JP2004211565A - Emission control system and emission control method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an emission control system and emission control method having sufficiently high NOx decomposability by combining a plasma reactor with an NOx selecting reducing catalyst. <P>SOLUTION: This emission control system 1 exhausts purified gas via an exhaust pipe by purifying exhaust gas generated by combustion in an oxygen excessive atmosphere, and has the plasma reactor 2, an NO<SB>2</SB>adsorption catalyst part 3 and an NOx selecting reducing catalyst part 4 from the exhaust pipe upstream side of the exhaust gas, and has an adding means 6 for adding a reducing agent to the exhaust pipe between the NO<SB>2</SB>adsorption catalyst part and the NOx selecting reducing catalyst part. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an exhaust gas purification system and an exhaust gas purification method. More specifically, NO in exhaust gas exhausted by combustion in an oxygen-excess atmosphere such as a diesel engine _x The present invention relates to an exhaust gas purification system and an exhaust gas purification method for purifying exhaust gas.
[0002]
[Prior art]
In recent years, due to the problem of global warming, engines that emit less carbon dioxide have attracted attention. Such engines include lean burn engines, gasoline direct injection engines, and diesel engines that burn fuel in an oxygen-rich atmosphere. Exhaust gas discharged from these engines includes nitrogen oxides (hereinafter referred to as NO _x That. ), So NO from exhaust gas _x NO as an exhaust gas after-treatment technology to remove NO _x A technique of applying an adsorption catalyst, UREA-SCR, or the like is general.
[0003]
For example, NO _x When an adsorption catalyst is applied, the air-fuel ratio needs to be changed from lean to rich, and then to stoichiometry.Therefore, it is necessary to add an equivalent or more hydrocarbon to the amount of oxygen to be inhaled. This results in significant fuel consumption loss.
[0004]
On the other hand, the UREA-SCR system is a system using a urea reduction type NOx catalyst (SCR = Selective Catalytic Reduction) using urea (Urea) as a reducing agent. In this UREA-SCE system, the exhaust gas first enters the oxidation catalyst, and converts the harmful substances CO (carbon monoxide) and HC (hydrocarbon) into harmless substances while increasing the ratio of NOx and NO2 in the exhaust gas. Purify. Then, urea [CO (NH) was introduced at the inlet of the SCR catalyst. _Two ) _Two ], And urea is converted into ammonia (NH _Three ) And this ammonia causes NO in the exhaust gas _x To reduce nitrogen (N _Two ) And water (H _Two O).
However, such a system always requires urea, which is a source of ammonia, and there remains a problem with the infrastructure development.
[0005]
Conventionally, NO _x NO as adsorption catalyst _x Although a selective reduction catalyst is used, in this case, NO _x Low unburned hydrocarbons required to purify the water.
NO in a lean atmosphere _x As a selective reduction catalyst, for example, as described in Patent Document 1, Pt-based NO _x A selective reduction catalyst is used. However, Pt-based NO is simply added to such exhaust gas. _x NO even if selective reduction catalyst is applied _x Poor purification rate. NO _x When a large amount of a reducing agent, that is, a hydrocarbon is added to exhaust gas to improve the purification rate of Pt, NO due to Pt-based NO _x Since the temperature falls outside the purification temperature range of the selective reduction catalyst, high NO _x Purification rates cannot be achieved.
[0006]
NO _x As a selective reduction catalyst, Patent Document 2 discloses an Ir-based NO _x A selective reduction catalyst is proposed. NO of this Ir system _x The selective reduction catalyst is NO _x Although the purification temperature range is high, the selectivity to paraffin (hydrocarbon), which is relatively large in the exhaust gas, is low, so that even if a large amount of hydrocarbon-based reducing agent is added, high NO _x Purification rates cannot be achieved.
[0007]
Further, Patent Document 3 discloses an Ag-based NO _x A selective reduction catalyst is proposed. According to Patent Document 3, this Ag-based NO _x The selective reduction catalyst has a high paraffin selectivity and a high NO by adding a large amount of a hydrocarbon reducing agent. _x It is said that a purification rate can be achieved. However, Ag-based NO described in Patent Document 3 _x The selective reduction catalyst is NO _x Since the purification temperature range is high, the activity is not sufficiently exhibited in the temperature range of diesel exhaust gas or the like.
[0008]
Therefore, in Patent Document 4 and Patent Document 5, high NO _x Plasma Reactor and NO to Achieve Purification _x A technique for combining with a selective reduction catalyst is described.
[0009]
[Patent Document 1]
Japanese Patent No. 2909553
[Patent Document 2]
JP-A-6-31173
[Patent Document 3]
JP-A-5-31173
[Patent Document 4]
JP-A-6-335621 (full text)
[Patent Document 5]
JP 2001-182525 A (full text)
[0010]
[Problems to be solved by the invention]
However, the plasma reactor and the NO _x NO used even when combined with selective reduction catalyst _x Due to the high purification temperature range of the selective reduction catalyst, NO _x NO of selective reduction catalyst _x At present, it is not possible to sufficiently exert the purifying ability.
Therefore, an object of the present invention is to provide a plasma reactor and a NO _x High enough NO in combination with selective reduction catalyst _x It is an object of the present invention to provide an exhaust gas purification system and an exhaust gas purification method having resolution.
[0011]
[Means for Solving the Problems]
The present invention for solving the above problems is an exhaust gas purification system that purifies exhaust gas generated by combustion in an oxygen-excess atmosphere and discharges the purified gas through an exhaust pipe. Reactor, NO _Two Adsorption catalyst part and NO _x A selective reduction catalyst section is provided (claim 1).
With this configuration, it is possible to efficiently purify the exhaust gas.
[0012]
The invention described in claim 2 is the exhaust gas purification system according to the present invention, wherein the NO _Two The adsorbing catalyst part is a porous carrier in which at least one metal element selected from the group consisting of (1) an alkali metal, an alkaline earth metal and a rare earth metal, and (2) a group selected from the group consisting of platinum, palladium and rhodium Carrying at least one type of metal atom _Two It is characterized by being composed of an adsorption catalyst.
With this configuration, it is possible to efficiently purify the exhaust gas in a wide exhaust gas temperature range.
[0013]
The invention according to claim 3 is the exhaust gas purification system according to the present invention, wherein the NO _x The selective reduction catalyst section is composed of a NO. _x It is characterized by comprising a selective reduction catalyst.
NO with silver supported on porous carrier _x The selective reduction catalyst has high NO _x While having a purifying ability, it has a disadvantage that the operating temperature range is high. In the present invention, such high NO _x It is possible to sufficiently exhibit the performance of a catalyst having a purifying ability.
[0014]
The invention described in claim 4 is the exhaust gas purification system according to the present invention, wherein the NO _x It is characterized by having a reducing agent adding means for adding a reducing agent to an exhaust pipe upstream of the selective reduction catalyst section.
With this configuration, the downstream NO _x NO in selective reduction section _x Purification efficiency can be improved.
[0015]
The invention according to claim 5 is the exhaust gas purification system according to the present invention, wherein the NO _Two It is characterized by having a reducing agent adding means for adding a reducing agent upstream of the adsorption catalyst section.
With this configuration, NO _Two It is easy to control the temperature of the adsorption catalyst section and the downstream thereof, and NO _Two Desorption temperature of adsorption catalyst and NO _x It becomes easy to raise the exhaust gas temperature to the operating temperature of the selective reduction catalyst.
[0016]
According to a sixth aspect of the present invention, an exhaust gas from an engine that burns fuel in an oxygen-excess atmosphere is supplied to a plasma reactor, _Two Adsorption catalyst part and NO _x An exhaust gas purification method for purifying via a selective reduction catalyst unit,
NO _Two The adsorption catalyst section has a component that raises the combustion reaction exhaust gas temperature of the reducing agent to the operating temperature of the NOx selective reduction catalyst section,
NO in exhaust gas in the plasma reactor _x NO _Two After oxidizing to NO _Two NO at adsorption catalyst _Two And adsorb the NO _Two NO in the adsorption catalyst section _Two Of adsorption by the engine speed and load _x Calculated from the integrated emission amount, and the calculated NO _Two If the amount of adsorption of NO has exceeded a predetermined value, the NO _Two A reducing agent is added upstream of the adsorption catalyst section to increase the reducing agent concentration in the exhaust gas, and the NO _x The NO constituting the selective reduction catalyst section _x While raising the exhaust gas temperature above the operating temperature of the selective reduction catalyst, the NO _Two NO from adsorption catalyst _Two Is discharged.
With this configuration, NO _x NO with high selectivity in the selective reduction catalyst section _x Can be purified.
[0017]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, the present invention will be described with reference to the accompanying drawings.
FIG. 1 is a schematic diagram showing an exhaust gas purification system according to the present invention. First, an exhaust gas purification system according to the present invention will be described with reference to FIG.
In the following description, a case in which the exhaust gas purification system according to the present invention is applied to a vehicle, a ship, and the like, and particularly a case in which the exhaust gas purification system is applied to a vehicle or a ship equipped with a diesel engine, will be mainly described. However, the present invention is not limited to such specific examples. Instead, the present invention is applied to an exhaust gas purification system for purifying various exhaust gases discharged by combustion in an oxygen-excess atmosphere.
[0018]
As shown in FIG. 1, an exhaust gas purification system 1 according to the present invention includes a pipe (P ₁ ~ P _Four ) Through the exhaust gas source side to the exhaust side (P ₁ P from the side _Four Side), at least one plasma reactor 2, NO _Two Adsorption catalyst unit 3 and NO _x And a selective reduction catalyst section 3.
[0019]
(Plasma reactor)
The plasma reactor 2 includes NOx contained in the exhaust gas due to plasma generated by combustion in an oxygen-excess atmosphere such as a lean burn engine, a gasoline direct injection engine, or a diesel engine. _x NO _Two Oxidizes to In addition, it is also possible to oxidize PM (particulate matter) using the oxidizing ability.
[0020]
The plasma reactor 2 of the present invention is not particularly limited as long as it achieves the object of the present invention, but a corona discharge, a pulse discharge, and a barrier discharge type can be applied. _x In consideration of the oxidizing ability of the above, a barrier discharge type is preferable. Although one plasma reactor 2 is arranged in FIG. 1, two or more plasma reactors 2 may be arranged (in series or in parallel) according to the type of exhaust gas, the form to be applied, and the like. It goes without saying that it is inside.
[0021]
(NO _Two Adsorption catalyst section)
NO _Two The adsorption catalyst section 3 contains NO oxidized by the plasma reactor 2. _Two It is composed of a catalyst for adsorbing.
Such catalysts have NO _Two In addition to the adsorption function, it has a heat-up function of heating the exhaust gas by causing a combustion reaction by the action of the reducing agent.
NO preferably used in the present invention _Two Examples of the adsorption catalyst include, but are not limited to, one or more of an alkali metal, an alkaline earth metal, or a rare earth metal and platinum (Pt), palladium (Pd), and rhodium (Rh) 1 on a porous body such as zeolite. A catalyst carrying a species or more can be suitably used.
Note that NO _Two NO constituting the adsorption catalyst unit 3 _Two The amount of the adsorption catalyst can be appropriately selected according to the amount of the gas to be treated. That is, NO _Two By determining the type and amount of the adsorption catalyst, NO _Two NO in adsorption catalyst section 3 _Two Is determined.
[0022]
In another embodiment of the present invention, the normal NO _Two A catalyst exhibiting an adsorbing action, for example, a catalyst in which one or more alkali metals, alkaline earth metals or rare earth metals are supported on a porous material such as zeolite, and a catalyst having a heat-up function, for example, a porous material such as zeolite And a catalyst in which one or more of platinum (Pt), palladium (Pd) and rhodium (Rh) are supported. Of course, NO having the heat-up function _Two The adsorption catalyst and the NO _Two The combination of the catalyst exhibiting the adsorption action and the catalyst having the heat-up function described above _Two It is also within the scope of the present invention to configure the adsorption catalyst section.
[0023]
In the present invention, NO _Two NO constituting the adsorption catalyst unit 3 _Two NO in adsorption catalyst _Two By adding a reducing agent such as hydrocarbon before the adsorption amount of NO is saturated, NO _Two The exhaust gas temperature is raised by the heat-up function of the adsorption _Two NO adsorbed on the adsorption catalyst _Two And NO _Two It is possible to revive the adsorption catalyst.
[0024]
(NO _x Selective reduction catalyst section)
NO _x The selective reduction catalyst section 4 is provided with NO in the exhaust gas. _x To selectively reduce NO _x Composed of a selective reduction catalyst, NO _Two It has a function of finally purifying and discharging the exhaust gas from the adsorption catalyst section 3. NO _x The selective reduction catalyst removes NO present in exhaust gas. _x And has a predetermined operating temperature range according to the type of the catalyst. NO _Two NO heated by the heat-up function of the adsorption catalyst unit 3 _Two NO constituting the adsorption catalyst unit 3 _Two NO of adsorption catalyst _Two Exhaust gas having a temperature higher than the desorption temperature is NO _Two After passing through the adsorption catalyst section 3, the downstream NO _x It flows into the selective reduction catalyst section 4.
[0025]
Therefore, NO _x NO constituting the selective reduction catalyst unit 4 _x The selective reduction catalyst has high NO _x It is desirable to use a catalyst having a purifying ability. The catalyst that can be suitably used in the present invention is not limited, and examples thereof include a catalyst in which Ag is supported on a carrier such as zeolite, for example, a catalyst described in JP-A-5-31173.
[0026]
With such a configuration, the exhaust gas purification system according to the present invention can efficiently purify exhaust gas generated by combustion in an oxygen-excess atmosphere such as combustion by a lean burn engine, a gasoline direct injection engine, or a diesel engine. It is possible.
[0027]
In the exhaust gas purification system according to the present invention, NO _Two The adsorption catalyst unit 3 and the NO _x There is provided a reducing agent adding means 6 for adding a reducing agent to the exhaust pipe P3 between the selective reduction catalyst unit 4 and the exhaust pipe P3.
The reducing agent adding means 6 increases the concentration of the reducing agent in the exhaust gas to reduce NO. _x NO constituting the selective reduction catalyst unit 4 _x Increase the selectivity of the selective reduction catalyst (ie, NO _x It is arranged in the exhaust gas purification system according to the present invention for the purpose of (improving purification performance).
The reducing agent adding means 6 may be the same as the reducing agent adding means 5, or may be provided separately from the reducing agent adding means 5 (in FIG. 1, the reducing agent adding means 6 is replaced with the reducing agent adding means 5). 5). Generally, in order to simplify the structure, the reducing agent adding means 5 and 6 are the same means, and it is preferable to change the adding position of the reducing agent by a valve or the like because the structure is simple.
[0028]
The reducing agent applicable to the exhaust gas purification system according to the present invention is not particularly limited, but a hydrocarbon used as a fuel of a combustion device to be treated is preferable. For example, when the exhaust gas purification system according to the present invention is an exhaust gas discharged from a diesel engine, it is preferable to use light oil used as fuel for the diesel engine as the reducing agent.
[0029]
NO _x The reducing agent adding means 6 for adding the reducing agent upstream of the selective reduction catalyst unit 4 _Two In one embodiment of the present invention, which is provided separately from the reducing agent adding means 5 for adding a reducing agent upstream of the adsorption catalyst section 3, the reducing agent adding means 6 removes NO from the fuel tank of the combustion device. _Two Adsorption catalyst unit 3 and NO _x A suction pipe (not shown) for drawing a fuel as a reducing agent into an exhaust pipe between the selective reduction catalyst section 4 is provided. A configuration in which spray means is provided can be adopted. When fuel is used as a reducing agent in this way, there is no need to develop a new reducing agent supply infrastructure, space can be saved, and simple improvements can be made to the fuel tank. preferable.
[0030]
NO _x The reducing agent adding means 6 for adding the reducing agent upstream of the selective reduction catalyst unit 4 _Two In another embodiment of the present invention provided separately from the reducing agent adding means 5 for adding a reducing agent upstream of the adsorption catalyst section 3, a reducing agent other than fuel, for example, a lower hydrocarbon other than fuel is used as the reducing agent. For example, when a reducing agent supply tank (not shown) is _Two Adsorption catalyst unit 3 and NO _x Spraying means for spraying a reducing agent to a predetermined position of the exhaust pipe between the selective reduction catalyst unit 4 and the exhaust pipe. This configuration has the advantage that the reducing power of the reducing agent can be freely selected.
Of course, the combined use of fuel and other reducing agents is also within the scope of the present invention.
[0031]
As described above, the exhaust gas purification system according to the present invention uses the NO oxidized in the plasma reactor 2. _Two NO _Two Adsorbed by the adsorption catalyst section 3 and NO _Two NO in adsorption catalyst section 3 _Two By increasing the exhaust gas temperature to the desorption temperature, NO _Two NO adsorbed on the adsorption catalyst unit 3 _Two Is discharged to the downstream NOx selective reduction catalyst unit 4, and the NOx is discharged at the operating temperature range of the NOx selective reduction catalyst constituting the NOx selective reduction catalyst unit 4. _Two To purify. However, when an engine such as a diesel engine is used, the temperature of the exhaust gas is unlikely to rise. _Two NO in the adsorption catalyst section 3 _Two The exhaust gas temperature does not rise to the desorption temperature, and NO _Two The adsorbing catalyst section 4 is provided with the NO flowing from the plasma reactor. _Two And the adsorption capacity may decrease. Further, since the exhaust gas temperature does not rise to the operating temperature of the NOx selective reduction catalyst in the NOx selective reduction catalyst section 4, NO _Two NO in the exhaust gas flowing to the NOx selective reduction catalyst unit 4 without being adsorbed by the adsorption catalyst unit 3 _Two Also passes through the NOx selective reduction catalyst unit 4 without being purified.
[0032]
Therefore, in the exhaust gas purification system according to the present invention, NO _x NO from integration of quantity _Two NO adsorbed on the adsorption catalyst unit 3 _Two Calculate the adsorption contact amount and set NO _Two NO constituting the adsorption catalyst unit 3 _Two By adding the reducing agent before the adsorption capacity of the adsorption catalyst is reduced, the reducing agent is burned by the heat-up function. This combustion heat reduces the exhaust gas temperature to NO. _Two NO in adsorption catalyst section 4 _Two It is possible to forcibly increase the temperature to the desorption temperature range and the operating temperature range of the NOx selective reduction catalyst in the NOx selective reduction catalyst unit 5.
[0033]
The exhaust gas purification system according to the present invention having such a configuration and operation can be suitably applied to vehicles such as vehicles and ships having a combustion engine involving combustion under excess oxygen such as a diesel engine. .
The exhaust gas purification system according to the present invention having such a configuration and operation has a very simple configuration and a high NO. _x NO with purification ability _x Since a selective reduction catalyst can be used, the present invention can be suitably applied to a vehicle, a ship or the like having a combustion engine accompanied by combustion under excess oxygen such as a diesel engine.
[0034]
[Operation of exhaust gas purification system (exhaust gas purification method)]
The exhaust gas purifying system according to the present invention has been described above. Next, the operation of the exhaust gas purifying system according to the present invention will be described with reference to FIG. 2 together with the exhaust gas purifying method according to the present invention.
FIG. 2 is a flowchart showing the operation of the exhaust gas purification system according to the present invention.
[0035]
First, the power of the plasma reactor 2 is turned on to turn off the NO in the exhaust gas. _x NO _Two Oxidized to NO _Two NO _Two Adsorption is performed by the adsorption catalyst unit 3 (S1).
Then, NO _Two NO in adsorption catalyst section 3 _Two Is measured (S2). NO _Two NO in adsorption catalyst section 3 _Two The adsorption amount of NO _Two NO constituting the adsorption catalyst unit 3 _Two There is a maximum value (saturation amount) determined in advance by the type and amount of the adsorption catalyst. In the present invention, a predetermined value that does not exceed the saturation amount, for example, 90% of the saturation amount is determined as the threshold.
[0036]
Note that NO _Two When the exhaust gas purification system according to the present invention is, for example, an engine of a vehicle or a ship, the adsorption amount of NO is first determined by the rotational speed and load of the engine. _x Integrate the emissions. Engine speed, load and NO _x The relationship with the emission amount is mapped in advance, and is obtained from the mapping value. NO _x Emissions and NO _Two Are proportional to each other (specifically, NO _Two NO if the adsorption amount of _x Emission amount = NO _Two Adsorption amount), NO _x NO from emissions _Two Is determined.
[0037]
Then, NO _Two It is determined whether or not the adsorption amount exceeds a predetermined amount (S3). _Two If the adsorption amount of NO does not exceed the predetermined amount (No), the process returns to S1, and NO in the exhaust gas _x NO _Two Oxidized to NO _Two NO _Two Adsorption is performed by the adsorption catalyst unit 3.
On the other hand, NO _Two If the adsorption amount exceeds a predetermined amount (Yes), the reducing agent is added downstream of the plasma reactor 2 to increase the reducing agent concentration in the exhaust gas (S4).
That is, the addition of fuel (reducing agent) _Two The heat-up function in the adsorption catalyst section 3 is induced by the addition of a reducing agent (initiation of a combustion reaction), and NO _Two NO constituting the adsorption catalyst unit 3 _Two NO of adsorption catalyst _Two Above the release temperature and NO _x NO constituting the selective reduction catalyst unit 4 _x The temperature of the exhaust gas is raised above the operating temperature of the selective reduction catalyst.
[0038]
And NO _x In order to promote the action of the selective reduction catalyst, NO _x It is preferable to add a reducing agent upstream of the selective reduction catalyst section 4 (S5: not shown).
In this way, the exhaust gas to which the reducing agent has been added to promote the reaction is NO _x Purification is efficiently performed by the selective reduction catalyst unit 4.
[0039]
【Example】
Hereinafter, the present invention will be described more specifically based on examples.
[Plasma reactor]
In the following Examples and Comparative Examples, the experimental plasma reactor 20 shown in FIG. 3 was used. That is, the experimental plasma reactor 20 has a configuration in which the electrode 22 on one side of the metal electrodes 21 and 22 facing each other is covered with the dielectric 22a, and plasma is generated between the dielectric and the metal electrode 21 on the other side. . The metal used for the metal electrodes 21 and 22 was SUS316 (thickness: 1.0 mm), and alumina (Al) was used for the dielectric 22a. _Two O _Three ) Ceramic (thickness: 0.5 mm) was used. The electrode size was 20 × 50 mm, and the thickness of the plasma space was 0.5 mm. In the experimental plasma reactor 20, the electrodes were stacked so that five layers of plasma space were generated, and the metal electrodes 22 were alternately set to the high electrode 21 and the ground electrode 22 and connected in parallel.
[0040]
The plasma generation conditions of the experimental plasma reactor 20 thus configured are as follows.
An AC sine wave of 200 MHz and an applied voltage of 7.6 V were input to the experimental plasma reactor 20. The power at this time was set to 3.1 W, the electric field strength was set to 7.6 kV / mm, and the power density was set to 1.2 W / cm. ^Three And
[0041]
NO _Two Preparation of adsorption catalyst (1):
80 g of dinitrodiammineplatinum / nitric acid solution (platinum: 5% by mass), 96 g of Na-Y type zeolite, and 1000 g of pure water are put in an eggplant-shaped flask. C. for 2 hours and in a muffle furnace at 600.degree. C. for 2 hours to obtain a platinum-supported Na-Y type zeolite powder.
90 g of the obtained powder, Si binder (SiO _Two (Concentration: 20%) 50 g, water 150 g and alumina balls were placed in a pot, and wet-pulverized for 12 hours to prepare a catalyst slurry.
The obtained catalyst slurry has a honeycomb volume of 30 cc and 400 cells / inch. ^Two (2.54cm ^Two ), A 6 mil cordierite honeycomb support was immersed, then the honeycomb support was taken out of the slurry, the excess was removed by air spraying, and the honeycomb support was fired at 150 ° C for 1 hour. This operation was repeated until a predetermined amount of supported catalyst was obtained. The honeycomb supporting a predetermined amount of the catalyst was calcined in a muffle furnace at 400 ° C. for 12 hours to obtain a Pt-supported Na-Y type zeolite catalyst (catalyst 1). The washcoat amount of this catalyst was 100 g / L.
[0042]
NO _Two Preparation of adsorption catalyst (2):
90 g of Na-Y type zeolite, Si binder (SiO _Two (Concentration: 20%) 50 g, water 150 g and alumina balls were placed in a pot, and wet-pulverized for 12 hours to prepare a catalyst slurry.
The obtained catalyst slurry has a honeycomb volume of 30 cc and 400 cells / inch. ^Two (2.54cm ^Two ), A 6 mil cordierite honeycomb support was immersed, then the honeycomb support was taken out of the slurry, the excess was removed by air spraying, and the honeycomb support was fired at 150 ° C for 1 hour. This operation was repeated until a predetermined amount of supported catalyst was obtained. The honeycomb supporting a predetermined amount of the catalyst was calcined in a muffle furnace at 400 ° C. for 12 hours to obtain a Na—Y type zeolite catalyst (catalyst 2). The washcoat amount of this catalyst was 100 g / L.
[0043]
NO _x Preparation of selective reduction catalyst
4.72 g of silver nitrate, 713.4 g of aluminum nitrate, 608.2 g of citric acid hydrate and 1000 g of pure water are put in an eggplant-shaped flask, excess water is removed by a rotary evaporator, and the mixture is dried at 200 ° C. in a drying furnace. It was calcined at 600 ° C. for 2 hours in a muffle furnace for 2 hours to obtain a silver-supported alumina powder.
90 g of the obtained powder, Si binder (SiO _Two (Concentration: 20%) 50 g, water 150 g and alumina balls were placed in a pot, and wet-pulverized for 12 hours to prepare a catalyst slurry.
The obtained catalyst slurry has a honeycomb volume of 30 cc and 400 cells / inch. ^Two (2.54cm ^Two ), A 6 mil cordierite honeycomb support was immersed, then the honeycomb support was taken out of the slurry, the excess was removed by air spraying, and the honeycomb support was fired at 150 ° C for 1 hour. This operation was repeated until a predetermined amount of supported catalyst was obtained. The honeycomb supporting a predetermined amount of the catalyst was fired in a muffle furnace at 500 ° C. for 2 hours to obtain an Ag-supported alumina catalyst (catalyst 3). The washcoat amount of this catalyst was 100 g / L, and the Ag loading was 3 g / L.
[0044]
(Examples 1 and 2 and Comparative Example 1)
The catalyst obtained in this manner was converted to 100 ppm of NO and HC (C _Ten H _{twenty two} ) 600 ppm (carbon equivalent), CO1100 ppm, CO _Two 4%, O _Two 15%, H _Two O4% and balance N _Two 4 (a) to 4 (c) using the model gas composed of _x The purification rate was examined. FIG. 5 shows the results.
[0045]
FIG. 4A is a schematic diagram showing a configuration of an exhaust gas treatment system according to one embodiment of the present invention, and FIG. 4B is a configuration of an exhaust gas treatment system according to another embodiment of the present invention. FIG. 4C is a schematic diagram illustrating a configuration of an exhaust gas treatment system according to a comparative example. 4 is a graph showing the relationship between the catalyst inlet temperature and the NOx purification rate using the present invention and the comparative exhaust gas treatment system.
[0046]
The exhaust gas purification system shown in FIG. 4 (a) heats an exhaust gas generated when a model gas is burned at a predetermined temperature in a heating furnace in an experimental plasma reactor 20, and generates NO. _Two Adsorption catalyst (catalyst 1) and NO _x This is an exhaust gas purification system of the present invention for purifying exhaust gas by a selective adsorption catalyst (catalyst 3). Note that NO _Two Adsorption catalyst (catalyst 1) and NO _x Between the selective adsorption catalyst (catalyst 3), a reducing agent adding means for adding a predetermined amount of hydrocarbon as a reducing agent is provided.
[0047]
The exhaust gas purifying system shown in FIG. 4 (b) heats the exhaust gas generated when the model gas is burned at a predetermined temperature in a heating furnace in the experimental plasma reactor 20, and generates NO. _Two Adsorption catalyst (catalyst 2) and NO _x This is an exhaust gas purification system of the present invention for purifying exhaust gas by a selective adsorption catalyst (catalyst 3). Note that NO _Two Adsorption catalyst (catalyst 2) and NO _x Between the selective adsorption catalyst (catalyst 3), a reducing agent adding means for adding a predetermined amount of hydrocarbon as a reducing agent is provided.
[0048]
The exhaust gas purifying system shown in FIG. 4 (c) heats the exhaust gas generated when the model gas is burned at a predetermined temperature in a heating furnace in the experimental plasma reactor 20, and generates NO. _Two NO without providing an adsorption catalyst (catalyst 1 or catalyst 2) _x This is a comparative exhaust gas purification system for purifying exhaust gas using a selective adsorption catalyst (catalyst 3). The plasma reactor 20 and NO _x Between the selective adsorption catalyst (catalyst 3), a reducing agent adding means for adding a predetermined amount of hydrocarbon as a reducing agent is provided.
[0049]
As shown in FIG. 5, the exhaust gas purification system of the present invention shown in FIG. _x Indicates the purification rate. Further, in the exhaust gas purification system of the present invention shown in FIG. 4 (b), although the purification rate is reduced at around 200 ° C. as compared with the exhaust gas purification system shown in FIG. _x Indicates the purification rate. On the other hand, the comparative exhaust gas purification system shown in FIG. _x It turns out that it hardly purifies.
[0050]
【The invention's effect】
As described above, the present invention has the following excellent effects.
According to the first aspect, it is possible to efficiently purify the exhaust gas.
According to the second aspect, the exhaust gas can be efficiently purified in a wide range of the exhaust gas temperature range.
According to the third aspect of the present invention, NO containing silver _x The selective reduction catalyst has high NO _x While having the purifying ability, it has a disadvantage that the operating temperature range is high, but in the present invention, such high NO _x It is possible to sufficiently exhibit the performance of a catalyst having a purifying ability.
According to claim 4, NO downstream _x NO in selective reduction section _x Purification efficiency can be improved.
According to claim 5, NO _Two It is easy to control the temperature of the adsorption catalyst section and the downstream thereof, and NO _Two Desorption temperature of adsorption catalyst and NO _x It becomes easy to raise the exhaust gas temperature to the operating temperature of the selective reduction catalyst.
According to claim 5, NO _x NO with high selectivity in the selective reduction catalyst section _x Can be purified.
[Brief description of the drawings]
FIG. 1 is a schematic view showing an exhaust gas purification system according to the present invention.
FIG. 2 is a flowchart showing the operation of the exhaust gas purification system according to the present invention.
FIG. 3 is a schematic view showing an experimental plasma reactor used in an example of the present invention.
FIG. 4 (a) is a schematic diagram showing a configuration of an exhaust gas treatment system according to one embodiment of the present invention, and FIG. 4 (b) is an exhaust gas treatment system according to another embodiment of the present invention. FIG. 4C is a schematic diagram illustrating a configuration of an exhaust gas treatment system according to a comparative example.
FIG. 5 is a graph showing the relationship between catalyst inlet temperature and NOx purification rate using the present invention and a comparative exhaust gas treatment system.
[Explanation of symbols]
1 Exhaust gas purification system
2 Plasma reactor
3 NO2 adsorption catalyst section
4 NOx selective reduction catalyst section
5,6 means for adding reducing agent

Claims (6)

An exhaust gas purification system for purifying exhaust gas generated by combustion in an oxygen-excess atmosphere and discharging purified gas through an exhaust pipe,
An exhaust gas purification system comprising: a plasma reactor, a NO ₂ adsorption catalyst section, and a NO _x selective reduction catalyst section from the exhaust pipe upstream of the exhaust gas. The NO ₂ adsorption catalyst section comprises a porous carrier comprising at least one metal element selected from the group consisting of (1) an alkali metal, an alkaline earth metal and a rare earth metal, and (2) platinum, palladium and rhodium. exhaust gas purifying system according to claim 1, characterized by being composed of at least one metal atom selected from the group from carrying the NO ₂ adsorptive catalyst. Wherein _the NO _x selective reduction catalyst unit, an exhaust gas purifying system according to claim 1 or claim 2, characterized in that it is composed of _the NO _x selective reduction catalyst supported silver on a porous support. The exhaust gas purification system according to claim 1, further comprising a reducing agent adding unit that adds a reducing agent to an exhaust pipe upstream of the NO _x selective reduction catalyst unit. The exhaust gas purifying system according to claim 1, further comprising a reducing agent adding means for adding a reducing agent upstream of the NO ₂ adsorption catalyst section. The exhaust gas from the engine burning the fuel in an oxygen-rich atmosphere, a plasma reactor, NO ₂ adsorptive catalyst unit and NO _x exhaust gas purification method for purifying through the selective reduction catalyst unit from the engine side,
The NO ₂ adsorptive catalyst unit is a combustion reaction gas temperature of the reducing agent has a component is raised to the operating temperature of the NOx selective reduction catalyst unit,
After oxidizing the NO _x in the exhaust gas to NO ₂ by the plasma reactor, adsorbs NO ₂ in the NO ₂ adsorptive catalyst unit,
The NO ₂ adsorption amount in the NO ₂ adsorption catalyst section is calculated from the integration of the NO _x emission amount due to the engine speed and load,
When the calculated adsorption amount of NO ₂ is equal to or more than a predetermined value, a reducing agent is added upstream of the NO ₂ adsorption catalyst unit to increase the concentration of the reducing agent in the exhaust gas, and the NO _x selective reduction catalyst unit the NO with increasing exhaust gas temperature above the operating temperature of _x selective reduction catalyst, method for purifying exhaust gas, characterized in that discharging the NO ₂ from the NO ₂ adsorptive catalyst unit constituting the.

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