Zonal Catalytic Wall-Flow Filter for Diesel Emissions
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Solution Overview
Problem
Catalytic wall-flow monoliths in diesel exhaust systems face challenges in achieving effective particulate matter regeneration without causing damage to the catalyst and substrate due to high temperatures, and in maintaining NOx reduction efficiency with durable SCR catalyst compositions that withstand varying temperature ranges.
Innovation Solution
A catalytic wall-flow monolith design with distinct zones, where one zone has catalytic material distributed throughout the substrate and the other has a surface coating, optimizing catalyst loading and distribution to reduce backpressure and enhance NOx conversion while controlling temperature gradients.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the filter temperature is increased to burn soot particles (500-550°C), then particulate matter regeneration is achieved, but the catalyst may sinter and lose activity, and thermal gradients can cause substrate cracking
Solution Approach 1:
The patent applies different catalytic materials to different zones of the filter substrate. The first zone (inlet side) contains a first catalytic material optimized for soot combustion at lower temperatures, while the second zone (outlet side) contains a second catalytic material optimized for NOx reduction. This zonal differentiation allows the filter to regenerate soot at controlled temperatures that prevent catalyst sintering and substrate cracking, while maintaining both particulate matter removal and NOx reduction functions.
2Productivity
If higher catalyst loading is applied to achieve desired NOx reduction rates, then NOx conversion efficiency is improved, but back pressure within the exhaust system increases unsuitably
Solution Approach 1:
The patent distributes catalytic materials non-uniformly across the filter substrate, with the first catalytic material concentrated in the first zone and the second catalytic material concentrated in the second zone. This localized distribution ensures that sufficient catalyst is present in each zone to perform its specific function (soot combustion or NOx reduction) while minimizing the total catalyst loading and associated back pressure across the entire filter.
Solution Approach 2:
The patent divides the filter substrate into distinct functional zones with different catalytic compositions. The first zone handles soot combustion with its dedicated catalytic material, while the second zone handles NOx reduction with its dedicated catalytic material. This segmentation allows each zone to be optimized for its specific function with appropriate catalyst loading, preventing the need for excessive overall catalyst loading that would increase back pressure.
3Ease of manufacture
If a single catalytic material is used throughout the filter, then manufacturing is simplified, but the filter cannot simultaneously optimize both soot combustion and NOx reduction across different temperature zones
Solution Approach 1:
The patent implements zonal catalytic distribution where the first zone contains a first catalytic material optimized for soot combustion and the second zone contains a second catalytic material optimized for NOx reduction. This local differentiation enables the filter to simultaneously perform both functions at optimal temperatures and conditions in each zone, improving overall productivity despite increased manufacturing complexity.
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 design reduces soot accumulation, backpressure, and light-off temperature, improving filter durability and NOx conversion efficiency, and allows for more efficient regeneration by directing soot combustion and optimizing catalyst activity.
Implementation Method 1
Passive regeneration burns the soot from the filter by increasing the concentration of NO2 over the catalyst on the filter
Implementation Method 2
A proven NOx abatement technology useful with lean exhaust conditions is Selective Catalytic Reduction (SCR). In this process, NOx is reduced with ammonia (NH3) to nitrogen (N2) over a catalyst
Implementation Method 3
Active regeneration removes soot from a soot filter by raising the temperature of soot trapped in the filter to about 500 - 550 °C to burn the soot and regenerate the filter. One way to increase the filter temperature is to intermittently introduce additional hydrocarbon fuel into the exhaust gas before the soot filter and combust this additional hydrocarbon to increase the filter temperature
Data Source
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AI summary
A catalytic wall-flow monolith filter for use in an emission treatment system comprises a wall flow substrate having a first face, a second face, and first and second 5 pluralities of channels, wherein the first plurality of channels is open at the first face and closed at the second face, and the second plurality of channels is open at the second face and closed at the first face. The monolith filter comprises a porous substrate having a first zone extending from the first face towards the second face and a second zone extending from the second face towards the first face, where each of the zones are less that filter length. A first 0 catalytic material is distributed throughout the first zone of the porous substrate, and a second catalytic material covers at least a portion of the surfaces in the second zone of the porous substrate and is not distributed throughout the porous substrate.