JP3221110B2 - 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 a relatively high concentration of N ₂ O is produced from a garbage incinerator or a sewage sludge incinerator. I have. 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. In order to solve such problems, the present inventors have already applied for a method of supporting various noble metals such as ruthenium or rhodium on a hydrophobic carrier (Heisei 4).
May 26). However, even with such a method, among the noble metals, Ru and Rh have an extremely high activity at first, but have a weak point such that they change over time during the reaction, resulting in a decrease in activity. Was.

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]

Means for Solving the Problems To achieve the above object, the catalyst for decomposing nitrous oxide according to the present invention comprises silica gel,
(A) at least one or more noble metals selected from ruthenium (Ru) and rhodium (Rh), and (b) N
b ₂ O _{5, TiO 2,} made by supporting the at least one oxide selected from ZrO _2.

The nitrous oxide decomposition catalyst 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 fine powders 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 or Rh, etc. for a certain period of time, impregnated with these noble metals, dried and then further dipped in an aqueous solution, such as niobium chloride, titanium sulfate or zirconyl nitrate, for a certain period of time. After impregnating the body and drying, firing at 300-500 ° C. for 3-5 hours,
Further, a reduction treatment is performed at 400 ° C. to 500 ° C. for 3 to 5 hours in a stream of H ₂ . 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. If the content is less than 0.3 wt%, these effects are not sufficiently exhibited, and even if the content exceeds 2 wt%, the activity corresponding to the improvement cannot be obtained. or,
Preferred loading amount of TiO _{2, Nb} 2 _O 5, an oxide such as ZrO ₂ is 5 to 20 wt% as oxide. 5wt
%, These effects are not sufficiently exerted, and the effect of 20%
Exceeding the wt% is not preferred because the hydrophobicity of the carrier is reduced.

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. Further, only the above-described hydrophobic carrier may be molded, and a precious metal or the like 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.

[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 Spherical activated alumina NKHD- manufactured by Sumitomo Chemical having a particle size of 2 mm to 4 mm, a pore volume of 0.65 ml / g, and a water absorption of 78%.
24 was immersed in an aqueous RhCl ₃ solution, and Rh was 1.5
It was impregnated so as to be wt%. After blowing off excess water, the resultant was dried at 100 ° C. for 2 hours. Next, this is immersed in an aqueous solution of niobium chloride (NbCl ₅ ) in hydrochloric acid, and Nb ₂ O ₆
5 wt%. After blowing off excess water, dry at 100 ° C for 2 hours,
It was baked at 0 ° C. for 2 hours. Next, they are placed in a stream of H ₂ for 40 minutes.
Reduction treatment was performed at 0 ° C. for 2 hours to obtain a catalyst in which 1.5 wt% of Rh and ₅ wt% of Nb ₂ O ₅ were supported on a spherical alumina carrier.

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, 1.5 wt% of Ru in spherical alumina carrier, a _Nb 2 _{O 5} 5 wt
% Supported catalyst was obtained.

Example 3 In Example 1, a RuC ₃ aqueous solution was used instead of RuCl ₃ aqueous solution.
and l ₃ aqueous solution, instead of the aqueous solution of hydrochloric acid niobium chloride (NbCl _5), nitric oxide aqueous solution of zirconium (ZrO (N
O ₃₎ except that the ₂ · _{2H 2} O) in the same manner as in Example 1, 1.5 wt% of Ru in spherical alumina support, ZrO ₂
Was obtained at 5 wt%.

Example 4 In Example 3, zirconium nitrate oxide (ZrO (N
_{O 3) 2 · 2H 2 O} ) except that twice the concentration of the aqueous solution, in the same manner as in Example 3, 1.5 wt% of Ru spherical alumina support, to obtain a catalyst of ZrO ₂ carrying 10 wt% .

Example 5 In Example 3, zirconium nitrate oxide (ZrO (N
_{O 3) 2 · 2H 2 O} ) except that the 3-fold the concentration of the aqueous solution, in the same manner as in Example 3, 1.5% Ru spherical alumina support, to obtain a catalyst of ZrO ₂ carrying 5 wt% .

Example 6 The procedure of Example 3 was repeated, except that the spherical activated alumina NKHD-24 was replaced with a particle size of 2 mm to 4 mm and a pore volume of 1.05 ml.
/ G, an average pore diameter of 500 °, and a water absorption of 111%, except that a spherical silica carrier CARIACT-50 manufactured by Fuji Devison Chemical Co., Ltd. was used.
A catalyst supporting 1.5 wt% and 5 wt% of ZrO ₂ was obtained.

Example 7 Fine powdery synthetic silica SYLOID manufactured by Fuji Devison Chemical having an average particle size of 2.5 μm and a pore volume of 1.25 ml / g
978 was re-pulped in water. Zirconium nitrate (ZrO (NO ₃ ) ₂ .2H) is added to the slurry so that ZrO ₂ becomes 5 wt% with respect to SYLOID-978I.
It was added ₂ O) aqueous solution, 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 ZrO ₂ -supported synthetic silica powder. Next, one part of this powder was passed through a granulator using a silica sol as a binder and passed through a sieve to obtain a granular material of about 1 mm. Using this as a nucleus, the remaining powder was passed through a tumbling granulator using the same silica sol as a binder, and passed through a sieve to obtain a spherical granulated product having a particle size of 2 mm to 4 mm. These granules were dried at 100 ° C. for 5 hours and fired at 500 ° C. for 4 hours. Next, this was immersed in an aqueous RuCl ₃ solution, and impregnated so as to be 1.5 wt% as Ru. After blowing off the excess water, firing was performed at 100 ° C. for 2 hours. Then. These were subjected to a reduction treatment at 400 ° C. for 2 hours in a stream of H ₂ , and 1.5% by weight of Ru was added to the spherical silica support.
A catalyst supporting 5 wt% of rO ₂ was obtained.

Comparative Example 1 In Example 1, Nb ₂ O ₅ was not impregnated and supported,
_A reduction treatment was carried out at 400 ° C. for 2 hours in _two air streams to obtain a catalyst in which 1.5 wt% of Rh alone was supported on a spherical alumina carrier.

Comparative Example 2 In Example 2, Nb ₂ O ₅ was not impregnated and supported,
_The catalyst was reduced at 400 ° C. for 2 hours in _two air streams to obtain a catalyst in which 1.5 wt% of Ru alone was supported on a spherical alumina carrier.

(II) Measurement of water adsorption amount The catalysts obtained in Examples 1 to 7 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 7 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. 1 hour after the start of the reaction,
The nitrous oxide decomposition rates after 0 hour and 100 hours were measured. Incidentally, nitrite nitrogen decomposition rate was calculated by quantifying the N ₂ by gas chromatography a conversion to N ₂ of nitrous oxide.

Test conditions Table 1 shows the results.

[0024]

[0025]

As described in detail above, the nitrous oxide decomposing catalyst according to the present invention can efficiently decompose nitrous oxide in exhaust gas, and at the same time, it hardly changes over time. Has an excellent specific effect.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-2-144147 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) B01J 21/00-38/74 B01D 53 / 86 B01D 53/94

Claims (1)

(57) [Claims] 1. The method of claim 1, wherein the hydrophobic carrier comprises (a) ruthenium (R)
u), at least one selected from rhodium (Rh)
0.3 to 2 Wt% (% by weight) , and (b) Nb ₂ O ₅ ,
At least one selected from ZrO ₂ 5 to 20 wt%
(Wt%) A catalyst for decomposing nitrous oxide, which is supported.