Segmented SCR Catalyst Filter for NOx Purification
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Solution Overview
Problem
Conventional SCR catalysts in exhaust gas purification systems face challenges in achieving high NOx purification performance while minimizing ammonia slip, as the NOx purification performance drops when a smaller amount of aqueous urea is supplied, and ammonia discharge increases with larger urea additions.
Innovation Solution
The exhaust gas purification material features a particulate filter with an SCR catalyst, where the maximum allowable ammonia adsorption amount differs between the upstream and downstream portions, allowing for enhanced NOx purification with smaller urea amounts and reduced ammonia slip by using a smaller adsorption capacity upstream and a larger capacity downstream.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If a smaller amount of aqueous urea is supplied to the filter, then ammonia discharge is reduced, but NOx purification performance drops
Solution Approach 1:
The filter is divided into upstream and downstream portions with different ammonia adsorption capacities. The upstream portion has a smaller maximum allowable adsorption amount to prevent ammonia discharge, while the downstream portion has a larger capacity to ensure sufficient NOx purification. This local differentiation resolves the contradiction by optimizing each zone's function.
Solution Approach 2:
The SCR catalyst is segmented into two distinct zones along the exhaust flow direction. The upstream zone uses catalyst with lower ammonia adsorption capacity, and the downstream zone uses catalyst with higher adsorption capacity. This segmentation allows the system to simultaneously achieve low ammonia slip and high NOx conversion efficiency.
2Productivity
If a larger amount of aqueous urea is supplied to the filter, then NOx purification performance improves, but ammonia discharge increases
Solution Approach 1:
Different regions of the filter are assigned different ammonia adsorption characteristics. The upstream region limits ammonia accumulation to prevent discharge, while the downstream region provides additional adsorption capacity to handle excess ammonia from high urea supply, thereby maintaining high NOx purification without compromising ammonia control.
Solution Approach 2:
The catalyst bed is segmented into upstream and downstream portions with progressively increasing ammonia adsorption capacities. This gradient structure allows the system to tolerate higher urea injection rates for improved NOx conversion while the upstream segment acts as a buffer to prevent ammonia slip.
3Object-generated harmful factors
If an SCR catalyst with large maximum allowable adsorption amount of ammonia is used, then ammonia discharge is suppressed, but NOx purification performance drops when smaller amount of aqueous urea is supplied
Solution Approach 1:
Instead of using a uniform catalyst throughout, the invention applies local quality differentiation where the upstream portion has catalyst properties optimized for preventing ammonia discharge, while the downstream portion has catalyst properties optimized for maximizing NOx conversion. This resolves the contradiction by allowing each zone to perform its specialized function.
Solution Approach 2:
The single catalyst material is segmented into two functional zones with different loading amounts or pore structures. The upstream zone uses catalyst with lower ammonia capacity to prevent slip, while the downstream zone uses catalyst with higher ammonia capacity to ensure complete NOx conversion when sufficient urea is supplied.
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 enables high NOx purification performance while effectively suppressing ammonia discharge, even with varying amounts of aqueous urea, thereby achieving a high-performance exhaust gas purification system.
Implementation Method 1
an SCR catalyst (for instance, a zeolite) for adsorbing ammonia and reducing NOx in the exhaust gas
Implementation Method 2
a maximum allowable adsorption amount of ammonia A in the upstream portion is smaller than a maximum allowable adsorption amount of ammonia B in the downstream portion
Data Source
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 a downstream portion 10b of the filter 10 including an exhaust gas outlet-side end 10d. The SCR catalyst contained in the upstream portion 10a and the SCR catalyst contained in the downstream portion 10b are qualitatively different. A ratio (B/A) of a maximum allowable adsorption amount of ammonia A in the upstream portion 10a and a maximum allowable adsorption amount of ammonia B in the downstream portion 10b satisfies the relationship 1.1≤(B/A)≤2.