SCR Catalyst Porous Structure for NOx Conversion
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Solution Overview
Problem
Current catalysts for exhaust gas treatment, particularly in motor vehicles, face inefficiencies due to suboptimal contact between exhaust gases and catalytically active material, leading to underutilization of catalyst volume and higher material input, which results in lower catalytic activity compared to washcoats.
Innovation Solution
A process involving functional particles with a pore former and a catalytically active material layer, where the particles are processed with inorganic components to form a ceramic body with porous, catalytically inactive cells surrounded by an active interface layer, enhancing catalytic activity by increasing the density of catalytically active material in the near-surface region.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If all-active extrudate honeycomb catalysts are used where all of the extruded body consists of the catalytically active composition, then the catalytic activity is improved, but large volume regions of the catalyst composition remain unutilized for the NOx conversion
Solution Approach 1:
The patent introduces a porous structure into the catalyst body by incorporating pore-forming agents (such as starch, cellulose, or synthetic polymers) that are removed during thermal treatment. This creates a three-dimensional network of pores and channels throughout the extruded catalyst body, allowing exhaust gas to penetrate deep into the interior regions and access catalytically active sites that would otherwise remain unused in dense all-active extrudates.
2Ease of manufacture
If a higher proportion of binder component is required for molecular sieve extrusion, then the extrusion process is improved, but the binder fractions form sinter bridges that reduce catalytic activity
Solution Approach 1:
The patent applies local quality by concentrating the binder component specifically at the outer surface or shell of the catalyst particles, while the interior regions contain higher proportions of catalytically active molecular sieves and pore-forming agents. This spatial differentiation allows the binder to provide necessary mechanical strength for extrusion and particle integrity, while minimizing its interference with catalytic reactions in the active interior regions.
Solution Approach 2:
The patent extracts or removes the pore-forming agents through thermal treatment (calcination or combustion) after the extrusion and shaping processes are complete. This extraction creates void spaces and pores throughout the catalyst structure, separating the binder's structural function from the catalytic function, allowing high binder proportions during manufacturing to be converted into beneficial porous structures that enhance rather than hinder catalytic activity.
3Productivity
If copper ion-exchanged zeolites are used for catalytic activity, then the NOx conversion is improved, but the material cost is significantly higher
Solution Approach 1:
The patent uses porous structures created by pore-forming agents to increase the surface area and accessibility of copper ion-exchanged zeolite particles throughout the catalyst body. This allows for more efficient utilization of the expensive copper-active sites, reducing the total amount of copper-containing material needed while maintaining or enhancing overall NOx conversion performance.
Solution Approach 2:
The patent creates composite catalyst materials by combining copper ion-exchanged zeolite particles with pore-forming agents, binders, and potentially other catalytically active or supportive materials. This composite approach allows for optimized distribution and utilization of the expensive copper component while incorporating cheaper materials that provide structural support, porosity, and additional catalytic 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 approach results in improved catalytic efficiency with a higher density of catalytically active material accessible via a porous structure, achieving better NOx conversion rates while reducing the binder content and maintaining mechanical stability.
Implementation Method 1
a layer of a catalytically active material is applied to the pore former
Implementation Method 2
The catalytic composition is finally subjected to a thermal treatment to form the catalyst
Data Source
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AI summary
To produce the catalyst (2), a) functional particles (8) are provided, having a catalytically inactive pore former (4) as support surrounded by a layer (5) of a catalytically active material, b) the functional particles (8) are processed with further inorganic particles (10) to give a catalytic material (12), c) the catalytic material (12) is treated thermally to form the ceramic catalyst (2), wherein the catalyst (2) comprises at least porous catalytically inactive cells (20) - which are formed by the pore formers (4) in the functional particles (8), - which are embedded in a matrix (24) comprising the further inorganic particles (10), - which form a porous structure (18) and - which are at least partly surrounded by an active interface layer (22) comprising the catalytically active material of the layer (5) of the functional particles (8). An SCR catalyst (2) produced in this way has an improved NOx conversion rate compared to a conventionally produced SCR catalyst.