WO2014073067A1

WO2014073067A1 - Honeycomb structure

Info

Publication number: WO2014073067A1
Application number: PCT/JP2012/078945
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: JPWO2014073067A1; CN104797333A

Abstract

Provided is a honeycomb structure which uses a TiO₂/V₂O₅/WO₃ catalyst, and which has excellent NO_X conversion efficiency and thermal durability. This honeycomb structure 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, and is characterized in that the hydrogen consumption from vanadium reduction in temperature-programmed reduction with hydrogen (H₂-TPR) is 0.6mmol or more per 1g of the honeycomb structure, and the molar ratio (W/V) of tungsten atoms to vanadium atoms is 0.8-1.2.

Description

Honeycomb structure

The present invention relates to a honeycomb structure which is a denitration catalyst for removing nitrogen oxides (NOx) in exhaust gas.

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 object of the present invention is to provide an excellent honeycomb structure.

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 honeycomb structure including a honeycomb unit,
The hydrogen consumption derived from vanadium reduction in the hydrogen-temperature reduction method (H ₂ -TPR) is 0.6 mmol or more per 1 g of the honeycomb structure, and the molar ratio (W / V) of tungsten atom to vanadium atom is 0. A honeycomb structure characterized by having 8 to 1.2.

(2) In the above (1), 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. The honeycomb structure described.

(3) The (1) or (2), wherein the honeycomb unit further includes one or more selected from the group consisting of inorganic fibers, scale-like substances, tetrapot-like substances, and three-dimensional needle-like substances. The honeycomb structure according to 1.

(4) 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. The honeycomb structure according to (3).

(5) A manufacturing method for obtaining the honeycomb structure according to any one of (1) to (4),
Forming a material containing titanium oxide, vanadium raw material, tungsten raw material and inorganic binder into a honeycomb shape to obtain a honeycomb formed body; and
A firing step of firing the honeycomb formed body,
A method for manufacturing a honeycomb structured body, wherein, in the firing step, an oxygen concentration is set to 21% or more and a temperature is set to 450 to 650 ° C.

(6) A manufacturing method for obtaining the honeycomb structure according to any one of (1) to (4),
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.

According to the present invention, it is possible to provide a honeycomb structure using a TiO ₂ / V ₂ O ₅ / WO ₃ catalyst and having an excellent NOx purification rate and thermal durability.

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] Fig. 5 is a perspective view showing a honeycomb unit constituting the honeycomb structure of Fig. 4.

The honeycomb structure of the present invention includes at least titanium oxide, vanadium oxide, 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 are formed by cell walls. A honeycomb structure provided with a honeycomb unit having a partitioned shape, wherein a hydrogen consumption amount derived from vanadium reduction in a hydrogen-temperature programmed reduction method (H ₂ -TPR) is 0.6 mmol or more per 1 g of the honeycomb structure, The molar ratio (W / V) of tungsten atoms and vanadium atoms is 0.8 to 1.2.

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-derived 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. In other words, it is only necessary to uniformly disperse V so that the bulk body does not exist. However, the present inventor (1) reduces the unreacted V raw material if the oxygen concentration is high when firing the molded body. V can be uniformly dispersed, and (2) in the mixing step of mixing each raw material, a solution in which ammonium metavanadate is previously dissolved in an alkaline solution is used as the V raw material, and titanium oxide, tungsten raw material, etc. It was found that the abundance ratio of the V bulk body showing no activity can be reduced by mixing with A. Since V can be attached to the TiO2 raw material in a sufficiently dispersed state in the solution, the dispersion state of V is higher than when the TiO2 raw material and the V raw material are mixed with each other to prevent a bulk body from being formed. It can be done. That is, in the above (1), the oxygen concentration in the firing step is set to 21% or more and the temperature is set to 450 to 600 ° C. In the above (2), the V raw material is previously formed on TiO ₂ before firing. By forming a uniformly dispersed state, V can be uniformly dispersed even after firing in any case, and as a result, the NOx purification performance and thermal durability can be improved.

FIG. 2 shows an example of the honeycomb structure of the present invention. The honeycomb structure 10 includes a titanium oxide, a vanadium oxide, a tungsten oxide, and an inorganic binder, and a single honeycomb unit 11 in which a plurality of through holes 11a are arranged in parallel in the longitudinal direction with a partition wall 11b interposed therebetween. Have Further, the outer peripheral coat layer 12 is formed on the outer peripheral surface excluding both end surfaces of the honeycomb unit 11.

In the honeycomb unit 11, the molar ratio (W / V) of vanadium atoms and tungsten atoms is 0.8 to 1.2. As described above, the initial NOx purification performance and thermal durability can be improved by setting the W / V addition molar ratio to 0.8 to 1.2. 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 sum of tungsten atoms and vanadium atoms ((W + V) / Ti) is preferably 0.02 to 0.2, more preferably 0.05 to 0.1.

Although it does not specifically limit as an inorganic binder contained in the honeycomb unit 11, From a viewpoint of maintaining the intensity | strength as a honeycomb structure, solid content contained in alumina sol, silica sol, titania sol, water glass, sepiolite, attapulgite, bentonite, boehmite, etc. Are preferable, and two or more of them may be used in combination.

The content of the inorganic binder in the honeycomb unit 11 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 order to improve the strength of the honeycomb unit 11, 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 to the raw material paste.

The inorganic fiber contained in the honeycomb unit 11 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 One or more selected from the group consisting of glass, muscovite, alumina and silica, the tetrapot-like substance is zinc oxide, and the three-dimensional needle-like substance is alumina, silica, silicon carbide, silica alumina It is preferably one or more selected from the group consisting of glass, wollastonite, 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 honeycomb unit 11 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.

Next, an example of a method for manufacturing the honeycomb structure 10 will be described. The manufacturing method includes a mixing step of mixing titanium oxide, a vanadium raw material, a tungsten raw material, and an inorganic binder, a forming step of forming the mixed material into a honeycomb shape to obtain a honeycomb formed body, and firing the honeycomb formed body. A firing step, and other steps as necessary.
Each step will be described below. In the manufacture of the honeycomb structure of the present invention, as described above, a predetermined means is adopted in order to uniformly disperse V so that the bulk body does not exist. The means will be described later. To do.

The mixing step includes a titanium oxide, a vanadium raw material, a tungsten raw material, and an inorganic binder, and is selected from the group consisting of inorganic fibers, scaly substances, tetrapot-like substances, and three-dimensional acicular substances as necessary. One or more types are mixed and kneaded to prepare a raw material paste.

As the titanium oxide, anatase-type titanium dioxide having a high specific surface area is preferably used.

Examples of the vanadium raw material include ammonium metavanadate, sodium metavanadate, potassium metavanadate, vanadyl oxalate, vanadyl acetate, etc. Among them, ammonium metavanadate is preferable because it is easy to handle. V ₂ O ₅ is generated by a decomposition reaction such as ammonium metavanadate (NH ₄ VO ₃ ), NH ₄ VO ₃ → V ₂ O ₅ + 2NH ₃ + H ₂ O, and plays a role as a catalyst in the SCR system.

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 set to 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 inorganic binder contained in the raw material paste is the same as the inorganic binder contained in the honeycomb unit 11 described above.

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.

Next, 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.

Next, in the forming step, extrusion molding is performed using the raw material paste, thereby producing 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.
By firing the obtained honeycomb degreased body, a cylindrical honeycomb unit 11 is obtained (firing step). The firing temperature is preferably 450 to 750 ° C, and more preferably 550 to 650 ° C. When the firing temperature is less than 450 ° C., the sintering does not proceed and the strength of the honeycomb unit 11 is lowered. On the other hand, when the firing temperature exceeds 750 ° C., the sintering proceeds too much and the reaction sites of TiO ₂ / V ₂ O ₅ / WO ₃ decrease.

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.

In the present invention, as described above, in order to improve the effective V amount in the TiO ₂ / V ₂ O ₅ / WO ₃ catalyst, (1) the oxygen concentration is set to a high concentration when the molded body is fired, or ( 2) In the mixing step of mixing the respective raw materials, a means is used in which a solution in which ammonium metavanadate is previously dissolved in an alkaline solution is used as the V raw material and mixed with the titanium oxide and tungsten raw materials. The means will be described below.

In the means (1), the oxygen concentration is 21% or more and the temperature is 450 to 650 ° C. in the firing step. The oxygen concentration is preferably 30 to 50%, more preferably 35 to 45% from the viewpoint that V can be more uniformly dispersed and NOx purification performance and thermal durability can be improved. In order to fire the oxygen concentration within the above range in the firing step, a mixed gas containing oxygen gas having the above concentration may be introduced into the firing furnace at an arbitrary flow rate. Components other than oxygen in the mixed gas are not particularly limited, and examples thereof include nitrogen.
The firing temperature is 450 to 650 ° C. as described above, but is preferably 500 to 600 ° C. When the firing temperature is less than 450 ° C., the sintering does not proceed and the strength of the honeycomb unit 11 is lowered. On the other hand, if the firing temperature exceeds 650 ° C., the NOx purification performance of TiO ₂ / V ₂ O ₅ / WO ₃ decreases due to the progress of sintering. The rate of temperature rise until reaching the firing temperature is preferably 0.1 to 10 ° C./min.
The firing time is a time until the firing is completed, and may be set as appropriate. For example, the firing time may be 1 to 5 hours.

In the above means (2), the mixing step includes titanium oxide, vanadium raw material, tungsten raw material and inorganic binder, and if necessary, inorganic fiber, scale-like material, tetrapot-like material and three-dimensional acicular material A raw material paste is prepared by mixing one or more selected from the group consisting of:
And as a vanadium raw material, the solution (henceforth a "premixed solution") which melt | dissolved ammonium metavanadate in the alkaline solution previously is used. In other words, in preparing the raw material paste, instead of mixing all the raw material components at once, only the vanadium raw material is prepared separately from the above premixed solution, and then the premixed solution is mixed with other components. is there.
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.

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]
3910 parts by mass of titanium oxide, 210 parts by mass of ammonium metavanadate as a vanadium raw material, 670 parts by mass of ammonium metatungstate (50% solution) as a tungsten raw material, 300 parts by mass of an alumina binder, 170 parts by mass of wollastonite fiber, as a molding aid A raw material paste 1 was prepared by mixing and kneading 300 parts by mass of methyl cellulose, 80 parts by mass of sorbitan trioleate as a molding lubricant, 150 parts by mass of diethanolamine as a pH adjusting agent, and 1750 parts by mass of ion-exchanged water. 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 gas flow furnace, and the heating rate was 5 ° C./min. The temperature was raised to 550 ° C., and the temperature was maintained for 3 hours and fired to produce a honeycomb fired body. During firing, a mixed gas having an oxygen concentration of 21% and a nitrogen concentration of 79% was introduced at a gas flow rate of 20 L / min.
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]
A honeycomb structure 10 ′ was produced in the same manner as in Example 1 except that the oxygen concentration in the mixed gas introduced at the time of firing was 40% (nitrogen concentration: 60%).

[Example 3]
170 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 obtain a dissolved premixed solution. Next, 670 parts by mass of ammonium metatungstate (50% solution) as a tungsten raw material and 80 parts by mass of sorbitan trioleate as a molding lubricant were added to prepare a solution raw material.
Next, 3950 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 premixed solution was added and mixed and kneaded to prepare a raw material paste 2 Was prepared. The molar ratio (W / V) of vanadium atoms in the vanadium raw material and tungsten atoms in the tungsten raw material was 0.80.
Next, using the raw material paste 2, a honeycomb structure 10 ′ was produced in the same manner as in Example 1.

[Comparative Example 1]
A honeycomb structure 10 ′ was produced in the same manner as in Example 1 except that the oxygen concentration in the mixed gas introduced during firing was 0% (nitrogen concentration: 100%).

[Effective V amount]
The honeycomb units manufactured in Examples 1 to 3 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, and the temperature was increased from 100 ° C. to 700 ° C./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 prepared in Examples 1 to 3 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 prepared in Examples 1 to 3 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 21% oxygen, 10% water, nitrogen, and a flow rate of 1 L / min.

From Table 1, the honeycomb structures of Examples 1 to 3 have an effective V amount of 0.3 mmol / g or more (hydrogen consumption derived from vanadium reduction in the hydrogen-temperature reduction method (H ₂ -TPR) is honeycomb structure) 0.6 mol or more per gram), and the molar ratio (W / V) of tungsten atom and vanadium atom is both 0.8, and the NOx purification performance before and after thermal endurance was satisfactory. I understand. On the other hand, in Comparative Example 1, the effective V amount was less than 0.3 mmol / g, and the NOx purification performance was inferior.

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 honeycomb structure comprising:
The hydrogen consumption derived from vanadium reduction in the hydrogen-temperature reduction method (H 2 -TPR) is 0.6 mmol or more per 1 g of the honeycomb structure, and the molar ratio (W / V) of tungsten atom to vanadium atom is 0. A honeycomb structure characterized by having 8 to 1.2.
The honeycomb structure according to claim 1, wherein 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. body.
The honeycomb structure according to claim 1 or 2, wherein the honeycomb unit further includes at least one selected from the group consisting of inorganic fibers, scale-like substances, tetrapot-like substances, and three-dimensional needle-like substances. .
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 4. The honeycomb structure according to Item 3.
A manufacturing method for obtaining the honeycomb structure according to any one of claims 1 to 4,
Forming a material containing titanium oxide, vanadium raw material, tungsten raw material and inorganic binder into a honeycomb shape to obtain a honeycomb formed body; and
A firing step of firing the honeycomb formed body,
A method for manufacturing a honeycomb structured body, wherein, in the firing step, an oxygen concentration is set to 21% or more and a temperature is set to 450 to 650 ° C.
A manufacturing method for obtaining the honeycomb structure according to any one of claims 1 to 4,
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.