JP3257686B2 - Exhaust gas purification catalyst and exhaust gas purification method using the same - Google Patents

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 combustion engines such as diesel vehicles, 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 and SUMMARY OF THE INVENTION Motor vehicles generally, the exhaust gas from an internal combustion engine and various industrial furnaces stationary are included large amounts NO, the nitrogen oxides represented by NO ₂ (NO _X) is ing. It is said that these NO _Xs not only cause photochemical smog, but also cause respiratory disorders for the human body.

[0003] For information on how to reduce these NO _X,
As gasoline vehicles, if a small amount of oxygen in the exhaust gas, carbon monoxide, NO _X is reduced and removed with a reducing agent such as hydrocarbons, the exhaust gas treatment of the so-called three-way catalyst systems have been established. On the other hand, when the gas contains a large amount of oxygen, such as a large stationary discharge source such as a boiler, a selective NO _X reduction method that reduces the amount of NO _X by adding ammonia from the outside is operating. , Has a certain effect. However, the former method can be applied only to exhaust gas from gasoline engines with extremely low oxygen concentration, and the latter method uses ammonia, so it should not be used for small stationary or mobile sources. Above, difficult.

Therefore, as a reducing agent other than ammonia,
Various methods using hydrogen, carbon monoxide or various hydrocarbons have been studied, but most of them are non-selective contacting methods that can remove nitrogen oxides only after oxygen in exhaust gas is completely consumed. It has the disadvantage of being a reduction method.
Conventionally, the following methods have been proposed as a novel selective catalytic reduction method (a method for selectively reducing and removing nitrogen oxides even in the presence of oxygen) which can solve such difficulties. However, satisfactory results have not been obtained.

That is, according to JP-A-2-149317,
Various fuels were burned using a catalyst composed of hydrogen-type mordenite or clinoptilolite, or a catalyst composed of hydrogen-type mordenite or clinoptyllite carrying metals such as Cu, Cr, Mn, Fe, and Ni. A method has been proposed in which flue gas containing oxygen generated at that time is brought into contact with these catalysts in the presence of an organic compound to remove nitrogen oxides in the flue gas. According to this method, a denitration rate of 30 to 60% is obtained under the conditions of a reaction temperature of 300 to 600 ° C. and a gas space velocity (GHSV) of 1200 h ⁻¹ , but it is close to practical use conditions, but under high GHSV conditions The denitration effect is unknown. Further, there is no description about the change over time of the catalyst activity, 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.

According to Japanese Patent Application Laid-Open No. 1-130735, a catalyst is used in which a zeolite ion-exchanged with a transition metal (Cu, Co, Ni, Fe, Mg, Mn, etc.) is supported on a refractory carrier. ,
A method capable of purifying nitrogen oxides even in an oxidizing atmosphere has been proposed. This method purifies exhaust gas from a gasoline engine with high efficiency 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 even when the oxygen concentration is 5 to 10% like exhaust gas from a diesel engine. Also in Example, with increasing oxygen concentration, No _X removal rate shows a tendency to decrease significantly.

According to JP-A-63-283727, SiO ₂ / A
l ₂ O ₃ ratio is 15 or more hydrophobic zeolite to Cu, V, Mn, Fe,
Using a catalyst carrying a metal such as Cr, carbon monoxide and 1
Methods have been proposed for reducing nitrogen oxides in the oxygen-containing exhaust gas of internal combustion engines in the presence of one or more hydrocarbons. In this method, when a zeolite catalyst supporting a metal other than copper is used, the denitration rate is as low as 4 to 26%. On the other hand, in the case of using a Cu-zeolite catalyst, a relatively high activity is obtained, there is a problem that the copper component is susceptible to poisoning by SO _X. The oxygen concentration in the exhaust gas of the example is 1.6%, and it is unclear whether nitrogen oxides can be selectively reduced and denitrated even when the oxygen concentration is high like exhaust gas of a diesel engine, for example. .

According to JP-A-63-100919, a catalyst comprising copper supported on a porous carrier such as alumina, silica, zeolite or the like is used, and nitrogen oxidation in an exhaust gas containing oxygen in the presence of hydrocarbons is carried out. Methods for removing objects have been proposed. In 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 unclear whether nitrogen oxides can be selectively reduced and denitrated even when the oxygen concentration is higher.

An object of the present invention is to provide an exhaust gas purifying catalyst which can purify nitrogen oxides into harmless gas with high efficiency even when oxygen in the exhaust gas has a high concentration, and a method for purifying exhaust gas 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 and gallium. It is characterized by being composed only of zeolite. The oxidizing atmosphere is used to completely oxidize carbon monoxide, hydrogen, hydrocarbons and the reducing substances of the hydrocarbons added as required in the present treatment and 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 necessary amount of oxygen.

As a Ga source of the gallium (Ga) component in the catalyst, a compound which can be converted to an oxide at the time of preparing the catalyst or using the reaction can be used. Such compounds include Ga nitrates, sulfates, oxides, halides,
There are carbonates, hydroxides, organic acid salts and the like.

The presence form of the Ga component in the catalyst is arbitrary, and can take the following forms. For example, the components of the zeolite (eg, ion-exchangeable cations, replacement atoms in the framework, or
During the pretreatment, during the reaction, etc.). Alternatively, the carrier containing the zeolite containing the Ga component, the zeolite not containing the Ga component, or a mixture thereof contains the Ga component in a form supported by, for example, an ion exchange method, an impregnation method, or a gas phase method. Or may be contained in a form physically mixed with those zeolites . Rather good better <br/> is Gallo metallosilicate zeolite, preferably set to gallosilicate zeolite or their modified zeolites.

The type of the zeolite is not particularly limited, but a zeolite having a silica (SiO ₂ ) / alumina (Al ₂ O ₃ ) molar ratio of 10 or more, for example, ZSM-5, ZSM- 8, MFI such as ZSM-11, silicalite, MEL zeolite, or MTT, FER,
It is preferable to use OFL zeolite or the like. This Si
When the O ₂ / Al ₂ O ₃ ratio is smaller than 10, the heat resistance of the zeolite is relatively low, so that the catalyst life may be shortened.

The shape of the catalyst is arbitrary, and may be, for example, a pellet, a plate, a column, or a lattice. The catalyst according to the present invention can be prepared, for example, using a compound containing Ga in zeolite by an ion exchange method, an impregnation method, a physical mixing method, or a gas phase method. Also, when synthesizing the zeolite, a Ga compound may be included in the gel at the same time. Further, a catalyst preparation method in which a catalyst is coated on a grid-like carrier such as cordierite, mullite or alumina and a base material such as a wire mesh may be employed.

Further, the method for purifying exhaust gas according to the present invention comprises:
In an oxidizing atmosphere, set the reaction temperature to 300 to 800 ° C, and
The exhaust gas is brought into contact with a catalyst consisting only of 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 following. The hydrocarbon may be a hydrocarbon remaining in the exhaust gas, but if the amount is insufficient to cause a denitration reaction, or if the exhaust gas does not contain any hydrocarbons, It is advisable to add hydrocarbons.

There is no particular limitation on the type of hydrocarbon to be added, and examples thereof include methane, LPG, gasoline, light oil, and kerosene. The abundance of hydrocarbons of this in the exhaust gas, when expressed in THC concentration / NO _X concentration, 1
20 is preferred. For example, if the NO _X concentration is 1000 ppm,
The THC concentration is preferably 0.1 to 2.0%. Where THC (t
otal hydrocarbon) The concentration is the concentration when hydrocarbons are converted to methane. When the amount of hydrocarbons is lower than the lower limit, the denitration performance is not exhibited, and when the amount is higher than the upper limit, the denitration rate increases, but the economic efficiency of the entire system decreases and the heat of combustion of hydrocarbons decreases. Is not preferable because of abnormal heat generation of the catalyst layer due to the

The catalyst reaction temperature is 300-800 ° C.
Preferably, the temperature is 300 to 600 ° C. Normally, the higher the temperature, the higher the denitration rate. However, if the temperature exceeds 800 ° C., the catalyst is deteriorated, which is not preferable. Gas space velocity (GHSV) is typically 2,000 to 20
0,000h ^-1 , preferably 5,000 to 100,000h ^-1 . GHSV
However, when it is slower than 2,000 h- ¹ , the denitration rate is high, but the amount of catalyst used increases, and when it is faster than 200,000 h- ¹ ,
The denitration rate decreases.

The exhaust gas targeted by the purification method of the present invention is:
Exhaust gas containing NO _X and oxygen, for example, exhaust gas emitted from gasoline vehicles in lean combustion, mobile internal combustion engines such as diesel vehicles, stationary internal combustion engines such as cogeneration, boilers, various industrial furnaces, etc. Can be

[0019]

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

Next, the solutions I and II were simultaneously mixed while gradually dropping into the solution III. The mixed solution was adjusted to pH 9.
After being adjusted to 5, the mixture was placed in an autoclave having a capacity of 1 liter and left for 20 hours while stirring at 170 ° C. and 300 rpm under its own pressure. After cooling, the mixed solution was filtered, and the precipitate was sufficiently washed with excess pure water. Thereafter, the galloaluminosilicate zeolite having the ZSM-5 structure was synthesized by drying at 120 ° C. for 20 hours.

Next, this zeolite was placed in an air stream at 540 ° C.
For 3 hours. After that, ion exchange, filtration, washing with water, drying at 120 ° C., and baking at 540 ° C. for 3 hours in a stream of air were performed at 80 ° C. for 2 hours using a 1N—NH ₄ NO ₃ solution.
Ion exchange, filtration, washing with water and drying at 120 ° C. were repeated for 2 hours at 80 ° C. using a 1N—NH ₄ NO ₃ solution, and then calcined at 720 ° C. for 3 hours in an air stream. The resulting galloaluminosilicate zeolite has an elemental composition of Si
O ₂ : Al ₂ O ₃ : Ga ₂ O ₃ = 80: 1: 0.7 (molar ratio). Next, after filling this catalyst precursor into a stainless steel reaction tube at 60 cc, the temperature was gradually increased while introducing dry air at GHSV = 5000 h ⁻¹ and treated at 500 ° C. for 30 minutes to obtain a catalyst according to the present example. Was prepared.

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

Examples 2 to 4 Except that the composition of the processing gas introduced into the reaction tube filled with the catalyst was changed as described below, the same exhaust gas purification treatment as in Example 1 was performed. It was evaluated NO _X removal rate in the example. The results are shown in Table 1 below. That is, the processing gas introduced in Example 2 is such that the diesel exhaust gas of Example 1 is LPG gas and the total hydrocarbon content is 0.14%.
(THC concentration 0.42%).

The processing gas introduced in the third embodiment is the same as that in the first embodiment.
LPG gas was added to the diesel exhaust gas of No. 2 so that the total hydrocarbons in the processing gas would be 0.28% (THC concentration 0.84%). In Example 3, the catalyst life was evaluated by measuring the denitration ratio with respect to the reaction time. The result is shown in FIG. The processing gas introduced in Example 4 is obtained by adding LPG gas to the diesel exhaust gas of Example 1 so that the total hydrocarbon content in the processing gas becomes 0.56% (THC concentration 1.68%).

Example 5 The composition of the solution I in Example 1 was changed to aluminum sulfate 7.
6 g, tetrapropylammonium 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 at 540 ° C. for 3 hours in an air stream. 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 with solution
C., ion exchange for 2 hours, filtration, washing with water, and drying at 120.degree. C. were repeated, and then calcined at 720.degree. C. for 3 hours in an air stream.

Next, the above-mentioned aluminosilicate zeolite was impregnated in a gallium nitrate solution by a usual impregnation method, so that gallium was supported 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 filling this catalyst precursor into a stainless steel reaction tube at 60 cc, the temperature was gradually increased while introducing dry air at GHSV = 5000 h ⁻¹ , and the temperature was increased to 500 ° C.
The catalyst according to this example was prepared by treating for 30 minutes. next,
As processing gas, the same diesel exhaust gas as in the above embodiment
During PG gas processing gas, total hydrocarbons using gas added as a 0.07% (THC concentration 0.21%) was evaluated in the above embodiment and similarly NO _X removal rate. Table 1 shows the results.

Examples 6 to 8 Except that the composition of the processing gas introduced into the reaction tube filled with the catalyst was changed as described below, the same exhaust gas purification treatment as in Example 5 was performed. It was evaluated NO _X removal rate in the example. Table 1 shows the results. That is, in the processing gas introduced in Example 6, LPG gas was added to the diesel exhaust gas of Example 5 and the total hydrocarbon content was 0.14% (TH
C concentration 0.42%).

The processing gas introduced in the seventh embodiment is the same as that in the fifth embodiment.
LPG gas was added to the diesel exhaust gas of No. 2 so that the total hydrocarbons in the processing gas would be 0.28% (THC concentration 0.84%). The processing gas introduced in Example 8 was obtained by adding LPG gas to the diesel exhaust gas of Example 5 in all the processing gases.
It is added so as to be 56% (THC concentration 1.68%).

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

Comparative Example 1 After preparing a catalyst in the same manner as in Example 1, LP was added to the reaction tube.
Introducing a diesel exhaust gas without addition of G gas was otherwise in the same manner as in Example 1 to evaluate the NO _X removal rate of the catalyst. 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. Table 2 shows the results.

Comparative Example 3 The composition of solution I in Example 1 was changed to aluminum sulfate 7.
6 g, tetrapropylammonium 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 at 540 ° C. for 3 hours in an air stream. 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 with solution
C., ion exchange for 2 hours, filtration, washing with water, and drying at 120.degree. C. were repeated, and then calcined at 720.degree. C. for 3 hours in an air stream.
The elemental composition of the resulting zeolite is SiO ₂ : A
l ₂ O ₃ = 80: 1 (molar ratio).

Next, 60 cc of the catalyst precursor was filled in a stainless steel reaction tube, and the temperature was gradually increased while introducing dry air at GHSV = 5000 h ⁻¹ , and the treatment was carried out at 500 ° C. for 30 minutes. Was prepared. Next, LPG gas was used as the processing gas in the same diesel exhaust gas as in the above embodiment,
Using the total hydrocarbon was added to a 0.14% (THC concentration 0.42%) gas was evaluated NO _X removal rate in the same manner as the above embodiment. Table 2 shows the results.

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

Example 17 The composition of Solution I in Example 1 was changed to gallium nitrate 6.9
g, a gallosilicate zeolite having a ZSM-5 structure was synthesized in the same manner as in Example 1 except that g, tetrapropylammonium bromide 26.4 g, sulfuric acid (97%) 15.0 g, and water 250 ml. Next, this zeolite was calcined at 540 ° C. for 3 hours in an air stream. Thereafter, 1N-NH ₄ N
Ion exchange using O ₃ solution at 80 ° C., 2 hours, filtration, washing with water, drying at 120 ° C., baking at 540 ° C. in an air stream for 3 hours, and then using a 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., and then calcined 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 =
80: 0.7 (molar ratio).

Next, 60 cc of the catalyst precursor was charged into a stainless steel reaction tube, and the temperature was gradually increased while introducing dry air at GHSV = 5000 h ⁻¹ , followed by treatment at 500 ° C. for 30 minutes. Was prepared. Next, LPG gas was used as the processing gas in the same diesel exhaust gas as in the above embodiment,
Using the total hydrocarbon was added to a 0.07% (THC concentration 0.21%) gas was evaluated of the NO _X removal rate as in the above embodiment. Table 1 shows the results.

Examples 18 to 20 Except that the composition of the processing gas introduced into the reaction tube filled with the catalyst was changed as described below, the same exhaust gas purification treatment as in Example 17 was performed. It was evaluated NO _X removal rate in the example. Table 1 shows the results. That is, the embodiment
The processing gas introduced in 18 was the diesel exhaust gas of Example 17 with LPG gas in the processing gas, and 0.14% of all hydrocarbons (TH
C concentration 0.42%).

The processing gas introduced in Example 19 was
LPG gas was added to the diesel exhaust gas of No. 2 so that the total hydrocarbons in the processing gas would be 0.28% (THC concentration 0.84%). The processing gas introduced in Example 20
The LPG gas is added to the diesel exhaust gas of No. 17 so that the total hydrocarbon becomes 0.56% (THC concentration 1.68%) in the processing gas.

Comparative Example 5 After a catalyst was prepared in the same manner as in Example 17, LP was added to the reaction tube.
The catalyst was evaluated in the same manner as in Example 17 except that a diesel exhaust gas to which no G gas was 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 gallium nitrate solution.
AA (trade name, manufactured by Toyo Soda Co., Ltd.)] was impregnated with a usual impregnation method to carry gallium on the zeolite. Next, the Ga-supported / Y-type zeolite was dried at 120 ° C. for 20 hours and calcined at 540 ° C. for 3 hours in an air stream. The elemental composition of this catalyst precursor is SiO ₂ : Al ₂ O ₃ : Ga ₂ O ₃ = 5.6:
1: 0.08 (molar ratio).

Next, 60 cc of the catalyst precursor was charged into a stainless steel reaction tube, and the temperature was gradually increased while introducing dry air at GHSV = 5000 h ⁻¹ , followed by treatment at 500 ° C. for 30 minutes. Was prepared. Next, LPG gas was used as the processing gas in the same diesel exhaust gas as in the above embodiment,
Using the total hydrocarbon was added to a 0.07% (THC concentration 0.21%) gas was evaluated of the NO _X removal rate as in the above embodiment. Table 1 shows the results.

Examples 22 to 24 Except that the composition of the processing gas introduced into the reaction tube filled with the catalyst was changed as described below, the same exhaust gas purification treatment as in Example 21 was performed. It was evaluated NO _X removal rate in the example. Table 1 shows the results. That is, the embodiment
In the processing gas introduced in step 22, LPG gas was added to the diesel exhaust gas of Example 21, and the total hydrocarbon content was 0.14% (TH
C concentration 0.42%).

The processing gas introduced in Example 23 was the same as Example 21
LPG gas was added to the diesel exhaust gas of No. 2 so that the total hydrocarbons in the processing gas would be 0.28% (THC concentration 0.84%). The processing gas introduced in Example 24
LPG gas was added to the diesel exhaust gas of No. 21 so that the total hydrocarbons in the processing gas became 0.56% (THC concentration 1.68%).

Comparative Example 6 After a catalyst was prepared in the same manner as in Example 21, LP was added to 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 the Y-type zeolite which does not carry the Ga synthesized as a catalyst precursor, in the same manner as in Example 21, using this catalyst precursor to prepare a catalyst, also was evaluated of the NO _X removal rate.
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 processing gas introduced in Comparative Example 7 was obtained by adding LPG gas to the processing gas in the diesel exhaust gas of Example 21.
It is added so that the total hydrocarbon becomes 0.07% (THC concentration 0.21%).

The processing gas introduced in Comparative Example 8 was the same as in Example 21
LPG gas is added to the diesel exhaust gas of No. 1 so that the total hydrocarbons in the processing gas become 0.14% (THC concentration 0.42%). The processing gas introduced in Comparative Example 9 was
LPG gas was added to the diesel exhaust gas of No. 21 so that the total hydrocarbon content in the processing gas was 0.28% (THC concentration 0.84%).

The processing gas introduced in Comparative Example 10 was the same as Example 21
LPG gas was added to the diesel exhaust gas of No. 1 so that the total hydrocarbons in the processing gas became 0.56% (THC concentration 1.68%). The processing gas introduced in Comparative Example 11 was LPG
Fig. 21 shows the diesel exhaust gas of Example 21 to which no gas was added.

[0047]

[Table 1]

[0048]

[Table 2]

From the above Tables 1 and 2, 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 set to 400 ° C. during the catalytic reaction. a gas hourly space velocity (GHSV) of 5,000H ^-1, by which a 2.1 to 16.8 the THC concentration / NO _X concentration, the oxygen concentration in the exhaust gas is as high as 8%, and also include SO _X. 35 to
A high denitration rate of 82% is obtained. Further, when the reaction temperature is raised to 500 ° C. as in Examples 9 to 12, the denitration rates are improved by several%, respectively. Further, as shown in FIG. 1, according to the result of measuring the life of the catalyst of Example 3, the catalyst according to the present example did not show a decrease in the denitration rate even when the reaction time exceeded 150 hours. It can be seen that the catalyst has a long life.

[0050] In contrast, according to Comparative Example 1, but using the same galloaluminosilicate zeolite Examples 1-4, since THC concentration / NO _X concentration during the catalytic reaction is 0.2%, Only a low denitration rate of 3% was obtained. According to Examples 5 to 8, SiO ₂ / Al ₂ O ₃ was used as a catalyst.
Using a Ga-supported / aluminosilicate zeolite with a ratio of 80, during the catalytic reaction, the temperature was 400 ° C and the GHSV was 5,000 hours.
^-1, by having a 2.1 to 16.8 the THC concentration / NO _X concentration, it can be seen that a high denitration rate 30 to 75% can be obtained. When the reaction temperature is raised to 500 ° C. as in Examples 13 to 16, the denitration rates are improved by several percent.

On the other hand, according to Comparative Example 2, the same Ga-supported / aluminosilicate zeolite as in Examples 5 to 8 was used, but the THC concentration at the time of the catalytic reaction / NO _X
Due to the concentration of 0.2, only a low denitration rate of 2% was obtained. Further, according to Comparative Example 3, since aluminosilicate zeolite not supporting Ga was 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 Ga Ni instead of using the aluminosilicate zeolite supported, THC concentration / NO _X concentration during the catalytic reaction even 4.2, it was 23% and the low denitration ratio.

According to Examples 17 to 20, SiO ₂ / A
l ₂ O ₃ ratio uses about 5000 gallosilicate zeolite, during the catalytic reaction, the temperature 400 ° C., the GHSV 5,000H
^-1, by having a 2.1 to 16.8 the THC concentration / NO _X concentration, high denitration rate of 31 to 79% is obtained. On the contrary,
According to Comparative Example 5, the same gallosilicate zeolite as in Examples 17 to 20 was used, but TH during the catalytic reaction was 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, the catalyst was SiO ₂ / A
Using a Ga-supported / Y-type zeolite with an l ₂ O ₃ ratio of 5.6, the temperature was 400 ° C., the GHSV was 5,000 h ⁻¹ ,
By that 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, although the same Ga-supported / Y-type zeolite as in Examples 21 to 24 was used, the THC concentration /
Since NO _X concentration is 0.2, it had only low denitration ratio of 2%.

Further, according to Comparative Examples 7 to 10, the use of the Y-type zeolite which is not supported in the Ga, even THC concentration / NO _X concentration is from 2.1 to 16.8 during catalysis, 6 Only low denitration rates of 1616% were obtained. Furthermore,
According to Comparative Example 11, since the Y-type zeolite not carrying Ga was used and the THC concentration / NO _X concentration at the time of the catalytic reaction was 0.2, only a low denitration rate of 2% was obtained. Was.

Examples 25 to 28 In order to examine the 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 for a gasoline vehicle. In a model gas atmosphere in an oxygen-excess lean state (air-fuel ratio (A / F) about 22), 500 ° C and
Heat treatment was performed at 800 ° C. for 5 hours. The composition of the model _{gas, 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 heat-treated catalyst, a powdery catalyst was pressed into a pellet having a diameter of about 3 mm,
This catalyst was charged into an experimental catalytic converter, and a lean exhaust model gas with excess oxygen of a gasoline vehicle was introduced.
The NO purification rates at 00 ° C, 500 ° C and 600 ° C were measured.
The composition of this exhaust model gas is: 0.1% CO, 4% O ₂ ,
_{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 . Table 3 below shows the measurement results for each example.
Shown in

COMPARATIVE EXAMPLES 12-14 In order to examine heat resistance and durability, the catalysts of Comparative Examples 3, 4 and 7 were used as the catalysts of Comparative Examples 12 and 14, respectively. The catalyst was heated at 500 ° C. and 800 ° C. for 5 hours in a model gas atmosphere. For these catalysts as well, gasoline vehicle exhaust model gas was introduced in the same manner as in
The NO purification rate at 00 ° C. was measured. Table 3 below shows the measurement results of the comparative examples.

[0058]

[Table 3]

As shown in Table 3, the catalysts of Examples 25 to 28 were compared with those of Comparative Examples 12 to 14 at 400 ° C., 500 ° C. and 60 ° C.
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 purifying method of the present invention, even if the concentration of oxygen in the exhaust gas is high, nitrogen oxides can be reduced and removed with high efficiency. The catalyst used has a high catalytic activity even at a low temperature and has a long life.

[Brief description of the drawings]

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

──────────────────────────────────────────────────続 き Continuation of the front page (51) Int.Cl. ⁷ Identification symbol FI B01D 53/36 104A (56) References JP-A-3-101836 (JP, A) JP-A-4-4045 (JP, A) JP-A-4-16239 (JP, A) JP-A-4-83516 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) B01J 21/00-38/74 B01D 53/86 B01D 53/94

Claims (3)

(57) [Claims] 1. A catalyst for reducing and removing nitrogen oxides in exhaust gas in an oxidizing atmosphere, comprising only gallium and zeolite.
It is made of an exhaust gas purifying catalyst according to claim. 2. A method for purifying exhaust gas, comprising contacting the exhaust gas with a catalyst comprising only gallium and zeolite in an oxidizing atmosphere in the presence of a hydrocarbon to reduce and remove nitrogen oxides in the exhaust gas. 3. A reaction temperature of 300 to 800 ° C. and TH
Method for purifying an exhaust gas according to claim 2, wherein the reducing removal of nitrogen oxides in the exhaust gas in the presence of hydrocarbons with 1-20 C-concentration / NO _X concentration.