JP2012522930A - HC-SCR system for lean burn engines - Google Patents

Abstract

Systems and methods are provided for reducing NOx emissions in an exhaust stream. A system comprising hydrocarbon conversion on a partial oxidation catalyst and a hydrocarbon selective catalytic reduction catalyst in a slip stream is described. The exhaust treatment system is advantageously used for the treatment of exhaust flows from lean combustion engines including diesel engines, lean burn gasoline engines, and locomotive engines.
[Selection figure] None

Description

CROSS REFERENCE TO RELATED PATENT This application was filed on April 2, 2009, US Provisional Application No. 61 / 166,047, filed April 2, 2009 under 35 USC §119 (e) US Provisional Application No. 61 / 166,603, and US Provisional Application No. 61 / 169,932, filed April 16, 2009, claim the benefit of priority, which is incorporated herein by reference. Incorporated.

  The present invention relates to an exhaust treatment system and method useful for reducing pollutants in an exhaust gas stream. Specifically, embodiments of the present invention are directed to an exhaust treatment system for reducing NOx, and a method of use, the system on a partial oxidation catalyst that produces a split between hydrogen and an exhaust gas stream. Includes hydrocarbon conversion.

  The operation of lean-burn engines, for example diesel engines, lean-burn gasoline engines, and locomotive engines, provides excellent fuel economy and because of their operation at high air-fuel ratios under lean fuel conditions, gas phase hydrocarbons And carbon monoxide emissions are very low. Diesel engines also offer significant advantages over gasoline engines, especially in terms of their durability and their ability to produce high torque at low speeds. Effective NOx reduction from lean burn engines is difficult to achieve because the NOx conversion rate under lean fuel conditions is very low. Thus, the conversion of the NOx component of the exhaust stream to a harmless component generally requires a special NOx reduction strategy for operation under fuel lean conditions.

One such strategy for the reduction of NOx in the exhaust stream from a lean burn engine is to use a NOx storage reduction (NSR) catalyst, also known in the art as a “lean NOx trap (LNT)”. It is. LNT catalysts can absorb or “trap” nitrogen oxides under lean conditions. LNT catalysts contain a NOx sorbent capable of absorbing or “trapping” nitrogen oxides under lean conditions, and a platinum group metal component that provides a catalyst with oxidation and reduction functions. In operation, the LNT catalyst facilitates a series of elementary processes described below in equations 1-5. In an oxidizing environment, NO is oxidized to NO ₂ (Equation 1), which is an important process of NOx storage. At low temperatures, this reaction is typically catalyzed by a platinum group metal component, such as a platinum component. The oxidation process does not stop here. Further oxidation of NO ₂ to nitric acid by incorporation of atomic oxygen is also a catalytic reaction (Equation 2). In the absence of the platinum group metal component, even when the NO ₂ is used as the NOx source, there is slight nitrate formation. The platinum group metal component has a dual function of oxidation and reduction. Because of its reduction role, the platinum group metal component firstly catalyzes the release of NOx upon introduction of reduction, for example, CO (carbon monoxide), H ₂ (hydrogen), or HC (carbonization). Hydrogen) is catalyzed to exhaust (Equation 3). This process can restore some NOx storage sites, but can contribute to the limited reduction of NOx species. The released NOx is then further reduced to gaseous N2 in a dense environment (Equations 4 and 5). NOx emissions can also be triggered by fuel injection, even in a net oxidizing environment. However, efficient reduction of NOx released by H ₂ , CO, or HC requires overall net dense conditions. Also, the rapid rise in temperature can trigger NOx release due to the high temperature and low stability of metallic nitric acid. The NOx trap catalyst is a circulating operation. It is conceivable that the metal compound undergoes carbonic / nitric acid conversion as the main pathway during lean / dense operation.

Oxidation of NO to ^{_{NO 2 NO + 1/2 O}} 2 → NO 2 (1)

NOx as nitrate occluding ^{_{2NO 2 + MCO 3 + 1/}} 2 4O 2 → M (NO 3) 2 + CO 2 (2)

NOx release M (NO ₃ ) ₂ + 2CO → MCO ₃ + NO ₂ + NO + CO ₂ (3)

NOx reduction to N ₂ NO ₂ + CO → NO + CO ₂ (4)
2NO + 2CO → N ₂ + 2CO ₂ (5)

  In Equations 2 and 3, M represents a divalent metal cation, and M is also a monovalent or trivalent metal compound, in which case the equations need to be re-equilibrated.

NO and NO ₂ to N ₂ reduction occur in the presence of the NSR catalyst during the dense period, while ammonia (NH ₃ ) can also form as a by-product of the dense pulse regeneration of the NSR catalyst. Has been observed. For example, the reduction of NO can proceed with equations 6 and 7.

Reduction from NO to NH ₃ CO + H ₂ O → H ₂ + CO ₂ (6)
2NO + 5H ₂ → 2NH ₃ + 2H ₂ O (7)

This property of the NSR catalyst also mandates that NH ₃ , which is itself a harmful component, must be immediately converted to a harmless species before the exhaust is released into the atmosphere.

In developing under automotive applications (including treating exhaust from lean burn engines), alternative strategies reduction of the NO _x uses selective catalytic reduction (SCR) catalyst technology. Strategies, such as flue gas treatment, have proven effective when applied to stationary sources. In this strategy, NO _x is reduced to nitrogen (N ₂ ) using a reductant, such as NH ₃ , over an SCR catalyst that typically consists of a base metal. This technique is capable of over 90% NO _x reduction, thus indicating that it is one of the best ways to achieve challenging NO _x reduction goals.

Ammonia is one of the most effective reductants for NO _{x in} lean conditions using SCR technology. One approach that has been investigated for the reduction of NO _x in diesel engines (mainly large diesel vehicles) is to use urea as a reductant. As the hydrolysis produces ammonia, urea is injected into the exhaust before the SCR catalyst at a temperature in the range of 200-600 ° C. One of the main disadvantages of this technology is the need for a very large reservoir to contain urea that is mounted on the vehicle. Another significant concern is the driver's involvement in replenishing the reservoir with urea as needed, and the equipment requirements for supplying the driver with urea. Therefore, a light and alternative technology that uses the onboard fuel as a reductant for NOx treatment of exhaust gas is desired.

Selective catalytic reduction of the NO _x that uses hydrocarbon (HC-SCR) has as a potential alternative method for the removal of NOx in an oxygen dense conditions, has been extensively studied. Typically, ion exchange group metal zeolite catalysts (eg, Cu-ZSM5) are not active enough under typical vehicle handling conditions and are susceptible to decomposition by sulfur dioxide and flooding. Catalysts using platinum group metals (eg, Pt / Al ₂ O ₃ ) operate effectively in a narrow temperature window between 180 ° C. and 220 ° C. and are very selective for N ₂ O production.

Catalytic devices using alumina-supported silver (Ag / Al ₂ O ₃ ) have received attention due to their ability to selectively reduce NO _x under lean exhaust conditions, along with a wide variety of hydrocarbon species. The use of hydrocarbons and alcohols, aldehydes, and functional organic compounds over Ag / Al ₂ O ₃ allows the reduction of NO _x at temperatures below 450 ° C. In addition to the molecules listed above, diesel fuel can also be used as a reductant. Diesel fuel does not require additional tanks for diesel-powered vehicles. Diesel fuel can be supplied to the emissions system by changing engine management or by supplying additional injectors of diesel fuel to the exhaust train. However, current HC-SCR catalyst systems exhibit poor durability. Catalyst coking due to fuel cracking, and catalyst and sulfur poisoning from fuel and petroleum on the deposit, cause catalyst performance degradation in relatively short operating times. The catalyst must undergo frequent and costly regeneration to maintain the desired performance.

  Despite these various alternatives, there are no commercially available practical hydrocarbon SCR catalysts that use diesel fuel as the reductant. Accordingly, there is a need in the art for systems and methods that provide durable NOx reduction activity using HC-SCR technology.

One or more embodiments of the present invention are directed to an exhaust treatment system for NOx reduction in the exhaust stream from a lean burn engine. One embodiment of the system includes a main exhaust pipe in fluid communication with the engine exhaust stream and a hydrocarbon selective catalytic reduction catalyst (HC-SCR) in fluid communication with the main exhaust pipe.
A slip exhaust flow pipe slips a portion of the exhaust stream from the main exhaust pipe to provide a slip exhaust flow, which flows through a catalytic partial oxidation (CPO) catalyst in fluid communication with the slip exhaust flow pipe. A first junction for bypassing into the exhaust flow pipe branches off from the main exhaust pipe and is connected to the main exhaust pipe. A hydrocarbon injector is installed upstream of the CPO catalyst in the slip stream. A second joint downstream from the first joint reintroduces the slip exhaust stream into the main exhaust pipe upstream of the HC-SCR. CPO is effective in converting some hydrocarbons to carbon monoxide and hydrogen.

  In one or more embodiments, the CPO is designed to provide sufficient hydrogen and an appropriate amount of hydrocarbons for the downstream HC-SCR catalyst. In one or more embodiments, the hydrocarbon injection device includes a metering device adapted to adjust the amount of hydrocarbon injected into the slip exhaust flow tube. According to one or more embodiments, the hydrocarbon is a fuel.

In one or more embodiments, the portion of the exhaust gas that is diverted into the slip exhaust flow tube has a total exhaust flow rate of up to about 10%. One or more embodiments further comprise a metering device at the first junction of the slip exhaust flow tube to limit the percentage of exhaust gas diverted to the slip exhaust flow tube. In one or more embodiments, the CPO catalyst contains a platinum group metal. Examples of platinum group metals for CPO catalysts include platinum, palladium, rhodium, and combinations thereof.

  In one or more embodiments, one or both of the CPO catalyst and HC-SCR are disposed on the flow-through monolith. In one or more embodiments, the system includes a diesel particulate filter (DPF) downstream of the HC-SCR catalyst. In one or more embodiments, the system includes a diesel particulate filter (DPF) upstream of the HC-SCR catalyst. In one or more embodiments, a diesel particulate filter (DPF) is installed between the first joint and the second joint in fluid communication with the main exhaust pipe. In one or more embodiments, the system includes a diesel oxidation catalyst (DOC) upstream of the DPF and HC-SCR catalyst. In one or more embodiments, the system includes a diesel oxidation catalyst (DOC) upstream of the DPF and HC-SCR catalyst. In one or more embodiments, the system includes a diesel oxidation catalyst (DOC) upstream of the DPF and HC-SCR catalyst. In one or more embodiments, the system includes a diesel oxidation catalyst (DOC) installed downstream of the first junction in fluid communication with the main exhaust pipe. In one or more embodiments, the system includes a diesel oxidation catalyst (DOC) installed downstream of the first junction in fluid communication with the main exhaust pipe. In one or more embodiments, the system includes a diesel oxidation catalyst (DOC) installed downstream of the first junction in fluid communication with the main exhaust pipe.

  In one or more embodiments, the system includes a diesel oxidation catalyst (DOC) installed downstream of the first junction and upstream of the DPF and in fluid communication with the main exhaust pipe. In one or more embodiments, the system includes the DOC and DPF being integrated into a single component. In one or more embodiments, the system includes an NH3-SCR catalyst downstream of the HC-SCR catalyst. In one or more embodiments, the system includes an oxidation catalyst downstream of the HC-SCR catalyst.

  Another aspect of the invention relates to a method of treating an exhaust stream. In one embodiment of the method, the exhaust stream passes through the main exhaust pipe and a portion of the exhaust stream passes through the slip exhaust flow pipe. The main exhaust pipe includes a hydrocarbon selective catalytic reduction catalyst (HC-SCR), the slip exhaust flow pipe is a catalytic partial oxidation (CPO) catalyst in fluid communication with the slip flow pipe and a hydrocarbon injector upstream of the CPO. including. The slip exhaust flow pipe branches from the main exhaust pipe at the first junction and is in fluid communication with the CPO. The slip exhaust flow pipe is rejoined to the main exhaust pipe at the second joint upstream of the HC-SCR. CPO is adapted to convert some hydrocarbons in slip exhaust flow tubes to carbon monoxide and hydrogen.

  In one or more embodiments of the method, the amount of hydrocarbon injector into the slip exhaust flow tube is adjusted by a metering device. In one or more embodiments, the hydrocarbon is an onboard fuel. In one or more embodiments, a first percentage of the exhaust flow passes through the main exhaust pipe, a second percentage of the exhaust flow passes through the slip exhaust flow pipe, and the first percentage is greater than the second percentage. large. In one or more embodiments, the second percentage of exhaust flow is adjusted by a metering device installed in a slip exhaust flow tube near the first junction. One or more embodiments of the method further include passing the exhaust stream through a diesel particulate filter installed upstream of the HC-SCR catalyst and into the main exhaust pipe.

One or more embodiments of the method may include passing the exhaust stream through a diesel particulate filter installed downstream of the HC-SCR catalyst and into the main exhaust pipe. One or more embodiments of the method may include passing the exhaust stream through a diesel particulate filter installed downstream of the first joint and upstream of the second joint into the main exhaust pipe. . One or more embodiments of the method may include passing the exhaust stream through a diesel oxidation catalyst installed upstream of the diesel particulate filter and into the main exhaust pipe. One or more embodiments of the method may include passing the exhaust stream through a diesel oxidation catalyst installed upstream of the diesel particulate filter and into the main exhaust pipe. One or more embodiments of the method may include passing the exhaust stream through a diesel oxidation catalyst installed upstream of the diesel particulate filter and into the main exhaust pipe. One or more embodiments of the method may include passing the exhaust stream through a diesel oxidation catalyst installed downstream of the first joint and into the main exhaust pipe. One or more embodiments of the method may include passing the exhaust stream through a diesel oxidation catalyst installed downstream of the first joint and into the main exhaust pipe.

  One or more embodiments of the method may include passing the exhaust stream through a diesel oxidation catalyst installed downstream of the first joint and into the main exhaust pipe. One or more embodiments of the method may include passing the exhaust stream through a diesel oxidation catalyst installed downstream of the first junction and upstream of the diesel particulate filter and into the main exhaust pipe. One or more embodiments of the method may include passing the exhaust stream through a diesel oxidation catalyst installed downstream of the first junction and upstream of the diesel particulate filter and into the main exhaust pipe. One or more embodiments of the method may include passing the exhaust stream through a diesel oxidation catalyst installed downstream of the first junction and upstream of the diesel particulate filter and into the main exhaust pipe.

  In one or more embodiments of the method, the diesel oxidation catalyst and the diesel particulate filter are integrated. In one or more embodiments of the method, the diesel oxidation catalyst and the diesel particulate filter are integrated. The method can include passing the exhaust stream through a NH3-SCR catalyst located downstream of the HC-SCR catalyst and into the main exhaust pipe according to one or more embodiments. One or more embodiments of the method include an exhaust stream in the main exhaust pipe through an oxidation catalyst installed downstream of the HC-SCR catalyst.

Various embodiments of the present invention include, but are not limited to, diesel oxidation catalysts, catalytic soot filters, HC selective catalytic reduction catalysts, NH ₃ selective catalytic reduction catalysts, and oxidation catalysts in numerous configurations. Various components may be included. Exhaust gas may pass through any of these components in various arrangements.

1 is a schematic diagram illustrating an engine exhaust treatment system according to a detailed embodiment. FIG. 3 is a schematic diagram illustrating an engine exhaust treatment system according to another embodiment. 1 is a schematic diagram illustrating an integrated engine emission processing system, according to one embodiment. FIG. 3 is an alternative emission processing system in accordance with one or more embodiments of the present invention. 3 is an alternative emission processing system in accordance with one or more embodiments of the present invention. 3 is an alternative emission processing system in accordance with one or more embodiments of the present invention. 3 is an alternative emission processing system in accordance with one or more embodiments of the present invention. 3 is an alternative emission processing system in accordance with one or more embodiments of the present invention. 3 is an alternative emission processing system in accordance with one or more embodiments of the present invention. 3 is an alternative emission processing system in accordance with one or more embodiments of the present invention. 3 is an alternative emission processing system in accordance with one or more embodiments of the present invention. 3 is an alternative emission processing system in accordance with one or more embodiments of the present invention. It is a perspective view of a wall flow filter base material. It is sectional drawing of one piece of a wall flow filter base material. Figure 5 shows a graph of percent NOx conversion as a function of catalyst inlet temperature for HC-SCR under various operating conditions.

  Provided are exhaust treatment systems that can be used to treat exhaust gases from lean burn engines, and methods of using these systems to treat engine exhaust. Lean burn engines include, but are not limited to, diesel engines, lean burn gasoline engines, and engine engines.

  The small amount of hydrogen present in the lean exhaust (typically <2000 ppm) can significantly improve the performance of the HC-SCR catalyst and reverse the damage done to the catalyst through normal operation. Embodiments of the present invention are directed to systems and methods that can provide fuel reductant and hydrogen to an HC-SCR catalyst. The system includes a catalytic partial oxidation catalyst (CPO) with slip flow from the main exhaust and net reduction conditions to produce hydrogen using the onboard fuel. The slip stream contains unconverted fuel species and hydrogen is combined with the main exhaust to provide favorable HC-SCR reaction conditions. Hydrogen can be generated from the hydrocarbon feed by a partial oxidation process in which a portion of the feed is reacted with oxygen in a slip stream under fuel rich conditions.

  FIG. 1 shows a graphical description of one aspect of the present invention and is described in detail below. Briefly, slip flow (typically 1-10% total exhaust flow discharged from the engine) is bypassed upstream of the HC-SCR catalyst installed downstream from the engine. A sufficient amount of fuel is introduced into the slip stream to produce fuel rich conditions. The catalytic partial oxidation catalyst is installed in a slip stream downstream of the fuel introduction point, as will be further described below. The slip stream contains unconverted fuel species and hydrogen is combined with the main exhaust and introduced into the HC-SCR catalyst. In one embodiment of the present invention, the HC-SCR can be placed downstream of the diesel oxidation catalyst and diesel particulate filter device so that the HC-SCR can be regenerated simultaneously with regeneration of the DOC and DPF devices. The system can optionally be optimized using a bypass flow regulating valve and fuel regulation delivery device to minimize the fuel penalty of the system.

  The following terms have the respective meanings set forth below for purposes of this specification.

  “Lean NOx catalyst”, “LNC”, “hydrocarbon selective catalytic reduction catalyst”, and “HC-SCR” may be used interchangeably herein. These are different from lean NOx traps (LNT) with NOx storage and release functions.

  A “lean gaseous stream” including a lean exhaust stream means a gas stream having λ> 1.0.

  A “lean period” refers to the period of an exhaust treatment in which the exhaust gas composition is lean, ie, has λ> 1.0.

  “Platinum group metal component” refers to one of the platinum group metals or their oxides.

  “Rare earth metal component” refers to one or more oxides of the lanthanum series defined in the element symbol table comprising lanthanum, cerium, praseodymium, and neodymium.

  A “dense gaseous stream” including a dense exhaust stream means a gas stream having λ <1.0.

  “Dense period” refers to the period of the exhaust treatment in which the exhaust gas composition is rich, ie, having λ <1.0.

  “Washcoat” has the usual meaning in the art of a thin adhesive coating consisting of a catalyst or other material applied to a refractory material such as a honeycomb flow-through monolith substrate or a filter substrate, Be sufficiently porous to allow passage through the treated gas stream

  “Fluid communication” means that components and / or tubes are adjacent so that exhaust gases or other fluids can flow between the components and / or tubes.

  “Downstream” refers to the location of a component in the exhaust gas flow in the path that is further away from the engine than a component in front of one component. For example, when a diesel particulate filter is said to be downstream from a diesel oxidation catalyst, exhaust gas emitted from the engine in the exhaust pipe will flow through the diesel oxidation catalyst before flowing through the diesel particulate filter. To do. Thus, “upstream” refers to a component that is installed closer to the engine relative to another component.

Reference to the “ammonia producing component” is determined by its design and the engine out emissions and the administration of the reductant (H ₂ , CO and / or HC) via engine management or injection into the exhaust. As a result of the configuration, it means a part of the exhaust system that supplies ammonia (NH ₃ ). Such components exclude gas dosing or other external sources of NH ₃ . Examples of ammonia generating components include NOx storage reduction (NSR) catalysts and lean NOx traps (LNT).

  FIG. 1 illustrates an exhaust treatment system 2 for NOx reduction in an exhaust stream from a lean burn engine 4 according to one embodiment. An exhaust gas stream containing gaseous pollutants (eg, unburned hydrocarbons, carbon monoxide, nitrogen oxides) and particulate matter is passed through a main exhaust pipe 6 in fluid communication with the lean combustion engine 4. Communicated. The exhaust gas stream in the main exhaust pipe 6 passes through a hydrocarbon selective catalytic reduction catalyst (HC-SCR) 8 in fluid communication with the pipe 6. The slip exhaust flow pipe 10 branches from the main exhaust pipe 6. The slip exhaust flow pipe 10 bypasses a part of the exhaust flow from the main exhaust pipe 6 into the slip exhaust flow pipe 10 to provide the slip exhaust flow, and is connected to the main exhaust pipe 6 by the first joint 12. Is done. The slip exhaust stream passes through a catalytic partial oxidation (CPO) catalyst 14 that is in fluid communication with the slip exhaust stream tube 10. The second joint 16 downstream from the first joint 12 reintroduces the slip exhaust flow from the slip exhaust flow pipe 10 into the main exhaust pipe 6 upstream of the HC-SCR 8. Line 20 leads to the tail tube and out of the system.

  The hydrocarbon feed may be introduced into a tube 18 in the slip stream upstream of the CPO catalyst 14. CPO14 is effective in converting some of the hydrocarbons to carbon monoxide and hydrogen. The CPO 14 is designed to provide enough hydrogen to improve the performance of the HC-SCR 8, according to one or more embodiments.

  In some embodiments, the main exhaust pipe 6 includes an optional additional exhaust system component 22 downstream of the first joint 12. The additional exhaust system component 22 can be, for example, one or more of a diesel oxidation catalyst, a diesel particulate filter, a reductant injector, and an air injector that are in fluid communication with the main exhaust pipe. In one specific embodiment, any additional exhaust system component 22 may be, for example, one or more diesel oxidation catalysts, and the diesel particulate filter is upstream of the first joint 12 of the main exhaust pipe 6. Can be installed.

  As shown in the embodiment of FIG. 2, the hydrocarbon injector 18 includes a metering device 24 that is adapted to adjust the amount of hydrocarbon injected into the slip exhaust flow tube 10. In a specific embodiment, the injected hydrocarbon is an onboard fuel.

  Detailed embodiments of the present invention include a metering device 26 at the first junction 12 of the slip exhaust flow tube 10 to limit the percentage of exhaust gas that is diverted to the slip exhaust flow tube 10. In some embodiments of the present invention, some exhaust gas that is diverted from the main exhaust pipe 6 into the slip exhaust flow pipe 10 has a total exhaust flow rate of up to about 10%. In other detailed embodiments, a portion of the exhaust gas is diverted from the main exhaust pipe 6 in the range of about 0.5% to about 15%, or in the range of about 1% to about 10%. In other detailed embodiments, a portion of the exhaust gas that is diverted from the main exhaust pipe 6 is a total exhaust flow rate. Up to about 15%, 14%, 13%, 12%, 11%, 10%, 9%, 8%, 7%, 6%, 5%, 4%, 3%, or 2%.

  In a specific embodiment, one or more of the CPO catalyst and HC-SCR are disposed on the flow-through monolith.

  As shown in FIG. 2, various embodiments of the exhaust treatment system are installed between a first joint 12 and a second joint 16 that are in fluid communication with the main exhaust pipe 6. A diesel particulate filter (DPF) 28 is further provided. In other embodiments, a diesel oxidation catalyst (DOC) 30 is installed downstream of the first joint 12 and upstream of the DPF 28 in fluid communication with the main exhaust pipe 6.

  In an alternative embodiment, the DOC 30 and DPF 28 shown in FIGS. 3 and 4 are integrated into a single component or substrate 32. For example, DOC 30 and DPF 28 may be located in different areas of the same substrate 32, where DOC 30 is located in the upstream segment of substrate 32 and CSF 28 is located on the downstream segment of substrate 32.

  Additional embodiments of the present invention are directed to a method of treating an exhaust stream from a lean burn engine. With reference to FIGS. 1, 2, and 4, the exhaust stream passes through the main exhaust pipe 6 and a portion of the exhaust stream passes through the slip exhaust pipe 10. The main exhaust pipe 6 includes a hydrocarbon selective catalytic reduction catalyst (HC-SCR) 8. The slip exhaust flow tube 10 includes a catalytic partial oxidation (CPO) catalyst 14, and hydrocarbons can be injected into the slip exhaust flow tube 10 upstream of the CPO 14 using a hydrocarbon injector 18. The slip exhaust flow pipe 10 branches from the main exhaust pipe 6 at the first joint 12 and is in fluid communication with the CPO 14. The slip exhaust flow pipe 10 is rejoined to the main exhaust pipe 6 at the second joint 16. The 2nd junction part 16 is installed in the upstream of HC-SCR8. The CPO 14 is adapted to convert hydrocarbons to carbon monoxide and hydrogen in the slip exhaust flow tube 10.

  The amount of hydrocarbon injected into the slip exhaust flow tube 10 can be adjusted by the metering device 24. In a detailed embodiment, the hydrocarbon is an onboard fuel.

  In accordance with one or more embodiments of the present invention, a first percentage of the exhaust flow passes through the main exhaust pipe 6, a second percentage of the exhaust flow passes through the slip exhaust flow pipe 10, and the first percentage is Greater than the second percentage. In some embodiments, the second percentage of exhaust flow is adjusted by a metering device 26 installed in the slip exhaust flow tube 10 near the first junction 12.

  Various embodiments of the present invention further allow the exhaust flow in the main exhaust pipe 6 to pass through a diesel particulate filter 28 installed downstream of the first joint 12 and upstream of the second joint 16. Including. In another embodiment, the exhaust flow in the main exhaust pipe 6 is passed through a diesel oxidation catalyst 30 installed downstream of the first joint 12 and upstream of the diesel particulate filter 28. In a detailed embodiment, as shown in FIG. 4, the diesel oxidation catalyst 30 and the diesel particulate filter 28 are integrated into a single component 32.

  CPO14, DOC30, DPF 28, and optional component 22 can be made from compositions well known in the art and include base metals (eg, ceria) and / or platinum group metals as catalyst agents. obtain. In the upstream position, the DOC and / or particulate filter provides several advantageous functions. The catalyst serves to oxidize unburned gaseous and non-volatile hydrocarbons (ie, the soluble organic components of diesel particulate matter), turning carbon monoxide into carbon dioxide and water. The removal of most of the SOF specifically helps to prevent enormous deposition of particulate matter on the HC-SCR8. In a specific embodiment, the platinum group metal is selected from the group consisting of platinum, palladium, rhodium, and combinations thereof.

In certain embodiments of the present invention, one or more of DOC 30, DPF 28, and optional component 22 assists in the removal of particulate material in the exhaust stream, particularly the soot (or carbon) portion of the particulate material. In order to do so, a smoke filter, for example, a wall flow filter is coated. In addition to the other oxidation functions described above, the DOC drops to a temperature at which the soot portion is oxidized to CO ₂ and H ₂ O. As soot accumulates on the filter, the catalyst coating helps regenerate the filter. As shown in FIG. 5, DPF 28 may be installed downstream of HC-SCR 8 to convert CO and unconverted fuel species. FIG. 6 shows another alternative embodiment in which the DPF 28 is installed upstream of the first junction 12 to minimize or prevent contamination of the downstream HC-SCR using particulate material. 7 illustrates an alternative embodiment in which the DOC 30 is installed upstream of the first junction 12 and the HC-SCR 8 and DPF 28 are installed downstream of the second junction. FIG. 8 shows an alternative embodiment in which the DOC 30 and the DPF 28 are installed upstream of the first joint. In another alternative embodiment, as shown in FIG. 9, the system is configured to convert NH ₃ -SCR catalyst downstream of HC-SCR to convert any NH ₃ emissions produced in the system. Is further provided. In another specific embodiment shown in FIG. 10, the system further comprises an oxidation catalyst downstream of the HC-SCR to oxidize CO and any unconverted fuel species. FIG. 11 shows an alternative embodiment of an exhaust treatment system comprising an ammonia oxidation (AMOX) catalyst 36 installed downstream of the HC-SCR8 catalyst. Ammonia oxidation catalyst 36 may be useful to remove or reduce residual ammonia, which may be referred to as slip ammonia, throughout the system.

FIG. 12 shows an alternative embodiment where the hydrogen source 38 is an off-line source or component other than a CPO catalyst. As shown herein, the hydrogen source 38 may include a metering device 40 that can regulate the amount of hydrogen injected into the main exhaust pipe 6. The off-line H ₂ source (and HC reductant) can include output from the CPO reaction (partial oxidation of fuel with oxygen), as explained above.

  Various optional components 22 may be included in the exhaust pipe 6. These optional components 22 can be installed upstream of the hydrogen injector 38, downstream of the hydrogen injector 38, or downstream of the HC-SCR catalyst 8. It is conceivable that any component can be installed in the hydrogen injector 38 before the junction of the main exhaust pipe 6. The alternative embodiments shown are merely illustrative of various ways in which the invention may be practiced and should not be construed as limiting. The components can be arranged in other configurations and remain within the scope of the present invention.

  As will be appreciated by those skilled in the art, various metering devices can also be connected to the regulator. The regulator may include other components, sensors, and processing devices. The sensor may be suitable for measuring components of the gaseous composition and may be installed at various locations within the exhaust pipe. The processor can evaluate the data from the sensors and adapt the metering device to optimize the function of the various catalyst components.

For use in various embodiments of the present invention, optional component 22 includes, for example, diesel oxidation catalyst, diesel particulate filter, reductant injection, or air injection, or ammonia in fluid communication with the main exhaust. It may be one of an oxidation catalyst and an ammonia selective catalytic reduction catalyst. Moreover, any component 22, including those shown in FIG. 3, may be a combination of integrated components is not limited thereto.

In a substrate detailed embodiment, any or all of the catalysts comprising HC-SCR8, CPO14, and DOC30 are disposed on the substrate. The substrate can be any of the materials typically used to prepare the catalyst, and typically includes a ceramic or metal honeycomb structure, such as a flow-through monolith. Any suitable substrate can be used, such as a monolith substrate of the type having a fine, parallel gas flow channel, with the channel open to the fluid flow therethrough (base Extending through the inlet or outlet face of the substrate (referred to as honeycomb flow through the material). Channels that are essentially linear paths from their fluid inlets to their fluid outlets are walls on which the catalyst material is coated as a washcoat so that the gas flowing through the channels contacts the catalyst material Defined by The flow path of the monolith substrate is a thin wall channel that can be any suitable cross-sectional shape and size, such as trapezoidal, rectangular, square, sine, hexagonal, elliptical, circular, and the like. Such a structure may contain about 60 to about 600 or more gas inlet openings (ie, cells) per square inch of cross section.

  FIGS. 13 and 14 illustrate a wall flow filter substrate 50 that has a plurality of alternatively nitrogenized channels 52 and can serve as a particulate filter. The flow path is tubularly surrounded by the inner wall 53 of the filter substrate. The substrate has an inlet end 54 and an outlet end 56. The alternative flow path is blocked with an inlet plug 58 at the inlet end 54 and with an outlet plug at the outlet end 56 to form an opposite checkerboard pattern at the inlet 54 and outlet 56. . The gas flow enters through the unblocked channel inlet 60, is blocked by the outlet plug, and diffuses through the channel wall 53 (which is porous) to the outlet side. Gas cannot return to the inlet side of the wall because of the inlet plug 58. When such a substrate is utilized, the resulting system can remove particulate matter along with gaseous contaminants.

  Wall flow filter base material is a ceramic-like material such as cordierite, alpha alumina, silicon carbide, aluminum titanate, silicon nitride, zirconia, mullite, spodumene, aluminum silicon magnesium, or zirconium silicate, or porous refractory metal It can consist of The wall flow substrate can also be formed from a ceramic fiber composite material. A specific wall flow substrate is formed from cordierite, silicon carbide, and aluminum titanate. Such materials can withstand the environments experienced in exhaust flow treatment, particularly high temperatures.

  For use in the system of the present invention, the wall flow substrate can include a thin porous wall honeycomb (monolith) through which fluid flow passes without greatly increasing the backside pressure or pressure across the article. The ceramic wall flow substrate used in the present system is formed from a material having a porosity of at least 40% (eg, 40-75%) having an average pore size of at least 10 microns (eg, 10-30 microns). Can be done.

  In a specific embodiment where additional functionality is applied to the filters (DOC30, DPF 28, and optional component 22), the substrate can have a porosity of at least 59% and is 10-20 microns. It can have an average pore diameter. When substrates having these porosities and these average pore sizes are coated using the techniques described below, an appropriate level of the desired catalyst composition is loaded onto the substrate. These substrates can further maintain proper exhaust flow characteristics, i.e., acceptable back pressure, despite catalyst loading. U.S. Pat. No. 4,329,162 is incorporated herein by reference with respect to disclosure of suitable wall flow substrates.

  Wall flow filters typical in commercial use are typically formed from a low wall porosity of, for example, about 42% to 50%. In general, the pore size distribution of commercial wall flow filters has an average pore size of less than 25 microns and is typically very broad.

  The porous wall flow filter can be catalyzed so that the walls of the element have one or more catalytic materials thereon, or contain one or more catalytic materials in the walls. The catalytic material can be present alone on the inlet side of the element wall, alone on both the outlet side, the inlet and outlet sides, or the wall itself can be entirely or partially composed of catalytic material. Including the use of one or more washcoats of catalyst material and one or more washcoats of catalyst material on the inlet and / or outlet walls. The filter can be coated by any of a variety of means well known in the art.

  Also, substrates that are useful in the catalysts of the present invention can be essentially metallic and can consist of one or more metals or metal alloys. The metal substrate can be used in various shapes such as a corrugated plate or a monolithic type. Suitable metal supports include refractory metals and metal alloys in which iron is a substantial or major component, such as titanium and stainless steel and other alloys. Such alloys may contain one or more of nickel, chromium, and / or aluminum, the total amount of these metals being at least 15% by weight of the alloy, for example, 10-25% by weight of chromium, 3-8% of aluminum. % By weight and up to 20% by weight of nickel may advantageously be included. The alloy may also contain one or more other metals such as minor or trace amounts of manganese, copper, vanadium, titanium, and the like. The surface or metal substrate can be oxidized at elevated temperatures, eg, 1000 ° C. or higher, to improve the resistance to corrosion of the alloy by forming an oxide layer on the surface, substrate. Such high temperature induced oxidation can enhance the adhesion of the refractory metal oxide support and catalytically promote the metal component relative to the substrate.

  In alternative embodiments, one or all of HC-SCR 8, CPO 14, DOC 30, DPF 28, and optional component 22 may be placed on an open cell foam substrate. Such substrates are well known in the art and are typically formed from ceramic refractory or metallic materials.

CPO Catalyst The principle of the CPO catalyst is the reaction of the fuel with oxygen to yield carbon monoxide and hydrogen according to Equation 8.

C _n H _m + (n / 2) O ₂ → nCO + (m / 2) H ₂ (8)

When a sufficiently high temperature and limited contact time of the reactive gas is provided using a catalyst (high space velocity), the catalytic partial oxidation reaction is extended. In a detailed embodiment, the CPO14 catalyst contains platinum and palladium. In a specific embodiment, the platinum group metal loading ranges from about 20 g / ft ³ to about 200 g / ft ³ . In a more specific embodiment, the ratio of platinum to palladium metal in CPO ranges from about 1: 9 to about 9: 1. In one or more embodiments, the CPO operates between 600 ° C. and 700 ° C. in excess of 100,000 hr ⁻¹ space velocity (sometimes> 250,000 hr ⁻¹ ). In a detailed embodiment, the metal ratio of platinum to palladium is about 1: 5 to about 5: 1, or about 1: 4 to about 4: 1, or about 1: 3 to about 3: 1, or about 1: It can range from 2 to about 2: 1, or about 1: 1.

In a specific embodiment, the CPO has a suitable high surface area refractory metal oxide support layer on the substrate, as described above, to serve as a support on which finely dispersed catalytic metals can expand. Including being placed in. In certain embodiments, a high surface area refractory metal oxide support, such as an alumina support also referred to as “gamma alumina” or “activated alumina” may be used, typically exceeding 60 square meters per gram ( “M ² / g”), indicating a BET surface area that is usually about 200 m ² / g or more. Such activated alumina is usually a mixture of gamma and delta phases of alumina, but also contains significant amounts of eta, kappa, and theta alumina phases. Refractory metal oxides other than activated alumina can be used as a support for at least some catalyst components in a given catalyst. For example, bulk ceria, zirconia, alpha alumina, and other materials are known for such use. Many of these materials have the disadvantage of having a significantly lower BET surface area than activated alumina, but the disadvantage is offset by the superior durability or performance enhancement of the resulting catalyst. It tends to be. “BET surface area” has its usual meaning with respect to Brunauer, Emme and Teller methods for defining surface area by N ₂ absorption. The pore diameter and pore volume can also be determined using BET type N ₂ absorption or desorption experiments.

  A specific support coating is alumina, for example, stable, high surface area transition alumina. As used herein and in the claims, “transition alumina” includes gamma, chi, eta, kappa, theta, and delta formation, and combinations thereof. To stabilize against a generally undesired high temperature phase transition to alpha alumina, which has a relatively low surface area, such as one or more rare earth metal oxides and / or alkaline earth metal oxides, etc. It is known that certain additives can be included in the transition alumina (usually including an amount of 2-10 weight percent of the stabilized coating). For example, one or more lanthanum, cerium, praseodymium, calcium, barium, strontium, and magnesium oxides may be used as stabilizers.

The platinum group metal catalyst component of the catalytic partial oxidation catalyst includes palladium and platinum, and optionally one or more other platinum group metals. As used herein and in the claims, “platinum group metal” means platinum, palladium, rhodium, iridium, osmium, and ruthenium. Preferred platinum group metal components are palladium and platinum, and optionally rhodium. The catalyst desired for partial oxidation should have at least one or more of the following properties. They should also be able to operate effectively under conditions that change from oxidation at the inlet to reduction at the outlet; they effectively range from about 427 ° C to 1315 ° C. They should operate without significant thermal decomposition at;); they should operate effectively in the presence of carbon monoxide, olefins, and sulfur compounds; they are carbon with H ₂ O Should provide a low level of coking, such as by preferentially catalyzing the reaction of, forming carbon monoxide and hydrogen, thereby allowing only low levels of carbon on the catalyst surface; Should resist poisoning from such common poisons as sulfur and halogen compounds. For example, in some otherwise suitable catalysts, carbon monoxide can be maintained by the catalytic metal at low temperatures, thereby reducing or modifying its activity. The combination of platinum and palladium is a very efficient oxidation catalyst for the purposes of the present invention. In general, the catalytic activity of platinum-palladium combination catalysts is not simply an arithmetic combination of their respective catalytic activities; the disclosed ranges of platinum and palladium ratios provide excellent resistance to high temperature operation and catalyst poisoning. It has been discovered that it provides efficient and effective catalytic activity in treating a fairly wide range of hydrocarbon feeds it has.

Rhodium can optionally be included with platinum and palladium. Under certain conditions, rhodium is an effective oxidation and steam reforming catalyst, especially for light olefins. The combined platinum group metal catalyst can catalyze autothermal reactions at a fairly low ratio of H ₂ O to carbon (carbon atoms in the feed) and oxygen to carbon without significant carbon deposition on the catalyst. it can. This property provides flexibility in selecting the ratio of H ₂ O to C and O ₂ to C in the inlet stream to be processed.

  The platinum group metal used in the catalyst of the embodiment of the present invention includes any other platinum group metal or metal, or a compound such as an oxide of a platinum group metal, elemental metal, alloy, intermetallic compound, etc. Any suitable formation of can also be present in the catalyst composition. As used in the claims, the terms palladium, platinum, and / or rhodium “catalytic component” or “catalytic component” include the specified platinum group metals or metals present in any suitable formation. Intended. In general, references to a platinum group metal or metal catalyst component or component in the claims and herein include one or more platinum group metals in any suitable catalyst formation. Suitable CPO catalysts are described in US Pat. No. 4,522,894, which is hereby incorporated by reference in its entirety.

HC-SCR catalysts comprising silver on an HC-SCR catalyst alumina support are generally useful for the exhaust treatment system of the present invention. In a detailed embodiment, the catalyst contains a “well-dispersed” silver species on the surface of alumina. In a specific embodiment, the catalyst is substantially free of metallic silver and / or silver aluminum.

The catalyst can be prepared by impregnation of ionic silver and an alumina support. The alumina support can be any suitable alumina including, but not limited to, boehmite pseudoboehmite, diaspore, nodal strand stone, bayerite, gibbsite, hydroxide hydroxide, calcined alumina, and combinations thereof. Exemplary silver-alumina catalysts on supported Ag ₂ O basis for over alumina, including silver about 3-4 weight percent (wt%). In one embodiment, the catalyst is prepared by placing ionic silver over highly hydroxylated alumina. As used herein, the term “hydroxylation” means that in the state it is obtained, the surface of the alumina has a high concentration of surface hydroxyl groups in the alumina, eg, added to the surface. Boehmite having a hydroxyl group, pseudoboehmite, or gelatinous boehmite, diaspore, nodal strand stone, bayerite, gibbsite, alumina, and combinations thereof. Pseudoboehmite and gelatinous boehmite are generally classified as amorphous or gelatinous materials, although diaspore, nodal strand stone, bayerite, gibbsite, and boehmite are generally classified as crystalline. In accordance with one or more embodiments of the invention, the alumina hydroxide is represented by the formula Al (OH) _x O _y , where x = 3-2y and y = 0-1 or ratio thereof. In their preparation, such alumina is not subject to high temperature firing and can eliminate many or most surface hydroxyl groups. In an alternative embodiment, the alumina may be of the type that is the subject of high temperature firing, providing gamma, delta, theta, and alpha alumina, and combinations thereof.

  Impregnation of alumina with water-soluble, ionic form of silver such as silver acetate, silver nitrate, etc., then ionic silver permeable alumina, enough to fix silver and decompose anion (if possible) Dry and fire at low temperature. Typically for nitrate, this is about 450 to 550 Celsius to provide alumina that is substantially free of silver particles greater than about 20 nm in diameter. In some embodiments, the diameter of silver is less than 10 nm, and in other embodiments, the silver is less than about 2 nm in diameter. In one or more embodiments, the processing is performed such that the silver is present substantially in ionic form and is determined by ultraviolet spectroscopy to be substantially free of metallic silver. In one or more embodiments, substantially no silver aluminum is present. The absence of metallic silver and silver aluminum can be confirmed by X-ray diffraction analysis. In the presence of small amounts of hydrogen and suitable hydrocarbon fuel species, the catalyst can still function when placed with carbonaceous and sulfur species.

The DOC-catalyzed oxidation catalyst can be formed from any composition that provides effective combustion of unburned gaseous and non-volatile hydrocarbons (ie, VOF) and carbon monoxide. In addition, the oxidation catalyst, a NO significant fraction of the NOx component, should be effective to convert NO _2. As used herein, the term “substantial conversion of NOx component NO to NO ₂ ” means at least 20%, specifically 30-60%. Catalyst compositions having these properties are known in the art and include platinum group metal and base metal based compositions. The catalyst composition can be coated on a honeycomb flow-through monolith substrate formed from a refractory metal or ceramic (eg, cordierite) material. Alternatively, the oxidation catalyst may be formed on a metal or ceramic foam substrate that is well known in the art. These oxidation catalysts provide some degree of particle removal due to the properties of the substrate on which they are coated (eg, open cell foam) and / or due to their inherent oxidation catalytic activity properties. The oxidation catalyst may remove some particulate matter from the exhaust stream upstream of the wall flow filter, because the reduction of the particle mass on the filter potentially extends time prior to forced regeneration.

One specific oxidation catalyst composition that can be used in an exhaust treatment system is a platinum group dispersed on a refractory oxide support (eg, gamma alumina) combined with a high surface area, zeolite component (eg, beta zeolite). Contains components (eg, platinum, palladium, or rhodium components). Specific platinum group metal components include platinum and palladium. When the composition is disposed on a refractory oxide substrate, such as a flow-through honeycomb substrate, the platinum group metal concentration is typically about 10 to 150 g / ft ³ . In specific embodiments, the platinum group metal is typically about 20 g / ft ³ to about 130 g / ft ³ , or about 30 g / ft ³ to about 120 g / ft ³ , or about 40 g / ft ³ to about 110 g / ft. ³ or in the range of about 50 g / ft ³ to about 100 g / ft ³ .
In other detailed embodiments, the platinum group metal comprises about 10 g / ft ³ , about 20 g / ft ³ , about 30 g / ft ³ , about 40 g / ft ³ , about 50 g / ft ³ , about 60 g / ft ³ , about It is present in concentrations greater than 70 g / ft ³ , about 80 g / ft ³ , about 90 g / ft ³ , about 100 g / ft ³ , about 110 g / ft ³ or about 120 g / ft ³ . In still other detailed embodiments, the platinum group metal is about 120 g / ft ³ , about 110 g / ft ³ , about 100 g / ft ³ , about 90 g / ft ³ , about 80 g / ft ³ , about 70 g / ft ³ , It is present at a concentration of less than about 60 g / ft ³ , about 50 g / ft ³ , about 40 g / ft ³ , or about 30 g / ft ³ . In a more detailed embodiment, the platinum group metal concentration range is between any combination of the minimum and maximum concentrations listed above.

  Platinum group metal-based compositions that are suitable for use in the formation of oxidation catalysts are also described in US Pat. No. 5,100,632 (the '632 patent), incorporated herein by reference. . The '632 patent states that magnesium oxide, calcium oxidation, wherein the atomic ratio of platinum group metal to alkaline earth metal is about 1: 250 to about 1: 1, specifically about 1:60 to about 1: 6. A composition having platinum, palladium, rhodium, and ruthenium such as strontium oxide or barium oxide, and an alkaline earth metal oxide gold-copper bud is described.

A catalyst composition suitable for an oxidation catalyst can also be formed using a base metal as a catalyst agent. For example, US Pat. No. 5,491,120 (the disclosure of which is incorporated herein by reference) includes a catalytic material having a BET surface area of at least about 10 m ² / g, and essentially comprises one or more Disclosed is an oxidation catalyst composition comprising a bulk second metal oxide that can be titania, zirconia, ceria zirconia, silica, alumina silica, and alpha-alumina.

Also useful are the catalyst compositions disclosed in US Pat. No. 5,462,907 (the '907 patent, the disclosure of which is incorporated herein by reference). The '907 patent describes ceria and alumina each having a surface area of at least about 10 m ² / g, for example, a catalyst material containing ceria and activated alumina in a weight ratio of about 1.5: 1 to 1: 1.5. A composition comprising is taught. Optionally, platinum is effective in promoting gas phase oxidation of CO and unburned hydrocarbons, but in an amount limited to prevent over oxidation of SO ₂ to SO ₃ in the '907 patent. In the composition described in. Alternatively, any desired amount of palladium can be included in the catalyst material.

In one embodiment of the NH ₃ -SCR catalyst present invention, the system, downstream of the HC-SCR catalyst may further comprise NH ₃ -SCR catalyst. The NH ₃ -SCR catalyst can also prevent any NH ₃ produced in the system from being released to the environment. Suitable NH ₃ -SCR catalyst useful in urea SCR applications, can be any of SCR catalysts known. CHAX ray crystal structure (e.g., Cu-CHA, Cu-SAPO ) comprising a molecular sieve having a is an advantage in that the NH ₃ -SCR catalyst is used. These molecular sieves having a CHA structure exhibiting excellent hydrothermal stability and durability are particularly useful in the present invention.

Gasoline lean-burn engine The above-described embodiments relate to a diesel engine having a DOC and DPF downstream of the diesel engine, although the system according to one or more embodiments of the present invention can be used in a gasoline lean-burn engine. Will be understood. Thus, an exemplary system comprises a lean combustion engine that includes a system of the type shown in FIG. 1 and is in fluid communication with component 22, which is a suitable catalyst for oxidizing carbon monoxide and hydrocarbons. It can be a catalyst. An example of a suitable catalyst for a gasoline engine is a three way catalyst (TWC). A TWC catalyst that exhibits excellent activity and long life span is one or more platinum group metals (eg, platinum or palladium, rhodium, ruthenium, etc.) placed on a high surface area, refractory oxide support, eg, a high surface area alumina coating. , And iridium).

Hydrogen Source In some alternative embodiments, hydrogen may be generated by an external source or hydrogen production. Suitable hydrogen sources include, but are not limited to, electrolyzers, plasma reformers, pyrolyzers, steam reformers, compressed gas containers, and liquefied gas containers.

  Electrolyzers such as proton exchange membranes (PEM) can be used to produce hydrogen that is mounted on automobiles. The PEM splits water into hydrogen and oxygen molecules that can then be compressed and injected into the exhaust. PEM systems require a small amount of water to be maintained in the system.

  Plasma reforming converts gaseous hydrocarbons to hydrogen, such as gasoline, diesel fuel, methane, ethane and the like. The reaction chamber is saturated with sufficient fuel and air and a plasma is ignited. Plasma based reactions result in hydrogen evolution. Hydrogen release can be optimized using catalyst components.

  The pyrolysis device decomposes or pyrolyzes the fuel, yielding hydrogen and carbon oxide species. Pyrolysis generally requires high temperatures for efficient conversion.

  A steam reformer can produce hydrogen by reacting fuel with water. The reaction is exothermic and results in an increased reaction rate. Similar to electrolysis, this type of hydrogen injector requires a small on-board water source.

In order to account for the drop in hydrogen present in the exhaust, separate experiments were performed in a laboratory scale reactor with engine aged HC-SCR catalyst samples. Simulated diesel exhaust containing 450 ppm carbon C1 (as diesel), 150 ppm NO, 5% CO ₂ , 5% H ₂ O, 10% O ₂ balance N ₂ at 30,000 hr ⁻¹ , engine It was introduced into the core sample taken from the inlet portion of the aged HC-SCR catalyst sample. Evaluation was performed using the lower slope of the catalyst inlet temperature from 500 ° C to 260 ° C. The HC-SCR catalyst sample was silver containing a monolith catalyst. A 1M solution of silver nitric acid was prepared using deionized water. The resulting solution was stored in a dark bottle away from the light source. The available pore volume of the various supports was determined by mixing the bare supports with water while mixing until initial moisture was achieved. This resulted in a liquid volume per gram of support. Using the final target Ag ₂ O level and the volume per gram of support that was available, the amount of IM AgNO ₃ solution required was calculated. If necessary, DI water was added to the silver solution so that the total volume of liquid was equal to the amount required to impregnate the support sample to the initial moisture. If the amount of AgNO ₃ solution required exceeded the pore volume of the support, then multiple impregnations were performed.

The appropriate AgNO ₃ solution was slowly added to the support with mixing. After initial moisture was achieved, the resulting solid was dried at 90 ° C. for 16 hours and then calcined at 540 ° C. for 2 hours. The catalyst was also optionally exposed to a flowing stream of about 10% flow in air at least typically at about 650 ° C. for about 16 hours.

The catalyst was prepared as described above using commercially available pseudoboehmite (Catapal.RTM.C1, 270 m ^{2 /} g produced by Sasol, pore volume of 0.41 cc / g, average pore diameter of 6.1 nm. North America) and boehmite (P200 (from Sasol), 100 m ^{2 /} g, 0.47 cc / g pore volume, 17.9 nm average pore diameter) alumina support. Each alumina was processed until the silver content of the finished catalyst was about 3% by weight on an Ag ₂ O basis. A monolith with about 300 cells per square inch is washcoated with alumina, resulting in a fill of about 2 g / in ³ . The HC-SCR catalyst was placed in front of the DOC / DPF in steric configuration in the engine exhaust system and aged on the engine for 50 hours. During aging, a number of fuel combustion cycles were used to simulate DOC / DPF regeneration.

The result of the NOx conversion is shown in FIG. Without any treatment, as-received engine aged samples show about 20% NOx conversion in all temperature ranges evaluated. The catalyst has NOx conversion better than 10% at 500 ° C., NOx conversion better than 20% at 400 ° C., and NOx conversion better than 50% at 300 ° C. when 1000 ppm of H ₂ is introduced into the simulated exhaust. Indicates. The presence of hydrogen in the exhaust greatly enhances the NOx performance of highly deactivated catalysts.

  Although the present invention has been described with an emphasis on preferred embodiments, variations on the preferred devices and methods may be used and the invention may be different from those specifically described herein. However, it will be apparent to those skilled in the art that it is intended to be practiced. Accordingly, this invention includes all modifications encompassed within the spirit and scope of the invention as defined by the scope of the following claims.

Claims (14)

An exhaust treatment system for reducing NOx in an exhaust stream from a lean combustion engine,
A main exhaust pipe in fluid communication with the engine exhaust stream; a hydrocarbon selective catalytic reduction catalyst (HC-SCR) in fluid communication with the main exhaust pipe;
A slip exhaust flow pipe connected to the main exhaust pipe for providing a slip exhaust flow through a catalytic partial oxidation (CPO) catalyst in fluid communication with the slip exhaust flow pipe. A first joint for diverting part of the exhaust flow from the pipe into the slip exhaust flow pipe, and for reintroducing the slip exhaust flow into the main exhaust pipe upstream of the HC-SCR A slip exhaust flow pipe branched from the main exhaust pipe by a second joint downstream of the first joint;
A hydrocarbon injector upstream of the CPO catalyst, the CPO catalyst comprising a hydrocarbon injector effective to convert a portion of the hydrocarbons to carbon monoxide and hydrogen. System.   The exhaust treatment system of claim 1, wherein the CPO catalyst is designed to provide sufficient hydrogen and an appropriate amount of hydrocarbons to the downstream HC-SCR catalyst.   The exhaust treatment system of claim 1, wherein the hydrocarbon injection device includes a metering device adapted to control the amount of hydrocarbon injected into the slip exhaust flow tube.   The exhaust treatment system of claim 1, further comprising a metering device for adjusting a percentage of exhaust gas that diverts to the slip exhaust flow pipe at the first junction of the slip exhaust flow pipe.   The exhaust treatment system according to claim 1, wherein the CPO catalyst contains a platinum group metal selected from platinum, palladium, rhodium, and mixtures thereof.   The exhaust treatment system according to claim 1, further comprising a diesel particulate filter (DPF) upstream or downstream of the HC-SCR catalyst.   The exhaust treatment system according to claim 6, wherein the diesel particulate filter (DPF) is installed between the first joint and the second joint that are in fluid communication with the main exhaust pipe.   The exhaust treatment system according to claim 6 or 7, further comprising a diesel oxidation catalyst (DOC) upstream of the DPF and the HC-SCR catalyst.   The exhaust treatment system of claim 8, wherein the diesel oxidation catalyst (DOC) is installed downstream of the first joint in fluid communication with the main exhaust pipe.   The emission processing system of claim 9, wherein the DOC and DPF are integrated into a single component.   The exhaust treatment system according to claim 1, further comprising an NH3-SCR catalyst downstream of the HC-SCR catalyst.   The exhaust treatment system according to claim 1, further comprising an oxidation catalyst downstream of the HC-SCR catalyst. A method of treating exhaust flow,
Passing the exhaust stream through a main exhaust pipe and passing a portion of the exhaust stream through a slip exhaust flow pipe, the main exhaust pipe comprising a hydrocarbon selective catalytic reduction catalyst (HC-SCR); The slip exhaust flow pipe comprises a catalytic partial oxidation (CPO) catalyst, the slip exhaust flow pipe branches from the main exhaust pipe at a first junction and is in fluid communication with the CPO catalyst; A slip exhaust flow pipe is rejoined to the main exhaust pipe at a second joint upstream of the HC-SCR, a hydrocarbon injector is upstream of the CPO catalyst, and the CPO catalyst is the hydrocarbon Characterized in that it is adapted to convert a portion of the carbon to carbon monoxide and hydrogen.   A method of treating an exhaust stream, comprising passing the exhaust stream through a system according to any of claims 2-12.

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