Reducing agent forming device and exhaust gas control system using the same

A reforming device includes a reforming part that subjects a hydrocarbon-based raw material to be reformed to a reforming reaction to form a reducing agent to be supplied to a reducing catalyst for reducing nitrogen oxide selectively. The reforming part has a reforming reaction region through which the raw material to be reformed passes and is reacted with supplied hydrogen atoms supplied so as to be reformed to the reducing agent. For example, a hydrogen permeable membrane having a first surface and a second surface may be provided in the reforming part to permeate hydrogen atoms from the first surface to the second surface and to produce the hydrogen atoms on the second surface. The reforming device can be suitably used for an exhaust gas control system for cleaning exhaust gas, for example.

CROSS REFERENCE TO RELATED APPLICATION

This application is based on Japanese Patent Applications No. 2005-277421 filed on Sep. 26, 2005, and No. 2006-156236 filed on Jun. 5, 2006, the contents of which are incorporated herein by reference in its entirety.

FIELD OF THE INVENTION

The present invention relates to a reforming device for forming a reducing agent capable of selectively reducing NOx, and an exhaust gas control system for cleaning exhaust gas of an automobile by the use of a reducing agent formed by this reforming device.

BACKGROUND OF THE INVENTION

Conventionally, technologies for removing NOx in exhaust gas of an internal combustion engine include mainly a method using a three-way catalyst such as a Pt-Rh based catalyst, a selective reducing method using ammonia (JP-A-2003-286826), a selective reducing method using urea or the like (JP-A-2004-529286), a selective reducing method using hydrocarbon (HC) or the like, and a NOx adsorbing method for adsorbing NOx by various kinds of adsorbents (JP patent No. 3248187 corresponding to U.S. Pat. No. 6,367,246).

However, the method using a three-way catalyst does not have any performance of cleaning NOx for an exhaust gas containing a large amount of oxygen such as the exhaust gas of a diesel engine, a lean burn engine of low fuel consumption, or the like. In this manner, the method of using a three-way catalyst presents a problem that the three-way catalyst cannot exert its effect in an oxygen excess atmosphere and cannot remove NOx sufficiently.

Moreover, in the selective reducing method, circumstances are different depending on a reducing agent to be used. When ammonia or urea is used as a reducing agent, there are presented a problem that a tank for the reducing agent is required separately and a problem that a device is enlarged in size. Moreover, the reducing agent needs to be replenished, which lays a burden on a user. Further, there is presented a problem that ammonia is discharged into the atmosphere to cause secondary pollution (ammonia slip). Still further, the NOx adsorbing method presents a problem that NOx adsorbed by an adsorbent needs to be post-treated by rinsing with water or the like.

Consequently, to solve these problems, a copper ion exchange zeolite for catalytically cracking NOx directly into N2, O2was developed and it was reported that a NOx cleaning rate higher than 90% could be obtained at an experiment stage. This copper ion-exchange zeolite is such that copper is carried on zeolite through ion exchange and has received attention as a reducing catalyst capable of cleaning NOx in an oxygen excess atmosphere and a catalyst device for cleaning exhaust gas having this copper ion-exchange zeolite set in the exhaust system of an engine is already publicly known (JP-A-5-68887).

However, the above-described catalyst device for cleaning exhaust gas does not have sufficient performance of cleaning HC and CO because the copper ion-exchange zeolite is low in the oxidizing ability of a catalyst in an oxygen excess atmosphere in a running automobile. For this reason, pretreatment is required to oxidize CH and CO, which becomes disadvantageous in terms of cost, space, and weight.

In contrast to these methods, in the selective reducing method using hydrocarbon as a reducing agent, a reducing agent can be obtained from the fuel of an internal combustion engine. Therefore, the selective reducing method using hydrocarbon as a reducing agent has received attention from the viewpoint of: eliminating the need for providing a separate tank, which is required in the method using ammonia and urea; reducing the size of a device; and load to be applied to a user. It is said that straight-chain alkane having 8 to 12 carbons is preferable as hydrocarbon used for the reducing agent of NOx (refer to non-patent documents 1,2).[Non-patent document 1] Preprints of Catalysis Society of Japan, 1999 (3G20)[Non-patent document 1] Preprints of Technology Conference No. 29-04, Society of Automotive Engineers of Japan

Moreover, oxygenated hydrocarbon containing oxygen such as alcohol, ethers, ketones, or the like is used as a reducing agent to reduce NOx and the like (JP-A-7-227523).

However, how to obtain a reducing agent required at the time of selectively reducing NOx in the exhaust gas and made of the above-described hydrocarbon from the fuel of the internal combustion engine becomes a problem. In addition, there is a demand for a technology that is plus in terms of energy balance and can reduce a total of NOx.

SUMMARY OF THE INVENTION

In view of the above-described problems, one object of the present invention is to provide a reforming device for forming a reducing agent capable of selectively reducing NOx. Moreover, another object of the present invention is to obtain a reducing agent used for a selective reduction reaction from an internal combustion engine, in an exhaust gas control system for cleaning the exhaust gas of the internal combustion engine by the selective reduction reaction.

According to an aspect of the present invention, a reforming device includes a reforming part that subjects a hydrocarbon-based raw material to be reformed to a reforming reaction to form a reducing agent to be supplied to a reducing catalyst for reducing nitrogen oxide selectively, and a hydrogen atom supply means for supplying hydrogen atoms to the reforming part. Furthermore, the reforming part has a reforming reaction region through which the raw material to be reformed passes and is reacted with the hydrogen atoms supplied by the hydrogen atom supply means so as to be reformed to the reducing agent. Accordingly, the reducing agent capable of selectively reducing NOx can be effectively obtained.

For example, the hydrogen atom supply means includes a hydrogen permeable membrane having a first surface and a second surface, and the hydrogen permeable membrane permeates hydrogen atoms from the first surface to the second surface to produce the hydrogen atoms on the second surface. In this case, the place to which the raw material to be reformed is supplied can be separate from the place where the hydrogen atoms are generated, thereby reforming the raw material in a liquid state. The reforming reaction region may be within a range of sub-micron from the second surface of the hydrogen permeable membrane.

Furthermore, a hydrogen supply means for supplying hydrogen molecules to the first surface of the hydrogen permeable membrane may be provided. In this case, the hydrogen permeable membrane dissociates the hydrogen molecules supplied to the first surface from the hydrogen supply means into hydrogen atoms and makes the hydrogen atoms permeate itself from the first surface to the second surface to produce the hydrogen atoms on the second surface. For example, the hydrogen supply means includes an electrolytic film through which electric current passes, and water supply means for supplying water to the first surface of the electrolytic film. In this case, when electric current is passed through the electrolytic film, the water supplied from the water supply means is decomposed on the first surface of the electrolytic film through electrolysis to produce hydrogen molecules on the second surface of the electrolytic film and the hydrogen molecules are supplied to the first surface of the hydrogen permeable membrane.

A raw material supply unit may be provided for supplying the raw material to be reformed to the first surface of the hydrogen permeable membrane. In this case, the first surface of the hydrogen permeable membrane may be provided with a hydrogen forming catalyst for forming hydrogen from the raw material to be reformed and a catalyst carrier for carrying the hydrogen forming catalyst. Alternatively, a promoter may be provided on the first surface of the hydrogen permeable membrane, for promoting hydrogen formation by the hydrogen forming catalyst.

In addition, an oxygen supply means for supplying oxygen into the reforming part may be provided. For example, the oxygen supply means is constructed so as to supply oxygen formed through the electrolysis to the reforming part.

Any reforming devices described above may be used for an exhaust gas control system for an internal combustion engine. In this case, the reducing catalyst can be located in the exhaust gas passage, and fuel used for the engine can be used as the raw material to be reformed. Accordingly, by reforming the fuel for the internal combustion engine, the reducing agent for selectively reducing nitrogen oxide in the exhaust gas can be obtained. This can eliminate the need for supplying a reducing agent for a selective reduction reaction from the outside and the need for providing a tank for holding the reducing agent.

The reforming part may be arranged in a fuel tank in which the fuel for the internal combustion engine is stored, or next to the fuel tank. In this case, it is possible to shorten piping for supplying the fuel for the internal combustion engine to the reforming part and to reduce the power of a pump to supply the fuel for the internal combustion engine to the reforming part.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

First Embodiment

Hereinafter, a first embodiment of the present invention will be described on the basis ofFIG. 1toFIG. 4.

FIG. 1is a schematic diagram of an exhaust gas control system mounted to a vehicle, which is provided with a reforming device of the present invention. As shown inFIG. 1, the vehicle is mounted with an internal combustion engine10, a fuel tank11filled with fuel for the internal combustion engine10, and an exhaust gas passage12through which the exhaust gas of the internal combustion engine10passes.

An engine, in which an exhaust gas contains a large amount of oxygen, such as a lean burn engine and a diesel engine can be suitably used as the internal combustion engine10. In this embodiment, a diesel engine is used as the internal combustion engine10and light oil is used as fuel for the internal combustion engine. The light oil contains mainly alicyclic hydrocarbon (naphthene base), aromatic hydrocarbon (aroma base), and straight-chain hydrocarbon (paraffin base). The fuel for the internal combustion engine corresponds to a raw material to be reformed.

The exhaust gas passage12is provided with a muffler13for muffling sound. Further, a reducing catalyst device14is provided in the exhaust gas passage12on the upstream side of the muffler13in an exhaust gas flow. The reducing catalyst device14is provided with a reducing catalyst for selectively reducing nitrogen oxide (NOx) contained in the exhaust gas. For example, a Ag-alumina-based catalyst can be used as the reducing catalyst.

A reducing agent forming device15is provided on a downstream side of the reducing catalyst device14and on an upstream side of the muffler13in the exhaust gas passage12. In the reducing agent forming device15, the fuel for the internal combustion engine is subjected to a reforming reaction to form a reducing agent for selectively reducing nitrogen oxide (NOx). This reducing agent is used for a reduction reaction in the reducing catalyst device14. A reducing agent in this embodiment is hydrocarbon in which the carbon number of a main chain ranges from 8 to 12 and contains straight-chain hydrocarbon mainly and contains also hydrocarbon having a plurality of side chains comprising carbon and hydrogen. Light oil itself of the fuel acts as a reducing agent for selectively reducing nitrogen oxides although the light oil is low in reforming efficiency. For this reason, it is also possible to use the light oil (fuel) as a first reducing agent (reducing agent before reforming) and to use a reducing agent formed by the reforming reaction of the light oil as a second reducing agent (reducing agent after reforming), that is, to form the second reducing agent capable of causing a reduction reaction efficiently by reforming the first reducing agent.

A reducing agent supply part16for supplying a reducing agent formed in the reducing agent forming device15is provided on an upstream side of the reducing catalyst device14in the exhaust gas passage12. The reducing agent supply part16is constructed as an injection nozzle for injecting the reducing agent. The reducing agent formed in the reducing agent forming device15is supplied to the reducing agent supply part16through a reducing agent passage17. The reducing agent injected from the reducing agent supply part16is supplied to the reducing agent catalyst part14along with the exhaust gas and is used for a reduction reaction in the reducing agent catalyst part14.

The fuel for the internal combustion engine10is supplied to the reducing agent forming device15from the fuel tank11through a fuel supply passage18. The fuel supply passage18is provided with a fuel supply pump19for sending the fuel for the internal combustion engine from the fuel tank11to the reducing agent forming device15. The fuel supply pump19may be operated by the use of a pump pressure for sending fuel to the internal combustion engine10or, for example, by an electric power supply from a battery (not shown).

The exhaust gas is introduced into the reducing agent forming device15through an exhaust gas branch passage20. The exhaust gas branch passage20is provided with a trap part21. The trap part21is, for example, a member that cools the exhaust gas by wind caused by the running vehicle to extract moisture contained in the exhaust gas. In this embodiment, moisture collected in the trap part21is supplied in a liquid state to the reducing agent forming device15.

FIG. 2is an enlarged view of the reducing agent forming device15. As shown inFIG. 2, the reducing agent forming device15is provided with a reforming part150, a hydrogen permeable membrane151, a hydrogen supply part152, an electrolytic film153, and a water supply part154. The inside of the reducing agent forming device15is partitioned into the reforming part150and the hydrogen supply part152by the hydrogen permeable membrane151, and is partitioned into the hydrogen supply part152and the water supply part154by the electrolytic film153. The heat of the exhaust gas is transmitted to the reducing agent forming device15through the exhaust gas passage12as heating means, thereby the hydrogen permeable membrane151and the electrolytic film153are heated.

In the reforming part150, the fuel is reformed, thereby a reducing agent for selectively reducing nitrogen oxides (NOx) is formed. The reforming of the fuel in this embodiment means the decomposition of fuel such as the depolymerization of the fuel. The reforming part150is provided with a dehydrogenation reaction part that dehydrogenates the fuel mainly to form unsaturated hydrocarbon and a depolymerization reaction part that depolymerizes the fuel mainly to reduce the carbon number of the fuel.

The fuel for the internal combustion engine is supplied to the reforming part150from the fuel tank11and moisture taken from the exhaust gas in the trap part21is supplied to the water supply part154. In this embodiment, both of the fuel for the internal combustion engine and the moisture are supplied in a liquid state. Hydrogen formed through electrolysis by the electrolytic film152is supplied to the hydrogen supply part152. The hydrogen supply part152, the electrolytic film153, and the water supply part154show a specific example of hydrogen supply means of this embodiment.

FIG. 3is a schematic diagram for explaining the reforming part150in detail. InFIG. 3, a region shown by broken diagonal lines shows a reforming reaction region150a. While the reforming reaction proceeds in the whole region of the reforming part150, the reforming reaction of the fuel is caused efficiently particularly in the reforming reaction region150a. For example, the reforming reaction region150ais close to a second surface151bof the hydrogen permeable membrane151in the reforming part150and is a region within a sub-micron (e.g., 0.1 micron) from the surface of the second surface151b. To proceed with the reforming reaction efficiently in the reforming part150, it is preferable that the fuel for the internal combustion engine is supplied to the reforming reaction region150a.

Returning toFIG. 2, the hydrogen permeable membrane151is constructed as a hydrogen dissociative permeable film that dissociates hydrogen, which is supplied to the hydrogen supply part152and is in a molecular state, into active hydrogen (hydrogen radical) in an atomic state on the surface of the first surface151aand makes this active hydrogen permeate the hydrogen permeable membrane151to the second surface151bto produce active hydrogen on the second surface151b. With this, the active hydrogen is supplied to the reforming part150.

Moreover, when the second surface151bof the hydrogen permeable membrane151is increased in its surface area, the second surface151bcan increase the discharge of active hydrogen and can enhance the efficiency of the reforming reaction. For this reason, in this embodiment, the second surface151bof the hydrogen permeable membrane151is formed into a curved surface, an uneven surface, or a wavy surface, thereby increasing its surface area. Moreover, the second surface151bof the hydrogen permeable membrane151may be constructed of a plurality of surfaces.

The hydrogen permeable membrane151has only to be a film in which hydrogen in an atomic state can permeate between film constituent atoms (usually, metal). For example, a film constructed of an elemental substance of Pd, Ta, Nb, V, Ni, or Zr, or an alloy comprising one or more element selected from a group consisting of Pd, Ta, Nb, V, and Zr, and one or more element selected from a group consisting of Pt, Ag, Au, Rh, Ru, Sn, Se, Te, Si, Zn, In, Ir, Ni, Ti, Mo, Y, and Fe can be used as the hydrogen permeable membrane151. Although the structure of the hydrogen dissociative permeable film may be crystalline or amorphous, considering the temperature of the exhaust gas, an amorphous hydrogen dissociative permeable film expected to be durable at low temperatures is preferable. Its film thickness can be, for example, from 0.01 mm to 0.1 mm.

The electrolytic film153is a proton permeable film and, for example, a solid polymeric electrolytic film can be used as the electrolytic film153. The electrolytic film153is so constructed as to have electric current passed therethrough. Specifically, the electrolytic film153is sandwiched between a pair of electrodes (not shown) and the respective electrodes have voltage applied thereto from a battery (not shown) or the like. The electrolytic film153decomposes water supplied to the water supply part154on the first surface153athrough electrolysis and makes protons formed through this electrolysis permeate the electrolytic film153to the second surface153bto produce hydrogen on the second surface153b. With this, the hydrogen is supplied to the hydrogen supply part152.

By adjusting a current value at the time of passing an electric current through the electrolytic film153, the amount of hydrogen produced by the electrolytic film153can be adjusted and hence the amount of hydrogen supplied to the hydrogen supply part152can be adjusted. With this, the amount of hydrogen atoms permeating the hydrogen permeable membrane151can be adjusted and hence the amount of hydrogen atoms supplied to the reforming part150can be adjusted, thereby the reforming reaction in the reforming part150can be controlled.

Moreover, the solid polymeric electrolytic film used as the electrolytic film153can reduce the amount of moisture required to make the protons permeate the electrolytic film153. For this reason, when the exhaust gas is supplied to the water supply part154, the electrolytic film153is moistened by moisture in the exhaust gas, thereby being able to produce hydrogen in a short time from a start-up.

Next, the operation of the exhaust gas control system of this embodiment will be described by the use ofFIG. 4.FIG. 4is a schematic diagram for explaining the exhaust gas cleaning mechanism of the exhaust gas control system.

First, when the internal combustion engine10is started, supply of the fuel from the fuel tank11to the internal combustion engine10is started. The exhaust gas produced in the internal combustion engine10is passed through the exhaust gas passage12and has its sound muffled by the muffler13and then is discharged outside. The reducing catalyst device14and the reducing agent forming device15have their temperature raised by the heat of the exhaust gas passed through the exhaust gas passage12. In this manner, when the temperature of the reducing catalyst device14is raised, reduction reaction efficiency in the reducing catalyst device14is enhanced, and when the temperature of the reducing agent forming device15is raised, hydrogen formation efficiency and reforming reaction efficiency in the reducing agent forming device15are enhanced. Here, the heating temperature of the reducing agent forming device15is set to be 100° C. or more.

At this time, the reducing agent forming device15is arranged on the downstream side of the reducing catalyst device14in the exhaust gas passage12, so it is possible to raise the temperature of the reducing catalyst device14on a priority basis by the heat of the exhaust gas and then to raise the temperature of the reducing agent forming device15. Further, to raise the temperature of the reducing catalyst to an active temperature, not only the exhaust heat of the exhaust gas but also combustion heat obtained by combusting the fuel can be used to heat the reducing agent. On this account, heat not yet to be used when the reducing catalyst is heated can be recovered by the reducing agent forming device15on the downstream side.

Moreover, the reducing agent forming device15is arranged on the upstream side of the muffler13in the exhaust gas passage12, so the temperature of the reducing agent forming device15can be raised before the heat of the exhaust gas is removed by the muffler13.

When the internal combustion engine10is started, supplying the fuel to the reforming part150of the reducing agent forming device15from the fuel tank11is started. Most part of the fuel (light oil) for the internal combustion engine supplied to the reforming part150is in a liquid state at the heating temperature of the reducing agent forming device15due to the exhaust heat of the exhaust gas. The reforming reaction of the fuel in the reforming part15is desirably developed in a state where the fuel is liquid but can be developed in a state where the fuel is in gaseous state. Moreover, moisture is taken out of the exhaust gas by the trap part21and the moisture is supplied to the water supply part154of the reducing agent forming device15.

When the internal combustion engine10is started, passing the electric current through the electrolytic film153is started and water supplied to the water supply part154is decomposed into hydrogen and oxygen through electrolysis, thereby hydrogen is produced in the hydrogen supply part152.

As shown inFIG. 4, hydrogen molecules produced in the hydrogen supply part152are dissociated into hydrogen atoms on the surface of the first surface151aof the hydrogen permeable membrane151to produce active hydrogen (H.). The active hydrogen permeates the hydrogen permeable membrane151and active hydrogen is produced on the second surface151b.

The active hydrogen reacts directly with the fuel for the internal combustion engine on the second surface151bof the hydrogen permeable membrane151to reform the fuel for the internal combustion engine. In this reforming reaction are developed the dehydrogenation reaction in which the fuel is mainly dehydrogenated to form unsaturated hydrocarbon and the depolymerization reaction in which the fuel is mainly depolymerized to reduce the carbon number of the fuel. In this embodiment, when the fuel for the internal combustion engine is in a liquid state, the fuel for the internal combustion engine is subjected to the reforming reaction. However, even when the fuel for the internal combustion engine is in a gaseous state, the fuel for the internal combustion engine can be subjected to the reforming reaction.

In the reaction between the active hydrogen and the fuel for the internal combustion engine, straight-chain hydrocarbon is mainly formed. At this time, straight-chain hydrocarbon in which the carbon number of a main chain ranges from 8 to 12 is formed as a reducing agent (reformed fuel) not only by the reaction in which the bond between hydrocarbons each having a long main chain is cut but also by the reaction of opening the ring of cyclic hydrocarbon such as alicyclic hydrocarbon and aromatic hydrocarbon.

The reducing agent formed by the reforming part150is supplied to the nozzle of the reducing agent supply part16and is injected into the exhaust gas passage12from the nozzle. The reducing agent injected from the reducing agent supply part16is supplied to the reducing catalyst device14along with the flow of the exhaust gas and is used for the reduction reaction in the reducing catalyst device14. In the reducing catalyst device14, a selective reduction reaction for selectively reducing nitrogen oxide (NOx) by the hydrocarbon-based reducing agent is developed to clean the exhaust gas.

As described above, the fuel for the internal combustion engine is reformed to form the reducing agent, thereby the reducing agent for reducing nitrogen oxide in the exhaust gas can be obtained. This eliminates the need for supplying the reducing agent for the selective reduction reaction from the outside. Moreover, a tank or the like for holding the reducing agent can be set as required.

Moreover, in the exhaust gas control system of this embodiment, heat necessary for the reforming reaction at the time of forming the reducing agent from the fuel for the internal combustion engine is obtained from the exhaust gas of the internal combustion engine10, so it is possible to make effective use of the exhaust heat of the exhaust gas and hence to enhance the efficiency of the entire system.

Moreover, since hydrogen atoms are supplied to the reforming part150by the use of the hydrogen permeable membrane151, if temperature is higher than the operating temperature of the hydrogen permeable membrane151, the hydrogen atoms can be supplied to the reforming part150, thereby the fuel can be subjected to the reforming reaction in the reforming part150. Further, since the hydrogen atoms are highly reactive, the hydrogen atoms can reform the fuel at low temperatures. Accordingly, even in the case of using the diesel engine having a low exhaust gas temperature, just as with this embodiment, the reducing agent can be formed by using the exhaust heat of the exhaust gas.

Further, when a site where hydrogen atoms are formed by the hydrogen permeable membrane151is separated from a site where the fuel is supplied, just as with this embodiment, if temperature is higher than the operating temperature of the hydrogen permeable membrane151, the active hydrogen can be supplied to the reforming part150and the reforming part150can proceed with the reforming reaction.

Still further, when the hydrogen atoms are formed on the first surface151aof the hydrogen permeable membrane151and the fuel is supplied to the second surface151bon the opposite side, just as with this embodiment, a site where the fuel is supplied can be made different from a site where hydrogen atoms are formed and hence the fuel can be subjected to the reforming reaction in a state where the fuel is in a liquid phase.

Second Embodiment

Next, a second embodiment of the present invention will be described with reference toFIG. 5andFIG. 6. As compared with the first embodiment, the second embodiment is different in that oxygen is supplied to the reforming part150of the reducing agent forming device15. Hereinafter, only parts where the second embodiment is different from the first embodiment will be mainly described.

FIG. 5is an enlarged view of the reducing agent forming device15of the second embodiment.FIG. 6is a schematic diagram for describing an exhaust gas cleaning mechanism of the exhaust gas control system.

As shown inFIG. 5, in the reducing agent forming device15of the second embodiment, the water supply part154is connected to the reforming part150by an oxygen supply passage22. Oxygen formed through electrolysis by the electrolytic film152is supplied to the reforming part150from the water supply part154via the oxygen supply passage22. The reforming of the fuel in this embodiment means not only the depolymerization of the fuel but also the oxygenation of the fuel. Here, the oxygen supply passage22corresponds to oxygen supply means of the present invention.

The reforming part150of the second embodiment is provided with not only a dehydrogenation reaction part that dehydrogenates the fuel mainly to form unsaturated hydrocarbon and a depolymerization reaction part that depolymerizes the fuel mainly to reduce the carbon number of the fuel, but also an oxygenation reaction part that oxygenates the fuel to add oxygen to depolymerized hydrocarbon.

With this construction, as shown inFIG. 6, the active hydrogen reacts directly with the fuel for the internal combustion engine on the second surface151bof the hydrogen permeable membrane151and also reacts with oxygen supplied to the reforming part150to form active oxygen species (O., OH., OOH., and the like) having higher oxidizing power. These active oxygen species have larger dissociation energy than the active hydrogen. That is, when oxygen is supplied to the reforming part150, active species having large dissociation energy and large degradability can be obtained.

The reducing agent formed by the reforming part150of the second embodiment contains not only straight-chain hydrocarbon but also oxygenated hydrocarbon containing oxygen atoms such as alcohol, ethers, and ketones and, in particular, contains a large amount of methyl ketone (CH3—CO—R) having a ketone group at the second carbon of straight-chain hydrocarbon. This oxygenated hydrocarbon has higher reduction efficiency than hydrocarbon not containing oxygen and hence can be used as an optimal reducing agent.

Moreover, since oxygen formed through electrolysis when hydrogen is formed is supplied to the reforming part150, oxygen does not need to be supplied from the outside and hence construction can be made compact.

Further, in the second embodiment, oxygen supplied to the reforming part150has an oxygen concentration of nearly 100% and hence can be expected to be converted to active oxygen at high efficiency. These active oxygen species react with the fuel for the internal combustion engine to reform the fuel for the internal combustion engine. With this, in the second embodiment, not only straight-chain hydrocarbon but also oxygenated hydrocarbon containing oxygen can be formed.

Still further, oxygen supplied to the reforming part150has a high concentration of nearly 100% and hence the amount of oxygen to be supplied to the reforming part150has only to be a minimal amount required for the reforming reaction. On this account, the oxygen supply passage22for supplying oxygen to the reforming part150can be constructed slimly.

Third Embodiment

Next, a third embodiment of the present invention will be described with reference toFIG. 7toFIG. 12. As compared with the first embodiment, this third embodiment is different mainly in hydrogen supply means. Hereinafter, only parts where the third embodiment is different from the first embodiment will be mainly described.

FIG. 7is a schematic diagram of an exhaust gas control system mounted on a vehicle in this third embodiment, andFIG. 8is an enlarged view of the reducing agent forming device15inFIG. 7.

This third embodiment is not constructed so as to introduce moisture contained in the exhaust gas into the reducing agent forming device15, which is different from the above-described respective embodiments, and the reducing agent forming device15is not provided with the electrolytic film153and the water supply part154.

As shown inFIG. 7andFIG. 8, this third embodiment is constructed in such a way that the fuel for the internal combustion engine is supplied to the reforming part150and the hydrogen supply part152from the fuel tank11. Moreover, this third embodiment is constructed in such a way that air containing oxygen is supplied to reforming part150from the outside through an air supply passage23. Here, the air supply passage23constructs the oxygen supply means of the present invention.

Hydrogen forming catalysts151cfor forming hydrogen from the fuel for the internal combustion engine are carried on the first surface151aof the hydrogen permeable membrane151. As the hydrogen forming catalysts151ccan be used, for example, Pt, Pd, Ni, Cu, or the like. Here, a fuel supply passage18and the hydrogen forming catalysts151ccorrespond to hydrogen supply means of this embodiment.

FIG. 9is a schematic diagram of the hydrogen permeable membrane151. The hydrogen forming catalysts151c, as shown inFIG. 9, are formed in such a way as to be diffused and carried in fine particles on the catalyst carriers151dconstructed on the surface of the first surface151a. The catalyst carriers151dcan be constructed, for example, as metal oxide constructing the hydrogen permeable membrane151.

FIG. 10is a schematic diagram for explaining the construction of the catalyst carrier151d. As shown inFIG. 10, in this embodiment, the catalyst carriers151dare constructed integrally with the hydrogen permeable membrane151. A metal oxide made by chemically combining metal (for example, Zr, Al, Ni, or the like) constructing the hydrogen permeable membrane151with oxygen is grown on the surface of the hydrogen permeable membrane151to form the catalyst carriers151d. Alternatively, the hydrogen permeable membrane151may be formed on the catalyst carriers151das metal oxide. The film thickness of the catalyst carrier151dhas only to be from about several tens nm to several nm.

According to the catalyst carriers151dof this structure, a continuous crystalline structure can be obtained between the catalyst carriers151dand the hydrogen permeable membrane151and hence the hydrogen permeable membrane151and the catalyst carriers151dcan be formed as an integrated continuous substance. Each of portions surrounded by broken lines inFIG. 10shows a portion where the hydrogen permeable membrane151and the catalyst carrier151dare integrated with each other. With this, as compared with a case where the catalyst carriers151dconstructed as substances separate from the hydrogen permeable membrane151are joined to the surface of the hydrogen permeable membrane151, the catalyst carriers151dare hard to separate from the hydrogen permeable membrane151and hence strength can be enhanced.

The hydrogen forming catalysts151cmay be used as single substances or may be used along with promoters for promoting the catalytic reaction (hydrogen forming reaction) by the hydrogen forming catalysts151c. For example, when Pt is used as the hydrogen forming catalyst151c, Pd can be used as the promoters.FIG. 11is an enlarged view to show the surroundings of the catalysts when the promoter151eis provided. Both of the hydrogen forming catalysts151cand the promoters151eare carried on each of the catalyst carriers151d. As shown inFIG. 11, the promoter151ecan be directly carried on the catalyst carrier151dand the hydrogen forming catalysts151ccan be carried on the promoter151e. Alternatively, the hydrogen forming catalysts151cand the promoter151emay be directly carried on the catalyst carrier151d.

On the surface of the first surface151aof the hydrogen permeable membrane151, alicyclic hydrocarbon (for example, cyclohexane) contained in the fuel for the internal combustion engine is converted to aromatic hydrocarbon (for example, benzene) by the hydrogen forming catalysts151c. When the alicyclic hydrocarbon is converted to aromatic hydrocarbon, hydrogen is formed. This hydrogen is in an atomic state and hence hydrogen atoms are supplied to the first surface151aof the hydrogen permeable membrane151.

Hydrogen formed on the first surface151aof the hydrogen permeable membrane151permeates the hydrogen permeable membrane151as active hydrogen in an atomic state to produce active hydrogen on the second surface151b. The fuel for the internal combustion engine containing aromatic hydrocarbon converted from the alicyclic hydrocarbon is return to the fuel tank11through a fuel return passage24.

According to this embodiment, by providing the first surface of the hydrogen permeable membrane151with the catalysts151chaving a high hydrogen forming capability, hydrogen can be formed on the surface of the hydrogen permeable membrane151from the fuel for the internal combustion engine. With this, hydrogen can be formed on the first surface151aof the hydrogen permeable membrane151and the reforming of the fuel for the internal combustion engine can be realized on the second surface151b, which can eliminate the need for electrolytic film153(refer toFIG. 2) for decomposing water through electrolysis and the need for electric power for driving the electrolytic film153and hence can make the reducing agent forming device15compact.

Fourth Embodiment

Next, a fourth embodiment of the present invention will be described with reference toFIG. 12andFIG. 13. As compared with the third embodiment, this fourth embodiment is different mainly in a place where the reducing agent forming device15is set. Hereinafter, only parts where the fourth embodiment is different from the respective embodiments will be mainly described.

FIG. 12is a schematic diagram of a vehicle mounted with an exhaust gas control system of this fourth embodiment, andFIG. 13is an enlarged view of the reducing agent forming device15inFIG. 12.

As shown inFIG. 12, in this fourth embodiment, the reducing agent forming device15is set in the fuel tank11. The reducing agent forming device15is housed in a case25located in the fuel tank11. Piping17,18,23, and24connected to the reducing agent forming device15and a fuel supply pump19are also housed in the case25.

Moreover, an exhaust gas introducing passage26for introducing exhaust gas from the exhaust gas passage12is provided in the case25. The exhaust gas introducing passage26is provided so as to branch from the exhaust gas passage12and to have its part put into contact with the reducing agent forming device15. The exhaust gas passes through the exhaust gas introducing passage26, thereby the reducing agent forming device15is heated by the exhaust heat of the exhaust gas. For example, the case25has a thermal insulating structure in such a way that heat when the reducing agent forming device15is heated is not transmitted to the fuel in the fuel tank11. Here, the exhaust gas introducing passage26corresponds heating means in this embodiment.

The above-described construction can shorten the length of piping18,24for connecting the fuel tank11and the reducing agent forming device15and can provide the advantage of reducing also the power of the pump19for sending fuel to the reforming part150of the reducing agent forming device15. While the reducing agent forming device15is set in the fuel tank11in the example shown inFIG. 12andFIG. 13, the reducing agent forming device15may be set at a site next to the fuel tank11outside the fuel tank11.

Next, experiment examples conducted to examine the effect of the above-described embodiments will be described.

First Example

A first experiment example is performed in the structure of the first embodiment. In the first experiment example, a pipe made of 100% Pd was used as a hydrogen permeable membrane151. Three kinds of simulation light oils were supplied as fuel for the internal combustion engine from the upstream side of the hydrogen permeable membrane151.

Simulation light oil A: n-hexadecane simple substance

Simulation light oil B: mixed liquid of n-tridecane and n-hexadecane (1:1)

Simulation light oil C: mixed liquid of n-tridecane, n-hexadecane, and naphthalene (2:2:1)

The results of the rate of formation of a reducing agent are shown inFIG. 14. The heating temperatures of the reducing agent forming device15were set at 140° C. and 200° C. for the simulation light oil A and at 200° C. for the simulation light oils B and C. Hydrogen of 1 atmospheric pressure was supplied to the hydrogen supply part152at a rate of 10 cc/min. Nitrogen was bubbled into the fuel for the internal combustion engine to expel dissolved oxygen. The results of the rate of formation of the reducing agent by the reforming reaction were 0.64×10−4[ml/min/cm2] at 140° C. and 2.0×10−4[ml/min/cm2] at 200° C. for the simulation light oil A, so the rate of formation of the reducing agent was brought to about three times by raising temperature. Moreover, the results of the rate of formation of the reducing agent by the reforming reaction were 0.91×10−4[ml/min/cm2] and 0.8×10−4[ml/min/cm2] for the simulation light oils B and C, respectively.

Second Example

A second experiment example is performed in the structure of the second embodiment. The second experiment example was different from the first experiment example in that oxygen (supply gas) was bubbled into the fuel for the internal combustion engine. The result of the second experiment example is shown inFIG. 15.

The heating temperatures of the reducing agent forming device15were set at 140° C. and 200° C. for the simulation light oil A and at 200° C. for the simulation light oils B and C. Hydrogen of 1 atmospheric pressure was supplied to the hydrogen supply part152at a rate of 10 cc/min. The results of rate of formation of the reducing agent by the reforming reaction were 1.1×10−4[ml/min/cm2] at 140° C. and 6.4×10−4[ml/min/cm2] at 200° C. for the simulation light oil A, so the rate of formation was brought to about six times by raising temperature. Moreover, the results of rate of formation of the reducing agent by the reforming reaction were 4.3×10−4[ml/min/cm2] and 2.5×10−4[ml/min/cm2] for the simulation light oils B and C, respectively. It was examined that a large rate of formation of a reducing agent could be obtained.

Other Embodiments

For example, in the above-described embodiments, the reforming device and the exhaust gas control system according to the present invention are typically used for a vehicle having an internal combustion engine. However, the reforming device and the exhaust gas control system according to the present invention can be suitably used for an internal combustion engine (for example, plant or thermal power plant) containing a large amount of oxygen in the exhaust gas.

Moreover, in the above-described embodiments, the reforming device according to the present invention is applied to the exhaust gas control system and the reducing agent formed by the reforming device is used for selectively reducing nitrogen oxide contained in the exhaust gas of the internal combustion engine. However, the reforming device according to the present invention may be used for usage other than an exhaust gas control system.

Further, the above-described embodiments are constructed in such a way that the reducing agent forming device15is arranged in the exhaust gas passage12and is heated by the heat of the exhaust gas. However, the reducing agent forming device15may be heated by other heating means. For example, it is possible to adopt a construction in which a cooling water pipe through which the cooling water of the internal combustion engine10is passed is used as heating means and in which the reducing agent forming device15is heated by the use of the heat of the cooling water. In addition, an electric heater may be used as the heating means.

Still further, the above-described embodiment is constructed in such a way that moisture extracted from the exhaust gas by the trap part21is supplied to the water supply part154of the reducing agent forming device15. However, the exhaust gas in the state of containing moisture may be directly introduced into the water supply part154of the reducing agent forming device15.

Still further, the second embodiment is constructed in such a way that pure oxygen is supplied to the reforming part150and the third embodiment is constructed in such a way that air containing oxygen molecules is supplied to the reforming part150. However, the substance to be supplied to the reforming part150by the oxygen supply means has only to be able to produce oxygen molecules in the reforming part150and, for example, liquid containing permanganate or hydrogen peroxide can be used as the substance.

Furthermore, in the above-described first and second embodiments, the reducing agent forming device15may be provided in the fuel tank15, similarly to the fourth embodiment.