Oxygen Storage Catalyst for Low-Temperature Hydrocarbon Oxidation
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Solution Overview
Problem
Conventional hydrocarbon traps face challenges in retaining adsorbed hydrocarbons until the three-way catalyst reaches sufficient temperature for efficient conversion, leading to potential hydrocarbon 'slip' due to oxygen depletion in the exhaust stream, especially during cold-start engine operations and with aging of the trap, which affects hydrocarbon conversion efficiency.
Innovation Solution
A catalyst/hydrocarbon trap system incorporating a platinum group metal impregnated onto an oxygen storage material, such as cerium-zirconium oxide, which provides oxygen for low-temperature oxidation of hydrocarbons and carbon monoxide, maintaining effective hydrocarbon adsorption and conversion capabilities by positioning the catalyst downstream of a close-coupled catalyst to manage exhaust temperatures below 850°C.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If a conventional three-way catalyst is used during cold-start, then it can convert hydrocarbons efficiently at high temperatures, but it cannot become catalytically active at low temperatures below light-off temperature
Solution Approach 1:
The patent introduces an oxygen storage capacity material that can store and release oxygen at different temperatures, changing the oxygen availability parameter to enable low-temperature oxidation of hydrocarbons. This material undergoes redox reactions to provide oxygen when the three-way catalyst is not yet active, effectively lowering the temperature at which hydrocarbon conversion can occur.
2Reliability
If a hydrocarbon trap is used to retain adsorbed hydrocarbons, then hydrocarbon emissions can be reduced, but oxygen depletion in the exhaust stream prevents sufficient oxygen for oxidation of released hydrocarbons
Solution Approach 1:
The oxygen storage capacity material acts as an intermediary between the hydrocarbon trap and the three-way catalyst. It stores oxygen when available and releases it when the hydrocarbon trap desorbs hydrocarbons, ensuring sufficient oxygen is available for oxidation even when the exhaust stream is oxygen-depleted. This mediator resolves the conflict between retaining hydrocarbons and maintaining oxygen availability for their subsequent oxidation.
Solution Approach 2:
The oxygen storage capacity material provides concentrated oxygen release to accelerate the oxidation of hydrocarbons at low temperatures. By delivering oxygen directly to the reaction site through redox reactions, it enables efficient oxidation even when ambient oxygen levels in the exhaust stream are insufficient.
3Quantity of substance
If gamma alumina and zeolites are used as hydrocarbon absorbents, then they provide good adsorption capability, but they lose adsorption capability at high exhaust temperatures over 800°C
Solution Approach 1:
The patent combines the hydrocarbon absorbent material (gamma alumina or zeolite) with an oxygen storage capacity material to create a composite catalyst system. This composite structure allows the absorbent to retain hydrocarbons at low temperatures while the oxygen storage material provides thermal stability and continues to function at high temperatures, compensating for the absorbent's temperature limitations.
4Speed
If the close-coupled TWC catalyst is positioned upstream to warm up quickly, then it reaches light-off temperature faster, but it depletes oxygen from the exhaust stream leaving insufficient oxygen for HC oxidation downstream
Solution Approach 1:
The patent segments the exhaust treatment function into two distinct components: the close-coupled three-way catalyst for rapid warm-up and nitrogen oxide reduction, and the downstream catalyst with oxygen storage capacity material for hydrocarbon oxidation. This segmentation allows each component to perform its specialized function optimally, with the oxygen storage material compensating for oxygen depletion caused by the upstream catalyst.
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 achieves efficient oxidation of hydrocarbons and carbon monoxide at low temperatures, maintaining hydrocarbon adsorption capability and catalyst conversion efficiency throughout the vehicle's life, reducing hydrocarbon emissions during cold-starts and minimizing thermal deterioration of adsorbent materials.
Implementation Method 1
provide sufficient oxygen to achieve oxidation of hydrocarbons and carbon monoxide (CO) at low temperatures
Implementation Method 2
a catalyst/hydrocarbon trap for reduction of cold-start vehicle emissions which contains oxygen storage materials
Implementation Method 3
trapping/adsorbing hydrocarbon (HC) emissions at low temperatures and releasing/desorbing them from the trap
Data Source
AI summary
A low-temperature catalyst is provided for reducing cold-start hydrocarbon emissions. The catalyst comprises a platinum group metal impregnated onto an oxygen storage material. The catalyst may be used alone or may be included in a hydrocarbon trap containing a hydrocarbon adsorption material therein. The catalyst/hydrocarbon trap is positioned in the exhaust system of a vehicle downstream from a close-coupled catalyst such that the exhaust temperature at the catalyst location does not exceed 850° C. during normal vehicle operation and when combined with a hydrocarbon adsorption material in a trap, the exhaust temperature does not exceed 700° C.