Multi-Layer Catalyst for Lean Burn Engines
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Solution Overview
Problem
Existing three-way catalysts face challenges in achieving high ammonia formation activity while maintaining hydrocarbon oxidation efficiency, especially during rich exhaust gas phases, and are often dependent on external reducing agents, which require precise control and regular maintenance.
Innovation Solution
A catalyst with a substrate coated with multiple layers, including Pd and Rh, Pt, and oxygen storage components like ceria-zirconia, supported on metal oxide particles, which enables in situ ammonia generation and efficient hydrocarbon oxidation without the need for external reducing agents.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If a three-way catalyst is designed to achieve high ammonia formation activity, then the ammonia yield increases, but the hydrocarbon oxidation activity decreases
Solution Approach 1:
The catalyst is divided into multiple functional zones with different metal compositions. The first zone contains Pd and Rh for hydrocarbon oxidation, while the second zone contains Pt for ammonia formation. This segmentation allows each zone to optimize its specific function without interfering with the other, resolving the contradiction between ammonia formation and hydrocarbon oxidation activities.
Solution Approach 2:
Different regions of the catalyst are assigned different metal compositions tailored to their specific functions. The inlet portion has a Pd-Rh mixture optimized for hydrocarbon oxidation, while the outlet side has a Pt-zeolite mixture optimized for ammonia formation. This local quality differentiation enables high ammonia yield without sacrificing hydrocarbon oxidation efficiency.
2Reliability
If an external reducing agent injection system is used to enable SCR reaction, then the nitrogen oxide conversion efficiency improves, but the system complexity and maintenance requirements increase
Solution Approach 1:
The three-way catalyst generates ammonia in situ from hydrocarbons during rich exhaust phases, eliminating the need for external reducing agent injection systems. The catalyst uses the engine's own hydrocarbon emissions as the reducing agent, making the system self-sufficient and reducing mechanical complexity while maintaining high nitrogen oxide conversion efficiency.
Solution Approach 2:
The catalyst converts hydrocarbons, which are harmful emissions, into ammonia, a beneficial reducing agent for SCR reactions. This transforms a harmful substance into a useful resource, eliminating the need for external reducing agents while maintaining high nitrogen oxide conversion efficiency.
3Quantity of substance
If the duration of rich exhaust gas phases is extended to generate sufficient ammonia, then the ammonia availability for SCR increases, but the hydrocarbon emissions increase
Solution Approach 1:
The catalyst replaces the mechanical approach of extending rich phase duration with a chemical approach using Pt-enhanced ammonia formation. The Pt component enables rapid ammonia generation from hydrocarbons during brief rich phases, providing sufficient ammonia availability without the need to prolong rich operation, thus avoiding increased hydrocarbon emissions.
Solution Approach 2:
The catalyst changes the chemical parameters of ammonia formation by introducing Pt, which significantly enhances the rate and efficiency of ammonia production from hydrocarbons. This parameter change allows sufficient ammonia generation during short rich phases, eliminating the need to extend rich duration and the associated increase in hydrocarbon emissions.
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 catalyst achieves high ammonia formation activity and efficient hydrocarbon oxidation in both lean and rich exhaust gas phases, reducing the duration of rich phases and overall emissions, particularly in lean burn engines, without sacrificing treatment efficiency.
Implementation Method 1
A catalyst with a substrate coated with multiple layers, including Pd and Rh, Pt, and oxygen storage components like ceria-zirconia, supported on metal oxide particles, which enables in situ ammonia generation
Implementation Method 2
oxygen storage components like ceria-zirconia
Implementation Method 3
efficient hydrocarbon oxidation
Implementation Method 4
high ammonia formation activity
Data Source
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AI summary
The present invention relates to a catalyst comprising a substrate and a catalyst coating, the catalyst coating comprising two or more layers, said layers comprising: (a) a first layer provided on the substrate, said first layer comprising Pd and Rh; and (b) a second layer provided on the first layer, said second layer comprising Pt and/or Pd; the first and second layers each further comprising: one or more particulate support materials; one or more oxygen storage component (OSC) materials; and one or more nitrogen oxide storage materials comprising one or more elements selected from the group of alkali and/or alkaline earth metals, wherein the total amount of alkali and alkaline earth metals comprised in the one or more nitrogen oxide storage materials contained in the catalyst ranges from 0.18 to 2.0 g/in³ calculated as the respective alkali metal oxides M2O and alkaline earth metal oxides MO, as well as to a method for the production of a catalyst, and to a process for the treatment of a gas stream, in particular of an exhaust gas stream resulting from an internal combustion engine.