Molecular Sieve Upstream of Transition Metal Catalyzer
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Solution Overview
Problem
The formation of harmful polychlorinated dibenzodioxins (PCDD) and polychlorinated dibenzofurans (PCDF) in catalyzers containing transition metals like iron, copper, or cobalt, due to the presence of hydrocarbons and chloride in exhaust gases, poses a challenge in reducing nitric oxide and fine particle emissions effectively.
Innovation Solution
A molecular sieve with specific pore diameters is placed upstream of the transition metal-containing catalyzer to prevent hydrocarbons from reaching the catalyzer, while allowing necessary gases like NO, NO2, O2, and NH3 to pass through, thereby preventing the formation of PCDD and PCDF.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If transition metal-containing catalyzers are used to reduce nitric oxide emissions, then NO conversion efficiency is improved, but formation of PCDD and PCDF increases
Solution Approach 1:
The exhaust treatment system is segmented into multiple functional zones: a first catalyzer for NO conversion, a molecular sieve layer for hydrocarbon adsorption, and a second catalyzer for further treatment. This segmentation allows each component to perform its specific function without interfering with others, preventing dioxin formation while maintaining NO conversion efficiency
Solution Approach 2:
A molecular sieve layer is introduced as an intermediary component between the transition metal-containing catalyzer and the exhaust stream. This molecular sieve selectively adsorbs hydrocarbons that would otherwise react with chloride on the catalyzer surface to form PCDD and PCDF, thereby preventing the harmful reaction while allowing the catalyzer to continue its NO conversion function
2Object-generated harmful factors
If molecular sieve is added to prevent hydrocarbons from reaching the catalyzer, then PCDD and PCDF formation is reduced, but device complexity increases
Solution Approach 1:
The molecular sieve layer is merged with the catalyzer structure to form an integrated composite component. The molecular sieve and catalytic material are combined in a single assembly that can be installed as one unit in the exhaust system, avoiding the need for separate molecular sieve and catalyzer components and simplifying the overall system architecture
Solution Approach 2:
A composite material structure is employed where molecular sieve particles are integrated with the catalytic washcoat or support material. This composite approach allows the molecular sieve and catalytic functions to coexist in a single layered structure, reducing the number of separate components needed and simplifying the device while maintaining both NO conversion and dioxin prevention functions
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 solution effectively reduces the formation of PCDD and PCDF, enhancing the durability and efficiency of catalyzers by maintaining the catalytic activity while minimizing the risk of dioxin and furan formation, even at high temperatures.
Implementation Method 1
A molecular sieve with specific pore diameters is placed upstream of the transition metal-containing catalyzer to prevent hydrocarbons from reaching the catalyzer
Implementation Method 2
allowing necessary gases like NO, NO2, O2, and NH3 to pass through
Data Source
AI summary
Apparatus for reducing emissions of PCDD and PCDF in exhaust gas of an internal combustion engine includes a transition metal-containing catalyzer for the selective catalytic reduction of nitric oxides, and a molecular sieve upstream of the catalyzer, either as a layer on the catalyzer or on a separate structure. The molecular sieve blocks hydrocarbons from reaching the transition metal-containing catalyzer.