JP3221115B2 - 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 in 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. However, in all of these methods, treatment of N ₂ O in 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 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 aforementioned 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 O are produced from garbage incinerators, sewage sludge incinerators, and the like. In addition, in recent years, N ₂ O has become CO ₂ , Freon, CH
Along with _4, etc., it has been particularly noted as a global pollutant that causes the destruction of the ozone layer in the stratosphere or a temperature increase due to the greenhouse effect.

[0004] 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.

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 which can efficiently decompose N ₂ O and has excellent simultaneous durability.

[0006]

In order to achieve the above object, a catalyst for decomposing nitrous oxide according to the present invention comprises α-Al ₂ O
₃ , ruthenium (Ru), rhodium (Rh), rhenium (Re), osmium (Os), iridium (Ir)
At least one noble metal selected from the group consisting of:

In the present invention, α-Al ₂ O ₃ includes
For example, spherical α-A of Fujimi Incorporated
l ₂ O ₃ , AM-S31, AM-S32, AM-S3
3, AM-S34 and powdered α-Al ₂ O manufactured by Sumitomo Chemical
₃ , A-26, AMS-2, AMS-9, AMS-12
And the like. Alternatively, Sumitomo Chemical's spherical activated alumina KHD-24 (-46), NKH
D-24 (-46) at 1200 ° C to 1300 ° C
It can also be obtained by baking for up to 5 hours.

The catalyst according to the present invention can be prepared, for example, by the following method. Α-Al ₂ O described above
₃ is immersed in an aqueous solution of chloride such as Ru, Rh, Re, Os, Ir for a certain period of time, impregnated with these noble metals, dried, reduced with hydrazine, dried, and dried at 400 ° C. to 50 ° C.
Bake at 0 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 R
h, Ru, Ir and the like.

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, the above-mentioned α-A
molded only l ₂ O _3, it may be impregnated precious metal, etc. 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.

[0011]

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 shape of Fujimi Incorporated having a particle size of ² mm to 4 mm, a specific surface area of 6.0 m ² / g, a pore volume of 0.33 ml / g, an average pore diameter of 1350 ° and a water absorption of 33%. α-
Al ₂ O ₃ and AM-S34 were immersed in an aqueous solution of RhCl ₃ and impregnated so as to have a Rh content of 1.5 wt%. After blowing off excess water, the resultant was dried at 100 ° C. for 2 hours.
Next, this is immersed in a 5% hydrazine solution until no bubbles are generated, reduced, blown off excess water, dried at 100 ° C. for 2 hours, and further baked at 500 ° C. for 4 hours to reduce Rh. A 0.5 wt% supported spherical catalyst was obtained.

Example 2 In Example 1, RuC3 aqueous solution was used instead of RuCl ₃ aqueous solution.
except that the l ₃ aqueous solution in the same manner as in Example 1, to obtain a spherical catalyst 1.5 wt% carries a Ru.

Example 3 The procedure of Example 1 was repeated, except that the aqueous solution of RhCl ₃ was replaced with ReC
except that the l ₃ aqueous solution in the same manner as in Example 1 to obtain a 1.5 wt% loaded with spherical catalyst with Re.

Example 4 In Example 1, OsC was replaced with RhCl ₃ aqueous solution.
except that the l ₃ aqueous solution in the same manner as in Example 1 to obtain a 1.5 wt% loaded with spherical catalyst with Os.

Example 5 The procedure of Example 1 was repeated, except that the aqueous solution of IrCl ₃ was replaced with IrC 3.
except that the l ₃ aqueous solution in the same manner as in Example 1 to obtain a 1.5 wt% loaded with spherical catalyst with Ir.

Example 6 In the same manner as in Example 1, except that the concentration of the aqueous RhCl ₃ solution was increased to 2/3 times, the Rh was reduced to 1.0 watt.
t%, a supported spherical catalyst was obtained.

Example 7 Rh was reduced to 0.75 in the same manner as in Example 1 except that the concentration of the RhCl ₃ aqueous solution was reduced by half.
By weight, a supported spherical catalyst was obtained.

Example 8 The procedure of Example 1 was repeated except that Fujimi Incorporated Co., Ltd.
Α-Al ₂ O ₃ , AM-S34
m-4mm spherical activated alumina KHD-2 manufactured by Sumitomo Chemical
4 was calcined at 1200 ° C. for 5 hours.
Rh in the same manner as in Example 1 except that α-Al ₂ O ₃ having m ² / g, a pore volume of 0.32 ml / g, and a water absorption of 32% was used.
Was obtained at 1.5 wt%.

Example 9 Powdered α-A manufactured by Sumitomo Chemical Co., Ltd. having an average particle size of 1.1 μm
l ₂ O ₃ and AMS-2 were immersed and impregnated in an aqueous RhCl ₃ solution prepared to be 1.5 wt% as Rh. While thoroughly mixing using a mortar, the mixture was carefully dried on hot water at 100 ° C. Further, after drying at 100 ° C. for 2 hours, it was immersed in a 5% hydrazine solution and reduced. This is filtered and dried, and calcined at 500 ° C. for 4 hours.
h-treated α-Al ₂ O ₃ powder was obtained.

Next, a part of this powder was passed through a sieve using an alumina sol as a binder and passed through a sieve to obtain a powder of about 1 mm.
Was obtained. Using this as a core, the remaining powder was passed through a tumbling granulator using the same alumina sol as a binder, and passed through a sieve to obtain a spherical product having a particle size of 2 mm to 4 mm. These granules were dried at 100 ° C. for 5 hours and then calcined at 500 ° C. for 4 hours to obtain a spherical catalyst carrying 1.5 wt% of Rh.

Comparative Example 1 In Example 1, Fujimi Incorporated Co., Ltd.
Α-Al ₂ O ₃ , AM-S34, and the particle size is 2
mm-4 mm, pore volume 0.38 ml / g, water absorption 48
% Of spherical activated alumina (γ-Al ₂ ) manufactured by Sumitomo Chemical Co., Ltd.
Except that the O ₃₎ KHD-24 was obtained with 1.5 wt% loaded with spherical catalyst of Rh in the same manner as in Example 1.

(II), Evaluation Test The catalysts obtained in Examples 1 to 9 and Comparative Example 1 were subjected to catalytic cracking of a nitrous oxide-containing gas using a normal pressure flow reactor under the following test conditions. the conversion to nitrous oxide content of N ₂ 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 250 ° C., 300 ° C., 350 ° C., 400 ° C. The results are shown in Table 1.

[0024]

[0025]

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.

Continuation of the front page (51) Int.Cl. ⁷ Identification symbol FI B01D 53/36 102B (56) References JP-A-57-87837 (JP, A) JP-A-4-156921 (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] (1) Ruthenium (Ru), α-Al ₂ O ₃
Rhodium (Rh), rhenium (Re), male Mi Umm (O
s), a catalyst for decomposing nitrous oxide, which carries at least one or more noble metals selected from iridium (Ir) in an amount of 0.3 to 2 Wt% (% by weight) and is used in the presence of oxygen.