JP3254742B2 - Catalyst for decomposition of nitrous oxide - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a catalyst for decomposing and removing nitrogen oxides, particularly nitrous oxide (N2O), in exhaust gas, and more particularly to disposal of factories, automobiles, garbage incinerators, sewage sludge incinerators and the like. The present invention relates to a nitrogen oxide decomposition catalyst suitable for use in decomposing and removing nitrous oxide contained in exhaust gas discharged from a waste treatment facility.

[0002]

2. Description of the Related Art Nitrogen oxides (hereinafter referred to as NOx) in various kinds of exhaust gas are harmful to health and may cause photochemical smog and acid rain. Is severely restricted, and it is desired to develop an effective means of removing the same. By the way, nitrogen oxides to which emission control is conventionally required are mainly nitric oxide (NO) and nitrogen dioxide (NO2). As a method for removing these NOx, several methods for reducing NOx in exhaust gas using a catalyst have already been put to practical use. For example, (a) a three-way catalytic method in gasoline vehicles, and (b) a selective catalytic reduction method using ammonia for exhaust gas from large equipment discharge sources such as boilers.

Recently, (c) as a method for removing NOx in exhaust gas using hydrocarbons, a catalyst such as zeolite supporting a metal such as copper or a metal oxide such as alumina is used to remove NO in the presence of hydrocarbons. A method of contacting with a contained gas has been proposed. However, in any of these methods, the treatment of N2O in the exhaust gas is not sufficient, if not impossible, and conventionally, these have been discharged untreated in the downstream of the above-mentioned denitration equipment. This is N
This is related to the fact that there are no legally regulated values for 2O and that no official measurement method such as JIS has been established. It was a reality that it had been done. However, in the above-described denitration method, it has been recognized that N2O is generated depending on the operating conditions, and recently, a relatively high concentration of N2O may be generated from a garbage incinerator or a sewage sludge incinerator. It has been reported. Additionally in recent years, N2O is, CO2, fluorocarbons, with CH4 and the like, destroy the ozone layer in the stratosphere, or have been of particular interest as a global contaminants to bring such temperature rise due to the greenhouse effect.

[0004] Under these circumstances, there has been an increasing interest in N2O treatment methods, particularly for its decomposition catalysts, and several methods have been proposed. These are, for example, those in which various transition metals are supported on a zeolite-based carrier, or those in which various transition metals are supported on a basic carrier such as magnesium oxide or zinc oxide. However, all of these have high temperatures at which the activity is high, and low performance cannot be obtained at low temperatures. Further, if moisture is present in the processing gas, they have the disadvantage that they are strongly affected by the effect and are deactivated. The present invention has been made in view of such circumstances, and an object of the present invention is to provide an N2O decomposition catalyst capable of efficiently decomposing N2O in exhaust gas.

[0005]

Means for Solving the Problems To achieve the above object, a catalyst for decomposing nitrous oxide according to the present invention comprises a zeolite,
On an acidic carrier such as alumina, titania, zirconia, or silica-alumina, copper (Cu), iron (F)
e), at least one metal or metal oxide selected from nickel (Ni), and ruthenium (Ru), rhenium (Re), osmium (O
s) and at least one noble metal selected from iridium (Ir). The acidic carrier according to the present invention is roughly classified into (I) zeolite and (II) oxide.

(I) The zeolite is obtained by treating a heat-resistant zeolite such as Na-mordenite, Na-ZSM.5 or Na-USY with an aqueous solution of ammonium salt such as ammonium sulfate or an acid such as sulfuric acid. Part of or all of the alkali metal is subjected to an ion exchange treatment with NH4 or H 2, and in the case of NH4 ion exchange, further calcination treatment is performed to obtain an acid zeolite. For example, Si
O2 / Al2O3 having a molar ratio of 13 to 20 and SiO2 / Na2O having a molar ratio of 10 to 200;
i, Zr substitution or carrier zeolite can be mentioned. (II) The oxide system is composed of Al2O3, TiO2, and Ti, filed on January 8, 1991 by the present inventors.
Single metal oxides such as O2 / SO4, ZrO2, ZrO4 / SO4, SiO2-Al2O3, TiO2-A
Complex oxides such as l2O3 and TiO2-ZrO2.

The catalyst powder according to the present invention can be prepared by various methods. The above acidic carrier is re-pulped in water, and Cu, Fe selected from the first component is added thereto.
A predetermined amount of a chloride of a noble metal such as Ru, Re, Os, and Ir selected from an aqueous nitrate solution such as Ni and the second component is added, and the mixture is stirred for a certain period of time. The precipitates are collected by filtration, washed with water and dried, and then immersed in a 5% hydrazine aqueous solution for a certain period of time to reduce. These are filtered, dried and dried.
Bake at 00 ° C to 600 ° C for 3 to 5 hours. Preparation of the catalyst is also possible by the ion exchange method. That is, first, the acidic carrier is re-pulped in an aqueous solution of the first component such as nitrate, stirred for a certain period of time while heating, ion-exchanged, filtered, washed with water, and dried.

Next, this was further re-pulped in an aqueous chloride solution of the second component, stirred for a certain period of time while heating, ion-exchanged, filtered, washed with water and dried, and then dried.
Bake at 0 ° C to 600 ° C for 3 to 5 hours. In the present invention, the method of ion exchange is not particularly limited, and can be performed by a conventionally known ordinary method. For example, the acidic carrier may be dispersed in water, and a cation or complex cation such as a transition metal to be ion-exchanged may be added with sufficient stirring. As described above, in the ion exchange, the cation or complex cation of the transition metal to be ion-exchanged does not cause precipitation, and by maintaining the pH as high as possible, the exchange capacity of the ion for ion exchange with the hydrogen ion having a hydroxyl group can be increased. Can be increased. Since the pH of the liquid decreases due to the exchanged hydrogen ions with the progress of the ion exchange, it is preferable to perform ion exchange while adding a neutralizing agent such as ammonia and maintaining the pH high as described above.

When the metal ions to be exchanged are not hydrolyzed by heating as in the case of copper, nickel or the like, in order to increase the ion exchange rate, the ion exchange may be carried out under the condition that the temperature is increased. Good. As described above, the catalyst powder according to the present invention is obtained, and the preferable loading amount of these metals is 1 to 10% by weight in terms of metal as the transition metal of the first component. Is 0.01 to 1.0% by weight in terms of metal. When the amount of the first component supported is more than the above range, no corresponding improvement in activity was observed. When the amount of the second component is not more than the above range, the effect is not sufficiently exhibited, but when the amount is more than the above range, it is possible to lower the temperature at which the activity is exhibited, but it is necessary to increase the use amount of these noble metals. That is an economic disadvantage.

After all, in the temperature range proposed by the present invention, the amount of the second component to be carried does not need to be higher than the above range. Among these catalyst powders, more preferred are those in which copper and ruthenium are supported on a zeolite-based carrier. The nitrous oxide decomposition catalyst according to the present invention can be formed into various shapes such as honeycomb spheres by a conventionally known forming method. Furthermore, only the above-mentioned acidic carrier may be molded, and the first component and the second component may be impregnated after molding. Further, the above-described catalyst powder may be wash-coated on a separately formed ceramic carrier, ceramic fiber base material, cordierite honeycomb, or the like.

In the molding, a molding aid, inorganic fibers,
An organic binder or the like may be appropriately blended. The optimum temperature at which the catalyst for decomposing nitrous oxide according to the present invention exhibits activity against N 2 O varies depending on the type of catalyst, but is usually from 300 ° C.
00 ° C., and in this temperature range, the space velocity (S
V) It is preferable to flow exhaust gas at about 500 to 500,000. The more preferable operating temperature range is 400
C. to 500C.

[0012]

EXAMPLES Hereinafter, the present invention will be described in more detail with reference to examples. However, the present invention is not limited to the following examples, and the present invention may be practiced by appropriately changing the gist of the invention. Is possible.

(I) Preparation of catalyst Example 1 SiO2 / Al2O3 molar ratio is 19.5, SiO2 / N
200 g of H-type mordenite (HM-23) manufactured by Nippon Kagaku having an a2O molar ratio of 165 was immersed in 2 l of water, and CuSO
4 so that the aqueous solution becomes 10 g as CuO and RuC
13 aqueous solution was added to be 0.2 g as Ru,
Stir for 30 minutes. Then, the mixture was neutralized with (1 + 1) NH4OH until the pH reached 7. This slurry was separated by filtration, sufficiently washed with water, and dried at 100 ° C. for 8 hours. The obtained powder was lightly pulverized, immersed in a 5% hydrazine solution for 10 minutes, and reduced. This slurry is filtered and washed with water at 100 ° C.
For 8 hours, and calcined at 500 ° C. for 4 hours.
Mordenite powders containing 4.91% and 0.095% of uO and Ru, respectively, were obtained. In addition, these analyzes were based on the atomic absorption method. Next, 100 g of this powder was added to 100 g of water.
g was added, and the mixture was pulverized with a ball mill for 10 minutes, and the viscosity was adjusted with water to obtain a slurry for washcoat. Using this slurry, catalyst powder was supported on a cordierite honeycomb having a pitch of 7 mm. The coating amount at this time is 0.
It was 12 g / cc.

Example 2 In Example 1, FeFe was used instead of the CuSO4 aqueous solution.
(NO3) In the same manner as in Example 1 except that 3 solutions were used,
4.93% and 0.09% Fe2O3 and Ru respectively
A mordenite powder containing 1% was obtained. Hereinafter, Example 1
A honeycomb catalyst was obtained in the same manner as described above, but the coating amount at this time was 0.122 g / cc.

Example 3 In Example 1, NiNi solution was used instead of CuSO4 aqueous solution.
(NO3) In the same manner as in Example 1 except that the solution was prepared as 2 solution,
4.91% and 0.091% of NiO and Ru, respectively
The resulting mordenite powder was obtained. Thereafter, a honeycomb catalyst was obtained in the same manner as in Example 1, but the coating amount at this time was 0.122 g / cc.

Example 4 The procedure of Example 1 was repeated, except that the aqueous solution of RuCl3 was replaced with ReC
CuO was prepared in the same manner as in Example 1 except that an aqueous solution of CuO was used.
And Re containing 4.9% and 0.095%, respectively, of mordenite powder. Hereinafter, a honeycomb catalyst was obtained in the same manner as in Example 1, except that the coating amount was 0.1%.
It was 23 g / cc.

Example 5 In Example 1, OsC was used instead of the RuCl 3 aqueous solution.
CuO was prepared in the same manner as in Example 1 except that an aqueous solution of CuO was used.
And mordenite powder containing 4.96% and 0.095% of Os, respectively. Hereinafter, a honeycomb catalyst was obtained in the same manner as in Example 1, except that the coating amount was 0.1%.
It was 21 g / cc.

Example 6 In Example 1, IrC3 aqueous solution was used instead of RuCl3 aqueous solution.
In the same manner as in Example 1 except that an aqueous solution of CuO
And mordenite powders containing 4.95% and 0.089% of Ir, respectively. Hereinafter, a honeycomb catalyst was obtained in the same manner as in Example 1, except that the coating amount was 0.1%.
It was 33 g / cc.

Example 7 In Example 1, a specific surface area of 110 was used instead of the HM23.
Example 1 except that m2 / g of anatase TiO2 was used.
4.96% each of CuO and Ru,
A TiO2 powder containing 0.093% was obtained. A honeycomb catalyst was obtained in the same manner as in Example 1, but the coating amount at this time was 0.122 g / cc.

Example 8 The same procedure as in Example 1 was repeated except that the aqueous CuSO4
g in the same manner as in Example 1 except that
A mordenite powder containing 2.95% and 0.094% of O and Ru, respectively, was obtained. Thereafter, a honeycomb catalyst was obtained in the same manner as in Example 1, but the coating amount at this time was 0.1.
It was 126 g / cc.

Example 9 In Example 1, the CuSO4 aqueous solution was changed to CuO
Cg in the same manner as in Example 1 except that the weight was set to 0 g.
Mordenite powders containing 9.92% and 0.095% of uO and Ru, respectively, were obtained. Thereafter, a honeycomb catalyst was obtained in the same manner as in Example 1, but the coating amount at this time was 0.122 g / cc.

Example 10 In Example 1, the RuCl 3 aqueous solution was used as the Ru solution.
C in the same manner as in Example 1 except that the weight was 4 g.
Mordenite powders containing 4.95% and 0.193% of uO and Ru, respectively, were obtained. Thereafter, a honeycomb catalyst was obtained in the same manner as in Example 1, but the coating amount at this time was 0.126 g / cc.

Embodiment 11 In the embodiment 1, the RuCl 3 aqueous solution is used as 0.1% as Ru.
The same procedure as in Example 1 was carried out except that the weight was 1 g.
A mordenite powder containing 4.95% and 0.048% of uO and Ru, respectively, was obtained. Thereafter, a honeycomb catalyst was obtained in the same manner as in Example 1, but the coating amount at this time was 0.122 g / cc.

COMPARATIVE EXAMPLE 1 In Example 1, without adding an aqueous RuCl 3 solution,
A mordenite powder containing 4.96% of CuO was obtained.
Thereafter, a honeycomb catalyst was obtained in the same manner as in Example 1, but the coating amount at this time was 0.123 g / cc.

Comparative Example 2 In Example 13, a mordenite powder containing 2.95% of CuO was obtained without adding an aqueous RuCl 3 solution. Hereinafter, a honeycomb catalyst was obtained in the same manner as in Example 1.
The coating amount at this time was 0.131 g / cc.

Comparative Example 3 In Example 14, a mordenite powder containing 9.95% of CuO was obtained without adding an aqueous RuCl 3 solution. Hereinafter, a honeycomb catalyst was obtained in the same manner as in Example 1.
The coating amount at this time was 0.131 g / cc.

Comparative Example 4 In Example 12, a TiO2 powder containing 4.95% CuO was obtained without adding an aqueous RuCl3 solution.
Thereafter, a honeycomb catalyst was obtained in the same manner as in Example 12, but the coating amount at this time was 0.133 g / cc.

(II) Evaluation Test The catalysts obtained in Examples 1 to 11 and Comparative Examples 1 to 4 were tested under the following test conditions.
Nitrous oxide-containing gas was subjected to catalytic cracking using an atmospheric pressure flow reactor, and the conversion rate of nitrous oxide to N2 was calculated by quantifying N2 by gas chromatography. Space velocity 5000Hr ¹ Reaction temperature 300 ° C, 400 ° C, 500 ° C The results are shown in Table 1.

[0029]

[Table 1]

As described above, the catalyst for decomposing nitrous oxide according to the present invention can efficiently decompose nitrous oxide in exhaust gas even at a relatively low temperature, and the exhaust gas does not exist. It has excellent characteristics such as being hardly affected by the influence.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-6-106027 (JP, A) JP-A-4-363144 (JP, A) JP-A-5-208138 (JP, A) JP-A-5-208138 317722 (JP, A) JP-A-52-52192 (JP, A) JP-A-5-305219 (JP, A) JP-A-57-159544 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) B01J 21/00-37/36 B01D 53/86

Claims (1)

(57) [Claims] 1. An acidic carrier containing copper (C) as a first component.
u), at least one metal or metal oxide selected from iron (Fe) and nickel (Ni), and as the second component, ruthenium (Ru), rhenium (Re), osmium (Os), iridium ( Ir), a catalyst for decomposing nitrous oxide, which carries at least one noble metal selected from the group consisting of: