JP2010051836A - Nitrogen oxide purifying catalyst and nitrogen oxide purifying method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an exhaust gas purifying catalyst which prevents a nitrogen oxide purifying catalyst, which removes nitrogen oxides from exhaust gas containing the nitrogen oxides, from being poisoned by phosphorus compounds contained in the exhaust gas, and is excellent in durability, and an exhaust gas purifying method. <P>SOLUTION: The exhaust gas purifying method is preferable which removes the phosphorus compounds in the exhaust gas upstream of the nitrogen oxide purifying catalyst by using the exhaust gas purifying catalyst made by combining the nitrogen oxide purifying catalyst and a trapping material for trapping the phosphorus compounds in the exhaust gas containing the nitrogen oxides and the phosphorus compounds. It is desirable for the trapping material used for the exhaust gas purifying catalyst that a metal oxide is supported inside a mesoporous body, the sum of pore volumes of 5-10 nm of the mesoporous bodies per total pore volume measured by a nitrogen adsorption isotherm measurement method is 50% or more, and the isoelectric point of the metal oxide is more than 3. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a catalyst for removing nitrogen oxides from exhaust gas containing nitrogen oxides and phosphorus compounds, and a nitrogen oxide purification method using the catalyst.

The method of reducing and removing nitrogen oxides (NOx) in the exhaust gas with ammonia (NH ₃ ) is simple and efficient, so the mainstream of the denitration process of various fixed source exhaust gas including boiler combustion exhaust gas It has become. This process requires a denitration catalyst to promote the reaction between NOx and NH ₃ .

  On the other hand, in recent years, low grade coal and low grade crude oil containing a large amount of mineral substances tend to be used as fuel. When such low-grade coal or low-grade crude oil is burned, volatile metal compounds mainly generated from mineral substances, especially oxides such as selenium, tellurium, thallium, arsenic, etc. will be contained in the exhaust gas. The poisoning of the catalyst by these oxides becomes a problem.

  In addition, since low grade coal is poor in combustibility and has a large amount of unburned ash, when such low grade coal is used, a method is often employed in which the ash is returned to the boiler and reburned. However, in this method, the above-mentioned catalytic poison material scattered in the boiler is deposited in fly ash as the exhaust gas temperature decreases, and the ash is returned to the boiler and recycled to be re-scattered in the exhaust gas. . Therefore, there is a problem that the concentration of the catalyst poison substance in the exhaust gas becomes higher than the value predicted from the original content in the fuel, and the deterioration of the catalyst is more likely to proceed.

  In order to prevent deterioration of the catalyst due to poisoning of volatile metal compounds contained in the exhaust gas, particularly oxides such as selenium, tellurium, thallium and arsenic, the average pore diameter is 8 mm or less and the silica / alumina ratio is 10 or more. It is possible to use a catalyst in which zeolite and titanium oxide are mixed and at least one element selected from copper, molybdenum, tungsten, vanadium, and iron is present at a higher concentration in the zeolite portion than in the titanium oxide portion. It is known (see, for example, Patent Document 1). Further, in order to prevent the NOx removal catalyst from being poisoned by the arsenic compound contained in the exhaust gas, it is known to use a catalyst having an active component supported on a carrier having a pore diameter of 3.6 to 5.8 mm. (For example, refer to Patent Document 2).

JP 63-12350 A (Claims) JP 63-51948 A (Claims)

  Recently, coal containing P as a fuel has come to be used. In this case, since the phosphorus compound is contained in the coal combustion exhaust gas, it is necessary to prevent poisoning of the catalyst by the phosphorus compound. Patent Documents 1 and 2 do not consider the prevention of catalyst poisoning by phosphorus compounds.

  Further, with the tightening of nitrogen oxide emission regulations in boilers, attempts have been made to reduce the generation of nitrogen oxides in the boiler by adjusting the air-fuel ratio. In this case, since the combustion temperature of the boiler increases, it is predicted that the phosphorus compound concentration in the exhaust gas will increase more than before.

  An object of the present invention is to provide a nitrogen oxide purification catalyst and a nitrogen oxide removal method having excellent durability, which can prevent poisoning of the catalyst by a phosphorus compound contained in exhaust gas.

  As a result of intensive studies on the exhaust gas purification catalyst and the exhaust gas purification method for solving the above problems, the present inventors have found that an exhaust gas purification method for removing phosphorus compounds in the exhaust gas before the exhaust gas contacts the nitrogen oxide purification catalyst has been found preferable. . And it has the active ingredient for removing the trap material and the nitrogen oxide in which the oxide for trapping the phosphorus compound was supported inside the nanoporous body with the pore diameter controlled and the pore of the nanoporous body An exhaust gas purification catalyst combined with a nitrogen oxide purification catalyst was found.

  The present invention relates to an exhaust gas purification catalyst that combines a nitrogen oxide purification catalyst and a trap material that traps a phosphorus compound in an exhaust gas containing nitrogen oxides and a phosphorus compound, and the trap material contains an oxide inside the mesoporous material. The mesoporous material has a total pore volume of 5 to 10 nm with respect to the total pore volume measured by the nitrogen adsorption thermometer method, and the oxide has an isoelectric point. It is characterized by being greater than 3.

  When the isoelectric point of the metal oxide is larger than 3, the phosphorus compound is trapped near the inlet from the inside of the pores of the mesoporous material. Furthermore, when the pore diameter of the mesoporous material is larger than 5 nm, pore clogging caused by the trapped phosphorus compound can be avoided. That is, ink-well pores (FIG. 1) are formed by the phosphorus compound.

  Therefore, diffusion of the phosphorus compound into the mesoporous material is prevented, and nitrogen oxides in the exhaust gas can diffuse into the mesoporous material.

  From the above, when a nitrogen oxide purification catalyst component is contained inside the pores of the trap material (FIG. 2), high nitrogen oxide while avoiding poisoning of the nitrogen oxide purification catalyst component by the phosphorus compound It is possible to maintain the purification performance.

  Further, as the structure of the exhaust gas purification catalyst, it is preferable that the exhaust gas contacts the trap material and the nitrogen oxide purification catalyst in this order.

For example, a two-layer structure in which a trap material is disposed on the upper layer of the nitrogen oxide purification catalyst. Also,
A double structure (FIG. 3) in which the trap material is disposed outside the nitrogen oxide purification catalyst particles. Further, a two-stage arrangement structure in which a trap material is arranged on the upstream side of the nitrogen oxide is adopted.

  In any structure, the phosphorus compound in the exhaust gas is trapped by the trap material, and the nitrogen oxide passes through the pores of the nanoporous body and reaches the nitrogen oxide purification catalyst. In addition, when the pores of the nanoporous body of the trap material are blocked by trapping the phosphorus compound, the nitrogen oxide purification catalyst in the two-layer structure and the double structure and the nitrogen oxide purification downstream of the two-stage arrangement structure Since the arrival of nitrogen oxides to the catalyst is remarkably suppressed, it is not preferable.

In general, in the case of zeolite, the pore diameter is less than 1 nm and the specific surface area is 300 to 600 m ² / g, whereas in the case of mesoporous material, the pore diameter is 2 to 50 nm. In addition, since the specific surface area is several hundred to 1000 m ² / g, it is reported that it is expected as a new material to replace zeolite (edited by the Ceramic Society of Japan, environmentally friendly material series catalyst) Materials, published by Nikkan Kogyo Shimbun, (2007) p188-200).

  The total pore volume by the nitrogen adsorption isotherm method is obtained by the following method.

  The adsorption isotherm of nitrogen at liquid nitrogen temperature is measured, and the pore distribution is obtained by applying the BJH (Barrett, Joyner, Halenda) method. This pore distribution is a plot of pore volume against pore diameter. Next, the total amount of pore volume in the pore diameter range of 2 to 50 nm and the total amount of pore volume in the pore diameter range of 5 to 10 nm are respectively calculated.

  In the case of the nanoporous material in the present invention, the ratio of the total pore volume in the pore diameter range of 5 to 10 nm is preferably 50% or more with respect to the total pore volume of 2 to 50 nm. On the other hand, if the ratio of the total amount of pore volume in the pore diameter range of 5 to 10 nm is less than 50% with respect to the total pore volume of 2 to 10 nm, pore clogging becomes remarkable when the phosphorus compound is trapped, which is not preferable.

  In particular, the ratio of the total pore volume in the pore diameter range of 7 to 10 nm is preferably 50% or more with respect to the total pore volume of 2 to 10 nm.

  An oxide having an isoelectric point larger than 3 is contained inside the mesoporous material. The isoelectric point is defined as follows in the dictionary of catalysts (Yoshio Ono, Makoto Mitake, Yoshihiko Morooka, Asakura Shoten (2000) p411-412).

The surface of the metal oxide is hydroxylated by the hydration reaction accompanying the contact between the metal oxide and water. In the region where the pH is low, the surface of the metal oxide is positively charged by protons. On the other hand, the pH is high In the region, the surface of the metal oxide surface is negatively charged by deprotonation, and the pH at which this solid surface charge becomes 0 is called the isoelectric point. It varies greatly depending on the type of object. "
Further, there is an electrophoresis method as a method for measuring the isoelectric point. That is, the isoelectric point can be obtained by measuring the moving speed of the metal oxide in the aqueous solution at various pH values and determining the pH when the moving speed becomes zero.

  It is considered that the phosphorus compound in the exhaust gas exists as phosphoric acid having an isoelectric point near 1.

  Accordingly, when the isoelectric point of the oxide contained inside the mesoporous material is 3 or less, the difference in isoelectric point between the phosphorus compound and the metal oxide is small, so that the phosphorus compound is inside the mesopore carrier. It is thought to spread.

  On the other hand, when the isoelectric point of the oxide contained in the mesoporous material is larger than 3, the phosphorus compound is likely to be adsorbed by the oxide, and the phosphorus compound is likely to be trapped near the entrance of the mesopore carrier.

  As a metal oxide having an isoelectric point larger than 3, there is a metal oxide having at least one selected from U, Mn, Sn, Ti, Fe, Zr, Ce, Al, Y, Zn, La, and Mg.

For example, in the dictionary of catalysts (Yoshio Ono, Makoto Mitake, Yoshihiko Morooka, Asakura Shoten (2000) p411-412), UO ₂ : 4.7 to 6.7 (isoelectric point), ZrO ₂ : 4 to 11 , Α-Al ₂ O ₃ : 9.1 to 9.5, γ-Al ₂ O ₃ : 7.4 to 8.6, ZnO: 8.2 to 9.7, MgO: 12.4 ing. Furthermore, in a chemical review No. 34 catalyst design (Academic Publishing Center, 1987, p33), MnO ₂ : 3.9 to 4.5, SnO ₂ : 5.5, TiO ₂ : 4.7 to 6.7 , Γ-Fe ₂ O ₃ : 6.5 to 6.9, CeO ₂ : 6.75, Cr ₂ O ₃ : 6.5 to 7.5, Y ₂ O ₃ : 8.9, La ₂ O ₃ : 10.4.

Examples of the metal oxide having an isoelectric point of 3 or less include WO ₃ : 0.5 or less, SiO ₂ : 1.0, Sb ₂ O ₅ : 0.4 or less.

  Examples of the mesoporous material of the present invention include mesoporous silica, mesoporous titania, mesoporous alumina, and aluminum phosphate. Further, there is a mesoporous material in which a part of mesoporous silica, mesoporous titania or the like is substituted with Al, titanium, Si or the like. By synthesizing these mesoporous materials using a template such as a surfactant, regular pores are formed and the pores are controlled. Therefore, the pore diameter can be controlled by adjusting the synthesis method.

  Furthermore, the mesoporous material after removing the template has pores having a two-dimensional shape and pores having a three-dimensional shape.

  That is, there are mesoporous silica having a two-dimensional through-hole in which long cylinders are arranged, and mesoporous silica having a three-dimensional through-hole opened in the X, Y, and Z directions. For example, there are two-dimensional hexagonal MCM-41, SBA-15, FMS-16, cubic MCM-48, SBA-1, and lamellar MCM-50.

  The active ingredient has an effect of reducing nitrogen oxides and can be appropriately selected according to the nitrogen oxide purification reaction.

  The nitrogen oxide purification catalyst of the present invention can be used in a denitration apparatus that removes nitrogen oxides in exhaust gas discharged from a boiler or the like. The nitrogen oxide purification catalyst can be appropriately coated on a substrate or the like and used as a catalyst plate. In the denitration apparatus, a reducing agent is supplied to the nitrogen oxide purification catalyst as necessary.

When titanium and vanadium are used as the nitrogen oxide purification catalyst component, it has high activity by causing ammonia denitration reaction. The content of titanium is preferably 18.0 to 60.0 wt% of the entire active ingredient in terms of oxide (TiO ₂ ). TiO ₂ has ammonia denitration reaction activity, but also serves as a carrier for dispersing vanadium. If the amount of TiO ₂ is less than 18 wt%, the inside and surface of the mesoporous material cannot be sufficiently covered with TiO ₂ , and vanadium cannot be dispersed on TiO _2, resulting in poor nitrogen oxide removal performance. . When the amount of TiO ₂ loaded is more than 60.0 wt%, the support material having a controlled pore diameter does not work effectively because TiO ₂ closes the pores of the mesoporous material. The vanadium content is preferably 1.0 to 17 wt% in terms of oxide (V ₂ O ₅ ). The vanadium content is preferably 1.0 to 12 wt% in terms of V ₂ O ₅ . When the amount of V ₂ O ₅ is less than 1%, the amount of the active ingredient is small and the nitrogen oxide removal performance is insufficient. When the amount of V ₂ O ₅ is more than 17 wt%, the vanadium oxide particles become large, the dispersibility is deteriorated, and the nitrogen oxide purification performance is deteriorated. Further, when the amount of V ₂ O ₅ loaded is sufficiently larger than 17 wt%, the pores of the mesoporous material are blocked by V ₂ O _5, so that it effectively acts as a carrier material having a controlled pore diameter. Disappear.

The content ratio of titanium and vanadium is preferably 0.07 to 0.60 in terms of a weight ratio V ₂ O ₅ / TiO ₂ in terms of oxide. In particular, 0.18 to 0.45 is optimal. When V ₂ O ₅ / TiO ₂ is less than 0.1, that is, the content of V ₂ O ₅ is very small, and the amount of active ingredient is small, so that the nitrogen oxide purification performance is insufficient. When V ₂ O ₅ / TiO ₂ is larger than 0.6, that is, since the content of V ₂ O ₅ is very large relative to TiO ₂ , the vanadium oxide particles become large, dispersibility becomes poor, and nitrogen oxidation occurs. The product purification performance will deteriorate. Vanadium contained in the active ingredient is a mixture of tetravalent and pentavalent charges, and the molar ratio V ⁴⁺ / V ^{5+ of the} tetravalent and pentavalent is preferably 0.5 to 0.7. The valence of vanadium is preferably such that both tetravalent and pentavalent coexist, and the more the pentavalent vanadium, the higher the catalytic activity. In the nitrogen oxide purification reaction using NH ₃ as a reducing agent, it is known that NH ₃ is adsorbed to OH groups on tetravalent vanadium, and V ⁴⁺ / V ⁵⁺ ranges from 0.5 to 0. When it is in the range of 0.7, it effectively acts as a nitrogen oxide purification catalyst.

  As in the case of vanadium, examples of active ingredients having nitrogen oxide purification activity include metals such as molybdenum, tungsten, iron, and manganese. Further, these may be added as additional active components to the catalytic active components of titanium and vanadium.

  Examples of embodiments in which the present invention is applied to an exhaust gas purification apparatus from an engine include the following.

  In the case of a power plant that uses coal as fuel, exhaust gas from the boiler contains nitrogen oxides, sulfur oxides, dust, and the like. After purifying nitrogen oxides coexisting in the exhaust gas from the boiler, sulfur oxides and dust are removed, and nitrogen oxides, sulfur oxides and dusts in the exhaust gas are excluded as much as possible and then discharged to the atmosphere. The Since phosphorus combustion compounds and arsenic compounds are contained in coal combustion exhaust gas, it is necessary to prevent poisoning of the catalyst by phosphorus compounds and arsenic compounds.

  From the above, an exhaust gas purification apparatus from an engine using the exhaust gas purification catalyst of the present invention as nitrogen oxide purification is effective.

  According to the said structure, the poisoning of the nitrogen oxide purification catalyst component by a phosphorus compound can be prevented, and the exhaust gas purification catalyst excellent in durability can be provided.

  The details of the present invention will be described. In order to remove nitrogen oxides in the exhaust gas discharged from the boiler or the like, a denitration device is provided in the exhaust passage at the rear stage of the boiler. Normally, other equipment such as a heat exchanger is provided in the flow path between the boiler and the denitration apparatus. An exhaust gas purification catalyst for removing nitrogen oxides is disposed in the denitration apparatus.

The exhaust gas purification catalyst is molded as it is or after a binder such as TiO ₂ , SiO ₂ , Al ₂ O ₃ or water is added. The shape of the molded product can be arbitrarily selected depending on the applied reactor and gas flow conditions, such as granular, pellet, honeycomb, and plate. When the molded product is dried at 100 ° C. or higher and then fired in an inert gas or air atmosphere at less than 800 ° C., preferably in the range of 300 ° C. to 700 ° C. for 1 hour to 10 hours, the strength can be improved.

  For example, in the case of a plate shape, a plurality of catalyst units each having a plate-like catalyst plate to which an exhaust gas purification catalyst is attached fixed to a frame member are provided, so that maintenance is facilitated.

  Hereinafter, the present invention will be described with reference to examples.

  The exhaust gas purification catalyst of the present invention can be used alone or in combination with other nitrogen oxide purification catalysts. In a honeycomb catalyst or a plate catalyst, a catalyst layer made of the exhaust gas purification catalyst of the present invention is formed on an upper layer of a conventional nitrogen oxide purification catalyst, and the reaction gas contacts the exhaust gas purification catalyst layer of the present invention prior to the conventional catalyst. The configuration is as follows. Thereby, the deterioration can be reduced and the life can be extended as compared with the conventional catalyst composed of the catalyst component alone.

  In order to remove nitrogen oxides (NOx) in the exhaust gas using the exhaust gas purification catalyst, a mixed gas of exhaust gas containing nitrogen oxides and ammonia gas as a reducing agent is circulated at a temperature of 300 ° C. or more to exhaust gas. What is necessary is just to contact with a purification catalyst. 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 exhaust gas purification catalyst of the present invention is hardly deteriorated by a phosphorus compound which is a catalyst poison in exhaust gas, and maintains high activity for a long time. The reason why the exhaust gas purifying catalyst of the present invention is not easily deteriorated with respect to the phosphorus compound is that the phosphorus compound is trapped in the vicinity of the pores of the mesoporous material whose pores are controlled, and the nitrogen inside the pores is trapped. This is because phosphorus poisoning of the oxide purification component is prevented.

  The detailed mechanism of catalyst deterioration due to the phosphorus compound contained in the exhaust gas is unknown, but the phosphorus compound adsorbs to the nitrogen oxide purification component that is the active point of the catalytic reaction, or forms a compound after adsorption, etc. It is thought that the reaction with nitrogen oxides, ammonia, oxygen, etc., which are reactants, is hindered and the activity decreases. Therefore, in order to suppress the deterioration, the nitrogen oxide purification catalyst component can be brought into contact with the reactant, but may be structured so as not to come into contact with the phosphorus compound which is a catalyst poison.

Various forms such as oxides, organic compounds, phosphoric acid, phosphates, and compounds with metals can be considered as specific forms of the phosphorus compounds in the combustion exhaust gas and when they are deposited on the catalyst. Most representative is an oxide (P ₂ O ₅ ), and P ₂ O ₅ exists in the form of two molecules of P ₄ O ₁₀ .

  In a mesoporous material containing a metal oxide, when the isoelectric point of the metal oxide is 3 or less, the phosphorus oxide is less likely to be trapped in the metal oxide and diffuses to the inside of the mesoporous material. On the other hand, when the isoelectric point of the metal oxide is larger than 3, the phosphorus oxide is easily trapped in the metal oxide, and diffusion into the mesoporous material is prevented.

  However, when the pore size of the mesoporous material is 5 nm or less, pore trapping is caused by the trapped phosphorus compound. On the other hand, it was found that when the pore diameter was larger than 5 nm, pore clogging by the phosphorus compound was avoided.

  From the above, in the mesoporous material containing a metal oxide, the mesoporous material has a total pore volume of 5 to 10 nm in a total pore volume measured by a nitrogen adsorption isotherm method of 50% or more, In addition, by making the isoelectric point of the metal oxide greater than 3, it is possible to prevent poisoning deterioration of the nitrogen oxide purification catalyst component.

  The present invention is effective in suppressing catalyst deterioration by a phosphorus compound, but is also applicable to treatment of exhaust gas containing a volatile metal compound such as selenium, tellurium, thallium, and arsenic together with a phosphorus compound. Is possible.

  Example catalysts 1 to 4 of the above catalyst and Comparative catalysts 1 to 6 were prepared.

(Example catalyst 1)
As the mesoporous material, mesoporous silica composed of silica was used. As a method for supporting the metal oxide and nitrogen oxide purification component on the mesoporous silica, a TMP (Thermolytic Molecular Precursor) method, which is a support method capable of introducing an active component into the pores, was used. The TMP method is an effective method in which an active component is reliably supported in pores because a precursor is formed by reacting a metal alkoxide containing a supported metal element with a surface hydroxyl group of mesoporous silica.

  The pore distribution of mesoporous silica was measured using ASAP2010 manufactured by Shimadzu Corporation. The adsorption isotherm of nitrogen gas adsorption at liquid nitrogen temperature was measured, and the differential pore volume for each average pore diameter of the pores of the catalyst was determined by the BJH method from the data. FIG. 4 shows the measurement results.

  The differential pore volume reached a maximum at a pore diameter of 7 nm. The pore volume of mesoporous silica at a pore diameter of 5 to 10 nm was 65% with respect to the total pore volume (pore diameter: 2 to 50 nm).

As a metal oxide, titania having an isoelectric point greater than 3 was supported on mesoporous silica by the TMP method. Mesoporous silica (15 g) was placed in a Schlenkners flask, connected to a Schlenk line, heated to 180 ° C. in an oil bath, and vacuum dried for 5 hours. Next, nitrogen gas was introduced into the eggplant-shaped flask, and 110 cc of tetrahydrofuran dehydrated and 2.98 g of titanium tetraisopropoxide were added under a nitrogen gas flow. The mixture was stirred at room temperature for 15 hours under a nitrogen gas flow. After the stirring was completed, the solid was allowed to settle and the supernatant was removed with a syringe. The solid matter remaining in the eggplant-shaped flask was vacuum-dried at room temperature for 5 hours using a Schlenk line. This dry powder was dried in air at 150 ° C. for 2 hours. Finally, it was calcined at 500 ° C. for 2 hours in the atmosphere. This operation of the TMP method was repeated three times. Finally, Example Catalyst 1 in which 18 wt% of TiO ₂ was supported on mesoporous silica was obtained.

(Example catalyst 2)
The operation of Example Catalyst 1 in the TMP method was repeated four times to obtain Example Catalyst 2 carrying 25 wt% of TiO ₂ on mesoporous silica. The pore volume of the mesoporous silica used in Example Catalyst 2 at a pore diameter of 5 to 10 nm was 65% with respect to the total pore volume (pore diameter: 2 to 10 nm), as in Example Catalyst 1.

(Example catalyst 3)
Example catalyst 1 was loaded with V as a nitrogen oxide purification catalyst component using the TMP method. 15 g of the obtained powder was put in a Schlenk-nas flask, connected to a Schlenk line, heated to 180 ° C. in an oil bath and vacuum dried for 5 hours. Next, nitrogen gas was introduced into the eggplant-shaped flask, and 110 cc of tetrahydrofuran dehydrated and 3.3 g of vanadium tri-n-butoxide oxide were added under a nitrogen gas flow. The mixture was stirred at room temperature for 15 hours under a nitrogen gas flow. After completion of stirring, the mixture was allowed to stand to settle the solid matter, and then the supernatant was removed with a syringe. The solid matter remaining in the eggplant-shaped flask was vacuum-dried at room temperature for 5 hours using a Schlenk line. This dry powder was dried in air at 150 ° C. for 2 hours. Finally, the catalyst was calcined in the atmosphere at 500 ° C. for 2 hours to obtain Example Catalyst 3. Finally, vanadium was supported so that the weight ratio of Example Catalyst 1 to V ₂ O ₅ was 94: 6.

(Example catalyst 4)
In the same manner as Example Catalyst 3, vanadium was supported on Example Catalyst 2 so that the weight ratio of 1 to V ₂ O ₅ was 94 to 6.

(Comparative Example Catalyst 1)
The mesoporous silica of Example Catalyst 1 was changed to the following. The differential pore volume of mesoporous silica reached a maximum at a pore diameter of 4 nm. The pore volume at a pore diameter of 5 to 10 nm was 28% with respect to the total pore volume (pore diameter: 2 to 10 nm).

(Comparative Example Catalyst 2)
The mesoporous silica of Example Catalyst 1 was changed to the following. The differential pore volume of mesoporous silica reached a maximum at a pore diameter of 5 nm. The pore volume at a pore diameter of 5 to 10 nm was 48% with respect to the total pore volume (pore diameter: 2 to 10 nm).

(Comparative Example Catalyst 3)
In the same manner as in Example Catalyst 3, vanadium was supported so that the weight ratio of Comparative Catalyst 1 to V ₂ O ₅ was 94: 6.

(Comparative catalyst 4)
In the same manner as Example Catalyst 3, vanadium was supported so that the weight ratio of Comparative Example Catalyst 2 to V ₂ O ₅ was 94: 6.

(Comparative catalyst 5)
Only mesoporous silica used in Example Catalyst 1 was used. The differential pore volume reached a maximum value at a pore diameter of 7 nm. The pore volume of mesoporous silica at a pore diameter of 5 to 10 nm was 65% with respect to the total pore volume (pore diameter: 2 to 50 nm). However, the isoelectric point of silica is reported to be smaller than 3 and 1.0 to 2.5 (Yoshio Ono, Ikusei Mitake, Yoshihiko Morooka, Asakura Shoten (2000) p411-412).

(Comparative Example Catalyst 6)
A solution obtained by dissolving 1.54 g of NH ₄ VO _{3 in} 30 g of an aqueous hydrogen peroxide solution was impregnated into 20 g of TiO ₂ powder (Rhône-Poulenc, G5, specific surface area 330 m ³ / g) and left for 30 minutes. This was dried at 120 ° C. and then calcined in air at 500 ° C. for 2 hours to obtain a comparative catalyst 5 in which vanadium was supported on TiO ₂ . The weight ratio of TiO ₂ to V ₂ O ₅ was 95 to 5.

The differential pore volume of the TiO ₂ powder reached a maximum value at a pore diameter of 3.5 nm. The pore volume of mesoporous silica at a pore diameter of 5 to 10 nm was 29% with respect to the total pore volume (pore diameter: 2 to 50 nm).

[Experimental Example 1]
About the catalyst of Example catalyst 1-4 and the catalyst of comparative example 1-5, the phosphorus poisoning process which simulated the phosphorus poisoning by the combustion exhaust gas containing a phosphorus compound was performed, and the adsorption isotherm measurement of nitrogen in liquid nitrogen temperature was implemented. did. A powder sample was used for the measurement. For the measurement of the adsorption isotherm, ASAP2010 manufactured by Shimadzu Corporation was used.

  The adsorption isotherm is a plot of the amount of nitrogen adsorbed against the relative partial pressure (P / P0), which is the ratio of the equilibrium pressure (P) to the nitrogen introduction pressure (P0).

  FIG. 5 shows adsorption isotherms before and after the phosphorus poisoning treatment of Example catalyst 1.

  First, before phosphorus poisoning treatment, in the adsorption operation, adsorption of nitrogen molecules to the catalyst surface occurs until the relative partial pressure is 0.4, and adsorption of multimolecular layers occurs when the relative partial pressure is 0.4 or more. When the relative partial pressure is 0.7 or more, capillary condensation occurs in the mesopores. In the case of a cylindrical pore (FIG. 6), an isotherm pattern equivalent to that of the adsorption operation is obtained even when the desorption operation is performed with the relative partial pressure lowered.

  On the other hand, in the case of phosphorus poisoning treatment, the adsorption isotherm during the desorption operation gradually decreases until the relative partial pressure decreases from 1.0 to 0.5, compared with the adsorption operation. The amount of adsorption decreases rapidly. Hysteresis of this adsorption isotherm is classified into ink cup-shaped pores (FIG. 7).

  Therefore, it is clear that the catalyst of Example 1 was changed from the cylinder shape to the ink tub-shaped pores by the phosphorous poisoning treatment. That is, as shown in FIG. 1, a model is obtained in which the phosphorus compound 3 is supported near the inlet of the mesoporous silica 1 on which the titania 2 is supported and the pores are narrowed.

  FIG. 8 shows adsorption isotherms before and after phosphorous poisoning treatment of Comparative Example Catalyst 2.

  The hysteresis of the adsorption isotherm before and after the phosphorus poisoning treatment became a cylinder shape. Therefore, when the pore volume at a pore diameter of 5 to 10 nm is 48% with respect to the total pore volume (pore diameter: 2 to 10 nm), it is clear that the pores after the phosphorous poisoning treatment do not have an ink bottle shape. It is. Furthermore, the amount of decrease in the pore volume after the treatment of the comparative example catalyst 2 before the phosphorous poisoning treatment was about 8 times the theoretical value when there was no pore blockage.

  From the above, in the case of the comparative example catalyst 2, it is determined that the phosphorus compound 3 is a model (FIG. 9) in which some of the pores of the mesoporous body 1 are closed.

  Based on the above analysis method, the catalysts of Examples 1 to 4 and Comparative Examples 1 to 5 were analyzed. Table 1 summarizes the analysis results.

  It was found that Example Catalysts 1 to 4 formed ink fountain-shaped pores in the mesoporous material by phosphorus poisoning treatment.

  On the other hand, it was found that the pores of the mesoporous material were clogged with Comparative Catalysts 1-5.

[Experimental example 2]
The catalysts of Examples 3 and 4 and Comparative Catalysts 3, 4 and 6 were subjected to phosphorous poisoning treatment simulating phosphorous poisoning by combustion exhaust gas containing phosphorous compounds, and nitrogen oxidation of the catalyst before and after phosphorous poisoning treatment The object removal performance was compared.

The 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. The phosphoric acid solution including phosphorus in 4 wt% corresponds the same amount in terms _of P ₂ O ₅ with respect to catalyst weight, was impregnated with particulate catalyst. After leaving it 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 phosphorus poisoning treatment.

  The nitrogen oxide removal performance of the catalyst before and after the above phosphorus poisoning treatment was measured using a normal pressure flow type reaction apparatus under the following conditions.

1. Gas composition
NO: 200ppm
NH ₃ : 240 ppm
CO ₂ : 12%
O ₂ : 3%
H ₂ O: 12%
N ₂ : Balance 2. Space velocity (SV): 120,000 h ⁻¹
3. Reaction temperature: 350 ° C
The purification performance of nitrogen oxides before and after the phosphorus poisoning treatment under the above conditions was examined, and the deterioration rate (α) by the phosphorus poisoning treatment was obtained. The deterioration rate (α) is defined by the ratio (formula (1)) between the reaction rate constant (k ₀ ) before the phosphorus poisoning treatment and the reaction rate constant (k) after the phosphorus poisoning treatment.

α = k / k ₀ (1)
Furthermore, k / k ₀ can be obtained from the ratio between the nitrogen oxide removal rate (η0) before the phosphorus poisoning treatment and the nitrogen oxide removal rate (η) after the phosphorus poisoning treatment. It shows in Formula (2).

α = k / k ₀ = ln (1 / (1-η)) / ln (1 / (1-η0)) (2)
When η = (inlet NOx concentration−outlet NOx concentration) ÷ inlet NOx concentration k / k ₀ = 1, it indicates that there is no deterioration of the catalyst, and a larger value of k / k ₀ indicates that there is less deterioration.

Table 2 shows the measurement results. In the case of Example Catalysts 3 and 4 that become ink fountain-shaped pores after phosphorus treatment, k / k ₀ = 1 and it is clear that there is no deterioration. On the other hand, it is clear that deterioration occurs in the case of Comparative Catalysts 3, 4 and 6 in which pore clogging occurs.

  Co, Cu or Fe was supported instead of V in Example catalyst 3. The supported amount was 94: 6 by weight ratio of 1 catalyst of Example to Co, Cu or Fe oxide. The catalyst supporting Co was designated as Example catalyst 5, the catalyst supporting Cu as Example catalyst 6, and the catalyst supporting Fe as Example catalyst 7.

  As a result of measuring the adsorption isotherm before and after phosphorus poisoning treatment in the same manner as in Experimental Example 1, the pore shapes in Example Catalysts 5, 6 and 7 were changed from cylinder to ink by phosphorus poisoning treatment. Changed to a saddle shape. That is, as shown in FIG. 1, the model is such that the phosphorus compound 3 is supported near the inlet of the mesoporous silica 1 to narrow the pores.

Next, in accordance with Experimental Example 2, the nitrogen oxide removal performance of the catalyst before and after the phosphorus poisoning treatment was examined. Also in the example catalysts 5, 6 and 7, k / k ₀ = 1 and it was found that there was no deterioration.

(Example catalyst 5)
1200 g titanium oxide (Ishihara Sangyo, specific surface area 250 m ² / g), 425 g ammonium metatungstate, 810 g silica sol (manufactured by Nissan Chemical Co., OXS sol) and water are mixed in a kneader for 20 minutes, and then 39.9 g ammonium metavanadate. Was added and kneaded for 20 minutes. While gradually adding 320 g of silica-alumina ceramic fibers (manufactured by Toshiba Fine Slex), the mixture was kneaded for 30 minutes to obtain a catalyst paste having a moisture content of 29%. The obtained paste was placed on a mullet-laminated base material made of SUS430 steel plate having a thickness of 0.2 mm, sandwiched between two polyethylene sheets, and passed through a pair of pressure rollers, and between the mesh of the metal lath base material and the surface. With coating. This was air-dried and then dried at 500 ° C. for 2 hours to prepare a Ti / W / V-based catalyst plate. The coating amount of the catalyst on the catalyst plate is 800 g / m ² . Further, 425 g of Example Catalyst 1 powder, 810 g of silica sol (manufactured by Nissan Chemical Co., Ltd., OXS sol) and water were placed in a kneader and kneaded for 20 minutes, and then coated on a Ti / W / V catalyst plate. The coating amount was 800 g / m ² .

  The catalyst obtained by coating Example Catalyst 1 on the upper layer of the Ti / W / V catalyst was referred to as Example Catalyst 5.

In accordance with Experimental Example 2, the nitrogen oxide removal performance of the catalyst before and after the phosphorus poisoning treatment was examined. k / k ₀ = 1 and it was found that there was no deterioration. The nitrogen oxide purification rate (η0) before phosphorus poisoning was 0.75.

It is an example of the ink well type | mold pore formed with the phosphorus compound. It is an example of the exhaust gas purification catalyst in which the nitrogen oxide purification catalyst component is contained inside the pores of the trap material. It is an example of the exhaust gas purification catalyst having a double structure in which the trap material is disposed outside the nitrogen oxide purification catalyst. It is a figure of the differential pore volume of an Example catalyst. It is an adsorption isotherm before and behind the phosphorus poisoning process of an Example catalyst. It is a cylindrical pore model of an example catalyst. It is a pore model of an ink bottle shape of an example catalyst. It is an adsorption isotherm before and after phosphorus poisoning treatment of a comparative example catalyst. This is a model in which part of the pores of the mesoporous material is closed by a phosphorus compound.

Explanation of symbols

1 Mesoporous material 2 Metal oxide 3 Phosphorus compound 4 Nitrogen oxide purification component 5 Nitrogen oxide purification catalyst 6 Trap material

Claims (9)

  An exhaust gas purification catalyst that combines a trap material that traps phosphorus compounds in exhaust gas containing nitrogen oxides and phosphorus compounds and a nitrogen oxide purification catalyst, the trap material having a metal oxide supported inside the mesoporous material In the mesoporous material, the total pore volume of 5 to 10 nm is 50% or more with respect to the total pore volume measured by the nitrogen adsorption temperature line measurement method, and the isoelectric point of the metal oxide is 3 An exhaust gas purification catalyst characterized by being large.   The metal oxide according to claim 1 is a metal oxide having at least one selected from U, Mn, Sn, Ti, Fe, Zr, Ce, Al, Y, Zn, La, and Mg. Exhaust gas purification catalyst.   An exhaust gas purification catalyst comprising a nitrogen oxide purification catalyst component in the pores of the trap material according to claim 1 or 2.   An exhaust gas purification catalyst having a double structure in which the trap material according to claim 1 or 2 is disposed outside the nitrogen oxide purification catalyst particles.   A multi-layer exhaust gas purification catalyst comprising a nitrogen oxide purification catalyst layer under the trap material according to claim 1 or 2.   The exhaust gas purification catalyst according to any one of claims 1 to 5, wherein the trapping mesoporous material has pores having a two-dimensional shape and pores having a three-dimensional shape.   The exhaust gas purification catalyst according to any one of claims 1 to 6, wherein the support of the nitrogen oxide purification catalyst is mesoporous silica.   The exhaust gas purification catalyst according to any one of claims 1 to 7, wherein the nitrogen oxide purification catalyst component contains at least one selected from Cu, Fe, Co, vanadium, molybdenum, and tungsten. A featured exhaust gas purification catalyst.   A method for removing nitrogen oxides, wherein an exhaust gas containing nitrogen oxides and a phosphorus compound and a reducing agent are brought into contact with a nitrogen oxide purification catalyst to reduce and remove nitrogen oxides in the exhaust gas. An exhaust gas purification method comprising reducing nitrogen oxides in a nitrogen oxide purification catalyst after removing the compounds.

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