JP3221071B2 - Catalyst for decomposition of nitrous oxide - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION This invention, nitrogen oxides in the exhaust gas, especially relates to a decomposition catalyst for removing nitrous oxide (N 2 _O), details plants, automobiles, garbage incinerators, sewage sludge incinerators, etc. 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 waste treatment facilities.

[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 regulations are conventionally required are mainly nitrogen monoxide (NO) and nitrogen dioxide (NO ₂ ). 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 from exhaust gas using hydrocarbons, zeolite supporting a metal such as copper, or a metal oxide such as alumina as a catalyst and a gas containing NO in the coexistence of hydrocarbons are used. A method of contacting has been proposed.

[0003] In any of these methods, however, the treatment of N ₂ O in exhaust gas is not impossible, but not sufficient. Conventionally, these have been discharged without treatment in the downstream of the aforementioned denitration equipment. This is related to the fact that there have been no legally regulated values for N ₂ O and that no official measurement method such as JIS has been established so far. However, it was a reality that the subject of denitration had been ignored.

However, in the above-described denitration method,
It has been recognized that N ₂ O is produced depending on the operating conditions, and it has recently been reported that relatively high concentrations of N _{2 are} produced from garbage incinerators, sewage sludge incinerators and the like. In addition, in recent years, N ₂ O, together with CO ₂ , CFCs, CH _{4, and the} like, has been particularly attracting attention as a global pollutant that causes the destruction of the ozone layer in the stratosphere or a temperature increase due to the greenhouse effect.

[0005] Under these circumstances, there has been increasing interest in a method of treating N ₂ O, particularly a decomposition catalyst thereof, 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.

[0006] The present invention has been made in view of such a situation, and an object of the present invention is to provide N ₂ O in exhaust gas.
It is an object of the present invention to provide an N ₂ O decomposition catalyst capable of efficiently decomposing N ₂ O.

[0007]

Means for Solving the Problems To achieve the above object, the catalyst for decomposing nitrous oxide according to the present invention comprises silica gel,
On a hydrophobic carrier such as activated alumina or silica-alumina, ruthenium (Ru), palladium (Pd), rhenium (Re), osmium (Os), iridium (I
r) and at least one noble metal selected from platinum (Pt).

The catalyst for decomposing nitrous oxide according to the present invention is prepared, for example, as follows. That is, the hydrophobic carrier in the present invention does not exhibit the ability to adsorb moisture in the temperature range in which it is used, or has a very small amount of adsorption. This water adsorption capacity can be determined by analyzing a TG-DTA curve of a sample in which water is saturated and adsorbed at room temperature. Examples of such a hydrophobic carrier include fine powder synthetic silica manufactured by Fuji Devison Chemical, SYLOID 978, 308, and 25.
5. Spherical silica gel CA also manufactured by Fuji Devison Chemical
RIACT10, 15, 15, 30, 50, and spherical activated alumina KHD-24 (-46) and NK manufactured by Sumitomo Chemical Co., Ltd.
HD-24 (-46) and the like. Alternatively, a precipitate is formed by a method of neutralizing or hydrolyzing a solution obtained by homogeneously mixing a water-soluble salt such as a soda salt or an alcohol solution of an alkoxide, and then drying, firing after repeating filtration, washing, and reparbing. By that, respectively, silica gel, alumina or also
It is also possible to prepare a fine powder such as silica-alumina.

The catalyst according to the present invention can be prepared, for example, by the following method. The above-mentioned hydrophobic carrier is represented by R
u, Pd, Re, Os, Ir, Pt, etc., immersed in an aqueous solution of a chloride of a noble metal for a certain period of time, impregnated with the noble metal, dried, reduced with humanrazine, dried, and dried at 400 ° C. to 50 ° C.
Bake at 0 ° C for 3-5 hours. As described above, the catalyst according to the present invention is obtained, and the preferable amount of the noble metal to be supported is 0.3 to 2% by weight as the metal. 0.3wt%
Below, these effects are not fully exhibited, and 2 wt.
%, The activity was not sufficiently improved. Of these noble metals, more preferred is Ru
Met.

The catalyst for decomposing nitrous oxide according to the present invention can be formed into various shapes such as a honeycomb spherical shape by a conventionally known forming method. Furthermore, only the above-mentioned hydrophobic carrier may be molded, and the precious metal 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. Further, at the time of molding, a molding aid, an inorganic fiber, an organic binder and the like may be appropriately compounded.

The catalyst for decomposing nitrous oxide according to the present invention comprises N
_The optimum temperature at which activity is exhibited with respect to ₂ O varies depending on the type of catalyst, but is usually 200 ° C to 600 ° C. In this temperature range, exhaust gas can be passed at a space velocity (SV) of about 500 to 500,000. preferable. Note that a more preferable use temperature range is 300 ° C to 500 ° C.

[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 A spherical silica CARIACT50 manufactured by Fuji Devison Chemical Co., Ltd., having a particle size of 2 mm to 4 mm, a pore volume of 1.05 ml / g, an average pore diameter of 500 °, and a water absorption of 111%, was immersed in an aqueous RuCl ₃ solution. Impregnation was performed so that Ru was 0.5 wt%. After blowing off excess water, the resultant was dried at 100 ° C. for 2 hours. Next, this was immersed in a 5% hydrazine solution until no air bubbles appeared, reduced, blown off excess water, dried at 100 ° C. for 2 hours, and further dried at 500 ° C.
Calcination was carried out at 4 ° C. for 4 hours to obtain a spherical catalyst carrying 0.5 wt% of Ru.

Example 2 In Example 1, PdC was used instead of the RuCl ₃ aqueous solution.
except that the l ₃ aqueous solution in the same manner as in Example 1 to obtain a 0.5 wt% loaded with spherical catalyst the Pd.

Example 3 The procedure of Example 1 was repeated, except that the aqueous solution of RuCl ₃ was replaced with ReC
except that the l ₃ aqueous solution in the same manner as in Example 1 to obtain a 0.5 wt% loaded with spherical catalyst with Re.

Example 4 In Example 1, OsC was used instead of the RuCl ₃ aqueous solution.
except that the l ₃ aqueous solution in the same manner as in Example 1 to obtain a 0.5 wt% loaded with spherical catalyst with Os.

Example 5 In Example 1, an IrC ₃ aqueous solution was used in place of the RuCl ₃ aqueous solution.
except that the l ₄ solution in the same manner as in Example 1 to obtain a 0.5 wt% loaded with spherical catalyst with Ir.

Example 6 In Example 1, H ₂ P was used instead of the RuCl ₃ aqueous solution.
Except that the aqueous solution of tCl ₆ was used, P
A spherical catalyst carrying 0.5 wt% of t was obtained.

Comparative Example 1 SiO ₂ / Al ₂ O ₃ molar ratio was 19.5, SiO ₂ / N
The H-type mordenite (HM-23) manufactured by Nippon Chemical Co., Ltd. having an a ₂ O molar ratio of 165 was reparved in water. In this slurry,
C so that the content of CuO is 5 wt% with respect to HM23.
The uSO ₄ solution was added and stirred for 30 minutes. Then (1+
1) Neutralized to pH 8 with NH ₄ OH.
The slurry was filtered, washed with water, dried, and calcined at 500 ° C. for 4 hours to obtain a copper-supported mordenite powder. Less than,
In the same manner as in Example 13, a spherical catalyst having a particle size of 2 mm to 4 mm and supporting 5 wt% of CuO was obtained.

Comparative Example 2 H-type mordenite (HM) manufactured by Nippon Chemical Co., Ltd.
-23) was re-pulped in water and heated to 50-60 ° C. Adding to the slurry a RhC1 ₃ aqueous solution so as to be 1.0 wt% with respect to HM-23 as Rh 2
Stirred for hours. Next, a 5% hydrazine solution was added to N ₂ H ₄ /
Ru ≒ 10 was added as a guide, and the mixture was further stirred for 1 hour. The slurry was filtered, washed with water, dried and calcined at 500 ° C. for 4 hours to obtain a Rh-supported mordenite powder. Hereinafter, a spherical catalyst having a particle diameter of 2 mm to 4 mm and carrying 1.0 wt% of Rh was obtained in the same manner as in Example 13.

(II), Measurement of water adsorption amount The catalysts obtained in Examples 1 to 6 and Comparative Examples 1 and 2 were lightly pulverized and placed in a desiccator filled with water placed in a 50 ° C. hot water tank. And left overnight for one day to adsorb water on the catalyst. This sample was taken from room temperature to 500 ° C. in a N ₂ gas flow using a SSC-5200 type thermal analysis system manufactured by Seiko Denshi Kogyo Co., Ltd.
The temperature was raised at a rate of ° C / min, and TG-DTA analysis was performed.
The amount of water adsorption at 00 ° C. was measured.

(III) Evaluation Test The catalysts obtained in Examples 1 to 6 and Comparative Examples 1 and 2 were subjected to catalytic cracking of a nitrous oxide-containing gas using a normal pressure flow reactor under the following test conditions. performed, the conversion to N ₂ of nitrous 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 0%, 2% He balance, space velocity 5000 Hr ¹ , reaction temperature 250 ° C., 350 ° C., 450 ° C., 550 ° C. The results are shown in Table 1.

[0023]

[0024]

As described above in detail, the catalyst for decomposing nitrous oxide according to the present invention can efficiently decompose nitrous oxide in exhaust gas even at a low temperature.
Even if moisture is present in the exhaust gas, it is not easily affected.
Has an excellent specific effect.

──────────────────────────────────────────────────続 き Continuation of front page (56) References JP-A-2-194818 (JP, A) JP-A-55-31463 (JP, A) JP-A-3-16641 (JP, A) JP-A-4-194 341324 (JP, A) (58) Field surveyed (Int. Cl. ⁷ , DB name) B01J 21/00-38/74 B01D 53/86 B01D 53/94

Claims (1)

(57) [Claims] To 1. A hydrophobic carrier, ruthenium (Ru), palladium (Pd), Les two um (Re), male Mi um (O
nitrous oxide characterized in that at least one noble metal selected from s), iridium (Ir) and platinum (Pt) is used in the presence of oxygen at 0.3 to 2 Wt% (wt%). Decomposition catalyst.