER) molecular sieve as the first SCR catalyst and a vanadium-based SCR catalyst arranged sequentially, with the Fe-FER catalyst contacting the exhaust gas first, followed by the vanadium catalyst, to enhance NOx conversion and reduce N2O selectivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single SCR catalyst is used to treat exhaust gas from lean-burn engines, then the device complexity is reduced, but the NOx conversion efficiency decreases and N2O selectivity increases at high temperatures
Solution Approach 1:
The catalyst system is divided into two distinct catalytic zones: a first zone containing an iron-exchanged zeolite (e.g., Fe-ZSM-5 or Fe-BEA) and a second zone containing a vanadium-based catalyst (e.g., V2O5-WO3/TiO2). This segmentation allows each zone to perform its specialized function - the iron-exchanged zeolite suppresses N2O formation at high temperatures, while the vanadium-based catalyst provides robust NOx conversion across a broad temperature range, thereby resolving the contradiction between device simplicity and conversion efficiency.
Solution Approach 2:
The invention employs a composite catalyst system combining two different catalytic materials with complementary properties. The iron-exchanged zeolite component provides high-temperature stability and low N2O selectivity, while the vanadium-based catalyst offers high NOx conversion activity. This composite approach enables the system to achieve both high productivity and controlled N2O emissions without requiring overly complex device architecture.
2Device complexity
If a single SCR catalyst is used to treat exhaust gas from lean-burn engines, then the device complexity is reduced, but N2O selectivity increases at high temperatures
Solution Approach 1:
The catalyst system is divided into two distinct catalytic zones: a first zone containing an iron-exchanged zeolite (e.g., Fe-ZSM-5 or Fe-BEA) and a second zone containing a vanadium-based catalyst (e.g., V2O5-WO3/TiO2). This segmentation allows each zone to perform its specialized function - the iron-exchanged zeolite suppresses N2O formation at high temperatures, while the vanadium-based catalyst provides robust NOx conversion across a broad temperature range, thereby resolving the contradiction between device simplicity and conversion efficiency.
Solution Approach 2:
The iron-exchanged zeolite acts as an intermediary component that modifies the exhaust gas composition before it reaches the vanadium-based catalyst. By selectively suppressing the oxidation of NH3 to N2O in the first zone, it protects the downstream vanadium catalyst from producing harmful N2O emissions, while still allowing effective NOx reduction to proceed.
3Productivity
If the exhaust gas contacts the vanadium catalyst first, then the NOx conversion is efficient, but the ammonia is oxidized to N2O due to high oxygen content
Solution Approach 1:
The iron-exchanged zeolite is positioned upstream to perform a preliminary function of suppressing N2O formation before the exhaust gas reaches the vanadium-based catalyst. This preliminary action modifies the reaction environment by reducing the oxidation of NH3 to N2O, thereby protecting the downstream vanadium catalyst from generating harmful emissions while maintaining its high NOx conversion efficiency.
Solution Approach 2:
Instead of placing the conventional vanadium-based catalyst first (which would efficiently convert NOx but produce N2O), the invention inverts the sequence by placing the iron-exchanged zeolite first. This inversion prioritizes N2O suppression in the high-oxygen environment, allowing the vanadium catalyst to operate in a more favorable condition downstream where N2O formation is minimized.
4Reliability
If the ammonia is oxidized to N2O due to high oxygen content, then the reducing agent is removed from the process, but this creates undesired secondary emissions
Solution Approach 1:
The iron-exchanged zeolite acts as an intermediary component that modifies the exhaust gas composition before it reaches the vanadium-based catalyst. By selectively suppressing the oxidation of NH3 to N2O in the first zone, it protects the downstream vanadium catalyst from producing harmful N2O emissions, while still allowing effective NOx reduction to proceed.
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 system achieves improved NOx conversion and reduced N2O formation, with NOx conversion rates of at least 75% and N2O selectivity below 10% over a broad temperature range, outperforming conventional systems.
Implementation Method 1
The selective catalytic reduction of nitrogen oxides (NOx) by ammonia (NH3-SCR) is considered to be the most practical and efficient technology for the abatement of NOx from exhaust gases
Implementation Method 2
a first SCR catalyst comprising an iron (Fe) ion-exchanged molecular sieve having a ferrierite (FER) framework
Implementation Method 3
a second SCR catalyst comprising vanadium, wherein the second SCR catalyst is provided on or within a substrate
Implementation Method 4
The reductant is absorbed onto the catalyst and the NOx reduction reaction takes place as the gases pass through or over the catalyzed substrate
Data Source
Figure 1~2
Figure 3~4
Figure 5
AI summary
The present invention provides a catalyst system for treatment of an exhaust gas comprising: a first SCR catalyst comprising an iron (Fe) ion-exchanged molecular sieve having a ferrierite (FER) or MFI framework, wherein the first SCR catalyst is provided on or within a substrate; and a second SCR catalyst comprising vanadium, wherein the second SCR catalyst is provided on or within a substrate; wherein the first and second catalysts are arranged such that in use exhaust gas contacts the first SCR catalyst prior to contact with the second SCR catalyst. Also provided is an exhaust system, a method, use and vehicle incorporating or utilizing such a catalyst system.