JPH09884A - Method and device for removing nitrous oxide or the like in exhaust gas and catalyst - Google Patents

Abstract

PURPOSE: To remove N2 O in exhaust gas by a method wherein N2 O in exhaust gas is removed at a lower temperature using a reducing agent and the quantity of flowing-out of CO and ammonia is small. CONSTITUTION: (1) A catalyst, in which iron is carried by mordenite and/or pentacyl type zeolite, is set in exhaust gas containing N2 O and an alcohol and/or hydrocarbon is injected to cause it to react with N2 O on the catalyst to reduce the N2 O to N2 . (2) In a method, in which N2 O in exhaust gas is reduced and removed using an alcohol and/or hydrocarbon in a contact manner, a catalyst comprising a first component composed of mordenite, pentacyl-type zeolite carrying Fe and/or β-type zeolite, and a second component composed of noble metal salts of Pt or Pd, or compositions of noble metals which are carried beforehand by a porous body such as zeolite, alumina, silica, etc., is used to decomposed CO and N2 O ion exhaust gas and residual ammonia also is decomposed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for removing nitrous oxide in exhaust gas, and more particularly to a method and apparatus for removing nitrous oxide and nitric oxide in exhaust gas at low temperature and a catalyst therefor.

[0002]

2. Description of the Related Art In recent years, the global warming phenomenon caused by the increase of carbon dioxide (CO ₂ ) in the atmosphere, the damage of forests due to acid rain caused by nitrogen oxides (NOx) and sulfur oxides (SO ₂ ), etc. Environmental damage is becoming apparent at the level, and countermeasures against it are becoming an urgent issue for humankind. One of these environmental destructions at the global level is the destruction of the ozone layer.
In addition to methane, nitrous oxide (N ₂ O) is listed as one of the causative substances. Particularly in recent years, low temperature combustion is often performed in order to suppress NOx, which is a causative substance of acid rain discharged from various combustors, to a low level, and in that case, the emission amount of N ₂ O increases. It is known. Similar to N ₂ O, nitric oxide (NO) is one of the environmentally destructive substances, and various measures for removing NO have been studied.

As a method of removing N ₂ O, a method of thermally decomposing using a catalyst at a high temperature is generally known, and a method using an oxide of various elements such as zinc as a catalyst has been studied. .

Separately from this, the present inventors used N ₂ with ammonia as a catalyst in which mordenite, clinoptilolite, faujasite, zeolite Y, pentasil-type zeolite, or β-type zeolite was replaced with Fe or hydrogen.
Invented a catalyst for reducing O and its process, and applied for a patent (Japanese Patent Publication No. 4-17084, Japanese Patent Application No. 5-213088).
No.) As shown in FIG. 2, this removal process is carried out in the reactor 5 provided in the flow path of various exhaust gases containing N ₂ O and NO discharged from the combustor 1 and N ₂ O and NO.
A removal catalyst is filled, and ammonia 6 is further injected into the exhaust gas to reduce N ₂ O and NO with ammonia 6 in a temperature range of 450 ° C. or higher.

[0005]

Among the conventional techniques for removing N ₂ O and NO, the method of reducing with ammonia using Fe-substituted zeolite is at least 500 ° C. in order to obtain sufficient removal performance. Since it is necessary, it causes problems such as thermal deterioration of the catalyst.

Therefore, an object of the present invention is to provide a method, an apparatus and a catalyst for removing N ₂ O and NO in exhaust gas at a lower temperature as compared with the above-mentioned prior art.

Further, an object of the present invention is to remove N ₂ O and NO in exhaust gas by using a reducing agent, and a method and apparatus for removing N ₂ O and NO in exhaust gas with less outflow of CO and ammonia. It is to provide a catalyst.

[0008]

The above object of the present invention can be achieved by the following constitutions. That is, a catalyst (first catalyst) in which iron is supported on at least one carrier of mordenite and pentasil-type zeolite is installed in an exhaust gas flow path containing N ₂ O, and a reducing agent for at least one of alcohol and hydrocarbon is installed. A method for removing N ₂ O from exhaust gas, characterized by injecting and reacting with N ₂ O on the catalyst to reduce N ₂ O to N ₂ , or mordenite in exhaust gas containing N ₂ O and NO. A catalyst in which iron is supported on at least one of a carrier and a pentasil-type zeolite is installed, a reducing agent of at least one of alcohol and hydrocarbon and ammonia are injected, and N _{2 is} added on the catalyst.
A method for removing N ₂ O and NO in exhaust gas, which is characterized by reducing O and NO to nitrogen.

In the present invention, when injecting ammonia into the exhaust gas, the injection amount is made proportional to the measured value of NO concentration in the exhaust gas, and the injection amount of the reducing agent of at least one of alcohol and hydrocarbon is adjusted to the exhaust gas. It is desirable to adjust in proportion to the measured value of the N ₂ O concentration therein.

Thus, the first catalyst of the present invention is N ₂
It is a catalyst that has both O decomposition activity and NO decomposition activity.

Alcohol as used herein refers to methanol, ethanol, propanol or the like having a relatively low carbon number, and hydrocarbon refers to methane, ethane, methylene, propane, propylene or the like having a relatively low carbon number.

The method of using the Fe-supported zeolite catalyst, which is the first catalyst of the present invention, and alcohol and / or hydrocarbon as the reducing agent, produces N ₂ O and NO at a lower temperature than the conventional method using ammonia as the reducing agent. Although it is an excellent method that can be removed, it has a problem that CO is produced by the decomposition of alcohol and / or hydrocarbon depending on the conditions, and therefore CO easily flows out from the exhaust gas flue outlet. Particularly in the case of alcohol, since the alcohol solution is injected into the exhaust gas flue, the ability to follow the load fluctuation of the alcohol solution supply system is poor, and it becomes difficult to suppress the reducing agent concentration by following the N ₂ O and NO fluctuations. Therefore, when a known catalyst having only N ₂ O removal performance is used, it is necessary to excessively inject a reducing agent in order to increase the N ₂ O removal rate above a certain level, and a larger amount of CO flows out. Cause a phenomenon.
Furthermore, when removing NO at the same time, NH ₃ is used as a reducing agent for NO, which causes a problem that ammonia as well as CO flows out.

In the present invention, the reducing agent is alcohol and / or
Alternatively, the following configuration for improving the denitration method using hydrocarbon is also included.

In a method of catalytically reducing and removing N ₂ O in exhaust gas using at least one reducing agent of alcohol and hydrocarbon, exhaust gas using a catalyst having both CO decomposition activity and N ₂ O decomposition activity Method for removing N ₂ O in the exhaust gas or N ₂ O, NO and CO in exhaust gas
In the method of catalytically reducing and removing using a reducing agent of at least one of H ₃ , alcohol and hydrocarbon,
N ₂ O in the exhaust gas using a catalyst having both a CO decomposition activity and NH ₃ decomposing activity and N ₂ O decomposition activity and NO decomposition activity,
This is a method of removing NO.

The catalyst (second catalyst) of the present invention having both the CO decomposing activity, the NH ₃ decomposing activity, the N ₂ O decomposing activity and the NO decomposing activity comprises a zeolite carrying iron (Fe) as the first component, A catalyst composition containing a noble metal salt selected from platinum (Pt) or palladium (Pd) or a noble metal composition previously supported on a porous material such as zeolite, alumina, or silica as a second component can be used.

As the zeolite carrying the first component, mordenite, pentasil-type zeolite and the like have a denitrification rate of N
₂ O removal rate is preferable because it gives good results.

Further, N ₂ O in exhaust gas or N ₂ O contained in the exhaust gas is passed through a catalyst layer filled with the first catalyst or the second catalyst using a reducing agent of at least one of alcohol and hydrocarbon or ammonia in addition to the reducing agent. / And N
An O removing device is also within the scope of the present invention.

[0018]

As a result of earnest studies by the present inventors, N ₂ O reduction reaction by alcohol and / or hydrocarbon on the mordenite and / or pentasil type zeolite catalyst (first catalyst) supporting iron (Fe) It became clear from the fact that it proceeds at a lower temperature than conventional ammonia reduction. Further, it has been found that this reaction proceeds only on the zeolite catalyst supporting Fe, and hardly progresses on the zeolite catalyst using a substance other than Fe as an active component or the catalyst supporting Fe on a carrier other than zeolite.

[0019] FIG 3 N ₂ O and methanol about N ₂ O removal using a Fe supported mordenite catalyst, the molar ratio characteristics of the molar ratio characteristic and NO and methanol and propane.
From this, it can be seen that N ₂ O and alcohol and N ₂ O and hydrocarbon react at a molar ratio of 1: 1 respectively. That is, the injection amount of alcohol and hydrocarbon required to obtain a sufficient N ₂ O removal rate is almost equimolar to N ₂ O, and the injection of the large catalyst causes the outflow from the catalyst layer gas outlet. , Not preferable.

Further, as is clear from FIG. 3, NO hardly reacts with alcohol (N ₂ O on the vertical axis of FIG. 3).
The removal rate shall be read as the NO removal rate. ). That is, the reaction proceeds with 1 mol of NO and 1 mol of NH ₃ , and N ₂
The reaction of O with alcohol or hydrocarbon proceeds in an equimolar manner. Therefore, when NO and N ₂ O coexist, NH ₃ and alcohol or hydrocarbon are used together, and NH ₃ is NO.
The amount of alcohol and hydrocarbon injected is equimolar to N ₂ O
When the same molar amount is injected, good results are obtained for both the denitration rate and the N ₂ O removal rate.

Further, in FIG. 2, when the catalyst layer 2 is filled with the second catalyst of the present invention, the exhaust gas of the combustor 1 is introduced into the catalyst layer 2 and Fe / zeolite or the like in the catalyst layer 2 is introduced. By the action of the first component of the second catalyst of the invention, the alcohol and / or hydrocarbon reducing agent 6 and N ₂ O are converted into the reactor 5
Reacting in to reduce N ₂ O to nitrogen (N ₂ ). At this time, part of the alcohol and / or hydrocarbon is decomposed to generate CO. However, when the second catalyst according to the present invention is used, the produced CO is oxidized by the action of the noble metal in the second catalyst and becomes harmless CO ₂ , so that the outflow of CO from the catalyst layer 2 can be prevented. Then, the purified exhaust gas exchanges heat with the heat exchanger 3 and is then discharged from the chimney 4. Further, even if an excessive reducing agent 6 is injected in anticipation of non-uniform injection of alcohol and / or hydrocarbon and fluctuation of N ₂ O, a large amount of CO does not flow out.

Furthermore, in the case of simultaneously removing NO in exhaust gas, when ammonia is used as a reducing agent for NO to reduce NO to N ₂ , the ammonia not used in the reaction is the second aspect of the present invention. Catalyst layer 2 filled with catalyst
Oxidized by the action of the precious metal inside and decomposed into harmless N ₂ and water, it is possible to prevent outflow to the outlet side.

[0023]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to embodiments. Example 1 A catalyst preparation example corresponding to the first catalyst of the present invention was carried out as follows. Mordenite (TSZ-65 manufactured by Tosoh Corporation)
0x0A, after turning into an aqueous solution 100ml containing SiO ₂ / A1 ₂ O ₃ ratio = 23) of iron nitrate and _{50g (Fe 2 (NO 3)} 3 · 9H 2 O) 18kg, with stirring over 0.99 ° C. sand bath evaporated Dried up. The obtained powder is 3to using a hydraulic press.
It was molded into a pellet at n / cm ² , and further crushed to obtain a 10 to 20 mesh catalyst.

A reaction tube was filled with the above-prepared catalyst, and N ₂
A pseudo gas containing O is circulated, and CH ₃ O is supplied from the upstream side of the reaction tube.
An aqueous solution prepared by dissolving 7.1 g of H in 1 liter of water was injected, and a N ₂ O removal test was conducted under the conditions shown in Table 1.

[0025]

[Table 1]

Comparative Example 1 N ₂ O removal test was conducted in the same manner as in Example 1 except that NH ₃ was used instead of CH ₃ OH and the ratio (molar ratio) of NH ₃ / N ₂ O was 1.2. I went.

The test results of Example 1 and Comparative Example 1 are shown in FIG. As is clear from this figure, the method according to the present invention has higher N ₂ O removal performance at the same temperature than the conventional method, and it is possible to remove N ₂ O at a lower temperature.

Examples 2 to 8 Using the catalyst of Example 1, the reducing agent CH ₃ OH was replaced with C ₂ H ₅ O.
H, C ₃ H ₈ OH, instead each _{CH 4, C 2 H 8,} C 2 H 6, C 3 H 8 and C ₃ H _8, the other is N ₂ O removal ratio in the same manner as in Example 1 It was measured.

[0029]

[Table 2]

Table 2 shows the N ₂ O removal rates at 450 ° C. by the reducing agents of Examples 1 to 8 and Comparative Example 1. When alcohol and hydrocarbon are used as the reducing agent, a higher N ₂ 0 removal rate than that of the conventional NH ₃ method can be obtained.

Example 9 A catalyst was prepared in the same manner as in Example 1, except that the mordenite of the catalyst preparation example was changed to a pentasil-type zeolite (ZSM-5 manufactured by PQ, SiO ₂ / Al ₂ O ₃ ratio = 30). did. A test for removing N ₂ O in a simulated gas was conducted on the same machine as in Example 1 except that this catalyst was used.

Comparative Examples 2 and 3 The iron nitrate of Example 1 was mixed with copper acetate (Cu (NO ₃ ) ₂ .3H).
₂ 0) 9.53 g, cobalt nitrate _{(Co (NO 3) 2 ·} 6
Change in H ₂ 0) 12.5g, others were認製the catalyst in the same manner as in Catalyst Preparation Example 1. Using this catalyst, a N ₂ O removal test was conducted in the same manner as in Example 1 except for the above.

Comparative Example 4 The mordenite of Example 1 was mixed with a slurry of metatitanate (TiO 2).
₂ content 30 wt%, and change the S0 ₄ content 8 wt%) 167 g, the other A catalyst was prepared in the same manner. Using this catalyst, a N ₂ O removal test was conducted on the same equipment as in Example 1 except for the above. Table 3 shows the results of Example 9 and Comparative Examples 2 to 4.

[0034]

[Table 3]

From the results shown in Table 3, if alcohol is used,
Even if the zeolite that is a carrier is replaced with a pentasil-type zeolite, N ₂ O removal performance higher than NH ₃ can be obtained. On the other hand, F
It can be seen that both the zeolite catalyst supporting an active component other than e and the titania supporting Fe have low N ₂ O removing activity, and only the combination according to the present invention is excellent.

Example 10 A reaction tube was filled with the catalyst prepared in Example 1, and NO and N ₂ were added.
A simulated gas containing O is circulated, and NH _{3 is} supplied from the upstream side of the reaction tube.
An aqueous solution prepared by dissolving (concentration 2% -remaining N ₂ ) and 7.1 g of CH ₃ OH in 1 liter of water was injected, and NO and N ₂ O removal test was conducted under the conditions of Table 4.

[0037]

[Table 4]

[0038] Table 4 1 Concentration of CH ₃ OH is N ₂ O concentration.
The reason for the doubling is that the equivalent amount or more is injected to stably evaluate the performance of the catalyst. Also, NH ₃
The reason is that the concentration is 1.2 times the NO concentration for the same reason. As a result, the NO removal rate was 80.0% and the N ₂ O removal rate was 65.5%.

Example 11 In this example, as in Example 10, the reaction tube was filled with the catalyst prepared in Example 1, and a simulated gas containing NO and N ₂ O and NH ₃ were added.
The test was carried out by injecting an aqueous solution containing CH ₃ OH and CH ₃ OH. At that time, regarding the control of the injection amount of NH ₃ and alcohol and / or hydrocarbon, the NH ₃ amount is NO
Depending on the concentration, the amount of alcohol and / or hydrocarbon is N ₂ O
The injection amount was controlled independently in proportion to the concentration. Specifically, the injection amounts of NH ₃ , alcohol and hydrocarbon were changed as shown in Table 5 below.

[0040]

[Table 5]

[0041] Condition 2 for the condition 1 is increased N ₂ O concentration, in the case where NO concentration decreases, CH ₃ accordingly
Inject so that OH increases and NH ₃ decreases. Condition 3
In the opposite case, the N ₂ O concentration is decreased and the NO concentration is increased, and the CH ₃ OH concentration is decreased and the NH ₃ concentration is increased accordingly. Removal rate of N ₂ O and NO is the same does not depend on the concentration of N ₂ O and NO in a change in this degree.

Example 12 As the second catalyst of the present invention, a catalyst was prepared by the following procedure. Mordenite (Tosoh Co., Ltd., _SiO 2 / Al
50 kg of ₂ O ₃ ratio = 23) in 100 kg of water and iron nitrate (F
_{e 2 (NO 3) 3 ·} 9H 2 O) after turning 18kg in an aqueous solution by dissolving, and evaporated to dryness with stirring on a 0.99 ° C. sand bath. 3 wt% by firing this in air at 500 ° C for 2 hours
Mordenite supporting Fe was prepared to obtain the N ₂ O removal catalyst as the first component.

On the other hand, chloroplatinic acid (H ₂ [PtCl ₆ ].
6H ₂ O) 0.665 g was dissolved in 1 liter of water, and 500 g of commercially available fine silica powder (manufactured by Tomita Pharmaceutical Co., Ltd., Microcomputer F) was added, and the mixture was evaporated to dryness on a sand bath. This was baked in air at 500 ° C. for 2 hours to obtain 0.05 wt% Pt.
The SiO ₂ is prepared carrying, to obtain a second component.

Separately from this, a net of 1400 threads of E glass fiber having a fiber diameter of 9 μm and having a roughness of 10 threads / inch was plain woven with a slurry of 40% titania, 20% silica sol and 1% polyvinyl alcohol. It was impregnated and dried at 150 ° C. to have rigidity to obtain a catalyst substrate.

To 20 kg of the first component and 816 g of the second component, 430 ml of nitric acid (containing 60%), 8.95 kg of activated alumina, 31 kg of water, and 8.95 kg of silica-alumina inorganic fiber were added and kneaded with a kneader to obtain a catalyst paste. Obtained. The prepared catalyst mixture in paste form is placed between the above two catalyst substrates, and the catalyst is pressure-bonded between the meshes and the surface of the substrate by passing through a pressure roller to a thickness of about 1.5 m.
m plate catalyst was obtained. The obtained catalyst was dried at 180 ° C. for 2 hours and then calcined in the air at 500 ° C. for 2 hours. The ratio of the first component to the second component in this catalyst was 4/96, and the Pt content was 20 ppm excluding the catalyst base material and the inorganic fibers.

Comparative Example 5 A catalyst was prepared in the same manner as in Example 12, except that the second component was not added.

Experimental Example 1 The catalysts obtained in Example 12 and Comparative Example 5 were cut into a piece having a width of 20 mm and a length of 100 mm.
One piece was filled, and a porcelain Raschig ring was filled on the top. A simulated gas containing N ₂ O was circulated from the upstream of the reactor, and 7.1 g of methanol (CH ₃ OH) as a reducing agent was added to water 1
An aqueous solution prepared by dissolving in liter was poured and evaporated on Raschig rings, and methanol was added to N ₂ O under the conditions shown in Table 6.
The N ₂ O removal rate and the CO outflow rate were measured when the ratio was changed with respect to. FIG. 4 shows the results.

[0048]

[Table 6]

As shown in FIG. 4, when the catalyst of Example 12 was used, when the molar ratio of methanol / N ₂ O was increased, N ₂
The O removal rate is as high as that of Comparative Example 5, and the outlet CO outflow rate is as low as 10's of ppm. On the other hand, when the catalyst of Comparative Example 5 is used, the amount of CO outflow from the outlet increases as the reducing agent / N ₂ O molar ratio increases. From this result, the method of the present invention can prevent the outflow of CO, which is a problem of the prior art, and further, even when the reducing agent is excessively injected, C
It turns out that O can be prevented.

Example 13 The chloroplatinic acid in Example 12 was converted into palladium nitrate (P
Instead of d (NO ₃ ) ₃ ), each carrying amount is 0.05w
It was prepared to be t. A plate-like catalyst was prepared in the same manner as in Example 12 except that this was the second component.

Examples 14 and 15 The fine silica powder of Example 12 (manufactured by Tomita Pharmaceutical Co., Ltd., Microcomputer F) was replaced with mordenite powder and γ-alumina powder (manufactured by Sumitomo Chemical Co., Ltd.), and the others were the same. To prepare a second component, and the first component of Example 12 was used to prepare a plate catalyst.

Example 16 Mordenite of Example 12 (manufactured by Tosoh Corporation, SiO ₂
/ Al ₂ O ₃ ratio = 23) was replaced with ZSM-5 (PQ, pentasil-type zeolite SiO ₂ / Al ₂ O ₃ ratio = 30), and otherwise the first component was prepared in the same manner as in Example 12. did. Furthermore, a plate-like catalyst was prepared in the same manner as in Example 12 using the second component of Example 12.

Experimental Example 2 The catalysts of Examples 12 to 16 were used, and the same as in Experimental Example 1 except that the reducing agent / N ₂ O molar ratios were 1.2 and 1.5.
At that time, the N ₂ O removal rate and the CO outflow rate were measured. Table 7 shows the results.

[0054]

[Table 7]

From these results, it can be seen that the method according to the present invention prevents the outflow of CO, which is caused by the decomposition of the reducing agent, to the outlet side.

Experimental Examples 3 and 4 Using the catalyst of Example 12, the reducing agent methanol was replaced by ethanol and methane, and the same as in Experimental Example 1 except that the reducing agent / N ₂ O molar ratio was 1.5. N ₂ O removal rate and C
The amount of O 2 outflow was measured. Even if the reducing agent was changed to ethanol and methane, the N ₂ O removal rates were 65 and 66%, respectively, and the high removal rates were obtained as in the case of methanol, and the amount of CO flowing out from the outlet side was 10 and 12 ppm, respectively. The same effect was obtained even if the reducing agent was changed.

[0057] was prepared so as to 200ppm NO to the gas composition in Experimental Example 5 Table 1, methanol was injected at 1.5 mol / mol relative to N ₂ O as N ₂ O of the reducing agent, separately NO from that As a reducing agent for NH ₃ with respect to NO, 1.2 mol / mol
Is injected from the reactor upstream so that, other using the catalyst of Example 12 performed N ₂ O and NO removal test in the same manner as in Experimental Example 1, N ₂ O removal ratio, denitrification rate, outlet C
O and ammonia effluent were measured. As a result, N ₂
O removal rate is 73%, denitration rate is 96%, CO from the outlet
Outflow is 11 ppm, and NH ₃ outflow is several pp
m was below the detection limit.

From these results, it is understood that the method of the present invention can prevent the outflow of unreacted ammonia even when NH ₃ is used as the reducing agent.

[0059]

According to the present invention, N ₂ O, which is a substance depleting the ozone layer, can be efficiently removed at 350 to 450 ° C. Further, according to the present invention, it is possible to prevent the outflow of CO and ammonia, which is a problem when the reducing agent is excessively injected to obtain a high removal rate.

[Brief description of drawings]

FIG. 1 is a diagram showing a comparison between Example 1 and Comparative Example 1 of the present invention.

FIG. 2 is a flow chart showing a desulfurization process.

FIG. 3 N ₂ O with methanol and propane of the present invention
FIG. 3 is a diagram showing the molar ratio characteristic of NO and the molar ratio characteristic of NO with methanol.

FIG. 4 is a diagram showing a comparison between Example 12 of the present invention and Comparative Example 5.

[Explanation of symbols]

1 ... combustor, 2 ... N ₂ O removing catalyst, 3 ... heat exchanger, 4
... chimney, 5 ... reactor, 6 ... reducing agent

Claims (8)

[Claims] 1. A catalyst having iron supported on at least one carrier of mordenite and pentasil-type zeolite is installed in an exhaust gas passage containing nitrous oxide, and a reducing agent of at least one of alcohol and hydrocarbon is injected. A method for removing nitrous oxide in exhaust gas, which comprises reacting nitrous oxide on the catalyst to reduce nitrous oxide to nitrogen. 2. A catalyst in which iron is supported on a carrier of at least one of mordenite and pentasil-type zeolite is installed in an exhaust gas containing nitrous oxide and nitric oxide, and a reducing agent for at least one of alcohol and hydrocarbon. And a method for removing nitrous oxide and nitric oxide in exhaust gas, which comprises injecting ammonia and reducing nitrous oxide and nitric oxide to nitrogen on the catalyst. 3. The amount of ammonia injected is proportional to the measured value of the concentration of nitric oxide in the exhaust gas, and the injected amount of the reducing agent of at least one of alcohol and hydrocarbon is the measured value of the concentration of nitrous oxide in the exhaust gas. The method for removing nitrous oxide and nitric oxide in exhaust gas according to claim 2, wherein the method is adjusted in proportion to 4. A catalyst having both nitrous oxide decomposing activity and nitric oxide decomposing activity, characterized in that iron is supported on at least one carrier of mordenite and pentasil-type zeolite. 5. The noble metal composition, wherein a zeolite having iron supported in an exhaust gas passage containing nitrous oxide is used as a first component, and a noble metal salt of platinum or palladium or a porous material such as zeolite, alumina or silica is preliminarily supported. Is installed as a second component, and a reducing agent for at least one of alcohol and hydrocarbon is injected to decompose and remove carbon monoxide and nitrous oxide on the catalyst. Removal of nitrous oxide in exhaust gas Method. 6. A zeolite having iron supported in an exhaust gas passage containing nitrous oxide and nitric oxide as a first component, which has been previously supported on a noble metal salt of platinum or palladium or a porous material such as zeolite, alumina or silica. A catalyst containing the noble metal composition as the second component is installed, and a reducing agent of at least one of alcohol and hydrocarbon and ammonia are injected to cause carbon monoxide, nitrous oxide, nitric oxide, and excess ammonia on the catalyst. Method for decomposing and removing nitrous oxide and nitric oxide in exhaust gas. 7. A catalyst comprising, as a second component, an iron-supported zeolite as a first component, a platinum or palladium noble metal salt or a noble metal composition previously supported on a porous material such as zeolite, alumina, or silica. A catalyst that combines carbon oxide decomposition activity, ammonia decomposition activity, nitrous oxide decomposition activity, and nitric oxide decomposition activity. 8. An exhaust gas is passed through a catalyst layer filled with the catalyst according to claim 4, using at least one of a reducing agent of alcohol and hydrocarbon or ammonia in addition to this as a reducing agent. A device for removing nitrogen oxides from exhaust gas.