Four-Way Diesel Catalyst Gas Impermeable Zone Design
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Solution Overview
Problem
Current diesel exhaust treatment systems face challenges in effectively reducing carbon monoxide, nitrogen oxides, hydrocarbons, and particulate matter while minimizing system size and backpressure, with existing catalyst configurations often leading to gas bypass and increased backpressure due to uneven catalyst distribution and temperature sensitivity.
Innovation Solution
A four-way catalyst system is implemented, where the SCR catalyst is evenly distributed throughout the filter wall and the oxidation catalyst is placed as a layer at the outlet end, creating a gas impermeable zone to ensure complete NOx and HC conversion without bypass, thereby minimizing backpressure and enhancing filtration efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the SCR catalyst is evenly distributed throughout the filter wall, then NOx conversion efficiency is improved, but the risk of gas bypass increases
Solution Approach 1:
The patent applies local quality by creating a gas impermeable zone at the outlet end of the filter wall where oxidation catalyst is concentrated. This localized catalyst placement prevents gas bypass in critical areas while maintaining SCR catalyst distribution in other regions for NOx conversion, thus resolving the contradiction between conversion efficiency and bypass prevention.
Solution Approach 2:
The patent uses composite materials by combining SCR catalyst and oxidation catalyst in a structured configuration. The SCR catalyst (e.g., Fe-ZSM-5 zeolite) is distributed throughout the filter wall for NOx conversion, while oxidation catalyst (e.g., Pt-Al2O3) is placed in a gas impermeable zone to prevent bypass. This composite approach allows both functions to coexist and address their respective challenges.
2Object-generated harmful factors
If the oxidation catalyst is placed as a layer at the outlet end creating a gas impermeable zone, then gas bypass is prevented, but backpressure increases
Solution Approach 1:
The patent applies partial action by creating a gas impermeable zone only at the outlet end portion of the filter wall rather than throughout the entire wall. This partial placement of oxidation catalyst is sufficient to prevent gas bypass at the critical outlet region while minimizing the impact on exhaust flow and backpressure compared to full-wall implementation.
3Reliability
If separate substrates are used for SCR and oxidation catalysts, then catalytic activity is maintained, but system size increases
Solution Approach 1:
The patent merges SCR catalyst and oxidation catalyst into a single integrated filter wall structure. The SCR catalyst is distributed throughout the filter wall while oxidation catalyst is placed in the gas impermeable zone at the outlet end. This merging maintains distinct catalytic zones for different functions while reducing overall system size compared to separate substrate arrangements.
Solution Approach 2:
The filter wall serves multiple functions simultaneously: it acts as both the support structure for SCR catalyst (for NOx conversion throughout the wall) and oxidation catalyst (for gas bypass prevention at the outlet). This multi-functionality of the single filter wall component eliminates the need for separate substrates while maintaining catalytic effectiveness.
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 achieves greater than 70% soot removal and effective conversion of CO, HC, and NOx, reducing system size and backpressure, and maintaining catalytic activity across varying temperatures, thus improving fuel efficiency and engine performance.
Implementation Method 1
An SCR catalyst composition is disposed within the porous walls
Implementation Method 2
an oxidation catalyst is disposed on the walls of the outlet passages
Implementation Method 3
a wall flow filter having a plurality of longitudinally extending passages formed by longitudinally extending porous walls
Data Source
AI summary
Provided are catalyst articles, emission treatment systems and methods for simultaneously remediating the carbon monoxide, nitrogen oxides (NOx), particulate matter, and gaseous hydrocarbons present in diesel engine exhaust streams. The emission treatment system of specific embodiment effectively treats diesel engine exhaust with a single catalyst article.