JPH0523546A - Waste gas cleaning catalyst and waste gas cleaning method using same - Google Patents

Abstract

PURPOSE:To provide a waste gas cleaning catalyst which is able to clean nitrogen oxides to harmless gases efficiently even if the concentration of oxygen in a waste gas is high and provide waste gas cleaning method using the catalyst. CONSTITUTION:Gallium and zeolite are contained to give a waste gas cleaning catalyst and nitrogen oxides in a waste gas are reduced and removed by using the catalyst at 300-800 deg.C reaction temperature, in an oxidative atmosphere, and in the presence of a hydrocarbon with 1-20 (THC concentration)/(NOX concentration) wherein THC concentration means the concentration of the hydrocarbon expressed in terms of methane.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention decomposes nitrogen oxides emitted from mobile internal combustion engines such as diesel automobiles, stationary internal combustion engines such as cogeneration, and various industrial furnaces such as boilers into harmless gases. The present invention relates to an exhaust gas purifying catalyst and an exhaust gas purifying method using the same.

[0002]

BACKGROUND ART Exhaust gas from automobiles, stationary internal combustion engines, and various industrial furnaces generally contains a large amount of nitrogen oxides (NO _X ) represented by NO and NO _2. ing. These NO _X is not only cause of photochemical smog, which is said to cause respiratory failure for the human body.

Regarding the method of reducing these NO _x ,
When the amount of oxygen in the exhaust gas is small, as in a gasoline vehicle, so-called three-way catalyst type exhaust gas treatment has been established, in which NO _X is reduced and removed with a reducing agent such as carbon monoxide or hydrocarbon. On the other hand, when a large amount of oxygen is contained in the gas, such as in a large stationary emission source such as a boiler, a selective NO _X reduction method that reduces the amount of NO _X by externally adding ammonia is in operation. , To some extent. However, the former method is applicable only to the exhaust gas from a gasoline engine with an extremely low oxygen concentration, and the latter method uses ammonia, so it is not suitable for use in small stationary emission sources and mobile emission sources. It's difficult.

Therefore, as a reducing agent other than ammonia,
Various methods using hydrogen, carbon monoxide, various hydrocarbons, etc. have been studied, but most of them are non-selective contact that enables removal of nitrogen oxides only after oxygen in exhaust gas is completely consumed. It has a drawback that it is a reduction method.
Conventionally, the following method has been proposed as a novel selective catalytic reduction method (a method for selectively reducing and removing nitrogen oxides even in the presence of oxygen) capable of solving such problems, but However, satisfactory results have not been obtained.

That is, according to Japanese Patent Laid-Open No. 2-149317,
Using a catalyst composed of hydrogen type mordenite or clinoptilolite, or a catalyst composed of hydrogen type mordenite or clinoptyllite carrying a metal such as Cu, Cr, Mn, Fe or Ni, various fuels were burned. It has been proposed to remove the nitrogen oxides in the flue gas by contacting the resulting flue gas containing oxygen with these catalysts in the presence of an organic compound. According to this method, a denitrification rate of 30 to 60% was obtained under the conditions of a reaction temperature of 300 to 600 ° C and a gas space velocity (GHSV) of 1200 h ^-1 , but under conditions of high GHSV, which is close to practical conditions. The denitrification effect is unknown. In addition, there is no description about the change in catalyst activity over time, and the life of the catalyst is unknown. Furthermore, since the evaluated catalyst in a pseudo-gas containing no SO _X, it is unclear resistant SO _X of the catalyst.

Further, according to Japanese Patent Laid-Open No. 1-130735, a catalyst in which a zeolite ion-exchanged with a transition metal (Cu, Co, Ni, Fe, Mg, Mn, etc.) is supported on a refractory carrier is used. ,
A method that can purify nitrogen oxides even in an oxidizing atmosphere has been proposed. This method is a method of purifying exhaust gas of a gasoline engine with high efficiency of nitrogen oxides even when the air-fuel ratio is lean, and the oxygen concentration in the exhaust gas is at most about 3%. Therefore, it is unclear whether nitrogen oxides can be selectively reduced and denitrated similarly even when the oxygen concentration is 5 to 10% like the exhaust gas of a diesel engine. Also in the examples, the No _X removal rate tends to remarkably decrease as the oxygen concentration increases.

According to Japanese Patent Laid-Open No. 63-283727, SiO ₂ / A
Cu, V, Mn, Fe, and hydrophobic zeolite with l ₂ O ₃ ratio of 15 or more
Using a catalyst supporting a metal such as Cr, carbon monoxide and 1
There has been proposed a method for reducing nitrogen oxides in exhaust gas containing oxygen of an internal combustion engine in the presence of one kind or two or more kinds of hydrocarbons. In this method, when a zeolite catalyst supporting a metal other than copper is used, the denitration rate becomes as low as 4 to 26%. On the other hand, when a copper zeolite catalyst is used, a relatively high activity is obtained, but there is a problem that the copper component is easily poisoned by SO _X. The oxygen concentration in the exhaust gas of the example is 1.6%, and it is unknown whether the nitrogen oxide can be selectively reduced and denitrated similarly even when the oxygen concentration is high, such as the exhaust gas of a diesel engine. .

According to JP-A-63-100919, a catalyst in which copper is supported on a porous carrier such as alumina, silica, or zeolite is used, and nitrogen oxidation in exhaust gas containing oxygen in the presence of hydrocarbons is carried out. Methods for removing things have been proposed. With this method, the denitration rate is 10 to 25%, and high denitration activity cannot be obtained. Also, since this catalyst contains copper,
There is a problem that the copper component is easily poisoned by SO _X. Furthermore, the oxygen concentration in the exhaust gas of the example is 2.1%, and it is not clear whether nitrogen oxide can be selectively denitrified similarly even when the oxygen concentration is higher.

It is an object of the present invention to provide an exhaust gas purifying catalyst which can purify nitrogen oxides into a harmless gas with high efficiency even if oxygen in the exhaust gas has a high concentration, and an exhaust gas purifying method using the same. And

[0010]

The exhaust gas-purifying catalyst according to the present invention is a catalyst for reducing and removing nitrogen oxides in exhaust gas in an oxidizing atmosphere, and serves as a main catalyst, gallium and a co-catalyst. It is characterized by containing zeolite. The oxidizing atmosphere is used to completely oxidize carbon monoxide contained in exhaust gas, hydrogen, hydrocarbons and reducing substances of hydrocarbons added as necessary in this treatment to convert them into H ₂ O and CO ₂ . This is a state in which an excess amount of oxygen is contained in excess of the oxygen amount required for.

As the Ga source of the gallium (Ga) component in the catalyst, a compound that can be converted into an oxide during catalyst preparation or reaction use can be used. Such compounds include Ga nitrates, sulfates, oxides, halides,
There are carbonates, hydroxides, organic acid salts and the like.

Further, the existence form of the Ga component in the catalyst is arbitrary, and the following forms can be adopted. For example, a component of zeolite (for example, an ion-exchangeable cation, a substitution atom in the framework, or when these are prepared in the catalyst,
It may be contained in the form of various forms produced by modification during the pretreatment or reaction. Alternatively, the zeolite containing the Ga component, a carrier comprising the zeolite not containing the Ga component or a mixture thereof, the Ga component is contained in a form supported by, for example, an ion exchange method, an impregnation method, a gas phase method or the like. Or may be contained in the form of being physically mixed with the zeolite. Furthermore,
Various metals may be supported on these. Preferably,
It is preferable to use a gallometallosilicate zeolite, a gallosilicate zeolite, or a modified zeolite thereof.

The type of the above-mentioned zeolite is not particularly limited, but a zeolite having a silica (SiO ₂ ) / alumina (Al ₂ O ₃ ) molar ratio of 10 or more when used in the reaction, such as ZSM-5 and ZSM-. 8, MSM such as ZSM-11, silicalite, MEL type zeolite, or MTT, FER,
It is preferable to use OFL type zeolite or the like. This Si
If the O ₂ / Al ₂ O ₃ ratio is less than 10, the heat resistance of the zeolite is relatively low, which may shorten the catalyst life.

The catalyst may have any shape, for example, pellet, plate, column, or lattice. The catalyst according to the present invention can be prepared, for example, by using a compound containing Ga in zeolite by an ion exchange method, an impregnation method, a physical mixing method, or a gas phase method. Further, when the zeolite is synthesized, the Ga compound may be contained in the gel at the same time. Further, a catalyst preparation method in which a catalyst is coated on a lattice-shaped carrier such as cordierite, mullite or alumina and a substrate such as a wire mesh may be adopted.

The exhaust gas purifying method according to the present invention is
In an oxidizing atmosphere, set the reaction temperature to 300-800 ℃, and
Exhaust gas is contacted with a catalyst containing gallium and zeolite in the presence of a hydrocarbon having a C concentration / NO _X concentration of 1 to 20 to reduce and remove nitrogen oxides in the exhaust gas to N ₂ and H ₂ O. It is characterized by The hydrocarbon may be a hydrocarbon that remains in the exhaust gas, but if it is insufficient than the amount necessary to cause the denitration reaction, or if the exhaust gas does not contain any hydrocarbons, the external It is advisable to add hydrocarbons from

The kind of hydrocarbon added for this purpose is not particularly limited, and examples thereof include methane, LPG, gasoline, light oil, and kerosene. Then, the amount of hydrocarbons present in the exhaust gas is 1 to when expressed by THC concentration / NO _x concentration.
20 is preferable. For example, if the NO _X concentration is 1000 ppm,
The THC concentration is preferably 0.1 to 2.0%. THC (t
Otal hydrocarbon) concentration is the concentration when hydrocarbon is converted to methane. When the abundance of hydrocarbons is lower than the lower limit, the denitration performance does not appear, and when it is higher than the upper limit, the denitration rate increases, but the economic efficiency of the entire system decreases and the combustion heat of hydrocarbons increases. It is not preferable because of abnormal heat generation of the catalyst layer.

The catalytic reaction temperature is 300 to 800 ° C,
The temperature is preferably 300 to 600 ° C. Usually, the higher the temperature, the higher the denitrification rate, but if the temperature exceeds 800 ° C, the catalyst will deteriorate, which is not preferable. For gas space velocity (GHSV), typically 2,000-20
It is set to 0,000 h ^-1 , preferably 5,000 to 100,000 h ^-1 . GHSV
However, if it is slower than 2,000h ^-1 , the denitration rate is high, but the amount of catalyst used is large, and if it is faster than 200,000h ^-1 ,
The denitrification rate becomes low.

The exhaust gas targeted by the purification method of the present invention is
Exhaust gas that contains NO _X and oxygen, such as exhaust gas emitted from lean combustion gasoline automobiles, mobile internal combustion engines such as diesel automobiles, stationary internal combustion engines such as cogeneration, boilers, various industrial furnaces, etc. To be

[0019]

Example 1 First, 7.6 g of aluminum sulfate, 6.9 g of gallium nitrate,
Tetrapropylammonium bromide 26.4 g, sulfuric acid (97%) 15.0 g, water 250 ml (solution I), water glass (SiO ₂ 28.4%, Na ₂ O 9.5%) 214 g, water
A solution of 212 ml (referred to as solution II) and a solution of 80 g of sodium chloride and 122 ml of water (referred to as solution III) were prepared.

Next, the solutions I and II were mixed into the solution III while being gradually added dropwise. This mixed solution was adjusted to pH 9.
After adjusting to 5, the mixture was placed in an autoclave having a volume of 1 liter and left for 20 hours while stirring at 170 ° C. and 300 rpm under self-pressure. After cooling, this mixed solution was filtered, and the precipitate was thoroughly washed with excess pure water. Then, by drying at 120 ° C. for 20 hours, a galloaluminosilicate zeolite having a ZSM-5 structure was synthesized.

Next, this zeolite was heated at 540 ° C. in an air stream.
It was baked for 3 hours. After this, 1N-NH ₄ NO ₃ solution was used for ion exchange at 80 ° C. for 2 hours, filtration, washing with water, drying at 120 ° C., and calcination at 540 ° C. for 3 hours in an air stream.
Ion exchange using a 1N-NH ₄ NO ₃ solution for 2 hours, filtration, washing with water, and drying at 120 ° C. were repeated for 2 hours, and then calcination was performed at 720 ° C. for 3 hours in an air stream. The elemental composition of the galloaluminosilicate zeolite obtained by this is Si
O ₂ : Al ₂ O ₃ : Ga ₂ O ₃ = 80: 1: 0.7 (molar ratio). Next, after 60 cc of this catalyst precursor was filled in a stainless steel reaction tube, the temperature was gradually raised while introducing dry air at GHSV = 5000 h ⁻¹ , and the catalyst according to this example was treated at 500 ° C. for 30 minutes. Was prepared.

Next, a gas prepared by adding LPG gas to diesel exhaust gas was introduced as a processing gas into the reaction tube kept at 400 ° C. at a temperature of GHSV = 5000 h ⁻¹ through a tube kept at 200 ° C. The composition of this diesel exhaust is NO _x : 1000.
ppm, O ₂ : 8%, SO _X : 140ppm, CO: 400ppm, CO ₂ : 10
%, THC: 230 ppm. In the process gas, the LPG gas contains 0.07% of all hydrocarbons (THC concentration of 0.21).
%). As a result, THC concentration / NO
_{The X} concentration is 2.1. Then, the gas from the outlet of the reaction tube was introduced into the chemiluminescence type analyzer through the tube also kept at 200 ° C., and the NO _X concentration was measured. The NO _X removal rate of the exhaust gas after the catalytic reaction was calculated by measuring and comparing the NO _X concentrations before and after the introduction into the reaction tube. The results are shown in Table 1 below.

Examples 2 to 4 Except that the composition of the treatment gas introduced into the reaction tube filled with the catalyst was changed as follows, the same exhaust gas purification treatment as in Example 1 was carried out, and each treatment was carried out. The NO _X removal rate in the examples was evaluated. The results are shown in Table 1 below. That is, the treated gas introduced in Example 2 is the diesel exhaust gas of Example 1 in which LPG gas is 0.14% in the treated gas.
(THC concentration is 0.42%).

The processing gas introduced in Example 3 is the same as that in Example 1.
The LPG gas was added to the diesel exhaust gas so that the total hydrocarbon content in the treated gas was 0.28% (THC concentration: 0.84%). In Example 3, the denitration rate with respect to the reaction time was also measured to evaluate the catalyst life. The result is shown in FIG. The process gas introduced in Example 4 is the diesel exhaust gas of Example 1 to which LPG gas is added so that the total hydrocarbon content in the process gas is 0.56% (THC concentration 1.68%).

Example 5 The composition of solution I in Example 1 was changed to aluminum sulfate 7.
6 g, tetrapropyl ammonium bromide 26.4 g,
An aluminosilicate zeolite having a ZSM-5 structure was synthesized in the same manner as in Example 1 except that 17.6 g of sulfuric acid (97%) and 250 ml of water were used. Next, this zeolite was calcined in an air stream at 540 ° C. for 3 hours. After this, 1N
-NH ₄ NO ₃ solution 80 ° C. using ion exchange for 2 hours, filtered, washed with water, dried at 120 ° C., after calcination for 3 hours in an air stream at _{540 ℃, 1N-NH 4 NO} 3 80 using solution
Ion exchange at 2 ° C for 2 hours, filtration, washing with water, and drying at 120 ° C were repeated, and then firing was carried out at 720 ° C for 3 hours in an air stream.

Then, the gallium nitrate solution was impregnated with the aluminosilicate zeolite by a usual impregnation method to support gallium on the zeolite. The elemental composition of the Ga-supported zeolite thus obtained was SiO ₂ : Al ₂ O ₃ : Ga ₂ O.
₃ = 80: 1: 0.7 (molar ratio). Next, after 60 cc of this catalyst precursor was filled in a stainless steel reaction tube, the temperature was gradually raised while introducing dry air at GHSV = 5000 h ⁻¹ , and at 500 ° C.
The catalyst according to this example was prepared by treating for 30 minutes. next,
As the processing gas, the same diesel exhaust gas as in the above embodiment was used as L
The NO _x removal rate was evaluated in the same manner as in the above-mentioned examples using a gas in which PG gas was added so that the total hydrocarbon content was 0.07% (THC concentration 0.21%) in the treated gas. The results are shown in Table 1.

Examples 6 to 8 Except that the composition of the treatment gas introduced into the reaction tube filled with the catalyst was changed as follows, the purification treatment of exhaust gas was carried out in the same manner as in Example 5, and each treatment was carried out. The NO _X removal rate in the examples was evaluated. The results are shown in Table 1. That is, in the process gas introduced in Example 6, the LPG gas in the diesel exhaust gas of Example 5 was 0.14% (TH) in the process gas.
C concentration was 0.42%).

The processing gas introduced in Example 7 is the same as that in Example 5.
The LPG gas was added to the diesel exhaust gas so that the total hydrocarbon content in the treated gas was 0.28% (THC concentration: 0.84%). The treated gas introduced in Example 8 was the diesel exhaust gas of Example 5 in which LPG gas was 0.
It was added so as to be 56% (THC concentration 1.68%).

Examples 9 to 16 Examples of Examples 1 to 8 in which only the temperature in the reaction tube was changed from 400 ° C. to 500 ° C. are referred to as Examples 9 to 16, respectively. To catalyst NO _x
The removal rate was evaluated. The results are shown in Table 1.

Comparative Example 1 After preparing a catalyst in the same manner as in Example 1, LP was placed in the reaction tube.
The NO _x removal rate of the catalyst was evaluated in the same manner as in Example 1 except that diesel exhaust gas to which G gas was not added was introduced. The results are shown in Table 2 below. Comparative Example 2 After preparing a catalyst in the same manner as in Example 5, LP was added to the reaction tube.
The catalyst was evaluated in the same manner as in Example 5 except that diesel exhaust gas to which G gas was not added was introduced. The results are shown in Table 2.

Comparative Example 3 The composition of solution I in Example 1 was changed to aluminum sulfate 7.
6 g, tetrapropyl ammonium bromide 26.4 g,
An aluminosilicate zeolite having a ZSM-5 structure was synthesized in the same manner as in Example 1 except that 17.6 g of sulfuric acid (97%) and 250 ml of water were used. Next, this zeolite was calcined in an air stream at 540 ° C. for 3 hours. After this, 1N
-NH ₄ NO ₃ solution 80 ° C. using ion exchange for 2 hours, filtered, washed with water, dried at 120 ° C., after calcination for 3 hours in an air stream at _{540 ℃, 1N-NH 4 NO} 3 80 using solution
Ion exchange at 2 ° C for 2 hours, filtration, washing with water, and drying at 120 ° C were repeated, and then firing was carried out at 720 ° C for 3 hours in an air stream.
The elemental composition of the zeolite thus obtained is SiO ₂ : A
It was l ₂ O ₃ = 80: 1 (molar ratio).

Next, after 60 cc of this catalyst precursor was filled in a stainless steel reaction tube, the temperature was gradually raised while introducing dry air at GHSV = 5000 h ⁻¹ and treated at 500 ° C. for 30 minutes to carry out this example. A catalyst according to 1. was prepared. Next, the same diesel exhaust gas as that used in the above-described embodiment was treated with LPG gas as a treatment gas.
The NO _x removal rate was evaluated in the same manner as in the above-mentioned examples using the gas added so that the total hydrocarbon content would be 0.14% (THC concentration 0.42%). The results are shown in Table 2.

Comparative Example 4 A catalyst was prepared in the same manner as in Example 5, except that nickel was loaded on the aluminosilicate zeolite in place of gallium. The elemental composition of this Ni-supported zeolite is SiO ₂ : Al ₂ O ₃ : NiO = 80: 1: 0.7.
(Molar ratio). Then, in the same manner as in the above embodiment
The NO _X removal rate was evaluated. The results are shown in Table 2.

Example 17 The composition of solution I in Example 1 was changed to gallium nitrate 6.9
g, tetrapropylammonium bromide 26.4 g, sulfuric acid (97%) 15.0 g, and water 250 ml, and a gallosilicate zeolite having a ZSM-5 structure was synthesized in the same manner as in Example 1 above. Next, this zeolite was calcined in an air stream at 540 ° C. for 3 hours. After this, 1N-NH ₄ N
Ion exchange using O ₃ solution for 2 hours, filtration, washing with water, drying at 120 ° C, baking at 540 ° C for 3 hours in an air stream, and then using 1N-NH ₄ NO ₃ solution. The ion exchange, filtration, washing with water, and drying at 120 ° C. were repeated for 2 hours at 80 ° C., followed by firing at 720 ° C. for 3 hours in an air stream. The elemental composition of the obtained gallosilicate zeolite is SiO ₂ : Ga ₂ O ₃ =
It was 80: 0.7 (molar ratio).

Next, after 60 cc of this catalyst precursor was filled in a stainless steel reaction tube, the temperature was gradually raised while introducing dry air at GHSV = 5000 h ⁻¹ , and the treatment was carried out at 500 ° C. for 30 minutes. A catalyst according to 1. was prepared. Next, the same diesel exhaust gas as that used in the above-described embodiment was treated with LPG gas as a treatment gas.
The NO _x removal rate was evaluated in the same manner as in the above-mentioned examples using the gas added so that the total hydrocarbon content was 0.07% (THC concentration 0.21%). The results are shown in Table 1.

Examples 18 to 20 Except that the composition of the treatment gas introduced into the reaction tube filled with the catalyst was changed as follows, the same purification treatment of exhaust gas as in Example 17 was performed, and each treatment was carried out. The NO _X removal rate in the examples was evaluated. The results are shown in Table 1. That is, the embodiment
The treated gas introduced in 18 is the diesel exhaust gas of Example 17, in which LPG gas is 0.14% (TH) in the treated gas.
C concentration was 0.42%).

The processing gas introduced in Example 19 was the same as in Example 17
The LPG gas was added to the diesel exhaust gas so that the total hydrocarbon content in the treated gas was 0.28% (THC concentration: 0.84%). The processing gas introduced in Example 20 was
It was obtained by adding LPG gas to 17 diesel exhaust gases so that the total hydrocarbon content in the treated gas was 0.56% (THC concentration 1.68%).

Comparative Example 5 A catalyst was prepared in the same manner as in Example 17, and then LP was charged in the reaction tube.
The catalyst was evaluated in the same manner as in Example 17 except that diesel exhaust gas to which G gas was not added was introduced. The results are shown in Table 2 below.

Example 21 A commercially available Y-type zeolite [TSZ-320N] was added to an aqueous solution of gallium nitrate.
AA (trade name), manufactured by Toyo Soda Co., Ltd.] was impregnated with 50 g by an ordinary impregnation method to support gallium on the zeolite. Next, this Ga-supported / Y-type zeolite was dried at 120 ° C. for 20 hours and then calcined in an air stream at 540 ° C. for 3 hours. The elemental composition of this catalyst precursor is SiO ₂ : Al ₂ O ₃ : Ga ₂ O ₃ = 5.6:
It was 1: 0.08 (molar ratio).

Next, after 60 cc of this catalyst precursor was filled in a stainless steel reaction tube, the temperature was gradually raised while introducing dry air at GHSV = 5000 h ⁻¹ and treated at 500 ° C. for 30 minutes to carry out this example. A catalyst according to 1. was prepared. Next, the same diesel exhaust gas as that used in the above-described embodiment was treated with LPG gas as a treatment gas.
The NO _x removal rate was evaluated in the same manner as in the above-mentioned examples using the gas added so that the total hydrocarbon content was 0.07% (THC concentration 0.21%). The results are shown in Table 1.

Examples 22 to 24 Except that the composition of the treated gas introduced into the reaction tube filled with the catalyst was changed as follows, the same exhaust gas purification treatment as in Example 21 was carried out to carry out each example. The NO _X removal rate in the examples was evaluated. The results are shown in Table 1. That is, the embodiment
The treated gas introduced in 22 is the diesel exhaust gas of Example 21, in which LPG gas is 0.14% (TH) in the treated gas.
C concentration was 0.42%).

The processing gas introduced in Example 23 is the same as that in Example 21.
The LPG gas was added to the diesel exhaust gas so that the total hydrocarbon content in the treated gas was 0.28% (THC concentration: 0.84%). The processing gas introduced in Example 24 is
The LPG gas was added to 21 diesel exhaust gases so that the total hydrocarbon content in the treated gas was 0.56% (THC concentration 1.68%).

Comparative Example 6 A catalyst was prepared in the same manner as in Example 21, and then LP was charged in the reaction tube.
The catalyst was evaluated in the same manner as in Example 21 except that diesel exhaust gas to which G gas was not added was introduced. The results are shown in Table 2 below.

Comparative Examples 7 to 11 Instead of the Ga-supported / Y-type zeolite in Example 21,
After synthesizing Y-type zeolite not supporting Ga as a catalyst precursor, a catalyst was prepared using this catalyst precursor in the same manner as in Example 21, and the NO _X removal rate was evaluated.
The results are shown in Table 2 below. However, the composition of the processing gas introduced into the reaction tube filled with the catalyst was changed as follows. That is, the process gas introduced in Comparative Example 7 was the diesel exhaust gas of Example 21 containing LPG gas,
The total hydrocarbon content was 0.07% (THC concentration 0.21%).

The processing gas introduced in Comparative Example 8 was the same as in Example 21.
The LPG gas was added to the diesel exhaust gas so that the total hydrocarbon content was 0.14% (THC concentration 0.42%). The processing gas introduced in Comparative Example 9 was
21 diesel exhaust gas was added with LPG gas so that the total hydrocarbon content was 0.28% (THC concentration 0.84%) in the treated gas.

The processing gas introduced in Comparative Example 10 was the same as in Example 21.
The LPG gas was added to the diesel exhaust gas so that the total hydrocarbon content in the treated gas was 0.56% (THC concentration: 1.68%). The processing gas introduced in Comparative Example 11 was LPG.
It is the diesel exhaust gas of Example 21 to which no gas is added.

[0047]

[Table 1]

[0048]

[Table 2]

From Tables 1 and 2 above, according to Examples 1 to 4, a galloaluminosilicate zeolite having a SiO ₂ / Al ₂ O ₃ ratio of 80 was used as a catalyst, and the temperature was 400 ° C. during the catalytic reaction. By setting the gas hourly space velocity (GHSV) to be 5,000 h ^-1 , and the THC concentration / NO _X concentration to be 2.1 to 16.8, the oxygen concentration in the exhaust gas is as high as 8%, and even if SO _X is included, it is 35 to
A high denitration rate of 82% can be obtained. When the reaction temperature is raised to 500 ° C. as in Examples 9 to 12, the denitration rate is improved by several percent. Furthermore, as shown in FIG. 1, according to the results of measuring the life of the catalyst of Example 3, the catalyst according to this Example did not show a decrease in the denitration rate even after the reaction time exceeded 150 hours, It can be seen that the catalyst has a long life.

On the other hand, according to Comparative Example 1, the same galloaluminosilicate zeolite as in Examples 1 to 4 is used, but since the THC concentration / NO _X concentration during the catalytic reaction is 0.2%, Only a low denitrification rate of 3% was obtained. According to Examples 5 to 8, SiO ₂ / Al ₂ O _{3 is} used as a catalyst.
A ratio of 80 Ga / aluminosilicate zeolite is used, and the temperature is 400 ° C and GHSV is 5,000h during the catalytic reaction.
^-1 , and by setting the THC concentration / NO _X concentration to 2.1 to 16.8, it can be seen that a high denitration rate of 30 to 75% can be obtained. When the reaction temperature is raised to 500 ° C. as in Examples 13 to 16, the denitration rate is improved by several percent.

On the other hand, according to Comparative Example 2, the same Ga-supporting / aluminosilicate zeolite as in Examples 5-8 was used, but the THC concentration / NO _x during the catalytic reaction was used.
Since the concentration was 0.2, only a low denitration rate of 2% was obtained. Further, according to Comparative Example 3, since the aluminosilicate zeolite in which Ga is not supported is used,
Even when the THC concentration / NO _X concentration during the catalytic reaction was 4.2, the denitration rate was as low as 19%. According to Comparative Example 4,
Since an aluminosilicate zeolite supporting Ni instead of Ga was used, the denitration rate was as low as 23% even when the THC concentration / NO _X concentration during the catalytic reaction was 4.2.

According to Examples 17 to 20, SiO ₂ / A was used as a catalyst.
Using a gallosilicate zeolite with an l ₂ O ₃ ratio of about 5000, the temperature was 400 ° C and the GHSV was 5,000 h during the catalytic reaction.
^-1 , and by setting the THC concentration / NO _X concentration to 2.1 to 16.8, a high denitration rate of 31 to 79% can be obtained. On the contrary,
According to Comparative Example 5, the same gallosilicate zeolite as in Examples 17 to 20 is used, but TH during the catalytic reaction is used.
Since the C concentration / NO _X concentration was 0.2, only a low denitration rate of 3% was obtained.

According to Examples 21 to 24, SiO ₂ / A was used as the catalyst.
Using a Ga-supported / Y-type zeolite with an l ₂ O ₃ ratio of 5.6, the temperature was 400 ° C., GHSV was 5,000 h ⁻¹ , and T during the catalytic reaction.
By adjusting the HC concentration / NO _X concentration from 2.1 to 16.8, 25
A high denitration rate of ~ 57% is obtained. On the other hand, according to Comparative Example 6, the same Ga-supporting / Y-type zeolite as in Examples 21 to 24 is used, but the THC concentration / catalytic reaction /
Since the NO _X concentration was 0.2, only a low denitration rate of 2% was obtained.

Further, according to Comparative Examples 7 to 10, the Y-type zeolite in which Ga is not supported is used, but even if the THC concentration / NO _X concentration during the catalytic reaction is 2.1 to 16.8, Only a low denitrification rate of ~ 16% was obtained. Furthermore,
According to Comparative Example 11, since the Y-type zeolite in which Ga is not supported is used and the THC concentration / NO _X concentration during the catalytic reaction is 0.2, only a low denitration rate of 2% can be obtained. It was

Examples 25 to 28 In order to examine heat resistance and durability, the catalysts of Examples 1, 5, 17, and 21 were used as the catalysts of Examples 25 to 28, and each catalyst was used in gasoline vehicles. In a lean model with excess oxygen (air-fuel ratio (A / F) approx. 22) in a model gas atmosphere at 500 ° C and
Heat treatment was performed at 800 ° C. for 5 hours. The composition of this model gas is: CO: 0.5%, O ₂ : 8%, H ₂ : 0.2%, CO ₂ : 9%, C
_{3 H 6: 0.1% (THC} : 3000ppm), NO: is 1000 ppm.

With respect to the catalyst subjected to the heat treatment, a powdery catalyst was pressure-molded into pellets having a diameter of about 3 mm,
This catalyst was packed into an experimental catalytic converter, and lean exhaust model gas with excess oxygen in a gasoline vehicle was introduced.
The NO purification rate at 00 ° C, 500 ° C and 600 ° C was measured.
The composition of this exhaust model gas is CO: 0.1%, O ₂ : 4%, CO
_{2: 10%, C 3 H} 6: 0.05% (THC: 1500ppm), NO: 700p
pm. The space velocity GHSV at the time of measurement is about 30,000h.
It was ^-1 . The measurement results for each example are shown in Table 3 below.
Shown in.

Comparative Examples 12-14 In order to investigate heat resistance and durability, the catalysts of Comparative Examples 3, 4 and 7 were used as the catalysts of Comparative Examples 12-14, respectively, and the same as in Examples 25-28 above. The catalyst was heat-treated at 500 ° C. and 800 ° C. for 5 hours in a model gas atmosphere. Also for these catalysts, the exhaust model gas of a gasoline vehicle was introduced in the same manner as in the above-mentioned examples, and 400 ° C, 500 ° C and 6
The NO purification rate at 00 ° C was measured. The measurement results for each comparative example are shown in Table 3 below.

[0058]

[Table 3]

From Table 3, the catalysts of Examples 25 to 28 are 400 ° C., 500 ° C. and 60 ° C. as compared with the catalysts of Comparative Examples 12 to 14.
It can be seen that the NO purification rate at 0 ° C is high and that it has excellent heat resistance and durability.

[0060]

According to the exhaust gas purification method of the present invention, nitrogen oxides can be reduced and removed with high efficiency even if oxygen in the exhaust gas has a high concentration. Further, the catalyst used has a high catalytic activity even at a low temperature and has a long life.

[Brief description of drawings]

FIG. 1 is a graph showing the measured lifetime of the catalyst used in Example 3.

Claims (3)

[Claims] 1. A catalyst for purifying exhaust gas by reducing and removing nitrogen oxides in exhaust gas in an oxidizing atmosphere, which contains gallium and zeolite. 2. A method for purifying exhaust gas, which comprises contacting exhaust gas with a catalyst containing gallium and zeolite in the presence of hydrocarbons in an oxidizing atmosphere to reduce and remove nitrogen oxides in the exhaust gas. 3. A reaction temperature of 300 to 800 ° C. and a TH
The exhaust gas purification method according to claim 2, wherein nitrogen oxides in the exhaust gas are reduced and removed in the presence of hydrocarbons having a C concentration / NO _X concentration of 1 to 20.