Abstract:
A method of providing an exhaust treatment device is disclosed. The method includes applying a catalyst including gold and a platinum group metal to a particulate filter. The concentration of the gold and the platinum group metal is sufficient to enable oxidation of carbon monoxide and nitric oxide.

Description:
CLAIM FOR PRIORITY 
       [0001]    The present application is a divisional of U.S. application Ser. No. 12/318,002, filed Dec. 19, 2008, now pending, which is hereby fully incorporated by reference. 
     
    
     GOVERNMENT RIGHTS 
       [0002]    This invention was made with Government support under the terms of the Oxidation CRADA, Contract No. PNNL230 awarded by the Department of Energy. The Government may have certain rights in this invention. 
     
    
     TECHNICAL FIELD 
       [0003]    The present disclosure relates generally to an exhaust system and, more particularly, to an exhaust system having a gold-platinum group metal catalyst. 
       BACKGROUND 
       [0004]    Internal combustion engines such as, for example, diesel engines, gasoline engines, natural gas engines, and other engines known in the art, exhaust a complex mixture of chemical pollutants. The chemical pollutants may include solid particulate matter, including hydrocarbon, and gaseous compounds, which may include nitrogen oxides (NOx) and carbon monoxide (CO). Due to increased attention on the environment, exhaust emission standards have become more stringent, and the amount of pollutants emitted to the atmosphere from an engine may be regulated depending on the type of engine, size of engine, and/or class of engine. 
         [0005]    One method that has been implemented by engine manufacturers to comply with the regulation of particulate matter exhausted to the environment has been to remove the matter from the exhaust flow of an engine with particulate filters. However, over time the particulate matter builds up in the filter medium, thereby reducing functionality of the filter and subsequent engine performance. To reduce the buildup of particulate matter and return functionality to the filter and engine, the particulate trap is periodically regenerated. Regeneration involves oxidizing, or combusting, the particulate matter, and is often achieved by increasing the temperature within the particulate filter with a fuel powered burner or an electrical grid. Although this method is generally successful, the combustion of the particulate matter, particularly hydrocarbon, in oxygen requires high combustion temperatures of approximately 600-700° C. Because these temperatures typically exceed the operating temperature of a diesel engine, in order to improve regeneration, it may be desirable to reduce the temperature at which the hydrocarbon combusts. 
         [0006]    One method of reducing the combustion temperature of particulate matter is disclosed in U.S. Pat. No. 4,902,487 (the &#39;478 patent), issued to Cooper et al. The &#39;478 patent discloses a method of providing nitrogen dioxide (NO 2 ) to the particulate matter in order to reduce the combustion temperature of the particulate matter. The method includes passing exhaust gas through a catalyst coated with platinum or another platinum group metal, so that nitric oxide (NO) in the exhaust gas is catalytically converted to NO 2 . The NO 2  is fed to the particulate filter where the particulate matter is combusted in a temperature range of 250-400° C. 
         [0007]    Although the method of the &#39;478 patent may reduce the combustion temperature of particulate matter, the temperature range required for regeneration may still exceed the operating temperature of the engine. In order to improve regeneration, it may be desirable to further reduce the combustion temperature. 
         [0008]    The disclosed exhaust system is directed to overcoming one or more of the shortcomings set forth above and/or other shortcomings in the art. 
       SUMMARY 
       [0009]    In one aspect, the present disclosure is directed to a method of providing an exhaust treatment device. The method includes applying a catalyst including gold and a platinum group metal to a particulate filter. The concentration of the gold and the platinum group metal is sufficient to enable oxidation of carbon monoxide and nitric oxide. 
         [0010]    In another aspect, the present disclosure is directed to an exhaust treatment device. The exhaust treatment device includes a gold-platinum group metal catalyst configured to increase a concentration of nitrogen dioxide, decrease a concentration of carbon monoxide, and reduce an oxidation temperature of hydrocarbon. 
         [0011]    In yet another aspect, the present disclosure is directed to a method of operating an exhaust treatment device. The method includes exposing a flow of exhaust to a gold-platinum group metal catalyst and decreasing a concentration of carbon monoxide within an exhaust stream. The method may also include increasing a concentration of nitrogen dioxide within an exhaust stream and oxidizing hydrocarbon within an exhaust stream. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]      FIG. 1  is a diagrammatic illustration of a power source having an exhaust system according to an exemplary disclosed embodiment. 
       
    
    
     DETAILED DESCRIPTION 
       [0013]      FIG. 1  illustrates an exemplary power source  10 . The power source  10  may include an engine  11  such as, for example, a diesel engine, a gasoline engine, a gaseous fuel-powered engine, or any other engine known in the art. The power source  10  may, alternatively, include a non-engine source of power such as a furnace. The power source  10  may include an exhaust system  16  that directs exhaust away from the engine  11 . 
         [0014]    The exhaust system  16  may include components that direct and/or treat exhaust from the engine  11 . In particular, the exhaust system  16  may include a filter system  32  and an exhaust outlet  34 . The exhaust from the engine  11  may pass through the filter system  32  to the exhaust outlet  34  before discharge to the atmosphere. It is contemplated that additional emission-controlling devices may be included within the exhaust system  16 , if desired. 
         [0015]    The filter system  32  may be placed downstream of the engine  11  to remove particulates, including hydrocarbon, from the exhaust and catalyze gaseous compounds. The filter system  32  may include a particulate filter  40  and a catalyst  42 . 
         [0016]    The particulate filter  40  may remove particulate matter from the exhaust. The particulate filter  40  may include, for example, a foam material. The foam material may be formed from sintered metallic particles such as, for example, alumina, titania, or any other high-temperature alloy. The foam material may also be formed from ceramic particles such as, for example, silicon carbide, cordierite, mullite, or any other ceramic particles known in the art. The foam material may be formed into a filter medium through a casting process, an injection molding process, or any other process that produces a porous material with a desired porosity. Alternatively, the filter  40  may include a monolith substrate in which the exhaust is forced through the walls of the substrate by alternatively blocking inlet and exit channels, in a manner known in the art. The monolith substrate may be formed from ceramic material such as cordierite, or from a suitable metal. 
         [0017]    The catalyst  42  may be incorporated throughout the particulate filter  40  and may be configured to oxidize CO and NOx to enable low temperature combustion of hydrocarbon within the particulate filter  40 . The catalyst  42  may be a gold and platinum group metal alloy. The platinum group alloy may be, for example, ruthenium, rhodium, palladium, osmium, iridium, or platinum. The catalyst  42  may be applied as a wash coating to the particulate filter  40  or incorporated into the filter material in any other manner known in the art. The catalyst  42  may be, for example, gold-palladium (Au—Pd) with a composition of between about 0.08% and 1.2% Au and between about 0.4% and 0.6% Pd, by weight, on a titania (TiO 2 ) support. For example, catalyst  42  comprise between about 0.9% and about 1.1% Au and between about 0.45% Pd and about 0.55% Pd by weight, such as about 1.0% Au and about 0.5% Pd. The catalyst  42  may enable low temperature combustion of hydrocarbon by achieving lightoff, that is, oxidation of about 50% of the CO present, at a temperature of about 60° C. The catalyst  42  may also oxidize NOx to form NO 2 , and may achieve lightoff of NOx at about 230° C. By reducing the concentration of CO in the exhaust gas and increasing the concentration of NO 2 , the catalyst  42  may enable the hydrocarbon within the particulate filter to combust at about 206° C. 
       INDUSTRIAL APPLICABILITY 
       [0018]    The disclosed exhaust treatment system may be applicable to any combustion-type device, such as an engine or a furnace, where the combustion of hydrocarbon within an exhaust stream thereof is desired. The disclosed exhaust treatment system may reduce a concentration of CO in an exhaust stream, while increasing a concentration of NO 2 . The resultant gas may facilitate combustion of hydrocarbon at reduced temperatures, and improve particulate filter regeneration. Operation of the exhaust treatment system  16  will now be explained. 
         [0019]    Atmospheric air may be drawn into a combustion chamber of the engine  11 . Fuel may be mixed with the air before or after entering the combustion chamber. This fuel-air mixture may be combusted by the engine  11  to produce mechanical work and an exhaust flow including hydrocarbon, CO, NOx, and other solid and gaseous compounds. 
         [0020]    The exhaust gas flow may be directed to the filter system  32  where hydrocarbon and other particulate matter entrained with the exhaust flow may be filtered by the particulate filter  40 . As the exhaust gas passes through the particulate filter  40 , CO and NOx gases may be exposed to the catalyst  42 . The catalyst  42  may be composed of gold-palladium and may oxidize CO and NOx present in the exhaust to form CO 2  and NO 2 , respectively. 
         [0021]    The gold-palladium catalyst  42  may be more efficient than using either a gold or a palladium catalyst alone, as is typically done. Specifically, the gold-palladium catalyst may achieve a CO to CO 2  conversion at temperatures lower than those possible with gold alone. For example, the gold-palladium catalyst  42  may convert 90% of the CO present in the exhaust to CO 2  at about 84° C., where as a gold catalyst alone may require a temperature of about 105° C. to convert the same amount of CO 2 . Because the gold-palladium catalyst  42  may convert CO to CO 2  at lower temperatures, the reaction may require less energy, and thus, be more efficient than a gold catalyst. 
         [0022]    Increasing CO 2  may have the added advantage of requiring less platinum group metal than is typically used to catalyze NOx. Specifically, reducing the concentration of CO in the vicinity of the platinum group metal may reduce the magnitude of CO poisoning of the platinum group metal. Typically, countering CO poisoning of platinum group metal catalysts is achieved by the use of excess platinum group metal, which may be costly. Thus, by reducing the effect of CO poisoning on the platinum group metal, the gold-palladium catalyst  42  may maintain its effectiveness in converting NOx to NO 2  within particulate filter  40  without the use of excess costly material. 
         [0023]    Due to the increased concentration of NO 2  and decreased concentration of CO, lightoff of the particulate matter may be achieved at a temperature of about 165° C., and 90% of the particulate matter may be oxidized at a temperature of about 206° C., which may be within an operating temperature of the engine  11 . Because regeneration may be achieved at temperatures within the operating range of the engine  11 , i.e. within the temperature range of exhaust from the engine  11 , the need for providing external energy in the form of electricity or fuel may be reduced or eliminated, and the efficiency of the regeneration event may be increased. 
         [0024]    The exhaust treatment system  16  of the present disclosure may reduce a concentration of CO in an exhaust stream while increasing a concentration of NO 2 . The resultant exhaust gas may facilitate combustion of hydrocarbon at reduced temperatures, and thus increase the efficiency of particulate filter regeneration. Furthermore, the disclosed exhaust treatment system may reduce the CO poisoning of platinum group metals within the catalyst  42 , thereby reducing the cost of the exhaust treatment system. 
         [0025]    It will be apparent to those skilled in the art that various modifications and variations can be made to the exhaust treatment system. Other embodiments will be apparent to those skilled in the art from consideration of the specification and practice of the disclosed exhaust treatment system. It is intended that the specification and examples be considered as exemplary only, with a true scope being indicated by the following claims and their equivalents.