Multi-Layer Catalyst for Lean Burn Engines with In-Situ Ammonia Generation
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing exhaust gas treatment systems for lean burn engines, such as diesel and gasoline engines, rely heavily on external reducing agents for NOx reduction in SCR units, which are prone to maintenance issues and weather sensitivity, particularly at low temperatures, and face challenges in maintaining ammonia yield while preserving hydrocarbon oxidation capacity.
Innovation Solution
A novel three-way catalyst with a substrate coated with multiple layers, including Pd and Rh, Pt, oxygen storage components, and nitrogen oxide storage materials, specifically optimized to enhance ammonia formation activity without compromising hydrocarbon oxidation efficiency, allowing for in-situ ammonia generation and reduced dependency on external reducing agents.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a combination of NOx storage catalyst and SCR catalyst with external reducing agent injection is used, then NOx treatment effectiveness is improved, but system complexity and maintenance requirements increase
Solution Approach 1:
The patent combines the NOx storage catalyst and SCR catalyst into a single integrated catalyst unit with multiple functional layers. The upstream layer stores NOx while the downstream layer performs SCR reduction, eliminating the need for separate catalyst units and external reducing agent injection systems, thus reducing system complexity while maintaining NOx treatment effectiveness
Solution Approach 2:
The catalyst system generates its own reducing agent (ammonia) through the ammonia formation reaction using hydrocarbons from the exhaust gas. This self-generated ammonia is then used for the SCR reduction of stored NOx, making the system self-sufficient and eliminating dependency on external reducing agent injection
2Productivity
If external reducing agents are injected into the exhaust stream, then SCR activity is optimized, but maintenance requirements and weather sensitivity increase
Solution Approach 1:
The catalyst system performs self-service by generating ammonia in situ through the ammonia formation reaction. The hydrocarbons present in the exhaust gas are converted to ammonia on the catalyst surface, which then serves as the reducing agent for NOx reduction. This eliminates the need for external urea or ammonia injection systems that require maintenance and are sensitive to weather conditions
Solution Approach 2:
The catalyst acts as an intermediary that facilitates the conversion of hydrocarbons to ammonia. The catalyst surface mediates the chemical reaction between hydrocarbons and oxygen to produce ammonia, which then mediates the reduction of NOx. This intermediary role of the catalyst eliminates the need for direct injection of external reducing agents
3Adaptability or versatility
If ammonia formation activity is enhanced in the three-way catalyst, then dependency on external reducing agents is reduced, but hydrocarbon oxidation capacity may be compromised
Solution Approach 1:
The catalyst is segmented into distinct functional layers: an upstream layer optimized for NOx storage and ammonia formation, and a downstream layer optimized for SCR reduction. This segmentation allows each layer to specialize in its function without interfering with the other, enabling high ammonia formation activity while preserving hydrocarbon oxidation capacity in the respective layers
Solution Approach 2:
Different regions of the catalyst have different local qualities optimized for specific functions. The upstream layer has properties favoring ammonia formation (such as specific metal compositions and surface characteristics), while the downstream layer has properties optimized for SCR reduction. This local quality differentiation allows simultaneous optimization of ammonia formation and hydrocarbon oxidation without compromise
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 while maintaining effective hydrocarbon oxidation, reducing the duration of rich phases and overall emissions, particularly in lean burn applications, without the need for external reducing agents, thus enhancing the efficiency and reliability of exhaust gas treatment systems.
Implementation Method 1
nitrogen oxide contained in an exhaust gas stream is stored at lower temperatures in the NOx storage catalyst, to be released at higher operation temperature
Implementation Method 2
an effective reduction thereof in the SCR unit may be achieved
Implementation Method 3
maintaining ammonia yield while preserving hydrocarbon oxidation capacity
Data Source
AI summary
Described is a catalyst comprising a substrate and a catalyst coating of two or more layers: (a) a first layer comprising Pd and Rh on the substrate; and (b) a second layer comprising Pt and/or Pd on the first layer; these 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 ranges from 0.18 to 2.0 g/in3 calculated as the respective alkali metal oxides M2O and alkaline earth metal oxides MO. Also described is a method for the production of a catalyst, as well as a process for the treatment of a gas stream, in particular of an exhaust gas stream resulting from an internal combustion engine.