JP2013071071A - Method for treating exhaust gas - Google Patents

Abstract

PROBLEM TO BE SOLVED: To effectively treat nitrogen oxides by suppressing influence of nitrogen oxide components group produced when treating the nitrogen oxides in exhaust gas and to provide a method for decomposing and removing NO with high efficiency preferably by suppressing influence of NOx.SOLUTION: The method for treating exhaust gas is characterized by that nitrogen oxide-containing exhaust gas is treated by a denitration catalyst and then is treated by nitrous oxide decomposition catalyst. Preferably, a reducing agent is added to the exhaust gas and then the exhaust gas is introduced to the denitration catalyst. The reducing agent is preferably ammonia and/or urea.

Description

  The present invention relates to treatment of exhaust gas containing nitrogen oxides, and particularly relates to technology for treatment of exhaust gas containing nitrous oxide.

Nitrous oxide (hereinafter referred to as N ₂ O) contained in various industrial exhaust gases discharged from chemical plants that produce nitric acid, adipic acid, etc., decomposes in the stratosphere to produce nitric oxide, Since the effect is shown, development of the efficient removal method is desired. As an effective method for that purpose, for example, decomposition and removal using a catalyst described in Patent Document 1 and Non-Patent Document 1 can be mentioned. Using this method, it is possible to efficiently decompose N ₂ O into harmless nitrogen or the like, but on the other hand, nitrogen monoxide and nitrogen dioxide (hereinafter collectively referred to as “NOx”) coexist in the exhaust gas. In this case, there is a problem that the N ₂ O removal efficiency is greatly reduced.

  Further, NOx is often contained in the exhaust gas of the plant, and these gas treatments are also desired.

JP 2007-152263 A

Applied Catalysis B Environmental 75 (2007) 167-174

The present invention is a technique for removing nitrogen oxides contained in exhaust gas, decomposing not only NOx in exhaust gas but also N ₂ O, and aims to decompose with high efficiency.

  In order to solve the above-mentioned problems, the present inventors have intensively studied and found the following configuration to complete the present invention. The present invention is specified below.

In the present invention, nitrogen oxides in exhaust gas are divided into two groups of NOx and N ₂ O. Specifically, the exhaust gas treatment method is characterized in that exhaust gas containing NOx and N ₂ O is treated with a denitration catalyst and further treated with an N ₂ O decomposition catalyst.

By using the present invention, it is possible to effectively treat exhaust gas by suppressing the influence of nitrogen oxide components generated when treating nitrogen oxide in exhaust gas. Specifically, the influence of NOx is suppressed. In addition, N ₂ O can be decomposed and removed with high efficiency.

FIG. 1 shows one embodiment which is an embodiment of the present invention.

The present invention divides nitrogen oxides in exhaust gas into two groups of NOx and N ₂ O and treats them with conditions and catalysts that effectively act on each group. Specifically, first, NOx and N ₂ are treated. An exhaust gas treatment method characterized in that exhaust gas containing O is treated with a denitration catalyst and further treated with an N ₂ O decomposition catalyst. Preferably, a reducing agent is added to the exhaust gas and then introduced into the denitration catalyst, and the amount of the reducing agent added is preferably an amount capable of converting NOx in the exhaust gas into nitrogen and water. The present invention will be specifically described below.

The present invention is composed of two-stage processes, the first process is a process 1 using a denitration catalyst, and the second process is a process 2 using a N ₂ O decomposition catalyst.

(Process 1)
The purpose of this step is to reduce NOx contained in the exhaust gas. The NOx, NO, is _{NO 2.} The amount of the NOx contained in the exhaust gas is 10,000 ppm or less (volume basis, hereinafter the same for the gas body), preferably 5,000 ppm or less. This is because if the amount of NOx exceeds 10,000 ppm, the amount of residual NOx after step 1 increases, which adversely affects the catalyst in step 2. As other components contained in the exhaust gas, there are carbon dioxide, carbon monoxide, water, sulfur dioxide, hydrogen halide, hydrocarbon, organic compound, ammonia, dust, etc., depending on the exhaust gas source. There is no problem even if these components are contained in amounts that do not interfere with the implementation of the technique according to the present invention. Since the present invention is a technique for treating nitrogen oxides, it is preferable that reducing components such as carbon monoxide, hydrogen, hydrocarbons, and ammonia are preferably contained in the exhaust gas. The amount of the reducing substance is preferably the same as the amount capable of decomposing NOx into nitrogen and water. However, the composition of the exhaust gas often fluctuates, and when a reducing substance is not present in the exhaust gas, it is preferable to add a reducing agent to the inlet side of the denitration catalyst.

  The reducing agent added to the inlet side of the denitration catalyst may be any compound as long as it is a compound capable of reducing nitrogen oxides. In particular, use of ammonia or urea is preferable because NOx removal efficiency is increased. Hereinafter, ammonia and / or urea will be described as representative examples of the “reducing agent”.

The amount of ammonia and / or urea added is 0.3 to 1.2 times, preferably 0.4 to 1.1 times, more preferably 0.5 to the equivalent of NOx that can be decomposed into nitrogen and water. 0.98 times is desirable. By making the addition amount of ammonia and / or urea within the above range, the treatment can be performed efficiently. An equivalent amount capable of decomposing NOx into nitrogen and water is as follows. That is, when the target substance is NO, ammonia is 1 mol and urea is 0.5 mol with respect to 1 mol of NO. When the target substance is NO ₂ , ammonia is 2 mol and urea is 1 mol with respect to 1 mol of NO ₂ .

The denitration catalyst used in this step is not particularly limited as long as it can efficiently decompose and remove NOx, but it is more preferable that N ₂ O is not by-produced from ammonia or urea used as a reducing agent. Specifically, one containing one or more elements selected from vanadium, niobium, tantalum, molybdenum, tungsten, manganese, iron, cobalt, nickel and / or zinc or compounds thereof as an active ingredient is preferable. In particular, vanadium, molybdenum and A material containing one or more elements selected from tungsten or a compound thereof as an active component is preferably used in that it has high NOx removal performance and does not cause N ₂ O to be a byproduct. The content of the active ingredient is preferably 0.1 to 20% by mass, more preferably 0.2 to 15% by mass, and still more preferably 0.4 to 10% by mass. If the content of the active ingredient is less than 0.1% by mass, sufficient NOx removal performance cannot be obtained. If the content exceeds 20% by mass, the oxidation of the reducing agent is promoted and the NOx removal efficiency is lowered. is there. In addition, when the active ingredient contains two or more elements selected from vanadium, niobium, tantalum, molybdenum, tungsten, manganese, iron, cobalt, nickel and / or zinc or compounds thereof, the content of each element or its The compound should be within the above range.

Further, the denitration catalyst used in this step is preferably one in which the active component is supported on at least one base material component made of oxide of titanium, aluminum, silicon and / or zirconium. The ratio of the base component to the entire catalyst is preferably 40 to 99.5% by mass, more preferably 60 to 99% by mass, and still more preferably 70 to 98% by mass, and the ratio of the base component By making this within this range, high NOx removal performance can be obtained. Furthermore, titanium oxide is particularly preferably used from the viewpoint of NOx removal performance and durability among the above-mentioned base material components. As the titanium oxide, in addition to titanium oxide, a complex oxide or mixed oxide of one or more elements selected from aluminum, silicon, zirconium, molybdenum, and / or tungsten and titanium can be used. Two or more composite oxides or mixed oxides may be mixed and used, and the composite oxide or mixed oxide may be mixed with titanium oxide. The titanium content in the composite oxide or mixed oxide is preferably 40 to 99 mol%, more preferably 60 to 98 mol%, still more preferably 70 to 97 mol%. By setting the titanium content in the above range, high NOx removal performance can be obtained, and N ₂ O by-product can be suppressed. In particular, in order to suppress the by-production of N ₂ O, it is preferable to contain one or more elements selected from silicon, molybdenum and / or tungsten and one or more complex oxides or mixed oxides of titanium. .

The specific surface area of the denitration catalyst used in this step should be in the range of 50 to ²⁰⁰ m ² / g, more preferably 60 to 150 m ² / g, and still more preferably in the range of 65 to 130 m ² / g. Good. If the specific surface area of the catalyst is too low, sufficient catalyst performance cannot be obtained, and active component sintering tends to occur. If it is too high, the catalyst performance will not improve much, but the amount of poisonous substances accumulated will increase. This is because the durability may be lowered.

  The pore volume of the denitration catalyst used in this step is such that the total pore volume is in the range of 0.2 to 0.7 mL / g, more preferably 0.3 to 0.6 mL / g, Preferably it is in the range of 0.35 to 0.5 mL / g. If the pore volume of the catalyst is too small, sufficient catalyst performance will not be obtained, and if it is too large, the catalyst performance will not improve so much, but the mechanical strength of the catalyst will be reduced and handling will be hindered and abrasion resistance This is not preferable because there is a risk of adverse effects such as lowering.

  As a preparation method of the denitration catalyst, a general preparation method using various metal compounds can be used. For example, an impregnation method, a coprecipitation method, a kneading method, an alkoxide method, and the like are used.

  As starting materials for each catalyst component, oxides, hydroxides, inorganic salts, organic salts, and the like of each element are used. Specific examples include ammonium salts, oxalates, sulfates, nitrates, halides, etc. For example, titanium sources include titanyl sulfate, titanium tetrachloride, tetraisopropyl titanate, etc. Silica sol, water glass, silicon tetrachloride and the like can be used. As the vanadium source, ammonium metatungsten vanadate is used, as the tungsten source, ammonium metatungstate, ammonium paratungstate, etc. are used, and as the molybdenum source, ammonium paramolybdate, molybdic acid, etc. are used.

  The denitration catalyst used in this step can be formed into a saddle, pellet, sphere, or honeycomb by extrusion, tableting, rolling granulation, or the like. Further, a saddle-shaped, pellet, sphere, or honeycomb-shaped carrier can be used by coating the components of the denitration catalyst. A honeycomb shape is preferable for reducing the pressure loss of the exhaust gas treatment apparatus.

The purpose of this step is to reduce the influence of NOx on the subsequent N ₂ O decomposition catalyst as much as possible. For this purpose, the exhaust gas on the denitration catalyst outlet side (that is, the N ₂ O decomposition catalyst inlet side) The NOx concentration therein is preferably 50 ppm or less, more preferably 10 ppm or less, and even more preferably 5 ppm or less.

From the above viewpoint, preferable catalyst use conditions are set for the processing temperature, space velocity (SV), etc. of the exhaust gas. Specifically, the treatment temperature of the exhaust gas is in the range of 150 to 600 ° C, preferably 170 to 550 ° C, more preferably 200 to 500 ° C. If the treatment temperature of the exhaust gas is less than 150 ° C., sufficient NOx removal efficiency for achieving the above-mentioned purpose cannot be obtained, and if it exceeds 600 ° C., the thermal deterioration of the catalyst increases and the oxidation of the reducing agent is promoted. This is because the removal efficiency is lowered. The space velocity during the exhaust gas treatment is 500 to 100,000 hr ⁻¹ (STP), preferably 1,000 to 50,000 hr ⁻¹ (STP), more preferably 1,500 to 30,000 hr ⁻¹ (STP). It should be in range. Not sufficient NOx removal efficiency can be obtained for the space velocity to achieve the object exceeds 100,000hr ^-1 (STP), does not change significantly NOx removal efficiency is less than ^{500 hr} -1 (STP) but the exhaust gas treatment apparatus This is because the pressure loss increases and the apparatus itself becomes large and inefficient. The linear velocity of the gas passing through the catalyst layer during exhaust gas treatment is 0.1 to 10 m / sec (Normal), preferably 0.5 to 7 m / sec (Normal), and more preferably 0.7 to 4 m / sec. It should be in the range of sec (Normal). If the linear velocity is less than 0.1 m / sec (Normal), sufficient NOx removal efficiency for achieving the above-mentioned purpose cannot be obtained, and if it exceeds 10 m / sec (Normal), the NOx removal efficiency does not change greatly. This is because the pressure loss of the apparatus becomes high.

  The denitration catalyst of this step is suitably used under the condition where oxygen is present in the exhaust gas. In this case, the oxygen concentration is preferably in the range of 1 to 50% by volume, more preferably 1.5 to It should be in the range of 20% by volume, more preferably 2-16% by volume. This is because if the oxygen concentration is less than 1% by volume, the NOx removal efficiency decreases, and if it exceeds 50% by volume, oxidation of the reducing agent may be promoted. When the exhaust gas contains moisture, the concentration is preferably 50% by volume or less, more preferably 40% by volume or less, and further preferably 30% by volume or less. This is because NOx removal efficiency decreases when the moisture concentration in the exhaust gas exceeds 50% by volume.

(Process 2)
The purpose of this step is to decompose and remove N ₂ O. The N ₂ O decomposition catalyst may be any catalyst as long as it can efficiently decompose and remove N ₂ O. For example, the catalyst described in Patent Document 1 can be used. Preferred catalyst compositions include those from groups 7 to 11 of the periodic table. There are at least one selected element or compound thereof, and at least one element selected from Groups 1 to 3 of the periodic table or compound thereof as an active ingredient. The N ₂ O decomposition catalyst can be used in the form of powder, granules, saddles, pellets, spheres, and honeycombs, and the N ₂ O decomposition catalyst can be used on spheres, saddles, and honeycombs. It can be used by coating.

The N ₂ O concentration of the exhaust gas in this step is preferably 20,000 ppm or less, more preferably 10,000 ppm or less, and even more preferably 5,000 ppm or less. This is because if the N ₂ O concentration exceeds 20,000 ppm, the heat generation in the catalyst layer increases and the catalyst may be thermally damaged. In some cases, a reducing agent for treating N ₂ O can be added before this step, and hydrogen, hydrocarbon, carbon monoxide, ammonia, urea, or the like is used as the reducing agent at that time. I can do things. The catalyst use conditions such as the treatment temperature and space velocity in this step are appropriately determined depending on the required N ₂ O decomposition rate. As a preferred range, the temperature of the exhaust gas is 150 to 650 ° C., more preferably 170 to 600 ° C. The space velocity is 100 to 50,000 hr ⁻¹ (STP), more preferably 500 to 30,000 hr ⁻¹ (STP), and the linear velocity of the gas passing through the catalyst layer is 0.1 to 10 m / sec. (Normal), more preferably 0.5 to 7 m / sec (Normal).

Further, the relationship between the catalyst of step 1 and the catalyst of step 2 is that the processing temperature of step 2 is preferably −50 to + 300 ° C., more preferably −30 to + 250 ° C., even more preferably compared to the processing temperature of step 1. Is preferably in the range of −20 to + 200 ° C. In some cases, it is preferable to heat the catalyst in Step 2. If the treatment temperature in step 2 is lower than 30 ° C. compared to the treatment temperature in step 1, sufficient N ₂ O treatment efficiency may not be obtained, and if it exceeds 300 ° C., the catalyst is thermally damaged. Because there is a thing. Further, the volume of the catalyst in Step 1 is preferably 0.1 to 5 times, more preferably 0.2 to 3 times, and still more preferably 0.3 to 2 times that of Step 2. If the volume of the catalyst in step 1 is less than 0.1 times that in step 2, the NOx treatment efficiency may be reduced and the effects of the present invention may not be sufficiently obtained. This is because the pressure loss increases and the apparatus itself becomes large and inefficient.

  The present invention will be described in detail below with reference to examples. However, the present invention is not limited to the following examples as long as the effects of the present invention are achieved.

Example 1
<Preparation of denitration catalyst>
While mixing 20 liters of silica sol (containing 20 mass% as SiO ₂ ) and 225 kg of 25 mass% ammonia water, 240 L of sulfuric acid solution of titanyl sulfate (125 g / L as TiO ₂ , sulfuric acid concentration 550 g / L) is gradually stirred. After adding dropwise to form a precipitate, an appropriate amount of aqueous ammonia was added to adjust the pH to 8. The slurry was aged, filtered, washed and dried at 150 ° C. for 10 hours. This was fired at 550 ° C. for 6 hours in an air atmosphere, and further pulverized using a hammer mill to obtain a Ti—Si composite oxide powder. The composition of the Ti—Si composite oxide powder thus prepared was Ti: Si = 85: 15 (molar ratio).

Next, 0.6 kg of ammonium metavanadate, 0.7 kg of oxalic acid, and 0.2 kg of monoethanolamine were mixed and dissolved in 2 L of water to prepare a uniform solution. 4.4 L of this vanadium-containing solution and 10 mass% aqueous solution of ammonium paratungstate methylamine (400 g / L as WO ₃ ) are added to 20 kg of the Ti-Si composite oxide prepared above together with a molding aid and an appropriate amount of water. The mixture was kneaded with a kneader and extruded into a honeycomb shape having an outer shape of 80 mm square, a length of 500 mm, an opening of 2.9 mm, and a wall thickness of 0.4 mm. The honeycomb formed body was dried at 80 ° C. and then calcined at 450 ° C. for 3 hours in an air atmosphere to obtain a denitration catalyst A.

The composition of the denitration catalyst A is (Ti—Si composite oxide): V ₂ O ₅ : WO ₃ = 90: 2: 8 (mass ratio), the BET specific surface area is 116 m ² / g, and the total pore volume is It was 0.46 mL / g.

<Preparation of N ₂ O decomposition catalyst>
A molding aid and an appropriate amount of water were added to 800 g of calcium carbonate and 200 g of nickel oxide (NiO), kneaded by a kneader, and then extruded into a pellet having a diameter of 5 mm and a length of 5 mm. The pellet was dried at 100 ° C. and then calcined at 500 ° C. for 5 hours in an air atmosphere to obtain an N ₂ O decomposition catalyst. The composition of this catalyst was CaO: NiO = 69: 31 (mass ratio), and the total pore volume was 0.25 mL / g.

<NOx, N ₂ O decomposition test>
A glass reaction tube was filled with the denitration catalyst A and the N ₂ O decomposition catalyst so that the denitration catalyst A was in front of the N ₂ O decomposition catalyst, and a synthesis gas having the following composition was introduced under the following processing conditions. In addition, the filling amount of each catalyst was determined according to the space velocity (SV) described in the following processing conditions.

[Syngas composition]
NOx: about 100 ppm, NH ₃ : about 110 ppm, N ₂ O: about 500 ppm, O ₂ : 5% by volume, H ₂ O: 10% by volume, N ₂ : balance
[Processing conditions]
・ Denitration catalyst (front)
Processing temperature: 450 ° C., space velocity: 15,000 hr ⁻¹ (STP), gas linear velocity: 2.0 m / sec (Normal)
・ N ₂ O decomposition catalyst (second stage)
Processing temperature: 450 ° C., space velocity: 5,000 hr ⁻¹ (STP), gas linear velocity: 0.8 m / sec (Normal)
Next, a denitration catalyst inlet, the denitration catalyst outlet _{(N 2} O decomposition catalyst inlet), _{N 2} O decomposition catalyst outlet of _NOx, the NH _{3, N} 2 O concentration was measured to calculate the _{N 2} O removal ratio according to the following equation . The results are shown in Table 1.
N ₂ O removal rate (%) = {(denitration catalyst inlet N ₂ O concentration) − (N ₂ O decomposition catalyst outlet N ₂ O concentration)} / (denitration catalyst inlet N ₂ O concentration) × 100
In addition, a NOx analyzer (Nippon Thermo Electron Co., Ltd., Model 5100) is used for measuring NOx concentration, and an N ₂ O analyzer (Nippon Thermo Electron Co., Ltd., Model 46-HL) is used for measuring N ₂ O concentration. The NH ₃ concentration was determined by collecting NH ₃ in the gas with a 0.5% boric acid aqueous solution and then analyzing it with an ion chromatograph (IC-2100, manufactured by Tosoh Corporation).

(Example 2)
<Preparation of denitration catalyst>
To 16 kg of the Ti—Si composite oxide powder prepared in Example 1, 4 kg of DT-51 (trade name) manufactured by Cristal Global was added as TiO ₂ and mixed. Next, 0.6 kg of ammonium metavanadate, 0.7 kg of oxalic acid, and 0.2 kg of monoethanolamine were mixed and dissolved in 2 L of water to prepare a uniform solution. The vanadium-containing solution and 4.4 L of 10% by weight aqueous methylamine solution of ammonium paratungstate (400 g / L as WO ₃ ) together with a molding aid and an appropriate amount of water were mixed with Ti-Si composite oxide and DT- In addition to the mixed powder of 51, the mixture was kneaded with a kneader, and then extruded into a honeycomb shape having an outer shape of 80 mm square, a length of 500 mm, an aperture of 2.9 mm, and a wall thickness of 0.4 mm. Then, after drying at 80 degreeC, it baked at 450 degreeC by air atmosphere for 3 hours, and the denitration catalyst B was obtained.

The composition of the denitration catalyst B is (Ti—Si composite oxide): TiO ₂ : V ₂ O ₅ : WO ₃ = 72: 18: 2: 8 (mass ratio), and the BET specific surface area is 108 m ² / g, all The pore volume was 0.44 mL / g.

<NOx, N ₂ O decomposition test>
In the NOx and N ₂ O decomposition test of Example 1, a NOx and N ₂ O decomposition test was performed in the same manner as in Example 1 except that the denitration catalyst B was used instead of the denitration catalyst A. The results are shown in Table 1.

(Example 3)
<Preparation of denitration catalyst>
3 kg of molybdic acid was added to a liquid obtained by mixing 15 kg of silica sol (containing 20% by mass as SiO ₂ ), 180 kg of 25% by mass ammonia water and 100 L of water, and stirred well to completely dissolve the molybdic acid to prepare a uniform solution. To this solution, 190 L of titanyl sulfate sulfuric acid solution (125 g / L as TiO ₂ , sulfuric acid concentration 550 g / L) was gradually added dropwise with good stirring to form a precipitate, and then an appropriate amount of aqueous ammonia was added to adjust the pH to 4 Adjusted. The slurry was aged, filtered, washed, and dried at 100 ° C. for 10 hours. This was calcined at 500 ° C. for 4 hours in an air atmosphere, and further pulverized using a hammer mill to obtain a Ti—Si—Mo mixed oxide powder. The composition of the Ti—Si—Mo mixed oxide powder thus prepared was Ti: Si: Mo = 81: 13: 6 (molar ratio).

  Next, 0.5 kg of ammonium metavanadate, 0.7 kg of oxalic acid, and 0.2 kg of monoethanolamine were mixed and dissolved in 2 L of water to prepare a uniform solution. This vanadium-containing solution is added to 20 kg of the previously prepared Ti—Si—Mo mixed oxide powder together with a molding aid and an appropriate amount of water, and after kneading with a kneader, the outer shape is 80 mm square, the length is 500 mm, and the mesh is 3. It was extruded into a honeycomb shape having a thickness of 65 mm and a thickness of 0.6 mm. Then, after drying at 80 degreeC, it baked at 450 degreeC by air atmosphere for 3 hours, and the denitration catalyst C was obtained.

The composition of the denitration catalyst C is (Ti—Si—Mo mixed oxide): V ₂ O ₅ = 98: 2 (mass ratio), the BET specific surface area is 101 m ² / g, and the total pore volume is 0.39 mL / g.

<NOx, N ₂ O decomposition test>
In the NOx and N ₂ O decomposition test of Example 1, a NOx and N ₂ O decomposition test was performed in the same manner as in Example 1 except that the denitration catalyst C was used instead of the denitration catalyst A. The results are shown in Table 1.

Example 4
<Preparation of denitration catalyst>
A solution obtained by mixing 7.5 L of a 10% by weight aqueous solution of methyl paratungstate methylamine (400 g / L as WO ₃ ) and 200 kg of 25% by weight aqueous ammonia with a sulfuric acid solution of titanyl sulfate (125 g / L as TiO ₂ , sulfuric acid concentration) (550 g / L) 216 L was gradually added dropwise with good stirring to form a precipitate, and then an appropriate amount of aqueous ammonia was added to adjust the pH to 5. The slurry was aged, filtered, washed and dried at 150 ° C. for 10 hours. This was fired at 500 ° C. for 6 hours in an air atmosphere, and further pulverized using a hammer mill to obtain a Ti—W mixed oxide powder. The composition of the Ti—W mixed oxide powder thus prepared was Ti: W = 96: 4 (molar ratio).

  To 10 kg of the Ti—W mixed oxide powder, 10 kg of the Ti—Si composite oxide powder prepared in Example 1 was added and mixed. Next, 0.5 kg of ammonium metavanadate, 0.7 kg of oxalic acid, and 0.2 kg of monoethanolamine were mixed and dissolved in 2 L of water to prepare a uniform solution. This vanadium-containing solution is added to the mixed powder of the Ti—W mixed oxide and Ti—Si composite oxide mixed together with the molding aid and an appropriate amount of water, and after kneading with a kneader, the outer shape is 80 mm square and length. It was extruded into a honeycomb shape having a thickness of 500 mm, an opening of 2.9 mm, and a wall thickness of 0.4 mm. Then, after drying at 80 degreeC, it baked at 450 degreeC by air atmosphere for 3 hours, and the denitration catalyst D was obtained.

The composition of the denitration catalyst D is (Ti—W mixed oxide) :( Ti—Si composite oxide): V ₂ O ₅ = 49: 49: 2 (mass ratio), and the BET specific surface area is 96 m ² / g, The total pore volume was 0.41 mL / g.

<NOx, N ₂ O decomposition test>
In the NOx and N ₂ O decomposition test of Example 1, a NOx and N ₂ O decomposition test was performed in the same manner as in Example 1 except that the denitration catalyst D was used instead of the denitration catalyst A. The results are shown in Table 1.

(Example 5)
In the NOx and N ₂ O decomposition test of Example 1, the NOx and N ₂ O decomposition test was performed in the same manner as in Example 1 except that the ammonia concentration in the synthesis gas was about 98 ppm. The results are shown in Table 1.

(Example 6)
In the NOx and N ₂ O decomposition test of Example 2, the NOx and N ₂ O decomposition test was performed in the same manner as in Example 2 except that the ammonia concentration in the synthesis gas was about 98 ppm. The results are shown in Table 1.

(Example 7)
In the NOx and N ₂ O decomposition test of Example 3, the NOx and N ₂ O decomposition test was performed in the same manner as in Example 3 except that the ammonia concentration in the synthesis gas was about 98 ppm. The results are shown in Table 1.

(Example 8)
In the NOx and N ₂ O decomposition test of Example 4, the NOx and N ₂ O decomposition test was performed in the same manner as in Example 4 except that the ammonia concentration in the synthesis gas was about 98 ppm. The results are shown in Table 1.

Example 9
<Preparation of denitration catalyst>
8.4 kg of chromium (III) nitrate nonahydrate was mixed and dissolved in 8 L of water to prepare a uniform solution. This chromium-containing solution was added to 20 kg of TiO ₂ powder (manufactured by Cristal Global, DT-51 (trade name)) together with a molding aid and an appropriate amount of water, and after kneading with a kneader, the outer shape was 80 mm square, length 500 mm Extrusion was performed in a honeycomb shape having a mesh opening of 2.9 mm and a wall thickness of 0.4 mm. The honeycomb formed body was dried at 80 ° C. and then calcined at 450 ° C. for 3 hours in an air atmosphere to obtain a denitration catalyst E.

The composition of the denitration catalyst E was TiO ₂ : Cr ₂ O ₃ = 98: 2 (mass ratio), the BET specific surface area was 78 m ² / g, and the total pore volume was 0.31 mL / g.

<NOx, N ₂ O decomposition test>
In the NOx and N ₂ O decomposition test of Example 1, a NOx and N ₂ O decomposition test was performed in the same manner as in Example 1 except that the denitration catalyst E was used instead of the denitration catalyst A. The results are shown in Table 1.

（比較例１）
実施例１のＮＯｘ、Ｎ_２Ｏ分解試験において、脱硝触媒Ａを充填せず、かつ合成ガス中にアンモニアを添加しなかった事以外は、実施例１と同様にしてＮＯｘ、Ｎ_２Ｏ分解試験を行なった。なお、この場合はＮ_２Ｏ分解触媒入口およびＮ_２Ｏ分解触媒出口のＮＯｘ、Ｎ_２Ｏ、ＮＨ_３濃度を測定し、Ｎ_２Ｏ除去率は次式に従って算出した。結果を表１に示す。
Ｎ_２Ｏ除去率（％）＝｛（Ｎ_２Ｏ分解触媒入口Ｎ_２Ｏ濃度）−（Ｎ_２Ｏ分解触媒出口Ｎ_２Ｏ濃度）｝／（Ｎ_２Ｏ分解触媒入口Ｎ_２Ｏ濃度）×１００

(Comparative Example 1)
NOx Example 1, the N 2 _O decomposition test, without filling the denitration catalyst A, and except that not adding ammonia in the synthesis gas, NOx in the same manner as in Example 1, N 2 _O decomposition test Was done. Incidentally, _NOx in the _{N 2} O decomposition catalyst inlet and _{N 2} O decomposition catalyst outlet if, N 2 O, by measuring the NH ₃ concentration, _{N 2} O removal ratio was calculated according to the following equation. The results are shown in Table 1.
N ₂ O removal rate (%) = {(N ₂ O decomposition catalyst inlet N ₂ O concentration) − (N ₂ O decomposition catalyst outlet N ₂ O concentration)} / (N ₂ O decomposition catalyst inlet N ₂ O concentration) × 100

The present invention can be used for the treatment of exhaust gas, and in particular, can be used in the field of exhaust gas treatment containing NOx and N ₂ O.

Claims (8)

An exhaust gas treatment method characterized in that exhaust gas containing nitrogen oxides is treated with a denitration catalyst and then treated with a nitrous oxide decomposition catalyst. The exhaust gas treatment method according to claim 1, wherein a reducing agent is added to the exhaust gas and then introduced into the denitration catalyst. The exhaust gas treating method according to claim 2, wherein the exhaust reducing agent is ammonia and / or urea. The addition amount of the ammonia and / or urea is 0.3 to 1.2 times the equivalent amount of nitrogen monoxide and nitrogen dioxide in the exhaust gas that can be converted into nitrogen and water. Item 6. An exhaust gas treatment method according to Item 3. The exhaust gas treatment method according to any one of claims 1 to 4, wherein in the exhaust gas treatment method, the total concentration of nitrogen monoxide and nitrogen dioxide contained in the exhaust gas at the nitrous oxide decomposition catalyst inlet is 50 ppm or less. The active component of the denitration catalyst is one or more elements selected from vanadium, niobium, tantalum, molybdenum, tungsten, manganese, iron, cobalt, nickel, and / or zinc, or a compound thereof. The exhaust gas treatment method according to -5. The exhaust gas treatment method according to claim 6, wherein the denitration catalyst contains titanium oxide. The titanium oxide is one or more elements selected from aluminum, silicon, zirconium, molybdenum and / or tungsten and one or more oxides of titanium and / or mixed oxides, or the compound oxidation. The exhaust gas treatment method according to claim 7, wherein the exhaust gas treatment method is a mixture of at least one oxide and / or mixed oxide and titanium oxide.

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