JP2004283823A - Exhaust gas purification system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an exhaust gas purification system having a high removal rate of NOx. <P>SOLUTION: This exhaust gas purification system 1 is provided with a plasma reactor 3 and an NOx selectively reducing catalyst unit 4 having an NOx selectively reducing catalyst layer acting on the exhaust gas in this order in an exhaust gas circulating route from the upstream side to the downstream side. A reducing agent adding means 2 is arranged on the upstream side of the reactor 3 for adding a reducing agent to the exhaust gas. Nickel of ≥0.9 mass% and ≤3.6 mass% and silver (an NOx selectively reducing catalyst) of ≥1.5 mass% and ≤5 mass% are contained in the NOx selectively reducing catalyst layer on the basis of the NOx selectively reducing catalyst layer. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

The present invention relates to an exhaust gas purification system, and more particularly, to an exhaust gas purification system that purifies NO _X in exhaust gas in an oxygen-excess atmosphere.

Conventionally, nitrogen oxides in the exhaust gases, such as oxygen concentration is high in exhaust gas of a diesel engine (hereinafter, collectively referred to as NO _X) as a system for purifying, NO _X adsorbing catalyst exhaust gas purification system and urea reduction NO _X catalyst using BACKGROUND ART An exhaust gas purification system using (UREA-SCR: UREA-Selective Catalytic Reduction) is known.

However, the exhaust gas purification system using the NO _X adsorbing catalyst, the air-fuel ratio from lean to rich, and it is necessary to further change to stoichiometric, there is a problem that results in a loss of significant fuel economy. Further, the exhaust gas purification system using the urea reduction NO _X catalyst, a problem remains in that the development of the infrastructure of the urea is essential.

Therefore, instead of the NO _X adsorbing catalyst and urea reduction NO _X catalyst, NO _X selective reducing catalyst, specifically, platinum catalyst (e.g., see Patent Document 1), an iridium-based catalyst (e.g., see Patent Document 2 ) Or a silver-based catalyst (for example, see Patent Document 3).

However, the exhaust gas purification system using the platinum catalyst, such as hydrocarbons (hereinafter referred to as HC) becomes a reducing agent such as low Without the addition of the exhaust NO _X purification rate, whereas a large amount of the added amount of HC If so, the heat of oxidation of HC deviates from the appropriate NO _x purification temperature range, so that a system with a high NO _x purification rate cannot be constructed.

Also, in the exhaust gas purification system using the iridium-based catalyst has high purification temperature range of proper NO _X, yet poor paraffin selectivity of the catalyst. Therefore, even if this exhaust gas purification system is applied to a diesel engine having a low exhaust gas temperature and a high paraffin concentration in the exhaust gas, it is not possible to sufficiently purify NO _X in the exhaust gas.

Further, in the exhaust gas purification system using the silver-based catalyst, for purifying temperature range of proper NO _X is high, even when applying this exhaust gas purification system exhaust gas temperature is low diesel engine, thoroughly NO _X in the exhaust gas It cannot be purified.

In connection with such technology, in combination with plasma reactor and silver / alumina catalyst "NO _X purifying plasma-assisted catalyst" has been proposed (e.g., see Patent Document 4).

Japanese Patent No. 2909553 (page 3, line 5, line 14-column 6, line 25) JP-A-6-31173 (page 4, column 5, line 4-column 6, line 20) JP-A-5-92125 (page 4, column 6, line 35-page 5, column 8, line 22) JP-A-2002-210366 (pages 2 to 5, FIG. 1)

However, the disclosed in Patent Document 4 "NO _X purifying plasma-assisted catalyst", the addition of HC and the like as a reducing agent to maintain the NO _X ratio, coking occurs, NO _X purification rate decreases There was a problem.

The factors that cause caulking are, for example, as follows.
As shown in FIG. 8, when the NO _X selective reduction catalyst layer 120 laminated to a support 111 having a pore 111a is exhaust gas containing HC and the like is supplied, HC and the like in deep positions open pore 124 intrusion and, on the surface of the porous support 121, or deposit 126 forms which contain a carbon or the like unburnt fuel in HC or engine generated by decomposition, silver or the like supported on the surface a porous support 121 NO _X It is expected that the deposit 126 is formed so as to cover the selective reduction catalyst 122. FIG. 8 is a partially enlarged drawing schematically showing a partially enlarged cross section of a conventional NO _X selective reduction catalyst layer.
With such deposit 126 forms, together with the catalytic function of the NO _X selective reducing catalyst 122 is impaired, finally closed continuous pores 124, reduces the contact area with the exhaust gas, NO _X purification rate It is thought to decrease.

The present invention aims to provide a high exhaust gas purification system of NO _X purification rate.

As a means for solving the above problem, the invention according to claim 1 comprises, from the upstream side of the exhaust gas flows to the downstream side, NO _X having a plasma reactor, the _the NO _X selective reducing catalyst layer acting on the exhaust gas An exhaust gas purification system comprising: a selective reduction catalyst unit; and a reducing agent adding means for adding a reducing agent to the exhaust gas on the upstream side of the plasma reactor, wherein the NO _X selective reduction catalyst layer comprises nickel and NO _X An exhaust gas purifying system comprising a selective reduction catalyst.

According to such an exhaust gas purification system, NO _X and NO ₂ with a reducing agent and _the NO _X selective reducing catalyst is decomposed, NO _X in the exhaust gas is purified.
By excess reducing agent is appropriately oxidized and removed by high oxidation capacity nickel, since coking does not easily occur, continuous also NO _X purification rate by the use of an exhaust gas purification system is less likely to decrease .

Invention, the content of the nickel, the exhaust gas according to claim 1, wherein the relative _the NO _X selective reducing catalyst layer is at least 0.9 wt% 3.6 wt% or less according to claim 2 It is a purification system.

According to such an exhaust gas purification system, by nickel contained 3.6 wt% to 0.9 wt% in _the NO _X selective reducing catalyst layer, without NO _X purification rate decreases, suitably NO _X Can be purified.

The invention according to claim 3, wherein _the NO _X selective reducing catalyst is an exhaust gas purifying system according to claim 1 or claim 2, characterized in that it comprises silver.

According to such an exhaust gas purification system, by containing the silver in the NO _X selective reduction catalyst, NO _X in the exhaust gas is suitably decomposed, without NO _X purification rate decreases, suitably purify NO _X can do.

The invention according to claim 4, the content of the silver, purification of exhaust gas according to claim 3, wherein the _the NO _X selective reducing catalyst layer with respect to at most 1.5 mass% to 5 mass% System.

According to such an exhaust gas purification system, by silver contained 1.5 wt% to 5 wt% or less in _the NO _X selective reducing catalyst layer, without NO _X purification rate decreases, suitably purify NO _X can do.

According to the present invention, an exhaust gas purification system having a high NO _X purification rate can be provided.

Hereinafter, an embodiment of the present invention will be described in detail with reference to FIGS.
In the drawings to be referred to, FIG. 1 is a block diagram schematically showing a configuration of an exhaust gas purification system according to the present embodiment. FIG. 2 is a partial cross-sectional view partially showing a catalyst member of the NO _X selective reduction catalyst unit of the exhaust gas purification system shown in FIG. Figure 3 is a partially enlarged view showing _the NO _X selective reducing catalyst layer of the catalyst member shown in FIG. 2 partially. FIG. 4 is a graph showing the relationship between the silver content in the NO _X selective reduction catalyst layer and the NO _X purification rate.

[Exhaust gas purification system]
As shown in FIG. 1, an exhaust gas purification system 1 includes a plasma reactor 3 and a NO _X from a flue gas generation side (upstream side) to an exhaust side (downstream side) via pipes (P _{1 to} P ₃ ). comprising a selective reduction catalyst unit 4 is configured by providing the reducing agent adding means 2 in front of the plasma reactor 3, a system for purifying NO _X in the exhaust gas under an oxygen rich atmosphere.

(Reducing agent addition means)
Reducing agent adding means 2 is for supplying the reducing agent into the exhaust gas in the pipe P ₁ on the upstream side of the plasma reactor 3. The reducing agent supply means 2 can be constituted by, for example, a known fuel injection mechanism or a post-injection mechanism for injecting fuel into the pipe of the engine.

The reducing agent used in the reducing agent adding means 2, as long as the reduction of NO _X in the exhaust gas is not particularly limited in the present invention can be used such as hydrocarbons (HC) and the like.
Further, for example, when the exhaust gas purification system 1 is applied to a diesel vehicle equipped with a diesel engine, a diesel engine fuel (light oil) containing HC is used as a reducing agent, and this fuel is supplied from the fuel tank to the pipe P _1. It can be easily configured by appropriately providing an ejector, a feed pump, a pipe, and the like so as to be supplied to the inside.

(Plasma reactor)
The plasma reactor 3 converts NO _X in exhaust gas by combustion into NO ₂ by combustion in an oxygen-excess atmosphere such as a lean burn engine, a gasoline direct injection engine, or a diesel engine.
The plasma reactor 3 generates active species such as radicals from the reducing agent such as HC added by the reducing agent adding means 2 by plasma.
Further, the plasma reactor 3 can also oxidize PM (Particulate Matter) such as sulfate generated from residual fuel particles and sulfur content in the fuel.

The plasma reactor 3 is not particularly limited as long as it achieves the object of the present invention, and may be appropriately selected from known plasma reactors such as a corona discharge type, a pulse discharge type, and a barrier discharge type. it can. Among this, considering the oxidizing ability of PM and NO _X, it is preferable to select a barrier discharge type of plasma reactor 3.
Further, in the present embodiment, as shown in FIG. 1, one plasma reactor 3 is arranged, but a plurality of plasma reactors are appropriately connected in series or in parallel according to the type of exhaust gas, the form to be applied, and the like. It may be arranged.

(NO _X selective reduction catalyst unit)
The NO _X selective reduction catalyst unit 4 is arranged at the subsequent stage of the plasma reactor 3 and includes therein a catalyst member 10 including a support 11 having a plurality of pores 11a through which exhaust gas flows (FIG. 2). reference). The catalyst member 10, the support 11 has a _the NO _X selective reducing catalyst layer 20 formed so as to cover the inner wall surface 11b surrounding the plurality of pores 11a of the support 11.
Here, the NO _X selective reduction catalyst layer 20 is generally called a “wash coat (layer)” because it is manufactured by impregnating the support 11 with a slurry-like NO _X selective reduction catalyst slurry as described later. .

The shape of the support 11 is not particularly limited in the present invention as long as it has a space through which the exhaust gas flows, and in the present embodiment, as shown in FIG. A honeycomb-shaped one having a plurality of pores 11a is used.
Further, the support 11 is preferably formed from a material having heat resistance. Examples of such a material include a porous body (ceramic) such as cordierite, mullite, and silicon carbide (SiC), and a metal (eg, stainless steel).

As shown in FIG. 3, the NO _x selective reduction catalyst layer 20 is formed mainly of a porous carrier 21 serving as a skeleton, and silver 22 and nickel 23 carried on the surface of the porous carrier 21. Inside of the NO _X selective reduction catalyst layer 20, a plurality of continuous pores 24 that is continuous with the pores 11a of the support 11 is formed. Since the NO _X selective reduction catalyst layer 20 has the plurality of continuous pores 24, the contact area with the exhaust gas is dramatically increased, so that NO _X can be efficiently purified.

  The porous carrier 21 can be formed by appropriately selecting and using, for example, alumina, zeolite, silica, titania, zirconia, silica-alumina and the like.

Silver 22 is a catalyst which promotes the NO _X, the decomposition reaction of NO ₂ with a reducing agent such as HC.

The content of silver 22 is preferably (preferable range) that relative to the mass of the NO _X selective reduction catalyst layer 20 is within the following 5 mass% to 1.5 mass%, further 2.0 mass % Is preferably in the range of 4.0% by mass or more (optimal range).
This is because, as shown in FIG. 4, when the content of silver 22 is below 1.5 wt%, small contact area with the NO _X, that is because the decomposition reaction sites of the NO _X is reduced, NO _X purification rate Is less than 70%, and there is a tendency that effective purification of NO _X cannot be expected. On the other hand, if the content of silver 22 exceeds 5% by mass, the reducing agent added to reduce NO _X is preferentially oxidized, and as a result, the NO _X purification rate falls below 70%, and NO _This is because effective purification of _X tends not to be expected. Furthermore, in the content of silver 22 is within 2.0 wt% to 4.0 wt%, NO _X purification rate since 80% or more, can be cleaned more favorably.
Incidentally, FIG. 4, for _the NO _X selective reducing catalyst layer of nickel 23 containing 1.8 g / L, is a graph showing the relationship between silver content and NO _X purification rate.

Nickel 23 is a substance having a high oxidizing ability. Therefore, nickel 23 is included in the NO _x selective reduction catalyst layer 20 to decompose (oxidize) a reducing agent such as HC. Therefore, caulking hardly occurs.
Further, in addition to nickel 23, platinum (Pt), palladium (Pd), rhodium (Rh) and the like can be cited as substances having an oxidizing ability. However, since these have too strong oxidizing ability, a reducing agent and HC-NO _X The intermediates and the like are burned, and the NO _X purification rate tends to decrease. However, nickel 23 has an appropriate oxidizing ability as compared with platinum (Pt) or the like, and thus can be used favorably.

The content of nickel 23, NO with respect to the mass of the _X selective reduction catalyst layer 20 is preferably in the range of 0.9 wt% and not more than 3.6 mass%. If the content of nickel 23 is less than 0.9% by mass, the oxidizing ability of nickel 23 as a whole is too low to decompose a reducing agent such as HC, so that coking is generated and the NO _X purification rate is reduced. This is because there is a tendency. On the other hand, when the supported amount of nickel 23 exceeds 3.6 wt%, will preferentially the oxidation of the reducing agent such as HC by nickel 23, i.e. the reducing agent is preferentially oxidized (burned) for reducing the NO _X It will be drain in, as a result, NO _X purification rate is because there is a tendency to decrease.

  Next, the operation of the exhaust gas purification system 1 according to the present embodiment will be described with reference to FIGS.

First, for example, when an engine (not shown) operates, exhaust gas is supplied from the upstream side of the exhaust gas purification system 1.
Then, a reducing agent is added to the exhaust gas from the reducing agent adding means 2.

It is preferable that the addition amount of the reducing agent is appropriately adjusted according to the amount of the exhaust gas. That is, for example, when the exhaust gas purification system 1 is applied to an exhaust system connected to an engine or the like of a vehicle or a ship, the relationship between the engine speed and the amount of NO _{X in} the exhaust gas discharged is measured in advance. Based on this, a reducing agent addition amount control device including a CPU or the like may be provided to automatically add an appropriate amount of reducing agent.

Then, the power of the plasma reactor 3 is turned on to generate plasma, convert NO _X in the exhaust gas to NO ₂ , and generate active species such as radicals from a reducing agent such as HC.

Exhaust gas containing active species such as HC and radicals (hereinafter referred to as “active HC”), NO ₂ , and NO _X is supplied to the pores 11a of the NO _X selective reduction catalyst unit 4 (see FIG. 2).

When the exhaust gas is supplied to the pores 11a, as shown in FIG. 3, HC, active HC, NO ₂ , NO _{X and the} like approach the surface of the NO _X selective reduction catalyst layer 20 and a part thereof is continuous. It penetrates the pores 24. Then, NO ₂ and NO _X are rapidly decomposed into CO ₂ , H ₂ O, and N ₂ by HC and active HC using silver 22 as a catalyst.

Further, for example, the supply amounts of HC and NO _X supplied to the fine holes 11 a fluctuate due to a rapid fluctuation of the engine speed, and, for example, excess HC is removed from the continuous fine holes 24 of the NO _X selective reduction catalyst layer 20. HC is decomposed by nickel 23 having high oxidizing ability.
Therefore, no deposit is formed on the surface of the porous carrier 21 so as to cover the silver 22 and the nickel 23. Further, the continuous pores 24 are not blocked. Therefore, even if the NO _X selective reduction catalyst unit 4 is continuously used, the NO _X purification rate does not decrease.

According to the exhaust gas purification system 1, without producing coking in high NO _X purification rate can be suitably purify NO _X in the exhaust gas.

  Hereinafter, the present invention will be described in more detail based on examples, but the present invention is not limited to the following examples.

(Example 1)
(1) NO _X production of silver nitrate selective reduction catalyst unit used to catalyze member (AgNO ₃₎ 4.72g, boehmite _{(γ-Al 2 O 3 ·} H 2 O) 127g, nickel nitrate [Ni (NO _{3) 2]} After 9.9 g and 1000 g of pure water were placed in an eggplant-shaped flask and stirred, excess water was removed with a rotary evaporator. Then, it was dried at 200 ° C. for 2 hours in an appropriate drying furnace. Then, it was calcined at 200 ° C. for 2 hours in a muffle furnace to obtain an Ag / Ni / Al ₂ O ₃ catalyst powder.

90 g of the Ag / Ni / Al ₂ O ₃ catalyst powder thus obtained, 50 g of alumina binder (Al ₂ O ₃ concentration: 20%) and 150 g of pure water were put into a pot together with alumina balls, and wet-pulverized for 12 hours. A slurry-like catalyst slurry was prepared.

The thus prepared catalyst slurry had a honeycomb volume of 30 mL, a density of pores per unit volume of 62.0 cells / cm ² (400 cells / square inch), and an opening diameter of pores of 152 μm ( (6 mil) cordierite honeycomb support was immersed for an appropriate time. Thereafter, the honeycomb support was taken out of the catalyst slurry, and the excessively attached catalyst slurry was removed by air spray, and then dried at 150 ° C. for 1 hour.
Such an operation was repeated until a predetermined amount of supported catalyst was obtained.
After a predetermined amount of catalyst was loaded, the honeycomb support was fired in a muffle furnace at 500 ° C. for 2 hours.
In this manner, comprises silver and nickel, _the NO _X selective reducing catalyst layer mainly composed of γ- alumina formed on the pore walls of the honeycomb support was produced a catalyst member used in Example 1.
To the unit volume of the pores of the honeycomb substrate, the amount of _the NO _X selective reducing catalyst layer (wash coat amount) is 150 g / L, the content of silver 4.1 g / L, nickel content 2.7 g / L.
Accordingly, the content of silver to _the NO _X selective reducing catalyst layer 2.7% by weight, the nickel content becomes 1.8 mass%.

(2) Configuration of Exhaust Gas Purification System Next, the configuration of the exhaust gas purification system according to the first embodiment will be described with reference to FIGS. FIG. 5 is a drawing schematically showing a configuration of the exhaust gas purification system according to the first embodiment of the present invention. FIG. 6 is a side sectional view schematically showing a configuration of a plasma reactor of the exhaust gas purification system shown in FIG.

As shown in FIG. 5, the exhaust gas purification system 50 according to the first embodiment, from the upstream side to the downstream side, a heating furnace 60 for heating the model gas, the plasma reactor 70, and _the NO _X selective reducing catalyst unit 80 It has. A desired amount of HC as a reducing agent can be added to the model gas between the heating furnace 60 and the plasma reactor 70 by an appropriate device. Further, at the subsequent stage of the exhaust gas purification system 50, an analyzer 90 for analyzing the composition of the purified gas is provided.

As shown in FIG. 6, the plasma reactor 70 used in the exhaust gas purification system 50 has metal electrodes 72, 73, 74 among metal electrodes 71, 72, 73, 74, 75, 76 arranged in order at predetermined intervals. , 75, and 76 are covered with dielectrics 72a, 73a, 74a, 75a, and 76a, respectively, and the metal electrodes 71, 73, and 75 are connected to the high-voltage input side, and the metal electrodes 72, 74, and 76 are connected. A plasma is generated between the dielectrics 72a, 73a, 74a, 75a, and 76a and the metal electrodes 71, 72, 73, 74, and 75 opposed to each other at the above-described interval by being connected to the ground side (GND) (plasma generation). Part).
That is, the plasma reactor 70 is formed with five plasma generating portions in a layered form, and a model gas to which HC is added is supplied to the five plasma generating portions.

The metal electrodes 71, 72, 73, 74, 75, and 76 were formed of SUS316, and had a thickness of 1.0 mm and a size of 20 × 50 mm. The dielectrics 72a, 73a, 74a, 75a, and 76a were formed of alumina (Al ₂ O ₃ ) ceramic, and the coating thickness was 0.5 mm.
Further, the distances between the metal electrode 71 and the dielectric 72a, the distance between the metal electrode 72 and the dielectric 73a, the distance between the metal electrode 73 and the dielectric 74a, the distance between the metal electrode 74 and the dielectric 75a, and the distance between the metal electrode 75 and the dielectric 76a are each 0. 5 mm.

The plasma generation conditions by the plasma reactor 70 were as follows.
A 200 Hz AC sine wave and an applied voltage of 7.6 kV were input to the plasma reactor 70. At this time, the power 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 ³ .

The NO _X selective reduction catalyst unit 80 was configured by loading the catalyst member manufactured in Example 1 in a predetermined casing.

As model gas, nitrogen monoxide (NO) 300 ppm, carbon monoxide (CO) 1100 ppm, carbon dioxide (CO ₂ ) 4% by volume, oxygen (O ₂ ) 11% by volume, water (H ₂ O) 6% by volume and A composition composed of the balance of nitrogen (N ₂ ) was used. The concentrations of the components in the model gas are values at 25 ° C. (room temperature) and 1 atm (atmospheric pressure).

As HC, normal hexadecane (nC ₁₆ H ₃₄ ) having a carbon equivalent of 2000 ppm was used.

(3) Evaluation Test of Exhaust Gas Purification System The following evaluation test was performed on the exhaust gas purification system according to Example 1.

(3-1) Time-dependent change test of NO _X purification rate and its evaluation In this test, a model gas heated to 300 ° C. was introduced into an exhaust gas purification system 50 equipped with the catalyst member of Example 1, and the exhaust gas purification system The amount of NO _X in the gas discharged from 50 was measured over time with an analyzer 90 (see FIG. 5). Then, to calculate the NO _X purification rate over time based on the measurement result. FIG. 7A shows the change over time of the NO _X purification rate in the exhaust gas purification system 50.

(3-2) Measurement Test of Maximum NO _X Purification Rate Using Exhaust Gas Purification System and Its Evaluation In this evaluation test, an exhaust gas purification system 50 provided with the catalyst members of Example 1, Examples 2 and 3 described later. In addition, a model gas heated to 300 ° C. is introduced into an exhaust gas purification system provided with a catalyst member of a comparative example, and the NO _X amount in the gas discharged from the exhaust gas purification system 50 is measured by an analyzer 90 (see FIG. 5). Was measured. Then, the NO _X purification rate of the exhaust gas purification system 50 was calculated using the following equation (1). The NO _X purification rate immediately after the start of the measurement was defined as the maximum NO _X purification rate. FIG. 7B shows the measurement results.

(Example 2)
A manufacturing method of the NO _X selective reduction catalyst layer according to the second _{embodiment, Ag / Ni / Al 2 O} 3 of nickel nitrate in making the catalyst powder (AgNO ₃₎ and 4.95 g, the unit of the pores of the honeycomb substrate with the exception that the content of nickel to volume 1.35 g / L (amount of nickel to _the NO _X selective reducing catalyst layer was 0.9 wt%) and, in the same manner as in example 1 forming the exhaust gas purifying system The NO _x purification rate was measured in the same manner as in Example 1. The result is shown in FIG.

(Example 3)
The method for producing the NO _x selective reduction catalyst layer according to Example 3 is as follows: 19.8 g of nickel nitrate (AgNO ₃ ) when producing the Ag / Ni / Al ₂ O ₃ catalyst powder, and the unit of pores of the honeycomb support. 5.4 g / L of nickel content to volume (nickel content for _the NO _X selective reducing catalyst layer is 3.6 mass%) except for using, as well as forming the exhaust gas purifying system in the same manner as in example 1 The NO _x purification rate was measured in the same manner as in Example 1. The result is shown in FIG.

(Comparative example)
The method for producing the NO _X selective reduction catalyst layer according to the comparative example is the same as that of Example 1 except that nickel / nitrate (AgNO ₃ ) was not used and the Ag / Al ₂ O ₃ catalyst powder was adjusted. Was configured. Incidentally, with respect to a unit volume of the pores of the honeycomb support, NO _X selective reduction catalyst layer 150 g / L, the content of the silver content of silver to 4.1g / L (NO _X selective reduction catalyst layer 2 0.7% by mass). Then, a measurement test of the NO _X purification rate was performed in the same manner as in Example 1.

The materials used in manufacturing the NO _X selective reduction catalyst layers according to Examples 1 to 3 and Comparative Examples described above, and the contents of silver and nickel in the manufactured NO _X selective reduction catalyst layers are shown in Table. 1 together.

(4) Measurement Results of Exhaust Gas Purification System Next, measurement results will be described with reference to FIGS. 7 (a) and 7 (b). FIG. 7A is a graph showing the change over time in the NO _X purification rate of the model gas heated to 300 ° C. in Example 1 and Comparative Example. FIG. 7B is a graph showing the relationship between the nickel content and the maximum NO _X purification rate immediately after the experiment for Examples 1 to 3 and Comparative Example.

(4-1) Example 1 and is apparent from graph showing the change in 7 of the NO _X purification rate of the exhaust gas purifying system (a) according to the comparative example, in Example 1 that contains nickel in the NO _X selective reducing catalyst layer According to the figure, it is understood that the rate of decrease in the NO _X purification rate with time is smaller than that in the comparative example containing no nickel. Therefore, nickel by being included in _the NO _X selective reducing catalyst layer, coking it is seen that improved hardly durability occurs.

(4-2) Maximum NO _X Purification Rate in Exhaust Gas Purification Systems According to Examples 1 to 3 and Comparative Example As is clear from FIG. 7B, the nickel content in the NO _X selective reduction catalyst layer is 0%. if it is within the range of .9 mass% and not more than 3.6 mass%, it can be seen that satisfactorily purify NO _X.
As apparent from FIG. 7 (b), an exhaust gas purification system according to the present invention with _the NO _X selective reducing catalyst layer containing nickel in 3.6 wt% or less with respect to _the NO _X selective reducing catalyst layer Also, a good maximum NO _X purification rate comparable to that of an exhaust gas purification system having a NO _X selective reduction catalyst layer containing no nickel (Comparative Example) is maintained. That is, if is less than 3.6 mass% content of nickel relative to the amount of _the NO _X selective reducing catalyst layer, it is understood that it is possible to satisfactorily purify NO _X in the exhaust gas.

  As described above, an example of the preferred embodiment of the present invention has been described. However, the present invention is not limited to the above-described embodiment, and for example, the following appropriate changes can be made without departing from the spirit of the present invention.

In the embodiment described above, the exhaust gas purification system 1, the reducing agent addition means 2 separate, but the plasma reactor 3 and _the NO _X selective reducing catalyst unit 4 was formed by connecting a pipe P ₁ to P _3, other example, without providing the piping the reducing agent adding means 2 may be constituted by an integrated plasma reactor 3 and _the NO _X selective reducing catalyst unit 4. Since the integrated exhaust gas purification system can be downsized as described above, it can be easily mounted on a small vehicle, for example.

It is a block diagram showing typically composition of an exhaust gas purification system concerning this embodiment. FIG. 2 is a partial cross-sectional view partially showing a catalyst member of a NO _X selective reduction catalyst unit of the exhaust gas purification system shown in FIG. 1. The _the NO _X selective reducing catalyst layer of the catalyst member shown in FIG. 2 is a partially enlarged view showing partially. 5 is a graph showing the relationship between the silver content in the NO _X selective reduction catalyst layer and the NO _X purification rate. 1 is a drawing schematically showing a configuration of an exhaust gas purification system according to one embodiment of the present invention. FIG. 6 is a side sectional view schematically showing a configuration of a plasma reactor of the exhaust gas purification system shown in FIG. 5. (A) is a graph showing a change with time of the NO _X purification rate. (B) is a graph showing the relationship between the nickel content of the NO _x selective reduction catalyst layer and the maximum NO _x purification rate immediately after the start of measurement. It is a partial enlarged drawing which shows the cross section of the conventional NO _X selective reduction catalyst layer in a partially enlarged manner.

Explanation of reference numerals

1 exhaust gas purification system 2 reducing agent adding means 3 plasma reactor 4 NO _X selective reduction catalyst unit 10 catalyst member 11 supports 11a pores 11b in the wall 20 NO _X selective reduction catalyst layer 21 porous support 22 silver 23 Nickel 24 open pore P _1, P _2, P ₃ pipes

Claims (4)

From the upstream side of the exhaust gas to flow toward the downstream side, and the plasma reactor, and a _the NO _X selective reducing catalyst unit having _the NO _X selective reducing catalyst layer which acts on the exhaust gas, the exhaust gas upstream of the plasma reactor An exhaust gas purification system provided with a reducing agent adding means for adding a reducing agent,
Wherein _the NO _X selective reducing catalyst layer, the exhaust gas purification system characterized by containing nickel and _the NO _X selective reducing catalyst. The content of the nickel, the exhaust gas purifying system according to claim 1, characterized in that with respect to the _the NO _X selective reducing catalyst layer is not more than 0.9 mass% to 3.6 mass%. Wherein _the NO _X selective reducing catalyst, the exhaust gas purifying system according to claim 1 or claim 2, characterized in that it comprises silver. The content of the silver, the exhaust gas purifying system according to claim 3, wherein the _the NO _X selective reducing catalyst layer with respect to at most 1.5 mass% to 5 mass%.

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