NOx Absorber Catalyst Segmented Washcoat for Low-Temperature Storage
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Solution Overview
Problem
NOx absorber catalysts face challenges in NOx storage and regeneration, especially under low temperature, high flow rate, and high hydrocarbon conditions in Diesel engine exhaust systems, with existing formulations showing poor fresh NOx storage activity and reduced activity upon aging.
Innovation Solution
A NOx absorber catalyst comprising a substrate monolith coated with washcoat layers, including a first component with a nitrogen oxide storage component and a dispersed rare earth oxide supported on a refractory material, and a second component with a precious metal supported on a bulk reducible oxide, such as cerium oxide, which is substantially free of nitrogen oxide storage material, enhancing NOx conversion and oxidation of carbon monoxide and hydrocarbons at low temperatures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If a significant quantity of NOx-storage component (e.g., barium) is used in the catalyst formulation, then NOx storage capacity is improved, but fresh NOx storage activity deteriorates under low temperature and high flow rate conditions
Solution Approach 1:
The catalyst is divided into two distinct functional components: a first component containing the NOx-storage material (barium) on a refractory support, and a second component containing the precious metal (platinum group metal) on a bulk reducible oxide support. This segmentation allows each component to optimize its specific function without interfering with the other, resolving the contradiction between storage capacity and fresh activity.
Solution Approach 2:
The bulk reducible oxide (such as cerium oxide) in the second component acts as an intermediary that enhances the overall catalyst performance. It promotes oxygen storage and release, facilitates NOx conversion, and improves fresh activity under low temperature conditions, thereby enabling the NOx-storage component to function effectively without compromising fresh storage activity.
2Productivity
If the catalyst operates under high flow rate conditions, then exhaust gas treatment throughput is improved, but NOx storage and conversion efficiency deteriorates
Solution Approach 1:
The invention changes the physical and chemical parameters of the catalyst supports. The bulk reducible oxide support in the second component has high oxygen storage capacity and catalytic activity, which maintains effective NOx conversion even at high flow rates. The reducible oxide can dynamically adjust oxygen availability, allowing the catalyst to maintain efficiency across varying flow conditions.
3Temperature
If the catalyst operates at low temperature, then oxidation of CO and hydrocarbons is improved, but NOx desorption and reduction activity deteriorates
Solution Approach 1:
The bulk reducible oxide introduces dynamic oxygen storage and release capability to the catalyst system. During lean phases, the reducible oxide stores oxygen; during rich phases, it releases oxygen to promote NOx desorption and reduction. This dynamic behavior allows the catalyst to maintain NOx desorption activity across a broader temperature range, including lower temperatures where conventional catalysts would fail.
4Stability of the object's composition
If the catalyst ages, then thermal stability is improved, but NOx conversion activity deteriorates
Solution Approach 1:
The invention uses composite material structures: the first component combines NOx-storage material with refractory support material for thermal stability; the second component combines precious metal with bulk reducible oxide for maintained catalytic activity. The synergistic interaction between these composite components ensures that thermal stability does not come at the cost of conversion activity, even after aging.
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 exhibits improved NOx storage and reduction activity, particularly under aged conditions, with increased exotherm and hydrogen generation promoting complete NOx desorption and oxidation of CO and hydrocarbons, meeting stringent emission standards like Euro 5 and Euro 6.
Implementation Method 1
BaO+NO2+1⁄2O2→Ba(NO3)2
Implementation Method 2
NO+CO→1⁄2N2+CO2
Implementation Method 3
the bulk reducible oxide is an oxide, a composite oxide or a mixed oxide comprising at least one of manganese, iron, cobalt, copper, tin or cerium
Implementation Method 4
increased exotherm and hydrogen generation promoting complete NOx desorption and oxidation of CO and hydrocarbons
Implementation Method 5
increased exotherm and hydrogen generation promoting complete NOx desorption and oxidation of CO and hydrocarbons
Data Source
AI summary
A NOx absorber catalyst comprising a substrate monolith coated with one or more washcoat layers and comprising a first component comprising a nitrogen oxide storage component, at least one precious metal and a dispersed rare earth oxide supported on a refractory support material, and a second component comprising a precious metal supported on a bulk reducible oxide that is substantially free of nitrogen oxide storage material, wherein the precious metal present in the second component comprises Pt, Pd or a combination of both Pt and Pd and wherein the bulk reducible oxide is an oxide, a composite oxide or a mixed oxide comprising at least one of manganese, iron, cobalt, copper, tin or cerium.