JPH06154611A - Catalyst for decomposition of nitrous oxide - Google Patents

Abstract

PURPOSE:To perform efficient catalytic decomposition of NOx in exhaust gas even at a relatively low temp. by carrying one or more kinds of specified metals or oxides of the metals as 1st components and one or more kinds of specified noble metals as 2nd components on an acidic carrier. CONSTITUTION:One or more kinds of metals selected among Cu, Fe, Co and Ni or oxides of the metals as 1st components and one or more kinds of noble metals selected among Ru, Rh, Pd, Re, Os, Ir and Pt as 2nd components are carried on an acidic carrier such as zeolite, alumina, titania, zirconia or silica- alumina to form the objective catalyst for decomposition of nitrous oxide. The optimum temp. at which this catalyst exhibits activity to N2O depends on the kinds of catalytic components but is usually 300-600 deg.C and exhaust gas is preferably allowed to flow at about 500-500,000 space velocity in the temp. range of 300-600 deg.C.

Description

Detailed Description of the Invention

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a catalyst for decomposing and removing nitrogen oxides in exhaust gas, particularly nitrous oxide (N ₂ O), and more specifically, factories, automobiles, refuse incinerators, sewage sludge incinerators, etc. The present invention relates to a suitable catalyst for decomposing nitrogen oxides, which is used when decomposing and removing nitrous oxide contained in exhaust gas discharged from the waste treatment facility.

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, so their emission Is severely limited, and the development of effective removal means is desired. By the way, the nitrogen oxides conventionally required to be emission regulated are mainly nitric oxide (NO) and nitrogen dioxide (NO ₂ ). As methods for removing these NOx, some methods for reducing NOx in exhaust gas using a catalyst have already been put into practical use. For example, (a) a three-way catalyst method in a gasoline automobile, and (b) a selective catalytic reduction method using ammonia for exhaust gas from a large facility emission source such as a boiler. Recently, as a method for removing NOx in exhaust gas using (c) hydrocarbons, zeolite containing a metal such as copper, or a gas containing NO in the presence of hydrocarbons using a metal oxide such as alumina as a catalyst is used. Methods such as contacting have been proposed. However, none of these methods is not sufficient, but not sufficient, to treat N ₂ O in the exhaust gas, and conventionally, these have been discharged untreated in the downstream of the above-mentioned denitration equipment. This is related to the fact that there is no legal regulation value for N ₂ O and no official measurement method such as JIS has been established so far. However, the reality is that they have been ignored as targets for denitration. However, in the above-described denitration method, N ₂ O may be added depending on the operating conditions.
It has been confirmed that methane is generated, and recently, a relatively high concentration of N ₂ O has been obtained from garbage incinerators and sewage sludge incinerators.
Are also reported to be generated. In addition, in recent years, N ₂ O
Has attracted particular attention as a global pollutant that causes destruction of the Ozo layer in the stratosphere, or temperature rise due to the greenhouse effect, together with CO ₂ , chlorofluorocarbon, CH _{4, and the} like. Under such circumstances, there has been increasing interest in N ₂ O treatment methods, particularly decomposition catalysts thereof, and several methods have been proposed. They are, for example, a zeolite-based carrier on which various transition metals are supported, or a basic carrier such as magnesium oxide or zinc oxide on which various transition metals are supported. However, all of them have a high temperature at which they are active, and they do not provide sufficient performance at low temperatures, and have a weak point that they are strongly affected by the presence of water in the process gas and are deactivated. The present invention has been made in view of such circumstances, and an object thereof is to provide a catalyst for decomposing N ₂ O that can efficiently decompose N ₂ O in exhaust gas.

The catalyst for decomposing nitrous oxide according to the present invention for achieving the above object is zeolite,
Copper (Cu), iron (F) as the first component in an acidic carrier such as alumina, titania, zirconia, or silica-alumina.
e), at least one metal or metal oxide selected from cobalt (Co), nickel (Ni), and second
As components, ruthenium (Ru), rhodium (Rh),
It comprises at least one or more noble metals selected from palladium (Pd), rhenium (Re), osmium (Os), iridium (Ir), and platinum (Pt). The acidic carrier according to the present invention is roughly classified into (I) zeolite and (II) oxide type. (I) Zeolite is a zeolite having excellent heat resistance such as Na-mordenite, Na-ZSM.5, and Na-USY, which is treated with an ammonium salt solution such as ammonium sulfate or an acid such as sulfuric acid so that the alkali metal Part or all of NH ₄ or H
In the case of NH ₄ ion exchange, the acid-type zeolite is obtained by further performing the ion exchange treatment in (1). For example, the SiO ₂ / Al ₂ O ₃ molar ratio is 13 to 20, and the SiO ₂ / Na ₂ O molar ratio is 10 to 20.
Examples thereof include those having a value of 0, and Ti, Zr-substituted or carrier zeolites filed as Japanese Patent Application No. 3-164094. The (II) oxide-based materials are Al ₂ O ₃ and TiO, which the present inventors applied for on January 8, 1991.
₂ , TiO ₂ / SO ₄ , ZrO ₂ , ZrO ₄ / SO ₄
Single metal oxide such as SiO ₂ —Al ₂ O ₃ , T
Examples thereof include complex oxides such as iO ₂ —Al ₂ O ₃ and TiO ₂ —ZrO ₂ . The catalyst powder according to the present invention can be prepared by various methods. The above-mentioned acidic carrier is repulsed in water, and Cu, F selected from the first component is added to this.
Ru, Rh, Pd, Re, Os, Ir, selected from aqueous nitrate solutions such as e, Co, Ni, and the second component.
After adding a predetermined amount of a noble metal chloride such as Pt and stirring for a certain period of time, the mixture is neutralized with NH ₄ OH water to pH 7 to form a precipitate, which is filtered, washed with water and dried, It is dipped in a 5% aqueous solution of hydrazine for a certain period of time to be reduced. These are separated by filtration, dried, and dried at 500 ° C to 600 ° C for 3
Bake for ~ 5 hours. The preparation of the catalyst is also possible by the ion exchange method. That is, first, first, an acidic carrier is repulsed in an aqueous solution of a nitrate or the like of the first component, stirred for a certain period of time while heating, ion-exchanged, filtered, washed with water, and dried. Next, this product is further repulsed in an aqueous chloride solution of the second component, stirred for a certain period of time while being heated, ion-exchanged, filtered, washed with water and dried,
Baking is performed at 500 ° C. to 600 ° C. for 3 to 5 hours. In the present invention, the ion exchange method is not particularly limited, and it can be performed by a conventionally known conventional method. For example, the acidic carrier may be dispersed in water, and a cation or a complex cation such as a transition metal for ion exchange may be added under sufficient stirring. As described above, in ion exchange, the exchange metal cations or complex cations to be ion-exchanged do not cause precipitation, and the pH is kept as high as possible to increase the exchange capacity of the ions exchanged with the hydrogen ions of the hydroxyl groups. Can be increased. As the ion exchange proceeds, the pH of the liquid decreases due to the exchanged hydrogen ions. Therefore, it is preferable to add a neutralizing agent such as ammonia and perform the ion exchange while maintaining the pH high as described above. When the metal ion to be exchanged is not hydrolyzed by heating, as in the case of copper, nickel or the like, the ion exchange may be performed under the condition of increasing the temperature in order to increase the ion exchange rate. 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 wt% in terms of metal as the transition metal of the first component, and the second component The noble metal is 0.01 to 1.0 wt% in terms of metal. First
When the amount of the component carried was more than the above range, the activity corresponding to the above amount was not improved. The amount of the second component carried is
If the amount is less than the above range, the effect is not sufficiently exhibited, but if the amount is more than the above range, the temperature at which the activity is exhibited can be lowered, but increasing the amount of these precious metals used is economically disadvantageous. After all, in the temperature range proposed by the present invention, it is not necessary that the amount of the second component carried is above the above range. Among these catalyst powders, more preferred is a zeolite-based carrier carrying copper and ruthenium or rhodium. The catalyst for decomposing nitrous oxide according to the present invention can be molded into various shapes such as a spherical shape by a conventionally known molding method. Furthermore, by molding only the above-mentioned acidic carrier,
The component and the second component may be impregnated after molding. Further, the above-mentioned catalyst powder may be wash-coated on a separately formed ceramic carrier, ceramic fiber base material, cordierite honeycomb, or the like. or,
At the time of molding, a molding aid, an inorganic fiber, an organic binder and the like may be appropriately mixed. The optimum temperature at which the catalyst for decomposing nitrous oxide according to the present invention is active with respect to N ₂ O varies depending on the catalyst species, but is usually 300 ° C to 600 ° C. In this temperature range, the space velocity (SV ) 500-50
It is preferable to let the exhaust gas flow at about 0000. A more suitable operating temperature range is 400 ° C to 500 ° C.

EXAMPLES The present invention will be described in more detail based on the following examples, but the invention is not intended to be limited to the following examples, and various modifications may be made without departing from the scope of the invention. Is possible. (I), Preparation of Catalyst Example 1 SiO ₂ / Al ₂ O ₃ molar ratio was 19.5, SiO ₂ / N
200 g of H-type mordenite (HM-23, manufactured by Nippon Kagaku Co., Ltd.) having an a ₂ O molar ratio of 165 was immersed in 2 l of water, and CuSO
₄ Aqueous solution to make CuO 10g, RuC
The l ₃ aqueous solution was added to a 0.2g as Ru,
Stir for 30 minutes. It was then neutralized with (1 + 1) NH ₄ OH until pH = 7. This slurry was filtered off, washed thoroughly with water, and dried at 100 ° C. for 8 hours. The obtained powder was lightly crushed and immersed in a 5% hydrazine solution for 10 minutes to reduce the powder. This slurry is filtered, washed with water and then at 100 ° C.
At 8 ° C for 8 hours, then calcination at 500 ° C for 4 hours.
A mordenite powder containing 4.91% and 0.095% of uO and Ru was obtained. In addition, these analyzes were based on the atomic absorption method. Next, 100 g of this powder is added to 100 g of water.
g was added, the mixture was pulverized with a ball mill for 10 minutes, and the viscosity was adjusted with water to obtain a washcoat slurry. Using this slurry, a catalyst powder was supported on a 7 mm pitch cordierite honeycomb. The coat amount at this time is 0.
It was 12 g / cc. Example 2 In Example 1, instead of the CuSO ₄ aqueous solution, Fe was used.
(NO ₃ ) ₃ solution was prepared in the same manner as in Example 1, except that
Fe ₂ O ₃ and Ru were 4.93% and 0.09, respectively.
A mordenite powder containing 1% was obtained. Hereinafter, Example 1
A honeycomb catalyst was obtained in the same manner as above, but the coating amount at this time was 0.122 g / cc. Example 3 In Example 1, instead of CuSO ₄ aqueous solution, Co
In the same manner as in Example 1 except that a (NO ₃ ) ₂ solution was used,
CoO and Ru are 4.92% and 0.093%, respectively
A mordenite powder containing was obtained. Thereafter, a honeycomb catalyst was obtained in the same manner as in Example 1, but the coating amount at this time was 0.131 g / cc. Example 4 In Example 1, the CuSO ₄ aqueous solution was replaced with Ni.
In the same manner as in Example 1 except that a (NO ₃ ) ₂ solution was used,
NiO and Ru are 4.91% and 0.091%, respectively
A mordenite powder containing 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 5 In Example 1, instead of the RuCl ₃ aqueous solution, RhC
except that the l ₃ aqueous solution in the same manner as in Example 1, CuO
A mordenite powder containing 4.92% and Ru of 0.011% was obtained. Hereinafter, a honeycomb catalyst was obtained in the same manner as in Example 1, but the coating amount was 0.1
It was 31 g / cc. Example 6 In Example 1, instead of the RuCl ₃ aqueous solution, RhC
except that the l ₃ aqueous solution in the same manner as in Example 1, CuO
A mordenite powder containing 4.95% and Ru of 0.048% was obtained. Hereinafter, a honeycomb catalyst was obtained in the same manner as in Example 1, but the coating amount was 0.1
It was 33 g / cc. Example 7 In Example 1, PdC was used instead of RuCl ₃ aqueous solution.
except that the l ₃ aqueous solution in the same manner as in Example 1, CuO
Thus, a mordenite powder containing 4.95% and Pd of 0.093% was obtained. Hereinafter, a honeycomb catalyst was obtained in the same manner as in Example 1, but the coating amount was 0.1
It was 26 g / cc. Example 8 In Example 1, instead of the RuCl ₃ aqueous solution, the ReC
except that the l ₃ aqueous solution in the same manner as in Example 1, CuO
A mordenite powder containing 4.95% and 0.095% Re was obtained. Hereinafter, a honeycomb catalyst was obtained in the same manner as in Example 1, but the coating amount was 0.1
It was 23 g / cc. Example 9 In Example 1, instead of the RuCl ₃ aqueous solution, OsC was added.
except that the l ₃ aqueous solution in the same manner as in Example 1, CuO
A mordenite powder containing 4.96% and Os of 0.095% was obtained. Hereinafter, a honeycomb catalyst was obtained in the same manner as in Example 1, but the coating amount was 0.1
It was 21 g / cc. Example 10 In Example 1, instead of the RuCl ₃ aqueous solution, IrC was used.
except that the l ₄ solution in the same manner as in Example 1, CuO
A mordenite powder containing 4.95% and 0.089% of Ir was obtained. Hereinafter, a honeycomb catalyst was obtained in the same manner as in Example 1, but the coating amount was 0.1
It was 33 g / cc. Example 11 In Example 1, H ₂ P was used instead of the RuCl ₃ aqueous solution.
C in the same manner as in Example 1 except that a tCl ₆ aqueous solution was used.
A mordenite powder containing 4.95% uO and 0.095% Pt was obtained. Hereinafter, a honeycomb catalyst was obtained in the same manner as in Example 1, but the coating amount at this time was 0.133 g / cc. Example 12 In Example 1, instead of HM23, a specific surface area of 110
Example 1 except that m ² / g of anatase type TiO ₂ was used.
In the same manner as described above, CuO and Ru are each 4.96%,
A TiO ₂ 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 13 In Example 1, the CuSO ₄ aqueous solution was used as CuO to obtain 6
Cu was prepared in the same manner as in Example 1 except that g was changed to g.
A mordenite powder containing O and Ru at 2.95% and 0.094% 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.
It was 126 g / cc. Example 14 In Example 1, the CuSO ₄ aqueous solution was used as CuO to obtain 2
C in the same manner as in Example 1 except that the amount is 0 g.
A mordenite powder containing 9.92% and 0.095% of uO and Ru 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 15 In Example 1, the RuCl ₃ aqueous solution was used as Ru to give a value of 0.
C in the same manner as in Example 1 except that the weight is 4 g.
A mordenite powder containing 4.95% and 0.193% of uO and Ru was obtained. Hereinafter, 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. Example 16 In Example 1, the RuCl ₃ aqueous solution was used as Ru to give a value of 0.
C, in the same manner as in Example 1 except that the amount was 1 g.
A mordenite powder containing 4.95% uO and 0.048% Ru 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, the RuCl ₃ aqueous solution was not added,
A mordenite powder containing 4.96% CuO was obtained.
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 A mordenite powder containing 2.95% CuO was obtained without adding the RuCl ₃ aqueous solution in Example 13. A honeycomb catalyst was obtained in the same manner as in Example 1 below.
The coating amount at this time was 0.131 g / cc. Comparative Example 3 A mordenite powder containing 9.95% CuO was obtained without adding the RuCl ₃ aqueous solution in Example 14. A honeycomb catalyst was obtained in the same manner as in Example 1 below.
The coating amount at this time was 0.131 g / cc. Comparative Example 4 In Example 12, a TiO ₂ powder containing 4.95% CuO was obtained without adding the RuCl ₃ aqueous solution.
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 16 and Comparative Examples 1 to 4 were catalytically decomposed with a nitrous oxide-containing gas by using a normal pressure flow reactor under the following test conditions. the conversion to N ₂ of nitrogen oxide was calculated by quantifying the N ₂ by gas chromatography. Test conditions , gas composition N ₂ O 50 ppm O ₂ 5% H ₂ O 2% He balance, space velocity 5000 Hr ¹ , reaction temperature 300 ° C., 400 ° C., 500 ° C. Results are shown in Table 1.

As described in detail above, the catalyst for decomposing nitrous oxide according to the present invention can efficiently catalytically decompose nitrous oxide in exhaust gas even at a relatively high temperature,
Further, it has an excellent peculiarity such that it is not easily affected by the presence of exhaust gas.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Masafumi Yoshimoto 5-1, Ebishimacho, Sakai City, Osaka Prefecture Sakai Chemical Industry Co., Ltd.

Claims (1)

[Claims] 1. Copper (C) as a first component in an acidic carrier
u), iron (Fe), cobalt (Co), nickel (N
at least one metal or metal oxide selected from i) and, as the second component, ruthenium (Ru), rhodium (Rh), palladium (Pd) rhenium (R
e), osmium (Os), iridium (Ir), platinum (Pt), at least one or more noble metals selected from the above, a catalyst for decomposing nitrous oxide.