NOx Trapping Catalyst Porous Layer for High-Temperature Diffusivity
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Solution Overview
Problem
Existing NOx trapping catalysts using metal substrates face challenges in maintaining high NOx purifying performance at elevated temperatures due to material migration and reduced diffusivity caused by thick catalyst layers at acute-angled corners, which impede exhaust gas flow.
Innovation Solution
A NOx trapping catalyst with a metal substrate and a catalyst layer containing noble metals, heat-resistant inorganic oxides, and a NOx trapping material, where pores are formed using a pore formation promoting material like magnesia, enhancing diffusivity and stability at high temperatures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If a metal substrate is used to prevent NOx trapping material migration at high temperatures, then thermal stability is improved, but the catalyst layer becomes thick at acute-angled corner portions reducing exhaust gas diffusivity
Solution Approach 1:
The patent introduces a porous structure in the catalyst layer to improve exhaust gas diffusivity. The porous structure allows exhaust gases to flow more easily through the thick catalyst layer at acute-angled corner portions, thereby maintaining high NOx purifying performance while using a metal substrate for thermal stability.
Solution Approach 2:
The patent applies different properties to different regions of the catalyst layer. Specifically, the porous structure is introduced to address the local issue of reduced diffusivity at thick portions, while maintaining the overall thick catalyst layer structure needed for high NOx trapping capacity on the metal substrate.
2Use of energy by moving object
If the lean operation range is expanded to improve fuel economy, then fuel consumption is reduced, but the catalyst temperature increases causing NOx trapping material to migrate and combine with substrate constituents
Solution Approach 1:
The patent uses a composite structure combining metal substrate with a specially designed catalyst layer containing porous structure. This composite approach allows the system to withstand high temperatures from expanded lean operation while preventing material migration through the stabilized porous architecture.
3Quantity of substance
If the catalyst layer is made thick to increase NOx trapping capacity, then NOx adsorption capacity is improved, but exhaust gas diffusivity is reduced at thick portions
Solution Approach 1:
The patent introduces a porous structure in the catalyst layer to improve exhaust gas diffusivity. The porous structure allows exhaust gases to flow more easily through the thick catalyst layer at acute-angled corner portions, thereby maintaining high NOx purifying performance while using a metal substrate for thermal stability.
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 catalyst achieves improved NOx reduction performance and stability at high temperatures by promoting exhaust gas diffusivity through the formation of pores, maintaining high NOx reduction rates even at elevated temperatures and reducing the risk of material migration.
Implementation Method 1
NOx in exhaust gases is adsorbed as nitrate X—NO3 in an oxidation atmosphere (a lean air-fuel ratio) in which the concentration of reductants is low
Implementation Method 2
the NOx so adsorbed is reduced to N2 in a reduction atmosphere (a stoichiometric air-fuel ratio or a rich air-fuel ratio) in which a large amount of reductants such as CO (carbon monoxide) and HC (hydrocarbons) exists
Implementation Method 3
a catalyst layer having pores formed by addition of a pore formation promoting material
Data Source
AI summary
A method of purifying an exhaust gas, includes: disposing a NOx trapping catalyst in an exhaust pipe of an internal combustion engine, the NOx trapping catalyst including: a metal substrate including cells, a corner portion of each of cells having an acute angle; and a catalyst layer supported in the metal substrate and including a noble metal, a heat-resistant inorganic oxide and a NOx trapping material, the catalyst layer having pores formed by addition of a pore formation promoting material, and the NOx trapping catalyst: adsorbing NOx in the exhaust gas when an exhaust air-fuel ratio is in a lean state; and desorbing and reducing the adsorbed NOx when the exhaust air-fuel ratio is in a stoichiometric state or a rich state; and removing the NOx by the exhaust air-fuel ratio being shifted between the lean state and the rich state.