JP2002331226A - Method and apparatus for cleaning exhaust gas - Google Patents

Abstract

PROBLEM TO BE SOLVED: To efficiently clean methane from a low temperature region and to also reduce the discharge amount of NOx . SOLUTION: An NOx occluding reduction type catalyst is arranged on the upstream side of an exhaust gas stream and a methane oxidizing catalyst is arranged on the downstream side thereof. Since NOx and SOx are not contained in the exhaust gas flowing in the methane oxidizing catalyst, the oxidation efficiency of methane is enhanced. Further, at the time of a rich atmosphere, the reaction of methane with NOx is generated even in the methane oxidizing catalyst.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exhaust gas purifying method, an exhaust gas purifying apparatus and an exhaust gas controlling method capable of efficiently oxidizing and purifying methane in exhaust gas containing methane. INDUSTRIAL APPLICABILITY The present invention is suitable for purifying exhaust gas from automobiles, and can be particularly preferably used for purifying exhaust gas containing a large amount of methane such as exhaust gas from a gas engine.

[0002]

2. Description of the Related Art In recent years, global warming due to carbon dioxide has become a problem, and reducing carbon dioxide emissions has become an issue. In automobiles, reduction of the amount of carbon dioxide in exhaust gas has become an issue, and lean burn engines have been developed in which fuel is burned lean in an oxygen-excess atmosphere. According to the lean burn engine, the emission of carbon dioxide can be suppressed by improving the fuel efficiency.

[0003] In this lean burn engine,
Is burned in an oxygen-excess fuel-lean condition,
Exhaust gas is reduced in a reducing atmosphere by stoichiometric to rich conditions.
NO as atmosphere_x Has been developed to reduce and purify
Has been used. And the best catalyst for this system
NO in fuel lean atmosphere_x Occluded and occluded NO _x 
To release NOx in fuel stoichiometric to rich atmosphere_x Occlusion material
NO used_x Oxidation reduction type exhaust gas purification catalyst was developed
I have.

For example, Japanese Patent Application Laid-Open No. 5-317652 proposes an exhaust gas purifying catalyst in which an alkaline earth metal such as Ba and Pt are supported on a porous oxide carrier such as γ-Al ₂ O ₃ . Also, JP-A-6-31139 discloses that an alkali metal such as K is used.
An exhaust gas purifying catalyst in which Pt is supported on a porous oxide carrier such as γ-Al ₂ O ₃ has been proposed. Further, Japanese Patent Application Laid-Open No. Hei 5-168860 proposes an exhaust gas purifying catalyst in which a rare earth element such as La and Pt are supported on a porous oxide carrier such as γ-Al ₂ O ₃ .

[0005] By using this NO _x storage-and-reduction type catalyst, by controlling the air-fuel ratio so that the fuel stoichiometric-rich side from the fuel-lean side in a pulsed manner, the stoichiometric-rich atmosphere exhaust gas from a lean atmosphere in pulses Becomes Therefore, on the lean side, NO _x is stored in the NO _x storage material,
It is released on the stoichiometric to rich side and is purified by reacting with reducing components such as hydrocarbons (HC) and carbon monoxide (CO) contained in the exhaust gas in large amounts. can efficiently purify NO _x even. The HC and CO in the exhaust gas, since it is consumed in the reduction of the NO _x while being oxidized by the noble metal, HC
And CO is also purified efficiently.

However, when the exhaust gas is in a low temperature range, such as when the engine is started, there is a problem that it is difficult to purify HC until the temperature reaches the activation temperature of the noble metal supported on the NO _x storage reduction catalyst. Therefore the HC purifying catalyst can purify the HC superior from a low temperature range in the purification activity of HC at the upstream side of the NO _x storage reduction catalyst, arranged in particular the exhaust gas temperature immediately below high engine, _the NO _x storage reduction catalyst downstream thereof It has been done to arrange. By adopting such a tandem arrangement,
In a low temperature range, HC can be purified by the HC purification catalyst, so that HC emission is suppressed. Since the heat generated by the oxidation of the HC is transmitted to the NO _x storage-and-reduction type catalyst by the exhaust gas, there is also an effect that Atsushi Nobori of the NO _x storage reduction catalyst is catalyst activity expressed early promoted.

[0007] Among HCs, olefinic hydrocarbons are relatively easy to purify, but saturated hydrocarbons are more difficult to purify than olefinic hydrocarbons, and methane is particularly difficult to purify by oxidation. Therefore, the development of a catalyst capable of purifying methane has been advanced, and it has been found that palladium (Pd) is effective as a catalyst metal. For example, Japanese Patent Application Laid-Open No. 11-137998 discloses a catalyst exhibiting methane purification ability in which Pd and at least one selected from Ru, Ir and Cu are supported on an alumina carrier. Also, JP-A-7-053976 discloses that
A methane oxidation catalyst using a coprecipitate of Pd and Co as a catalyst metal is disclosed.

The use of these methane oxidation catalysts in place of the HC purification catalyst has been recalled, and Japanese Patent Laid-Open No. 2000-27976 has been proposed.
No., the methane oxidation catalyst disposed on the exhaust gas upstream side, the exhaust gas purifying apparatus is disclosed which is arranged _the NO _x storage reduction catalyst downstream thereof. According to this exhaust gas purifying apparatus, methane can be oxidized and purified by the methane oxidation catalyst when the exhaust gas is in a lean atmosphere containing excess oxidizing components. Further, when the exhaust gas is rich atmosphere over the reducing component is methane oxidation catalyst does not function, NO _x is reduced and purified by the NO _x storage-and-reduction type catalyst on the downstream side.

[0009]

However, even a methane oxidation catalyst supporting Pd has a problem that its purification activity for methane is low particularly in a low temperature range.

[0010] In the exhaust gas purifying apparatus arranged methane oxidation catalyst on the upstream side of the NO _x storage reduction catalysts, because the exhaust gas HC is oxidized by the methane oxidation catalyst even when the rich atmosphere, NO _x storage-and-reduction type catalyst _the NO _x purification rate was a problem that decreases the amount of reducing components flowing is reduced to.

According to the study of the present inventors, NO,
When the SO _x such as NO _x or SO _2, SO _3, such as NO ₂ coexist with methane oxidation component in the distribution of an exhaust gas of excess lean atmosphere than reducing component, methane in the methane oxidation catalyst It has been clarified that the oxidation activity is greatly reduced. Therefore, when the exhaust gas first flows into the methane oxidation catalyst as in JP-A-2000-27976, NO _x
Or SO _x oxidation reaction of methane is inhibited by, as a result, especially methane removal activity at low-temperature region is lowered.

The present invention has been made in view of such circumstances, and an object of the present invention is to make it possible to efficiently purify methane from a low-temperature region and to reduce the amount of NO _x emitted.

[0013]

Means for Solving the Problems The characteristics of the exhaust gas purifying method of the present invention to solve the above problems comprises methane NO _x and SO
Exhaust gas from which at least one, and preferably both, of _x is removed is brought into contact with a methane oxidation catalyst capable of oxidizing methane.

In this exhaust gas purification method, methane and
Contacting a NO _x and SO _x methane oxidation catalyst with exhaust gas containing at least either after contact with the capturing material for capturing at least one of the NO _x and SO _x is desirable.

Further features of another exhaust gas purifying method of the present invention, the methane after the exhaust gas of excess lean atmosphere oxidizing components than reducing component is contacted with the capture material for capturing at least one of the NO _x and SO _x Contact with an oxidizable methane oxidation catalyst.

[0016] In the exhaust gas purifying method of the present invention described above, it is desirable that the capture member is a NO _x storage-and-reduction type catalyst.

Further features of the exhaust gas purifying apparatus of the present invention for solving the above-mentioned problems, NO _x on the upstream side of the exhaust gas stream containing methane
And arrange a capturing material for capturing at least one of SO _x ,
That is, a methane oxidation catalyst capable of oxidizing methane is disposed downstream of the trapping material.

In this exhaust gas purifying apparatus, the trapping material is
It is desirable that the catalyst be a NO _x storage reduction catalyst.

[0019] The features of the exhaust gas purifying apparatus of the present invention to solve the above problems, after the oxidizing component a reducing component of the exhaust gas of excess lean atmosphere has been contacted with the capturing material for capturing at least one of the NO _x and SO _x Contacting methane with an oxidizable methane oxidation catalyst.

In this exhaust gas purifying apparatus, it is desirable to alternately switch the exhaust gas atmosphere between a lean atmosphere in which the oxidizing component is more than the reducing component and a stoichiometric atmosphere or a rich atmosphere in which the reducing component is more than the oxidizing component.

In yet exhaust gas purifying apparatus of the present invention, the capture member is a NO _x storage-and-reduction type catalyst comprising _the NO _x storage material, occludes at least one of the NO _x and SO _x in _the NO _x storage material in lean atmosphere it is desirable that at least one of the released NO _x and sO _x from _the NO _x storage material by intermittently supplying the exhaust gas of the stoichiometric atmosphere or rich atmosphere is reduced with _the NO _x storage-reduction catalyst.

[0022]

BEST MODE FOR CARRYING OUT THE INVENTION In a methane oxidation catalyst, an active site that causes an oxidation reaction of methane under a lean atmosphere is considered to be an MO species when noble metal is M. If NO _x or SO _x is present in the gas, it is an active site
It has been clarified that the oxidation of NO or SO ₂ selectively progresses on MO species, and that poisoning occurs due to the generation of MO-SO ₃ , which significantly inhibits the oxidation reaction of methane. Was.

Therefore, in the exhaust gas purifying method of the present invention, NO _x
And at least one of SO _x and NO _x and
Exhaust gas substantially free of at least one of SO _x is brought into contact with a methane oxidation catalyst capable of oxidizing methane. Therefore, the inhibition of the methane oxidation reaction described above is suppressed, so that methane can be efficiently oxidized and purified from a low temperature range. 30ppm Note By substantially free, it is particularly desirable that the state in which both of the NO _x and SO _x from the exhaust gas is sufficiently removed, a total concentration of at least one of both of the NO _x and SO _x If it is below, inhibition of the methane oxidation reaction can be effectively suppressed.

Examples of the methane oxidation catalyst capable of oxidizing methane include an oxide carrier composed of at least one of Al ₂ O ₃ , ZrO ₂ , TiO ₂ , SiO ₂ , CeO ₂ , and MgO, or a composite oxidation composed of a plurality of these. A catalyst in which at least one noble metal selected from Pt, Pd, Rh, Ir and the like is supported on a substance carrier can be used. The amount of the noble metal carried is optimally in the range of 0.1 to 10% by weight in the catalyst. Among them, a catalyst supporting Pd is particularly preferable.

The effect of the present invention is remarkable when the exhaust gas contacted with the methane oxidation catalyst has a lean atmosphere in which the oxidizing component is in excess of the reducing component. The exhaust gas stoichiometric-rich atmosphere, because inhibition of oxidation of methane by NO _x or SO _x is not caused. This exhaust gas contains at least methane, and hydrocarbons other than methane (HC)
And carbon monoxide (CO).

In order to positively remove at least one of NO _x and SO _x , for example, activated carbon, porous glass or A
l ₂ O ₃ , ZrO ₂ , CeO _2, etc., a method of physically adsorbing / absorbing a porous adsorbent, or at least one of NO _x and SO _x by an oxide of alkali metal or alkaline earth metal or A method of reacting with an occluding material such as a carbonate and chemically occluding the material may be employed. In the present invention, a substance that physically adsorbs and absorbs at least one of NO _x and SO _x or occludes it by a chemical reaction is defined as a trapping material.

[0027] Therefore, in the exhaust gas purifying apparatus of the present invention, the capturing material for capturing at least one of the NO _x and SO _x on the upstream side of the exhaust gas stream containing methane is disposed, methane oxidizable methane downstream of the capture member An oxidation catalyst is provided. Thus since at least one of which is flue gas of methane oxidation catalyst NO _x and SO _x flows, expressed high methane removal activity.

In the exhaust gas purifying apparatus of the present invention, the exhaust gas in a lean atmosphere in which the oxidizing component is in excess of the reducing component is converted to NO _x
And has methane is contacted with oxidizable methane oxidation catalyst after contacting the capturing material for capturing at least one of SO _x. This can prevent the inhibition of the oxidation of methane by NO _x or SO _x in the exhaust gas of lean atmosphere excess oxidizing component.

The exhaust gas atmosphere changes from stoichiometric to reducing components.
NO for excessive rich atmosphere _x Or SO_x By
No inhibition of the oxidation reaction of tan
The exhaust gas purifying apparatus of the present invention and the exhaust
Gas control methods can be used. Also, the trapping material is
Potassium metal or alkaline earth metal oxide or carbonate
In some cases, lean and stoic to rich atmosphere
It is also preferable to alternately switch between.

That is, in the exhaust gas purifying apparatus of the present invention, it is preferable to alternately switch the exhaust gas atmosphere between a lean atmosphere in which the oxidizing component is more than the reducing component and a rich atmosphere in which the reducing component is more than the oxidizing component. By doing so, NO in a lean atmosphere
_Since at least one of _x and SO _x is captured by the capturing material, inhibition of the methane oxidation reaction in the methane oxidation catalyst is prevented. When the exhaust gas atmosphere becomes stoichiometric-rich atmosphere, even if capturing material from the NO _x or SO _x is released, HC containing methane, NO by reducing component such as CO or H ₂ over methane oxidation catalyst _x or SO _{Since x} is reduced, emission of NO _x or SO _x can be suppressed. Also even if NO _x or SO _x is in contact with the methane oxidation catalyst, since the stoichiometric-rich atmosphere no inhibition of methane oxidation reaction, the oxidation reaction of methane is also well expressed.

As the trapping material, as described above, activated carbon, porous glass or an adsorbent made of porous material such as Al ₂ O ₃ , ZrO ₂ , CeO ₂ , alkali metal, alkaline earth metal and rare earth element An occluding material made of an oxide or a carbonate is exemplified. Further, a porous body such as Al ₂ O ₃ , ZrO ₂ , CeO ₂ or the like which carries a catalytic metal may be used as a trapping material, or a porous body which carries the above-mentioned occluding material may be used as a trapping material. .

In particular, the porous body contains noble metal and alkali metal,
It is desirable that the NO _x storage-and-reduction type catalyst carrying and _the NO _x storage material consisting of alkaline earth metals and rare earth elements and capturing material. That is, the NO _x storage reduction catalyst is arranged on the upstream side, and the methane oxidation catalyst is arranged on the downstream side. According to the exhaust gas purifying apparatus of the present invention, is to become NO ₂ is oxidized NO in the exhaust gas at the upstream side of the NO _x storage reduction catalyst in a lean atmosphere, also SO ₂ is oxidized SO ₃ or SO _{Since it is 4} , the storage efficiency of the NO _x storage material is significantly improved. Therefore, since NO _x and SO _x do not flow into the downstream methane oxidation catalyst, inhibition of methane oxidation reaction can be further suppressed, and HC containing methane can be oxidized and removed by the methane oxidation catalyst.

As the NO _x storage reduction catalyst, Al ₂ O ₃ , Zr
Oxide carrier composed of at least one of O ₂ , TiO ₂ , SiO ₂ , CeO ₂ , MgO, etc. or composite oxide carrier composed of a plurality of these are added to at least one kind selected from alkali metals, alkaline earth metals and rare earth elements. NO _x storage material, Pt,
A catalyst supporting at least one noble metal selected from Pd, Rh, Ir and the like can be used. The optimal amount of the NO _x occluding material carried is about 0.1 to 1 mol per liter of the carrier. The amount of the noble metal carried is optimally in the range of 0.1 to 10% by weight in the catalyst, and it is most preferable to use Pt and Rh together.

The distance between the trapping material and the methane oxidation catalyst is not particularly limited, and may be in contact with or apart from each other. Further, it is also possible to form a trapping material on the upstream half of one monolith carrier substrate and form a methane oxidation catalyst on the downstream half.

Further, the exhaust gas purifying apparatus of the present invention may be any apparatus in which the trapping material is arranged on the upstream side and the methane oxidation catalyst is arranged on the downstream side in this order, and another catalyst is further arranged on the upstream side or further downstream side. They can also be placed. For example It may be further arranged NO _x storage-and-reduction type catalyst on the downstream side of the exhaust gas purifying apparatus of the present invention may be arranged HC oxidation catalyst for purifying HC in further low temperature range on the upstream side.

By the way to occlude at least one of the NO _x and SO _x in _the NO _x storage material by using a NO _x storage-and-reduction type catalyst as a capture material, it is necessary that the exhaust gas atmosphere stoichiometric-lean atmosphere. However than shed the exhaust gas always stoichiometric-lean atmosphere, at least one of the storage amount is saturated of the NO _x and SO _x to be occluded in _the NO _x storage material, thereafter the NO _x or SO _x methane oxidation catalyst Because of the inflow, it becomes difficult to purify methane by oxidation after a predetermined time has elapsed.

Therefore, in the exhaust gas purifying apparatus of the present invention, NO _x
A storage-reduction type catalyst is arranged on the upstream side and a methane oxidation catalyst is arranged on the downstream side, and the exhaust gas is converted into a lean atmosphere where the oxidizing component is more than the reducing component and a stoichiometric atmosphere or a rich atmosphere where the reducing component is more than the oxidizing component. The atmosphere is switched alternately. This allows NO in lean atmosphere
occluding at least one of the NO _x and SO _x to _x storage material, at least one of the released NO _x and SO _x exhaust gas stoichiometric atmosphere or rich atmosphere from _the NO _x storage material by intermittently supplying NO _x It is reduced with a storage reduction catalyst. According to the exhaust gas purifying apparatus, the following special effects can be obtained.

First, the state in which the exhaust gas in the lean atmosphere is flowing
In the state, NO and SO in exhaust gas_Two Is NO _x For storage reduction catalyst
NOx is selectively oxidized by the supported noble metal,_x 
And SO_x Become NO_x It is stored in the storage material. Also exhaust gas
NO HC and CO components except methane in NO_x Absorption reduction type catalyst
Is purified by oxidation. And NO_x And SO_x At least one of
Exhaust gas flows into the methane oxidation catalyst
As a result, methane in exhaust gas can be efficiently oxidized and purified.
Wear. Also NO_x HC that could not be oxidized by the storage reduction catalyst
And CO are oxidized and purified by the methane oxidation catalyst.

[0039] Then the exhaust gas intermittently stoichiometric or rich atmosphere is flowed, at least one of which is released storage capacity of the NO _x storage material from _the NO _x storage material NO _x and SO _x is restored. At least one of the released NO _x and SO _x is reduced by reacting with a reducing component such as HC, CO and H ₂ containing methane which is present in a large amount in the atmosphere on the NO _x storage-reduction catalyst. , NO _x or SO _x can be suppressed.

[0040] When the exhaust gas of a lean atmosphere is flowed again, NO NO _x storage material storage capacity is restored again _x and SO _x
At least one of them. By repeating this, it is possible to efficiently purify the methane and NO _x.

Further, in the NO _x storage reduction catalyst, the stored NO _x may be released without being reduced to N ₂ when the atmosphere changes from lean to rich. In some cases, reducing components such as HC and CO are released without reacting. This is the NO _x catalyst temperature has been elevated occluded by heat generated by the oxidation of reducing components in the rich atmosphere is released, the reducing component at that time not sufficiently supplied, and
NO _x storage-and-reduction type catalyst is due to low redox capacity in stoichiometric-rich atmosphere, like.

However, in the present invention, a highly active methane oxidation catalyst exists on the downstream side. Therefore, even NO _x or reducing component from _the NO _x storage reduction catalyst is released, since the reaction between NO _x and reducing components on the methane oxidation catalyst progresses, further increasing NO _x, the purification activity of HC and CO It becomes possible. In the case of a rich atmosphere, a reaction between methane and NO _x also occurs, so that methane and NO _x can be purified at the same time.

The further arrangement of a conventional methane oxidation catalyst on the upstream side, the catalyst device disposed NO _x storage-and-reduction type catalyst on the downstream side, HC containing methane is oxidized in the upstream side in the case of the stoichiometric-rich atmosphere Therefore, there is a problem that the reduction component flowing into the NO _x storage-reduction type catalyst is reduced and the purification rate of NO _x is low. However, the exhaust gas purifying apparatus of the present invention, since the flows into the NO _x storage-and-reduction type catalyst of the exhaust gas is first upstream, the reduction reaction proceeds sufficiently _the NO _x purification activity of the NO _x in stoichiometric-rich atmosphere improves.

It is desirable that the gas of the lean atmosphere always flowed is equivalent to the exhaust gas burned at an air / fuel ratio (A / F) of 18 to 22, and the gas of the stoichiometric to rich atmosphere intermittently flowed is an empty gas. It is desirable that the fuel ratio (A / F) is 14.6 or less for a gasoline engine and 16.9 or less for a gas engine, which corresponds to exhaust gas burned. In order to make the rich gas flow intermittently, the air-fuel ratio may be adjusted, or a reducing component may be externally introduced into the exhaust gas.

To control the exhaust gas as described above,
By detecting the amount of NO _x or O ₂ in the exhaust gas using a NO _x sensor, oxygen sensor, etc., and controlling the air-fuel ratio according to the value, or by supplying a reducing component such as fuel to the exhaust gas. It can be carried out. It is particularly desirable to detect the NO _x and SO _x concentrations in the exhaust gas flowing into the methane oxidation catalyst and perform feedback control.

[0046]

The present invention will be specifically described below with reference to examples and comparative examples.

Example 1 (1) Preparation of NO _x Storage-Reduction Catalyst Starting from titanium tetrachloride, zirconyl nitrate and aluminum nitrate, a TiO ₂ -ZrO ₂ -Al ₂ O ₃ composite oxide was prepared by a coprecipitation method. A powder was prepared. Rh / ZrO ₂ powder in which Rh is supported on ZrO ₂ was also prepared. These were mixed with an alumina binder and water to prepare a slurry, which was wash-coated on a 35 cc test piece honeycomb substrate, and fired at 500 ° C. for 1 hour to form a coat layer. Coat layer is 2 per 1L of honeycomb substrate
50 g are formed, of which 200 g is TiO ₂ -ZrO ₂ -Al ₂ O ₃ composite oxide powder and 50 g is Rh / ZrO ₂ powder. Therefore, the supported amount of Rh is 0.5 g per liter of the honeycomb substrate.

The honeycomb substrate having the coating layer was immersed in an aqueous solution of dinitrodiammine platinum, pulled up and fired at 300 ° C. for 3 hours to carry 5 g / L of Pt. Next, a predetermined amount of a mixed aqueous solution of potassium acetate and barium acetate is absorbed in the coat layer, and calcined at 300 ° C. for 3 hours to obtain 0.6 mol / K.
L and Ba were supported at 0.1 mol / L.

(2) Preparation of methane oxidation catalyst A slurry was prepared by mixing alumina powder with an alumina binder and water, wash-coated on a 35 cc test piece honeycomb substrate, and fired at 500 ° C. for 1 hour to form a coat layer. Formed. The coat layer was formed in an amount of 120 g per liter of the honeycomb substrate.

A predetermined amount of an aqueous solution of palladium nitrate is absorbed in the coat layer, pulled up, baked at 300 ° C. for 3 hours, and
Was carried at 5 g / L.

(3) Exhaust gas purifying device As shown in FIG. 1, the NO _x storage reduction catalyst 1 (35
cc) was arranged on the upstream side of the evaluation device, and the methane oxidation catalyst 2 (10 cc) described above was arranged on the downstream side. The methane oxidation catalyst 2 was cut to 10 cc. Hereinafter, the catalyst volume was similarly adjusted.

[0052] (Example 2) NO _x storage reduction catalyst (30 cc)
Is placed upstream of the evaluation device and a methane oxidation catalyst (13cc)
Is the same as that of the first embodiment except that is disposed on the downstream side.

(Embodiment 3) The exhaust gas purifying apparatus of Embodiment 1 was subjected to an endurance test in which the model gas shown in Table 1 was circulated in a pattern shown in FIG. The device.

[0054]

[Table 1]

(Comparative Example 1) The same as Example 1 except that only the methane oxidation catalyst (10 cc) was disposed in the evaluation device.

[0056] (Comparative Example 2) NO _x storage reduction catalyst (35 cc)
This is the same as Example 1 except that only the evaluation device was provided.

(Comparative Example 3) The exhaust gas purifying apparatus of Comparative Example 1 was subjected to a durability test in which model gas shown in Table 1 was circulated in the pattern shown in FIG. The device.

(Comparative Example 4) The exhaust gas purifying apparatus of Comparative Example 2 was subjected to a durability test in which the model gas shown in Table 1 was circulated in the pattern shown in FIG. The device.

[0059] (Comparative Example 5) disposed upstream of the evaluation device methane oxidation catalyst (13 cc), NO _x storage reduction catalyst (30 cc)
Is the same as that of the first embodiment except that is disposed on the downstream side. That is, the arrangement order of the exhaust gas purifying apparatus of Comparative Example 5 is reverse to that of Example 2.

<Test Examples and Evaluations> (1) Effect of NO on Methane Oxidation Activity Only the methane oxidation catalyst (13 cc) was placed in the evaluation apparatus, and Table 2
Using model gas A and model gas B shown in Fig. 4, the change in methane concentration in the outgas at inlet gas temperatures of 400 ° C and 450 ° C was measured while alternately repeating 46 seconds of lean gas and 2 seconds of rich gas (rich spike). did. At the same time, the methane purification rates were measured respectively. The results are shown in FIGS.

[0061]

[Table 2]

[0062]

[Table 3]

From FIG. 3 and FIG. 4, the model gas A in which NO coexists
Indicates that the concentration of methane in the output gas is higher than that of model gas B in which NO does not coexist. Table 3 also shows that the model gas B in which NO does not coexist has a higher methane purification rate than the model gas A in which NO coexists. That is, it is clear that the oxidation of methane is inhibited by NO.

(2) Comparison of Purification Activities Using the exhaust gas purifying devices of the respective Examples and Comparative Examples, and using the model gas shown in Table 4, lean gas 46 seconds-rich gas 2
While alternately repeating seconds (rich spikes), the purification rates of NO _x , CH _4, and CO at an inlet gas temperature of 400 ° C. and 450 ° C. were measured, respectively. Table 5 shows the results.

[0065] As for Comparative Example 3-4 Example 3 enters the change in concentration of the NO _x and CH ₄ in the exit gas at the gas temperature 450 ° C. were measured, and the results are shown in Figure 5-6.

[0066] Further Comparative Example 5 Example 2 enters the density change of the NO _x and CH ₄ in the exit gas at the gas temperature 450 ° C. were measured, and the results are shown in Figure 7-8. The NO _x emissions in the lean time and the rich spike and CH ₄ emissions were measured and the results are shown in Figure 9-10.

[0067]

[Table 4]

[0068]

[Table 5]

From a comparison between Example 1 and Comparative Examples 1 and 2 and a comparison between Example 3 and Comparative Examples 3 and 4, the NO _x storage reduction catalyst was provided on the upstream side, and the methane oxidation catalyst was provided on the downstream side. By arranging, it is clear that not only the sum of the effects but also the synergistic effect is exhibited at the initial stage and after the endurance.

From the comparison between Example 2 and Comparative Example 5, it can be seen that when the arrangement order is reversed, the purifying activity of NO _x and CH ₄ also decreases.

[0071]

According to the exhaust gas purifying method and the exhaust gas purifying apparatus and an exhaust gas control method of the Effects of the Invention] The present invention, together with can be efficiently oxidized and purified methane, NO _x, because also improved purification rate of HC and CO, gas engine, etc. It is suitable for purifying exhaust gas.

[Brief description of the drawings]

FIG. 1 is an explanatory view schematically showing a configuration of an exhaust gas purifying apparatus according to one embodiment of the present invention.

FIG. 2 is a time chart showing endurance test conditions in Examples.

FIG. 3 is a graph showing a change in methane concentration at a reaction temperature of 400 ° C. in Test Example 1.

FIG. 4 is a graph showing a change in methane concentration at a reaction temperature of 450 ° C. in Test Example 1.

FIG. 5 is a graph showing a change in NO _x concentration in Test Example 2.

FIG. 6 is a graph showing a change in methane concentration in Test Example 2.

FIG. 7 is a graph showing a change in NO _x concentration in Test Example 2.

FIG. 8 is a graph showing a change in methane concentration in Test Example 2.

9 is a graph showing NO _x emissions of purifying apparatus of Example 2 and Comparative Example 5.

FIG. 10 is a graph showing CH ₄ emissions of the purification devices of Example 2 and Comparative Example 5.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme court ゛ (Reference) F01N 3/24 F01N 3/24 R 3/28 301C 3/28 301 F02D 41/04 305A F02D 41/04 305 B01D 53/36 103Z (72) Inventor Hideo Sobukawa 41-Cho, Yokomichi, Nagakute-cho, Aichi-gun, Aichi Prefecture F-term in Toyota Central Research Laboratory Co., Ltd. 3G091 AA02 AA17 AA19 AB02 AB06 AB09 BA01 BA14 BA15 BA39 CB01 EA33 EA34 GA06 GB02Y GB03Y GB04Y GB05W GB06W GB07W GB10X GB17X HA09 3G301 HA01 HA22 JA25 JA26 KA01 KA05 LB04 MA01 ND01 NE13 NE14 NE15 PD01Z PD02A PD02Z 4D048 AA06 AA18 AB01 BA02 BA03XBA07X08 BA03X BA07X08 BA05B BB06B BC03B BC13B BC71B BC72B BC75B CA03 CA07 CA08 CA13 CA15 DA06 EA19 EE09 FA02 FB14 FB23

Claims (9)

[Claims] An exhaust gas purification method comprising contacting an exhaust gas containing methane from which at least one of NO _x and SO _x has been removed with a methane oxidation catalyst capable of oxidizing methane. 2. Methane and NO_x And SO_x At least one of
NO containing exhaust gas _x And SO_x Capture at least one of
Contact with the methane oxidation catalyst after contact with the trapping material
The method for purifying exhaust gas according to claim 1, wherein
Law. Wherein said contacting with oxidizable methane oxidation catalyst methane after the exhaust gas of excess lean atmosphere oxidizing components than reducing component is contacted with the capture material for capturing at least one of the NO _x and SO _x Exhaust gas purification method. Wherein said capturing material is an exhaust gas purifying method according to any one of claims 2 and 3, characterized in that a NO _x storage-and-reduction type catalyst. 5. A trapping material for trapping at least one of NO _x and SO _x is disposed upstream of an exhaust gas flow containing methane, and a methane oxidation catalyst capable of oxidizing methane is disposed downstream of the trapping material. An exhaust gas purifying device characterized by the above-mentioned. 6. The exhaust gas purifying apparatus according to claim 5, wherein the trapping agent is an NO _x storage-and-reduction type catalyst. 7. characterized by contacting the oxidizable methane oxidation catalyst methane after the exhaust gas of excess lean atmosphere oxidizing components than reducing component is contacted with the capture material for capturing at least one of the NO _x and SO _x Exhaust gas purifier. 8. The exhaust gas purification method according to claim 7, wherein the exhaust gas atmosphere is alternately switched between a lean atmosphere in which the oxidizing component is more than the reducing component and a stoichiometric atmosphere or a rich atmosphere in which the reducing component is more than the oxidizing component. apparatus. Wherein said capturing material is a NO _x storage-and-reduction type catalyst comprising _the NO _x storage material, occludes at least one of the _the NO _x storage material in NO _x and SO _x in the lean atmosphere, the stoichiometric atmosphere or The exhaust gas of a rich atmosphere is intermittently supplied, and at least one of NO _x and SO _x released from the NO _x storage material is reduced by the NO _x storage reduction catalyst. Exhaust gas purification equipment.