JPH07289897A - Catalyst for decomposition of ammonia and decomposing method of ammonia using the same - Google Patents

Abstract

PURPOSE:To obtain a catalyst for decomposition of ammonia into nitrogen gas and water by oxidation with which harmful ammonia (NH3) is decomposed in various waste gases such as waste gas from a coke oven or various kinds of factories, waste gas from a denitrifying process for flue gas using ammonia as a reducing agent for selective contact reduction and also waste gas from a municipal scauengery plant, municipal water purifying plant, sludge, or disposed plant. CONSTITUTION:This catalyst for decomposition of ammonia contains the following components (A)-(C). The component (A) is at least one kind of multiple oxide selected from binary double oxides containing Ti and Si, binary double oxides containing Ti and Zr, and ternary oxides containing Ti, Si and Zr. The component (B) is at least one kind of oxide of V, W and Mo, and the component (C) is at least one kind of noble metal selected from Pt, Pd, Rh, Ru and Ir and its compd. The decomposing method of ammonia uses this catalyst.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention converts harmful ammonia (NH ₃ ) contained in various exhaust gases into nitrogen gas (N ₂ ) and water (H ₂ O) as represented by the following formula (1). The present invention relates to an ammonia decomposition catalyst for oxidative decomposition. As the ammonia-containing gas, exhaust gas from a coke oven or various factories, gas from an ammonia stripping process in which ammonia is released by air or steam from an aqueous solution containing ammonia, and flue gas denitration by selective catalytic reduction using ammonia as a reducing agent Exhaust gas from processes, gas discharged from city cleaning facilities, city water purification facilities, sludge treatment facilities, etc.

[0002]

[Equation 1]

[0003]

2. Description of the Related Art Ammonia stripping process has recently been particularly studied as a method for reducing the total nitrogen concentration in wastewater in order to prevent eutrophication in lakes and closed waters, in which case ammonia discharged from the wastewater is included. Gas treatment is required.

Further, the flue gas denitration method by selective catalytic reduction using ammonia as a reducing agent, which is adopted as an effective method for removing nitrogen oxides (NOx) in flue gas discharged from power plants, etc. Widely used in power plants. In recent years, NO from gas turbines for power generation, etc., which are being installed mainly in urban areas to cope with fluctuations in power demand
Since x emission is a problem in terms of environmental protection because it is adjacent to the living area, the installation area is often the area subject to the NOx total amount regulation, and the NOx amount in the exhaust gas discharged from the equipment is suppressed to an extremely low level. That is, a high degree of denitration is required.

For this purpose, a method of operating the denitration apparatus at a high denitration rate by increasing the amount of injected ammonia above the stoichiometric amount required by the required denitration rate has been studied.
In this case, it is necessary to reduce unreacted ammonia (hereinafter referred to as “leak ammonia”) that was added in excess of the stoichiometric amount and was not used in the denitration reaction. For this purpose, a combination of denitration catalyst and ammonia decomposition catalyst is required. Is being considered. In this case, as a matter of course, a large amount of NOx is not generated due to the oxidation of ammonia even in the high temperature region, that is, a catalyst having a high selectivity ammonia decomposition characteristic for nitrogen and water is required.

Thus, even at high temperatures and under conditions where the oxygen concentration is excessive with respect to the ammonia concentration, a large amount of NOx is not generated due to the oxidation of ammonia.
That is, there is a strong demand for ammonia decomposition characteristics with high selectivity to nitrogen and water. Furthermore, examples of the gas to be treated by the ammonia decomposition catalyst of the present invention include a gas discharged from a city cleaning facility, a city water purification facility, a sludge treatment facility, and the like. Usually, exhaust gas from these facilities includes sulfur oxides along with ammonia, Contains components that cause offensive odors such as hydrogen sulfide, sulfur-containing organic compounds, and nitrogen-containing organic compounds.

Conventionally, the following catalysts have been proposed for purification of exhaust gas containing ammonia.
For example, a noble metal-based catalyst such as a Pt-Al ₂ O ₃ -based catalyst (Japanese Patent Publication No. 57-58213), Ni, Mn, Cu, Fe.
And other metal oxide catalysts (JP-A-2-198638).

[0008]

However, in the above-mentioned conventional catalyst, for example, in the case of a Pt-based catalyst, a large amount of NOx is generated due to the oxidation of ammonia under a high temperature condition or under an excessive oxygen concentration condition relative to the ammonia concentration. However, there is a problem that base metal oxide catalysts such as Ni and Mn have low activity at low temperatures and cause generation of N ₂ O. Further, there is a problem that the durability is remarkably lowered when the processing gas contains hydrogen sulfide or a sulfur-containing organic compound. In addition, when the process gas contains other nitrogen-containing organic compounds together with ammonia, there are problems such as a decrease in ammonia decomposing activity and an increase in NOx production. As an ammonia decomposing catalyst having a denitration function, a catalyst composed of a composition of an oxide of an element selected from titanium, vanadium, tungsten and molybdenum and a noble metal salt or an oxide of an element selected from titanium, vanadium, tungsten and molybdenum and a noble metal A catalyst composed of a supported porous material such as zeolite has also been proposed (JP-A-5-146634).

However, as shown in the examples of the publication, the former, that is, titanium, vanadium, tungsten, molybdenum is simply selected by supporting a noble metal salt on an oxide of an element selected from titanium, vanadium, tungsten, and molybdenum. The activity of decomposing ammonia is extremely low compared to a catalyst composed of a porous material such as zeolite carrying an oxide of an element and a noble metal, and the latter requires a porous material such as zeolite in addition to the catalyst component. There is a problem that the manufacturing process becomes complicated, for example, a step of supporting a noble metal and a step of mixing the obtained noble metal-supporting porous body with an oxide of an element selected from titanium, vanadium, tungsten, and molybdenum are required. .

Therefore, an object of the present invention is to show a high ammonia decomposing activity in a wide temperature range from low temperature to high temperature even in the presence of excess oxygen and other nitrogen-containing organic compounds.
The production of NOx is extremely low, and even if the processing gas contains a sulfur compound, it has excellent durability and does not require a complicated manufacturing process. Another object of the present invention is to provide a method for decomposing a gas containing at least one compound selected from oxides, hydrogen sulfide, sulfur-containing organic compounds and nitrogen-containing organic compounds.

[0011]

[Means for Solving the Problems] The present inventors have conducted extensive research and study in order to achieve the above object. As a result, it was found that by selecting a composite oxide of a specific metal, and further by combining the composite oxide with an oxide of a specific metal and a noble metal component, a target highly active and long-life ammonia decomposition catalyst can be obtained. Further, when the catalyst is applied to a gas containing ammonia and at least one compound selected from the group consisting of sulfur oxides, hydrogen sulfide, sulfur-containing organic compounds and nitrogen-containing organic compounds, an excellent decomposition treatment effect can be obtained. The present invention has been completed and the present invention has been completed. That is, the present invention is specified as follows.

(1) Binary complex oxide containing Ti and Si; Binary complex oxide containing Ti and Zr; T
Catalyst A component which is at least one kind of complex oxide selected from the group consisting of ternary complex oxides containing i, Si and Zr, and at least one kind selected from the group consisting of vanadium, tungsten and molybdenum. And a catalyst C component which is at least one noble metal selected from the group consisting of platinum, palladium, rhodium, ruthenium and iridium, or a compound thereof. Ammonia decomposition catalyst.

(2) A method for decomposing ammonia using the catalyst of the above item 1.

(3) Decomposition of ammonia using the catalyst described in 1 above in a gas containing ammonia and at least one compound selected from the group consisting of sulfur compounds, hydrogen sulfide, sulfur-containing organic compounds and nitrogen-containing organic compounds. Method.

The present invention will be described in more detail below. The first feature of the components constituting the ammonia decomposition catalyst of the present invention is that a complex oxide of a specific metal is used as the catalyst component A. This metal complex oxide is composed of Ti and S
It is selected from the group consisting of a binary complex oxide consisting of i, a binary complex oxide consisting of Ti and Zr, and a ternary complex oxide consisting of Ti, Si and Zr.

Binary composite oxides generally composed of titanium and silicon, for example, Kozo Tabe (Catalyst, Vol. 17, No.
3, 72, 1975), it is known as a solid acid, and each of them has a remarkable acidity which is not found in a single oxide, and has a high surface area. That is, the above TiO ₂ —SiO ₂ (composite oxide of titanium and silicon; hereinafter, as a method of indicating each complex oxide, “−” may be used between oxides). It is not a mixture of titanium oxide and silicon oxide, but titanium and silicon are recognized to exhibit their specific physical properties by forming a so-called binary oxide. In addition, the ternary compound oxide composed of titanium, silicon and zirconium is also TiO ₂
A composite oxide having the same properties as -SiO ₂ . Further, the above complex oxide was analyzed by X-ray diffraction,
It was found to have a fine structure that is amorphous or nearly amorphous.

Although the reason why such a composite oxide of a metal brings about an excellent effect in the present invention is not clear,
It is considered that this is attributed to the properties of the composite oxide, which are not observed by the oxides constituting the metal composite oxide alone, that is, ammonia adsorption performance, high surface area, high pore volume, sulfur compound resistance, and the like. That is, the composite oxide used in the present invention is not easily affected by sulfur oxides coexisting in the gas, has excellent ammonia adsorption performance, has a high surface area and a high pore volume, and has a high active component of the catalyst. Since it can be dispersed, it is presumed that a small amount of active ingredient exhibits high activity in a wide temperature range and a long-life catalyst can be obtained without thermal deterioration due to sintering. Regarding the above points, the effect can be more clearly understood by comparing a commonly used oxide such as alumina with the composite oxide according to the present invention. For example, when alumina is used in place of the composite oxide according to the present invention, the activity of decomposing ammonia (decomposition into water and nitrogen gas) becomes low, and when a sulfur compound is present in the gas to be treated, the alumina becomes It is sulphated, resulting in a decrease in decomposition activity and a decrease in catalyst strength.

When silica is used, the activity of decomposing ammonia is low, and when a gas containing water is treated at a high temperature, sintering occurs and the surface area is greatly reduced, so that the activity of decomposing ammonia is further reduced. It is a thing.

When zeolite is used, it is inferior in heat resistance, the crystal structure changes under high temperature conditions to cause a large decrease in surface area, and the decomposition activity also remarkably decreases. The above-mentioned drawbacks are few in the composite oxide according to the present invention and are effective as an ammonia decomposition catalyst.

When the catalyst A component and the catalyst B component, which are the complex oxides according to the present invention, are combined, NOx is hardly generated by the decomposition of ammonia, and even if the process gas contains NOx, the ammonia is not generated. Almost no NOx exists in the outlet gas due to the denitration reaction by However, when NOx does not exist in the process gas, the ammonia decomposing activity becomes low especially at low temperature. When the catalysts A and C are combined,
Although it is excellent in terms of ammonia decomposing activity, it is not preferable because NOx is highly generated.

On the other hand, by combining the catalysts A, B and C components, in addition to the excellent ammonia adsorption capacity of the catalyst A component, the functions of the catalysts B and C can be effectively exerted, and the ammonia decomposition It is possible to obtain the synergistic effect that the activity and the generation of NOx can be reduced.

For these reasons, the physical properties and composition of the catalyst A component used in the present invention have a great influence on the characteristics of the ammonia decomposition catalyst of the present invention. For example the BE
If the T surface area is too low, the ammonia decomposing activity is low and the durability is also lowered, so that it is preferably 30 m ² / g or more, and more preferably 40 m ² / g or more. The upper limit of the surface area is not particularly limited, but the metal composite oxide in the present invention generally has a surface area of 1000 m ² / g or less, and more preferably 40 to 300 m ² / g.
When it is less than 40 m ² / g, the ammonia decomposing activity becomes low, and when it exceeds 1000 m ² / g, the initial activity is high but the change with time in the catalytic performance may become large, so that it is not suitable for long-term use. There are also unfavorable things.

The two-component composite oxide of the present invention, Ti
It is a binary complex oxide of O ₂ —SiO ₂ or TiO ₂ —ZrO _2. Of these, TiO ₂ —SiO ₂ is preferable in view of the surface area, the ease of decomposition of ammonia, and the like.
Is a complex oxide of.

TiO ₂ --SiO ₂ or TiO ₂ --Zr
The composition ratio of each component in the case of a binary compound oxide of O ₂ is converted to an oxide (TiO _{2 for} titanium oxide, SiO _{2 for} silicon oxide, ZrO _{2 for} zirconium oxide), and the total molar amount of the two components is When the amount is 100 mol%, TiO ₂ —Si
When it is a binary compound oxide of O ₂ , TiO ₂ is 40 to 40%.
It is 95 mol%, preferably 60 to 95 mol%. 40
This is because when it is less than mol% and when it exceeds 95 mol%, the decomposability of ammonia becomes low.

[0025] When a two-component composite oxide of TiO ₂ -ZrO _2, TiO ₂ is from 45 to 98 mol%, preferably, 6
It is 5 to 95 mol%. When it is less than 45 mol%,
This is because the surface area becomes low and the decomposition activity of ammonia also becomes low. When it exceeds 98 mol%, the ammonia decomposition activity becomes low.

When the catalyst A component is a ternary complex oxide, the composition ratio is converted to oxide (titanium oxide is Ti
O ₂ , silicon oxide is SiO ₂ , zirconium oxide is ZrO
_When the total of ₂ ) is 100 mol%, TiO ₂ is 40 to 40%.
It is preferably in the range of 95 mol%, more preferably 60 to 95 mol%. When TiO ₂ exceeds the range, the characteristics of the composite oxide are not sufficiently exhibited, and when it is below the range, the catalytic activity decreases.

SiO ₂ is 1 to 60 mol%, preferably
This is because when the amount is 5 to 40 mol% and less than 1 mol%, the surface area becomes low and the ammonia decomposing activity also becomes low.
This is because when it exceeds 0 mol%, the ammonia decomposing activity becomes low.

ZrO ₂ is 1 to 55 mol%, preferably
When it is 5 to 40 mol%, less than 1 mol%, the above properties as a ternary complex oxide are not sufficiently exhibited, and when it exceeds 55 mol%, the surface area is low and the ammonia decomposing activity is low. Is.

In the present invention, the binary compound oxide and the ternary compound oxide may be used together depending on the use conditions.

The method for preparing such a metal complex oxide will be described with reference to a binary complex oxide composed of, for example, Ti and Si. The titanium source may be an inorganic titanium compound such as titanium chloride or titanium sulfate, or tetraisoprovir. It can be appropriately selected and used from organic titanium compounds such as titanate. Further, as the silicon source, colloidal silica,
Water glass, fine particle silicic acid, inorganic silicon compounds such as silicon tetrachloride, organic silicon compounds such as tetraethyl silicate, and the like can be appropriately selected and used. Some of these raw materials may contain trace amounts of impurities, contaminants, etc., but if they are in a certain amount, they do not significantly affect the physical properties of the target titanium-silicon composite oxide. So it can be used without problems. A preferred method for preparing the above titanium-silicon composite oxide can be achieved by the following procedure.

(1) Titanium tetrachloride is mixed with silica sol, ammonia is added to cause precipitation, the resulting precipitate is washed, dried, and then calcined at 300 to 650 ° C. to obtain the desired composite. Can be obtained.

(2) An aqueous solution of sodium silicate is added to titanium tetrachloride to cause a reaction to cause a precipitate, the resulting precipitate is washed, dried, and then calcined at 300 to 650 ° C.
The desired composite can be obtained.

(3) To a water-alcohol solution of titanium tetrachloride, ethyl silicate ((C ₃ H ₆ O) ₄ Si) was added, followed by hydrolysis to form a precipitate,
The precipitate obtained is washed and dried, then 300-65
The desired composite can be obtained by firing at 0 ° C.

(4) Titanium oxide chloride (TiOCl ₃ )
Ammonia is added to a water-alcohol solution of ethyl silicate to cause precipitation, and the resulting precipitate is washed, dried, and then calcined at 300 to 650 ° C. to obtain a target composite. it can.

Of the above-mentioned methods, the method (1) is particularly preferable, and more specifically, the method is performed so that the molar ratio of the titanium source (TiO ₂ ) and the silicon source (SiO ₂ ) becomes a predetermined amount, and the acidic Aqueous solution or sol in the concentration of aqueous solution or sol state (1 to 100 g / liter (hereinafter, expressed as L, this amount is calculated as TiO ₂ for titanium source and SiO ₂ for silicon source)) Condition), 10 to 100 ℃
Keep it in, and add ammonia water as a neutralizing agent into it,
It is kept at pH 2 to 10 for 10 minutes to 3 hours to form a coprecipitate with titanium and silicon, the precipitate is filtered, thoroughly washed, and then dried at 80 ° C to 140 ° C for 10 minutes to 3 hours,
The titanium-silicon composite oxide can be obtained by firing at 400 to 700 ° C. for 1 to 10 hours. Further, instead of silicon, zirconium chloride, zirconium nitrate, inorganic zirconium compounds such as zirconium sulfate, or organic zirconium such as zirconium oxalate, or in some cases by using a zirconia sol, titanium-zirconia composite oxide titania- A composite oxide of zirconia and titanium-silica-zirconia can be obtained.

The addition of the catalyst B component, ie, the oxide of at least one metal selected from the group consisting of vanadium, tungsten and molybdenum, which is the second feature of the present invention, to the powder or slurry of the above complex oxide. It is also possible to add and mix such metal salts or a solution thereof and knead with a kneader or the like to form a honeycomb shape, or to form a composite obtained by molding, drying and firing the composite oxide. It is also possible to add it by a method of impregnating and supporting a solution of such a metal salt. Examples of such metal salts include ammonium metavanadate, ammonium paratungstate, and ammonium paramolybdate.

The third feature of the present invention, the catalyst C component, that is, at least one noble metal selected from the group consisting of platinum, palladium, rhodium, ruthenium and iridium, or a compound thereof, is the catalyst A component or the catalyst A component. To the powder or slurry of the mixture of the catalyst B component and, for example, salts of these noble metals or solutions thereof,
Alternatively, the catalyst A component or a molded product composed of the catalyst A component and the catalyst B component can be added by a method of impregnating and supporting a solution of these noble metal salts.

That is, the molded product of the ammonia decomposition catalyst provided by the present invention may be used by molding from a powder or slurry of the above-mentioned catalyst A component, catalyst B component, catalyst C component or salts thereof. Further, the catalyst C component may be supported on the molded product composed of the catalyst A component and the catalyst B component, or the catalyst B component and the catalyst C component may be supported on the molded product composed of the catalyst A component. Further, the catalyst composition obtained by the present invention may be molded into a plate shape, a corrugated plate shape, a net shape, a honeycomb shape, a columnar shape, a cylindrical shape, or the like, and may be used, or alumina, silica, silica-alumina, or cordy. It may be used by being carried on a carrier having a plate shape, a corrugated plate shape, a net shape, a honeycomb shape, a columnar shape, a cylindrical shape or the like made of light, titania, stainless metal or the like.

In the ammonia decomposing catalyst thus obtained according to the present invention, the composition ratio of the catalyst A component to the catalyst B component and the catalyst C component has a great influence on the ammonia decomposing characteristics. If the amount of the catalyst A component is too large, the effect of adding the components of the catalyst B and the catalyst C cannot be sufficiently obtained, and if it is too small, the ammonia decomposing activity decreases. If the amount of the component B of the catalyst is too small, the catalytic activity at high temperature becomes low, and even if it exceeds a certain level, the catalytic activity is not significantly improved. Further, if the amount of the catalyst C component is small, the ammonia decomposing activity becomes low, especially at low temperature. If it is too large, the cost of the catalyst becomes high, and in addition, NOx production due to ammonia oxidation tends to increase especially at high temperature. .

The component B of the catalyst according to the present invention is an oxide of at least one metal selected from the group consisting of vanadium, tungsten and molybdenum. Of these components, preferably at least one of vanadium and tungsten is used. is there. When the catalyst B component is also used, it can be mixed at a ratio of 1 to 99 mol%, preferably 2 to 98 mol%.

As the catalyst C component according to the present invention, platinum,
At least one noble metal selected from the group consisting of palladium, rhodium, ruthenium, and iridium or a compound thereof, and among these components, preferably platinum or at least one of palladium having high ammonia decomposing activity, and more preferably palladium Is. When the catalyst B component is also used, it can be mixed at a ratio of 1 to 99 mol%, preferably 2 to 98 mol%.

The above ratio of the catalysts A, B and C components is preferably 70 to 99% by weight in the form of oxide of the catalyst A component,
More preferably 75 to 95% by weight, the catalyst B component is 0.5 to 30% by weight in the form of an oxide, more preferably 1 to 20% by weight, and the catalyst C component is 0.001 to 5% by weight as a metal.
More preferably, it is in the range of 0.005 to 2.5% by weight.

When the amount of the catalyst A component is less than 70% by weight, the activity of decomposing ammonia and the durability are low, and
This is because the ammonia decomposing activity is similarly reduced when the content exceeds the weight%.

This is because when the content of the catalyst component B is less than 0.5% by weight, the activity of decomposing ammonia at high temperature becomes low, and the addition of more than 30% by weight does not significantly improve the activity of ammonia.

When the content of the catalyst component C is less than 0.001% by weight, the activity of decomposing ammonia at low temperature becomes low, and
When it exceeds the weight%, NOx production at high temperature increases, which is not preferable.

The physical properties of the obtained catalyst are, as described in the physical properties of the component A of the catalyst, for example, the BET surface area thereof is 30 m ² / g or more because the ammonia decomposing activity is low and the durability is lowered if the BET surface area is too low. Is preferred and 40 ²
It is more preferably m / g or more. Further, if the pore volume is too low, the catalyst activity will be low, and if it is too high, the strength of the catalyst generally prepared will be low.
It is preferably in the range of c / g, 0.3 to 0.7c
It is more preferably in the range of c / g. 0.25cc
If it is less than / g, the catalytic activity becomes low, and 0.9c
When it exceeds c / g, the catalyst strength is lowered, and problems such as filling of the catalyst occur.

Further, the volume of pores having a pore diameter of 0.5 μm or more is 0.05 to 0.6 with respect to the total pore volume.
The ratio is preferably in the range of 0.1 to 0.5, more preferably 0.1 to 0.5. If it is less than 0.05, the decomposition activity of ammonia will be low, and if it exceeds 0.6, the strength of the catalyst will be reduced, which is not preferable.

Below, TiO ₂ --SiO ₂ was used as the catalyst A component.
An example of the method for preparing the catalyst of the present invention, which comprises a composite oxide, vanadium and tungsten oxide as the catalyst B component, and platinum as the catalyst C component, will be shown.

First, TiO ₂ --S obtained by the above-mentioned method
An aqueous monoethanolamine solution of ammonium metavanadate and ammonium paratungstate and a molding aid such as starch and polyethylene oxide are added to the iO ₂ composite oxide powder, and the mixture is sufficiently kneaded and then extruded into a honeycomb shape. At this time, it is possible to add glass fiber or glass powder to increase the catalyst strength. Then, this molded body is 5
After drying at 0 ~ 150 ℃, 1 ~ 10 at 300 ~ 700 ℃
Bake for an hour. The honeycomb molded body thus obtained was impregnated with an aqueous solution of chloroplatinic acid and dried at 50 to 200 ° C.
Calcination gives the desired catalyst.

The target gas for the ammonia decomposition treatment using the catalyst of the present invention is exhaust gas containing ammonia from various plants, coke oven exhaust gas, and flue gas denitration process by selective catalytic reduction using ammonia as a reducing agent. Exhaust gas containing leaked ammonia from ammonia, ammonia-containing gas from ammonia stripping process, gas discharged from city cleaning facilities, city water purification facilities, sludge treatment facilities, and the like. These gases are excellent in the characteristics of the catalyst obtained by the present invention, that is, they have high activity for decomposing ammonia in a wide temperature range from low temperature to high temperature, have extremely low generation of nitrogen oxides, and contain sulfur compounds in the treated gas. In particular, it is preferably selected as a gas to be treated in order to fully utilize the characteristic of having durability.

When the catalyst of the present invention is applied to a gas containing at least one compound selected from sulfur oxides, hydrogen sulfide, sulfur-containing organic compounds and nitrogen-containing organic compounds together with ammonia, a decomposition treatment effect superior to the conventional one is obtained. To be That is, hydrogen sulfide, sulfur-containing organic compounds, and nitrogen-containing organic compounds contained together with ammonia are easily decomposed together with ammonia by the catalyst of the present invention, and the durability of the catalyst is also high. In this case, components contained together with ammonia include sulfur oxides such as sulfur dioxide, hydrogen sulfide, and sulfur-containing organic compounds such as methyl mercaptan, methyl sulfide, and methyl disulfide, and nitrogen-containing organic compounds include amines. There is a class of compounds such as trimethylamine, and the effects of the present invention are markedly exhibited, so that the gas to be treated is particularly preferably selected.

If the concentration of ammonia contained in the gas to be subjected to the ammonia decomposition treatment in which the catalyst of the present invention is used is too low, the decomposition efficiency will be low, and if it is too high, the amount of heat generated by the catalyst will be large and heat removal will be difficult. As the local temperature rises and the decomposition selectivity decreases with it, 0.5ppm ~
It is preferably in the range of 50% (volume concentration), and more preferably in the range of 1 ppm to 5% (volume concentration).
When it is less than 0.5 ppm, the efficiency of ammonia decomposition becomes low, and when it exceeds 50%, the calorific value of the catalyst becomes large and it becomes difficult to remove heat, resulting in a local temperature rise and a decrease in ammonia decomposition activity. This is because the durability is reduced.

The concentration of hydrogen sulfide or sulfur-containing organic compound contained together with ammonia is 0 to 5000 pp.
It is preferably in the range of m. This is because if it exceeds 5000 ppm, if it is too high, the catalytic activity is lowered.

The concentration of the nitrogen organic compound contained together with ammonia is preferably in the range of 0 to 1%, and if it exceeds 1%, NOx production increases if it is too high. In order to suppress the generation of NOx and improve the decomposition efficiency of both ammonia and nitrogen organic compounds, the concentration is preferably lower than the ammonia concentration. Normally, it is not necessary to add oxygen in particular because oxygen is excessively present in the gas to be treated with respect to ammonia, but when it is present at an extremely low concentration relative to the number of moles of ammonia or nitrogen organic compound, ammonia is not necessary. It is preferable to add 0.01 mol or more of the nitrogen organic compound in an amount of 0.01 mol or more relative to the target decomposition rate (%) per 1 mol of the organic compound, because the decomposition efficiency is improved. When oxygen is present in a very large excess with respect to the number of moles of ammonia or a nitrogen organic compound, the amount of NOx produced increases, so the oxygen concentration is preferably 21% or less.

The space velocity of the gas to be treated with respect to the catalyst of the present invention is 100 to 100,000 hr to ¹ , preferably 20.
It is preferably in the range of 0 to 50000 hr- ¹ . 100h
This is because if it is less than r ~ ¹ , the processing apparatus becomes too large and inefficient, and if it exceeds 100000 hr ~ ¹ , if it is too high, the decomposition efficiency decreases.

The decomposition treatment gas temperature is preferably in the range of 25 to 700 ° C., more preferably 100 to 50.
A range of 0 ° C is preferable. This is because when the temperature is lower than 25 ° C, the decomposition efficiency is low, and when the temperature is higher than 700 ° C, the production of NOx is increased. Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples, but the present invention is not limited to these Examples.

[0057]

【Example】

Example 1 A binary complex oxide composed of Ti and Si was prepared by the method described below. SNOWTEX -20 to 10 wt% aqueous ammonia 700 liters was stirred added and mixed (manufactured by Nissan Chemical silica sol, about 20 wt% -SiO ₂ containing) 35.5 kg, as aqueous sulfuric acid solution (TiO ₂ titanyl sulfate 1
25 g / liter, sulfuric acid concentration 0.55 g / liter) 3
00 liters were gradually added dropwise with stirring. The gel obtained is left for 3 hours, filtered and washed with water, and then at 150 ° C. for 1 hour.
It was dried for 0 hours. Then, it was baked at 500 ° C. for 6 hours. The composition of the obtained powder is Ti: Si = 4: 1 (molar ratio) and B
The ET surface area was 210 m ² / g. The X-ray diffraction chart of the powder thus obtained was that a complex oxide composed of Ti and Si having an amorphous fine structure due to a broad diffraction peak with no apparent specific peaks of TiO ₂ or SiO _2. Was confirmed. Ti thus obtained
20 kg of a complex oxide powder composed of Si and Si, 12 kg of a 10% monoethanolamine aqueous solution containing 0.56 kg of ammonium metavanadate and 1.79 kg of ammonium paratungstate are added, and starch is further added as a molding aid and mixed by a kneader. After kneading, using an extrusion molding machine, the outer shape is 80 mm square, the opening is 4.0 mm, the wall thickness is 1.0 mm,
It was formed into a honeycomb shape having a length of 500 mm. 80 ° C
After drying at 450 ° C., it was baked in an air atmosphere at 450 ° C. for 5 hours. The composition of the obtained honeycomb formed body, Ti-Si composite _{oxide: V 2 O 5: WO 3} = 91: 2: was 7 (weight ratio). An aqueous solution of chloroplatinic acid (0.5 g-Pt /
Liter) and then dried at 150 ° C. for 3 hours and subsequently calcined in an air atmosphere at 450 ° C. for 3 hours. The BET surface area of the catalyst thus obtained was 130 m ² / g and the pore volume was 0.45 cc / g. The volume of pores having a pore diameter of 0.5 μm or more is 0.1
It was 1 cc / g (ratio of 0.24 to the total pore volume). The composition of the catalyst is Ti-Si composite oxide: V ₂ O ₅ : W.
O ₃ : Pt = 90.8: 2.0: 7.0: 0.2 (weight ratio).

Example 2 A binary complex oxide composed of Ti and Zr was prepared by the method described below. A binary complex oxide composed of Ti and Zr was prepared in the same manner as in Example 1 except that zirconium oxide chloride (ZrOCl ₂ .8H ₂ O) was used instead of Snowtex. The composition of the obtained powder is Ti: Zr =
It was 4: 1 (molar ratio), and Ti was found from the X-ray diffraction chart.
No clear specific peaks of O ₂ and ZrO ₂ were observed, and Ti having an amorphous fine structure was observed due to a broad diffraction peak.
It was confirmed to be a composite oxide composed of Zr and Zr.
A honeycomb-shaped catalyst was obtained in the same manner as in Example 1 by using the powder of the binary composite oxide composed of Ti and Zr. The BET surface area of the obtained catalyst was 85 m ² / g and the pore volume was 0.38 cc / g. The composition of the catalyst is
Ti-Zr composite _{oxide: V 2 O 5: WO 3} : Pt = 90.
It was 9: 2.0: 7.0: 0.1 (weight ratio).

Example 3 A ternary complex oxide composed of Ti, Si and Zr was prepared by the method described below. A ternary complex oxide composed of Ti, Si and Zr was prepared in the same manner as in Example 1 except that zirconium oxide chloride (ZrOCl ₂ .8H ₂ O) was used as a Zr source. The composition of the obtained powder is Ti: Si:
Zr = 20: 4: 1 (molar ratio), and no clear intrinsic peaks of TiO ₂ , SiO ₂ , and ZrO ₂ are observed from the X-ray diffraction chart, and a broad diffraction peak has an amorphous fine structure. It was confirmed to be a composite oxide composed of Ti, Si and Zr. A honeycomb catalyst was obtained in the same manner as in Example 1 using the ternary composite oxide composed of Ti, Si and Zr. The BET surface area of the obtained catalyst was 115 m ² / g and the pore volume was 0.43 cc / g. The composition of the catalyst, Ti-Si-Zr composite _{oxide: V 2 O 5: WO 3} : Pt = 90.9: 2.0: 7.0:
It was 0.1 (weight ratio).

Example 4 A catalyst was prepared in the same manner as in Example 1 except that ammonium paramolybdate was used in place of ammonium metavanadate. The BET surface area of the obtained catalyst was 121 m ² / g and the pore volume was 0.42 cc / g.
Met. The composition of the catalyst, Ti-Si composite _{oxide: MoO 3: WO 3: Pt} = 90.6: 2.0: 7.
It was 0: 0.4 (weight ratio).

Example 5 A catalyst was prepared in the same manner as in Example 1, except that the amount of raw materials used was changed and the palladium nitrate solution was used in place of the chloroplatinic acid solution. Obtained Ti and S
The composition of the binary complex oxide powder consisting of i is Ti: Si =
It was 9: 1 (molar ratio), and Ti was found from the X-ray diffraction chart.
No clear intrinsic peaks of O ₂ and SiO ₂ are observed, and Ti having an amorphous microstructure due to a broad diffraction peak.
It was confirmed that the composite oxide was composed of Si and Si.
The BET surface area of the finally obtained catalyst is 110 m ² / g.
And the pore volume was 0.41 cc / g. Also,
The composition of the catalyst is Ti-Si composite oxide: V ₂ O ₅ : W.
O ₃ : Pd = 89.6: 5.0: 5.0: 0.4 (weight ratio).

Example 6 Example 1 was repeated except that the amount of raw material used was changed and a rhodium nitrate solution was used instead of the chloroplatinic acid solution.
A catalyst was prepared in the same manner as in. The composition of the obtained binary complex oxide powder composed of Ti and Si is Ti: Si = 4:
1 (molar ratio), and TiO ₂ was found from the X-ray diffraction chart.
No clear intrinsic peak of SiO ₂ or SiO ₂ was observed, and a broad diffraction peak confirmed that the compound oxide was a complex oxide composed of Ti and Si having an amorphous fine structure. The finally obtained catalyst had a BET surface area of 95 m ² / g and a pore volume of 0.39 cc / g. The composition of the catalyst, Ti-Si composite _{oxide: V 2 O 5: WO 3} : R
It was h = 84.8: 10.0: 5.0: 0.2 (weight ratio).

Example 7 A catalyst was prepared in the same manner as in Example 5 except that the amount of raw materials used was changed and ammonium metavanadate was not added. The composition of the obtained binary composite oxide powder consisting of Ti and Si is Ti: Si = 4: 1.
(Molar ratio), and no clear specific peaks of TiO ₂ and SiO ₂ are observed from the X-ray diffraction chart, and it is a complex oxide composed of Ti and Si having an amorphous fine structure due to a broad diffraction peak. It was confirmed. The finally obtained catalyst had a BET surface area of 132 m ² / g and a pore volume of 0.44 cc / g. The composition of the catalyst, Ti-Si composite oxide: WO _3: Pd = 89.
It was 6: 10.0: 0.4 (weight ratio).

Example 8 A catalyst was prepared in the same manner as in Example 1 except that the ruthenium chloride solution was used in place of the chloroplatinic acid solution by changing the amount of the example. The composition of the obtained binary complex oxide powder composed of Ti and Si was Ti: Si = 4: 1 (molar ratio), and the clear characteristic peaks of TiO ₂ and SiO ₂ were found from the X-ray diffraction chart. It was confirmed by a broad diffraction peak that was not observed, and it was confirmed to be a composite oxide composed of Ti and Si having an amorphous fine structure. The finally obtained catalyst has a BET surface area of 117 m ² / g and a pore volume of 0.1.
It was 43 cc / g. The composition of the catalyst is Ti-S.
i composite _{oxide: V 2 O 5: WO 3} : Ru = 92.6: 3.
It was 0: 4.0: 0.4 (weight ratio).

Example 9 In the same manner as in Example 1 except that the amount of raw material used was changed and an alcohol solution of iridium chloride was used instead of the chloroplatinic acid solution and ammonium paratungstate was not used. A catalyst was prepared. The composition of the obtained binary complex oxide powder composed of Ti and Si is Ti: Si.
= 4: 1 (molar ratio), and it is T from the X-ray diffraction chart.
No clear intrinsic peaks of iO ₂ and SiO ₂ are observed, and T having a fine amorphous structure due to a broad diffraction peak.
It was confirmed to be a composite oxide composed of i and Si. The BET surface area of the finally obtained catalyst is 92 m ² /
and the pore volume was 0.40 cc / g. The composition of the catalyst, Ti-Si composite oxide: V ₂ O _5: I
It was r = 89: 10: 1 (weight ratio).

Example 10 A catalyst was prepared in the same manner as in Example 1 except that the amount of the raw materials used was changed and ammonium paramolybdate was used instead of ammonium metavanadate and ammonium paratungstate. Obtained Ti and S
The composition of the binary complex oxide powder consisting of i is Ti: Si =
It was 4: 1 (molar ratio), and Ti was found from the X-ray diffraction chart.
No clear intrinsic peaks of O ₂ and SiO ₂ are observed, and Ti having an amorphous microstructure due to a broad diffraction peak.
It was confirmed that the composite oxide was composed of Si and Si.
The BET surface area of the finally obtained catalyst is 127 m ² / g.
And the pore volume was 0.40 cc / g. Also,
The composition of the catalyst, Ti-Si composite oxide: MoO _3: Pt
= 89.8: 10.0: 0.2 (weight ratio).

Comparative Example 1 The same operation as in Example 1 was carried out except that the silica sol was not used, to obtain a powder of TiO2.
The BET surface area of the obtained powder was 75 m ² / g and X
From the line diffraction chart, a clear unique peak of TiO ₂ was recognized. In the TiO ₂ powder thus obtained, Ti:
Fine silica powder (average particle size 2.4 μm, specific surface area 180 m ² / g, pore volume 0.58 cc / g) was mixed so that Si = 4: 1 (molar ratio). The surface area of the obtained powder was 110 m ² / g. Using this mixed powder, a catalyst was prepared in the same manner as in Example 1. BE of the obtained catalyst
T surface area is 102 m ² / g and pore volume is 0.33 c
It was c / g. The composition of the catalyst is TiO ₂ --Si.
O ₂ mixed powder: V ₂ O ₅ : WO ₃ : Pt = 90.8: 2.
It was 0: 7.0: 0.2 (weight ratio).

Test Example 1 Using the catalysts prepared in Examples 1 to 10 and Comparative Example 1, an ammonia decomposition reaction was carried out under the following conditions. The results are shown in Table 1.
Shown in. In neither case was N ₂ O produced. The ammonia decomposition rate, that is, the ammonia removal rate and the NO generation rate were calculated by the following equations.

[0069]

[Equation 2]

[0070]

[Table 1]

Example 11 A catalyst was prepared in the same manner as in Example 1 except that the amount of raw materials used was changed. Obtained Ti and S
The composition of the binary complex oxide powder consisting of i is Ti: Si =
It was 4: 1 (molar ratio), and Ti was found from the X-ray diffraction chart.
No clear intrinsic peaks of O ₂ and SiO ₂ are observed, and Ti having an amorphous microstructure due to a broad diffraction peak.
It was confirmed that the composite oxide was composed of Si and Si.
The BET surface area of the finally obtained catalyst is 112 m ² / g.
And the pore volume was 0.42 cc / g. Also,
The composition of the catalyst is Ti-Si composite oxide: V ₂ O ₅ : W.
O ₃ : Pt = 89.98: 5.00: 5.00: 0.02
(Weight ratio).

Example 12 Example 1 A catalyst was prepared in the same manner as in Example 1 except that the amount of raw materials used was changed and the palladium nitrate solution was used instead of the chloroplatinic acid solution. The composition of the obtained binary complex oxide powder composed of Ti and Si was Ti: Si = 4: 1 (molar ratio), and TiO ₂ and Si were found from the X-ray diffraction chart.
No clear intrinsic peak of O ₂ is observed, and a broad diffraction peak shows Ti and Si having an amorphous fine structure.
It was confirmed that the composite oxide was The BET surface area of the finally obtained catalyst is 114 m ² / g,
The pore volume was 0.40 cc / g. The composition of the catalyst, Ti-Si composite _{oxide: V 2 O 5: WO 3} : Pt =
84.96: 5.00: 10.00: 0.04 (weight ratio)
Met.

Comparative Example 2 A catalyst was prepared in the same manner as in Comparative Example 1 except that the contents of vanadium, tungsten and platinum were changed in Example 1. The BET surface area of the obtained catalyst was 95 m ² / g, and the pore volume was 0.32 cc / g. The composition of the catalyst is TiO ₂ —SiO ₂ mixed powder: V ₂ O ₅ : W.
O ₃ : Pt = 89.98: 5.00: 5.00: 0.02
(Weight ratio).

Test Example 2 Using the catalysts prepared in Examples 11 to 12 and Comparative Example 2, an ammonia decomposition reaction was carried out in the presence of NO under the following conditions. The results are shown in Table 1. In neither case was N ₂ O produced. The denitration rate and the unreacted ammonia decomposition rate (decomposition rate of unreacted ammonia in the denitration reaction) were calculated by the following equations.

[0075]

[Equation 3]

[0076]

[Table 2]

Example 13 Using the catalysts prepared in Example 1, Example 5 and Comparative Example 1, a decomposition treatment reaction was carried out using a gas containing hydrogen sulfide together with ammonia under the following conditions. The results are shown in Table 3. In neither case was N ₂ O produced. The ammonia decomposition rate, NO generation rate, and hydrogen sulfide decomposition rate were obtained by the following equations.

[0078]

[Equation 4]

[0079]

[Table 3]

Example 14 Using the catalysts prepared in Examples 1, 5 and Comparative Example 1, a decomposition treatment reaction was carried out under the following conditions using ammonia and a gas containing methyl mercaptan as a sulfur-containing organic compound. The results are shown in Table 4. N2 in either case
No O formation was observed. Ammonia decomposition rate and N
The O production rate and the methyl mercaptan decomposition rate were determined by the following equations.

[0081]

[Equation 5]

[0082]

[Table 4]

Example 15 Using the catalysts prepared in Examples 1, 5 and Comparative Example 1, a decomposition treatment reaction was carried out under the following conditions using ammonia and a gas containing methyl sulfide as a sulfur-containing organic compound. The results are shown in Table 5. In neither case was N ₂ O produced. The ammonia decomposition rate, NO generation rate, and methyl sulfide decomposition rate were calculated by the following equations.

[0084]

[Equation 6]

[0085]

[Table 5]

Example 16 Using the catalysts prepared in Examples 1, 5 and Comparative Example 1, a decomposition treatment reaction was carried out using ammonia and a gas containing methyl disulfide as a sulfur-containing organic compound under the following conditions. . The results are shown in Table 6. In neither case was N ₂ O produced. The ammonia decomposition rate, NO generation rate, and methyl disulfide decomposition rate were calculated by the following equations.

[0087]

[Equation 7]

[0088]

[Table 6]

Example 17 Using the catalysts prepared in Example 1, Example 5 and Comparative Example 1, a decomposition treatment reaction was carried out under the following conditions using ammonia and a gas containing trimethylamine as a nitrogen-containing organic compound. The results are shown in Table 7. In neither case was N ₂ O produced. The ammonia decomposition rate, NO generation rate, and trimethylamine decomposition rate were calculated by the following equations.

[0090]

[Equation 8]

[0091]

[Table 7]

Example 18 Using the catalysts prepared in Example 1, Example 5 and Comparative Example 1, a decomposition treatment reaction was carried out under the following conditions using ammonia and a gas containing hydrogen sulfide and trimethylamine as a nitrogen-containing organic compound. did. The results are shown in Table 8. In neither case was N ₂ O produced.

[0093]

[Equation 9]

[0094]

[Table 8]

Example 19 Using the catalyst prepared in Example 5, a decomposition treatment reaction was carried out using ammonia and a gas containing sulfur dioxide as a sulfur oxide under the following conditions. The results are shown in Table 9. In neither case was N ₂ O produced. The ammonia decomposition rate and the NO generation rate were calculated by the following equations.

[0096]

[Equation 10]

[0097]

[Table 9]

[0098]

EFFECTS OF THE INVENTION By using the catalyst of the present invention, it has a high ammonia decomposing activity in a wide temperature range from low temperature to high temperature even in the presence of excess oxygen and the presence of other nitrogen-containing compounds and sulfur compounds. N ₂ with high selectivity
Generation of O and NOx is also extremely low, and it is possible to process gas containing ammonia. Moreover, the ammonia decomposition catalyst of the present invention does not require a complicated manufacturing process. Furthermore, when a gas containing at least one compound selected from hydrogen sulfide, a sulfur-containing organic compound and a nitrogen-containing organic compound together with ammonia is decomposed by using the ammonia decomposition catalyst of the present invention, not only ammonia but also the coexisting compounds thereof are simultaneously highly efficient. It can be decomposed. According to the present invention, exhaust gas containing ammonia from various plants, coke oven exhaust gas, exhaust gas containing leaked ammonia from flue gas denitration process by selective catalytic reduction using ammonia as a reducing agent, ammonia-containing gas from ammonia stripping process, city Highly efficient decomposition treatment of gas discharged from cleaning facilities, urban water purification facilities, sludge treatment facilities, etc. is achieved.

Claims (3)

[Claims] 1. A binary complex oxide containing Ti and Si; a binary complex oxide containing Ti and Zr; Ti,
Catalyst A component which is at least one complex oxide selected from the group consisting of ternary complex oxides containing Si and Zr, and at least one metal selected from the group consisting of vanadium, tungsten and molybdenum. Component B which is an oxide of at least one selected from the group consisting of platinum, palladium, rhodium, ruthenium and iridium.
A catalyst for decomposing ammonia, which contains a catalyst C component which is a noble metal or a compound thereof. 2. A method for decomposing ammonia using the catalyst according to claim 1. 3. A gas containing ammonia and at least one compound selected from the group consisting of sulfur oxides, hydrogen sulfide, sulfur-containing organic compounds and nitrogen-containing organic compounds, wherein ammonia containing the catalyst according to claim 1 is used. Disassembly method.