Textured SCR Catalyst for Lean Engine NOx Reduction
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Solution Overview
Problem
Current SCR catalysts for lean-burn engines face challenges in achieving high nitrogen oxide conversion rates across a wide temperature range while maintaining selectivity, especially at low temperatures, due to the high oxygen content in exhaust gases, which leads to inefficient ammonia usage and secondary emissions of nitrous oxide.
Innovation Solution
A structured SCR catalyst with multiple catalytically active material zones, where the first zone is composed of iron-exchanged zeolites and the second zone contains copper-exchanged zeolites, arranged vertically to optimize temperature profiles, ensuring effective nitrogen oxide conversion below 350°C without significant selectivity loss above this temperature.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If conventional SCR catalysts are used to achieve high nitrogen oxide conversion rates, then conversion efficiency is improved, but the operating temperature range is limited to above 350°C and selectivity is lost at lower temperatures due to ammonia oxidation
Solution Approach 1:
The catalyst is divided into multiple zones with different catalytic activities: a first zone containing iron-exchanged zeolite for high-temperature SCR reactions and a second zone containing copper-exchanged zeolite for low-temperature SCR reactions. This segmentation allows each zone to operate optimally in its respective temperature range, thereby expanding the overall operating temperature window while maintaining high conversion rates and selectivity across the full range.
2Temperature
If high oxidation power is provided to enable low-temperature SCR reactions, then low-temperature conversion is improved, but ammonia is oxidized to nitrous oxide at high temperatures
Solution Approach 1:
Different zones of the catalyst are assigned different catalytic properties: the first zone uses iron-exchanged zeolite with moderate oxidation power optimized for high-temperature operations to prevent ammonia oxidation, while the second zone uses copper-exchanged zeolite with higher oxidation power optimized for low-temperature operations. This local differentiation of catalytic properties allows low-temperature conversion without generating harmful nitrous oxide at high temperatures.
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
This configuration significantly broadens the catalyst's activity window into the low-temperature range, enhancing nitrogen oxide conversion while minimizing nitrous oxide emissions, thus improving the overall efficiency and selectivity of the SCR reaction.
Implementation Method 1
A structured SCR catalyst for the reduction of nitrogen oxides in the lean exhaust gas of internal combustion engines using ammonia or a compound that decomposes into ammonia as a reducing agent
Implementation Method 2
the first zone is composed of iron-exchanged zeolites and the second zone contains copper-exchanged zeolites
Data Source
Figure 1~2
Figure 3A~3B
Figure 4~5
AI summary
The reductive removal of nitrogen oxides from the exhaust gases of predominantly lean-mixture internal-combustion engines is difficult to achieve due to the high oxygen content. A known procedure for this is the selective catalytic reduction (SCR) of the nitrogen oxide with ammonia or with a binding that decomposes with ammonia as reduction agent for SCR catalytic converters that are suitable for this purpose. A relatively small working temperature window is typical for conventional SCR catalytic converters in which good nitrogen oxide conversions can be achieved with sufficient selectivity. This working window is mostly in a temperature range between 350°C and 500°C. In addition there are catalyzing formulas with a working window in a temperature range between 150°C and 3500°C. As a rule these cannot be used at higher temperatures since the ammonia that is necessary as reduction agent oxidizes into nitrogen oxide at temperatures above 3,500°C. In order to cover the entire range of exhaust gas temperatures ranging from 2,000°C to 6,000°C that is typical for vehicles with predominantly lean-mixture internal-combustion engines, complex exhaust systems have for the most part been required up to now that contain several catalytic converters with various working temperature ranges. The present invention relates to a textured SCR catalyst with a working window that covers a significantly wider temperature window and with the help of which complex exhaust systems can be significantly simplified with a reduction in the cost of components.