JP3242946B2 - Exhaust gas purification catalyst and exhaust gas purification method using the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[Industrial applications]

The present invention relates to a catalyst for purifying exhaust gas which decomposes nitrogen oxides discharged from mobile internal combustion engines such as diesel automobiles, stationary internal combustion engines such as cogeneration, various industrial furnaces such as boilers, etc. into harmless gases. And a method for purifying exhaust gas 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. Regarding the method of reducing these NO _X , when the amount of oxygen in the exhaust gas is small, such as in a gasoline-powered vehicle, NOx is reduced with a reducing agent such as carbon monoxide or hydrocarbon.
_A so-called three-way catalytic exhaust gas treatment for reducing and removing _X has been established.

On the other hand, when a large amount of oxygen is contained in the gas, such as a large stationary discharge source such as a boiler, a selective NO _X reduction method for reducing the amount of NO _X by adding ammonia from the outside operates. And 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 under conditions of high GHSV, which are close to practical conditions. The denitration effect of is not clear. 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%. For example, it is unclear whether nitrogen oxides can be selectively reduced and denitrated even when the oxygen concentration is high, for example, in the exhaust gas of a diesel engine. .

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.

On the other hand, the applicant of the present application has proposed, in Japanese Patent Application No. 2-296242, a catalyst for purifying exhaust gas containing gallium and zeolite, and a method for purifying exhaust gas using the same. However, the catalyst according to the present invention
At a low temperature (for example, about 300 ° C.), a sufficient denitration rate cannot be obtained. Therefore, the present invention provides an exhaust gas purifying catalyst which can purify nitrogen oxides into harmless gas with high efficiency even at low temperature and high concentration of oxygen in exhaust gas, and a method of purifying exhaust gas using the same. The purpose is to do.

[0010]

The exhaust gas purifying catalyst according to the present invention is characterized in that nitrogen oxides in exhaust gas are oxidized in an oxidizing atmosphere, at a reaction temperature of 200 to 800 ° C., and at a total THC concentration / N.
Reduction and removal in the presence of a hydrocarbon having an Ox concentration of 0.5 to 50
(1) gallium as a main catalyst and (2) among transition elements as a co-catalyst, iron, nickel, cobalt, zirconium, manganese, chromium, molybdenum,
It is characterized by containing at least one or more components selected from copper and rare earth elements and zeolite (3) serving as a carrier. The oxidizing atmosphere is defined as H ₂ O and C by completely oxidizing carbon monoxide, hydrogen, and hydrocarbons contained in exhaust gas and reducing substances of hydrocarbons added as required in the present treatment.
This is a state in which oxygen is contained in excess of the amount of oxygen necessary for conversion to O ₂ .

As the Ga source of the (1) gallium (Ga) component, a compound which can be converted to an oxide at the time of preparing a catalyst or using a reaction can be used. Examples of such a compound include nitrate, sulfate, oxide, halide, carbonate, hydroxide, and organic acid salt of Ga. The content of gallium in the catalyst is usually 0.01 to 10% by weight, preferably 0.1 to 5% by weight, based on the whole catalyst. The content is 0.01
If it is less than wt%, the high purification rate of the present invention cannot be obtained, and if it exceeds 10 wt%, no further improvement in the purification rate is observed.

As the above (2) iron, nickel, cobalt, zirconium, manganese, chromium, molybdenum, copper and rare earth elements, compounds which can be converted to oxides at the time of preparing the catalyst or using the reaction can be used. Examples of such compounds include nitrates, sulfates, oxides, halides, carbonates, hydroxides, and organic acid salts. The content of these promoters in the catalyst is usually 0.01 to 20% by weight, preferably 0.03 to 10% by weight, based on the whole catalyst.
If the content is less than 0.01 wt%, the high purification rate of the present invention cannot be obtained, and even if it exceeds 20 wt%, no further improvement in the purification rate is observed.

The type of the zeolite is not particularly limited, but when the reaction is used, Si / Al (atomic ratio) is 5%.
For those in which part or all of the elements (M) such as B, P, and Ti are substituted for the above zeolite and Al atoms, Si is used.
/ [Al + M] (atomic ratio) is 5 or more zeolites, for example, MFI such as ZSM-5, ZSM-8, ZSM-11, silicalite, MEL zeolite, or MTT, FER,
It is preferable to use OFL zeolite or the like. This Si
If / Al or Si / [Al + M] (atomic ratio) is less than 5, the heat resistance of the zeolite is relatively low, and the catalyst life may be shortened.

The form in which Ga and the cocatalyst component are present in the catalyst is arbitrary, and can take the following forms. For example, the constituents of zeolite (eg, ion-exchangeable cations, substituted atoms in the framework, or various forms resulting from modification of the catalysts during preparation, pretreatment, reaction, etc.) )). Alternatively, the zeolite containing this Ga and the co-catalyst component, the carrier consisting of the zeolite not containing these or a mixture thereof, the Ga and the co-catalyst component are, for example, ion exchange method, impregnation method, gas phase method It may be contained in a supported form, or may be contained in a form physically mixed with those zeolites. Furthermore, various metals may be supported on these. Preferably, gallometallosilicate zeolite, gallosilicate zeolite or a modified zeolite thereof is used.

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, by using a compound containing Ga and the above-mentioned promoter component in zeolite, by an ion exchange method, an impregnation method, a physical mixing method, or a gas phase method. Further, when synthesizing the zeolite, Ga and the compound of the promoter component may be simultaneously contained in the gel. 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:
Exhaust gas in an oxidizing atmosphere, reaction temperature 1200-800 ° C,
And in the presence of a hydrocarbon of the total THC Temperature / NOx temperature 0.5 to 50, in contact with the front Symbol catalyst, characterized in that the nitrogen oxides in the exhaust gas to reduce and remove the N ₂ and H ₂ O . 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 In this case, it is preferable to add a hydrocarbon from outside. The type of hydrocarbon added for this purpose is not particularly limited, and examples thereof include methane, LPG, gasoline, light oil, kerosene, and heavy oil A.

[0017] Then, the abundance of hydrocarbons of the flue gas, when expressed in THC concentration / NO _X concentration from 0.5 to 50, preferably 1 to 20. Where THC (thermal hydroca
rbon) Concentration is the concentration when hydrocarbons are converted to methane. For example, if the NO _X concentration is 1,000 ppm, THC
The concentration is between 0.05 and 5.0%. 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 200-800 ° C.
Preferably, the temperature is 300 to 600 ° C. Usually, the higher the temperature, the higher the denitration rate. However, if the temperature exceeds 800 ° C., the catalyst deteriorates, which is not preferable. If the temperature is lower than 200 ° C., the denitration rate decreases. 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 mobile combustion engines such as gasoline vehicles and diesel vehicles in lean combustion, stationary internal combustion engines such as cogeneration, boilers, various industrial furnaces, etc. Can be

[0020]

EXAMPLE 1 First, 7.6 g of aluminum sulfate, 6.9 g of gallium nitrate,
26.4 g of tetrapropylammonium bromide, 15.0 g of sulfuric acid (97%), 250 ml of water (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. After adjusting the pH of the mixed solution to 9.5 with sulfuric acid, the mixed solution was placed in an autoclave having a capacity of 1 l, and allowed to stand at 170 ° C. and 300 rpm under self pressure for 20 hours while stirring.
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. in an air stream for 3 hours 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. Thereafter, the catalyst precursor was impregnated into an iron (III) nitrate solution by a usual impregnation method to carry iron. The elemental composition of the catalyst precursor obtained in this way is SiO ₂ : Al ₂ O ₃ : Ga ₂ O ₃ : Fe ₂ O ₃ = 9 by weight ratio.
5.2: 2.0: 2.6: 0.2 and SiO ₂ : Al ₂ O ₃ : Ga ₂ O ₃ : Fe _{2 in} molar ratio
O ₃ = 80: 1: 0.7: 0.08. Next, after 60 cc of the catalyst precursor was filled in a stainless steel reaction tube, dry air was
The temperature was gradually raised while introducing at SV = 5000 h ⁻¹ and treated at 500 ° C. for 30 minutes to prepare a catalyst according to the present example.

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 500 ° C. at GHSV = 5000 h ⁻¹ , and the catalyst was subjected to the following process. An evaluation test was performed. The composition of this diesel exhaust gas is as follows: NO _X : 1000 ppm, O ₂ : 8%, SO _X : 140
ppm, CO: 400 ppm, CO ₂ : 10%, THC: 230 ppm.
Further, LPG gas was added at a THC concentration of 0.19% so that all hydrocarbons in the processing gas became 0.21% as a whole THC concentration. Therefore, the total THC concentration / NO _X concentration is 2.1. Then, introduced into a chemiluminescence analyzer through a tube that is holding the gas from the outlet to 200 ° C. in the reaction tube was measured NO _X concentration. 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 and 3 Examples 2 and 3 are the same as Example 1 except that the composition of the processing gas introduced into the reaction tube filled with the catalyst during the evaluation test of the catalyst was changed as follows. It is. Table 1 shows the evaluation results of the NO _X removal rate in each example. That is, the processing gas introduced in Example 2 is obtained by adding LPG gas to the diesel exhaust gas of Example 1 so that all hydrocarbons in the processing gas become 0.42% in total THC concentration. The processing gas introduced in the third embodiment is obtained by adding L
When the PG gas is processed gas, all hydrocarbons have a THC concentration of 0.
It is added so as to be 84%.

Example 4 This example is similar to Example 1 except for the preparation of the catalyst.
Nickel (II) nitrate was used instead of iron (III) nitrate. The elemental composition of the catalyst precursor in this example is SiO ₂ : Al ₂ O ₃ : Ga ₂ O ₃ : NiO = 95.2: 2.0: 2.6: 0 by weight ratio.
2, and SiO ₂ : Al ₂ O ₃ : Ga ₂ O ₃ : NiO = 80: 1: 0.7: 0 in molar ratio.
It was 16. Thereafter, the results of evaluation of the NO _X removal rate in the same manner as in Example 1 in Table 1.

Examples 5 and 6 Examples 5 and 6 are the same as Example 4 except that the composition of the processing gas introduced into the reaction tube filled with the catalyst during the evaluation test of the catalyst was changed as follows. It is. Table 1 shows the evaluation results of the NO _X removal rate in each example. That is, the processing gas introduced in Example 5 is obtained by adding LPG gas to the diesel exhaust gas of Example 4 so that all hydrocarbons in the processing gas become 0.42% in total THC concentration. The processing gas introduced in Example 6 is the same as the diesel exhaust gas of Example 4
When the PG gas is processed gas, all hydrocarbons have a THC concentration of 0.
It is added so as to be 84%.

Example 7 This example illustrates the procedure of Example 1 when preparing the catalyst.
Cobalt (III) nitrate was used instead of iron (III) nitrate. The elemental composition of the catalyst precursor in this example is SiO ₂ : Al ₂ O ₃ : Ga ₂ O ₃ : Co ₂ O ₃ = 95.1: 2.0: 2 by weight ratio.
6: 0.3, and a molar ratio of SiO ₂ : Al ₂ O ₃ : Ga ₂ O ₃ : Co ₂ O ₃ = 80: 1:
0.7: 0.08. Thereafter, NO was performed in the same manner as in Example 1.
Table 1 shows the results of evaluating the _X removal rate.

Embodiments 8 and 9 Embodiments 8 and 9 differ from Embodiment 7 in that the composition of the processing gas introduced into the reaction tube filled with the catalyst during the evaluation test of the catalyst was changed as follows. It is. Table 1 shows the evaluation results of the NO _X removal rate in each example. That is, the processing gas introduced in Example 8 is obtained by adding LPG gas to the diesel exhaust gas of Example 7 so that all hydrocarbons in the processing gas become 0.42% in total THC concentration. The processing gas introduced in Example 9 is the same as the diesel exhaust gas of Example 7
When the PG gas is processed gas, all hydrocarbons have a THC concentration of 0.
It is added so as to be 84%.

Example 10 This example illustrates the procedure of Example 1 when preparing the catalyst.
Lanthanum (III) nitrate was used instead of iron (III) nitrate. The elemental composition of the catalyst precursor in this example is SiO ₂ : Al ₂ O ₃ : Ga ₂ O ₃ : La ₂ O ₃ = 95.1: 2.0: 2 by weight ratio.
6: 0.3, and the molar ratio of SiO ₂ : Al ₂ O ₃ : Ga ₂ O ₃ : La ₂ O ₃ = 80: 1:
0.7: 0.04. Thereafter, NO was performed in the same manner as in Example 2.
Table 1 shows the results of evaluating the _X removal rate.

Example 11 This example is a modification of Example 1 when preparing the catalyst.
Copper (II) nitrate was used in place of iron (III) nitrate. The elemental composition of the catalyst precursor in this example is SiO ₂ : Al ₂ O ₃ : Ga ₂ O ₃ : CuO = 95.1: 2.0: 2.6: 0.3 in weight ratio, and SiO ₂ : Al ₂ O ₃ : Ga ₂ O ₃ : CuO = 80: 1: 0.7: 0.17. Thereafter, the results of evaluation of the NO _X removal rate in the same manner as in Example 2 in Table 1.

Example 12 This example illustrates the procedure of Example 1 when preparing the catalyst.
It uses zirconium nitrate instead of iron (III) nitrate. The elemental composition of the catalyst precursor in this example is
SiO ₂ : Al ₂ O ₃ : Ga ₂ O ₃ : ZrO _{2 by} weight ratio = 95.1: 2.0: 2.6: 0.2,
SiO ₂ : Al ₂ O ₃ : Ga ₂ O ₃ : ZrO ₂ = 80: 1: 0.7: 0.08 by molar ratio
Met. Thereafter, the results of evaluation of the NO _X removal rate in the same manner as in Example 2 in Table 1.

[0031]

[Table 1]

Comparative Example 1 Using the catalyst prepared in Example 1, in the same catalyst evaluation test as in Example 1, a diesel exhaust gas to which no LPG gas was added was introduced into the reaction tube. Table 1 shows the results. Comparative Example 2 Using the catalyst prepared in Example 4, in the same catalyst evaluation test as in Example 4, a diesel exhaust gas to which no LPG gas was added was introduced into the reaction tube. Table 1 shows the results.

Comparative Example 3 Using the catalyst prepared in Example 7, in the same catalyst evaluation test as in Example 7, a diesel exhaust gas without the addition of LPG gas was introduced into the reaction tube. Table 1 shows the results. Comparative Example 4 Using the catalyst prepared in Example 10, in the same catalyst evaluation test as in Example 10, a diesel exhaust gas to which no LPG gas was added was introduced into the reaction tube. Table 1 shows the results.

Comparative Example 5 Using the catalyst prepared in Example 11, in the same catalyst evaluation test as in Example 11, a diesel exhaust gas to which no LPG gas was added was introduced into the reaction tube. Table 1 shows the results. Comparative Example 6 The same catalyst evaluation test as in Example 12 was performed using the catalyst prepared in Example 12, except that diesel exhaust gas to which no LPG gas was added was introduced into the reaction tube. Table 1 shows the results.

Comparative Example 7 This comparative example is the same as Example 1 except that
Iron was not supported on the catalyst precursor. Thereafter, the results of evaluation of the NO _X removal rate in the same manner as in Example 1 in Table 1. Using the catalyst prepared in Comparative Example 8 Comparative Example 6, in the same manner as in Example 2 to evaluate the NO _X removal rate of the catalyst. Table 1 shows the results.

Comparative Example 9 The composition of the solution I in Example 1 was changed to aluminum sulfate 7.
6 g, tetrapropylammonium bromide 26.4 g,
A catalyst was prepared in the same manner as in Example 1 except that 17.6 g of sulfuric acid (97%) and 250 ml of water were used. The elemental composition of the catalyst precursor in this comparative example was SiO ₂ : Al ₂ O ₃ :
Fe ₂ O ₃ = 97.6: 2.1: 0.3, and SiO ₂ : Al ₂ O ₃ : Fe ₂ O in molar ratio
₃ = 80: 1: 0.08. Thereafter, in the same manner as in Example 2 to evaluate the NO _X removal rate of the catalyst. Table 1 shows the results.

Embodiments 13 to 18 Embodiments 13 to 18 correspond to Embodiments 2, 5, 8 and
In 10, 11, and 12, only the temperature of the reaction tube in the catalyst evaluation test was changed from 500 ° C to 400 ° C. Table 2 shows the evaluation results. Examples 19 to 24 Examples 19 to 24 correspond to Examples 2, 5, 8,
In 10, 11, and 12, only the temperature of the reaction tube in the catalyst evaluation test was changed from 500 ° C to 300 ° C. Table 2 shows the evaluation results.

Comparative Example 10 In this comparative example, in the evaluation test of the catalyst of Comparative Example 8, only the temperature of the reaction tube was changed from 500 ° C. to 400 ° C. Table 2 shows the evaluation results. Comparative Example 11 In this comparative example, in the evaluation test of the catalyst of Comparative Example 8, only the temperature of the reaction tube was changed from 500 ° C. to 300 ° C. Table 2 shows the evaluation results.

Comparative Example 12 In this comparative example, in the evaluation test of the catalyst of Comparative Example 9, only the temperature in the reaction tube was changed from 500 ° C. to 400 ° C. Table 2 shows the evaluation results. Comparative Example 13 In this comparative example, in the evaluation test of the catalyst of Comparative Example 9, only the temperature in the reaction tube was changed from 500 ° C. to 300 ° C. Table 2 shows the evaluation results.

[0040]

[Table 2]

Discussion of Examples and Comparative Examples As shown in Examples 1 to 12, according to the exhaust gas purifying method according to the examples, the promoters of Fe, Co, Ni, Cu, Zr or
La uses a catalyst supported on a galloaluminosilicate carrier containing Ga as a main catalyst. During the catalytic reaction, the temperature is 500 ° C., and the total THC concentration / NO _X concentration is 2.1 to 8.
Since the evaluation test was performed as No. 4, it was found that a high denitration rate of 60 to 95% was obtained even when the oxygen concentration in the exhaust gas was as high as 8%. For example, as seen in Comparative Example 1-3, when for purifying exhaust gas using the same catalyst, the greater the total THC concentration / NO _X concentration is higher denitrification rate. On the other hand, according to Comparative Examples 1 to 6, Example 1
While using the same catalyst as 12, without the addition of LPG, THC concentration / NO _X concentration is lower than the range according to the present invention
Since it was 0.2, only a low denitration rate of 3 to 10% was obtained.

According to Comparative Examples 7 and 8, even if the galloaluminosilicate according to the present invention is contained in the catalyst,
Because it does not contain promoter, but THC concentration / NO _X concentration is within the range of the present invention, as compared with Examples 1 to 12, the denitration rate is seen that 40 to 55% and less. According to Comparative Example 9, even though the aluminosilicate according to the present invention and the co-catalyst Fe were included in the catalyst, Ga as the main catalyst was not included, so that compared to Examples 1 to 12, Denitration rate is 21
%.

According to Examples 13 to 18, since the reaction temperature was lowered from 500 ° C. in Examples 1 to 12 to 400 ° C.,
Compared with Examples 1 to 12, the denitration rate was as low as 60 to 66%, but 50% of Comparative Example 10 in which the promoter was not contained in the catalyst.
It can be seen that the denitration rate was superior to that of Comparative Example 12 containing no Ga and 19%. Further, Examples 19 to 2
According to Example 4, the reaction temperature was changed from 500 ° C. of Examples 1 to 12 to 30 ° C.
Since the temperature was lowered to 0 ° C., the denitration rate was 3 compared to Examples 1 to 12.
Although it is as low as 0 to 46%, the denitration rate is superior to 9% of Comparative Example 11 in which Ga and the co-catalyst are not contained in the catalyst and 16% of Comparative Example 13 in which Ga is not contained, It can be seen that the composition has an excellent denitration rate even at a low reaction temperature.

[0044]

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

Continuation of the front page (58) Field surveyed (Int. Cl. ⁷ , DB name) B01J 21/00-38/74 B01D 53/94 B01D 53/86

Claims (2)

(57) [Claims] 1. A in nitrogen oxides in the exhaust gas oxidizing atmosphere, reaction
Reaction temperature 200-800 ° C and total THC concentration / NOx concentration
Catalyst for reducing and removing in the presence of a hydrocarbon having a degree of 0.5 to 50
A is, (1) gallium, (2) among the transition elements,
An exhaust gas purifying catalyst comprising: at least one component selected from iron, nickel, cobalt, zirconium, manganese, chromium, molybdenum, copper, and rare earth elements; and (3) zeolite. 2. An exhaust gas in an oxidizing atmosphere at a reaction temperature of 200 to 200.
800 ° C. and total THC concentration / NOx concentration 0.5 to 50
In the presence of hydrocarbons,請 Motomeko 1 catalyst and contacting the described method for purifying exhaust gas which comprises reducing removal of nitrogen oxides in the flue gas.