JPH08131832A - Ammonia decomposition catalyst and method for decomposing and removing ammonia - Google Patents

Abstract

PURPOSE: To provide a catalyst for decomposition and removal of ammonia contained in various waste gases as nitrogen and to decompose and remove ammonia with the catalyst. CONSTITUTION: One or more of oxides of V, W and Mo and Pt and/or Ir are deposited on a titanium oxide carrier to obtain the objective ammonia decomposition catalyst and ammonia in ammonia-contg. gas is decomposed and removed with the catalyst.

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 into harmless nitrogen and a method for decomposing and removing ammonia using the catalyst.

[0002]

Ammonia is used in a wide range of fields such as a raw material for producing fertilizer and nitric acid, a refrigerant, and a reducing agent for removing nitrogen oxides in exhaust gas. Therefore, a large amount of ammonia is emitted from various chemical product manufacturing plants, waste treatment plants such as refrigerators, and combustion exhaust gas treatment facilities. Ammonia is a gas with a unique irritating odor, and its release into the atmosphere must be suppressed as much as possible. However, in many places, such as the generation of ammonia due to the decay of living organisms, the emission of ammonia from the refrigerant in waste, and the ammonia used for the reduction of nitrogen oxides in flue gas, is released into the atmosphere without reaction. At present, ammonia is released into the atmosphere.

[0003]

As one of the methods for preventing the release of ammonia into the atmosphere, a catalyst in which iron oxide or nickel oxide is supported on an alumina or silica-alumina type carrier is used to make ammonia harmless according to the following reaction formula. A method of decomposing it into pure nitrogen is known.

## STR00001 ## 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 in addition to the above reaction, NO, Generation of NO ₂ , N ₂ O, etc. was recognized, and there was a possibility that air pollution would be newly generated.

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

The object of the present invention is to solve the above-mentioned problems of the prior art, to suppress by-products of nitrogen oxides that cause air pollution as much as possible, and to decompose and remove ammonia with high yield. Another object of the present invention is to provide a method for decomposing and removing ammonia using the same catalyst.

[0005]

According to the present invention, a titanium oxide carrier is loaded with at least one oxide of an element selected from the group consisting of vanadium, tungsten and molybdenum and platinum and / or iridium. And a method of decomposing and removing ammonia from an ammonia-containing gas, which comprises bringing the ammonia-containing gas into contact with the above-mentioned ammonia decomposition catalyst.

The catalyst of the present invention is composed of platinum and / or iridium having excellent decomposition activity of ammonia on a titanium oxide support, 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.

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 a high activity in the low temperature range around 300 ° C,
Body titanium oxide and vanadium, tungsten and
And at least one selected from the group consisting of molybdenum
Oxides of the above elements have high activity. That is, the formula
If the reaction of
Select Monia N₂It can be decomposed into White
Gold and / or iridium can be applied to various carriers by the impregnation method or the like.
Prepared, high NH ₃Degradation activity, especially denitrification
Titania (TiO used as a medium₂) On a carrier
It shows sufficient activity. In addition, vanadium, tungsten and
And at least one element selected from the group consisting of molybdenum
The oxide of is usually used as a denitration catalyst.
A V on the carrier₂O_Five, WO₃, MoO₃One or more of
Are supported by the impregnation method or the coprecipitation method.

[0008]

If desired, it is preferable to use a binder component such as titania sol, alumina sol, silica sol or a base material such as cordierite as the catalyst, and make a honeycomb by a wash coating method or a solid method. By bringing a gas containing ammonia into contact with the catalyst at a temperature of 100 to 600 ° C., ammonia in the gas is mainly decomposed into nitrogen. This decomposition reaction selectively progresses and N
Almost no harmful gases such as O, NO ₂ and N ₂ O are produced as by-products. Furthermore, the present catalyst maintains a stable ammonia decomposing performance without degrading the ammonia decomposing activity even in exhaust gas in which SO ₂ coexists. In addition, since the ability to oxidize SO ₂ to SO ₃ is low, there is no problem with the formation of ammonium acid sulfate.

[0009]

EXAMPLES The catalyst and the method for decomposing and removing ammonia according to the present invention will be specifically described below with reference to examples.

[0010] (Example 1) 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} with 10% methylamine aqueous solution,
4 wt% of ₂ O ₅ and 8 wt% of WO ₃ were supported by an impregnation method, evaporated and dried, and calcined at 500 ° C. for 6 hours to obtain a powder catalyst. Further, this powder catalyst is impregnated with an aqueous solution of iridium chloride (IrCl ₄ · H ₂ O) to make Ir 0.5.
The powder catalyst 1 was supported by wt%, evaporated and dried, and then calcined at 500 ° C. for 6 hours to obtain a powder catalyst 1.

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

(Example 2) In the above-mentioned method for preparing the honeycomb catalyst 1, V
₂ O ₅ loading amount is 5 wt%, WO ₃ loading amount is 9 wt%
Otherwise, prepared in the same manner as in Example 1 to prepare the honeycomb catalyst 2.
I got

In addition, in the method for preparing the honeycomb catalyst 1 described above, ammonium molybdate {(NH ₄ ) ₂ MoO ₄ } is used instead of ammonium paratungstate to prepare MoO _3.
A honeycomb catalyst 3 was prepared in the same manner as in Example 1 except that 8 wt% was loaded.

Furthermore, 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 in the above-mentioned method for preparing the honeycomb catalyst 1 and the amount of platinum supported (Pt) was 0.05 wt%. A honeycomb catalyst 4 was obtained.

In addition, a honeycomb catalyst 5 was prepared in the same manner as in Example 1 except that ammonium paratungstate was not used in the above-mentioned method for preparing the honeycomb catalyst 1.

(Example 3) In the method for preparing 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 to obtain V ₂ O ₅ , WO ₃ , and I.
The powder catalyst 6 and the honeycomb catalyst 6 were obtained by co-impregnation with rO ₂ and firing treatment with the same composition as in Example 1.

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

[0018]

[Table 1]

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

Ammonia decomposition rate (%) = [(inlet N
H ₃ −Outlet NH ₃ ) / Inlet NH ₃ ] × 100

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

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

The results are shown in Table 2 below. In the ammonia decomposing method using the denitration catalyst of the present invention, it was confirmed that the ammonia decomposing rate is about 90%, the NOx producing rate is 2 to 3%, and the SO ₂ oxidizing rate is about 1%, which are all high performance.

[0024]

[Table 2]

(Example 5) Example 4 using honeycomb catalysts 1 to 5
A durability evaluation test was conducted by passing gas under the same conditions as above for 3000 hours. Table 3 shows the results. Even after supplying for 3000 hours under the above gas conditions, the ammonia decomposition rate, the NOx production rate and the SO ₂ oxidation rate, which are almost the same as those in Table 2, were maintained, and it was confirmed that the catalyst had excellent durability.

[0026]

[Table 3]

[0027]

According to the present invention, SO ₂ oxidation and NOx
It is possible to decompose ammonia into harmless nitrogen by suppressing by-products such as. Such a decomposition treatment method has never been used before, and its industrial utility value is extremely high.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification number Office reference number FI technical display location B01J 23/652 F01N 3/10 A B01J 23/64 103 A

Claims (2)

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