LNT Layered Catalyst for Lean Burn Gasoline Engine NOx Purification
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Solution Overview
Problem
Existing LNT catalysts for lean burn gasoline engines face challenges in maintaining high NOx storage and purification rates, especially under varying air-fuel ratios and harsh operating conditions, due to the dependence of NOx storage amounts on environmental temperature and the lack of sufficient reductants like HC and CO.
Innovation Solution
The development of an LNT layered catalyst with a specific configuration, including a first catalyst layer with ceria-alumina-based base material particles, Pt, Pd, and BaO, and a second layer with ceria-alumina-based particles and Rh, optimized to enhance NOx storage and purification by controlling the distribution of catalytically active components and adjusting the amount of NOx storage material, ensuring stable performance across different air-fuel ratios.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a conventional LNT catalyst is used for lean burn gasoline engines, then HC and CO oxidation is facilitated due to excessive oxygen, but NOx reduction and purification becomes difficult due to shortage of reductive components
Solution Approach 1:
The catalyst is divided into multiple functional layers: a first catalyst layer containing NOx storage material (barium oxide) for capturing NOx during lean operation, and a second catalyst layer containing precious metals (Pt, Pd, Rh) for reducing stored NOx during rich operation. This segmentation allows independent optimization of oxidation and reduction functions, resolving the contradiction between facilitating oxidation and enabling reduction.
Solution Approach 2:
The invention changes the operational parameters by alternating between lean and rich air-fuel ratio conditions. During lean operation, NOx is stored on barium oxide while HC and CO are oxidized. During subsequent rich operation, the stored NOx is reduced by reductive components. This parameter change enables both oxidation efficiency and reduction efficiency to be achieved at different operational phases.
2Use of energy by moving object
If the air-fuel ratio is kept significantly beyond stoichiometric ratio for fuel efficiency, then fuel efficiency improves, but NOx formation increases and purification becomes extremely difficult
Solution Approach 1:
The catalyst performs preliminary NOx storage action during lean operation before the rich operation phase. The barium oxide in the first catalyst layer captures and stores NOx as it forms during efficient lean combustion, preventing immediate release. This preliminary storage action allows the engine to maintain high fuel efficiency while preparing for subsequent NOx reduction during rich operation.
Solution Approach 2:
The exhaust gas purification system operates in periodic cycles alternating between lean and rich air-fuel ratio conditions. During lean phases, NOx is stored and fuel efficiency is maximized. During rich phases, the stored NOx is reduced and purified. This periodic action enables continuous purification while maintaining overall fuel efficiency.
3Quantity of substance
If NOx storage material amount is increased to improve storage capacity, then NOx storage amount increases, but catalyst complexity and manufacturing difficulty increase
Solution Approach 1:
The invention applies local quality by concentrating NOx storage function in the first catalyst layer containing barium oxide, while the second catalyst layer contains reduction catalysts. Each layer has optimized composition and thickness for its specific function. This local quality approach achieves high NOx storage capacity without requiring the entire catalyst structure to be uniformly complex.
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 significantly enhances NOx storage and purification rates, maintaining high performance even under harsh conditions with varying air amounts, effectively addressing the limitations of previous catalysts by optimizing the distribution and composition of active components.
Implementation Method 1
These promoter components such as ceria and zirconia promote aqueous gas shift reaction and steam reforming reaction during a fuel-rich operation period (rich) to convert CO and HC in exhaust gas into H2
Implementation Method 2
These promoter components such as ceria and zirconia promote aqueous gas shift reaction and steam reforming reaction during a fuel-rich operation period (rich) to convert CO and HC in exhaust gas into H2
Implementation Method 3
components including oxides of alkaline earth metals such as barium, magnesium, calcium, and strontium; oxides of alkali metals such as lithium, sodium, potassium, and rubidium; and oxides of rare earth elements such as cerium, lanthanum,praseodymium, and neodymium are used as NOx storage material or the like
Implementation Method 4
precious metal-based active species such as platinum, palladium, and rhodium and promoter components such as ceria, zirconia, and ceria-zirconia-based composite oxides are often used in addition to the above-described NOx storage catalysts
Data Source
AI summary
Provided are an LNT layered catalyst for a lean burn gasoline engine having an enhanced NOx storage rate and capable of developing a higher NOx purification rate, and an exhaust gas purification apparatus using the same, the LNT layered catalyst including a substrate, a first catalyst layer including ceria-alumina particles carrying Pt, Pd, and BaO, and a second catalyst layer including ceria-alumina particles carrying Pt and Rh, in which a content of Pt in the first catalyst layer is 0.45 to 0.85 mass %; among Pt included in the first catalyst layer, a content proportion in a first depth region is 88 to 90 mass %, and a content proportion in a second depth region is 10 to 12 mass %; a content of Ba in the first catalyst layer is 4 to 11 mass %; and the second catalyst layer is substantially free from Ba.