JP2022105849A - Ammonia-decomposing catalyst and exhaust treatment method using the same - Google Patents

Abstract

To provide an ammonia-decomposing catalyst that can maintain excellent ammonia-decomposing capability for a long time and can express excellent low-temperature activity.SOLUTION: The inventive ammonia-decomposing catalyst is to treat exhaust containing ammonia and moisture and comprises a first layer including a noble metal, an inorganic oxide, a first protic zeolite or a first ion-exchange zeolite having been ion-exchanged with Cu, Co or Fe ions, and a second layer that is provided on the surface of the first layer and includes a second protic zeolite or a second ion-exchange zeolite having been ion-exchanged with Cu, Co or Fe ions. The first and second protic zeolites, and the first and second ion-exchange zeolites have CHA type structures.SELECTED DRAWING: Figure 2

Description

The present disclosure relates to an ammonia decomposition catalyst for treating an exhaust gas containing ammonia and water, and an exhaust gas treatment method using the same.

A catalyst that decomposes ammonia contained in exhaust gas is known. Patent Document 1 discloses an ammonia decomposition catalyst including a lower layer and an upper layer. The lower layer contains a noble metal, an inorganic oxide, phosphorus and a predetermined zeolite. On the other hand, the upper layer contains a predetermined zeolite. Patent Document 2 discloses an ammonia decomposition catalyst containing copper oxide, zeolite, a noble metal, and phosphorus.

International Publication No. 2015/099024 International Publication No. 2009/075311

According to the studies by the present inventors, the ammonia decomposition catalyst described in Patent Document 1 can maintain excellent ammonia resolution for a long period of time, but has a processing ability under low temperature conditions of 300 ° C. or lower and a higher spatial velocity ( There was room for improvement in the processing under the SV) condition.

The present disclosure provides an ammonia decomposition catalyst capable of maintaining excellent ammonia resolution for a long period of time and exhibiting excellent low temperature activity, and an exhaust gas treatment method using the same.

One aspect of the present disclosure relates to an ammonia decomposition catalyst. This ammonia decomposition catalyst is for treating exhaust gas containing ammonia and water, and is a first ion exchanged with a noble metal, an inorganic oxide, and a first proton-type zeolite or Cu, Co, or Fe ions. A first layer containing the ion-exchange type zeolite of the above, and a second ion exchange provided on the surface of the first layer and ion-exchanged with the second proton-type zeolite or Cu, Co or Fe ions. The first and second proton type zeolites and the first and second ion exchange type zeolites are provided with a second layer containing a type zeolite, and have a CHA type structure.

One aspect of the present disclosure relates to an exhaust gas treatment method. This exhaust gas treatment method includes a step of bringing an exhaust gas containing ammonia and water into contact with the above-mentioned ammonia decomposition catalyst according to the present disclosure to decompose ammonia into nitrogen and water.

According to the present disclosure, there is provided an ammonia decomposition catalyst capable of maintaining excellent ammonia resolution for a long period of time and exhibiting excellent low temperature activity, and an exhaust gas treatment method using the same.

FIG. 1 is a cross-sectional view schematically showing how the decomposition reaction of ammonia proceeds in the ammonia decomposition catalyst according to the embodiment of the present disclosure. FIG. 2 is a graph showing the durability test results of the catalyst A-4 (inlet temperature: 340 ° C., SV: 10000h ^-1 , NH ₃ concentration: 1%). FIG. 3 is a graph showing the durability test results of catalyst B-6 (inlet temperature: 340 ° C., SV: 10000h ^-1 , NH ₃ concentration: 1%).

<Definition of terms>
Unless otherwise specified, the meanings of the terms used in the present specification are as follows.
-Ammonia decomposition rate: Represents the ratio (%) of the ammonia concentration in the exhaust gas before and after contact with the catalyst.
-NO _X production rate: Represents the ratio (%) of the NO _X concentration generated in the exhaust gas after contact to the ammonia concentration in the exhaust gas before contact with the catalyst.
N ₂ O production rate: Represents the ratio (%) of N ₂ O produced in the exhaust gas after contact with respect to the ammonia concentration in the exhaust gas before contact with the catalyst.
-Nitrogen oxide: Refers to both NO _X and N ₂ O, and may be expressed as NO _X or the like.
-N ₂ selectivity: Represents a value obtained by subtracting the production rate of NO _X , etc. in the exhaust gas after contact with the catalyst from the ammonia decomposition rate. That is, it is the ratio of ammonia converted to N ₂ before it comes into contact with the catalyst.

Hereinafter, embodiments of the present disclosure will be described in detail. The present invention is not limited to the following embodiments.

[Ammonia decomposition catalyst]
FIG. 1 is a cross-sectional view schematically showing how the decomposition reaction of ammonia proceeds in the ammonia decomposition catalyst according to the present embodiment. The ammonia decomposition catalyst 10 shown in this figure includes a support S, a lower layer 1 (first layer) provided on the surface of the support S, and an upper layer 2 (first layer) provided on the surface of the lower layer 1. It has two layers).

<Support>
The support S preferably has a shape in which the differential pressure generated during gas flow is small and the contact area with the gas is large. Specific examples of the support S include honeycombs, sheets, meshes, fibers, pipes, filters, spheres and the like. The material of the support is, for example, a known catalyst carrier such as cordierite or alumina, a metal such as carbon fiber, metal fiber, glass fiber, ceramic fiber, titanium, aluminum or stainless steel.

<Lower layer>
The lower layer 1 contains a noble metal, an inorganic oxide, and a first proton-type zeolite or a first ion-exchange type zeolite ion-exchanged with Cu, Co or Fe ions. The lower layer 1 is provided on the surface of the support S. The thickness of the lower layer 1 is preferably 10 to 200 μm, more preferably 30 to 100 μm. In the lower layer 1, the oxidation reaction represented by the following formula (1) mainly proceeds, and the denitration reaction represented by the following formula (2) also proceeds.
Oxidation reaction: NH ₃ + O ₂ → NO _X + N ₂ O + H ₂ O + N ₂ ... (1)
Denitration reaction: NO _X + NH ₃ + O ₂ → N ₂ + O ₂ ... (2)

(Precious metal)
The lower layer 1 contains a precious metal. Examples of the noble metal include Pt, Pd, Ir, Rh and composites thereof. Among these, Pt is particularly preferable because it has a large effect of improving the decomposition activity and the _N2 selectivity.

The content of the noble metal is preferably 0.3 to 10% by mass, more preferably 0.5 to 8% by mass, based on the total amount of the noble metal, the inorganic oxide and the zeolite contained in the lower layer 1. The amount of the noble metal supported is preferably 0.03 to 1 g / L, more preferably 0.1 to 0.9 g / L, and further preferably 0.15 to 0.8 g / L with respect to the catalyst volume. It is L. When the amount of the noble metal is within the above range, better results can be obtained with respect to the ammonia decomposition rate, the NO _X production rate and the N ₂ O production rate.

(Inorganic oxide)
The lower layer 1 contains an inorganic oxide. Inorganic oxides are represented by titania (TIO ₂ ), zirconia (ZrO ₂ ), silica (SiO ₂ ), alumina, and composite oxides and solid solutions (CeO ₂ and ZrO ₂ ) of ceria and zirconia, and CeO ₂ : ZrO. The ₂ molar ratio is 1: 3 to 3: 1). Of these, one type may be used alone, or two or more types may be used in combination. Inorganic oxides contribute to the action of precious metals, that is, the improvement of decomposition activity, especially the sustainability of decomposition activity during long-term use. Among the above-mentioned inorganic oxides, TiO ₂ , ZrO ₂ and ceria zirconia (composite oxide or solid solution) are particularly excellent in the effect of sustaining the decomposition activity in long-term use. The content of the inorganic oxide is preferably 5 to 50% by mass, more preferably 10 to 35% by mass, based on the total amount of the noble metal, the inorganic oxide and the zeolite contained in the lower layer 1. The amount of the inorganic oxide supported is preferably 1 to 50 g / L, and more preferably 5 to 20 g / L with respect to the catalyst volume. When the amount of the inorganic oxide is within the above range, better results can be obtained with respect to the ammonia decomposition rate, the _NOX production rate and the _N2O production rate.

It is particularly effective to contain the inorganic oxide in the catalyst in a state where the noble metal is supported. For example, particles (referred to as Pt / TiO ₂ ) in which 0.1 to 10% by mass (based on the mass of TiO ₂ ) of Pt are previously supported on TiO ₂ particles are prepared, and the particles are used as other particles. By mixing with the components of, a catalyst composition containing a noble metal and an inorganic oxide can be prepared.

The inorganic oxide is preferably in the form of particles from the viewpoint of more effectively exerting the function of the noble metal component in the catalyst composition. The average particle size of the inorganic oxide is, for example, 0.1 to 100 μm. Here, the particle size is the size of the secondary particles, and is the length of the major axis when observed by SEM. The average particle size is an average value when the major axis is measured using SEM for at least 10 particles.

When TiO ₂ particles are used as the inorganic oxide, the BET specific surface area of the TiO ₂ particles is preferably 5 to 200 m ² / g, and more preferably 10 to 150 m ² / g. When ZrO ₂ particles are used as the inorganic oxide, it is preferable to use porous ZrO ₂ particles having a specific surface area of 10 m ² / g or more. ZrO ₂ may be monoclinic, tetragonal, or cubic. Further, a composite system ZrO ₂ (for example, ZrO ₂ · nCeO ₂ , ZrO ₂ · nSiO ₂ , ZrO ₂ · nTIO ₂ and n are generally 0.25 to 0.75) may be used. When SiO ₂ is used as the inorganic oxide, it is preferable to use a high silica zeolite having a zeolite structure (for example, mordenite).

(Zeolite)
The lower layer 1 contains a zeolite having a CHA type structure. The CHA type structure has a three-dimensional pore structure. As the CHA-type structure zeolite, in addition to the proton type (H type), an ion exchange type zeolite ion-exchanged with Cu, Co or Fe can be used. One of these zeolites may be used alone, or two or more of them may be used in combination.

Zeolites are preferably in the form of particles. The average particle size of the zeolite is, for example, 0.1 to 5.0 μm. Here, the particle size is the size of the zeolite crystal, and is the length of the major axis when observed by SEM. The average particle size is an average value when the major axis is measured using SEM for at least 10 particles.

From the viewpoint of NO _X suppression performance and durability, it is preferable to use Cu ion exchange CHA type zeolite as the zeolite having a CHA type structure, and Cu ion exchange SSZ zeolite (SSZ-13) or Cu ion exchange SAPO-34. It is more preferable to use zeolite. The silica-alumina ratio (SAR, Si / Al) of the Cu ion-exchanged SSZ zeolite is preferably 10 to 50, more preferably 10 to 20. When the SAR is less than 10, the NOx reducing ability tends to increase but the resistance under hydrothermal conditions tends to decrease, while when it exceeds 50, the resistance under hydrothermal conditions increases but the NOx reducing ability decreases. Tend to do. The amount of aluminum phosphate (Al + P) / Si of the Cu ion-exchanged SAPO zeolite with respect to silica is preferably 1 to 30, and more preferably 5 to 30. When the (Al + P) / Si ratio is less than 1, the durability tends to decrease under hydrothermal conditions, while when it exceeds 30, the NOx reduction performance tends to decrease.

The _NOX reduction performance (denitration performance) of Cu ion-exchanged zeolite by NH ₃ tends to be better when the dispersibility of Cu is high, and when the amount of solid acid held by the zeolite is large. In general, the acid content of zeolite is higher when the SAR is low, but zeolite with a low SAR is more hydrophilic, dealuminum is likely to proceed under high temperature and high moisture conditions, the acid content decreases over time, and denitration is performed. Performance tends to deteriorate. Similarly, it can be inferred that the lower the (Al + P) / Si of the SAPO-based zeolite, the higher the acid content and the same tendency. The Cu ion-exchanged SSZ zeolite (SSZ-13) or the Cu ion-exchanged SAPO zeolite (SAPO-34) in the present embodiment has structurally high hydrothermal stability, and thus has a higher hydrothermal stability than β-zeolite (SAR: 35). Since it can be catalyzed with a composition having a large amount of acid, it is presumed that both NO _X suppression performance and durability can be achieved.

The content of the CHA-type structure zeolite contained in the lower layer 1 is preferably 40 to 95% by mass, more preferably 50 to 90% by mass, based on the total amount of the noble metal, the inorganic oxide and the zeolite contained in the lower layer 1. %. The amount of zeolite supported on the CHA-type structure in the lower layer 1 is preferably 5 to 95 g / L, and more preferably 10 to 90 g / L with respect to the catalyst volume. When the amount of zeolite in the lower layer 1 is within the above range, better results can be obtained with respect to the ammonia decomposition rate, the NO _X production rate and the N ₂ O production rate.

The ammonia decomposition catalyst described in Patent Document 1 contains predetermined phosphorus in the lower layer from the viewpoint of improving water heat resistance. On the other hand, since the lower layer 1 of the ammonia decomposition catalyst according to the present embodiment has excellent water heat resistance due to the zeolite having a CHA type structure, the lower layer 1 does not have to contain phosphorus. Even if the lower layer 1 contains phosphorus, its content (based on the total of precious metals, inorganic oxides, phosphorus and zeolite contained in the lower layer 1) may be less than 0.05% by mass and less than 0.01% by mass. There may be. The evaluation test carried out by the present inventors has experimentally shown that the low temperature activity of the lower layer 1 is improved by not adding phosphorus to the lower layer 1 (see Examples 1 and 13).

<Upper layer>
The upper layer 2 contains a second proton-type zeolite or a second ion-exchange type zeolite ion-exchanged with Cu, Co or Fe ions. The upper layer 2 is provided on the surface of the lower layer 1. The thickness of the upper layer 2 is preferably 10 to 200 μm, more preferably 30 to 100 μm. The denitration reaction represented by the following formula (2) mainly proceeds in the upper layer 2.
Denitration reaction: NO _X + NH ₃ + O ₂ → N ₂ + O ₂ ... (2)

The zeolite contained in the upper layer 2 has a CHA type structure like the zeolite contained in the lower layer 1. As the CHA-type structure zeolite, in addition to the proton type (H type), an ion exchange type zeolite ion-exchanged with Cu, Co or Fe can be used. One of these zeolites may be used alone, or two or more of them may be used in combination. Like the lower layer 1, the zeolite contained in the upper layer 2 is preferably a Cu ion exchange CHA type zeolite, and may be a Cu ion exchange SSZ zeolite (SSZ-13) or a Cu ion exchange SAPO zeolite (SAPO-34). More preferred. The zeolite contained in the upper layer 2 may be the same as or different from the zeolite contained in the lower layer 1.

The amount of zeolite supported on the CHA-type structure in the upper layer 2 is preferably 20 to 150 g / L, and more preferably 30 to 130 g / L with respect to the catalyst volume. When the amount of zeolite in the upper layer 2 is within the above range, better results can be obtained with respect to the ammonia decomposition rate, the NO _X production rate and the N ₂ O production rate.

The amount of zeolite contained in the upper layer 2 (total amount of proton-type zeolite and ion-exchange-type zeolite) is preferably 20 to 400 parts by mass, assuming that the total amount of noble metal, inorganic oxide and zeolite contained in the lower layer 1 is 100 parts by mass. Parts, more preferably 50 to 150 parts by mass. When this amount is 50 parts by mass or more, the NO _X production rate tends to be lower due to the denitration reaction in the upper layer 2, while when it is 150 parts by mass or less, ammonia is efficiently transferred to the lower layer 1. It tends to be decomposed by contact.

[Manufacturing method of ammonia decomposition catalyst]
Hereinafter, a method for producing the ammonia decomposition catalyst of the present embodiment will be described. However, the manufacturing method is not limited to the following methods.

First, a noble metal-containing aqueous solution is placed in a container, and an inorganic oxide is added thereto. After sufficiently impregnating the inorganic oxide with the noble metal-containing aqueous solution, the mixture is heated with stirring to evaporate the water content and dry. Then, it is further heated in a dryer, and the obtained powder is calcined in air to obtain inorganic oxide particles carrying a predetermined amount of noble metal (as a metal component).

After mixing this powder with deionized water, a predetermined amount of the inorganic binder and the above-mentioned zeolite are mixed therein to prepare a slurry composition for a lower layer. This slurry is applied to the support S, and the surplus is blown off by an air blow. Then, the lower layer 1 is formed on the surface of the support S by heating, drying, and firing in a high-temperature furnace under air flow. Examples of the inorganic binder blended in the slurry include colloidal silica, silica sol, alumina sol, silicate sol, titania sol, boehmite, white clay, kaolin, and sepiolite. An organic binder may be used instead of the inorganic binder.

Deionized water, a predetermined amount of the inorganic binder and the above-mentioned zeolite are mixed to prepare a slurry for the upper layer. This slurry is applied on the surface of the lower layer 1 and the surplus is blown off by an air blow. Then, drying and baking are carried out in the same manner as described above. As a result, the ammonia decomposition catalyst 10 composed of two layers, the lower layer 1 and the upper layer 2, is obtained.

[Exhaust gas treatment method]
The exhaust gas treatment method according to the present embodiment includes a step of decomposing ammonia into nitrogen and water by bringing the exhaust gas containing ammonia and water into contact with the ammonia decomposition catalyst 10. Specific examples of exhaust gas containing ammonia (ammonia exhaust gas) include treatment of ammonia water in factories such as semiconductor factories, coke oven exhaust gas, leak gas from flue gas denitration process, strike of ammonia-containing wastewater in sewage treatment plants, sludge treatment facilities, etc. Exhaust gas generated by ripping can be mentioned.

The ammonia concentration of the ammonia exhaust gas is, for example, 10% by volume ppm to 5% by volume. Ammonia exhaust gas and air are brought into contact with the ammonia decomposition catalyst 10, and ammonia is converted into harmless nitrogen gas and water for oxidative decomposition. This oxidative decomposition temperature is appropriately determined depending on the properties (water vapor concentration and ammonia concentration) in the exhaust gas, reaction conditions (temperature, space velocity), the degree of catalyst deterioration, etc., but is usually 200 to 500 ° C, preferably 250 to 450 ° C. It is appropriate to select from the temperature range of. The water vapor concentration of the ammonia exhaust gas is, for example, 10% by volume or more, and may be 20 to 50% by volume.

The space velocity (SV) of the exhaust gas to be treated with respect to the catalyst may be appropriately selected from the range of 100 to 100,000 h ^-1 in consideration of the properties of the gas (ammonia concentration and water concentration), the target value of the ammonia decomposition rate, and the like. The concentration of ammonia in the gas supplied to the catalyst reactor is preferably adjusted to 3% by volume or less, preferably 2% by volume or less. When the concentration of ammonia exceeds 3% by volume, the temperature of the catalyst layer rises too much due to the heat generated by the reaction, and the catalyst tends to deteriorate.

When treating exhaust gas that does not contain sufficient oxygen required for the decomposition reaction, the oxygen amount / theoretical required oxygen amount ratio is, for example, 1.03 or more (preferably 2.0 or more) at the inlet of the catalytic reactor. ), Air or oxygen-containing gas may be mixed from the outside. Here, the theoretical required oxygen amount is a stoichiometric oxygen amount obtained from the following formula (3), and when the inlet ammonia concentration of the reactor is 1.0% by volume, the oxygen concentration is, for example, 0.77. The above (preferably 0.83% by volume or more).
4NH ₃ + 3O ₂ → 6H ₂ O + 2N ₂ ... (3)

Instead of the ammonia decomposition catalyst 10 having the lower layer 1 and the upper layer 2, a first catalyst having the same structure as the lower layer 1 and a second catalyst having the same structure as the upper layer 2 are prepared, and these catalysts are prepared. Ammonia contained in the exhaust gas may be decomposed by alternately installing the exhaust gas and sequentially contacting the exhaust gas. That is, the exhaust gas treatment method includes a step of bringing the exhaust gas into contact with the first catalyst and a step of bringing the generated gas generated by the contact of the exhaust gas with the first catalyst into contact with the second catalyst. May be good.

The following is an example of ammonia stripping exhaust gas. After adjusting the pH of the ammonia-containing wastewater (for example, cleaning liquid in semiconductor manufacturing, sulfuric acid scrubber liquid that collects ammonia, dehydration liquid of sewage sludge) to around 10 with sodium hydroxide, etc., and heating to 50 ° C to 90 ° C, Ammonia is released into the gas phase by sending air, nitrogen, and steam. After that, steam (exhaust gas) containing high-concentration water and ammonia is introduced into the catalytic reaction device, a required amount of air is separately introduced from the outside, and the ammonia is decomposed into nitrogen and steam by contacting the catalyst to make it harmless. To process.

According to the ammonia decomposition catalyst according to the present embodiment, excellent ammonia resolution is exhibited even if the amount of the noble metal supported is reduced as compared with the conventional case. It is presumed that this is because the CHA-type structure zeolite contained in the lower layer and the upper layer has excellent denitration performance. In addition to this, the CHA-type structure zeolite has excellent water heat resistance, so that excellent ammonia resolution is maintained for a long period of time. Further, when the phosphorus content in the ammonia decomposition catalyst is sufficiently low or the phosphorus is substantially not contained, excellent ammonia resolution is exhibited even under low temperature conditions of about 300 ° C. According to the studies by the present inventors, phosphorus has an effect of lowering the low temperature activity while improving the water heat resistance of the ammonia decomposition catalyst.

Hereinafter, the present invention will be described in detail with reference to Examples. The present invention is not limited to these.

[Catalyst preparation]
<Catalyst A-1>
TIO ₂ powder (manufactured by Ishihara Sangyo Co., Ltd., average particle size 1 μm, BET specific surface area; 60 m ² / g) is added to an aqueous solution of dinitrodiamine platinum ₍ Pt concentration; 4.5% by mass) in an evaporating dish. The powder was sufficiently impregnated with an aqueous solution. Then, at a temperature of 80 to 90 ° C., the water was evaporated with stirring and dried. Then, it was further heated to 150 ° C. in a dryer. The obtained powder was calcined in air at a temperature of 500 ° C. for 1 hour, and TIO ₂ particles carrying 5.0% by mass of Pt (as a metal content) (referred to as Pt (5.0) / TiO ₂ ). I got.). This powder and 64.4 g of deionized water were mixed to form a slurry. This slurry is mixed with 249 g of silica sol (Snowtex C manufactured by Nissan Chemical Industries, Ltd.) and 142.3 g of Cu ion-exchanged SSZ zeolite (manufactured by Zeolite, hereinafter sometimes referred to as "Cu-SSZ-13"). To prepare a slurry for the lower layer. This lower layer slurry is applied to a support of 200 cells of Kojilite honeycomb (number of cells: 200 cells / square inch, length 50 mm x width 50 mm x height 50 mm, volume: 0.125 liters), and the excess is blown off by air blow. rice field. Then, it was dried in a dryer at 150 ° C. for 4 hours, and further fired in a high temperature furnace under air flow at 500 ° C. for 4 hours to obtain a catalyst for the lower layer. At this time, the amount of Pt was 0.5 g per liter of the catalyst, and the amount of Cu ion-exchanged SSZ zeolite was 70 g.

Next, 64.4 g of deionized water, 249 g of silica sol (Snowtex C manufactured by Nissan Chemical Industries, Ltd.) and 142.3 g of Cu ion exchange SSZ zeolite (manufactured by Zeolist) are mixed to form an upper layer slurry (Cu-SSZ slurry). Was prepared. This slurry was applied on the lower layer catalyst, and the surplus was blown off by an air blow. Then, drying and firing were carried out in the same manner as above to obtain a catalyst A-1 having a two-layer structure. At this time, the amount of Cu ion-exchanged SSZ zeolite supported on the upper layer was 64 g per liter of catalyst volume.

<Catalyst A-2>
Same as catalyst A-1 except that the amount of Pt was changed from Pt (5.0) / TiO ₂ (0.5 g / L) to Pt (3.0) / TiO ₂ (0.3 g / L). Catalyst A-2 was obtained.

<Catalyst A-3>
Same as catalyst A-1 except that the amount of Pt was changed from Pt (5.0) / TiO ₂ (0.5 g / L) to Pt (7.5) / TiO ₂ (0.75 g / L). Catalyst A-2 was obtained.

<Catalyst A-4>
The catalyst A-4 was obtained in the same manner as the catalyst A-1 except that the thickness of the lower layer was adjusted so that the mass per unit area of the lower layer was half that of the catalyst A-1.

<Catalyst A-5>
The catalyst A-5 was obtained in the same manner as the catalyst A-1 except that the thickness of the lower layer was adjusted so that the mass per unit area of the lower layer was 1.5 times that of the catalyst A-1.

<Catalyst A-6>
The catalyst A-6 was obtained in the same manner as the catalyst A-1 except that the loading amount of the upper layer of the catalyst A-1 was changed from 64 g / L to 50 g / L.

<Catalyst A-7>
The catalyst A-6 was obtained in the same manner as the catalyst A-1 except that the loading amount of the upper layer was changed from 64 g / L to 100 g / L.

<Catalyst A-8>
The catalyst A-8 was obtained in the same manner as the catalyst A-4 except that the loading amount of the upper layer was changed from 64 g / L to 50 g / L.

<Catalyst A-9>
Catalyst A-9 was obtained in the same manner as catalyst A-4 except that the loading amount of the upper layer was changed from 64 g / L to 100 g / L.

<Catalyst A-10>
Instead of Cu ion-exchanged SSZ zeolite, Fe ion-exchanged SSZ (H-type SSZ-13 manufactured by Zeorist with ion-exchanged Fe) may be hereinafter referred to as "Fe-SSZ-13". ) Was used, and the catalyst A-10 was obtained in the same manner as the catalyst A-1.

<Catalyst A-11>
The catalyst A-11 was obtained in the same manner as the catalyst A-1 except that ZrO ₂ powder was used instead of the TiO ₂ powder as the inorganic oxide in the lower layer.

<Catalyst A-12>
Instead of Cu ion exchange SSZ zeolite for the formation of the lower layer and the upper layer, Cu ion exchange SAPO-34 (H-type SAPO-34 manufactured by UOP with Cu ion exchange supported), hereinafter referred to as "Cu-SAPO-34". Sometimes. ) Was used, and the catalyst A-12 was obtained in the same manner as the catalyst A-1.

<Catalyst A-13>
First, a lower layer was formed on the surface of the cozy light honeycomb in the same manner as the catalyst A-1.
Next, a phosphorus solution was applied to the surface of the lower layer, and the excess liquid was blown off by an air blow. Then, the upper layer was formed in the same manner as the catalyst A-1. As the phosphorus solution, a mixture of 50 g of an 85% phosphoric acid solution and 500 g of deionized water was used.

<Comparative catalyst B-1>
A slurry was prepared by mixing Pt (5.0) / TiO ₂ powder, deionized water and silica sol. This slurry was applied to the support of the Kojilite honeycomb 200 cell, and the surplus was blown off by an air blow. Then, it was dried in a dryer at 150 ° C. for 4 hours, and further fired in a high temperature furnace under air flow at 500 ° C. for 4 hours to obtain a comparative catalyst B-1.

<Comparative catalyst B-2>
Pt (5.0) / TiO ₂ powder, deionized water, silica sol, and Cu ion-exchanged β-zeolite (manufactured by Clariant catalyst, hereinafter sometimes referred to as “Cuβ”) were mixed to prepare a slurry. A comparative catalyst B-2 was obtained in the same manner as the comparative catalyst B-1, except that a slurry containing Cuβ was used.

<Comparative catalyst B-3>
A lower layer was formed on the surface of the cordylite support in the same manner as in the comparative catalyst B-2. Next, 50 g of an 85% phosphoric acid solution and 500 g of deionized water were mixed to prepare a phosphorus solution. This solution was applied to the surface of the lower layer, and the excess liquid was blown off by an air blow. Then, it was dried in a dryer at 150 ° C. for 4 hours, and further fired in a high temperature furnace under air flow at 500 ° C. for 4 hours to obtain a comparative catalyst B-3.

<Comparative catalyst B-4>
A slurry (Cuβ slurry) was prepared by mixing 64.4 g of deionized water, 249 g of silica sol (Snowtex C manufactured by Nissan Chemical Industries, Ltd.) and 142.3 g of Cu ion-exchanged β-zeolite (manufactured by Clariant Catalyst). This slurry was applied onto the comparative catalyst B-2, and the surplus was blown off by an air blow. Then, it was dried in a dryer at 150 ° C. for 4 hours, and further fired in a high temperature furnace under air flow at 500 ° C. for 4 hours to obtain a comparative catalyst B-4.

<Comparative catalyst B-5>
A comparative catalyst B-5 was obtained in the same manner as the comparative catalyst B-4, except that the upper layer slurry (Cuβ slurry) was applied on the comparative catalyst B-1.

<Comparative catalyst B-6>
A comparative catalyst B-5 was obtained in the same manner as the comparative catalyst B-4, except that the upper layer slurry (Cuβ slurry) was applied on the comparative catalyst B-3.

Table 1 shows the composition and the amount of the lower layer and the upper layer of each catalyst.

<Activity evaluation test>
A columnar (diameter 21 mm, length 50 mm) honeycomb catalyst was collected from the honeycomb catalyst obtained as described above, and the catalyst was filled in a flow-type reactor. A predetermined amount of gas was circulated by controlling the flow rate with a mass flow controller. By heating the catalyst in an electric furnace, the ammonia decomposition activity was evaluated with the temperature at the catalyst inlet (inlet temperature) as a predetermined temperature. Tables 2 and 3 show the evaluation conditions and initial activity data.

<Gas analysis method>
・ Ammonia: gas chromatography (TCD detector) or gas detector tube ・ NO _X : chemiluminescence (chemiluminescence type) analyzer ・ N2O: gas chromatography ₍ TCD detector)

<Calculation>
-NH ₃ decomposition rate (%): 100-{(outlet NH ₃ concentration) / (inlet NH ₃ concentration) x 100}
-NO _X generation rate (%): (outlet NO _X concentration) / (inlet NH ₃ concentration) x 100
N ₂ O generation rate (%): {(outlet N ₂ O concentration) / (inlet NH ₃ concentration)} × 100
N ₂ selectivity (%): 100-{(100-NH ₃ decomposition rate) + NO _X generation rate + N ₂ O generation rate x 2}

<Durability test>
Durability tests were performed using catalyst A-4, catalyst A-12, catalyst A-13, and catalyst B-6, respectively. The results are shown in Table 4.

FIG. 2 is a graph showing the durability test results of the catalyst A-4 (inlet temperature: 340 ° C., SV: 10000h ^-1 , NH ₃ concentration: 1%). FIG. 3 is a graph showing the durability test results of catalyst B-6 (inlet temperature: 340 ° C., SV: 10000h ^-1 , NH ₃ concentration: 1%). As shown in these graphs, the catalyst A-4 (catalyst according to the example) maintains a low NO _X production rate for a long period of time as compared with the catalyst B-6, despite the small amount of platinum carried. did it.

<Performance evaluation under high SV conditions>
Performance tests were performed under high SV conditions using catalyst A-1, catalyst A-4 and catalyst B-6, respectively. The results are shown in Table 5.

As shown in Table 5, the catalyst A-1 and the catalyst A-4 were able to maintain a low NO _X production rate as compared with the catalyst B-6 even when the SV was increased.

Claims (12)

An ammonia decomposition catalyst for treating exhaust gas containing ammonia and water.
A first layer containing a noble metal, an inorganic oxide, and a first proton-type zeolite or a first ion-exchange type zeolite ion-exchanged with Cu, Co, or Fe ions.
A second layer provided on the surface of the first layer and containing a second proton-type zeolite or a second ion-exchange type zeolite ion-exchanged with Cu, Co or Fe ions.
Equipped with
An ammonia decomposition catalyst in which the first and second proton-type zeolites and the first and second ion-exchange-type zeolites have a CHA-type structure. The ammonia decomposition catalyst according to claim 1, wherein the noble metal is at least one selected from the group consisting of Pt, Pd, Ir and Rh. The ammonia decomposition catalyst according to claim 1 or 2, wherein the inorganic oxide is at least one selected from the group consisting of titania, zirconia, ceria zirconia, alumina and silica. The ammonia decomposition catalyst according to any one of claims 1 to 3, wherein at least one of the first and second ion exchange type zeolites is a Cu ion exchange CHA type zeolite. The ammonia decomposition catalyst according to any one of claims 1 to 4, wherein at least one of the first and second ion exchange type zeolites is a Cu ion exchange SSZ zeolite. The ammonia decomposition catalyst according to any one of claims 1 to 4, wherein at least one of the first and second ion exchange type zeolites is a Cu ion exchange SAPO zeolite. The ammonia decomposition catalyst according to any one of claims 1 to 6, further comprising a support provided on the opposite side of the first layer from the second layer. Assuming that the total amount of the noble metal, the inorganic oxide and the zeolite in the first layer is 100 parts by mass, the contents of the noble metal, the inorganic oxide and the zeolite in the first layer are in the following ranges, respectively, according to claims 1 to 1. 7. The ammonia decomposition catalyst according to any one of 7.
-Precious metal: 0.3 to 10 parts by mass-Inorganic oxide: 5 to 50 parts by mass-Zeolite: 40 to 95 parts by mass Claims 1 to 8, wherein the amount of zeolite contained in the second layer is 20 to 400 parts by mass, assuming that the total amount of the noble metal, the inorganic oxide and the zeolite contained in the first layer is 100 parts by mass. The ammonia decomposition catalyst according to any one of the above. Any of claims 1 to 9, wherein the phosphorus content of the first layer is less than 0.05 parts by mass, assuming that the total amount of the noble metal, the inorganic oxide and the zeolite contained in the first layer is 100 parts by mass. The ammonia decomposition catalyst according to item 1. It is an exhaust gas treatment method for treating exhaust gas containing ammonia and water.
A method for treating exhaust gas, which comprises a step of bringing the ammonia decomposition catalyst according to any one of claims 1 to 10 into contact with the exhaust gas to decompose ammonia into nitrogen and water. It is an exhaust gas treatment method for treating exhaust gas containing ammonia and water.
It includes a step of sequentially contacting the exhaust gas with the first catalyst and the second catalyst installed alternately.
The first catalyst comprises a noble metal, an inorganic oxide and a first proton-type zeolite or a first ion-exchange type zeolite ion-exchanged with Cu, Co or Fe ions.
A method for treating exhaust gas, wherein the second catalyst comprises a second proton-type zeolite or a second ion-exchange type zeolite ion-exchanged with Cu, Co or Fe ions.

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