KR20120041162A - 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 is described in which a hydrocarbon is converted over a partial oxidation catalyst in an exit stream and comprises a hydrocarbon selective catalytic reduction catalyst. The emission treatment system is advantageously used for the treatment of exhaust streams from lean combustion engines, including diesel engines, lean burn gasoline engines and locomotive engines.

Description

HC-SC system for lean burn engine {HC-SCR SYSTEM FOR LEAN BURN ENGINES}

[Cross-Reference to Related Applications]

This application claims U.S. Provisional Application No. 61 / 166,047, filed April 2, 2009, under 35 USC §119 (e), U.S. Provisional Application No. 61 / 166,603, filed April 2, 2009 and April 16, 2009. It claims the benefit of priority to US Provisional Application No. 61 / 169,932, which is incorporated by reference, which is incorporated herein by reference.

[Technical Field]

The present invention relates to emissions treatment systems and methods useful for reducing contaminants in an exhaust stream. In particular, embodiments of the present invention relate to an emission treatment system for reducing NOx, and a method of use, wherein the system includes converting hydrocarbons on a partial oxidation catalyst to produce hydrogen and exhaust stream fractionation.

The operation of lean burn engines, such as diesel engines, lean burn gasoline engines and locomotive engines, provides excellent fuel economy due to their high air / fuel ratio operation under fuel lean conditions, resulting in very low gaseous hydrocarbons and carbon monoxide. Indicates the emission of. Diesel engines in particular also offer significant advantages over gasoline engines in terms of their durability and their ability to generate high torque at low speeds. Effective reduction of NOx in lean combustion engines is difficult to achieve because the NOx conversion rate is very low under fuel lean conditions. Thus, in operation under fuel lean conditions, the conversion of NOx components into harmless components in the exhaust stream generally requires specialized NOx abatement strategies.

One such strategy for the reduction of NOx in exhaust streams from lean combustion engines uses NOx storage reduction (NSR) catalysts, also well known in the art as "lean NOx traps (LNT)". LNT catalysts contain NOx adsorbent materials that can adsorb or "capture" oxides of nitrogen under lean conditions, and platinum group metal components that provide oxidation and reduction functions to the catalyst. In operation, the LNT catalyst promotes a series of basic steps described in Schemes 1-5 below. In an oxidizing environment, NO is oxidized to NO ₂ (Scheme 1), which is an important step in NOx occlusion. At low temperatures, such reactions are typically catalyzed by platinum group metal components, such as platinum components. The oxidation process is not stopped here. Further oxidation of NO ₂ to nitrate by introduction of atomic oxygen is also a catalytic reaction (Scheme 2). In the absence of the platinum group metal component, little nitrate is formed even if NO ₂ is used as the NOx source. The platinum group metal component has a dual function of oxidation and reduction. In its reducing role, the platinum group metal component first catalyzes the release of NOx upon introduction of a reducing agent such as CO (carbon monoxide), H ₂ (hydrogen) or HC (hydrocarbon) into the exhaust gas (Scheme 3). This step can restore some NOx occlusion sites, but causes limited reduction of the NOx species. The released NOx is then further reduced to gas N ₂ in a rich environment (Scheme 4 and 5). NOx emissions can be induced by fuel injection even in pure oxidizing environments. However, efficient reduction of the released NO x by H ₂ , CO or HC requires global net enrichment conditions. Since metal nitrate is less stable at high temperatures, temperature spikes can also cause NOx emissions. NOx trap catalysis is a cyclic operation. During lean / rich operation, metal compounds are believed to undergo carbonate / nitrate conversion as the main route.

Oxidation of NO to NO ₂

(1)

(One)

NOx occlusion as nitrate

(2)

(2)

NOx emission

(3)

(3)

NOx reduction to N ₂

(4)

(4)

(5)

(5)

In Schemes 2 and 3, M represents a divalent metal cation. M may be a monovalent or trivalent metal compound, in which case the reaction scheme must be readjusted.

It has been observed that ammonia (NH ₃ ) may form as a by-product of rich pulse regeneration of NSR catalysts, while the reduction of NO and NO ₂ to N ₂ takes place in the presence of the NSR catalyst in the enrichment period. . For example, the reduction of NO can proceed according to Schemes 6 and 7.

Reduction of NO to NH ₃

(6)

(6)

(7)

(7)

This property of NSR catalysts requires that NH ₃ , which itself is a hazardous component, is now converted to a harmless species before exhaust gases are released to the atmosphere.

Alternative NOx abatement strategies, including the treatment of lean combustion engine exhaust gases, with the development of automotive applications use selective catalytic reduction (SCR) catalyst technology. The strategy has proven to be effective when applied to stagnant materials, for example in the treatment of flue gases. In this strategy, NOx is reduced to nitrogen (N ₂ ) by a reducing agent such as NH ₃ , typically on an SCR catalyst consisting of a base metal. Such techniques can achieve NOx reduction in excess of 90%, thus representing one of the best approaches to achieving aggressive NOx reduction targets.

Ammonia is one of the most effective NOx reducing agents in lean conditions using SCR technology. One of the approaches investigated to reduce NOx in diesel engines (most large diesel vehicles) uses urea as a reducing agent. The elements that produce ammonia upon hydrolysis are injected into the exhaust gas in the temperature range of 200-600 ° C. in front of the SCR catalyst. One of the major drawbacks of this technique is the need for a separate large container for accommodating the elements in the vehicle. Another serious concern is the duty of the vehicle driver to replenish the container when needed, and the need for infrastructure to supply the driver to the driver. Thus, a less burdensome alternative technique is to utilize fuel in the vehicle as a reducing agent for NOx treatment of exhaust gas.

As a potential and alternative method for the removal of NOx under oxygen-rich conditions, selective catalytic reduction of NOx with hydrocarbons (HC-SCR) has been extensively studied. Ion-exchange base metal zeolite catalysts (such as Cu-ZSM5) are typically not sufficiently active under typical vehicle operating conditions and are susceptible to degradation by sulfur dioxide and water exposure. Catalysts using platinum-group metals (eg, Pt / Al ₂ O ₃ ) operate effectively in a narrow temperature range between 180 ° C. and 220 ° C. and are highly selective for N ₂ O production.

Catalytic apparatus using alumina-supported silver (Ag / Al ₂ O ₃ ) has attracted attention because of its ability to selectively reduce NOx under lean exhaust gas conditions using a wide variety of hydrocarbon species. The use of hydrocarbons and alcohols, aldehydes and functionalized organic compounds on Ag / Al ₂ O ₃ allows the reduction of NOx at temperatures below 450 ° C. In addition to the molecules listed above, diesel fuel may also be used as the reducing agent. Diesel fuel does not require additional tanks for diesel-propelled vehicles. Diesel fuel can be supplied to the exhaust system by changing engine management or by supplying additional diesel fuel injectors to the exhaust train. However, current HC-SCR catalyst systems exhibit insufficient durability. Catalytic coking, caused by fuel cracking and deposition on the catalyst, and sulfur poisoning from fuels and oils causes catalyst performance deterioration within a relatively short period of time of operation. In order to maintain the desired performance, the catalyst must undergo frequent and costly regeneration.

Despite these various alternatives, there are no commercially available practical hydrocarbon SCR catalysts using diesel fuel as reducing agent. Thus, there is a need in the art for systems and methods for providing sustained NOx reducing activity using HC-SCR technology.

SUMMARY OF THE INVENTION [

One or more embodiments of the invention relate to an emission treatment system for NOx reduction in an exhaust stream from a lean combustion engine. One embodiment of the system includes a main exhaust conduit in communication with the engine exhaust stream, and a hydrocarbon selective catalytic reduction catalyst (HC-SCR) in communication with the main exhaust conduit. A slip exhaust stream conduit is branched from the main exhaust conduit and the escape exhaust stream communicates with the escape exhaust stream conduit by diverting a portion of the exhaust stream from the main exhaust conduit to the escape exhaust stream conduit. To a main exhaust conduit by means of a first connection which is circulated to the catalytic partial oxidation (CPO) catalyst. The hydrocarbon injector is located upstream of the CPO catalyst in the exit stream. A second connection downstream of the first connection reintroduces the exiting exhaust stream into the main exhaust conduit upstream of the HC-SCR. The CPO is effective to convert some of the 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 injector device comprises a metering device suitable for controlling the amount of hydrocarbon injected into the exit exhaust stream conduit. The hydrocarbon is a fuel according to one or more embodiments.

In one or more embodiments, the proportion of exhaust gas bypassed to the exit exhaust stream conduit is no greater than about 10% of the total exhaust gas flow rate. One or more embodiments further comprise a metering device for adjusting the percentage of exhaust gas diverted to the escape exhaust stream conduit at the first connection of the escape exhaust stream conduit. In one or more embodiments, the CPO catalyst contains a platinum group metal. Examples of platinum group metals of CPO catalysts include platinum, palladium, rhodium and mixtures thereof.

In one or more embodiments, one or both of the CPO catalyst and HC-SCR are disposed on a flow through monolith. In one or more embodiments, the system comprises a diesel particulate filter (DPF) downstream of the HC-SCR catalyst. In one or more embodiments, the system comprises a diesel particulate filter (DPF) upstream of the HC-SCR catalyst. In at least one embodiment, the diesel particulate filter (DPF) is located between the first connection and the second connection in communication with the main exhaust conduit. In one or more embodiments, the system comprises a diesel oxidation catalyst (DOC) upstream of the DPF and HC-SCR catalyst. In one or more embodiments, the system comprises a diesel oxidation catalyst (DOC) upstream of the DPF and HC-SCR catalyst. In one or more embodiments, the system comprises a diesel oxidation catalyst (DOC) upstream of the DPF and HC-SCR catalyst. In one or more embodiments, the system comprises a diesel oxidation catalyst (DOC), which is located downstream of the first connection in communication with the main exhaust conduit. In one or more embodiments, the system comprises a diesel oxidation catalyst (DOC), which is located downstream of the first connection in communication with the main exhaust conduit. In one or more embodiments, the system comprises a diesel oxidation catalyst (DOC), which is located downstream of the first connection in communication with the main exhaust conduit.

In one or more embodiments, the system comprises a diesel oxidation catalyst (DOC), which is located in communication with the main exhaust conduit downstream of the first connection, upstream of the DPF. In one or more embodiments, the system comprises a DOC and a DPF, which are integrated as a single component. In one or more embodiments, the system comprises an NH ₃ -SCR catalyst downstream of the HC-SCR catalyst. In one or more embodiments, the system comprises an oxidation catalyst downstream of the HC-SCR catalyst.

Another aspect of the invention is directed to a method of treating an exhaust stream. In one method embodiment, the exhaust stream is passed to the main exhaust conduit and a portion of the exhaust stream is passed to the evacuation exhaust stream conduit. The main exhaust conduit comprises a hydrocarbon selective catalytic reduction catalyst (HC-SCR), the escape exhaust stream conduit comprises a catalytic partial oxidation (CPO) catalyst in communication with the escape stream conduit, and a hydrocarbon injector upstream of the CPO. The exiting exhaust stream conduit is branched from the main exhaust conduit at the first connection and in communication with the CPO. The exiting exhaust stream conduit is recombined with the main exhaust conduit at the second connection upstream of the HC-SCR. CPO is suitable for converting some of the hydrocarbons to carbon monoxide and hydrogen in the off-gas stream conduit.

In one or more method embodiments, the amount of hydrocarbon injector entering the exit exhaust stream conduit is controlled by the metering device. In one or more embodiments, the hydrocarbon is in-vehicle fuel. In one or more embodiments, a first percentage of the exhaust stream is passed through the main exhaust conduit and a second percentage of the exhaust stream is passed through the exit exhaust stream conduit, wherein the first percentage is greater than the second percentage. Is bigger. In one or more embodiments, the second percentage of the exhaust stream is controlled by a metering device located in the exit exhaust stream conduit near the first connection. One or more method embodiments further comprise passing an exhaust stream in the main exhaust conduit to a diesel particulate filter located upstream of the HC-SCR catalyst.

One or more method embodiments may include passing an exhaust stream in the main exhaust conduit to a diesel particulate filter located downstream of the HC-SCR catalyst. One or more method embodiments may include passing an exhaust stream in the main exhaust conduit to a diesel particulate filter located downstream of the first connection and upstream of the second connection. One or more method embodiments may include passing an exhaust stream in the main exhaust conduit to a diesel oxidation catalyst located upstream of the diesel particulate filter. One or more method embodiments may include passing an exhaust stream in the main exhaust conduit to a diesel oxidation catalyst located upstream of the diesel particulate filter. One or more method embodiments may include passing an exhaust stream in the main exhaust conduit to a diesel oxidation catalyst located upstream of the diesel particulate filter. One or more method embodiments may include passing an exhaust stream in the main exhaust conduit to a diesel oxidation catalyst located downstream of the first connection. One or more method embodiments may include passing an exhaust stream in the main exhaust conduit to a diesel oxidation catalyst located downstream of the first connection.

One or more method embodiments may include passing an exhaust stream in the main exhaust conduit to a diesel oxidation catalyst located downstream of the first connection. One or more method embodiments may include passing an exhaust stream in the main exhaust conduit to a diesel oxidation catalyst located downstream of the first connection, upstream of the diesel particulate filter. One or more method embodiments may include passing an exhaust stream in the main exhaust conduit to a diesel oxidation catalyst located downstream of the first connection, upstream of the diesel particulate filter. One or more method embodiments may include passing an exhaust stream in the main exhaust conduit to a diesel oxidation catalyst located downstream of the first connection, upstream of the diesel particulate filter.

In one or more method embodiments, the diesel oxidation catalyst and diesel particulate filter are integrated. In one or more method embodiments, the diesel oxidation catalyst and diesel particulate filter are integrated. In one or more embodiments, the method may comprise passing the exhaust stream in the main exhaust conduit to an NH ₃ -SCR catalyst located downstream of the HC-SCR catalyst. One or more method embodiments include passing an exhaust stream in the main exhaust conduit to an oxidation catalyst located downstream of the HC-SCR catalyst.

Various embodiments of the present invention include, in a number of configurations, various components including, but not limited to, diesel oxidation catalysts, catalytic soot filters, HC-selective catalytic reduction catalysts, NH ₃ -selective catalytic reduction catalysts, and oxidation catalysts. can do. The exhaust gas may pass through any of these components in various orders.

1 is a schematic diagram illustrating an engine emissions treatment system in accordance with a detailed embodiment.
2 is a schematic diagram illustrating an engine emissions treatment system according to another embodiment.
3 is a schematic diagram illustrating an integrated engine emissions treatment system according to one embodiment.
4 is an alternative emission treatment system in accordance with one or more embodiments of the present invention.
5 is an alternative emission treatment system in accordance with one or more embodiments of the present invention.
6 is an alternative emission treatment system in accordance with one or more embodiments of the present invention.
7 is an alternative emission treatment system in accordance with one or more embodiments of the present invention.
8 is an alternative emission treatment system in accordance with one or more embodiments of the present invention.
9 is an alternative emission treatment system in accordance with one or more embodiments of the present invention.
10 is an alternative emissions treatment system in accordance with one or more embodiments of the present invention.
11 is an alternative emissions treatment system in accordance with one or more embodiments of the present invention.
12 is an alternative emission treatment system in accordance with one or more embodiments of the present invention.
13 is a perspective view of a wall flow filter substrate.
14 is a cross-sectional view of a portion of a wall flow filter substrate.
15 shows a graph of% NOx conversion as a function of catalyst inlet temperature for HC-SCR under various operating conditions.

Emission treatment systems that can be used to treat exhaust gases from lean combustion engines, and methods of using such systems for treating engine exhaust gases. Lean combustion engines include, but are not limited to, diesel engines, lean burn gasoline engines, and locomotive engines.

The small amount of hydrogen present in lean exhaust gas (typically <2000 ppm) significantly improves the performance of the HC-SCR catalyst and can reverse the damage done to the catalyst through normal operation. Embodiments of the present invention relate to systems and methods capable of providing fuel reducing agents and hydrogen to HC-SCR catalysts. The system includes an escape stream from the main exhaust for producing hydrogen using in-vehicle fuel and catalytic partial oxidation catalyst (CPO) at net reduction conditions. The escape stream containing unconverted fuel species and hydrogen is combined with the main exhaust to provide the desired HC-SCR reaction conditions. Hydrogen may be produced from a hydrocarbon feed by a partial oxidation process in which a portion of the feed reacts with oxygen in the leaving stream under fuel rich conditions.

1 shows a schematic description of one aspect of the invention, which is described in greater detail below. In short, upstream of the HC-SCR catalyst located downstream of the engine, the escape stream (typically 1-10% of the total exhaust gas flow rate exiting the engine) is bypassed. As the leaving stream, a sufficient amount of fuel is introduced to create fuel rich conditions. Downstream of the fuel introduction point of the breakaway stream is a catalytic partial oxidation catalyst as further described below. The escape stream containing unconverted fuel species and hydrogen is combined with the main exhaust gas and introduced into the HC-SCR catalyst. In one embodiment of the present invention, the HC-SCR can be located downstream of the diesel oxidation catalyst and diesel particulate filter device, such that the HC-SCR can be regenerated simultaneously with the regeneration of DOC and DPF devices. The system can optionally be optimized by a bypass flow control valve and a fuel control delivery device to minimize fuel phase losses of the system.

For the purposes of the present application, the following terms will have the respective meanings disclosed below.

"Rare NOx catalyst", "LNC", "hydrocarbon selective catalytic reduction catalyst" and "HC-SCR" may be used interchangeably within this specification. These are different from lean NOx traps (LNTs), which have NOx occlusion and release capabilities.

By "lean gas stream" it is meant a gas stream with λ> 1.0.

The "lean period" refers to an exhaust gas treatment period in which the exhaust gas composition is sparse, that is, λ> 1.0.

"Platinum group metal component" refers to a platinum group metal or one of its oxides.

"Rare earth metal component" refers to one or more oxides of the lanthanide series, as defined in the periodic table of the elements, including lanthanum, cerium, praseodymium, and neodymium.

By "enriched gas stream" is meant a gas stream with λ <1.0.

"Rich period" refers to an exhaust gas treatment period rich in exhaust gas composition, that is, λ <1.0.

"Washcoat" is known in the industry as a thin, adhesive coating of a catalyst or other material applied to a refractory substrate such as a honeycomb penetrating monolithic substrate or a filter substrate that is porous enough to allow passage of a gas stream to be treated therethrough. Has his general meaning.

"Communication" means that the components and / or conduits are connected such that exhaust gas or other fluid can flow between the components and / or conduits.

"Downstream" refers to the position of a component in the exhaust stream further away from the engine than the preceding component. For example, if the diesel particulate filter is referred to downstream from the diesel oxidation catalyst, the exhaust gas from the engine in the exhaust gas conduit is distributed to the diesel oxidation catalyst before being distributed to the diesel particulate filter. Thus, "upstream" refers to a component located closer to the engine with respect to another component.

References to "ammonia-generating components" are the result of their design and configuration driven by the engine-emission emissions and the input of reducing agents (H ₂ , CO and / or HC) via engine management or injection into the exhaust gas. As part of an exhaust system, which supplies ammonia (NH ₃ ). In such components gaseous administration of NH ₃ or other externally supplied sources are excluded. Examples of ammonia-generating components include NOx storage reduction (NSR) catalysts and lean NOx traps (LNT).

1 shows an emission treatment system 2 for reducing NOx in an exhaust stream from a lean combustion engine 4 according to one embodiment. An exhaust stream containing gaseous contaminants (eg unburned hydrocarbons, carbon monoxide, nitrogen oxides) and particulate matter is conveyed through the main exhaust conduit 6 in communication with the lean combustion engine 4. The exhaust stream of the main exhaust conduit 6 is passed to a hydrocarbon selective catalytic reduction catalyst (HC-SCR) 8 in communication with the conduit 6. A departure exhaust stream conduit 10 branches from the main exhaust conduit 6. The escape exhaust stream conduit 10 is connected to the main exhaust conduit 6 by a first connection 12, so that a portion of the exhaust gas stream exits the main exhaust conduit 6. Bypassing to provide a leaving exhaust stream. The escape exhaust stream is circulated to a catalytic partial oxidation (CPO) catalyst 14 in communication with the escape exhaust stream conduit 10. The second connection 16 downstream of the first connection 12 reintroduces the escape exhaust stream from the escape exhaust stream conduit 10 to the main exhaust conduit 6 upstream of the HC-SCR 8. Line 20 runs out of the rear exhaust pipe and the system.

The hydrocarbon feed may be introduced into the escape stream upstream of the CPO catalyst 14 via conduit 18. CPO 14 is effective to convert some of the hydrocarbons to carbon monoxide and hydrogen. CPO 14 according to one or more embodiments is designed to provide sufficient hydrogen to enhance the performance of HC-SCR 8.

In some embodiments, the main exhaust gas conduit 6 includes any additional exhaust system component 22 downstream of the first connection 12. The additional exhaust system component 22 may be, for example, one or more of a diesel oxidation catalyst, a diesel particulate filter, a reducing agent injector and an air injector in communication with the main exhaust conduit. In one particular embodiment, any additional exhaust system component 22, such as at least one of a diesel oxidation catalyst and a diesel particulate filter, is located upstream of the first connection 12 of the main exhaust conduit 6. Can be.

As shown in the embodiment of FIG. 2, the hydrocarbon injector 18 may include a metering device 24 suitable for controlling the amount of hydrocarbon injected into the exit exhaust stream conduit 10. In certain embodiments, the hydrocarbon injected is fuel in the vehicle.

Detailed embodiments of the present invention include a metering device 26 for adjusting the percentage of exhaust gas diverted to the escape exhaust stream conduit 10 at the first connection 12 of the escape exhaust stream conduit 10. . In some embodiments of the invention, the proportion of exhaust gas diverted from the main exhaust conduit 6 to the escape exhaust stream conduit 10 is no greater than about 10% of the total exhaust flow rate. In another detailed embodiment, the proportion of exhaust gas bypassed from the main exhaust conduit 6 ranges from about 0.5% to about 15%, or from about 1% to about 10%. In another detailed embodiment, the proportion of exhaust gas bypassed from the main exhaust conduit 6 is about 15%, 14%, 13%, 12%, 11%, 10%, 9%, 8% of the total exhaust gas flow rate. , 7%, 6%, 5%, 4%, 3% or 2% or less.

In certain embodiments, at least one of the CPO catalyst and HC-SCR is disposed on a flow-through monolith.

As shown in FIG. 2, the emission treatment system of various embodiments includes a diesel particulate filter (DPF) located between a first connection 12 and a second connection 16 in communication with the main exhaust conduit 6. 28) additionally. In another embodiment, a diesel oxidation catalyst (DOC) 30 is located in communication with the main exhaust conduit 6 downstream of the first connection 12, upstream of the DPF 28.

In alternative embodiments shown in FIGS. 3 and 4, DOC 30 and DPF 28 are integrated into a single component or substrate 32. For example, DOC 30 and DPF 28 are formed of one substrate 32 in which DOC 30 is disposed upstream of substrate 32 and CSF 28 is disposed downstream of substrate 32. May be arranged in a separate zone.

A further embodiment of the present invention is directed to a method of treating an exhaust stream from a lean combustion engine. 1, 2 and 4, the exhaust stream is passed through the main exhaust conduit 6, with some of the exhaust stream passing through the exit exhaust stream conduit 10. The main exhaust conduit 6 comprises a hydrocarbon selective catalytic reduction catalyst (HC-SCR) 8. The escape exhaust stream conduit 10 comprises a catalytic partial oxidation (CPO) catalyst 14, wherein hydrocarbons are injected into the escape exhaust stream conduit 10 using a hydrocarbon injector 18 upstream of the CPO 14. Can be. Breakaway exhaust stream conduit 10 is branched from main exhaust conduit 6 at first connection 12 and in communication with CPO 14. The exiting exhaust stream conduit 10 is recombined to the main exhaust conduit 6 at the second connection 16. The second connector 16 is located upstream of the HC-SCR 8. CPO 14 is suitable for converting hydrocarbons in the off-gas stream conduit 10 to carbon monoxide and hydrogen.

The amount of hydrocarbon injected into the exit exhaust stream conduit 10 can be controlled by the metering device 24. In a specific embodiment, the hydrocarbon is in-vehicle fuel.

According to one or more embodiments of the present invention, a first percentage of the exhaust stream is passed through the main exhaust conduit (6), and a second percentage of the exhaust stream is passed through the exiting exhaust stream conduit (10), where The first percentage is greater than the second percentage. In some embodiments, said second percentage of exhaust stream is controlled by a metering device 26 located in the exit exhaust stream conduit 10 near the first connection 12.

In addition, various embodiments of the present invention allow the exhaust gas stream in the main exhaust conduit 6 to pass through a diesel particulate filter 28 located downstream of the first connection 12 and upstream of the second connection 16. It includes. In another embodiment, the exhaust stream in the main exhaust conduit 6 is passed to a diesel oxidation catalyst 30 located downstream of the first connection 12, 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.

The CPO 14, DOC 30, DPF 28 as well as any component 22 can be made from a composition well known in the art and can be used as a catalyst for non-metal (eg ceria) and / or platinum group metals. It may include. In the upstream position, the DOC and / or particulate filter provide several advantageous functions. The catalyst serves to oxidize unburned gaseous and non-volatile hydrocarbons (ie, soluble organic fractions in diesel particulate material) and carbon monoxide to carbon dioxide and water. Removal of a substantial portion of the SOF helps to prevent too much deposition of particulate material, especially on HC-SCR 8. In certain embodiments, the platinum group metal is selected from the group consisting of platinum, palladium, rhodium, and combinations thereof.

In certain embodiments of the present invention, at least one of DOC 30, DPF 28, and optional component 22 is coated on a soot filter, such as a wall flow filter, to provide particulate material in the exhaust stream. , In particular, helps to remove soot fractions (or carbonaceous fractions) in particulate matter. DOC lowers the temperature at which the soot fraction is oxidized to CO ₂ and H ₂ O, in addition to the other oxidation functions mentioned above. Since soot accumulates on the filter, the catalyst coating assists in the regeneration of the filter. As shown in FIG. 5, DPF 28 may be located downstream of HC-SCR 8 to convert CO and unconverted fuel species. 6 shows another alternative embodiment in which the DPF 28 is located upstream of the first connection 12 to minimize or prevent the deposition of downstream HC-SCR by particulate matter. 7 shows an alternative embodiment where DOC 30 is located upstream of first connection 12 and HC-SCR 8 and DPF 28 are located downstream of second connection. 8 shows an alternative embodiment where DOC 30 and DPF 28 are located upstream of the first connection. In another alternative embodiment, as shown in FIG. 9, the system further comprises an NH ₃ -SCR catalyst for converting any NH ₃ emissions produced in the system downstream of the HC-SCR. In another particular embodiment shown in FIG. 10, the system further includes an oxidation catalyst for oxidizing CO and any unconverted fuel species downstream of the HC-SCR. 11 shows an alternative embodiment of an emission treatment system comprising an ammonia oxidation (AMOX) catalyst 36 located downstream of the HC-SCR 8 catalyst. The ammonia oxidation catalyst 36 may be useful for removing or reducing residual ammonia, which may also be referred to as leaving ammonia through the system.

FIG. 12 shows an alternative embodiment where the hydrogen source 38 is an out-of-line source or component other than a CPO catalyst. The hydrogen source 38 as shown herein can include a metering device 40 capable of controlling the amount of hydrogen injected into the main exhaust conduit 6. The out-of-line H ₂ source (and HC reducing agent) may comprise the product of the CPO reaction (partial oxidation of the fuel with oxygen) as described above.

Various optional components 22 can be included in the exhaust conduit 6. This optional component 22 can be located upstream of the hydrogen injector 38, downstream of the hydrogen injector 38, or downstream of the HC-SCR catalyst 8. It is also contemplated that any component is located in the hydrogen injector 38 prior to the connection with the main exhaust conduit 6. The alternative embodiments shown are merely representative of various ways in which the invention may be practiced and should not be taken as limiting. The components may be arranged in other configurations while falling within the scope of the present invention.

As will be appreciated by those skilled in the art, a variety of metering devices can also be connected to the controller. The control device may include, among other components, a sensor and a processor in particular. The sensor may be suitable for measuring the components of the gaseous composition and may be located at various locations within the exhaust conduit. The processor can evaluate the data from the sensors and adjust the metering devices to optimize the function of the various catalyst components.

Optional components 22 for use with the various embodiments of the present invention are, for example, diesel oxidation catalysts, diesel particulate filters, reducing agent injectors, air injectors, ammonia oxidation catalysts, ammonia selective catalysts in communication with the main exhaust conduit. It may be at least one of the reduction catalysts. In addition, any component 22 may be a combination of integrated components, including but not limited to those shown in FIG. 3.

Equipment ( substrate)

In a detailed embodiment, any or all of the catalysts, including HC-SCR (8), CPO (14), and DOC (30), are disposed on a substrate. The substrate can be any material typically used to make catalysts and will typically include ceramic or metal honeycomb structures, for example through-hole monoliths. Any suitable substrate, such as a monolithic substrate (referred to as a honeycomb flowable substrate) of the type having fine parallel parallel airflow passages extending therethrough from the inlet or outlet side of the substrate such that the passage is open to fluid flow therethrough. Can be used. The passageway, which is an essentially straight path from the fluid inlet to the fluid outlet, is defined by a wall coated with the catalyst material with the washcoat so that the gas flowing into the passage is in contact with the catalyst material. The flow passage of the monolithic substrate is a thin-walled channel and may be of any suitable cross-sectional shape and size, such as trapezoidal, rectangular, square, sinusoidal, hexagonal, elliptical, circular, and the like. Such structures may include from about 60 to about 600 or more gas inlet holes (ie, cells) per square inch of cross section.

13 and 14 illustrate a wall flow filter substrate 50 having a number of alternating blocked channels 52 and capable of functioning as a particulate filter. The passages are tubularly surrounded by the inner wall 53 of the filter substrate. The substrate has an inlet end 54 and an outlet end 56. The alternating passageways are blocked by inlet plugs 58 at the inlet end 54 and outlet plugs at the outlet end 56 to form opposing checkerboard patterns at the inlet 54 and the outlet 56. The gas stream enters through the unobstructed channel inlet 60 and is stopped by the outlet plug, thereby diffusing to the outlet side through the channel wall 53 (porous). Due to the inlet plug 58, gas cannot pass back to the inlet side of the wall. If such a substrate is used, such a system will be able to remove particulate matter along with gaseous contaminants.

Wall-flow filter substrates are ceramic-type materials such as cordierite, α-alumina, silicon carbide, aluminum titanate, silicon nitride, zirconia, mullite, spodumene, alumina-silica-magnesia or zirconium silicate, or porous refractory metals. Can be done. The wall flow substrate may be formed of a ceramic fiber composite material. Certain wall flow substrates are formed from cordierite, silicon carbide, and aluminum titanate. Such materials can withstand the environments encountered, particularly high temperatures, in the treatment of exhaust streams.

Wall flow substrates for use in the systems of the present invention may include a honeycomb (mono) of thin porous walls through which a fluid stream passes without causing back pressure or too large an increase in pressure across the object. The ceramic wall flow substrate used in the system may be formed of a material having a porosity of at least 40% (such as 40 to 75%) and an average pore size of at least 10 micrometers (such as 10 to 30 micrometers).

In certain embodiments where additional functionality is applied to the filters (DOC 30, DPF 28, and any component 22), the substrate may have a porosity of at least 59%, with an average between 10 and 20 micrometers. It may have a pore size. When a substrate having such porosity and this average pore size is coated using the following technique, an appropriate level of the desired catalyst composition may be supported on the substrate. In spite of the catalyst loading, such substrates can maintain proper exhaust gas flow characteristics, i.e., acceptable back pressure. With regard to the disclosure of suitable wall flow substrates, US Pat. No. 4,329,162 is incorporated herein by reference.

Conventional wall flow filters commercially available are typically formed with low wall porosities, such as from about 42% to 50%. In general, the pore size distribution of commercial wall flow filters is typically very wide at average pore sizes of less than 25 micrometers.

Porous wall flow filters may be catalyzed in that the walls of the component have or contain therein one or more catalytic materials. The catalytic material may be present only at the inlet side, only at the outlet side, at both the inlet and outlet sides of the component walls, or the wall itself may be composed entirely or partly of the catalytic material. The present invention includes the use of a combination of one or more washcoats of catalyst material and one or more washcoats of catalyst material on the inlet and / or outlet walls of the components. The filter may be coated by any of a variety of means well known in the art.

Substrates useful in the catalysts of the invention may be metallic in nature and may consist of one or more metals or metal alloys. The metallic substrate can be used in various shapes such as corrugated sheet or monolithic form. Suitable metallic supports include heat resistant metals and metal alloys such as titanium and stainless steel, as well as other alloys in which iron is a substantial or major component. Such alloys may contain one or more of nickel, chromium and / or aluminum and the total amount of these metals is advantageously 10-25% by weight of chromium, 3-8% by weight of aluminum and up to 20% by weight. Like nickel, it may account for at least 15% by weight of the alloy. The alloy may also contain small or minor amounts of one or more other metals such as manganese, copper, vanadium, titanium, and the like. In order to improve the resistance of the alloy to corrosion by forming an oxide layer on the substrate surface, the surface or metal substrate may be oxidized at high temperatures, such as at least 1000 ° C. Such hot-induced oxidation can enhance the adhesion of the refractory metal oxide support and the catalyst promoting metal component to the substrate.

In alternative embodiments, one or all of the HC-SCR (8), CPO (14), DOC (30), DPF (28) and any component (22) may be deposited on a continuous foamed foam substrate. Can be. Such substrates are well known in the art and are typically formed of refractory ceramic or metal materials.

CPO  catalyst

The principle of the CPO catalyst is that the fuel reacts with oxygen to yield carbon monoxide and hydrogen according to Scheme 8 below.

(8)

(8)

The catalytic partial oxidation reaction prevails when sufficient high temperature and limited contact time (high space velocity) of the reactive gas with the catalyst are provided. In a specific embodiment, the CPO 14 catalyst contains platinum and palladium. In certain embodiments, the platinum group metal loading is in the range of about 20 g / ft ³ to about 200 g / ft ³ . In another particular embodiment, the platinum to palladium metal ratio in the CPO ranges from about 1: 9 to about 9: 1. In one or more embodiments, the CPO is operated between 600 ° C. and 700 ° C. at a space velocity greater than 100,000 hours ⁻¹ (sometimes> 250,000 hours ⁻¹ ). The platinum to palladium metal ratio of the specific embodiments can be from about 1: 5 to about 5: 1, or from about 1: 4 to about 4: 1, or from about 1: 3 to about 3: 1, or from about 1: 2 to about 2 : 1, or about 1: 1.

In certain embodiments, the CPO comprises a suitable high surface area refractory metal oxide support layer, which is deposited on a substrate as described above to serve as a support onto which finely dispersed catalytic metals can diffuse. In certain embodiments, high surface area refractory metal oxide supports, such as alumina support materials, also referred to as "gamma alumina" or "active alumina," may be used, typically 60 square meters per gram ("m ² / g"). Excess, often up to about 200 m ² / g or more. Such activated aluminas are usually a mixture of gamma and delta phases of alumina, but may also contain net, eta, kappa and theta alumina phases. Refractory metal oxides other than activated alumina may be used as a support for at least some of the catalyst components of a given catalyst. For example, bulk ceria, zirconia, alpha alumina, and other materials are known for such use. Although many of these materials have the disadvantage of having a significantly lower BET surface area compared to activated alumina, such disadvantages tend to be counteracted by greater durability or improved performance of the resulting catalyst. "BET surface area" has its general meaning, referred to as Brunauer, Emmett, Teller's method for measuring surface area by N ₂ adsorption. Pore diameters and pore volumes may be measured using BET-type N ₂ adsorption or desorption experiments.

Specific support coatings are alumina, for example stabilized high surface area transition alumina. As used herein and in the claims, “transition alumina” includes gamma, chi, eta, kappa, theta and delta forms, and mixtures thereof. Certain additives such as, for example, one or more rare earth metal oxides and / or alkaline earth metal oxides are included in the transition alumina (usually in an amount comprising from 2 to 10% by weight of a stabilized coating), thereby making it an alpha alumina (relatively low surface area). It is known to be able to stabilize from undesirable high temperature phase transitions to). For example, one or more oxides of lanthanum, cerium, praseodymium, calcium, barium, strontium and magnesium can be used as stabilizers.

The platinum group metal catalyst component of the catalytic partial oxidation catalyst comprises 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. Suitable platinum group metal components are palladium and platinum, and optionally rhodium. Preferred catalysts for partial oxidation should have one or more of the following properties. They must be able to operate effectively under varying conditions from oxidation at the inlet to reduction at the outlet; Must operate effectively without significant temperature degradation over a temperature range of about 427 ° C to 1315 ° C; Must work effectively in the presence of carbon monoxide, olefins and sulfur compounds; Only low levels of carbon should be allowed on the catalyst surface by providing low levels of coking, for example by catalyzing the reaction of carbon monoxide with H ₂ O to form hydrogen; It must be resistant to poisoning by common catalytic poisons such as sulfur and halogen compounds. For example, in some other suitable catalysts, carbon monoxide may be retained 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 a simple arithmetic combination of their respective catalytic activity; The ratio ranges of the disclosed platinum to palladium have been found to provide efficient and effective catalytic activity in treating a fairly wide range of hydrocarbon feeds with high temperature operation and good resistance to catalyst poisoning.

Rhodium may optionally be included with platinum and palladium. Under certain conditions, rhodium is an effective oxidation catalyst and steam reforming catalyst, especially for light olefins. The combined platinum group metal catalysts can catalyze the autothermal reaction without significant carbon deposition on the catalyst at very low H ₂ O to carbon (carbon atoms in the feed) and oxygen to carbon ratios. This feature provides flexibility in selecting the H ₂ O to C and O ₂ to C ratios in the inlet stream to be treated.

The platinum group metals used in the catalysts of embodiments of the present invention are in any suitable form, for example as elemental metals, as other platinum group metals or as alloys or intermetallic compounds with a given metal, or as compounds such as oxides of platinum group metals. May be present. As used in the claims, the terms palladium, platinum and / or rhodium "catalyst component" or "catalyst components" are intended to encompass platinum group metals or metals present in all suitable forms. In general, the claims and platinum references to platinum group metals or metal catalyst components or components encompass one or more platinum group metals in all suitable catalyst forms. Suitable CPO catalysts are described in US Pat. No. 4,522,894, which is incorporated herein by reference in its entirety.

HC - SCR  catalyst

HC-SCR catalysts comprising silver on an alumina support are generally useful for the emission treatment system of the present invention. In a specific embodiment, the catalyst contains silver species "well dispersed" on the surface of the alumina. In certain embodiments, the catalyst is substantially free of silver metal and / or silver aluminic acid.

The catalyst can be prepared by impregnation of the alumina support with ionic silver. The alumina support can be any suitable alumina number, including but not limited to boehmite, pseudoboehmite, diaspore, norstrandite, vialite, gibbsite, hydroxylated alumina, calcined alumina, and mixtures thereof. have. Exemplary silver-alumina catalysts comprise about 3 to 4 weight percent (wt%) of silver based on Ag ₂ O supported on alumina. In one embodiment, the catalyst is prepared by depositing ionic silver on highly hydroxylated alumina. As used herein, the term "hydroxylation" refers to alumina as obtained, for example boehmite, pseudoboehmite or gelatinous boehmite, diaspore, nordstrandite, vialite, gib By the site, alumina having hydroxyl groups added to the surface, and mixtures thereof, it is meant that the surface of the alumina has a high concentration of surface hydroxyl groups. Pseudoboehmite and gelatinous boehmite are generally classified as non-crystalline or gelatinous materials, while diaspore, nordstrandite, viarite, gibbsite, and boehmite are generally classified as crystalline do. In one or more embodiments of the invention, the hydroxylated alumina is represented by the formula Al (OH) _x O _y , wherein x = 3-2y and y = 0 to 1 or the corresponding fraction. In its manufacture, no high temperature firing will drive the majority or most of the surface hydroxyl groups into the alumina. In alternative embodiments, the alumina may be of the type that is hot calcined to provide gamma, delta, theta and alpha-alumina and combinations thereof.

Silver in water-soluble ionic form, such as acetic acid, is impregnated with alumina using silver nitrate and the like, and then dried and calcined ionic silver-impregnated alumina at a temperature low enough to fix the silver and collapse the anions (when possible). . Typically for nitrates this will be about 450-550 ° C. to provide alumina that is substantially free of silver particles having a diameter greater than about 20 nm. In certain embodiments, the diameter of silver is less than 10 nm and in other embodiments the diameter of silver is less than about 2 nm. In one or more embodiments, the treatment is performed such that the silver is substantially in ionic form and substantially free of silver metal as measured by UV spectroscopy. In one or more embodiments, substantially no aluminic acid is present. The absence of silver metal and silver aluminate can be confirmed by x-ray diffraction analysis. In the presence of small amounts of hydrogen and suitable hydrocarbon fuel species, it can still function well even when the catalyst is deposited by carbonaceous and sulfur species.

DOC  catalyst

The 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 must be effective to convert a substantial proportion of NO in the NO x component into NO ₂ . As used herein, the term "substantial conversion of NO to NO ₂ in the NO x component" means at least 20%, specifically between 30 and 60%. Catalyst compositions having such properties are known in the art and include platinum group metal- and nonmetal-based compositions. The catalyst composition may be coated on a honeycomb penetrating monolithic substrate formed from a refractory metal or ceramic (eg cordierite) material. Alternatively, the oxidation catalyst can be formed on metal or ceramic foam substrates well known in the art. Such oxidation catalysts provide some level of particulate removal due to the substrate on which it is coated (eg, continuous bubble ceramic foam) and / or due to its intrinsic oxidation catalyst activity. The oxidation catalyst may remove some particulate matter from the exhaust stream upstream of the wall flow filter because the reduction of particulate matter on the filter potentially prolongs the time to forced regeneration.

One particular oxidation catalyst composition that can be used in an emission treatment system is a platinum group component (such as platinum, palladium or rhodium component) dispersed on a high surface area refractory oxide support (such as γ-alumina) in combination with a zeolite component (such as beta zeolite). It contains. Specific platinum group metal components include platinum and palladium. When the composition is disposed on a refractory oxide substrate, such as a flowable honeycomb substrate, the concentration of platinum group metal is typically about 10 to 150 g / ft ³ . In certain embodiments, the platinum group metal is typically from about 20 g / ft ³ to about 130 g / ft ³ , or from about 30 g / ft ³ to about 120 g / ft ³ , or from about 40 g / ft ³ to about 110 g / ft ³ , or from about 50 g / ft ³ to about 100 g / ft ³ . In other detailed embodiments, the platinum group metal is 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 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 another detailed embodiment, 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 , about 60 g / ft ³ , about 50 g / ft ³ , about 40 g / ft ³ , or about 30 g / ft ³ . In further detailed embodiments, the range of platinum group metal concentrations is between any combination of the minimum and maximum concentrations listed above.

Platinum group metal-based compositions suitable for use in forming oxidation catalysts are also described in US Pat. No. 5,100,632 (the '632 patent), which is incorporated herein by reference. The '632 patent discloses platinum, palladium, rhodium, and ruthenium, and alkaline earth metal oxides in an atomic ratio between the platinum group metal and the alkaline earth metal that is about 1: 250 to about 1: 1, in particular about 1:60 to about 1: 6. For example, compositions having a mixture of magnesium oxide, calcium oxide, strontium oxide, or barium oxide are described.

Catalyst compositions suitable for oxidation catalysts may be formed using base metals as catalyst formulations. For example, US Pat. No. 5,491,120, the disclosure of which is incorporated herein by reference, has a BET surface area of at least about 10 m ² / g and consists essentially of titania, zirconia, ceria-zirconia, silica, alumina-silica, and α- An oxidation catalyst composition comprising a catalyst material composed of a bulk secondary metal oxide, which may be at least one of alumina, is disclosed.

Also useful are 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 discloses a composition comprising a catalyst material containing ceria and active alumina in a weight ratio of ceria and alumina, each having a surface area of at least about 10 m ² / g, for example about 1.5: 1 to 1: 1.5. Teaching Optionally, platinum may be included in the compositions described in the '907 patent above in amounts that are effective at promoting gas phase oxidation of CO and unburned hydrocarbons, but are limited to exclude excessive oxidation of SO ₂ to SO ₃ . Alternatively, palladium may be included in the catalytic material in any desired amount.

NH ₃ - SCR  catalyst

In one particular embodiment of the present invention, the system may further comprise an NH ₃ -SCR catalyst downstream of the HC-SCR catalyst. The NH ₃ -SCR catalyst can prevent any NH ₃ produced in the system from being released into the environment. Suitable NH ₃ -SCR catalysts can be any of the known SCR catalysts useful for urea-SCR applications. It is advantageous to use NH ₃ -SCR catalysts comprising molecular sieves having a CHA X-ray crystal structure (eg Cu-CHA, Cu-SAPO). Such molecular sieves having a CHA structure exhibiting excellent hydrothermal stability and durability are particularly useful in the present invention.

Gasoline lean combustion engine

Although the above embodiments relate to diesel engines having DOC and DPF downstream of a diesel engine, it will be understood that systems according to one or more embodiments of the present invention can be used in gasoline lean combustion engines. Thus, the exemplary system would include a system of the type shown in FIG. 1 in which exhaust gas from the lean combustion engine is in communication with component 22, which may be a catalyst suitable for oxidizing carbon monoxide and hydrocarbons. An example of a suitable catalyst for a gasoline engine is a three way catalyst (TWC). TWC catalysts that exhibit good activity and long life include one or more platinum group metals (such as platinum or palladium, rhodium, ruthenium and iridium) located on high surface area refractory oxide supports, such as high surface area alumina coatings.

Hydrogen source

In some alternative embodiments, hydrogen may be generated by an external source or hydrogen generator. Suitable hydrogen sources include, but are not limited to, electrolyzers, plasma reformers, pyrolysis devices, steam reformers, compressed gas vessels, and liquefied gas vessels.

Electrolyzers, such as proton exchange membranes (PEMs), can be used to generate hydrogen in vehicles. PEM decomposes water into molecules of hydrogen and oxygen, which can then be compressed and injected into the exhaust gas. PEM systems only require a small amount of water to be maintained in the system.

Plasma reformers convert gaseous hydrocarbons such as gasoline, diesel fuel, methane, ethane and the like into hydrogen. Sufficient fuel and air are charged to the reaction chamber, and the plasma is ignited. The reaction based on the plasma results in hydrogen evolution. Hydrogen generation can be optimized by the catalyst component.

The pyrolysis device may crack or pyrolyze the fuel to yield hydrogen and carbon oxide species. Pyrolysis generally requires high temperatures for efficient conversion.

Steam reformers can produce hydrogen by reacting fuel with water. The reaction is exothermic, leading to increased reaction rates. As with electrolyzers, this type of hydrogen injector requires a small in-vehicle water supply.

[Example]

In order to illustrate the effect of hydrogen present in the exhaust gas, separate experiments were carried out using a sample of engine deteriorated HC-SCR catalyst in a laboratory reactor. Engine degradation of 450 ppm carbon C1 (as diesel), 150 ppm NO, 5% CO ₂ , 5% H ₂ 0, 10% O ₂ , remaining N ₂ to engine deterioration to 30,000 hours ⁻¹ It was introduced into the core sample taken from the inlet portion of the HC-SCR catalyst sample. The evaluation was performed using a downward slope of catalyst inlet temperature of 500 ° C to 260 ° C. The HC-SCR catalyst sample was a silver containing monolithic catalyst. Deionized water was used to prepare a 1 M solution of silver nitrate. The resulting solution was isolated from the light source and stored in a dark bottle. The available pore volume of the various supports was determined by titrating the exposed support with water while mixing until initial infiltration was achieved. This is expressed as the liquid volume per gram of support. Using the final target Ag ₂ O level and available volume per gram of support, the amount of 1 M AgNO ₃ solution required was calculated. By adding deionized water to the silver solution as needed, the total volume of liquid was made equal to the amount required to impregnate the support sample up to initial infiltration. If the amount of AgNO ₃ solution required exceeds the pore volume of the support, a number of impregnations were performed.

The appropriate AgNO ₃ solution was slowly added to the support while mixing. After initial infiltration 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 applied to a flow stream of about 10% water vapor in air, typically at 650 ° C. for at least about 16 hours.

Commercially available pseudoboehmite (Catapal.RTM. C1, 270 m ² / g, pore volume of 0.41 cc / g, average pore diameter of 6,1 nm, manufactured by Sasol, North America) and Boe The catalyst was prepared as described above using a mite (P200 (Sasol), 100 m ² / g, pore volume of 0.47 cc / g, average pore diameter of 17.9 nm) alumina support. Each alumina was treated until the silver content of the final catalyst was about 3% by weight based on Ag ₂ O. A wash amount of about 2 g / in ³ was produced by washcoating a monolith having about 300 bubbles per square inch with alumina. In the configuration of the engine exhaust system, the HC-SCR catalyst was placed in front of the DOC / DPF and degraded for 50 hours in the engine. During degradation, numerous fuel combustion cycles have been used to simulate the regeneration of DOC / DPF.

The NOx conversion result is shown in FIG. 13. The engine degraded sample as received without any treatment showed a NOx conversion of about 20% over the entire temperature range evaluated. The catalyst has 10% better NOx conversion rate at 500 ° C, 20% better NOx conversion rate at 400 ° C, and 50% better NOx conversion rate at 300 ° C when 1000 ppm H ₂ is introduced into the simulated exhaust gas. Indicated. The presence of hydrogen in the exhaust gas dramatically improved the NOx performance of the highly deactivated catalyst.

Although the present invention has been described with reference to preferred embodiments, it will be apparent to one skilled in the art that modifications of the preferred apparatus and methods may be used and that the present invention is intended to be practiced otherwise than as specifically described herein. Accordingly, the present invention includes all modifications encompassed within the spirit and scope of the invention as defined by the following claims.

Claims (14)

A main exhaust conduit in communication with the engine exhaust stream, and a hydrocarbon selective catalytic reduction catalyst (HC-SCR) in communication with the main exhaust conduit;
Exit exhaust stream branched from the main exhaust conduit and circulated as a catalytic partial oxidation (CPO) catalyst in communication with the exit exhaust stream conduit by diverting a portion of the exhaust stream from the main exhaust conduit to the exit exhaust stream conduit A departure exhaust stream conduit connected to the main exhaust conduit by a first connection providing a first connection, and a second connection downstream of the first connection reintroducing the escape exhaust stream into the main exhaust conduit upstream of the HC-SCR; And
Hydrocarbon injectors upstream of CPO (The CPOs are effective at converting some of the hydrocarbons to carbon monoxide and hydrogen)
An emission treatment system for reducing NOx in an exhaust stream from a lean combustion engine comprising a. The emission treatment system of claim 1, wherein the CPO is designed to provide sufficient hydrogen and an appropriate amount of hydrocarbons to the downstream HC-SCR catalyst. The emission treatment system of claim 1, wherein the hydrocarbon injector device comprises a metering device suitable for controlling the amount of hydrocarbon injected into the exit exhaust stream conduit. The emission treatment system of claim 1, further comprising a metering device at the first connection of the escape exhaust stream conduit for adjusting the percentage of exhaust gas bypassing the escape exhaust stream conduit. The emission treatment system of claim 1, wherein the CPO catalyst comprises a platinum group metal selected from platinum, palladium, rhodium, and mixtures thereof. The emission treatment system of claim 1, further comprising a diesel particulate filter (DPF) upstream or downstream of the HC-SCR catalyst. 7. The emission treatment system of claim 6, wherein a diesel particulate filter (DPF) is positioned in communication with the main exhaust conduit between the first and second connections. 8. The emission treatment system of claim 6 or 7, further comprising a diesel oxidation catalyst (DOC) upstream of the DPF and HC-SCR catalysts. 9. An emission treatment system according to claim 8, wherein a diesel oxidation catalyst (DOC) is located in communication with the main exhaust conduit downstream of the first connection. 10. The emission treatment system of claim 9, wherein the DOC and the DPF are integrated into a single component. The emission treatment system of claim 1 further comprising an NH ₃ -SCR catalyst downstream of the HC-SCR catalyst. The emission treatment system of claim 1, further comprising an oxidation catalyst downstream of the HC-SCR catalyst. Passing the exhaust stream through the main exhaust conduit and passing a portion of the exhaust stream through the evacuation exhaust stream conduit, wherein the main exhaust conduit comprises a hydrocarbon selective catalytic reduction catalyst (HC-SCR); The exhaust stream conduit comprises a catalytic partial oxidation (CPO) catalyst and a hydrocarbon injector upstream of the CPO (CPO is suitable for converting some of the hydrocarbons to carbon monoxide and hydrogen), and the exit exhaust stream conduit is the main exhaust at the first connection. And exiting the gas conduit and in communication with the CPO, wherein the exiting exhaust stream conduit is recombined to the main exhaust conduit at a second connection upstream of the HC-SCR. A method of treating an exhaust stream, comprising passing the exhaust stream to the system according to claim 2.

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