Lean-Burn Catalyst Regeneration via Periodic Rich Exhaust Switching
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Solution Overview
Problem
Conventional Diesel oxidation catalysts suffer from reduced activity at low temperatures and loss of active catalyst sites due to PGM sintering at high temperatures, necessitating higher temperatures for complete light-off.
Innovation Solution
The method involves intermittently contacting a platinum-based oxidation catalyst with rich exhaust gas to recover its oxidation activity, utilizing a catalyst structure with a reducible oxide support and a second oxidation catalyst layer with a precious metal, both disposed on separate layers of a honeycomb monolith substrate.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional platinum-based oxidation catalysts are used in lean-burn engines, then oxidation activity is maintained at high temperatures, but catalyst activity is lost at low temperatures due to PGM sintering and platinum oxidation
Solution Approach 1:
The patent changes the chemical state of platinum from oxidized to metallic form by controlling the exhaust gas atmosphere. By periodically switching between lean and rich operating modes, the platinum catalyst is reduced to its metallic state, which maintains activity at lower temperatures. This parameter change in the chemical state of the catalyst resolves the contradiction between maintaining activity at high temperatures and losing activity at low temperatures.
Solution Approach 2:
The patent implements periodic switching between lean and rich exhaust gas conditions to regenerate the catalyst. The catalyst is exposed to rich conditions periodically to reduce oxidized platinum back to metallic form, then returned to lean operation for normal oxidation catalysis. This periodic action restores and maintains catalyst activity across different temperature ranges.
2Productivity
If higher temperatures are used to maintain catalyst activity, then oxidation reactions are effective, but energy consumption increases and light-off is delayed
Solution Approach 1:
By changing the catalyst's chemical state through periodic rich/exhaust gas exposure, the system maintains high oxidation reaction efficiency at lower temperatures. The metallic platinum form achieved through reduction provides superior catalytic activity compared to oxidized platinum, thereby reducing the temperature threshold for effective oxidation reactions and lowering energy consumption.
3Reliability
If platinum is exposed to high temperature lean-burn exhaust gases, then oxidation activity is maintained, but platinum becomes oxidized and loses catalytic activity
Solution Approach 1:
The system periodically exposes the platinum catalyst to rich exhaust gas conditions, which reduces oxidized platinum back to metallic form. This periodic reduction cycle prevents permanent oxidation of the catalyst, maintaining its compositional stability and catalytic activity over extended periods of operation in lean conditions.
Solution Approach 2:
The engine control system monitors exhaust gas conditions and catalyst performance, adjusting the timing and duration of rich/exhaust gas exposure to optimize platinum reduction. This feedback mechanism ensures the platinum remains in the most active form while minimizing energy consumption and preventing over-reduction.
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
This approach effectively regenerates the active form of platinum, maintaining catalyst activity in lean operating conditions for a substantial duration and reducing the need for higher temperatures to achieve complete light-off.
Implementation Method 1
A primary purpose of a Diesel Oxidation Catalyst (DOC) is to oxidise certain components of Diesel engine exhaust gas in order to meet a relevant emission standard, such as vehicular regulations including Euro 5. Particularly important reactions include oxidation of carbon monoxide to carbon dioxide, oxidation of gas phase hydrocarbons (derived from unburned fuel) to carbon monoxide and water (H2O)
Implementation Method 2
by contacting an oxidation catalyst comprising platinum and a reducible oxide intermittently and momentarily with a rich exhaust gas, the oxidation catalyst can recover oxidation activity caused by the platinum becoming oxidised at higher temperatures
Data Source
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AI summary
An apparatus comprises a lean-burn internal combustion engine, engine management means and an exhaust system for treating exhaust gas of the engine, which exhaust system comprises a first oxidation catalyst disposed on a first flow-through honeycomb monolith substrate in combination with a second different oxidation catalyst different from the first oxidation catalyst, which first oxidation catalyst comprises platinum supported on a first metal oxide support comprising at least one reducible oxide and the second oxidation catalyst comprises at least one precious metal supported on a second metal oxide support, wherein the first oxidation catalyst is substantially free of alkali metals and alkaline earth metals and wherein the first and second oxidation catalysts are each disposed in separate layers, wherein the engine management means is arranged, when in use, intermittently to modulate the lambda composition of the exhaust gas entering the first oxidation catalyst to a rich lambda composition.