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Oxidation Catalysts
Description
Oxidation catalysts (OC), referred to as diesel oxidation catalysts (DOC) for diesel applications, can be used with lean burn spark ignition engines as well as compression ignitions engines and are effective in reducing carbon monoxide (CO) and hydrocarbon (HC) emissions. The oxidation catalyst promotes the oxidation, or addition of oxygen, of the pollutant constituents. In a typical 2-way catalyst the CO would be oxidized to carbon dioxide (CO2) and the unburned HC would be oxidized to water (H2O) and CO2. The oxidation catalysts require the use of low diesel fuel to prevent clogging in compression ignition engine applications. Special orders & custom designs can be offered to meet your specific requirements.
How Oxidation Catalysts Work
The oxidation catalyst consists of three distinct parts: the substrate, washcoat and active metal. The catalyst substrate, sometimes referred to as the catalyst carrier, is a ceramic structure which gives the catalyst its honeycomb shape and support for the active metal. The washcoat is a coating applied to the substrate which increases the surface area of the catalyst structure prior to the application of the active metal. The active metal is the primary contributor to the oxidation of the pollutants and is typically palladium or platinum. The precious metal applied to the catalyst structure is the active component in the combustion reaction and is responsible for the oxidation which occurs to the exhaust gases. The catalyst material is not consumed during the oxidation process but simply promotes the process.
The oxidation catalyst promotes the following oxidation reactions to occur:
CO + 1/2 O2 = CO2
[Hydrocarbons] + O2 = CO2 + H2O
The exhaust pollutants are converted into harmless non-toxic substances. Because both reactions require oxygen to complete the reaction, oxidation catalysts only work with lean burn combustion processes where there is excess oxygen in the exhaust stream.
Catalyst activity increases with increased temperature and therefore a higher exhaust temperature at the catalyst is desirable. The EPA recommends a minimum temperature of 450 F to maintain performance of the catalyst system. The length of the carbon chain also affects the required conversion temperature with longer carbon chains requiring a lower conversion temperature. Propane applications have short carbon chains in the exhaust and therefore require a higher temperature to reach the same conversion efficiency as long carbon chain fuels.
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