Layered Lean Burn Catalyst for NOx and CO Purification
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional catalysts for lean-burn engines face challenges in effectively purifying NOx and CO over a wide temperature range, particularly at high temperatures, due to the deterioration of NOx storage capacity and reduced reductant availability.
Innovation Solution
A catalyst with an integrally structured support and a layered configuration, featuring a proton-substituted β-type zeolite and ceria-based oxide supporting rhodium in the upper layer, and a NOx storage component with an alkaline-earth metal compound and ceria-based oxide in the lower layer, along with platinum and palladium, to enhance NOx reduction and CO oxidation performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional LNT catalyst is used to reductively remove NOx, then NOx purification is achieved, but the catalyst deteriorates at high temperatures and loses NOx storage capacity
Solution Approach 1:
The catalyst is divided into multiple functional layers: a first washcoat layer containing NOx storage material (barium oxide), a second washcoat layer containing hydrocarbon trap material (zeolite), and a nitrogen oxide conversion material layer. This segmentation allows each layer to perform its specific function optimally while protecting the overall system from high temperature deterioration.
Solution Approach 2:
The catalyst uses composite material structures including barium oxide-ceria composite in the NOx storage layer, and combines multiple materials (zeolite, precious metals, oxygen storage components) in different layers to create a synergistic system that maintains stability and performance at high temperatures.
2Productivity
If the amount of air is increased for lean burn operation, then fuel efficiency improves, but NOx becomes difficult to reductively remove due to insufficient reducing components
Solution Approach 1:
The catalyst performs preliminary oxidation of CO and HC in the lean exhaust gas before the rich spike operation. The hydrocarbon trap material in the second washcoat layer stores reactive hydrocarbons that are then used during the rich spike for efficient NOx reduction, eliminating the need for external fuel injection.
Solution Approach 2:
The catalyst uses the exhaust gas components themselves (CO and HC) as reducing agents for NOx conversion. The system is self-sufficient by utilizing the fuel's own combustion products rather than requiring additional external reducing agents or complex control systems.
3Reliability
If a three-way catalyst is used for stoichiometric operation, then CO and HC are easily oxidized, but the system cannot effectively purify NOx in lean burn conditions
Solution Approach 1:
The catalyst is designed with multi-functionality to handle both lean and rich conditions. The first washcoat layer stores NOx during lean operation, the second washcoat layer traps hydrocarbons, and the nitrogen oxide conversion material reduces NOx during rich spikes. This universal design allows a single catalyst to replace both TWC and LNT functions.
Solution Approach 2:
The catalyst operates by changing the air-fuel ratio parameter dynamically - maintaining lean operation for most of the time for efficiency, then briefly switching to rich conditions for NOx reduction. The catalyst materials are selected to respond to these parameter changes, with barium oxide storing NOx under lean conditions and releasing it under rich conditions.
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 purification performance for NOx, CO, and HC across a wide temperature range, maintaining activity and stability even at high temperatures, thereby addressing the limitations of existing technologies.
Implementation Method 1
the upper layer containing at least a proton-substituted β-type zeolite and a ceria-based oxide supporting rhodium
Implementation Method 2
the lower layer containing at least a NOx storage component and an inorganic oxide supporting platinum, wherein the NOx storage component contains an alkaline-earth metal compound and a ceria-based oxide
Implementation Method 3
an inorganic oxide supporting platinum
Implementation Method 4
hydrocarbon (HC) and carbon monoxide (CO), which are reducing components, can be oxidatively removed easily by excess oxygen
Data Source
Figure 1
Figure 2~4
AI summary
The present invention relates to catalysts for lean burn and provides a catalyst for lean burn that is capable of purifying NOx sufficiently and that has a high ability to purify CO and HC over a wide temperature range from low to high temperatures. The present invention provides a catalyst for a lean-burn engine to purify exhaust gas, the catalyst including: an integrally structured support; and a catalyst layer containing a precious metal element, provided on the integrally structured support and having at least two layers that include an upper layer and a lower layer; wherein the upper layer of the catalyst layer contains at least a proton-substituted β-type zeolite and a ceria-based oxide supporting rhodium, and the lower layer of the catalyst layer contains at least a NOx storage component and platinum supported on an inorganic oxide.