CeZr Mixed Oxide Catalyst for Ultrafine Particle Filtration
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Solution Overview
Problem
Current three-way catalyst (TWC) systems face challenges in maintaining stoichiometric exhaust gas composition for efficient NOx reduction, CO oxidation, and HC treatment, especially when the engine operates under transient conditions, and struggle to effectively filter ultrafine particulate matter from positive ignition engines, leading to increased backpressure and reduced filtration efficiency.
Innovation Solution
A catalyst article comprising a wall-flow filter with a substrate coated with a first and second catalyst composition, each containing a CeZr mixed oxide sol and a particulate inorganic oxide, optimized to reduce backpressure and enhance filtration efficiency for particles smaller than 23 nm, while maintaining TWC activity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional TWC system is used, then NOx reduction, CO oxidation, and HC treatment can be achieved under stoichiometric conditions, but the system fails to effectively filter ultrafine particulate matter and experiences increased backpressure under transient engine conditions
Solution Approach 1:
The patent employs a wall-flow filter substrate with controlled porosity and pore size distribution to achieve effective ultrafine particle filtration. The porous structure allows the filter to capture particles smaller than 23 nm while maintaining acceptable backpressure levels through optimized pore geometry and distribution throughout the filter media.
Solution Approach 2:
The patent uses a composite catalyst composition combining CeZr mixed oxide sol with particulate inorganic oxide on the filter substrate. This composite material provides both the filtration function and catalytic activity for TWC reactions, integrating multiple functions into a single component to improve overall system efficiency under transient conditions.
2Productivity
If the engine operates under transient conditions, then power demand changes require rapid air-to-fuel ratio adjustments, but this causes oscillations that reduce TWC efficiency for NOx reduction and particulate filtration
Solution Approach 1:
The patent modifies the catalyst composition parameters by incorporating CeZr mixed oxide sol with specific particle size distribution and inorganic oxide content. These parameter changes enhance the catalyst's ability to maintain performance during transient operations by improving oxygen storage capacity and catalytic activity across varying air-to-fuel ratios.
Solution Approach 2:
The patent implements a closed-loop control system using an exhaust gas oxygen sensor to monitor lambda values and adjust the air-to-fuel ratio in real-time. This feedback mechanism reduces oscillations and maintains the exhaust composition within the optimal range for TWC efficiency during transient engine conditions.
3Manufacturing precision
If a filter substrate with smaller pore size is used to improve ultrafine particle filtration, then filtration efficiency increases, but backpressure increases significantly
Solution Approach 1:
The patent utilizes a wall-flow filter substrate with specifically engineered porosity and pore size distribution. The porous structure is designed to capture ultrafine particles through diffusion and interception mechanisms while maintaining adequate permeability to minimize backpressure. The pore size distribution includes both small pores for particle capture and larger pathways for gas flow.
Solution Approach 2:
The patent employs a wall-flow filter configuration where gas flow transitions from inlet channels to outlet channels through the filter walls, adding a dimensional aspect to the filtration process. This wall-flow mechanism enhances particle capture efficiency by forcing exhaust gases to pass through the porous substrate walls rather than straight through, increasing contact time and filtration effectiveness without proportionally increasing backpressure.
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 solution effectively reduces the emission of ultrafine particles by at least 20% and maintains desirable backpressure levels, addressing the limitations of existing TWC systems in handling transient engine conditions and ultrafine particulate matter.
Implementation Method 1
each independently comprising an oxygen storage component (OSC) derived from a CeZr mixed oxide sol
Implementation Method 2
TWCs are intended to catalyse three reactions simultaneously: (i) oxidation of carbon monoxide to carbon dioxide; (ii) oxidation of unburned hydrocarbons to carbon dioxide and water
Implementation Method 3
oxidation of carbon monoxide to carbon dioxide; oxidation of unburned hydrocarbons to carbon dioxide and water
Implementation Method 4
reduction of nitrogen oxides to nitrogen and oxygen
Implementation Method 5
reduction of nitrogen oxides to nitrogen and oxygen
Implementation Method 6
struggle to effectively filter ultrafine particulate matter from positive ignition engines
Data Source
AI summary
A catalyst article and its use in an exhaust system for internal combustion engines is disclosed. The catalyst article comprises a substrate which is a wall-flow filter, a first catalyst composition, and a second catalyst composition. The first and second catalyst compositions each independently comprise an oxygen storage component (OSC) derived from a CeZr mixed oxide sol having a D90 of less than 1.3 micron and a particulate inorganic oxide having a D90 of from 1 to 20 microns.