Post-SCRF Catalyst for Exhaust Gas Purification
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Solution Overview
Problem
In exhaust gas purification systems for internal combustion engines, ammonia or its precursors can be oxidized to produce NOx, leading to incomplete oxidation of hydrocarbons (HC) and carbon monoxide (CO) by selective catalytic reduction (SCR) catalysts, and unconsumed ammonia may escape, necessitating a solution to effectively remove these components from the exhaust gas.
Innovation Solution
A post-catalyst system is introduced downstream of the SCR filter, comprising an adsorption reduction part to adsorb and reduce NOx using ammonia, a first oxidation part to oxidize ammonia, and a second oxidation part with higher oxidation ability to oxidize HC and CO, ensuring efficient removal of HC, CO, and ammonia from the exhaust gas.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If SCRF carries a catalyst with high oxidizing ability, then HC and CO can be oxidized more effectively, but ammonia is oxidized to produce NOx which worsens purification efficiency
Solution Approach 1:
The post-SCRF catalyst is divided into multiple functional layers: a first catalyst layer with lower oxidizing ability (to avoid excessive ammonia oxidation and NOx production), and a second catalyst layer with higher oxidizing ability (to effectively oxidize HC and CO). This segmentation allows each layer to perform its specific function without interfering negatively with the other, resolving the contradiction between oxidation efficiency and NOx production.
2Productivity
If SCRF is used to reduce NOx by ammonia, then NOx purification is improved, but HC and CO may pass through without being oxidized and ammonia may escape unconsumed
Solution Approach 1:
A post-SCRF catalyst is introduced as an intermediary device between the SCRF and the exhaust discharge. This catalyst performs three functions: (1) oxidizing unconsumed ammonia to provide additional NOx reduction capacity, (2) oxidizing unoxidized HC and CO, and (3) ensuring complete purification of the exhaust gas. The intermediary catalyst compensates for the limitations of the SCRF without interfering with its NOx reduction function.
3Temperature
If the SCR catalyst is arranged upstream in the exhaust gas passage, then warming-up performance is improved, but HC and CO oxidation may be insufficient downstream
Solution Approach 1:
The exhaust purification system is segmented into two distinct catalytic zones: the upstream SCRF containing the SCR catalyst optimized for NOx reduction and warming-up performance, and the downstream post-SCRF catalyst optimized for HC and CO oxidation. This spatial segmentation allows each catalyst to be positioned and designed for its optimal performance, with the post-SCRF catalyst addressing the oxidation needs that the upstream SCR catalyst cannot fulfill.
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 post-catalyst system effectively removes HC, CO, and ammonia from the exhaust gas by adsorbing and oxidizing them, preventing excessive ammonia oxidation and improving the overall purification efficiency of the exhaust gas purification apparatus.
Implementation Method 1
an adsorption reduction part which adsorbs ammonia
Implementation Method 2
a first oxidation part which oxidizes ammonia
Implementation Method 3
a second oxidation part which oxidizes HC and CO
Implementation Method 4
The SCR catalyst reduces NOx contained in the exhaust gas by using ammonia (NH3) as a reducing agent
Data Source
AI summary
An object of the present invention is to appropriately remove, from an exhaust gas, HC, CO, and ammonia flowing out from a filter (SCRF) on which an SCR catalyst is carried. In the present invention, a post-catalyst 8 is provided for an exhaust gas passage of an internal combustion engine on a downstream side from SCRF along with a flow of the exhaust gas. The post-catalyst 8 is constructed to include an adsorption reduction part 81c which adsorbs ammonia and which reduces NOx by using ammonia as a reducing agent, a first oxidation part 81b which oxidizes ammonia, and a second oxidation part 82 which oxidizes HO and CO.