JPH09150061A - Catalyst for ammonia decomposition - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a catalyst for ammonia decomposition capable of removing ammonia from an exhaust gas containing ammonia and oxygen in an extensive temperature area, especially in a low temperature area by causing a carrier containing zeolite to carry a ruthenium component. SOLUTION: The zeolite content of a carrier containing zeolite should preferably be at least, 20wt.%, more preferably 50-100wt.% for the total weight of the carrier. If the zeolite content of the carrier is 20wt.% or less, the desired ammonia decomposition activity might not be obtained depending upon occasion. The ruthenium content to be borne by the carrier should be 0.001-10wt.% for the total weight of the carrier and preferably be within the range of 0.01-2wt.%. If the carrying amount of the ruthenium component is 0.001wt.% or less, the desired ammonia decomposition activity might not be obtained depending upon occasion. On the other hand, if the carrying amount of the ruthenium component is 10wt.% or more, it is not desirable because the ammonia decomposition activity is deteriorated on account of the flocculation of ruthenium and also byproducts of NOx and N2 O tends to increase.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a catalyst that decomposes ammonia contained in exhaust gas to oxidize and decompose it into harmless nitrogen and water. More specifically, the present invention relates to a catalyst for oxidizing and decomposing residual ammonia after reducing and decomposing nitrogen oxides in exhaust gas discharged from an incinerator, various industrial devices, etc. with ammonia gas.

[0002]

2. Description of the Related Art Recently, from the viewpoint of environmental problems, it has been desired to reduce the amount of nitrogen oxides (sometimes called NOx) in exhaust gas discharged from combustion furnaces, incinerators, etc. to a low level. ing. The mainstream method for removing NOx in exhaust gas is to inject ammonia into the exhaust gas as a reducing agent and catalytically decompose NOx into nitrogen and water in the presence of a catalyst to remove it. In this case, in order to highly remove NOx, the injection amount of ammonia is increased and
It is necessary to increase the H ₃ / NOx ratio to 1 or more. However, if the NH ₃ / NOx ratio is increased to 1 or more, the amount of NOx in the exhaust gas can be suppressed to a low level,
There is a problem that the amount of unreacted ammonia increases.
Ammonia has a strong offensive odor, and it is not preferable to directly release a gas containing ammonia into the atmosphere from the viewpoint of environmental protection and pollution prevention. As a method for treating ammonia in exhaust gas, an absorption method using an acid aqueous solution, a method using an adsorbent containing iron sulfate, activated carbon, zeolite, etc. as a main component, a method using a catalyst for oxidative decomposition at a low temperature of 300 ° C. or lower, etc. It has been known. As a conventional ammonia decomposition catalyst, alumina-based platinum group (Pt, Ru, Pd, RPh,
Ir, Os) and / or metal oxides (Co, Cr,
Catalyst supporting Cu, Fe, Ni, Mn)
No. 161460), a catalyst in which chromium oxide, cobalt oxide and platinum group are supported on a carrier such as SiC (Japanese Patent Laid-Open No. 50-26796), or a catalyst composed of manganese oxide and titanium oxide (Japanese Patent Publication No. 61-52727). Further, a catalyst in which a compound of nickel and a rare earth element is carried on a carrier such as alumina, silica, titania (JP-A-2-198639), 5 to 50 wt% cobalt and 2 to 30 as lanthanum oxide are carried on the carrier. A catalyst in which 0.01 to 3 wt% of a platinum group element is further supported on lanthanum of wt% (Japanese Patent Laid-Open No. 5-329372) has been proposed. Further, as an ammonia decomposition catalyst having a denitration function, a composition containing an oxide of one or more elements selected from titanium, vanadium, tungsten, and molybdenum as a first component, and a precious metal selected from platinum, palladium, and rhodium Salt or zeolite, alumina, composed of a composition containing a noble metal previously supported on a porous body such as silica as a second component, unreacted injected as a reducing agent at the same time as catalytic reduction of nitrogen oxides A catalyst for decomposing ammonia has been proposed (Japanese Unexamined Patent Publication No. Hei 5 (1999))
No. 146634). However, in these ammonia decomposition catalysts, the literature [Journal of the Chemical Society of Japan (5), p. 612
-618 (1977)], etc.
Although the ammonia decomposition rate is high in a relatively high temperature range of 400 ° C, there is a problem that the ammonia decomposition rate is generally low in a low temperature range of about 200 to 300 ° C.

[0003]

Therefore, in consideration of the above-mentioned circumstances, an object of the present invention is to extract from exhaust gas containing ammonia and oxygen,
It is an object of the present invention to provide an ammonia decomposing catalyst having a high ammonia removing ability in a wide temperature range, and particularly having a high ammonia removing ability in a low temperature range.

[0004]

The present invention relates to an ammonia decomposition catalyst in which a ruthenium component is supported on a carrier containing zeolite.

[0005]

BEST MODE FOR CARRYING OUT THE INVENTION The carrier containing the zeolite of the present invention has a zeolite content in the carrier of preferably 20% by weight or more, more preferably 50% by weight or more, based on the total weight of the carrier.
１００100% by weight. The content of zeolite in the carrier is 2
If it is less than 0% by weight, the desired ammonia decomposing activity may not be obtained. The carrier containing zeolite may contain the above-mentioned zeolite and components other than zeolite, such as known binders such as titania, silica, alumina and clay minerals, and molding aids. The ruthenium component supported on the carrier is supported as Ru in the range of 0.001 to 10% by weight, preferably 0.01 to 2% by weight, based on the total weight of the catalyst. The supported amount of ruthenium component is 0.
If the amount is less than 001% by weight, the desired ammonia decomposing activity may not be obtained, whereas if the amount supported is more than 10% by weight, the activity is reduced due to the aggregation of ruthenium, and NOx, N _It is not preferable because a large amount of ₂ O is produced as a by-product. In addition to the ruthenium component, the catalyst of the present invention may contain other active metals such as copper, manganese, cobalt, nickel, molybdenum, tungsten, vanadium and bismuth.

The zeolite used in the present invention includes, for example, faujasite type (X type, Y type, USY type) L type,
Offretite / erionite mixed crystal type, mordenite type,
Examples thereof include, but are not limited to, synthetic zeolites such as ferrierite type and ZSM-5 type or natural zeolites. As these zeolites, those obtained by exchanging ammonium ions with alkali metals are usually used. The catalyst of the present invention is prepared by mixing the above-mentioned zeolite with a binder such as titania powder or silica sol, molding it into a desired shape, drying and firing it to prepare a zeolite-containing carrier, and ruthenium component of the carrier. The raw material is supported by a known method such as ion exchange, dipping or impregnation, and if necessary, neutralized, washed, dried and fired to produce. Further, the above-mentioned zeolite is loaded with a raw material of a ruthenium component by a known method such as ion exchange, immersion, and impregnation, and then mixed with a binder such as titania powder to form a desired shape, followed by drying and firing. It is also possible to produce a catalyst. As the raw material of the above-mentioned ruthenium component, ruthenium oxide,
Ruthenium hydroxide, ruthenium chloride, ruthenium bromide,
Examples thereof include ruthenium iodide, ruthenium sulfide, and hexaammine ruthenium (II) chloride. In the production of the catalyst of the present invention, a molding aid such as clay mineral, glass fiber or pulp may be used in addition to the above-mentioned catalyst component and binder. The precursor of the catalyst formed into any shape such as a columnar shape, a pipe shape, a honeycomb shape, or a sheet shape is usually calcined at a temperature of 400 to 900 ° C. to obtain a catalyst. The catalyst of the present invention produced as described above can be used under the condition that a usual ammonia decomposition catalyst is used.
Specifically, the reaction temperature is in the range of 150 to 600 ° C., and the space velocity is in the range of 1,000 to 50,000 h ⁻¹ .

[0007]

The present invention will be described in more detail with reference to the following examples, but the present invention is not limited thereto.

Example 1 As the zeolite, 1020 g of mordenite powder having a SiO ₂ / Al ₂ O ₃ molar ratio of 20 was used, and 180 g of clay was added as an inorganic binder and mixed. To this, 24 g of methyl cellulose, 24 g of polyethylene oxide and 1000 g of water were added, and the mixture was kneaded for 1 hour to adjust the water content, and then formed into a columnar shape by a piston extruder. This molded product was dried at 110 ° C. overnight and calcined at 500 ° C. for 5 hours.
The pellets had a diameter of 4 mm and an average length of 6 mm. The pellets were impregnated with an aqueous solution of RuCl ₃ .3H ₂ O and calcined at 500 ° C. for 5 hours to give 0.5 wt% Ru.
A zeolite catalyst A containing was obtained.

Example 2 As zeolite, U having a SiO ₂ / Al ₂ O ₃ molar ratio of 8 was used.
Using 255 g of SY type zeolite, 25 g of clay as an inorganic binder is added and mixed. To this, 6 g of methyl cellulose, 6 g of polyethylene oxide and 2 parts of water
After adding 50 g and kneading for 1 hour to adjust the water content, the mixture was molded into a cylindrical shape by a piston extruder. This molded product is at 110 ° C
It was dried overnight at 50 ° C. and calcined at 500 ° C. for 5 hours. The pellets had a diameter of 4 mm and an average length of 6 mm. The pellets were impregnated with an aqueous solution of RuCl ₃ .3H ₂ O and the temperature was 500 ° C.
And was calcined for 5 hours to obtain a zeolite catalyst B containing 0.5 wt% as Ru.

Example 3 A zeolite catalyst C was obtained in the same manner as in Example 1, except that the Ru content was adjusted to 2.0 wt%.

Example 4 Mordenite powder 2 having a SiO ₂ / Al ₂ O ₃ molar ratio of 16
13 g, 213 g of anatase type titanium oxide powder having a specific surface area of 90 (m ² / g), and 75 g of clay as an inorganic binder
Add and mix. To this, 5 g of carboxymethyl cellulose, 5 g of polyethylene oxide and 250 of water
After adding g, the mixture was kneaded for 1 hour to adjust the water content, and then formed into a cylindrical shape by a piston extruder. This molded product was dried at 110 ° C. overnight and calcined at 500 ° C. for 5 hours. The pellets had a diameter of 4 mm and an average length of 6 mm. The pellets were impregnated with an aqueous solution of RuCl ₃ .3H ₂ O and heated at 500 ° C. for 5
It was calcined for an hour to obtain a zeolite catalyst D containing 0.5 wt% as Ru.

Comparative Example 1 25 g of clay as an inorganic binder was added to 475 g of anatase type titanium oxide powder having a specific surface area of 90 (m ² / g) and kneaded. 60 g of ammonia water is added to this kneaded product to adjust the pH of the kneaded product to 9.0. To this, 10 g of carboxymethyl cellulose, 10 g of polyethylene oxide and 300 g of water are added and kneaded for 1 hour. After heat was applied to this mixture to adjust the water content, it was formed into a columnar shape by a piston extruder. After drying the molded product at 110 ° C. overnight, 500
Fired at ℃. The pellets had a diameter of 4 mm and an average length of 6 mm. The pellet was impregnated with an aqueous solution of RuCl ₃ .3H ₂ O and calcined at 500 ° C. for 5 hours to obtain a zeolite catalyst E containing 0.5 wt% as Ru.

Comparative Example 2 In Example 4, instead of ruthenium, chloroplatinic acid (H
Except impregnated into ₂ aqueous PtC ₁₆ · 6H ₂ O) is the catalyst was prepared in the same manner as in Example 4, 0.5 w as Pt
A zeolite catalyst F containing t% was obtained.

Comparative Example 3 Aluminum oxide 380 having a specific surface area of 230 (m ² / g)
20 g of clay as an inorganic binder is added to g and mixed. To this, 2 g of carboxymethyl cellulose, 2 g of polyethylene oxide and 250 g of water were added, and the mixture was kneaded for 1 hour to adjust the water content, and then formed into a cylindrical shape by a piston extruder. This molded product was dried at 110 ° C. overnight and calcined at 500 ° C. for 5 hours. The pellets had a diameter of 4 mm and an average length of 6 mm. RuCl ₃ · 3H ₂ O in the pellet
Was impregnated with the aqueous solution of and was calcined at 500 ° C. for 5 hours to obtain a zeolite catalyst G containing 0.5 wt% as Ru.

Example 5 Catalysts A to D of Examples 1 to 4 and Catalyst E of Comparative Examples 1 to 3
For ~G, it was measured decomposition rate of NH ₃ in the respective reaction temperature flowing ammonia-containing gas. The reaction conditions are shown below. Space velocity; 15,000h ^-1 reaction temperature; 200,250,300,350,380 ℃ ammonia-containing _{gas; NH 3 = 200ppm O 2 =} 5% N 2 = balance ( gas analysis) NH ₃ spectrometry: indophenol By law. NOx analysis method: By chemiluminescence method. N ₂ O analysis method: By a non-dispersive infrared absorption method. The reaction results are shown in Tables 1-2.

The NH ₃ decomposition rate was calculated as follows.

[0017]

[Table 1]

[0018]

[Table 2] From the reaction results shown in Tables 1 and 2 above, the catalyst of the present invention was 200
It can be seen that the NH ₃ decomposition rate is high even in the low temperature range of ℃ to 250 ℃.

[0019]

[Effect] An ammonia decomposition catalyst having a high ability to remove ammonia from exhaust gas containing ammonia in a wide temperature range, particularly in a low temperature range was provided.

Claims (3)

[Claims] 1. An ammonia decomposition catalyst in which a ruthenium component is supported on a carrier containing zeolite. 2. The ammonia decomposition catalyst according to claim 1, wherein the amount of the ruthenium component supported is 0.001 to 10% by weight based on the total weight of the catalyst as Ru. 3. The ammonia decomposition catalyst according to claim 1, wherein the content of zeolite in the carrier is 20% by weight or more based on the total weight of the carrier.