JP3219613B2 - Ammonia decomposition catalyst and method for decomposing and removing ammonia - 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 ammonia contained in various exhaust gases and the like into harmless nitrogen and a method for decomposing and removing ammonia using the catalyst.

[0002]

2. Description of the Related Art Ammonia is used in a wide variety of fields such as raw materials for producing fertilizers and nitric acid, refrigerants, and reducing agents for removing nitrogen oxides from exhaust gas. Therefore, a large amount of ammonia is discharged from various chemical manufacturing plants, a waste treatment plant such as a refrigerator, or a combustion exhaust gas treatment facility. Ammonia is a gas having a peculiar pungent odor, and its release into the atmosphere must be minimized. However, in many places, such as the production of ammonia due to the decay of organisms, the emission of ammonia from refrigerants in waste, and the release of ammonia used for the reduction of nitrogen oxides in flue gas without being reacted to the atmosphere At present, ammonia is released to the atmosphere.

[0003]

As one of the methods for preventing the release of ammonia into the atmosphere, ammonia is made harmless by the following reaction formula using a catalyst in which iron oxide or nickel oxide is supported on an alumina or silica-alumina carrier. There is known a method of decomposing into nitrogen.

2NH ₃ + 3 / 2O ₂ → N ₂ + 3H ₂ O However, the conventional catalyst has poor reaction activity at a low temperature of 400 ° C. or lower, and further has NO, Generation of NO ₂ , N ₂ O and the like was recognized, and there was a possibility that air pollution would newly occur.

Embedded image 2NH ₃ + 5 / 2O ₂ → 2NO + 3H ₂ O 2NH ₃ + 7 / 2O ₂ → 2NO ₂ + 3H ₂ O 2NH ₃ + 2O ₂ → N ₂ O + 3H ₂ O

An object of the present invention is to solve the above-mentioned problems of the prior art, and to minimize the by-product of nitrogen oxides, which cause air pollution, and to decompose and remove ammonia with a high yield. And a method for decomposing and removing ammonia using the same catalyst.

[0005]

According to the present invention, at least one oxide of an element selected from the group consisting of vanadium, tungsten and molybdenum and platinum and / or iridium are supported on a titanium oxide carrier. A method for decomposing and removing ammonia from an ammonia-containing gas, comprising contacting an ammonia-containing gas with the ammonia decomposition catalyst described above.

[0006] The catalyst of the present invention is selected from the group consisting of platinum and / or iridium having excellent ammonia decomposition activity on a titanium oxide carrier and vanadium, tungsten and molybdenum having excellent denitration activity when ammonia is used as a reducing agent. It is composed of an oxide of at least one selected element. Each reaction formula is as follows.

Embedded image 2NH ₃ + 5 / 2O ₂ → 2NO + 3H ₂ O 4NH ₃ + 4NO + O ₂ → 4N ₂ + 6H ₂ O

That is, the formula is platinum and / or iridium.
Has high activity in the low temperature range around 300 ° C,
Titanium oxide and vanadium, tungsten and
At least one selected from the group consisting of molybdenum and molybdenum
Oxides of the above elements have high activity. That is, the expression
If the reaction of the formula can proceed sequentially,
Monia selectively N_TwoCan be decomposed into White
Gold and / or iridium can be impregnated with various carriers by impregnation, etc.
High NH _ThreeShows decomposition activity, especially denitration
Titania (TiO 2) used as a medium_Two) On the carrier
Shows sufficient activity. Vanadium, tungsten and
At least one element selected from the group consisting of molybdenum and molybdenum
Oxides are usually used as denitration catalysts,
V on the carrier_TwoO_Five, WO_Three, MoO_ThreeOne or more of
Is supported by an impregnation method or a coprecipitation method.

[0008]

The above catalyst is preferably used as a honeycomb by a wash coat method or a solid method using a binder component such as titania sol, alumina sol, silica sol or the like or a base material such as cordierite, if necessary. By bringing the gas containing ammonia into contact with the catalyst at a temperature of 100 to 600 ° C., the ammonia in the gas is mainly decomposed into nitrogen. This decomposition reaction proceeds selectively, and N
Hazardous gases such as O, NO ₂ and N ₂ O are hardly produced as by-products. Further, the present catalyst maintains a stable ammonia decomposition performance without reducing the ammonia decomposition activity even in an exhaust gas in which SO ₂ coexists. Further, since the ability to oxidize SO ₂ to SO ₃ is low, there is no problem in producing acidic ammonium sulfate.

[0009]

EXAMPLES Hereinafter, the catalyst and the method for decomposing and removing ammonia of the present invention will be described in detail with reference to examples.

(Example 1) On a titania (TiO ₂ ) carrier, ammonium metavanadate (NH ₄ VO ₃ ), ammonium paratungstate {(NH ₄ ) ₁₀ H ₁₀ W ₁₂ O _46.6
H ₂ O｝ is dissolved in a 10% aqueous solution of methylamine.
4 wt% of ₂ O ₅ and 8 wt% of WO ₃ were supported by impregnation, evaporated, dried and calcined at 500 ° C. for 6 hours to obtain a powdered catalyst. Further, this powder catalyst was impregnated with an iridium chloride (IrCl ₄ .H ₂ O) aqueous solution to reduce Ir to 0.5%.
wt%, and evaporated and dried, and then calcined at 500 ° C. for 6 hours to obtain a powder catalyst 1.

For 100 parts of the obtained powder catalyst, 40 parts of titania sol as a binder (TiO ₂ : 20 wt%)
Then, 200 parts of water and 200 parts of water were added thereto, and the slurry was wash-coated on a 7.6 mm pitch, wall thickness cordierite honeycomb substrate to carry a coating amount of 200 g / m ² per substrate surface area. The obtained catalyst is referred to as “honeycomb catalyst 1”.

(Example 2) In the preparation method of the honeycomb catalyst 1 described above, V
5% by weight of ₂ O ₅ supported and 9% by weight of WO ₃ supported
Other than that, the honeycomb catalyst 2 was prepared in the same manner as in Example 1 and
I got

Further, in the above-mentioned method for preparing the honeycomb catalyst 1, MoO ₃ was replaced by ammonium molybdate {(NH ₄ ) ₂ MoO ₄ } instead of ammonium paratungstate.
The honeycomb catalyst 3 was prepared in the same manner as in Example 1 except that the catalyst was supported by 8 wt%.

Further, a honeycomb catalyst was prepared in the same manner as in Example 1 except that chloroplatinic acid was used in place of the iridium chloride aqueous solution and 0.05% by weight of platinum was supported (Pt). A honeycomb catalyst 4 was obtained.

In addition, a honeycomb catalyst 5 was obtained in the same manner as in Example 1, except that ammonium paratungstate was not used.

(Example 3) In the preparation method of the above-mentioned honeycomb catalyst 1, ammonium metavanadate, ammonium paratungstate and iridium chloride were simultaneously dissolved in a methylamine aqueous solution on a titania carrier, and V ₂ O ₅ , WO ₃ , I
The mixture was impregnated with rO ₂ and calcined at the same composition as in Example 1 to obtain a powder catalyst 6 and a honeycomb catalyst 6.

(Example 4) 40 mm × 50 mm × 150 mm
Three L ammonia decomposition catalysts were installed in series, and a reaction test was performed. The experimental conditions are as shown in Table 1 below.

[0018]

[Table 1]

The performance was evaluated by measuring the ammonia decomposition rate, NOx (NO, NO ₂ , N ₂ O) production rate and SO ₂ oxidation rate in the initial state of the reaction. The ammonia decomposition rate and the NOx generation rate were determined by the following equations.

〇 Ammonia decomposition rate (%) = [(Inlet N
H ₃ -outlet NH ₃ ) / inlet NH ₃ ] × 100

〇 NOx generation rate (%) = [outlet (N ₂ O
× 2 + NO + NO ₂ ) / Inlet NH ₃ ] × 100

酸化 SO ₂ oxidation rate (%) = [outlet SO ₃ /
Inlet SO ₂ ] × 100

The results are shown in Table 2 below. In the ammonia decomposition method using the present invention denitration catalyst, the ammonia decomposition rate is about 90%, NOx formation rate is 2 to 3%, SO ₂ oxidation rate was confirmed to have about 1% and both high performance.

[0024]

[Table 2]

Example 5 Example 4 using honeycomb catalysts 1 to 5
A durability evaluation test was performed by passing gas for 3,000 hours under the same conditions as described above. Table 3 shows the results. Almost Table 2 the same ammonia decomposition rate even after supply 3000 hours the gas conditions, maintains the NOx generation rate and SO ₂ oxidation rate, it was confirmed that excellent catalysts in durability.

[0026]

[Table 3]

[0027]

According to the present invention, oxidation of SO ₂ and NOx
And other by-products can be suppressed as much as possible to decompose ammonia into harmless nitrogen. Such a decomposition treatment method has not been available in the past, and its industrial utility value is extremely large.

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int. Cl. ⁷ , DB name) B01J 21/00-38/74 B01D 53/86 B01D 53/94

Claims (2)

(57) [Claims] Ammonia characterized in that at least one oxide of an element selected from the group consisting of vanadium, tungsten and molybdenum and platinum and / or iridium are supported on a titanium oxide carrier. Cracking catalyst. 2. A method for decomposing and removing ammonia from an ammonia-containing gas, comprising bringing the ammonia-containing gas into contact with the ammonia decomposition catalyst according to claim 1.