Gradient Catalyst Layer for Exhaust Gas Diffusion
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Solution Overview
Problem
Existing exhaust gas purifying catalysts face challenges in increasing gas diffusibility and miscibility within the catalyst layer, leading to insufficient purifying performance due to inadequate void continuity and size.
Innovation Solution
A catalyst layer comprising alumina particles, ceria-zirconia composite oxide particles, and a catalytically active component, with voids that satisfy specific size and shape conditions, including a ratio of void cross-sectional area to circumference greater than or equal to 2, and an average void radius of 10 to 20 µm, enhancing gas flow paths and diffusibility.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If a precious metal is supported by a particulate catalyst carrier having high specific surface area, then the catalytically active component can be supported in a highly dispersed state, but the gas diffusibility to the deep part of the catalyst layer is reduced
Solution Approach 1:
The invention creates a gradient structure where the catalyst layer has different properties at different depths. The surface region contains fine particles for high dispersion and activity, while the deeper regions contain coarser particles that create void spaces for improved gas diffusion. This local differentiation resolves the contradiction between maximizing precious metal dispersion and maintaining gas diffusibility throughout the layer.
Solution Approach 2:
The catalyst layer is segmented into multiple regions with different particle size distributions. Rather than using a uniform particle size throughout, the invention divides the layer into zones where fine particles (5-20 μm) are concentrated at the surface and coarser particles (20-50 μm) are present deeper in the layer, creating a hierarchical structure that simultaneously achieves high dispersion and good diffusion.
2Quantity of substance
If the catalyst layer is made dense to support sufficient precious metal, then the catalytic activity is improved, but the exhaust gas is hardly diffused to the deep part of the catalyst layer
Solution Approach 1:
The invention applies local quality differentiation by creating regions of high catalyst loading at the surface where gas first contacts the layer, and regions of lower loading with more void space deeper in the layer. This allows the catalyst to be highly active where needed while maintaining diffusion pathways throughout the structure.
Solution Approach 2:
The catalyst layer is formulated as a composite material system combining particles of different sizes (5-20 μm and 20-50 μm) with different functions. The fine particles provide high surface area for catalysis, while the coarser particles create the void network for diffusion, forming a composite structure that achieves both high metal loading and good mass transfer.
3Speed
If voids are formed in the catalyst layer to increase gas diffusibility, then the purifying performance is improved, but the continuity and size of voids are insufficient
Solution Approach 1:
The void structure is segmented into multiple generations of spaces created by the hierarchical particle size distribution. The coarser particles (20-50 μm) create large primary voids that provide continuous diffusion pathways, while the fine particles (5-20 μm) fill interstices to maintain structural integrity. This segmented void architecture ensures both continuity and adequate size for effective gas transport.
Solution Approach 2:
The invention changes the physical parameters of the void structure by controlling particle size distribution and ratios. By adjusting the proportion of fine to coarse particles and optimizing the particle size ranges, the void continuity and size are tuned to achieve optimal gas diffusibility while maintaining structural 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 proposed catalyst layer achieves improved gas diffusibility and miscibility, resulting in enhanced purifying performance for CO, HC, and NOx, with increased continuity and size of voids securing main flow paths and effective utilization of precious metals.
Implementation Method 1
it is necessary to simultaneously purify each harmful component using an oxidation-reduction reaction
Implementation Method 2
to purify hydrocarbon (THC) by oxidizing the hydrocarbon (THC) to convert it to water and carbon dioxide, to purify carbon monoxide (CO) by oxidizing the carbon monoxide (CO) to convert it to carbon dioxide
Implementation Method 3
to purify nitrogen oxide (NOx) by reducing the nitrogen oxide (NOx) to convert it to nitrogen
Implementation Method 4
a precious metal has been supported by a particulate catalyst carrier having high specific surface area
Implementation Method 5
the exhaust gas has posed a problem that the exhaust gas is hardly diffused to a deep part of a catalyst layer
Data Source
Figure 1
AI summary
The present invention proposes a new exhaust gas purifying catalyst in which gas diffusibility and miscibility in a catalyst layer are high, and thereby excellent catalyst performance can be exhibited. There is proposed an exhaust gas purifying catalyst comprising a catalyst layer comprising two or more types of inorganic porous particles each having a different particle size, a catalytically active component, and voids, wherein; as a first characteristic, 50% or more by number of all the voids in the catalyst layer satisfies a condition of the following (formula 1); L/2/πS1/2≥2 wherein S represents a void cross-sectional area, and L represents a void cross-sectional circumference in the (formula 1), and; as a second characteristic, in the void cross-sectional area in the catalyst layer, the average void radius, determined assuming that the void shape is a perfect circle, is 10 µm to 20 µm.