SCR Catalyst Distribution in Particulate Filter for NOx Purification
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Solution Overview
Problem
Conventional SCR catalysts in exhaust gas purification systems face a trade-off between NOx purification performance and ammonia slip, where high NOx purification requires a larger amount of aqueous urea, leading to increased ammonia discharge, and low urea supply results in decreased purification performance.
Innovation Solution
The exhaust gas purification material features a particulate filter with an SCR catalyst, where the upstream portion has a smaller maximum allowable ammonia adsorption amount and the downstream portion has a larger adsorption amount, with a ratio of 1.1 to 2, allowing for efficient NOx purification with reduced ammonia slip by optimizing the SCR catalyst distribution and content within the filter.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a large amount of aqueous urea is supplied to the filter, then high NOx purification performance is achieved, but ammonia discharge increases
Solution Approach 1:
The filter is divided into upstream and downstream portions with different SCR catalyst characteristics. The upstream portion uses SCR catalyst with smaller maximum allowable ammonia adsorption amount for efficient NOx purification, while the downstream portion uses SCR catalyst with larger ammonia adsorption amount to suppress ammonia slip. This local differentiation resolves the contradiction between purification performance and ammonia discharge.
Solution Approach 2:
The filter is segmented into two functional zones: upstream portion for NOx purification with low ammonia adsorption capacity, and downstream portion for ammonia storage with high adsorption capacity. This segmentation allows each zone to perform its specific function optimally, achieving both high purification performance and low ammonia discharge.
2Object-generated harmful factors
If a small amount of aqueous urea is supplied to the filter, then ammonia discharge is suppressed, but NOx purification performance decreases
Solution Approach 1:
The upstream portion is designed with SCR catalyst having smaller maximum allowable ammonia adsorption amount, enabling efficient NOx purification even with limited urea supply. This local optimization ensures high purification performance without requiring excessive urea that would cause ammonia slip.
3Object-generated harmful factors
If SCR catalyst with large maximum allowable ammonia adsorption amount is used, then ammonia discharge is suppressed, but more aqueous urea must be added to achieve high NOx purification
Solution Approach 1:
The filter is divided into upstream and downstream portions. The downstream portion contains SCR catalyst with large ammonia adsorption amount to suppress ammonia discharge, while the upstream portion contains SCR catalyst with smaller adsorption amount that requires less urea for effective NOx purification. This segmentation reduces overall urea consumption while maintaining ammonia slip control.
Solution Approach 2:
The downstream portion acts as an intermediary ammonia storage buffer. It receives and stores excess ammonia from the urea decomposition, preventing ammonia discharge while allowing the upstream portion to use less urea for NOx purification.
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 achieves high NOx purification performance while minimizing ammonia discharge, even with varying amounts of aqueous urea, thereby enhancing the overall purification efficiency and reducing emissions.
Implementation Method 1
ammonia is generated through hydrolysis of the aqueous urea. The ammonia adsorbs onto the filter, and NOx in the exhaust gas is purified through the reducing action of the adsorbed ammonia
Implementation Method 2
an SCR (Selective Catalytic Reduction) catalyst that selectively reduces NOx in the exhaust gas as a result of the reducing action of ammonia
Implementation Method 3
NOx in the exhaust gas is purified through the reducing action of the adsorbed ammonia
Implementation Method 4
aqueous urea is supplied upstream of a filter that supports an SCR catalyst, whereupon ammonia is generated through hydrolysis of the aqueous urea
Data Source
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AI summary
An exhaust gas purification material according to the present invention is provided with a particulate filter 10 that traps particulate matter in exhaust gas and contains an SCR catalyst for adsorbing ammonia and reducing NOx in the exhaust gas. A maximum allowable adsorption amount of ammonia adsorbable by the filter 10 differs between an upstream portion 10a of the filter 10 including an exhaust gas inlet-side end 10c, and an downstream portion 10b of the filter 10 including an exhaust gas outlet-side end 10d. A maximum allowable adsorption amount of ammonia A in the upstream portion 10a is smaller than a maximum allowable adsorption amount of ammonia B in the downstream portion 10b (A<B).