JP2011045849A - Nitrogen oxide removal catalyst and nitrogen oxide removal apparatus using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a nitrogen oxide removal catalyst with little deterioration by a catalytic poisoning component such as phosphorus and arsenic and excellent in oxidation resistance and heat resistance. <P>SOLUTION: The nitrogen oxide removal catalyst includes a carrier having fine pores and an active component for removing the nitrogen oxide in an exhaust gas and the average diameter of the fine pores is 20 to 100 Å, the volume of the fine pores with a diameter of 20 to 100 Å is 80% or more in the total volumes of all fine pores and the volume of the fine pores with a diameter of 20 to 100 Å is 0.1 to 0.4 cm<SP>3</SP>per gram of the catalyst. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a nitrogen oxide removing catalyst and a nitrogen oxide removing apparatus using the same.

Nitrogen oxides (NOx) in exhaust gas discharged from power plants, various factories, automobiles, and the like are causative substances for environmental degradation. As an effective removal method, a flue gas denitration method by selective catalytic reduction using ammonia (NH ₃ ) as a reducing agent is mainly used in thermal power plants. As the catalyst, a titanium oxide (TiO ₂ ) -based catalyst containing vanadium (V), molybdenum (Mo) or tungsten (W) as an active component is used. In particular, a catalyst containing vanadium as one of the active components is not only highly active, but also has a small deterioration due to impurities contained in exhaust gas, and can be used from a relatively low temperature. (Patent Document 1).

  In recent years, in the United States, boilers using low-grade coal such as subbituminous coal and bituminous coal called PRB coal tend to increase. Moreover, since exhaust gas regulations have been strengthened, the installation of denitration devices in boilers is increasing.

  In general, some sub-bituminous coals produced in the United States contain more phosphorus in the exhaust gas and ash during combustion than high-grade coals. Since phosphorus becomes a catalyst poison for the denitration catalyst, in the combustion exhaust gas treatment of coal containing a large amount of phosphorus, there has been a problem that the performance of the denitration catalyst is greatly reduced compared to the case of using high-grade coal. However, no measures have been taken so far to prevent deterioration due to phosphorus.

Patent Document 2 discloses an exhaust gas treatment catalyst for purifying exhaust gas discharged from an incinerator, a pyrolysis furnace, a melting furnace, etc., comprising a carrier made of titanium oxide, vanadium, tungsten, molybdenum, niobium, tantalum, and the like. And a catalyst component containing at least one selected from the group consisting of oxides of two or more solid solutions of these metal elements, and an acid strength (H 2 _{O 2} ) of −5 An exhaust gas treatment catalyst characterized by being a catalyst weaker than .6 (H 2 _O ≧ −5.6) is disclosed. In addition, the fact that the specific surface area of the catalyst is 90 m ² / g or more is also disclosed as a constituent requirement.

  Patent Document 3 discloses a nitrogen oxide removing catalyst for removing nitrogen oxides in exhaust gas containing nitrogen oxides and phosphorus compounds, a porous carrier, and an active component carried on the pores of the carrier. And the average pore diameter of the pores of the carrier is 8 to 9 mm as measured by a gas adsorption method for measuring pores having a diameter of 3.4 to 14 mm. A catalyst is disclosed.

Japanese Patent Publication No.57-36012 JP 2000-70712 A JP 2008-221203 A

  An object of the present invention is to provide a catalyst for removing nitrogen oxides which is less deteriorated by catalyst poison components such as phosphorus and arsenic and has excellent acid resistance and heat resistance.

The nitrogen oxide removal catalyst of the present invention is a nitrogen oxide removal catalyst having a carrier having pores and containing an active component for removing nitrogen oxide in exhaust gas, wherein the average diameter of the pores is 20 to 100 mm. The volume of the pores having a diameter of 20 to 100 mm is 80% or more based on the total pore volume, and the volume of the pores having a diameter of 20 to 100 mm is 0.1 to 0.4 cm ³ per 1 g of the catalyst. It is characterized by being.

  According to the present invention, it is possible to provide a nitrogen oxide removal catalyst that is less deteriorated by catalyst poison components such as phosphorus and arsenic and that has excellent acid resistance and heat resistance.

It is a schematic block diagram which shows the nitrogen oxide removal apparatus of the Example by this invention. It is a schematic block diagram which shows the denitration system of this invention. It is a schematic cross section which shows an example in case the pore diameter of a nitrogen oxide removal catalyst is less than 20cm. It is a schematic cross section which shows an example in case the pore diameter of a nitrogen oxide removal catalyst is 20-100cm. It is a schematic cross section which shows an example in case the pore diameter of a nitrogen oxide removal catalyst is larger than 100cm.

  The present invention relates to a nitrogen oxide removing catalyst (also simply referred to as a catalyst), a method for producing the same, and a nitrogen oxide removing apparatus, and in particular, a nitrogen oxide removing catalyst capable of preventing deterioration due to a phosphorus compound and nitrogen oxidation. The present invention relates to an object removal device.

  Nitrogen oxide removal catalysts are often used with titanium oxide as a carrier and an active component supported thereon, but in order to impart durability against catalyst poison components such as phosphorus and arsenic in exhaust gas, the diameter 20 When measured by a gas adsorption method for measuring pores of ˜3000 cm, it is desirable that the diameter of the pores of the catalyst is 20-100 Å. For this reason, the titanium oxide having the pores is effective.

  In order to prevent catalyst deterioration due to phosphorus, it is desirable to optimize the ratio of the volume occupied by pores of 100 mm or less to the average pore diameter of the titanium oxide support and the total volume of all pores. Furthermore, the average pore diameter as a catalyst after supporting the active component and the ratio of the volume occupied by pores of 100 mm or less to the total volume of all pores are optimized, and the integrated volume of all pores of the catalyst is optimized. It is desirable to make it.

The nitrogen oxide removal catalyst of the present invention has an average pore diameter of 20 to 100 mm measured by a gas adsorption method for measuring pores having a diameter of 20 to 3000 mm, and the average pore diameter of 20 to 100 mm. The volume of the pores is 80% or more with respect to the total pore volume of the pores measured by the gas adsorption method, and the pore volume having the average pore diameter of 20 to 100 mm is 0.000 per gram of the catalyst. It is characterized by being 1 to 0.4 cm ³ .

  In the nitrogen oxide removal catalyst of the present invention, the support contains titanium oxide, and the active component is zirconium (Zr), niobium (Nb), molybdenum (Mo), tantalum (Ta), tungsten (W). And at least one metal selected from the group of vanadium (V).

  The nitrogen oxide removal catalyst of the present invention is characterized in that the ratio of the active ingredient to the number of moles of titanium contained in the titanium oxide is 1/4 to 1/9 in terms of mole ratio.

  The nitrogen oxide removing apparatus of the present invention is characterized by using the above-described nitrogen oxide removing catalyst.

  The denitration system of the present invention includes a combustor and an exhaust gas flow path, and includes the above-described nitrogen oxide removing device.

  Hereinafter, the present invention will be described in detail.

  In the PRB charcoal fired boiler, phosphorus is considered to exist in a gaseous state in the exhaust gas as phosphorous acid or organic phosphoric acid having strong reducibility. The phosphorus compound in the exhaust gas is adsorbed by the catalyst component when it reaches the nitrogen oxide removal catalyst. Since the phosphorus compound is strongly adsorbed at the same point as ammonia as the reducing agent, it is estimated that the adsorption of ammonia is inhibited and the denitration activity of the catalyst is lowered.

  Arsenic is another component similar to phosphorus. Arsenic is also considered to be present in the exhaust gas in the form of arsenous acid in a gaseous state.

  Assuming the behavior of phosphorus and arsenic as described above, the formation of mesopores into which phosphorus compounds and arsenic compounds are unlikely to enter and supporting the denitration active component element in the mesopores can maintain the denitration activity. It is possible to prevent deterioration of the catalyst due to phosphorus poisoning or arsenic poisoning.

  Specifically, in the catalyst of the present invention, the carrier is preferably titanium oxide, and a nitrogen oxide removing component is preferably supported on the carrier.

  Further, the catalyst having a nitrogen oxide removing component supported on the carrier has an average pore diameter of 20 to 100 mm measured by a gas adsorption method for measuring pores having a diameter of 20 to 3000 mm. It is desirable that the volume of the pores of 20 to 100% occupy 80% or more with respect to the total pore volume of the pores measured by the gas adsorption method.

  Thereby, it is possible to maintain the nitrogen oxide removal performance and to prevent the catalyst from being deteriorated due to phosphorus poisoning. That is, at least a part of the pores can diffuse and adsorb nitrogen oxides on the active components inside the pores even if the poisoning substance is adsorbed on the pores.

  The relationship between the pore diameter of the catalyst and poisoning substances such as phosphorus and arsenic is considered as follows.

  This will be described with reference to FIGS.

  FIG. 3A is a schematic cross-sectional view showing an example where the pore diameter of the nitrogen oxide removal catalyst is less than 20 mm. FIG. 3B is a schematic cross-sectional view showing an example of the case where the pore diameter of the nitrogen oxide removal catalyst is 20 to 100 mm. FIG. 3C is a schematic cross-sectional view showing an example in which the pore diameter of the nitrogen oxide removal catalyst is larger than 100 mm.

In FIG. 3A, the support 101 of the nitrogen oxide removing catalyst has an active component 102 that removes nitrogen oxide inside the pores 111 having a diameter of less than 20 mm. When the poisoning substance 103 is phosphorus oxide (V) (P ₄ O ₁₀ ), the molecular diameter is about 9 mm, and when the poisoning substance 103 is arsenic oxide (V) (As ₄ O ₁₀ ), the molecular diameter is about It is 8cm. The poisoning substance 103 is adsorbed on the inlet portion of the pore 111 and blocks all or most of the inlet portion.

For this reason, it is considered that nitrogen monoxide 104 (NO) having a molecular diameter of about 4 mm and ammonia 105 (NH ₃ ) having a molecular diameter of about 3 mm are less likely to diffuse into the pores 111 and are less likely to be adsorbed to the active component 102.

  In FIG. 3B, the support | carrier 101 of a nitrogen oxide removal catalyst has the pore 111 of diameter 20-100cm. In this case, even if the poisonous substance 103 is adsorbed to the inlet portion of the pore 111, it only blocks part of the inlet portion, and the nitric oxide 104 and ammonia 105 diffuse into the pore 111 and become active components. It can be adsorbed to 102.

  In FIG. 3C, the support 101 of the nitrogen oxide removal catalyst has pores 111 that are larger than 100 mm in diameter. In this case, the poisoning substance 103 diffuses to the inside of the pores 111 and is easily adsorbed on the active ingredient 102. For this reason, even if the active ingredient 102 is poisoned and nitrogen monoxide 104 or ammonia 105 diffuses inside the pores 111, it cannot be adsorbed by the active ingredient 102.

  The above explanation does not strictly prove an appropriate range of the pore diameter of the nitrogen oxide removal catalyst, but is effective from the viewpoint of explaining the experimental facts described later.

  That is, the meaning of having mesopores having a pore diameter in the range of 20 to 100 mm is as follows.

  When the pore diameter is smaller than 20 mm, the phosphorus compound in the exhaust gas closes the inlet portion of the pore, so that the nitrogen oxide removing component (active component) supported inside the pore is nitrogen oxide removing performance. Cannot be fully demonstrated.

  Conversely, when the pore diameter is larger than 100 mm, the molecular diameter of the phosphorus compound is much smaller than the pore diameter, and the phosphorus compound easily penetrates into the pores to poison the nitrogen oxide removing component. Nitrogen oxide removal performance cannot be exhibited sufficiently.

  Next, the nitrogen oxide removing method of the present invention will be described.

  The nitrogen oxide removal method of the present invention is called a selective catalytic reduction method using a reducing agent. Ammonia may be used as the reducing agent.

  As the reducing agent, a compound other than ammonia, for example, a substance such as urea that decomposes to generate ammonia, a hydrocarbon, carbon monoxide (CO), or the like may be circulated.

The nitrogen oxides targeted by the present invention may include NO, N ₂ O ₃ , NO ₂ , N ₂ O _4, etc., but when these compounds coexist, all these reactions are separated and analyzed. It is difficult.

When ammonia is used as the reducing agent, the following reaction occurs in a temperature range of about 200 to 450 ° C., and N ₂ and H ₂ O are generated.

3NO ₂ + 4NH ₃ → 7 / 2N ₂ + 6H ₂ O
4NO + 4NH ₃ + O ₂ → 4N ₂ + 6H ₂ O
That is, it is a method of reducing hundreds of ppm of NO on a catalyst using ammonia in the presence of about several percent of oxygen gas.

  Next, the nitrogen oxide purification apparatus of the present invention will be described.

  FIG. 1 is a schematic configuration diagram showing a nitrogen oxide removing apparatus of the present invention.

  In this figure, the nitrogen oxide purification apparatus is filled with a flue 2 (exhaust gas passage) through which exhaust gas 1 containing NOx passes, a nozzle 4 for spraying ammonia 3 into the flue 2, and a catalyst layer 5. A nitrogen oxide purifier 6 and a flue 8 through which exhaust gas 7 purified by nitrogen oxide and rendered harmless is introduced. The nitrogen oxide purifier 6 is filled with the catalyst for removing and purifying nitrogen oxide of the present invention. The shape of the nitrogen oxide purification catalyst is a plate shape. In addition to the plate shape, a particle shape or a honeycomb shape may be used.

First, the exhaust gas 1 containing NOx is led to the flue 2. A nozzle 4 for spraying ammonia 3 is installed in the flue 2, and the exhaust gas containing ammonia is led to the nitrogen oxide remover 6. A catalyst layer 5 is disposed in the nitrogen oxide remover 6, and NOx is reduced on the heated catalyst layer 5 to generate harmless N ₂ and H ₂ O. N ₂ and H ₂ O are mixed with the exhaust gas 7 and discharged through the flue 8.

  FIG. 2 is a schematic configuration diagram showing a denitration system of the present invention.

  In this figure, the denitration equipment 10, the electrostatic precipitator 13, the desulfurization tower 11, and the chimney 14 are arrange | positioned in the downstream of the boiler 9 (combustor). A nozzle 4 is installed in the flue 2 so that ammonia can be sprayed uniformly into the exhaust gas. The nozzle 4 is connected to the ammonia production facility 15.

The combustion exhaust gas from the boiler 9 is guided to a denitration facility 10 heated to a predetermined temperature while containing ammonia sprayed from the nozzle 4 in the flue 2. The denitration facility 10 has substantially the same configuration as the nitrogen oxide remover 6 in FIG. 1, and NOx in the exhaust gas is reduced into harmless N ₂ and H ₂ O in the denitration facility 10. The electric dust collector 13 is arranged to remove dust in the exhaust gas. In the case of a coal fired boiler, since the SOx concentration is high, a desulfurization tower 11 is installed at the rear stage of the electrostatic precipitator 13 so that SOx can be removed.

  Next, the nitrogen oxide removal catalyst will be described.

  Titanium sol, sulfate, chloride, oxalate, ammonium peroxocitrate tetrahydrate or metal alkoxide containing titanium such as titanium tetraisopropoxide is used as a raw material of titanium. A sol solution containing titanium hydroxide or titania can also be used. It is also possible to use a commercially available titanium oxide powder.

(Preparation of catalyst)
In the present invention, four types of catalysts of Examples 1 to 4 were prepared.

  In these examples, the carrier was titanium oxide. Titanium tetrachloride was used as a raw material for titanium. Molybdenum and vanadium were used as active ingredients.

  In preparing the catalyst, first, an aqueous titanium tetrachloride solution was prepared by weighing 50 g of high-purity titanium tetrachloride (purity 98% or more) in 1 L (liter) of pure water. A further 66 g of this aqueous solution was precisely weighed and mixed with pure water to prepare a total amount of 3 L of titanium tetrachloride aqueous solution.

  15% ammonia water was added to this titanium tetrachloride aqueous solution at a rate of 2 g / min to synthesize titanium hydroxide precipitate. The endpoint of precipitation synthesis was pH 7.

  The precipitate formation solution was allowed to stand to sufficiently settle the precipitate, and then washed by filtration to collect the precipitate. The collected precipitate was dried at 120 ° C. for 5 hours or more, and then sufficiently pulverized in a mortar and heated at 300 ° C. for 2 hours to prepare a titania carrier.

  In Example 1, a method of simultaneously supporting molybdenum and vanadium as active ingredients was used.

  An ammonium molybdate reagent and ammonium vanadate were simultaneously dissolved in an aqueous hydrogen peroxide solution, and this solution was added dropwise to a titania carrier powder and impregnated. Further, instead of ammonium vanadate, an ammonium metavanadate reagent may be used. The mixing ratio of molybdenum and vanadium was molybdenum: vanadium = 2.5: 1.0 in molar ratio. After impregnation, the titania carrier powder was dried and fired at 500 ° C.

  The active ingredient loading method in Example 2 is a method in which molybdenum and vanadium are impregnated stepwise into a titania carrier.

  An ammonium molybdate reagent was dissolved in an aqueous hydrogen peroxide solution, dropped into a titania carrier powder, impregnated, dried, and fired at 500 ° C. to obtain a molybdenum-supporting titania powder.

  Subsequently, a solution of an ammonium metavanadate reagent dissolved in an aqueous hydrogen peroxide solution was dropped into the molybdenum-supporting titania carrier powder, impregnated, dried, and calcined at 500 ° C. to obtain a catalyst of this example. The compounding amounts of molybdenum and vanadium are the same as in Example 1.

  The active ingredient loading method in Example 3 is a method in which a titania carrier is impregnated with molybdenum and vanadium simultaneously.

  As the impregnation liquid, a monoethanolamine aqueous solution in which monoethanolamine was dissolved in pure water was used, and molybdenum oxide and vanadium oxide were dissolved in this aqueous solution. The compounding amounts of molybdenum oxide and vanadium oxide were molybdenum: vanadium = 2.5: 1.0 in terms of the molar ratio of molybdenum to vanadium. After impregnation, it was dried and baked at 500 ° C.

  As an active ingredient in Example 4, a method of supporting molybdenum was used.

  An ammonium molybdate reagent was dissolved in an aqueous hydrogen peroxide solution, and this solution was dropped into a titania carrier powder and impregnated. The compounding ratio of molybdenum and vanadium was titanium: molybdenum = 9: 1 in molar ratio. After impregnation, it was dried and baked at 500 ° C.

(Comparative Example 1)
In Comparative Example 1, the carrier is the same titanium oxide as in Examples 1 to 4, and vanadium is used as the active ingredient. The vanadium loading method is an impregnation method. As the impregnating solution, a solution obtained by dissolving an ammonium metavanadate reagent in an aqueous hydrogen peroxide solution was dropped into the titania carrier powder to impregnate, dried, and calcined at 500 ° C. to obtain a catalyst of Comparative Example 1.

(Comparative Example 2)
As a raw material of the titanium oxide carrier, 53.0 g of titanium oxide powder G manufactured by Millennium Inoganic Chemicals was used. The amount of vanadium supported is 95: 5 in terms of a molar ratio of titanium to vanadium. For vanadium impregnation, an ammonium metavanadate reagent was used as a vanadium raw material, and a predetermined amount of 0.231 g was dissolved in a mixed solution of 2.3 g of water and 1.0 g of hydrogen peroxide.

  First, ammonium vanadate was added to water little by little, and then a small amount of hydrogen peroxide was added to prepare a solution for impregnation. During the impregnation, the ammonium vanadate solution is dripped evenly over the surface of the titanium oxide powder, the whole amount is dripped, left to stand at room temperature for 30 minutes, further dried at 120 ° C. for 1 hour and then calcined at 500 ° C. for 2 hours. A catalyst of Comparative Example 2 carrying vanadium was obtained.

(Comparative Example 3)
Comparative Example 3 is a two-component catalyst of titanium oxide and vanadium oxide. As a raw material of the titanium oxide carrier, 53.0 g of titanium oxide powder G manufactured by Millennium Inoganic Chemicals was used. The amount of vanadium supported is 95: 5 in terms of a molar ratio of titanium to vanadium. For vanadium impregnation, an ammonium metavanadate reagent was used as a vanadium raw material, and a predetermined amount of 0.231 g was dissolved in a mixed solution of 2.3 g of water and 1.0 g of hydrogen peroxide.

  First, ammonium vanadate was added to water little by little, and then a small amount of hydrogen peroxide was added to prepare a solution for impregnation. During the impregnation, the ammonium vanadate solution was dripped evenly over the surface of the titanium oxide powder, and the whole amount was dropped, left at room temperature for 30 minutes, further dried at 120 ° C. for 1 hour, and then fired at 600 ° C. for 2 hours. A catalyst of Comparative Example 3 carrying vanadium was obtained.

[Nitrogen oxide removal rate measurement method]
The measuring method of nitrogen oxide removal performance is as follows.

  The prepared catalyst powder was pulverized after press molding and classified into 10 to 20 mesh (1.7 mm to 870 μm) to obtain a granular catalyst. About the nitrogen oxide purification | cleaning performance of the granular catalyst before use, it measured on condition of the following using the atmospheric pressure flow type reaction apparatus.

The gas composition is NO: 200 ppm, NH ₃ : 240 ppm, CO ₂ : 12%, O ₂ : 3%, H ₂ O: 12%, N ₂ : balance.

The space velocity (SV) is 120,000 h ⁻¹ .

  The reaction temperature is 350 ° C.

  The initial NOx removal rate ηo was calculated by the following formula (1).

ηo (%) = (inlet NOx concentration−outlet NOx concentration) ÷ (inlet NOx concentration) × 100 (1)
The speed constant ko at the initial NOx removal rate ηo has the relationship of the following formula (2).

ko∝ln {1 / (1-ηo / 100)} (2)
[Phosphorus poisoning treatment]
A post-poisoning catalyst simulating a phosphorus compound, which is a poisoning substance in actual exhaust gas, was prepared by the following method.

The granular catalyst was impregnated with an aqueous phosphoric acid solution containing phosphorus in an amount equivalent to 4 wt% in terms of P ₂ O ₅ with respect to the catalyst weight. After leaving at room temperature for 30 minutes, it was dried at 120 ° C. and then calcined at 350 ° C. for 2 hours to obtain a catalyst after phosphorous poisoning treatment.

  The post-phosphorus poisoning NOx removal rate η was measured using the post-poisoning catalyst prepared by this treatment.

  The NOx removal rate η by the catalyst after phosphorus poisoning can be calculated by the following equation (3).

η (%) = (inlet NOx concentration−outlet NOx concentration) ÷ (inlet NOx concentration) × 100 (3)
The relationship between η and the speed constant k is as shown in the following formula (4).

k∝ln {1 / (1-η / 100)} (4)
The deterioration rate k / k ₀ was determined from the following formula (5) to determine the poisoning resistance.

k / k ₀ = ln {1 / (1-η / 100)} / ln {1 / (1-ηo / 100)} (5)
Here, the degradation rate k / k ₀ is the rate constant ratio when the k ₀ as the initial catalytic rate constant, k a catalytic rate constant after the treatment of poisoning by phosphorus in the (phosphorus poisoning pretreatment).

When k / k ₀ = 1, there is no deterioration of the catalyst, and the smaller the value of k / k ₀ is, the greater the degree of deterioration is.

Table 1 shows the results of evaluating specific surface area, total pore volume, initial NOx removal rate ηo, NOx removal rate η after phosphorus poisoning, and deterioration rate k / k ₀ for Examples 1 to 4 of the present invention. Shown in

Examples 1 to _3, a _{TiO 2 / MoO 3 / V 2} O 5 3 -component composition. The initial NOx removal rate is 81 to 87% and the deterioration rate is 0.7 or more, which is a satisfactory result as the NOx removal performance of the present invention.

Example 4 is a two-component system with a TiO ₂ / MoO ₃ composition. The initial NOx removal rate is 72% and the deterioration rate is 0.7. When the active component is MoO ₃ alone, both the initial NOx removal rate and the deterioration rate are reduced as compared with a three-component system in which V ₂ O ₅ is added to MoO ₃ . This is the difference in effect due to the presence or absence of V ₂ O ₅ .

The catalyst component of Comparative Example 1 has the same components and composition as in Examples 1 to 3. The initial NOx removal rate is 79% and the degradation rate is 0.5, and the degree of degradation after phosphorus poisoning is greater than in Examples 1 to 3 of the present invention. The catalyst of Comparative Example 2 had a TiO ₂ / V ₂ O ₅ composition, and the deterioration rate remained at 0.5.

  In Comparative Example 3, the deterioration rate was as high as 0.9, but the initial NOx removal rate was only 50%.

  The result of examining the difference between the initial NOx removal rate and the deterioration rate shown in Table 1 is shown in Example 2.

  Table 2 shows the physical property values of the catalysts of Examples 1 to 4 and Comparative Examples 1 to 3. The values in Table 2 are the results at a firing temperature of 500 ° C.

In Examples 1 to 4, the pore volume (total pore volume) having a pore diameter (pore diameter) of 20 to 3000 mm is 0.1 cm ³ / g or more, and pores having a diameter of 20 to 3000 mm are measured. The average pore diameter measured by the gas adsorption method is 50 to 60 mm, and the ratio of the pore volume of 20 to 100 mm (pore volume ratio) with respect to the total pore volume is 89 to 97%, which is an extremely high value. Indicates.

On the other hand, Comparative Example 1 is a catalyst having a large pore volume with a total pore volume of 0.2 cm ³ / g or more, but has an average pore diameter of 65 mm and a fine pore size of 20 to 100 mm with respect to the total pore volume. The pore volume ratio is 54%, which is outside the range of physical property values that are considered effective by the present invention.

In Comparative Example 2, the total pore volume is 0.3 cm ³ / g or more, but the average pore diameter is 161 mm, and the pore volume ratio of 20 to 100 mm is 25%, which is also effective according to the present invention. It is out of the range of physical property values considered.

Further, in Comparative Example 3, the total pore volume is 0.1 cm ³ / g or less, which is outside the range of physical property values considered effective by the present invention. The initial NOx removal rate shown in Table 1 is the target value. Not reached.

In addition, it was difficult to produce a nitrogen oxide removing catalyst having a pore diameter of 20 to 100 mm and larger than 0.4 cm ³ per gram of catalyst and having a desired activity.

  1: exhaust gas, 2: flue, 3: ammonia, 4: nozzle, 5: catalyst layer, 6: nitrogen oxide purifier, 7: exhaust gas, 8: flue, 9: boiler, 10: denitration equipment, 11: Desulfurization tower, 13: electric dust collector, 14: chimney, 15: ammonia production equipment, 101: carrier, 102: active ingredient, 103: poisonous substance, 104: nitric oxide, 105: ammonia, 111: pores.

Claims (5)

A carrier having pores and a catalyst for removing nitrogen oxides containing an active ingredient for removing nitrogen oxides in exhaust gas, wherein the pores have an average diameter of 20 to 100 mm and a diameter of 20 to 100 mm. Nitrogen oxide removal, wherein the pore volume is 80% or more with respect to the total pore volume, and the pore volume having a diameter of 20 to 100 mm is 0.1 to 0.4 cm ³ per gram of catalyst. catalyst.   2. The nitrogen oxidation according to claim 1, wherein the carrier includes titanium oxide, and the active component includes at least one metal selected from the group consisting of zirconium, niobium, molybdenum, tantalum, tungsten, and vanadium. Product removal catalyst.   The nitrogen oxide removal catalyst according to claim 2, wherein the ratio of the active ingredient to the number of moles of titanium contained in the titanium oxide is 1/4 to 1/9 in terms of mole ratio.   The nitrogen oxide removal apparatus using the nitrogen oxide removal catalyst as described in any one of Claims 1-3.   A denitration system comprising a combustor and an exhaust gas flow path and comprising the nitrogen oxide removing device according to claim 4.

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