Binary Catalyst for Cold Start NOx Reduction
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Solution Overview
Problem
Current diesel engine aftertreatment systems face challenges in achieving effective emissions control during cold start conditions, particularly in reducing nitrogen oxides (NOx) emissions, due to insufficient ammonia availability at low exhaust temperatures, which is crucial for meeting stringent greenhouse gas and ultra-low NOx regulations.
Innovation Solution
A catalyst aftertreatment system featuring a dosing compartment, mixing chamber with a static metallic mixer, and a SCR unit coated with a binary catalyst that includes zeolite with covalently bound metal oxide or metal oxide nanoparticles, enabling simultaneous urea hydrolysis, ammonia storage, and NOx reduction within 60 seconds of a cold start event without visible urea deposit formation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If DEF dosing commences at temperatures of at least 200°C, then emissions control is effective, but cold start emissions cannot be controlled during the heat-up period
Solution Approach 1:
The patent changes the temperature parameter threshold for DEF dosing from 200°C to below 200°C by introducing a hydrolysis catalyst that enables urea decomposition at lower temperatures. This allows the dosing system to commence DEF injection during the cold start heat-up period while maintaining effective emissions control through catalytic hydrolysis of urea to ammonia.
Solution Approach 2:
The patent introduces a hydrolysis catalyst as an intermediary component between the DEF dosing system and the SCR catalyst. This catalyst mediates the urea decomposition process at lower temperatures, producing ammonia that can be immediately utilized by the SCR catalyst for NOx reduction during cold start conditions.
2Reliability
If a close-coupled SCR/AMOX is added to improve cold start emissions, then ammonia availability increases, but system complexity and cost increase with dual DEF dosing
Solution Approach 1:
The patent merges the hydrolysis catalyst function with the existing SCR catalyst into a single integrated component. The SCR catalyst is designed to perform both urea hydrolysis and ammonia oxidation functions, eliminating the need for a separate close-coupled SCR/AMOX system and reducing overall system complexity while maintaining ammonia availability for cold start emissions control.
Solution Approach 2:
The patent makes the SCR catalyst multi-functional by enabling it to perform both urea hydrolysis and ammonia oxidation. This universal catalyst design allows a single component to fulfill multiple roles that previously required separate systems, thereby reducing device complexity and eliminating the need for dual DEF dosing systems.
3Reliability
If a passive NOx adsorber is used to achieve ultra-low NOx targets, then low temperature NOx trapping is possible, but durability is insufficient for heavy-duty applications
Solution Approach 1:
The patent employs a composite catalyst material that combines the NOx trapping capability of passive adsorbers with the thermal stability and durability of SCR catalyst materials. This composite structure maintains the ultra-low NOx performance at low temperatures while incorporating durable components capable of withstanding heavy-duty application conditions over extended periods.
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 system effectively reduces NOx emissions by converting urea to ammonia and storing it for immediate use, maintaining catalyst cleanliness and extending the lifespan of the SCR catalyst, thus meeting ultra-low NOx targets and improving emissions control during cold starts.
Implementation Method 1
The binary catalyst is configured to simultaneously hydrolyze urea to generate ammonia, store NH3, and reduce NOx within 60 seconds of a cold start event
Implementation Method 2
store NH3
Implementation Method 3
an SCR catalyst configured to facilitate reduction of nitrogen oxide (NOx) in the diesel exhaust with NH3
Data Source
AI summary
The present disclosure describes a catalytic aftertreatment system that includes a dosing compartment including a doser configured to introduce a diesel exhaust fluid (DEF) including urea into a diesel exhaust; a mixing chamber subsequent to the doser configured to mix the DEF with the diesel exhaust, the mixing chamber including an optional static metallic mixer, and a catalyst substrate including a combined urea hydrolysis-selective catalytic reduction binary catalyst coated thereon; and a SCR unit subsequent to the mixing chamber unit, including an SCR catalyst configured to facilitate reduction of nitrogen oxide (NOx) in the diesel exhaust with NH3.