JP2003024784A - Catalyst for decomposing ammonia and its production method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a compact catalyst for decomposing ammonia which is high in activity and does not generate NOx and N2 O and a method for producing the catalyst. SOLUTION: The catalyst comprises the first component of silica or zeolite supporting at least one noble metal selected from platinum (Pt), palladium (Pd), iridium (Ir), and rhodium (Rh) and the second component of a composition comprising an oxide of at least, one metal selected from titanium (Ti), tungsten (W), and vanadium (V). The quantity of a carried noble metal per area of the first component carrier is 0.1-11 g/m<2> , and the quantity of a metal per area of the second component carrier is 50-300 g/m<2> .

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ammonia decomposition catalyst and a method for producing the same, and particularly to ammonia (N) contained in wastewater and exhaust gas discharged from factories and power plants.
The present invention relates to an ammonia decomposition catalyst for efficiently removing H ₃ ) and a method for producing the same.

[0002]

2. Description of the Related Art NH ₃ (ammonia) emitted from various factories such as coke ovens and semiconductor factories, and thermal power plants due to the establishment of environmental standards and wastewater standards for nitrogen and phosphorus from 1993. There is a growing need to efficiently treat wastewater containing water. NH ₃ in the method of processing waste water containing, after migration the NH ₃ in the waste water in the gas by means such as stripping, on NH ₃ decomposing catalyst, the method (environmental creation to detoxify nitrogen, 8, (9 ), 6
7 (1978)) is compact and has high controllability, so biological treatment methods (water treatment engineering, P
No. 206, etc.) is becoming popular.

Further, in the above various factories, not only NH ₃ -containing wastewater but also NH ₃ -containing exhaust gas is generated. Therefore, in order to treat this, the NH ₃ decomposition catalyst is installed in the exhaust gas flue to make it harmless to nitrogen. Method is used.

This NH ₃ decomposition catalyst is conventionally platinum (P
t), a noble metal catalyst obtained by supporting a noble metal such as palladium (Pd) on a carrier such as alumina, silica, and titania (Japanese Patent Publication No. 57-58213) and the like have been used. However, these NH ₃ decomposition catalysts produce harmful nitrogen oxides (NO, NO ₂ ,
A large amount of N ₂ O) is generated. Therefore, in order to prevent NOx by-products, denitration catalyst components (Ti, Mo, V, W, etc.)
And oxidation catalyst components (Pt, Pd, Fe, Ni, Mn, Co
And the like) (see Japanese Patent Laid-Open No. 05-146634)
Japanese Patent Laid-Open No. 08-24651 and the like) have been proposed and have been used in place of conventional catalysts. As a method for producing these catalysts, there is a method in which an active ingredient and a carrier are kneaded in a paste form and then formed into a plate shape or a honeycomb shape.

[0005]

[Problems to be Solved by the Invention] NH₃Decomposition catalyst is semi-conductive
It is often applied to small exhaust systems such as body factories.
Therefore, it is required to be as compact as possible. When
By the time, NH ₃Conventional decomposition catalysts
The ingredients are kneaded into a paste, which is then used as a honeycomb or plate
The method of forming into a honeycomb shape is used.
In the manufacturing method, strength cannot be maintained if the rib thickness is below a certain level.
In addition, in the plate molding method, the thickness of the catalyst is thinner than the base material.
Both of them are limited to narrow pitches
Boundaries, it is difficult to reduce the catalyst volume above a certain level
There was a problem.

On the other hand, a slurry coating method for coating a metal or ceramic substrate with a slurry of a catalyst component powder is a narrow pitch honeycomb shape,
Since the corrugated carrier can be coated with the catalyst, there is an advantage that it can be easily made compact as compared with the conventional honeycomb extrusion molding method or plate molding method.

[0007] However the decomposition of NH _3, the balance was good performed conflicting functions of oxidation and NOx reduction of NH _3, or is important can be suppressed how the amount of NOx by-product with the oxidation of NH ₃ However, the influence of the adjusting method and adjusting conditions on the performance of such an NH ₃ decomposition catalyst is large. In particular, it is known that the performance of the denitration catalyst is remarkably reduced only by adding a few ppm of a noble metal component such as platinum. The NH ₃ decomposition catalyst is composed of a noble metal component that is an oxidizing component of NH ₃ and a denitration catalyst component that is a component that reduces NOx produced as a by-product, that is, an oxide selected from titanium, molybdenum, tungsten, and vanadium. As a method for coating these, it is conceivable to use a slurry prepared by suspending these components in water.
However, in the method of adding a salt of a noble metal component to the denitration catalyst component, the activity of the denitration component is deactivated by the noble metal component, so that high performance was not obtained even if coating was possible.

The object of the present invention is to have high activity and NOx, N
An object of the present invention is to provide a more compact and highly active NH ₃ decomposition catalyst that does not cause a problem such as a by-product of ₂ O, and a method for producing the same.

[0009]

[Means for Solving the Problems]
t), a first component which is silica and / or zeolite carrying one or more noble metals selected from palladium (Pd), iridium (Ir) and rhodium (Rh);
The second component, which is a composition composed of an oxide of one or more elements selected from titanium (Ti), tungsten (W), and vanadium (V), has a loading amount of the first component per carrier area. 0.1 to 11 g / m ² , and the amount of the second component carried per carrier area is 50 to 300 g / m ^2, which is achieved by the ammonia decomposition catalyst.

The inventors of the present invention have earnestly studied a coating method having a high NH ₃ decomposition performance without producing by-products such as NOx, and arrived at the present invention. That is, as a method for adjusting the catalyst slurry for coating, a noble metal-supported catalyst (first component) in which a noble metal is previously supported on silica or zeolite.
And the denitration catalyst (second component) are separately prepared, and these are physically mixed and then mixed with water to form a slurry. At this time, the ratio of both components and the slurry concentration are adjusted so that the amount of each component supported on the carrier is within the range of the present invention to obtain a coating slurry.

By preparing the first component and the second component separately and then physically mixing the two, it is possible to prevent the denitrification activity of the noble metal component from being adversely affected, and to obtain a high NH ₃ content.
It becomes possible to suppress NOx and N ₂ O by-products while maintaining the decomposition rate.

What is more important is the amount of catalyst component supported. The decomposition of NH ₃ by this catalyst is
₃ of the oxidation reaction (1), (2) and by-product N of the second component
Since the Ox removal reaction (3) occurs in a complicated manner,
If too much or too little of each component, NOx by-product and N
This leads to a decrease in the H ₃ oxidation rate, and the performance and the ratio of the first component and the second component and the supported amount greatly affect the performance. That is, a high NH ₃ decomposition rate can be obtained with almost no NOx by-product for the first time within the range of the present invention.

[0013]

Embedded image NH ₃ +3/4/4 O ₂ → 1 / 2N ₂ + 3 / 2H ₂ O (1) NH ₃ + 5 / 4O ₂ → NO + 3 / 2H ₂ O (2) NH ₃ + NO + 1 / 4O ₂ → N ₂ +3 / 2H ₂ O (3) In the catalyst of the present invention, the first component and the second component are water,
Alternatively, a slurry obtained by suspending in a mixed solution of water and silica sol is impregnated into a catalyst carrier and then dried and calcined, or obtained by suspending the first component in water or a mixed solution of silica sol and water in advance. It is prepared by impregnating the catalyst carrier with the slurry, followed by drying and firing, and then impregnating the second component and then drying and firing. The catalyst carrier used here can be any as long as it is usually used as a catalyst carrier, but it is obtained by laminating a carrier substance squeezed between inorganic fibers, flattened or paper-shaped. A paper-like carrier, a corrugate-shaped carrier or a honeycomb-shaped carrier, an expanded metal or other metal substrate, a corrugated-shaped carrier, a staircase-shaped or a honeycomb-shaped carrier, and the like are preferably used. To be

What is important in the catalyst of the present invention is the loading amount of the first component and the second component. The loading amount of the first component is 0.1 to 11 g / m ² per carrier area, preferably 0.25 to
5 g / m ² , the loading amount of the second component per carrier area is 50
It is important that the range is ˜300 g / m ² , preferably 75 to 250 g / m ² . When the amount of the first component carried is less than this, the NH ₃ removal rate is lowered, and when it is more than this, NOx and N ₂ O are by-produced. When the amount of the second component carried is less than this, the amount of by-products of NOx and N ₂ O increases. If the second component loading is greater than this, NH ₃
Although it does not significantly affect the decomposition rate and the amount of NOx and N ₂ O by-products, if the loading amount is too large, problems such as clogging of the carrier and easy separation of catalyst components from the carrier, and catalyst thickness May increase, resulting in a problem such as an increase in pressure loss in the reactor.

The first component of the catalyst used in the present invention is platinum (Pt), palladium (Pd), iridium (Ir).
Or salts of rhodium (Rh) chloride, nitrate, etc.,
Alternatively, a method of heating and kneading an aqueous solution of an oxo acid salt of such a metal with silica or zeolite powder, or in the case of zeolite, immersing the zeolite in the solution and performing ion exchange, etc., is added to 0.1 to 0.001 wt. % Supported. The obtained first component is used after being washed with water, dried, and fired if necessary.

The second component of the catalyst used in the present invention is a denitration catalyst, that is, a titanium oxide-based catalyst powder, preferably a catalyst composition in which vanadium (V) or tungsten oxide is mixed with titanium oxide powder is used. To be Such a catalyst composition can be obtained by, for example, kneading vanadium (V), tungsten (W) oxoacid salt, oxide, chloride or the like with titanium oxide powder, metatitanic acid, orthotitanic acid, or V, W. It can be obtained by a coprecipitation method from a mixed solution of a soluble salt of titanium and a soluble salt of titanium. After firing these compositions at 400-700 ° C,
It is desirable to grind the powder so that 1 μm or less becomes 50% or more before use.

In order to support the first component and the second component on the carrier, the two components are physically mixed and suspended in water or a mixed solution of silica sol and water to form a slurry, or Alternatively, the slurry obtained by suspending the first component in water or a mixed solution of silica sol and water is previously supported on a carrier, dried, and optionally baked, and then the second component is mixed with water or silica sol and water. The slurry obtained by suspending with the mixed solution of (1) is carried, dried and calcined. The slurry concentration varies depending on the structure and properties of the carrier, but the weight of the powder with respect to the liquid is 10 to 60% by weight, preferably 20 to 50%.
Gives good results. If the slurry concentration is lower than this, the amount supported is small and sufficient activity cannot be obtained, so the operation becomes complicated, for example, several loading operations are required to support the required amount. On the other hand, if the concentration is higher than this, the viscosity of the liquid increases and it is difficult to form a slurry state, and it becomes difficult to support the components inside the carrier.

The catalyst according to the present invention contains noble metal in advance.
Noble metal-supported catalyst supported on silica or zeolite (1st generation
Minute) and a denitration catalyst (second component) are separately prepared, and
Supported on a carrier after making a physically mixed mixture into slurry
As a result, a small amount of precious metal catalyst is evenly distributed on the denitration catalyst.
The amount of precious metal that can be maintained in the existing
But enough NH₃Who can get the oxidation performance of
Without reducing the NOx reduction ability due to the noble metal loading
There is no. In addition, by the reaction of the formula (2) on the noble metal catalyst
NO generated is the denitration catalyst existing around the noble metal catalyst.
NH immediately above ₃And reacts with nitrogen according to formula (4).
It is rendered harmless.

The present inventors have also found that N ₂ on the oxidation catalyst
O is generated by the oxidation of NH _{3 as shown in} formula (5)
It is estimated that it is generated from O _{2 as shown in} equation (6). In the catalyst of the present application, since a small amount of the noble metal catalyst is evenly present on the denitration catalyst, NO ₂ produced on the noble metal catalyst is immediately produced on the denitration catalyst by the equation (7) together with NO produced by the equation (2). It is highly probable that they react with each other to become N ₂ and, as a result, the by-product of N ₂ O can be reduced.

[0020]

Embedded image NH ₃ + 7 / 4O ₂ → NO ₂ + 3 / 2H ₂ O (5) NH ₃ + NO ₂ + 1 / 4O ₂ → N ₂ O + 3 / 2H ₂ O (6) NO + NO ₂ + 2NH ₃ → 2N ₂ + 3H ₂ O (7) In the present invention, a noble metal-supported catalyst (first component)
It is possible to obtain the same effect as described above by a method in which the denitration catalyst (second component) is supported after the catalyst is previously supported on the carrier.

[0021]

DETAILED DESCRIPTION OF THE INVENTION

EXAMPLES Examples of the present invention will be shown below. Example 1 1.33 × 10 ^-2 wt% chloroplatinic acid (H ₂ [PtCl
₆ ] · 6H ₂ O) 1l, 100 g of fine silica powder (trade name, Microcomputer F, manufactured by Tomita Pharmaceutical Co., Ltd.) was added, and the mixture was evaporated to dryness in a sand bath and calcined in air at 500 ° C. for 2 hours to give 0.1. 05w
t% Pt.SiO ₂ was prepared to obtain a catalyst composition powder of the first component.

On the other hand, titanium oxide powder (commercially available from Ishihara Sangyo Co., Ltd.
Product name, MCH, SO_FourContent: 3wt%) 46.7kg
Ammonium paratungstate ((NH_Four) 10H_Ten
・ W ₁₂O₄₆・ 6H₂O) 7.43 kg, metavanadate
Add 3.0 kg of ammonium and knead using a kneader,
The obtained paste is dried after granulation and baked at 550 ° C for 2 hours.
did. The obtained granules are crushed to obtain a catalyst component which is the second component.
A product powder was obtained. The composition is Ti / W / V = 91/5/4
(Atomic ratio).

20 g of the first component and 2.02 kg of the second component were suspended in 3.06 kg of water and added to a slurry to obtain a paper honeycomb carrier (manufactured by Nichias Co., trade name, Hanicle 3722, 15).
The support was impregnated with the slurry by immersing it in a 0 mm × 150 mm square, 50 mm long) and then drained by air blow to obtain the catalyst of the present invention. After air-drying this for 12 hours in the air,
Burned for hours. The first component / second component ratio of the first component and the second component in this catalyst was 1/99 (weight ratio, the same below), and the Pt content in the catalyst component corresponded to 5 ppm, and the catalyst loading The amount of the first component and the second component combined was 150 g / m ² per carrier surface area. A test piece was obtained by cutting a length of 5 mm × 8 cells (11 × 14 mm) and a length of 50 mm from the obtained honeycomb catalyst.

Example 2 The first component of Example 1 was 10 g, the second component was 2.02 kg,
A catalyst of the present invention was obtained in the same manner as in Example 1 except that the amount of water was changed to 3.04 kg. The first component / second component ratio of the first component and the second component in this catalyst was 0.5 / 99.5, and the Pt content in the catalyst component corresponded to 2.5 ppm. Is 15 per surface area of the carrier including the first and second components.
It was 0 g / m ² .

Examples 3 to 4 Using the first and second components obtained in Example 1, the amount of water added during slurry preparation was changed to 476 and 816 kg,
The resulting slurry was used as a paper honeycomb carrier (Nichias,
A catalyst of the present invention was obtained by carrying the same on Example 1 (trade name: HANicle 3319, 150 mm × 150 mm square, length 50 mm) in the same manner as in Example 1. The first component / second component ratio of the first component and the second component in this catalyst was 1/99, and the Pt content in the catalyst component corresponded to 5 ppm. The supported amounts of the catalyst are 80 and 50 g / m 2 per surface area of the carrier including the first and second components, respectively.
^{Was 2} .

Example 6 The paper honeycomb carrier of Example 1 was replaced with a metal lath (SUS3).
No. 04, plate thickness 0.2 mmt, 150 mm × 150 mm square), except that the catalyst of the present invention was obtained in the same manner as in the example. The first component / second component ratio of the first component and the second component in the catalyst is 1
/ 99, and the Pt content in the catalyst component corresponds to 5 ppm. The supported amount of the catalyst was 200 g / m ² per surface area of the carrier in total of the first component and the second component. Example 7 The water for slurry preparation of Example 1 was mixed with colloidal silica (Nissan Chemical Co., Ltd., trade name, OS sol, SiO ₂ content 20%) /
A catalyst of the present invention was prepared in the same manner except that water was changed to 3/7. Example 8 20 g of the first component prepared in Example 1 was suspended in 1000 g of a liquid of colloidal silica / water = 3/7, and a paper honeycomb carrier was immersed in this to impregnate the carrier with a slurry,
Drain by air blow, air dry in air for 12 hours, and then 5
It was baked at 00 ° C. for 2 hours. The obtained catalyst was immersed in a slurry obtained by suspending 2.02 kg of the second component of Example 1 in 3.06 kg of water, drained, air-dried, and then calcined at 500 ° C. for 2 hours to obtain the catalyst of the present invention. Was prepared.

Comparative Example 1 Titanium oxide powder (manufactured by Ishihara Sangyo Co., Ltd., trade name, MCH, SO
₄ content: 3wt%) 46.7kg ammonium paratungstate _{((NH 4) 10H 10 ·} W 12 O 46 · 6H 2
O) 7.43 kg, ammonium metavanadate 3.0 k
g, 1.33 × 10 ^-2 wt% chloroplatinic acid (H ₂ [Pt
Cl ₆ ] · 6H ₂ O) 2.14 ml was added and kneaded using a kneader, and the obtained paste was dried after granulation, 550 ° C.
It was baked for 2 hours. The obtained granules were crushed to obtain a catalyst powder. The composition is Ti / W / V = 91/5/4 (atomic ratio)
Therefore, the Pt content corresponds to 5 ppm. Using a slurry obtained by suspending 2.02 kg of the obtained catalyst powder in 3.06 kg of water, a catalyst was supported on a paper honeycomb in the same manner as in Example 1. The supported amount was 151 g / m ² .

Comparative Example 2 Using the first component and the second component obtained in Example 1, the amount of water added during the preparation of the slurry was changed to 10 kg, and the obtained slurry was loaded in the same manner as in Example 1, A catalyst was obtained. The first component / second component ratio of the first component and the second component in the catalyst is 1 /
99, and the Pt content in the catalyst component corresponds to 5 ppm. The supported amount of the catalyst was 30 g / m ² per surface area of the carrier including both the first component and the second component.

Using the oxidation catalysts of Examples 1 to 8 and Comparative Examples 1 and 2, a simulated gas was flown through the flow reactor and the NH ₃ decomposition rate and NO and N ₂ O production of each catalyst under the conditions shown in Table 1. The rate was measured.

[Equation 1] NH ₃ removal rate = (Inlet NH ₃ ppm-Outlet NH ₃ ppm
) / Inlet NH ₃ ppm × 100 (%) NO, N ₂ O generation rate = (Outlet NO, N ₂ Oppm) / Inlet NH ₃ ppm × 100 (%)

[0030]

[Table 1]

[0031]

[Table 2]

The results are shown in Table 2. NH at 400 ° C
_{3 The} removal rate is high in all of Examples 1 to 8 and is 99% or more. However, the catalyst of Comparative Example 1 has an NH ₃ decomposition rate of 99.
%, But NO and N ₂ O generation rates are very high. This is because Pt, which is an oxidizing component, was loaded at the same time as the denitration component, so that the oxidizing ability was maintained, but the denitration performance was significantly reduced. In addition, the catalyst of Comparative Example 2 has a low NH ₃ removal rate because the amount of the catalyst supported is small. It can be seen that high activity cannot be obtained with a loading amount smaller than the range of the present invention.

Further, using the catalysts of Example 1 and Comparative Example 1, the temperature under the conditions of Table 1 was changed to 300 to 450 ° C.
The H ₃ removal activity and the NO and N ₂ O production rates were examined. The obtained results are shown in FIG. As can be seen from FIG. 1, NH ₃
The temperature characteristics of the removal rate were almost the same as those of Example 1 and Comparative Example 1, and the removal rate of all catalysts was about 10 at 300 ° C. or higher.
It is 0%. However, the catalyst of Comparative Example 1 has NO at each temperature.
And the N ₂ O generation rate is high. On the other hand, the catalyst of Example 1 has NO and N ₂ O even in the temperature range of 300 to 450 ° C.
Is low and is less than 1% of NH ₃ . As described above, the catalyst used in the present invention has a wide N range from 300 to 450 ° C.
It can be seen that H ₃ can be completely decomposed.

[0034]

According to the invention described in claim 1, by using the catalyst composed of the specific first component and the specific second component, NH in the gas after stripping the NH ₃ -containing exhaust gas or NH ₃ -containing wastewater ₃ can be efficiently decomposed and removed without producing NOx and N ₂ O as by-products.

According to the invention described in claims 2 to 4, it is possible to provide a preferable method for producing the catalyst described in claim 1.

[Brief description of drawings]

FIG. 1 is a diagram for explaining the effect of the catalyst of the present invention.

Front page continued (51) Int.Cl. ⁷ Identification code FI theme code (reference) B01J 35/06 B01J 37/02 101E 37/02 101 37/08 23/64 103A 37/08 B01D 53/36 ZABE F term (Reference) 4D048 AA08 AB03 BA06X BA07X BA11Y BA23X BA27X BA30X BA31Y BA33Y BA41X BB02 BB03 BB08 4G069 AA03 AA08 BA02A BA02B BA04A BA04B BA07A FB18 FA EA18 FB04 FA20 EA18 FB04 FA20 EA20 FA20 FA20 EA04 BB04A BB04A BB04A BB04A BB04A BB04A BB04A BC14A BC20B07A02 FC08 ZA01A

Claims (4)

[Claims] 1. A first component which is silica and / or zeolite carrying one or more noble metals selected from platinum (Pt), palladium (Pd), iridium (Ir) and rhodium (Rh), and titanium (Ti). ), Tungsten (W) and vanadium (V), and a second component which is a composition consisting of an oxide of one or more elements selected from the group consisting of oxides of tungsten (W) and vanadium (V). ~ 11
g / m ² , the loading amount of the second component per carrier area is 50 to
An ammonia decomposition catalyst, which is 300 g / m ² . 2. A first component which is silica and / or zeolite carrying one or more noble metals selected from platinum (Pt), palladium (Pd), iridium (Ir) and rhodium (Rh), and titanium (Ti). ), Tungsten (W) and vanadium (V) and a second component which is a composition consisting of an oxide of one or more elements selected from the above, and a slurry obtained by suspending it in water or a mixed solution of water and silica sol. A method for producing an ammonia decomposition catalyst, comprising impregnating a particulate matter with a catalyst carrier, followed by drying and firing. 3. Platinum (Pt), palladium (Pd), iridium (Ir) and rhodium (Rh) in advance.
A slurry obtained by suspending the first component, which is silica and / or zeolite supporting one or more noble metals selected from the above, in water or a mixed solution of silica sol and water, is impregnated with a catalyst carrier, and then dried and calcined. Ammonia characterized by being impregnated with a second component, which is a composition consisting of an oxide of one or more elements selected from titanium (Ti), tungsten (W) and vanadium (V), and then dried and fired. Method for producing decomposition catalyst. 4. A paper-shaped carrier obtained by laminating a carrier material, in which a carrier material is laid between inorganic fibers and formed into a flat plate / paper form, which is wound in a corrugated form or in a honeycomb form. The method for producing an ammonia decomposing catalyst according to claim 2 or 3, wherein the laminated body, a metal substrate such as expanded metal, or the like, which is wound in a corrugated shape or laminated in a step shape or a honeycomb shape.