JPH06126185A - Catalyst for purifying exhaust gas and purifying method for exhaust gas by using its - Google Patents

Abstract

PURPOSE:To provide a catalyst for purifying exhaust gas which is capable of purifying nitrogen oxide to harmless gas with high efficiency and is enhanced in durability even when the concentration of oxygen contained in exhaust gas is high and the temperature of exhaust gas is low. CONSTITUTION:The catalyst is constituted by carrying copper on pentasil type crystalline aluminosilicate to produce a catalyst precursor and adding carbonate having at least one kind of component selected from alkaline earth metals to the catalyst precursor by a physical mixing method. The pentasil type crystalline aluminosilicate has an MFI structure and SiO2/Al2O3 (mol ratio) is regulated to >=10. Further exhaust gas is purified by using the catalyst in the oxidative atmosphere at the reaction temperature of 200-800 deg.C in the existence of hydrocarbon of 0.5-200 as THC concentration to NOx concentration.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a gas that is harmless to nitrogen oxides discharged from mobile internal combustion engines such as gasoline automobiles and diesel automobiles, stationary internal combustion engines such as cogeneration, and various industrial furnaces such as boilers. TECHNICAL FIELD The present invention relates to a method for producing an exhaust gas purifying catalyst that decomposes into.

[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 gasoline automobiles, it is possible to use NO with a reducing agent such as carbon monoxide or hydrocarbon.
_A so-called three-way catalyst type 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 emission source such as a boiler, a selective NO _X reduction method in which ammonia is externally added to reduce the NO _X amount is operated. And has some effect. 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.

For example, Japanese Patent Laid-Open No. 3-131345 proposes a method for purifying nitrogen oxides in an oxygen excess atmosphere using a catalyst in which one or more kinds of copper and alkaline earth metal are supported on zeolite. There is. In the case of the catalyst according to the present invention, when the alkaline earth metal is ion-exchanged and carried, the carrying amount of copper decreases, and as a result, both copper and alkaline earth metal are obtained by carrying a predetermined amount. It was not possible to obtain the desired catalytic performance.

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 in a gasoline engine under lean conditions where the air-fuel ratio is higher, or when the oxygen concentration is 5 to 10% as in exhaust gas from a diesel engine. is there. Also in the examples, the No _X removal rate tends to remarkably decrease as the oxygen concentration increases. Moreover, it is unclear as to durability.

According to Japanese Patent Laid-Open No. 63-283727, SiO ₂
Cu, V, Mn, and hydrophobic zeolite with an Al / Al ₂ O ₃ ratio of 15 or more
A method of reducing nitrogen oxides in exhaust gas containing oxygen of an internal combustion engine in the presence of carbon monoxide and one or more hydrocarbons using a catalyst supporting a metal such as Fe or Cr is proposed. Has been done. In this method, when a zeolite catalyst supporting a metal other than copper is used, the denitration rate is 4 to 26.
It becomes as low as%. On the other hand, when a copper zeolite catalyst is used, a relatively high activity is obtained, but its durability is unknown. The oxygen concentration in the exhaust gas of the example is 1.6%, and even if the oxygen concentration is high, such as the exhaust gas under lean conditions with a high air-fuel ratio in a gasoline engine or the exhaust gas of a diesel engine, the nitrogen oxidation is similar. It is unclear whether or not substances can be selectively denitrified.

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 in exhaust gas is used in an oxidizing atmosphere in the presence of hydrocarbons. Methods for removing oxides have been proposed.
With this method, the denitration rate is 10 to 25%, and high denitration activity cannot be obtained. Further, the oxygen concentration in the exhaust gas of the example,
It is 2.1%, and it is unclear whether nitrogen oxides can be selectively reduced and denitrated even when the oxygen concentration is higher. Furthermore, the durability is unknown. Therefore, the present invention is a highly efficient exhaust gas purification catalyst that can purify nitrogen oxides into harmless gas with high efficiency even if oxygen in the exhaust gas has a high concentration, and an exhaust gas purification method using the same. The purpose is to provide.

[0009]

SUMMARY OF THE INVENTION The present invention is directed to an exhaust gas
Nitrogen oxides (NO_X) Of the hydrocarbon in an oxidizing atmosphere
A catalyst for reducing and removing in the presence of a pentasil-type catalyst.
The crystalline aluminosilicate was added to the copper-supported catalyst precursor as
Physical mixing of one or more carbonates in Lucari earth metal
It is characterized by being added by the method. The oxidizing atmosphere
Qi means carbon monoxide, hydrogen, hydrocarbons contained in exhaust gas
Reducibility of hydrogen and hydrocarbons added as necessary in this treatment
Completely oxidize the substance, H₂O and CO₂ Needed to convert to
When the amount of oxygen exceeds the amount of oxygen
It

The pentasil-type crystalline aluminosilicate is a zeolite whose basic structural unit is an oxygen 5-membered ring. For example, ferrilite, mordenite, ZSM-5, ZSM-11 and the like are applicable. Zeolites other than the pentasil-type crystalline aluminosilicate have relatively low hydrothermal resistance, and therefore there is a risk that the durability after supporting carbonates of copper and alkaline earth metals may be reduced.

Among such pentasil-type crystalline aluminosilicates, those having SiO ₂ / Al ₂ O ₃ (molar ratio) of 10 or more are preferable. When SiO ₂ / Al ₂ O ₃ is less than 10,
Since the hydrothermal resistance is relatively low, there is a possibility that the durability after supporting the carbonates of copper and alkaline earth metals may be reduced.

Of the above pentasil-type crystalline aluminosilicates, those having an MFI or MEL structure are preferable. The MFI structure refers to a structure similar to ZSM-5, for example, ZSM-8, zeta 1, zeta 3, Nu.
-4, Nu-5, TZ-1, TPZ-1 and the like are applicable. In addition, the MEL structure refers to a structure similar to ZSM-11. This pentasil-type crystalline aluminosilicate is
Those having a lattice spacing (d value) shown in Table 2 below in powder X-ray diffraction are preferable.

[0013]

[Table 2]

The content of copper in the pentasil-type crystalline aluminosilicate supporting copper is 1.0 to 5.0 wt%, preferably 2.0 to 5.0 wt% in terms of CuO with respect to the aluminosilicate.
4.0 wt% The alkaline earth metal includes magnesium, calcium, strontium and the like, and calcium and strontium are particularly preferable. The amount of the alkaline earth metal carbonate compounded is 10 to 100% by weight, preferably 30 to 70% by weight, based on the aluminosilicate.

The catalyst may have any shape, for example, pellet, plate, column, or lattice. Further, a catalyst may be coated on a lattice-shaped carrier such as cordierite, mullite or alumina, and a base material such as wire mesh. The catalyst according to the present invention is obtained by synthesizing a pentasil-type crystalline aluminosilicate by using a seed crystal, and then adding a carbonate of an alkaline earth metal to a catalyst precursor in which copper is supported on the crystalline aluminosilicate. Can be added by a physical mixing method.

As a copper source added to support copper on the crystalline aluminosilicate, an ion exchange method, an impregnation method,
Alternatively, a soluble salt can be used when a method of incorporating a copper component in synthesizing zeolite. Examples of such soluble salts include nitrates, halogen compounds, carbonates, organic acid salts, copper ammine complexes and the like. When copper is added by the physical mixing method, oxides and hydroxides can be used in addition to the soluble salts.

The thermal decomposition temperature of copper carbonate is 220 ° C.
Since it is low, it is converted to an oxide during firing. On the other hand, in the case of alkaline earth metal carbonate, it is difficult to undergo heat conversion during firing. As described above, the catalyst according to the present invention is obtained by adding the carbonate of at least one component in the alkaline earth metal to the catalyst precursor composed of the copper-supported pentasil-type crystalline aluminosilicate by the physical mixing method. Therefore, it becomes possible to carry the alkaline earth metal carbonate without affecting the carried amount of the already carried copper. As a result, a highly durable catalyst can be obtained by the combined action of copper and a carbonate of an alkaline earth metal.

[0018]

Example 1 First, 13.5 g of aluminum sulfate, 14.5 g of sulfuric acid (97%),
A solution consisting of 330 g of water (referred to as solution I), water glass (Si
O ₂ 28.4%, Na ₂ O 9.5%) 211 g, water 200 g (Solution II) and sodium chloride 39.5 g, water 92
A solution of g (referred to as solution III) was prepared. next,
Solutions I and II were mixed simultaneously into solution III with gradual dropwise addition. After adjusting the reaction mixture to pH 9.5 with sulfuric acid, mordenite [SiO ₂ / Al ₂ O ₃ = 20
(Molar ratio)] 0.5 g was added.

Next, the reaction 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, the reaction mixture was filtered and the precipitate was thoroughly washed with excess pure water. After that, by drying at 120 ℃ for 20 hours, ZSM-5
An aluminosilicate zeolite having a structure (MFI structure) was synthesized. Powder X of this aluminosilicate zeolite
Table 3 shows the measurement results by line diffraction. Next, this zeolite was calcined in an air stream at 550 ° C. for 6 hours.

Next, with respect to this zeolite, 0.2 mol / l
Copper ion exchange was performed by treating with an aqueous solution of copper acetate for 6 hours. Then, after filtration and washing with water,
Allowed to dry for hours. Further, by baking at 500 ° C. for 2 hours, a catalyst precursor supporting copper was obtained. The SiO ₂ / Al ₂ O ₃ (molar ratio) of this catalyst precursor was 32, and the content of copper was 3.8 wt% in terms of CuO with respect to the catalyst precursor. Next, 50 wt% of calcium carbonate was added to this catalyst precursor and thoroughly mixed in a mortar to obtain an aluminosilicate zeolite supporting copper and calcium carbonate according to this example.

Next, this catalyst was evaluated for initial activity and activity after steaming (hydrothermal) treatment as described below. That is, regarding the evaluation of the initial activity, first, 2 cc of this catalyst was filled in a stainless steel reaction tube, and then a model gas as a processing gas was charged into the reaction tube kept at 350 ° C.
It was introduced at = 80,000h ^-1 . The composition of this model gas is N
O _X : 500ppm, O ₂ : 4.5%, LPG: 833ppm (THC
The concentration is about 2500ppm). Therefore, THC concentration /
The NO _X concentration is 5. Next, the gas from the outlet of this reaction tube was introduced into a chemiluminescence analyzer to measure the NO _X concentration.
The NO _X removal rate of the model gas after the catalytic reaction was calculated by comparing the NO _X concentration of the model gas before and after introducing the reaction tube.

Regarding the evaluation of the activity after the steaming treatment, first, as the steaming treatment, the catalyst prepared in this example was treated with 10% water, 4.5% oxygen, GHSV = 80,000 h ^-1 and a temperature of 6%.
It was kept at 50 ° C. for 8 hours. Next, as in the case of the evaluation of the initial activity, the cooled catalyst was filled in a stainless steel reaction tube, and then a model gas as a processing gas was introduced into the reaction tube kept at 350 ° C, and then the same as above. The NO _X removal rate was calculated. The initial activity when the temperature inside the reaction tube was kept at 400 ° C and the activity after the steaming treatment were also evaluated in the same manner as above. The results are shown in Table 4 below.

[0023]

[Table 3]

Example 2 The aluminosilicate zeolite obtained in the same manner as in Example 1 was treated with a 1.6 mol / l ammonium nitrate aqueous solution for 9 hours for ammonium ion exchange, filtered and washed with water,
It was dried at 120 ° C. for 20 hours to synthesize an aluminosilicate zeolite having an MFI structure. Next, with respect to this zeolite, a catalyst precursor supporting copper was obtained in the same manner as in Example 1. The copper content is 3.5 in terms of CuO based on the catalyst precursor.
It was wt%.

Next, 50 wt% of calcium carbonate was added to this catalyst precursor and thoroughly mixed in a mortar to obtain an aluminosilicate zeolite supporting copper and calcium carbonate according to this example. Also for this catalyst, the initial activity and the activity after the steaming treatment were evaluated in the same manner as in Example 1. The results are shown in Table 4.

Example 3 To the copper-supported catalyst precursor obtained in the same manner as in Example 2, 50 wt% of strontium carbonate was added and sufficiently mixed in a mortar to give the copper and carbonic acid according to this Example. An aluminosilicate zeolite supporting strontium was obtained. Also for this catalyst, the initial activity and the activity after the steaming treatment were evaluated in the same manner as in Example 1. The results are shown in Table 4.

Example 4 In Example 1, the introduced model gas was changed to one having a higher oxygen concentration than that in Example 1 as described below, and the initial activity of the catalyst and the activity after the steaming treatment were evaluated. That is,
The composition of the introduced model gas is NO _X : 500 ppm, O ₂ : 10
%, LPG: 833 ppm. The results are shown in Table 4 below.

Comparative Example 1 An aluminosilicate zeolite supporting copper was obtained in the same manner as in Example 1 except that calcium carbonate was not supported. Also for this catalyst,
In the same manner as in Example 1, the initial activity and the activity after steaming treatment were evaluated. The results are shown in Table 4.

Comparative Example 2 An aluminosilicate zeolite supporting copper was obtained in the same manner as in Example 2 except that calcium carbonate was not supported. Also for this catalyst,
In the same manner as in Example 1, the initial activity and the activity after steaming treatment were evaluated. The results are shown in Table 4.

Comparative Example 3 Aluminosilicate zeolite obtained in the same manner as in Example 1 was treated with a 0.05 mol / l calcium acetate aqueous solution to give 6 parts.
After treatment for time, calcium ion exchange was carried out, filtration, washing with water, and drying at 120 ° C. for 20 hours to synthesize aluminosilicate zeolite supporting calcium.

Next, this calcium-supporting zeolite was treated with a 0.2 mol / l copper acetate aqueous solution for 6 hours to carry out copper ion exchange. Subsequently, the mixture was filtered, washed with water, and dried at 120 ° C for 12 hours. Further, by firing at 500 ° C. for 2 hours, an aluminosilicate zeolite catalyst supporting calcium and copper was obtained. The loadings of calcium and copper on this catalyst were 0.3 wt% and 3.3 wt% in terms of CaO and CuO, respectively. Also for this catalyst, the initial activity and the activity after the steaming treatment were evaluated in the same manner as in Example 1. The results are shown in Table 4.

[0032]

[Table 4]

From Table 4, the catalysts according to Examples 1 to 4 are obtained by adding calcium carbonate or strontium carbonate by a physical mixing method to a catalyst precursor composed of pentasil-type crystalline aluminosilicate supported on copper. , The content of copper to the crystalline aluminosilicate before and after supporting calcium carbonate or strontium carbonate did not change, and the obtained catalyst was
In both cases, the NO _{x was} relatively high compared to the comparative example.
It can be seen that it has removal performance. On the other hand, in the catalyst of Comparative Example 1, since the aluminosilicate zeolite supporting copper does not support calcium carbonate, after the steaming treatment, both at 350 ° C. and 400 ° C., compared with the catalyst of Example 1. , NO _X removal performance is low.

In the catalyst of Comparative Example 2, since the aluminosilicate zeolite supporting copper did not support calcium carbonate, 350 ° C. and 400 ° C. were obtained after the steaming treatment.
It can be seen that in all cases, the NO _X removal performance is lower than in Example 2. According to Comparative Example 3, after the calcium was supported on the aluminosilicate zeolite by the ion exchange method and the copper was supported by the copper ion exchange, the obtained catalyst had a temperature of 350 ° C. and 400 ° C. after steaming treatment. It can be seen that the NO _X removal performance is lower than that in Example 1 at any of the temperatures.

[0035]

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

Claims (8)

[Claims] 1. A catalyst precursor for reducing and removing nitrogen oxides (NO _x ) in exhaust gas in the presence of hydrocarbons in an oxidizing atmosphere, wherein a pentasil-type crystalline aluminosilicate supports copper. A catalyst for purifying exhaust gas, characterized in that a carbonate of one or more components in an alkaline earth metal is added by a physical mixing method. 2. The exhaust gas purifying catalyst according to claim 1, wherein the mixing ratio of the alkaline earth metal carbonate is 10 to 100 wt% with respect to the catalyst precursor. 3. The exhaust gas according to claim 1 or 2, wherein the pentasil-type crystalline aluminosilicate has a SiO ₂ / Al ₂ O ₃ (molar ratio) of 10 or more. Purification catalyst. 4. The exhaust gas-purifying catalyst according to any one of claims 1 to 3, wherein the pentasil-type crystalline aluminosilicate has an MFI structure. 5. The pentasil-type crystalline aluminosilicate has a lattice spacing (d value) shown in Table 1 below in powder X-ray diffraction, wherein any one of claims 1 to 4 is characterized. The exhaust gas-purifying catalyst according to Item 1. [Table 1] 6. The method according to claim 1, wherein the alkaline earth metal is calcium or strontium.
A method for producing the exhaust gas-purifying catalyst according to any one of 5th items. 7. The concentration of THC / NO _x in an oxidizing atmosphere
Exhaust gas in the presence of 0.5 to 200 hydrocarbons.
In contact with the catalyst according to any one of items 6 to 6,
A method for purifying exhaust gas, which comprises reducing and removing nitrogen oxides in the exhaust gas. 8. The exhaust gas according to claim 7, wherein nitrogen oxide in the exhaust gas is reduced and removed in the presence of a hydrocarbon having a reaction temperature of 200 to 800 ° C. and a THC concentration / NO _X concentration of 1 to 100. Purification method.