JP3132960B2 - Ammonia decomposition catalyst - 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 ammonia contained in various kinds of exhaust gas into harmless nitrogen.

[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]

SUMMARY OF THE INVENTION Ammonia release to the atmosphere
Alumina or silica-alumina type
Utilize a catalyst with iron oxide or nickel oxide supported on a carrier
Decomposes ammonia into harmless nitrogen by the following reaction formula
Methods are known. 2NH_Three+ 3 / 2O_Two → N_Two+ 3H_TwoO However, in the conventional catalyst, in addition to the above reaction,
NO, NO by reaction _Two, N_TwoO and the like are recognized,
There was a risk of new air pollution. 2NH_Three+ 5 / 2O_Two → 2NO + 3H_TwoO 2NH_Three+ 7 / 2O_Two → 2NO_Two+ 3H_TwoO 2NH_Three+ 2O_Two → N_TwoO + 3H_TwoO

A catalyst having both a NOx generation function (first component) and a denitration function (second component) has been disclosed in Japanese Unexamined Patent Publication No. 5-1.
No. 46634, etc., the first component and the second component are kneaded and coexist, or the first component is supported on an upper layer of the second component, so that the ammonia is not always sufficient. No conversion to harmless N ₂ was possible. An object of the present invention is to solve the above-mentioned problems of the prior art and to provide an ammonia decomposition catalyst capable of decomposing and removing ammonia in a high yield without the risk of by-producing nitrogen oxides that cause air pollution. Is to do.

[0005]

The present invention has the specific X-ray diffraction pattern shown in Table A and, in the dehydrated state, expressed as (1 ± 0.8) R ₂ O ・
_{[AM 2 O 3 · bM'O · cAl} 2 O 3 ] · ySiO ₂
(In the above formula, R: alkali metal ion and / or hydrogen ion, M: group VIII element, rare earth element, titanium, vanadium, chromium, niobium, antimony, gallium, M ′: magnesium, calcium, strontium, barium,
a ≧ 0, 20> b ≧ 0, a + c = 1, 3000>y> 1
The porous material 1) becomes crystalline Shirike DOO as a carrier,
The catalyst A having at least one noble metal selected from the group consisting of platinum, palladium, rhodium and ruthenium as the active metal has at least one element selected from the group consisting of titanium, vanadium, tungsten and molybdenum on the upper layer. This is an ammonia decomposition catalyst comprising a layered catalyst coated with catalyst B. The crystalline silicate constituting the catalyst is characterized by having a crystal structure showing an X-ray diffraction pattern as shown in Table A below.

[0006]

[Table 2]

[0007]

The catalyst A of the present invention has the ability to decompose annonia at a low temperature, but also has the disadvantage of producing NOx as a by-product. Therefore, by coating the upper layer of the catalyst A with the catalyst B, which is a general denitration catalyst component, the by-product of NOx is prevented and the action of selectively converting NH ₃ to N ₂ is promoted. That is, the by-produced NOx has an effect of being converted into N ₂ by the following reaction by the catalyst B. 4NH ₃ + 4NO + O ₂ → 4N ₂ + 6H ₂ O The catalyst of the present invention preferably uses a binder component such as alumina sol or silica sol or a base material such as cordierite as necessary, and is preferably used in a honeycomb form by a wash coat method or a solid method.

FIG. 1 shows a model for supporting the catalyst A and the catalyst B constituting the catalyst of the present invention on a honeycomb substrate. When NOx by-produced by the lower catalyst A in FIG. 1 is diffused and desorbed, a denitration reaction with the adsorbed NH ₃ occurs on the upper catalyst B and NOx
Is removed. The content ratio of the catalyst A to the catalyst B is constituted in a wide range from 1:99 to 99: 1 by weight.

In the catalyst A, at least one noble metal selected from the group consisting of platinum, palladium, rhodium and ruthenium as an active metal is supported on various supports by an ion-exchange method. Or an impregnation method of impregnating with an aqueous solution of a noble metal salt such as chloride. The active metal (noble metal) to be supported exhibits sufficient activity at 0.002 wt% or more, and preferably has high activity at 0.02 wt% or more. Further, the layered catalyst of the present invention maintains a stable ammonia decomposition performance without reducing the ammonia decomposition activity even in an exhaust gas in which SO ₂ coexists. Also, S
Since the ability to oxidize O ₂ to SO ₃ is low, there is no problem in producing acidic ammonium sulfate. In addition,
By bringing the gas containing ammonia into contact with the layered catalyst of the present invention at a temperature of 100 to 600 ° C., the ammonia in the gas is decomposed into nitrogen. This decomposition reaction proceeds selectively, and no harmful gas such as NO, NO ₂ , N ₂ O is produced as a by-product.

[0010]

EXAMPLES Examples of the present invention will be described below to illustrate the catalyst of the present invention.
Clarify the effect. (Example 1) Preparation of powder catalysts 1 to 29 belonging to catalyst A 調製 Preparation of powder catalyst 1 Water glass No. 1 (SiO_Two: 30%): 5616 g of water:
The solution was dissolved in 5429 g, and this solution was designated as solution A. on the other hand,
Water: 4175 g, aluminum sulfate: 718.9 g, salt
Ferric chloride: 110 g, calcium acetate: 47.2 g, salt
Mix 262 g of sodium chloride and 2020 g of concentrated hydrochloric acid
This solution was used as solution B. Solution A and Solution B
Is supplied at a constant rate to produce a precipitate,
A slurry of H = 8.0 is obtained. 20 liters of this slurry
Into an autoclave and add
Add 500 g of monium bromide and add 7 g at 160 ° C.
Perform hydrothermal synthesis for 2 hours, wash with water, dry after synthesis, and further
Is fired at 500 ° C. for 3 hours to obtain crystalline silicate 1.
Was. This crystalline silicate 1 has a molar ratio of oxide (crystal
Water is omitted) is represented by the following composition formula, and the crystal structure is X-ray diffraction
In the above Table A. 0.5Na_TwoO ・ 0.5H_TwoO · [0.8Al_TwoO_Three・
0.2Fe_TwoO_Three・ 0.25CaO] ・ 25SiO_Two The above crystalline silicate 1 is converted to 4N NH_FourCl aqueous solution 40
Stir for 3 hours at_FourIon exchange was performed. Io
After washing and drying at 100 ° C for 24 hours,
Baking at 00 ° C. for 3 hours to obtain H-type crystalline silicate 1
Was. 100 g of this crystalline H-type crystalline silicate 1
Gold acid aqueous solution (H_TwoPtCl ₆・ 6H_TwoO: 0.15 g /
100 cc: water) and thoroughly kneaded, then 200 ° C
And evaporated to dryness. Then at 500 ° C in a nitrogen atmosphere
Purge treatment was performed for 2 hours to obtain powder catalyst 1.

(2) Preparation of Powdered Catalysts 2 to 15 In the method for synthesizing the crystalline silicate 1 in the preparation of the powdered catalyst 1 described above, instead of ferric chloride, cobalt chloride, ruthenium chloride, rhodium chloride, lanthanum chloride, cerium chloride, The same operation as that of crystalline silicate 1 was repeated except that titanium chloride, vanadium chloride, chromium chloride, antimony chloride, gallium chloride and niobium chloride were each added in the same mole number as Fe ₂ O _{3 in} terms of oxide. 2-12 were prepared. The crystal structures of these crystalline silicates are those shown in Table A above by X-ray diffraction,
Its composition is expressed as a molar ratio of oxide (dehydrated form) of 0.5Na ₂ O · 0.5H ₂ O · (0.2M ₂ O _3.
It is a _{0.8Al 2 O 3 · 0.25CaO) ·} 25SiO 2. Where M is Co, Ru, Rh, La, Ce, T
i, V, Cr, Sb, Ga, Nb.

Further, in the method for synthesizing the crystalline silicate 1, magnesium acetate, strontium acetate, and barium acetate are used in place of calcium acetate in terms of oxides, respectively.
The same operation as that of the crystalline silicate 1 was repeated except that the same mole number as that of the aO was added, and the crystalline silicates 13 to 1 were added.
5 was prepared. The crystal structures of these crystalline silicates are shown in Table A above by X-ray diffraction, and their compositions are expressed in terms of a molar ratio of oxides (dehydrated form) of 0.5.
Na ₂ O · 0.5H ₂ O · (0.2Fe ₂ O ₃ · 0.8
Al ₂ O ₃ · 0.25MeO) · 25SiO ₂ .
Here, Me is Mg, Sr, and Ba.

Using the above crystalline silicates 2 to 15, the H-type crystalline silicates 2 to 1 are prepared in the same manner as the powder catalyst 1.
5 was obtained, and this silicate was immersed in an aqueous solution of chloroplatinic acid,
Powdered catalysts 2 to 15 were obtained in the same manner as in powdered catalyst 1. The properties of the above powder catalysts 1 to 15 are summarized in Table B below.

[0014]

[Table 3]

[0015]

[0016]

[0017]

Example 2 Powder Catalyst 1 belonging to Catalyst B
Preparation of 6 to 18 ○ Preparation of powder catalyst 16 Metatitanate slurry (TiO ₂ content: 30 wt%, S
O _4: 8wt%): 670g of ammonium paratungstate _{{(NH 4) 10 H 10} · W 12 O 66 · 6H 2 O}:
36 g and 13 g of ammonium metavanadate were added, and the mixture was heated at 200 ° C. while kneading to evaporate water.
Next, air calcination was performed at 550 ° C. for 3 hours to obtain a denitration catalyst powder 33 of Ti-WV. The composition of this catalyst is Ti: W:
V = 91: 5: 4 (atomic ratio).

{Preparation of Powdered Catalysts 17 and 18 } Powdered catalyst 16 was prepared by adding Ti-V in the same manner as powdered catalyst 16 without adding ammonium paratungstate.
A denitration catalyst powder 17 was obtained. The composition of this catalyst is Ti: V =
95: 5 (atomic ratio). Furthermore, ammonium paramolybdate in place of ammonium paratungstate powder catalyst _{16 {(NH 4) 6 ·} Mo 7 O 24 · 4H
Ti-M using ₂ O｝ in the same manner as the powder catalyst 16
An oV denitration catalyst powder 18 was obtained. The composition of this catalyst is T
i: Mo: V = 91: 5: 4 (atomic ratio).

Example 3 Preparation of Honeycomb Catalyst (Layered Type) Alumina sol: 3 g, silica sol: 55 g (SiO ₂ : 20%) as a binder for 100 g of powder catalyst 1
And water: 200 g were added and sufficiently stirred to obtain a wash coat slurry. Next, a monolith base material for cordierite (a grid of 400 cells) was immersed in the above slurry, taken out, and then sprayed with excess slurry and dried at 200 ° C. The coating amount was 10 g per 100 cc of the substrate.
Next, a slurry for wash coating was prepared by using the powder catalyst 16 in place of the powder catalyst 1, and a monolith substrate coated with the powder catalyst 1 was coated in a layer at 10 g per 100 cc of the substrate, dried at 200 ° C., and dried at 200 ° C. I got

Powder catalysts 2 to 15 were first coated on a monolith substrate in the same manner as in the above-mentioned honeycomb coated product 1, and then a layered catalyst coated with powder catalyst 16 was prepared to obtain honeycomb coated products 2 to 15 . .

Further, powder catalysts 17 and 18 were coated on the upper layer in place of the powder catalyst 16 in the same manner as the honeycomb coated material 1 to obtain honeycomb coated products 16 and 17 .

Further, in the method of preparing the honeycomb coated article 1, 1 g of the lower layer powder catalyst 1 and 19 g of the upper layer powder catalyst 16 , 4 g of the lower layer powder catalyst 1 and 16 g of the upper layer powder catalyst 16 per 100 cc of the base material were used. Powder catalyst 1 of 16
g of powder catalyst 16 of the upper layer and 4 g of powder catalyst 1 of the lower layer
9 g and 1 g of the upper layer powder catalyst 16 were each coated in layers, and the same as the honeycomb coat 1, the honeycomb coat 18 was coated.
~ 21 .

Comparative Example 1 Honeycomb coated product 1 was prepared by using only powder catalyst 1 or powder catalyst 16.
20g per 100cc of honeycomb substrate in the same manner as
Coating was performed to obtain honeycomb coated products 22 and 23 .

(Experimental Example 1) An ammonia decomposition test was performed using honeycomb catalysts 1 to 23 . 14 x 15 x 15 x 60 mm in the reaction tube
Honeycomb catalysts 1 to 23 each consisting of 4 cells were charged, and an ammonia-containing gas having the following composition was flowed under the conditions of SV = 16300 h ^-1 and a flow rate of 5.54 Nm ³ / m ² , and the reaction temperature was 300 ° C.
At 400 ° C. and at 400 ° C. (Gas _{composition) NH 3: 20ppm SO 2:} 20ppm CO 2: 7% H 2 O: 6% O 2: 14.7% N 2: Ammonia decomposition rate remaining performance evaluation in the reaction initial and NOx (NO, NO ₂ , N ₂ O) production rate and SO ₂ oxidation rate were measured. The ammonia decomposition rate and the NOx generation rate were determined by the following equations. ○ Ammonia decomposition rate (%) = [(inlet NH ₃ −outlet NH ₃ ) / inlet NH ₃ ] × 100 ○ NOx generation rate (%) = [(outlet (N ₂ O × 2 + NO + NO ₂ )) / inlet N
H ₃ ] × 100 ○ SO ₂ oxidation rate (%) = [outlet SO ₃ / inlet SO ₂ ]
× 100 The results of these measurements are shown in Table C.

[0026]

[Table 4]

[0027]

(Experimental Example 2) A durability evaluation test was conducted by using honeycomb catalysts 1 to 21 and passing gas for a long time under the same conditions as in Example 1. As a result, even after supplying for 1000 hours under the above gas conditions, the same ammonia decomposition rate, NOx generation rate and SO2 oxidation rate as those in Table C were maintained, and it was confirmed that the catalyst was excellent in durability.

[0029]

According to the catalyst for ammonia decomposition of the present invention, ammonia can be decomposed into harmless nitrogen without oxidizing SO ₂ or generating by-products such as NOx.
Such a decomposition treatment method has not been available in the past, and its industrial utility value is extremely large.

[Brief description of the drawings]

FIG. 1 is a schematic view of supporting a powder catalyst constituting a honeycomb catalyst according to one embodiment of the present invention.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-50-53295 (JP, A) JP-A-57-84724 (JP, A) JP-A-50-131690 (JP, A) 16462 (JP, A) (58) Field surveyed (Int. Cl. ⁷ , DB name) B01J 21/00-38/74 B01D 53/86

Claims (1)

(57) [Claims] (1) It has a specific X-ray diffraction pattern shown in Table A, and expressed as (1 ± 0.8) R ₂ O · [aM ₂ O ₃・ BM'O
· CAl ₂ O ₃ ] · ySiO ₂ (wherein, R is an alkali metal ion and / or hydrogen ion, M is a group VIII element,
Rare earth element, titanium, vanadium, chromium, niobium, antimony, gallium, M ': magnesium, calcium, strontium, barium, a ≧ 0, 20> b ≧
0, a + c = 1,3000>y> 11) as comprising a crystalline silicate <br/> cable preparative porous material carrier, at least one selected platinum, palladium, from the group consisting of rhodium and ruthenium as active metal A catalyst B having at least one element selected from the group consisting of titanium, vanadium, tungsten and molybdenum in an upper layer of the catalyst A having a noble metal
A catalyst for ammonia decomposition comprising a layered catalyst coated with a. [Table 1]