Dual-Layer NOx Storage Catalyst for Low-Temperature Exhaust Purification
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Solution Overview
Problem
Existing NOx storage materials for lean-burn engines face challenges in achieving uniform dispersion, sufficient storage capacity, and effective NOx storage at low exhaust gas temperatures, particularly with noble metals like Pt and Pd, leading to decreased purification performance.
Innovation Solution
A monolith catalyst with a dual-layer structure comprising a first catalyst layer containing a first supported catalyst with zirconia-based carriers and Rh, and a second catalyst layer with a spinel-type Al-Mg-based composite oxide supporting Pt, enhancing NOx storage and reduction capabilities.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If the amount of NOx storage material is excessively increased, then the NOx storage capacity increases, but the uniformity of dispersion in the catalyst deteriorates
Solution Approach 1:
The catalyst is divided into multiple layers with different functions. The first layer contains the spinel-type Al-Mg-based composite oxide as NOx storage material, while the second layer contains Pt and Pd for catalytic reduction. This segmentation allows each layer to be optimized independently, ensuring uniform dispersion of NOx storage material in the first layer while providing sufficient total storage capacity across the entire catalyst structure.
2Manufacturing precision
If rare earth metal elements are used as NOx storage materials, then the dispersion uniformity improves, but the NOx adsorption ability decreases
Solution Approach 1:
The patent uses a spinel-type Al-Mg-based composite oxide as the NOx storage material, which combines the advantages of uniform dispersion capability with high NOx adsorption ability. This composite material approach overcomes the limitation of rare earth metals by providing both good dispersibility and strong adsorption performance through the synergistic combination of Al and Mg in the spinel structure.
3Use of energy by moving object
If the exhaust gas temperature is relatively low, then the fuel consumption decreases, but the NOx storage ability of the catalyst deteriorates
Solution Approach 1:
The patent introduces Pd in addition to Pt as a catalyst metal, and optimizes the ratio of Pt to Pd to be 95:5 to 50:50 by mass. Pd has different catalytic properties compared to Pt, particularly in low-temperature conditions. This parameter change in the catalyst composition enables effective NOx storage and reduction at lower exhaust gas temperatures, maintaining catalyst reliability while allowing lean-burn operation with lower fuel consumption.
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 dual-layer catalyst design improves NOx storage capacity and purification performance across a wide temperature range, particularly at low temperatures, by optimizing the distribution and function of noble metals and NOx storage materials.
Implementation Method 1
a spinel-type Al-Mg-based composite oxide supporting Pt
Implementation Method 2
a first supported catalyst with zirconia-based carriers and Rh, and a second catalyst layer with a spinel-type Al-Mg-based composite oxide supporting Pt
Data Source
Figure 1~2
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Figure 5~6
AI summary
A technology capable of achieving excellent NOx storage ability is provided. An exhaust gas-purifying catalyst 1 according to the present invention includes a substrate 10 and a catalyst layer 20 supported on the substrate 10, wherein the catalyst layer 20 contains a first supported catalyst 21 containing a first heat resistant carrier 210 and rhodium 211 supported on the first heat resistant carrier 210, a second supported catalyst 22 containing a second heat resistant carrier 220 and platinum 221 supported on the second heat resistant carrier 220, the second heat resistant carrier 220 containing an inorganic oxide which has a spinel structure and contains alumina and magnesia, a third supported catalyst 25 containing a third heat resistant carrier 250 and platinum 251a and a noble metal 251b other than platinum which are supported on the third heat resistant carrier, and a nitrogen oxide storage material 24 and 26, wherein a proportion of a mass of platinum contained in the second supported catalyst 22 in an entire mass of platinum contained in the catalyst layer is in a range of 15% by mass to 35% by mass.