JP2001113134A - Method for cleaning waste gas containing nox - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a method for reductive denitration by hydrocarbon at a wide temperature range of 300-600 deg.C by adding hydrogen in the waste gas so as to drastically shift an active temperature region to low temperature side at the time of purifying the gas containing NOX and oxygen by a silver/ alumina catalyst or an alumina catalyst. SOLUTION: In the method for cleaning the waste gas containing NOX and oxygen by the silver/alumina catalyst or the alumina catalyst using the hydrocarbon as a reducing agent, the hydrogen is added to the NOX-containing waste gas.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a novel and useful method for purifying NOx-containing exhaust gas using a catalyst comprising silver supported on alumina (hereinafter referred to as "silver / alumina catalyst" as appropriate) or an alumina catalyst. About.

[0002]

2. Description of the Related Art When incinerating industrial waste and municipal garbage, NOx (nitrogen oxide), CO (carbon monoxide), or NOx (nitrogen oxide) or CO (carbon monoxide) depends on the origin, type and composition of the waste. SOx (sulfur oxide such as SO ₂ ), hydrogen chloride, odor and the like are generated. Various measures have been taken against exhaust gases including these, and further research and development have been promoted. In this regard, exhaust gases emitted from automobiles, thermal power generation, cogeneration systems using gas engines, etc. and GHP systems The same applies to.

[0003] Among the harmful components in various exhaust gases, various methods are known as a so-called flue gas denitration technology, particularly for the treatment of NOx. Among them, the catalytic reduction method of purifying using a catalyst in the treatment is usually performed using N
It is of particular interest because it is an innocuous changed Ox to finally N _2. There are various catalysts used in this catalytic reduction method, and one of them is a silver / alumina catalyst.

[0004] In the catalytic reduction method, a separate reducing agent is required in addition to the catalyst. However, the silver / alumina catalyst is capable of removing NOx from oxygen-excess exhaust gas by using an oxygen-containing organic compound such as alcohol or aldehyde or a lower hydrocarbon as a reducing agent. It is an effective catalyst as a practical catalyst because it can be efficiently reduced and removed. In the case where an oxygen-containing compound such as alcohol is added as a reducing agent, this catalyst is used in a low temperature range of about 300 to 500 ° C.
Ox can be reduced and removed, and when residual hydrocarbons in exhaust gas are used as a reducing agent, NOx can be reduced and removed in a high temperature range of about 400 ° C to about 600 ° C.

[0005] To reduce and remove NOx on a silver / alumina catalyst using hydrocarbons as a reducing agent, as described above, at 400 ° C.
A temperature higher than or equal to about 450 ° C. is required. On the other hand, for example, the exhaust gas temperature of a lean burn gas engine varies depending on the combustion system and output, but is in the range of about 300 to 600 ° C. Therefore, in the case of a lean burn gas engine having a relatively low exhaust gas temperature, the silver / alumina catalyst does not work effectively unless a method of adding alcohols or the like is used.

For this reason, a method of converting a hydrocarbon into an oxygen-containing compound by installing a catalyst for converting the hydrocarbon into an oxygen-containing compound such as an alcohol in the first stage to improve the denitration activity in a lower temperature range has been proposed. Proposed. For example, Japanese Patent Application Laid-Open No. 9-141056 discloses that when catalytically reducing nitrogen oxides contained in exhaust gas using hydrocarbons as a reducing agent, the first step is to convert exhaust gas containing hydrocarbons together with nitrogen oxides into a metal such as platinum or palladium. Or by contacting the catalyst with an oxide thereof to convert the hydrocarbon into an oxygen-containing organic compound or a lower-molecular hydrocarbon having excellent selective reactivity with nitrogen oxides. That is, the reaction is reduced stably and efficiently.

In JP-A-9-201515, copper ions, copper oxides and copper aluminates are used as the catalyst for the first stage. However, although these techniques seem to be effective for lowering the temperature of the denitration reaction, they require a separate device for the first stage, that is, conversion to oxygen-containing organic compounds and lower-molecular hydrocarbons. When the fuel is used as a fuel, the residual hydrocarbons are mostly low-grade saturated hydrocarbons, and at present, there is no catalyst that can efficiently convert them into oxygen-containing compounds.

[0008] Alumina, of course, as the catalyst itself,
It is also effectively used as a carrier for supporting silver as a catalyst metal. In a denitration reaction using a silver / alumina catalyst, for example, as disclosed in Japanese Patent Application Laid-Open No. 5-92124, a gaseous alkane and / or alkene is added to a combustion exhaust gas containing an excessive amount of oxygen to reduce the amount of the exhaust gas. Of nitrogen oxides can be removed. However, with respect to alumina used as a carrier in the catalyst of the publication, only the specific surface area is set to 30 m ² / g or more, and conventionally, the influence of alumina itself was considered to be small [Miyadera, Journal of the Japan Institute of Energy. 73, 11
No. 987-993 (1994)].

The present inventors have further pursued the catalytic properties and practicality of the silver / alumina catalyst on the premise of the above-mentioned points and the like. There are considerable differences between the two, due to impurities from raw materials and manufacturing methods,
Moreover, it was found that this was due to the influence of specific three components of SiO ₂ , Na ₂ O and chlorine,
₂ , NO that simultaneously reduces Na ₂ O and chlorine below a predetermined value
A silver / alumina catalyst for purifying x-containing exhaust gas has been previously developed (Japanese Patent Application No. 10-198008).

In the catalyst disclosed in Japanese Patent Application No. Hei 10-198008, the specific surface area of alumina is 100 m ² / g or more, the SiO ₂ content in alumina is 180 ppm or less, and Na ₂ O
Is 100 ppm or less and chlorine is 50 ppm or less, whereby the NOx purification effect is improved, and even when the NOx concentration in the exhaust gas is extremely low, for example, 91 ppm, an excellent NOx purification effect is obtained. Obtainable.

Although these are improvements in the catalyst itself, the inventors of the present invention did not install a catalyst for converting hydrocarbons into oxygen-containing compounds such as alcohols in the first stage, and it was found that silver /
In pursuit of a technique capable of denitration effectively using only an alumina catalyst or an alumina catalyst, the addition of hydrogen to NOx-containing exhaust gas not only allows the denitration active temperature range to be largely shifted to a lower temperature side, but also increases the temperature.
The inventors have found that reductive denitration with hydrocarbons can be performed in a wide temperature range from a low temperature range to a high temperature range of 0 to 600 ° C., and have reached the present invention.

[0012]

According to the present invention, not only can the active temperature range be greatly shifted to a lower temperature side by adding hydrogen to the exhaust gas, but also it can be reduced to 300 to 60.
It is an object of the present invention to provide a method for purifying a NOx-containing exhaust gas containing oxygen using a silver / alumina catalyst or an alumina catalyst which enables reductive denitration with a hydrocarbon in a wide temperature range from a low temperature range to a high temperature range of 0 ° C.

[0013]

The present invention provides (1) a method for purifying an NOx-containing exhaust gas containing oxygen by a silver / alumina catalyst utilizing a hydrocarbon as a reducing agent, wherein hydrogen is added to the NOx-containing exhaust gas. The present invention also provides a method for purifying NOx-containing exhaust gas, which comprises: (2) NO containing oxygen by an alumina catalyst utilizing a hydrocarbon as a reducing agent;
In the method for purifying x-containing exhaust gas, a method for purifying NOx-containing exhaust gas is provided, wherein hydrogen is added to the NOx-containing exhaust gas.

[0014]

DETAILED DESCRIPTION OF THE INVENTION The present invention is a method for purifying an NOx-containing exhaust gas containing oxygen using a silver / alumina catalyst or an alumina catalyst as a catalyst and using a hydrocarbon as a reducing agent, wherein hydrogen is added to the NOx-containing exhaust gas. It is characterized by. The invention presupposes the use of hydrocarbons as reducing agents and is effectively applied to exhaust gases containing oxygen and to exhaust gases containing excess oxygen. In the present invention, hydrogen is added to these exhaust gases. As the reducing agent or hydrocarbon, for example, methane, ethane, ethylene, propane, propylene, butane, isobutane,
Pentane or two or more of these are used. For example, the exhaust gas from a lean burn gas engine usually contains one or more of these hydrocarbons, and can be used as they are. If these hydrocarbons are not contained in the gas to be treated, they are added separately, and if they are contained, they are added in an amount sufficient to make up for them.

According to the present invention, by adding hydrogen to the NOx-containing exhaust gas, not only can the active temperature range be largely shifted to a lower temperature side, but when a silver / alumina catalyst is used as a catalyst, 300 A NOx conversion of 20% or more can be achieved in a wide temperature range from a low temperature range of ℃ to a high temperature range of 600 ° C. When an alumina catalyst is used as the catalyst, 470 to 6
NOx conversion rate of 20 over a wide temperature range of 70 ° C
% Or more can be achieved.

The hydrogen added in the present invention only needs to be added to the exhaust gas, and does not need to be purified because it is not affected by purity or coexisting gas. For this reason, commercially available hydrogen filled in cylinders, hydrogen obtained by electrolysis, reformed gas obtained by steam reforming of fuel gas or gas obtained by partial combustion, or hydrogen-containing off-gas discharged from various factories is used. Since it is possible, it is very advantageous in practice. Although a small amount of hydrogen is contained in exhaust gas from a gas engine or the like, the amount of hydrogen originally contained in the exhaust gas is not an effective amount for denitration in the present invention. The desired denitration effect in the present invention is obtained.

The silver / alumina catalyst used in the present invention is a catalyst comprising silver supported on alumina. The production method is not particularly limited as long as silver can be uniformly supported on alumina. Preferably, an impregnation method or a wet kneading method can be applied. As an example of the impregnation method as an example, an aqueous solution of silver nitrate or an aqueous solution in which silver is dissolved in an acetate, a complex salt, or another form is used, and powder, granules,
Granular (including: spherical), pellet (cylindrical, annular),
Tablet (tablet) or honeycomb (monolithic)
Alumina or alumina hydrate in the form of, for example, is charged, immersed and stirred to impregnate the alumina with the silver compound. Thereafter, it is obtained by drying and baking by a conventional method. As the alumina, commercially available or known alumina or alumina hydrate can be used, as well as the alumina used in the catalyst of Japanese Patent Application No. 10-198008. This also applies to alumina in the alumina catalyst. The alumina catalyst is produced by calcining the alumina or alumina hydrate.

The amount of silver supported on alumina is in the range of 0.1 to 10% by weight, more preferably 0.8 to 9.0% by weight, based on alumina. It is still effective when the amount of silver carried is less than 0.1 wt%, but the catalytic effect is reduced accordingly. The amount of each of them is 10wt%
When the amount exceeds about 10%, an effective catalytic effect can be similarly obtained. However, if silver is supported up to about 10% by weight, the desired catalytic effect can be obtained.
About wt% is sufficient. Of course, the above range 0.1 to
It may be around 10 wt%. When the catalyst is used as a monolith body, silver according to the above is supported.

The catalyst may be used in the form of powder, granule,
Granular (including: spherical), pellet (cylindrical, annular),
Tablet (tablet) or honeycomb (monolithic)
It is used as an appropriate shape such as a shape. However, in the present invention, since it is necessary to pass NOx-containing exhaust gas through these, when the catalyst is in the form of powder, a catalyst layer filled with the powder (for example, a catalyst layer filled between mesh plates or perforated plates) In order not to dissipate, it is desirable that the particles are sized or granulated in a predetermined particle size range, or that they are formed by pressing or extrusion. Among them, in the case of extrusion molding, it is cut into a predetermined length and pelletized before use. This applies to the case of the alumina catalyst used in the present invention.

Further, a honeycomb shape is a more preferable use mode. The honeycomb (monolithic) form is produced in such a manner that (1) the catalyst is extruded together with a binder or the like as necessary to form a honeycomb form, and (2) the catalyst is supported on, for example, a ceramic honeycomb.
In this case, a ceramic or metal such as cordierite can be used as a honeycomb substrate in the honeycomb catalyst, and a metal made of stainless steel or an iron-aluminum-chromium alloy is preferably used as the metal.
This applies to the case where an alumina catalyst is used in the present invention.

FIG. 1 is a diagram showing an example of an apparatus mode for carrying out the present invention. In FIG. 1, A is a pipe for introducing the exhaust gas to be treated and hydrogen (hydrogen-containing gas), B is a denitration catalyst layer (reaction tube), C is an outlet pipe for the treated exhaust gas, and an arrow (→) indicates a flow direction of the exhaust gas. is there. The denitration catalyst is not limited to the apparatus mode as shown in FIG. 1, but may be used in various apparatus modes as long as it can be arranged for the exhaust gas flow. In order to set the honeycomb-shaped denitration catalyst in the catalyst layer as shown in FIG. 1, it is arranged such that its cross-section opening faces the flow direction of the exhaust gas.

[0022]

EXAMPLES Hereinafter, the present invention will be described in more detail with reference to examples, but it is needless to say that the present invention is not limited to the examples. Silver / alumina catalysts and alumina catalysts were prepared as described below and various hydrogenation effects were tested on the silver / alumina catalysts and alumina catalysts.

Example 1 <Catalyst Preparation 1: Silver / Alumina Catalyst> As alumina, a commercially available high-purity alumina hydrate (boehmite) was used. On the other hand, 3.15 g of silver nitrate was dissolved in 150 mL of distilled water to prepare an aqueous solution of silver nitrate. This aqueous solution was mixed with 136 g of the alumina hydrate powder and stirred for 10 minutes. In this case, the amount of silver in the aqueous solution was adjusted to 2% by weight based on the total weight of the catalyst after calcination. Then, it is transferred to a porcelain dish and dried in a thermostat at a temperature of 120 ° C. for 6 hours to evaporate excess water.
For 3 hours in the air to obtain a powdery solid. Then
The powdery solid obtained above was formed into pellets by press molding, then pulverized, and sized to have a particle size in the range of 355 μm to 710 μm.

<Hydrogenation Effect Test 1> The catalyst obtained in Catalyst Preparation 1 was tested for hydrogenation effect by the following method. 4.5 mL of the catalyst was weighed and charged into a reaction tube having an inner diameter of 10 mm in a normal pressure flow reactor, and the test was carried out under the following test conditions. Ethane, ethylene, propane, propylene and isobutane were used as hydrocarbon reducing agents. As Comparative Example 1, the same test was conducted except that H ₂ was not added. Test conditions: SV = 44,000 h ⁻¹ , reaction temperature = 300
C to 600 ° C, the composition of the gas to be treated (volume,
The same applies hereinafter): NO = 91 ppm, hydrocarbon (in terms of CH ₄ ) = 270 ppm, H ₂ O = 9.1%, O ₂ = 9.1.
_{%, H 2 = 455ppm, He} = balance.

Here, the NOx conversion rate is the NOx conversion rate before the treatment.
Assuming that the concentration is X and the NOx concentration after treatment is Y, the following equation (1)
It is calculated by: In this regard, the same applies to the NOx conversion rate in Examples described later.

[Equation 1]

FIG. 2 is a diagram showing the results of the hydrogenation effect test 1. As shown in FIG. 2, when hydrogen was not added, that is, Comparative Example 1 was effective in a high temperature range of 470 to 600 ° C., but its effective temperature range was narrow. It can be seen that the peak of the rate is about 46% around 510 ° C. On the other hand, when hydrogen is added, that is, in Example 1, the effective temperature extends to a lower temperature range, and shows a high NOx conversion over a wide temperature range. NOx conversion rate of 20 even at a low temperature of 300 ° C
% Is obtained. NOx conversion peak also 49
It shows a value of about 53% around 0 ° C., and shows a value of 20% NOx conversion even at a high temperature of 600 ° C.

Table 1 shows the results for each type of reducing agent. It can be seen that in the case where hydrogen was added, that is, in Example 1, the NOx conversion in the low temperature region was remarkably improved as compared with the case where hydrogen was not added, that is, in Comparative Example 1. For example, when ethane is used as the reducing agent, in Comparative Example 1, 35
At 0 ° C., the NOx conversion is only 4.5%, at 400 ° C. 6.4%, and even at 450 ° C., 11.1%. On the contrary,
In Example 1, 14.7% at 350 ° C., 400 ° C.
Shows a NOx conversion of 19.0% and 26.2% at 450 ° C., and NOx is effectively removed even in such a low temperature range.

[0028]

[Table 1]

Example 2 <Catalyst Preparation 2: Alumina Catalyst> The commercially available high-purity alumina hydrate (boehmite) powder was placed in an electric furnace at a temperature of 600 ° C.
After sintering in air for 3 hours, forming into pellets by press molding, pulverizing, and sizing so as to have a particle size in the range of 355 μm to 710 μm.

<Hydrogenation Effect Test 2> The hydrogenation effect of the alumina catalyst obtained in Catalyst Preparation 2 was tested. 4.5 mL of the catalyst was weighed, filled into a reaction tube having an inner diameter of 10 mm in a normal pressure flow reactor, and the test was carried out under the following test conditions. As Comparative Example 2, except that no addition of H _2, was tested in the same manner. Test conditions: SV = 44,000 h ^-1 , 400 ° C to 70
Range up to 0 ° C., composition of gas to be treated: NO = 91 pp
m, hydrocarbon (in terms of CH ₄ ) = 270 ppm, H ₂ O =
9.1%, O ₂ = 9.1%, H ₂ = 455 ppm, He =
balance.

FIG. 3 is a diagram showing the results of the hydrogenation effect test 2, some examples of which are shown in Table 2. FIG.
As described above, when hydrogen is not added, that is, Comparative Example 2 is effective in a high temperature range of 520 to 700 ° C.
Below 500 ° C., there is almost no effect. It can be seen that the NOx conversion peak is also about 48% at around 570 ° C.
On the other hand, when hydrogen is added, that is, in Example 2, the effective temperature extends to a lower temperature range, and shows a high NOx conversion over a wide temperature range. Even at a low temperature of 470 ° C., an effect of a NOx purification rate of 20% can be obtained. The NOx conversion peak also showed a value of about 66% around 550 ° C.
Even at a high temperature of 70 ° C., the NOx purification rate is about 20%.

[0032]

[Table 2]

Example 3 <Hydrogenation effect test 3: Influence of hydrogenation amount> Catalyst preparation 1
The effect of the amount of hydrogen added on the catalyst obtained in 1) was tested. 4.5 mL of the catalyst was weighed, filled into a reaction tube having an inner diameter of 10 mm in a normal pressure flow reactor, and the test was carried out under the following test conditions. Comparative Example 3 is a case where the amount of hydrogen added is 0 ppm. Test conditions: SV = 44,000 h ^-1 , temperature = 300-6
00 ° C., composition of gas to be treated: NO = 91 ppm, hydrocarbon (propane) = 91 ppm, H ₂ O = 9.1%, O ₂ =
9.1%, H ₂ = 0 to 1,818 ppm, He = balance.

Table 3 shows that in the hydrogenation effect test 3, the hydrogenation amount was 0 ppm (Comparative Example 3), 455 ppm, 909
ppm and 1,818 ppm,
℃, 350 ℃, 400 ℃, 450 ℃, 500 ℃, 550
It shows the NOx conversion at each temperature of 600C and 600C. As shown in Table 3, the NOx conversion rate in Example 3 was 3
In the range of 00 to 450 ° C., there is a tendency to increase as the amount of hydrogen added increases. On the other hand, 500-600 ° C
In the range of, there is a tendency to decrease somewhat as the amount of hydrogen added increases, but the amount of hydrogen added is 0 ppm (Comparative Example 3).
As is clear from comparison with the above case, at 500 ° C. or lower, the expected effect can be obtained at any temperature by adding hydrogen.

[0035]

[Table 3]

FIG. 4 is a diagram showing the results of a hydrogenation effect test 3 at 450 ° C. As shown in FIG. 4, the NOx conversion rate rapidly increased as the amount of added hydrogen increased, and reached about 50% at a hydrogen addition amount of about 500 ppm and about 60% at a hydrogen addition amount of about 600 ppm. The NOx conversion rate is maintained. From this fact, for example, at 450 ° C., the amount of hydrogen
pm, NOx conversion around 50% can be achieved at all times.
It is clear that NOx conversions around 0% can be achieved.

Example 4 <Hydrogenation Effect Test 4: Influence of Space Velocity> The effect of space velocity on the hydrogenation effect of the catalyst obtained in Catalyst Preparation 1 was tested. 4.5 mL of the catalyst was weighed, filled into a reaction tube having an inner diameter of 10 mm in a normal pressure flow reactor, and the test was carried out under the following test conditions. Test conditions: SV = 2,000 to 150,000 h ⁻¹ , temperature = 300 to 600 ° C., composition of gas to be treated: NO = 91
ppm, hydrocarbon (propane) = 91 ppm, H ₂ O =
9.1%, O ₂ = 9.1%, H ₂ = 455 ppm, He =
balance.

[0038] Table 4, in the hydrogenation effect test 4, for the case of the amount of hydrogen addition amount 0ppm and 455 ppm, each space of SV = 44,000h ^-1, 88.000h ^-1 and 132,000H ^-1 At a speed of 300 ° C.
The NOx conversion at each of 350 ° C., 400 ° C., 450 ° C., 500 ° C., 550 ° C., and 600 ° C. is shown. As shown in Table 4, the NOx conversion rate in Example 4 was
Up to about 450 ° C., there is a tendency to decrease as the space velocity increases, but at about 500 ° C. or more, there is almost no effect of the space velocity or it increases contrary to the increase. For example, even under a severe condition of SV = 132,000 h ^-1 , for example, 27.5% at 400 ° C. and 3% at 450 ° C.
7.8%, 47.2% at 500 ° C, 36.0 at 550 ° C
% Indicates an effective NOx conversion rate. On the other hand, in the case of the hydrogen addition amount of 0 ppm, that is, in the case of Comparative Example 4, the NOx conversion effect is hardly recognized or hardly recognized at any space velocity in a low temperature range of 300 to 400 ° C. Even at 450 ° C. or higher, the NOx conversion rate
It is significantly inferior to Example 4, and decreases as the space velocity increases.

[0039]

[Table 4]

FIG. 5 is a diagram showing the results of a hydrogenation effect test 4 at 500 ° C. As shown in FIG. 5, when hydrogen was added, that is, in Example 4, the NOx conversion rate was SV =
There is almost no change even at 30,000 h ^-1 or more, indicating a NOx conversion of about 50%. On the other hand, when hydrogen was not added, that is, in Comparative Example 4, the NOx conversion began to drop sharply from about SV = 30,000 h ⁻¹ ,
The NOx conversion at SV = 135,000 h ^-1 is almost zero.

[0041]

According to the present invention, when purifying a NOx-containing exhaust gas containing oxygen with a silver / alumina catalyst or an alumina catalyst, hydrogen is added to the exhaust gas to purify the NOx-containing exhaust gas.
Not only can the active temperature range be greatly shifted to a lower temperature side, but the reductive denitration with hydrocarbons can be effectively performed in a wide temperature range of 300 to 600 ° C.

[Brief description of the drawings]

FIG. 1 is a diagram showing an example of an apparatus embodiment for implementing the present invention.

FIG. 2 is a view showing the results of a hydrogenation effect test 1 (silver / alumina catalyst).

FIG. 3 is a view showing the results of a hydrogenation effect test 2 (alumina catalyst).

FIG. 4 is a view showing the results of a hydrogenation effect test 3 (influence of hydrogen concentration, 450 ° C.).

FIG. 5 is a view showing the results of a hydrogenation effect test 4 (effect of space velocity, 500 ° C.).

[Explanation of symbols]

 A Exhaust gas and hydrogen introduction pipe B DeNOx catalyst layer (reaction pipe) C Discharge pipe of treated exhaust gas

 ──────────────────────────────────────────────────続 き Continued on front page F term (reference) 3G091 AA12 AA19 AB05 BA04 BA14 BA39 CA18 CA19 FB10 GA01 GA02 GA06 GB01W GB05W GB10W GB16W 4D048 AA06 AB02 AC01 BA03X BA34X BA41X BB01 CC38 DA03 DA06 4G069 AA03 CA01 BC EA01Y EB18Y

Claims (7)

[Claims] 1. A method for purifying an NOx-containing exhaust gas containing oxygen using a silver / alumina catalyst utilizing a hydrocarbon as a reducing agent, wherein hydrogen is added to the NOx-containing exhaust gas. 2. The temperature of the NOx-containing exhaust gas is 300 to 6
The method for purifying NOx-containing exhaust gas according to claim 1, wherein the temperature is in the range of 00 ° C. 3. A method for purifying NOx-containing exhaust gas containing oxygen using an alumina catalyst utilizing hydrocarbon as a reducing agent, wherein hydrogen is added to the NOx-containing exhaust gas. 4. The temperature of the NOx-containing exhaust gas is 470-6.
The method for purifying NOx-containing exhaust gas according to claim 3, wherein the temperature is in a range of 70 ° C. 5. The method for purifying NOx-containing exhaust gas according to claim 1, wherein the hydrogen to be added is hydrogen or a hydrogen-containing gas. 6. The space velocity of the NOx-containing exhaust gas is 2,0.
The method for purifying NOx-containing exhaust gas according to any one of claims 1 to 5, wherein the range is from 00 to 150,000 h ^-1 . 7. The method for purifying NOx-containing exhaust gas according to claim 1, wherein said NOx-containing exhaust gas is exhaust gas from a lean burn gas engine.