WO2014073066A1

WO2014073066A1 - Honeycomb structure and manufacturing method thereof

Info

Publication number: WO2014073066A1
Application number: PCT/JP2012/078944
Authority: WO
Inventors: 康文深沢; 吉村　健
Original assignee: イビデン株式会社
Priority date: 2012-11-08
Filing date: 2012-11-08
Publication date: 2014-05-15
Also published as: JPWO2014073066A1; CN104768643A

Abstract

Provided is a manufacturing method capable of manufacturing a honeycomb structure which uses a TiO₂/V₂O₅/WO₃ catalyst, and which has excellent NO_X conversion efficiency and thermal durability. This manufacturing method is of a honeycomb structure which is provided with a honeycomb unit in a shape in which multiple cells are partitioned by cell walls, said cells containing at least titanium oxide, vanadium oxide, tungsten oxide and an inorganic binder and extending in the longitudinal direction from one end surface to the other end surface; this manufacturing method is characterized by involving a mixing step for mixing titanium oxide, a vanadium raw material, a tungsten raw material, and an inorganic binder, a molding step for molding the aforementioned mixed material to obtain a honeycomb molded body, and a firing step for firing the honeycomb molded body, wherein in the mixing step, vanadium raw material is a solution comprising ammonium metavanadate dissolved in advance in an alkaline solution.

Description

Honeycomb structure and manufacturing method thereof

The present invention relates to a honeycomb structure which is a denitration catalyst for removing nitrogen oxide (NOx) in exhaust gas and a method for manufacturing the honeycomb structure.

As a system for purifying NOx in exhaust gas, an SCR (Selective Catalytic Reduction) system that uses ammonia to reduce NOx to nitrogen and water is known. As a catalyst used in this SCR system, vanadium pentoxide (V ₂ O ₅ ) is known to have high denitration performance, and V ₂ O ₅ and tungsten trioxide (WO ₃ ) are added to titanium dioxide (TiO ₂ ). Is used. Such a catalyst in which V ₂ O ₅ and WO ₃ are supported on titanium oxide (hereinafter also referred to as “TiO ₂ / V ₂ O ₅ / WO ₃ catalyst”) is disclosed in, for example, Patent Document 1. It is disclosed.

Japanese Patent Laid-Open No. 2005-21780

However, the SCR system using the TiO ₂ / V ₂ O ₅ / WO ₃ catalyst as described above has the following problems.
The NOx purification performance of the TiO ₂ / V ₂ O ₅ / WO ₃ catalyst varies depending on the addition amounts of the catalyst species V and W, but becomes an active site when the addition amount and ratio of V and W are not appropriate. V cannot be uniformly dispersed, and a bulk body cannot be formed and used effectively. Furthermore, there is a problem that V forms a bulk body and is deactivated by heat. Further, when the amount of addition of V and W is increased, the cost of the catalyst becomes a problem.

The present invention has been made in view of the above-described conventional problems, and an object thereof is a honeycomb structure using a TiO ₂ / V ₂ O ₅ / WO ₃ catalyst, which has a NOx purification rate and thermal durability. An excellent honeycomb structure and a method for manufacturing the same are provided.

The present invention for solving the above problems is as follows.
(1) A shape in which a plurality of cells including at least titanium oxide, vanadium oxide, tungsten oxide, and an inorganic binder and extending from one end face to the other end face along the longitudinal direction are partitioned by cell walls. A method for manufacturing a honeycomb structure including a honeycomb unit,
Mixing step of mixing titanium oxide, vanadium raw material, tungsten raw material and inorganic binder;
Forming the mixed material into a honeycomb shape and obtaining a honeycomb formed body; and
A firing step of firing the honeycomb formed body,
In the mixing step, the vanadium raw material is a solution in which ammonium metavanadate is previously dissolved in an alkaline solution.

(2) The method for manufacturing a honeycomb structure according to (1), wherein the alkaline solution is at least one selected from a diethanolamine solution, a monoethanolamine solution, a diethylaminoethanol solution, and aqueous ammonia.

(3) The method for manufacturing a honeycomb structure according to (2), wherein the alkaline solution is a diethanolamine solution, and when the ammonium metavanadate is dissolved in the diethanolamine solution, the alkaline solution is heated to 80 ° C. or higher. .

(4) The above (1) to (3), wherein the molar ratio (W / V) of vanadium atoms in the vanadium raw material and tungsten atoms in the tungsten raw material is 0.8 to 1.2. A method for manufacturing a honeycomb structure according to any one of the above.

(5) The inorganic binder is a solid content contained in one or more selected from the group consisting of alumina sol, silica sol, titania sol, water glass, sepiolite, attapulgite, bentonite and boehmite. (4) The method for manufacturing a honeycomb structure according to any one of (4).

(6) In the mixing step, at least one selected from the group consisting of inorganic fibers, scale-like substances, tetrapot-like substances, and three-dimensional needle-like substances is further mixed. The method for manufacturing a honeycomb structure according to any one of the above.

(7) The inorganic fiber is at least one selected from the group consisting of alumina, silica, silicon carbide, silica alumina, glass, wollastonite, potassium titanate and aluminum borate,
The scaly substance is at least one selected from the group consisting of glass, muscovite, alumina and silica,
The tetrapot-like substance is zinc oxide,
The three-dimensional acicular material is at least one selected from the group consisting of alumina, silica, silicon carbide, silica alumina, glass, wollastonite, potassium titanate, aluminum borate and boehmite. A method for manufacturing a honeycomb structured body according to (6).

(8) A honeycomb structure obtained by the method for manufacturing a honeycomb structure according to any one of (1) to (7),
Hydrogen consumption by vanadium per 1 g of honeycomb structure by the hydrogen-temperature reduction method (H ₂ -TPR) is 0.6 mmol or more, and the molar ratio of W / V addition amount is 0.8 to 1.2. A honeycomb structure characterized by the above.

According to the present invention, a honeycomb structure using a TiO ₂ / V ₂ O ₅ / WO ₃ catalyst, a honeycomb structure excellent in NOx purification rate and thermal durability, and a method for manufacturing the honeycomb structure can be provided. .

Is a diagram showing a NOx purification cycle _{_{_{TiO 2 / V 2 O 5 /}}} WO 3 catalyst. It is a perspective view which shows an example of the honeycomb structure of this invention. It is sectional drawing which shows an example of the exhaust gas purification apparatus which has a honeycomb structure of this invention. It is a perspective view which shows the other example of the honeycomb structure of this invention. FIG. 5 is a perspective view showing a honeycomb unit constituting the honeycomb structure of FIG. 4.

The method for manufacturing a honeycomb structure of the present invention includes at least a titanium oxide, a vanadium oxide, a tungsten oxide, and an inorganic binder, and a plurality of cells extending from one end face to the other end face along the longitudinal direction. A manufacturing method of a honeycomb structure including a honeycomb unit having a shape defined by cell walls, a mixing step of mixing a titanium oxide, a vanadium raw material, a tungsten raw material, and an inorganic binder, and the mixed material into a honeycomb shape A forming step of forming a honeycomb formed body and a firing step of firing the honeycomb formed body, and in the mixing step, the vanadium raw material is a solution in which ammonium metavanadate is previously dissolved in an alkaline solution. It is a feature.
Further, the honeycomb structure of the present invention is a honeycomb structure obtained by the method for manufacturing a honeycomb structure of the present invention, and depends on V per 1 g of the honeycomb structure by a hydrogen-temperature-reduction reduction method (H ₂ -TPR). The hydrogen consumption is 0.6 mmol or more.

In SCR reaction _{_{_{TiO 2 / V 2 O 5 /}}} WO 3 catalyst, since it proceeds by the redox reaction of V (5 valence ⇔4 valence) of on TiO ₂ as shown in FIG. 1, TiO ₂ above The reactivity is improved by increasing the amount of V (pentavalent). To increase the amount of V on TiO ₂ (5-valent) may Tosureba V-O-W is coupled with V and W on TiO _2, thereby maintaining the dispersed state of V, and heat Can prevent V from being bulked and deactivated. That is, by combining W with V on TiO ₂ to form VO—W, the amount of pentavalent V ions on TiO ₂ can always be kept large. Then, in order to all effectively use the V on TiO ₂ as a pentavalent ion, at least a molar ratio of V and W on the TiO ₂ 1: it is considered necessary to bond such that the 1.

The present inventor found that V is a dispersed state of V, that is, V (pentavalent) that contributes to the reaction at 250 ° C., SV (space velocity) 60000 hr ⁻¹ , NO ₂ / NOx = 0, which are general conditions of automobile exhaust gas. As a result of quantifying the amount (hereinafter referred to as “effective V amount”), the NOx purification rate is improved with an increase in the added amount of W, and further the NOx purification rate is increased with an increase in the effective V amount is 0.3 mmol / g or more. It was found to be saturated at.
Here, a hydrogen-temperature reduction method (H ₂ -TPR) is used as a method for deriving the effective V amount. In order to satisfy the effective V amount of 0.3 mmol or more per 1 g of the honeycomb structure, the relationship between the hydrogen consumption calculated from the pentavalent vanadium reduction peak (350 to 580 ° C.) and the accompanying vanadium valence change. Therefore, the hydrogen consumption in this measurement must be 0.6 mmol / g or more.
From the above, the hydrogen consumption derived from vanadium reduction in the hydrogen-temperature reduction method is 0.6 mmol or more per 1 g of honeycomb structure (effective V amount is 0.3 mmol / g or more), and the W / V addition amount molar ratio is 0.00. By setting the ratio to 8 to 1.2, the initial NOx purification performance and thermal durability can be improved.

As described above, the initial NOx purification performance and thermal durability can be improved by increasing the effective V amount in the TiO ₂ / V ₂ O ₅ / WO ₃ catalyst. That is, V may be uniformly dispersed so that the bulk body does not exist. However, in the mixing step of mixing each raw material, the present inventor is a solution in which ammonium metavanadate is previously dissolved in an alkaline solution as the V raw material. It was found that the abundance ratio of V bulk bodies that do not show activity can be reduced by mixing with titanium oxide and tungsten raw materials. In other words, since V can be attached to the TiO ₂ raw material in a sufficiently dispersed state in the solution, the dispersion state of V is higher than that in the case where the TiO ₂ raw material and the V raw material are mixed with each other, resulting in a bulk body. Can be prevented. By forming a state in which the V raw material is uniformly dispersed on TiO ₂ in advance before firing, V can be evenly dispersed even after firing, thereby improving NOx purification performance and thermal durability. be able to.

Hereinafter, in describing the method for manufacturing a honeycomb structure of the present invention, an example of the honeycomb structure will be described with reference to FIG.
A honeycomb structure 10 shown in FIG. 2 includes titanium oxide, vanadium oxide, tungsten oxide, and an inorganic binder, and a plurality of through holes 11a are arranged in parallel in the longitudinal direction with partition walls 11b interposed therebetween. The honeycomb unit 11 is provided. Further, the outer peripheral coat layer 12 is formed on the outer peripheral surface excluding both end surfaces of the honeycomb unit 11.
Each step of the production method of the present invention for producing such a honeycomb structure will be described below.

[Mixing process]
In this step, a titanium oxide, a vanadium raw material, a tungsten raw material, and an inorganic binder are included. The raw material paste is prepared by mixing the above.
As described above, as the vanadium raw material, a solution in which ammonium metavanadate is previously dissolved in an alkaline solution (hereinafter also referred to as “premixed solution”) is used. In other words, in preparing the raw material paste, instead of mixing all the raw materials at once, for the vanadium raw material only, the above premixed solution is prepared separately, and then the premixed solution is mixed with other components. .
More specifically, this process is performed in the order of the following (1) and (2).
(1) A premixed solution in which ammonium metavanadate is dissolved in an alkaline solution is prepared.
(2) A premixed solution and at least a titanium oxide, a tungsten raw material, and an inorganic binder are mixed.

In the present invention, ammonium metavanadate (NH ₄ VO ₃ ) is preferably used because it is easy to handle. Then, V ₂ O ₅ is generated by a decomposition reaction such as NH ₄ VO ₃ → V ₂ O ₅ + 2NH ₃ + H ₂ O and plays a role as a catalyst in the SCR system.

The concentration of ammonium metavanadate in the premixed solution is preferably 1 to 25% by mass, more preferably 5 to 15% by mass.

The alkaline solution used for the preparation of the premixed solution is preferably at least one selected from a diethanolamine solution, a monoethanolamine solution, a diethylaminoethanol solution, and aqueous ammonia, and among them, a diethanolamine solution is preferable. This is because these solutions do not contain alkali metals or alkaline earth metals that, when added to titanium-vanadium, degrade the NOx purification performance. Moreover, since the boiling point is 500 ° C. or less, it is removed by volatilization when the honeycomb unit is fired. Therefore, when the honeycomb structure is formed, the NOx purification performance is not deteriorated.

The concentration of the alkaline component in the alkaline solution is preferably 0.1 to 2 mol / L, and the pH is preferably 7 to 11.

In the case of using a diethanolamine solution as the alkaline solution, it is preferable to heat to 80 ° C. or higher when ammonium metavanadate is dissolved in the diethanolamine solution. This is because by heating to 80 ° C. or higher, ammonium metavanadate can be sufficiently dissolved, V can be uniformly dispersed, and no bulk body can be present. The heating temperature is more preferably 80 to 95 ° C.

As the titanium oxide, it is preferable to use anatase type titanium dioxide having a high specific surface area.

Examples of the tungsten raw material include ammonium metatungstate, tungsten oxide, and ammonium paratungstate. Among them, ammonium metatungstate is preferable.

In the raw material paste, the molar ratio (W / V) of vanadium atoms in the vanadium raw material and tungsten atoms in the tungsten raw material is preferably 0.8 to 1.2. This is because the initial NOx purification performance and thermal durability can be improved by setting the W / V addition amount molar ratio in the honeycomb structure to 0.8 to 1.2 as described above. The molar ratio is more preferably 0.9 to 1.1, still more preferably 0.95 to 1.05.
The molar ratio of titanium atoms to the total of tungsten atoms and vanadium atoms ((W + V) / Ti) is preferably 0.02 to 0.2, and more preferably 0.05 to 0.1.

In order to improve the strength, it is preferable to add one or more selected from the group consisting of inorganic fibers, scale-like substances, tetrapot-like substances and three-dimensional needle-like substances into the raw material paste.

The inorganic fiber is at least one selected from the group consisting of alumina, silica, silicon carbide, silica alumina, glass, wollastonite, potassium titanate and aluminum borate, and the scaly substance is glass, muscovite. One or more selected from the group consisting of alumina and silica, the tetrapot-like substance is zinc oxide, and the three-dimensional needle-like substance is alumina, silica, silicon carbide, silica alumina, glass, wallast It is preferably at least one selected from the group consisting of knight, potassium titanate, aluminum borate and boehmite.
This is because all of them have high heat resistance, and even when used as a catalyst carrier in an SCR system, there is no melting damage and the effect as a reinforcing material can be maintained.

The aspect ratio of the inorganic fiber is preferably 2 to 1000, more preferably 5 to 800, and still more preferably 10 to 500. When the aspect ratio of the inorganic fibers contained in the honeycomb unit 11 is less than 2, the effect of improving the strength of the honeycomb unit 11 is reduced. On the other hand, when the aspect ratio of the inorganic fibers contained in the honeycomb unit 11 exceeds 1000, the mold is clogged when the honeycomb unit 11 is extruded, or the inorganic fibers break and the strength of the honeycomb unit 11 is increased. The effect of improving the quality is reduced.

The scaly substance means a flat substance, preferably having a thickness of 0.2 to 5.0 μm, preferably having a maximum length of 10 to 160 μm, and having a ratio of the maximum length to the thickness. It is preferably 3 to 250.

The tetrapot-like substance means a substance in which the needle-like portion extends three-dimensionally, the needle-like portion preferably has an average needle-like length of 5 to 30 μm, and the needle-like portion has an average diameter of 0.00. It is preferably 5 to 5.0 μm.

The three-dimensional acicular substance means a substance in which the acicular parts are bonded by an inorganic compound such as glass near the center of each acicular part, and the average acicular length of the acicular parts is 5 to 30 μm. The average diameter of the needle-like part is preferably 0.5 to 5.0 μm.

The three-dimensional acicular substance may have a plurality of acicular portions that are three-dimensionally connected, and preferably has a needle-like diameter of 0.1 to 5.0 μm and a length of 0.3 to It is preferably 30.0 μm, and the ratio of length to diameter is preferably 1.4 to 50.0.

The content of the inorganic fiber, scale-like substance, tetrapot-like substance and three-dimensional needle-like substance is preferably 3 to 50% by mass in the honeycomb unit 11, more preferably 3 to 30% by mass. More preferred is mass%. When the content of the inorganic fiber, the scale-like substance, the tetrapot-like substance, and the three-dimensional needle-like substance in the honeycomb structure is less than 3% by mass, the effect of improving the strength of the honeycomb structure becomes small. On the other hand, when the content of inorganic fibers, scale-like substances, tetrapot-like substances and three-dimensional needle-like substances in the honeycomb structure exceeds 50% by mass, TiO ₂ / V ₂ O ₅ / WO _{3 in the} honeycomb structure is obtained. The catalyst content decreases, and the NOx purification performance decreases.

The inorganic binder is not particularly limited, but from the viewpoint of maintaining the strength as a honeycomb structure, a solid content contained in alumina sol, silica sol, titania sol, water glass, sepiolite, attapulgite, bentonite, boehmite and the like is preferable. 2 or more may be used in combination.

The content of the inorganic binder is preferably 5 to 30% by mass in the honeycomb unit 11 and more preferably 10 to 20% by mass. When the content of the inorganic binder in the honeycomb unit 11 is less than 5% by mass, the strength of the honeycomb structure is lowered. On the other hand, when the content of the inorganic binder in the honeycomb structure exceeds 30% by mass, it becomes difficult to extrude the honeycomb formed body.

In addition, an organic binder, a dispersion medium, a molding aid and the like may be appropriately added to the raw material paste as necessary.

The organic binder is not particularly limited, and examples thereof include methyl cellulose, carboxymethyl cellulose, hydroxyethyl cellulose, polyethylene glycol, phenol resin, and epoxy resin, and two or more kinds may be used in combination. Note that the amount of the organic binder added is from 1 to the total mass of titanium oxide, vanadium oxide, tungsten oxide, inorganic binder, inorganic fiber, scaly substance, tetrapot-like substance, and three-dimensional acicular substance. 10% is preferable.

The dispersion medium is not particularly limited, and examples thereof include water, organic solvents such as benzene, alcohols such as methanol, and the like.

The molding aid is not particularly limited, and examples thereof include ethylene glycol, dextrin, fatty acid, fatty acid soap, polyalcohol and the like, and two or more kinds may be used in combination.

When preparing the raw material paste, it is preferable to mix and knead, and it may be mixed using a mixer, an attritor or the like, or may be kneaded using a kneader or the like.

[Molding process]
In this step, extrusion molding is performed using the raw material paste obtained in the mixing step, and a cylindrical honeycomb formed body in which a plurality of through holes are arranged in parallel in the longitudinal direction with a partition wall therebetween is produced.

After producing the honeycomb formed body, the honeycomb formed body is dried using a dryer such as a microwave dryer, a hot air dryer, a dielectric dryer, a vacuum dryer, a vacuum dryer, or a freeze dryer.

[Baking process]
In the firing step, the honeycomb formed body obtained as described above is fired. The firing temperature is preferably 450 to 750 ° C., and more preferably 550 to 650 ° C.
The firing time may be set as appropriate until the firing is completed, and may be 1 to 5 hours, for example.

[Other processes]
Other steps such as a step of forming an outer peripheral coat layer can be provided after the above baking step.
In the step of forming the outer peripheral coat layer, the outer peripheral coat layer paste is applied to the outer peripheral surface excluding both end surfaces of the columnar honeycomb unit 11.

Although it does not specifically limit as a paste for outer periphery coating layers, The mixture of an inorganic binder and an inorganic particle, the mixture of an inorganic binder and an inorganic fiber, the mixture of an inorganic binder, an inorganic particle, and an inorganic fiber etc. are mentioned.

The inorganic binder contained in the outer periphery coating layer paste is not particularly limited, but is added as silica sol, alumina sol or the like, and two or more kinds may be used in combination. Among these, it is preferable to add as silica sol.

The inorganic particles contained in the outer periphery coating layer paste are not particularly limited, but may include carbide particles such as silicon carbide particles, nitride particles such as silicon nitride particles and boron nitride particles, and the like. Good. Of these, silicon carbide particles are preferred because of their excellent thermal conductivity.

The inorganic fiber contained in the outer periphery coat layer paste is not particularly limited, and examples thereof include silica alumina fiber, mullite fiber, alumina fiber, silica fiber and the like, and two or more kinds may be used in combination. Among these, alumina fibers are preferable.

The outer periphery coating layer paste may further contain an organic binder.

Although it does not specifically limit as an organic binder contained in the paste for outer periphery coating layers, Polyvinyl alcohol, methylcellulose, ethylcellulose, carboxymethylcellulose, etc. are mentioned, You may use 2 or more types together.

The outer peripheral coat layer paste may further contain balloons, pore formers, and the like, which are fine hollow spheres of oxide ceramics.

The balloon contained in the outer periphery coating layer paste is not particularly limited, and examples thereof include alumina balloons, glass micro balloons, shirasu balloons, fly ash balloons, mullite balloons, and the like, and two or more kinds may be used in combination. Among these, an alumina balloon is preferable.

Although it does not specifically limit as a pore making material contained in the paste for outer periphery coating layers, A spherical acrylic particle, a graphite, etc. are mentioned, You may use 2 or more types together.

Next, the honeycomb unit 11 to which the outer peripheral coat layer paste has been applied is dried and solidified to produce a columnar honeycomb structure 10. At this time, when the outer peripheral coat layer paste contains an organic binder, it is preferably degreased. The degreasing conditions can be appropriately selected depending on the type and amount of the organic substance, but it is preferably 20 minutes at 700 ° C.

The honeycomb unit 11 manufactured as described above preferably has a porosity of 30 to 60%. If the porosity of the honeycomb unit 11 is less than 30%, the exhaust gas hardly enters the partition walls 11b of the honeycomb unit 11, and the TiO ₂ / V ₂ O ₅ / WO ₃ catalyst is effectively used for NOx purification. It will not be done. On the other hand, when the porosity of the honeycomb unit 11 exceeds 60%, the strength of the honeycomb unit 11 becomes insufficient.

Note that the porosity of the honeycomb unit 11 can be measured using a mercury intrusion method.

The honeycomb unit 11 preferably has an opening ratio of a cross section perpendicular to the longitudinal direction of 50 to 75%. When the opening ratio of the cross section perpendicular to the longitudinal direction of the honeycomb unit 11 is less than 50%, the TiO ₂ / V ₂ O ₅ / WO ₃ catalyst is not effectively used for NOx purification. On the other hand, if the opening ratio of the cross section perpendicular to the longitudinal direction of the honeycomb unit 11 exceeds 75%, the strength of the honeycomb unit 11 becomes insufficient.

In the honeycomb unit 11, the density of the through holes 11a having a cross section perpendicular to the longitudinal direction is preferably 31 to 155 / cm ² . When the density of the through-holes 11a having a cross section perpendicular to the longitudinal direction of the honeycomb unit 11 is less than 31 / cm ² , the TiO ₂ / V ₂ O ₅ / WO ₃ catalyst and the exhaust gas are less likely to come into contact with each other, thereby purifying NOx. Performance decreases. On the other hand, when the density of the through holes 11a having a cross section perpendicular to the longitudinal direction of the honeycomb unit 11 exceeds 155 / cm ² , the pressure loss of the honeycomb structure 10 increases.

The thickness of the partition wall 11b of the honeycomb unit 11 is preferably 0.1 to 0.4 mm, and more preferably 0.1 to 0.3 mm. When the thickness of the partition wall 11b of the honeycomb unit 11 is less than 0.1 mm, the strength of the honeycomb unit 11 decreases. On the other hand, when the thickness of the partition wall 11b of the honeycomb unit 11 exceeds 0.4 mm, the exhaust gas hardly enters the partition wall 11b of the honeycomb unit 11, and the TiO ₂ / V ₂ O ₅ / WO ₃ catalyst is NOx. It will not be used effectively for purification.

The outer peripheral coat layer 12 preferably has a thickness of 0.1 to 2.0 mm. When the thickness of the outer peripheral coat layer 12 is less than 0.1 mm, the effect of improving the strength of the honeycomb structure 10 becomes insufficient. On the other hand, when the thickness of the outer peripheral coat layer 12 exceeds 2.0 mm, the content of the TiO ₂ / V ₂ O ₅ / WO ₃ catalyst per unit volume of the honeycomb structure 10 is reduced, and the NOx purification performance is improved. descend.

The shape of the honeycomb structure 10 is not limited to a cylindrical shape, and examples thereof include a prismatic shape, an elliptical cylindrical shape, a long cylindrical shape, and a rounded chamfered prismatic shape (for example, a rounded chamfered triangular prism shape).

The shape of the through hole 11a is not limited to a quadrangular prism shape, but may be a triangular prism shape, a hexagonal prism shape, or the like.

FIG. 3 shows an example of an exhaust gas purifying apparatus having the honeycomb structure of the present invention. The exhaust gas purification apparatus 100 can be manufactured by canning the metal container (shell) 30 in a state where the holding sealing material 20 is disposed on the outer peripheral portion of the honeycomb structure 10. Further, the exhaust gas purification apparatus 100 includes an injection nozzle that injects ammonia or a compound that decomposes to generate ammonia into a pipe (not shown) on the upstream side of the honeycomb structure 10 with respect to the direction in which the exhaust gas flows. Injecting means (not shown) is provided. As a result, ammonia is added to the exhaust gas flowing through the pipe, so that the NOx contained in the exhaust gas is reduced by the TiO ₂ / V ₂ O ₅ / WO ₃ catalyst contained in the honeycomb unit 11.

The compound that decomposes to generate ammonia is not particularly limited as long as it can be heated by exhaust gas in the pipe and generate ammonia, but urea water is preferable because of excellent storage stability.

The urea water is heated by the exhaust gas in the pipe and hydrolyzes to generate ammonia. *

FIG. 4 shows another example of the honeycomb structure of the present invention. In the honeycomb structure 10 ′, a plurality of honeycomb units 11 ′ (see FIG. 5) in which a plurality of through holes 11 a are arranged in parallel in the longitudinal direction with a partition wall 11 b therebetween are bonded via an adhesive layer 13. Other than this, the configuration is the same as that of the honeycomb structure 10.

The honeycomb unit 11 ′ preferably has a cross-sectional area of 10 to 200 cm ² in a cross section perpendicular to the longitudinal direction. When the cross-sectional area of the cross section perpendicular to the longitudinal direction of the honeycomb unit 11 ′ is less than 10 cm ² , the pressure loss of the honeycomb structure 10 ′ increases. On the other hand, when the cross-sectional area of the cross section perpendicular to the longitudinal direction of the honeycomb unit 11 ′ exceeds 200 cm ² , the strength against the thermal stress generated in the honeycomb unit 11 ′ becomes insufficient.

Note that the honeycomb unit 11 ′ has the same configuration as the honeycomb unit 11 except for the cross-sectional area of the cross section perpendicular to the longitudinal direction.

The adhesive layer 13 preferably has a thickness of 0.5 to 2.0 mm. When the thickness of the adhesive layer 13 is less than 0.5 mm, the adhesive strength of the honeycomb unit 11 ′ becomes insufficient. On the other hand, when the thickness of the adhesive layer 13 exceeds 2.0 mm, the pressure loss of the honeycomb structure 10 ′ increases.

Next, an example of a method for manufacturing the honeycomb structure 10 ′ will be described. First, in the same manner as the honeycomb structure 10, a quadrangular columnar honeycomb unit 11 ′ is manufactured. Next, an adhesive layer paste is applied to the outer peripheral surface excluding both end faces of the honeycomb unit 11 ′, the honeycomb units 11 ′ are sequentially bonded, and dried and solidified to produce an aggregate of the honeycomb units 11 ′.

The adhesive layer paste is not particularly limited, and examples thereof include a mixture of inorganic binder and inorganic particles, a mixture of inorganic binder and inorganic fibers, a mixture of inorganic binder, inorganic particles, and inorganic fibers.

The inorganic binder contained in the adhesive layer paste is not particularly limited, but is added as silica sol, alumina sol or the like, and two or more kinds may be used in combination. Among these, it is preferable to add as silica sol.

The inorganic particles contained in the adhesive layer paste are not particularly limited, and examples thereof include carbide particles such as silicon carbide particles, nitride particles such as silicon nitride particles and boron nitride particles, and the like. . Of these, silicon carbide particles are preferred because of their excellent thermal conductivity.

The inorganic fiber contained in the adhesive layer paste is not particularly limited, and examples thereof include silica alumina fiber, mullite fiber, alumina fiber, silica fiber and the like, and two or more kinds may be used in combination. Among these, alumina fibers are preferable.

Further, the adhesive layer paste may contain an organic binder.

The organic binder contained in the adhesive layer paste is not particularly limited, and examples thereof include polyvinyl alcohol, methyl cellulose, ethyl cellulose, carboxymethyl cellulose and the like, and two or more kinds may be used in combination.

The adhesive layer paste may further contain balloons that are fine hollow spheres of oxide ceramics, a pore-forming agent, and the like.

The balloon contained in the adhesive layer paste is not particularly limited, and examples thereof include an alumina balloon, a glass microballoon, a shirasu balloon, a fly ash balloon, and a mullite balloon, and two or more kinds may be used in combination. Among these, an alumina balloon is preferable.

The pore former contained in the adhesive layer paste is not particularly limited, and examples thereof include spherical acrylic particles and graphite, and two or more kinds may be used in combination.

Next, after the aggregate of the honeycomb units 11 ′ is cut into a cylindrical shape, the aggregate of the cylindrical honeycomb units 11 ′ is manufactured by polishing as necessary.

Instead of cutting the aggregate of the honeycomb units 11 ′ into a columnar shape, the honeycomb unit 11 ′ whose cross section perpendicular to the longitudinal direction is formed into a predetermined shape is bonded to the columnar honeycomb unit 11 ′. You may produce the aggregate | assembly of. At this time, the shape of the cross section perpendicular to the longitudinal direction of the honeycomb unit 11 ′ is preferably a sector shape with a central angle of 90 °.

Next, the outer peripheral coat layer paste is applied to the outer peripheral surface excluding both end surfaces of the aggregate of the cylindrical honeycomb unit 11 ′.

The outer periphery coat layer paste may be the same as or different from the adhesive layer paste.

Next, a columnar honeycomb structure 10 ′ is manufactured by drying and solidifying the aggregate of columnar honeycomb units 11 ′ coated with the outer periphery coating layer paste. At this time, when an organic binder is contained in the adhesive layer paste and / or the outer peripheral coat layer paste, it is preferable to degrease. The degreasing conditions can be appropriately selected depending on the type and amount of the organic substance, but it is preferably 20 minutes at 700 ° C.

Note that the outer peripheral coat layer 12 may not be formed in the

honeycomb structures

10 and 10 ′.

Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited to the following examples.

[Example 1]
210 parts by mass of ammonium metavanadate was added to an 8% diethanolamine aqueous solution prepared with 150 parts by mass of diethanolamine and 1750 parts by mass of ion-exchanged water, and heated to 100 ° C. to dissolve to obtain a premixed solution. Next, 670 parts by mass of ammonium metatungstate (50% solution) as a tungsten raw material and 80 parts by mass of Rhedol O30V as a molding lubricant were added to prepare a solution raw material.
Next, 3910 parts by mass of titanium oxide, 300 parts by mass of alumina binder, 170 parts by mass of wollastonite fiber, and 300 parts by mass of methylcellulose as a molding aid were mixed, and then the above raw materials of the solution were added and mixed and kneaded to obtain a raw material paste 1 Prepared. The molar ratio (W / V) of vanadium atoms in the vanadium raw material and tungsten atoms in the tungsten raw material was 0.8.

Next, the raw material paste 1 was extrusion-molded using an extruder to produce a regular quadrangular prism-shaped honeycomb formed body. Then, after the honeycomb formed body was dried at a drying pressure of 86.7 kPa for 6 minutes using a batch microwave dryer, the honeycomb formed body was put into a muffle furnace, and the temperature was increased to 550 at a heating rate of 1 ° C./min. The temperature was raised to 0 ° C., and the temperature was maintained for 3 hours and fired to produce a honeycomb fired body.
The honeycomb unit 11 ′ has a regular quadrangular prism shape with a side of 35 mm and a length of 150 mm, the density of the through holes 11 a is 62 / cm ² , and the thickness of the partition walls 11 b is 0.28 mm.

Next, 767 parts of alumina fiber having an average fiber diameter of 0.5 μm and an average fiber length of 15 μm, 2500 parts of silica glass, 17 parts of carboxymethylcellulose, 600 parts of silica sol having a solid content of 30% by mass, and 167 parts of polyvinyl alcohol Part, 167 parts of surfactant and 17 parts of alumina balloon were mixed and kneaded to prepare an adhesive layer paste.

The adhesive layer paste was applied to the outer peripheral surface excluding both ends of the honeycomb unit 11 ′ so that the thickness of the adhesive layer 13 was 2.0 mm, and 16 honeycomb units 11 ′ were adhered to each other at 150 ° C. Solidified for a minute. Next, a diamond cutter was used to cut into a cylindrical shape so that the cross section perpendicular to the longitudinal direction was substantially point-symmetric, thereby producing an aggregate of honeycomb units 11 ′.

Furthermore, after applying the adhesive layer paste to the outer peripheral surface excluding both ends of the aggregate of the honeycomb unit 11 ′ so that the outer peripheral coat layer 12 has a thickness of 1.0 mm, the microwave dryer and the hot air dryer are applied. Then, the adhesive layer paste was dried and solidified at 150 ° C. for 10 minutes and degreased at 400 ° C. for 2 hours to prepare a cylindrical honeycomb structure 10 ′ having a diameter of 160 mm and a length of 150 mm.

[Example 2]
In Example 1, a honeycomb structure was manufactured in the same manner as in Example 1 except that the premixed solution was prepared by adding 170 parts by mass of ammonium metavanadate.

[Comparative Example 1]
A honeycomb structure was manufactured in the same manner as in Example 1 except that 170 parts by mass of ammonium metavanadate was used as it was instead of the premixed solution as the vanadium raw material in the mixing and kneading of each component of Example 1.

[Effective V amount]
The honeycomb units produced in Examples 1 and 2 and Comparative Example 1 were pulverized into powder and H ₂ -TPR measurement was performed according to the following procedure. The effective V amount was half of the hydrogen consumption as the measurement result. The results are shown in Table 1.
(1) As a pretreatment, He was introduced into the furnace at a flow rate of 50 cm ³ / min, the temperature was raised from 100 ° C. to 500 ° C. at a heating rate of 10 ° C./min, and the temperature was maintained for 1 hour. Next, the temperature was lowered to 100 ° C.
(2) Next, a mixed gas of H ₂ : 5.04%, Ar; 94.96% was introduced into the furnace at a flow rate of 30 cm ³ / min. The temperature was raised to 0 ° C. and the temperature was maintained for 20 minutes. Next, He was introduced into the furnace at a flow rate of 50 cm ³ / min and the temperature was lowered to 100 ° C.

[NOx purification performance]
From the honeycomb units produced in Examples 1 and 2 and Comparative Example 1, a square prism-shaped test piece having a side of 30 mm and a length of 40 mm was cut out using a diamond cutter. NOx flowing out from the sample using a catalyst evaluation device (SIGU-2000 / MEXA-6000FT, manufactured by Horiba, Ltd.) while flowing a simulated gas at a space velocity (SV) of 80000 / hr through these test pieces. Measure the outflow amount of NOx, and the formula (NOx inflow amount-NOx outflow amount) / (NOx inflow amount) x 100
The NOx purification rate [%] expressed by The calculation results are shown in Table 1. The constituent components of the simulated gas are 350 ppm of nitrogen monoxide, 350 ppm of ammonia, 14% of oxygen, 10% of water, and nitrogen (balance).

[Thermal durability]
From the honeycomb units produced in Examples 1 and 2 and Comparative Example 1, a square prism-shaped test piece having a side of 30 mm and a length of 40 mm was cut out using a diamond cutter. These test pieces were heat-treated at 550 ° C. for 100 hours using a catalyst endurance device (manufactured by Horiba, Ltd., SIGU-1000), and performance evaluation was performed under the above NOx purification rate measurement conditions.
The simulated gas conditions during the heat treatment are 20% oxygen, 10% water, nitrogen, and a flow rate of 1 L / min.

As shown in Table 1, the honeycomb structures of Examples 1 and 2 had a larger amount of effective V than the honeycomb structure of Comparative Example 1, and obtained results that could satisfy both NOx purification performance before and after thermal durability. I understand. In particular, Example 2 and Comparative Example 1 show that the amount of effective V is larger in Example 2 although the amount of ammonium metavanadate used as the V raw material is exactly the same. Also from this, the effective V amount can be increased by the manufacturing method of the present invention, and the NOx purification performance can be improved.

DESCRIPTION OF SYMBOLS 10, 10 'Honeycomb structure 11, 11' Honeycomb unit 11a Through- hole 11b Partition 12 Outer periphery coating layer 13 Adhesive layer 20 Holding sealing material 30 Metal container 100 Exhaust gas purification apparatus

Claims

A honeycomb unit having a shape in which a plurality of cells including at least a titanium oxide, a vanadium oxide, a tungsten oxide, and an inorganic binder and extending from one end surface to the other end surface along a longitudinal direction are partitioned by cell walls. A method for manufacturing a provided honeycomb structure,
Mixing step of mixing titanium oxide, vanadium raw material, tungsten raw material and inorganic binder;
Forming the mixed material into a honeycomb shape and obtaining a honeycomb formed body; and
A firing step of firing the honeycomb formed body,
In the mixing step, the vanadium raw material is a solution in which ammonium metavanadate is previously dissolved in an alkaline solution.
The method for manufacturing a honeycomb structure according to claim 1, wherein the alkaline solution is at least one selected from a diethanolamine solution, a monoethanolamine solution, a diethylaminoethanol solution, and aqueous ammonia.
The method for manufacturing a honeycomb structure according to claim 2, wherein the alkaline solution is a diethanolamine solution, and the ammonium metavanadate is heated to 80 ° C or higher when dissolved in the diethanolamine solution.
4. The molar ratio (W / V) of vanadium atoms in the vanadium raw material and tungsten atoms in the tungsten raw material is 0.8 to 1.2. The manufacturing method of the honeycomb structure as described.
The inorganic binder is a solid content contained in one or more selected from the group consisting of alumina sol, silica sol, titania sol, water glass, sepiolite, attapulgite, bentonite and boehmite. 2. A method for manufacturing a honeycomb structured body according to item 1.
6. The mixing process according to claim 1, wherein in the mixing step, at least one selected from the group consisting of inorganic fibers, scale-like substances, tetrapot-like substances and three-dimensional needle-like substances is further mixed. A method for manufacturing a honeycomb structured body according to claim 1.
The inorganic fiber is at least one selected from the group consisting of alumina, silica, silicon carbide, silica alumina, glass, wollastonite, potassium titanate and aluminum borate,
The scaly substance is at least one selected from the group consisting of glass, muscovite, alumina and silica,
The tetrapot-like substance is zinc oxide,
The three-dimensional acicular material is at least one selected from the group consisting of alumina, silica, silicon carbide, silica alumina, glass, wollastonite, potassium titanate, aluminum borate and boehmite. Item 7. A method for manufacturing a honeycomb structured body according to Item 6.
A honeycomb structure obtained by the method for manufacturing a honeycomb structure according to any one of claims 1 to 7,
Hydrogen consumption by vanadium per 1 g of honeycomb structure by the hydrogen-temperature reduction method (H 2 -TPR) is 0.6 mmol or more, and the molar ratio of W / V addition amount is 0.8 to 1.2. A honeycomb structure characterized by the above.