阅读说明：本技术 多孔质陶瓷结构体 (Porous ceramic structure ) 是由 泉有仁枝 日高宪一 于 2020-02-26 设计创作，主要内容包括：本发明提供一种压力损失低、且具有高催化能力的多孔质陶瓷结构体。多孔质陶瓷结构体具备：主成分为堇青石的多孔质结构体主体(即、蜂窝结构体)、以及固定于蜂窝结构体的锰(Mn)及钨(W)。由此,能够减少多孔质陶瓷结构体中的压力损失,并且,还能够降低多孔质陶瓷结构体中的NO燃烧温度。换言之,通过使多孔质陶瓷结构体为上述构成,能够提供压力损失低、且具有高催化能力的多孔质陶瓷结构体。(The present invention provides a porous ceramic structure having low pressure loss and high catalytic performance. A porous ceramic structure is provided with: a porous structure body (i.e., a honeycomb structure) mainly composed of cordierite, and manganese (Mn) and tungsten (W) fixed to the honeycomb structure. This can reduce the pressure loss in the porous ceramic structure and also can reduce the NO combustion temperature in the porous ceramic structure. In other words, by employing the above-described porous ceramic structure, a porous ceramic structure having a low pressure loss and a high catalytic ability can be provided.)

1. A porous ceramic structure comprising:

a porous structure body whose main component is cordierite; and

manganese and tungsten fixed to the structure body.

2. The porous ceramic structure according to claim 1,

the manganese and the tungsten are components of metal oxide particles fixed inside pores of the structure body,

the metal oxide particles are provided with:

a fixing portion located inside the structure body; and

and a protrusion part coupled to the fixing part and protruding into the air hole.

3. The porous ceramic structure according to claim 1 or 2,

the content of tungsten is as in WO₃Converted to 0.1 to 1.5 mass%.

4. The porous ceramic structure according to any one of claims 1 to 3,

content of manganese in terms of Mn₂O₃Is 0.5 to 3.0 mass% in terms of the content.

5. The porous ceramic structure according to any one of claims 2 to 4,

the metal oxide particles comprise MnWO₄The particles of (1).

6. The porous ceramic structure according to claim 5,

MnWO₄the content of (b) is 0.2 to 2.0 mass%.

7. The porous ceramic structure according to claim 5 or 6,

MnWO₄the aspect ratio of the particles of (a) is 5.5 or more.

8. The porous ceramic structure according to any one of claims 5 to 7,

MnWO₄the shape of the particles of (a) is granular or fibrous,

MnWO₄the particle of (a) comprises:

the fixed portion is present in a grain boundary of a cordierite crystal of the structure body; and

the protruding portion protrudes from the grain boundary into the gas hole.

Technical Field

The present invention relates to a porous ceramic structure.

Background

Jp 2017 a 186220 (document 1) proposes cerium oxide particles having a transition metal oxide containing iron and manganese on the surface or inside thereof. The ceria particles are assumed to be used as an oxidation catalyst in a dpf (diesel particulate filter) including doc (diesel oxidation catalyst) and csf (catalyzed Soot filter), for example.

Jp 2018-30105 a (document 2) and jp 2017-171543 a (document 3) propose techniques in which a sufficient amount of catalyst can be supported on a porous ceramic structure used for a DPF or the like so as to maintain catalytic activity. In this porous ceramic structure, part of the ceria particles enters the structure, and the other part is exposed to the pore surface of the structure. In the porous ceramic structure of document 2, iron oxide is provided at the part of the ceria particles exposed to the pore surface. In the porous ceramic structure of document 3, the catalyst fine particles of a platinum group element are supported on the sites of the ceria particles exposed to the pore surfaces.

Porous ceramic structures used in DPFs and the like are required to achieve both reduction in pressure loss and increase in catalytic performance.

Disclosure of Invention

The present invention is applicable to a porous ceramic structure, and an object thereof is to provide a porous ceramic structure having a low pressure loss and a high catalytic ability.

A porous ceramic structure according to a preferred embodiment of the present invention includes: a porous structure body whose main component is cordierite; and manganese and tungsten fixed to the structure body. Thus, a porous ceramic structure having a low pressure loss and a high catalytic ability can be provided.

Preferably, the manganese and the tungsten are components of metal oxide particles fixed inside pores of the structure body. The metal oxide particles are provided with: a fixing portion located inside the structure body; and a protruding portion connected to the fixing portion and protruding into the air hole.

Preferably, the content of tungsten in the porous ceramic structure is WO₃Converted to 0.1 to 1.5 mass%.

Preferably, the content of manganese in the porous ceramic structure is Mn₂O₃Is 0.5 to 3.0 mass% in terms of the content.

Preferably, the metal oxide particles comprise MnWO₄The particles of (1).

Preferably, MnWO in the porous ceramic structure₄The content of (b) is 0.2 to 2.0 mass%.

Preferably, MnWO₄The aspect ratio of the particles of (a) is 5.5 or more.

Preferably, MnWO₄The particles of (a) are granular or fibrous in shape. MnWO₄The particle of (a) comprises: the fixed portion is present in a grain boundary of a cordierite crystal of the structure body; and the protruding portion protruding from the grain boundary into the pore.

The above and other objects, features, aspects and advantages of the present invention will become apparent from the following detailed description of the present invention with reference to the accompanying drawings.

Drawings

Fig. 1 is a diagram showing a configuration of an exhaust gas purification system.

FIG. 2 is a view showing a porous ceramic structure.

FIG. 3 is a cross-sectional view showing a porous ceramic structure.

Fig. 4 is an enlarged view of a part of the partition wall.

Fig. 5 is an SEM image showing the surface of the pores of the honeycomb structure.

Fig. 6 is an SEM image showing the surface of the pores of the honeycomb structure.

Fig. 7 is a sectional view of a portion near the metal oxide particle.

FIG. 8 is a flowchart showing a method for producing a porous ceramic structure.

Fig. 9 is an SEM image showing the surface of the pores of the porous ceramic structure of the example in an enlarged manner.

Fig. 10 is an SEM image showing the surface of the porous ceramic structure of the comparative example.

Description of the symbols

1 … porous ceramic structure, 2 … metal oxide particles, 10 … honeycomb structure, 21 … fixed part, 22 … protruding part, and steps S11 to S13 ….

Detailed Description

Fig. 1 is a diagram showing the configuration of an exhaust gas purification system 8. The exhaust gas purification system 8 purifies exhaust gas discharged from the engine. The exhaust gas purification system 8 includes: a DPF (diesel Particulate Filter)81, an SCR (Selective catalytic reduction) catalytic converter 85, and a urea injector 86. The DPF81, the urea injector 86, and the SCR catalytic converter 85 are arranged in this order along the direction in which exhaust gas flows.

The DPF81 includes: DOC (diesel Oxidation catalyst)82 and CSF (catalyzed SooFinter) 83. The DOC82 includes: a honeycomb structure having a plurality of cells partitioned by partition walls, and a noble metal oxidation catalyst supported on the partition walls. The CSF83 includes: a honeycomb structure similar to the above, and a metal-based oxidation catalyst supported on the partition walls of the honeycomb structure. Hereinafter, the detailed structure of CSF83 will be explained. The urea injector 86 is disposed in the exhaust path between the DPF81 and the SCR catalytic converter 85. The SCR catalytic converter 85 includes: the same honeycomb structure as described above, and an SCR catalyst supported on the partition walls of the honeycomb structure.

Exhaust gas discharged from the engine flows into the DOC82 of the DPF 81. The exhaust gas contains Nitric Oxide (NO) and oxygen (O)₂) Nitrogen (N)₂) In DOC82, reactions of the following formulae 1 and 2 occur. In the reaction of formula 1, nitrogen dioxide (NO) is formed₂). Note that SOF (Soluble Organic Fraction) in the following formula 2 is contained in PM (particulate matter) in the exhaust gas.

2NO+O₂＝2NO₂(formula 1)

SOF+O₂＝CO、CO₂、H₂O (formula 2)

In the CSF83, carbon (soot) contained in the exhaust gas is trapped. In addition, in CSF83, the soot and NO take place₂By the following reactions (combustion reactions) of the following formulae 3, 4 and 5, respectively, with NO₂NO is generated.

C (soot) +2NO₂＝CO₂+2NO (formula 3)

C (soot) + NO₂CO + NO (formula 4)

C (soot) +1/2O₂+NO₂＝CO₂+ NO (formula 5)

The urea injector 86 mixes urea with the exhaust gas discharged from the CSF83, and includes ammonia (NH) generated by decomposition of urea₃) Flows into the SCR catalytic converter 85. In the SCR catalytic converter 85, the reactions of the following formulas 6, 7, and 8 occur, thereby purifying NOx contained in the exhaust gas.

4NO+4NH₃+O₂＝4N₂+6H₂O (formula 6)

NO+NO₂+2NH₃＝2N₂+3H₂O (formula 7)

6NO₂+8NH₃＝7N₂+12H₂O (formula 8)

The reaction of formula 7 is called Fast SCR reaction, and the reaction rate is faster than those of the reactions of formulae 6 and 8. According to equation 7, the amount of NO and the amount of NO flowing into the SCR catalytic converter 85 are required₂The mass of (1): 1 in order to efficiently perform the reaction in the SCR catalytic converter 85. On the other hand, in CSF83, much NO is consumed by the combustion of soot as in the above-described formulas 3, 4 and 5₂NO is produced.

Therefore, in the exhaust gas purification system 8 according to the present invention, a porous ceramic structure (described later) provided with an oxidation catalyst is provided as the CSF 83. The porous ceramic structure oxidizes a part of NO to generate NO₂I.e. conversion of NO to NO₂. This enables the amount of substance of NO and NO flowing into the SCR catalytic converter 85 to be controlled₂The amount of substance (c) is close to 1: 1, so that the reaction in the SCR catalytic converter 85 proceeds efficiently.

In the exhaust gas purification system 8, when a certain amount or more of soot is deposited on the CSF83, a combustion process (i.e., a regeneration process) of the soot is performed. In this case, also in CSF83, the reactions (combustion reactions) of formulae 3, 4 and 5 described above occur. If a large amount of carbon monoxide (CO) generated by this reaction flows into the SCR catalytic converter 85, the NOx purification efficiency in the SCR catalytic converter 85 may decrease. In the combustion treatment of soot, a large amount of Hydrocarbons (HC) contained in the fuel supplied to the CSF83 flow into the SCR catalytic converter 85 in the same manner.

In the exhaust gas purification system 8 according to the present invention, the porous ceramic structure provided with the oxidation catalyst is provided as CSF83, and thereby a part of CO is oxidized to generate carbon dioxide (CO)₂) Oxidizing a portion of HC to CO₂And H₂And O. This can suppress inflow of CO, HC, and the like into the SCR catalytic converter 85, and suppress a decrease in the NOx purification efficiency in the SCR catalytic converter 85.

Fig. 2 and 3 are simplified diagrams of the porous ceramic structure 1 used as the CSF83 (see fig. 1). The porous ceramic structure 1 is a tubular member long in one direction, and fig. 2 shows an end face on one side in the longitudinal direction of the porous ceramic structure 1. Fig. 3 is a sectional view showing the porous ceramic structure 1, and fig. 3 shows a part of a section of the porous ceramic structure 1 along the longitudinal direction.

The porous ceramic structure 1 includes: a honeycomb structure 10 as a porous structure body, and an oxidation catalyst fixed to the honeycomb structure 10. The oxidation catalyst is preferably metal oxide particles (i.e., fine particles mainly composed of a metal oxide) fixed to the honeycomb structure 10. The metal oxide particles contain manganese (Mn) and tungsten (W) as constituent elements. In the porous ceramic structure 1, in addition to the metal oxide particles described above, fine particles other than the metal oxide particles, and the like may be fixed to the honeycomb structure 10.

The honeycomb structure 10 includes a cylindrical outer wall 11 and partition walls 12. The cylindrical outer wall 11 is cylindrical and extends in the longitudinal direction. The cross-sectional shape of the cylindrical outer wall 11 perpendicular to the longitudinal direction may be, for example, circular or polygonal. The partition walls 12 are provided inside the cylindrical outer wall 11 to divide the inside into a plurality of compartments 13. The honeycomb structure 10 is a cell structure in which the inside is partitioned into a plurality of cells 13 by partition walls 12. The cylindrical outer wall 11 and the partition walls 12 are formed of a porous material. As described later, the exhaust gas passes through the pores of the partition walls 12. The thickness of the partition walls 12 is, for example, 50 μm (micrometer) or more, preferably 100 μm or more, and more preferably 150 μm or more, in order to improve the strength of the porous ceramic structure 1. The thickness of the partition wall 12 is, for example, 500 μm or less, preferably 450 μm or less, in order to reduce the pressure loss in the partition wall 12.

Each compartment 13 is a space extending in the longitudinal direction. The cross-sectional shape of the cells 13 perpendicular to the longitudinal direction may be, for example, a polygon (triangle, quadrangle, pentagon, hexagon, etc.), or a circle. The typical scheme is as follows: the plurality of compartments 13 have the same sectional shape. The plurality of compartments 13 may include compartments 13 having different cross-sectional shapes. The cell density is, for example, 8 cells/cm²(square centimeter) or more, preferably 15 compartments/cm²This improves the oxidation performance of the porous ceramic structure 1. The cell density is, for example, 95 cells/cm²Hereinafter, it is preferably 78 cells/cm²In order to reduce pressure loss.

The porous ceramic structure 1 used in the CSF83 has one end side of the honeycomb structure 10 in the longitudinal direction as an inlet and the other end side as an outlet, and the exhaust gas from the DOC82 flows therethrough. A sealing portion 14 is provided at an inlet-side end portion of the predetermined number of compartments 13, and a sealing portion 14 is provided at an outlet-side end portion of the remaining compartments 13. Therefore, the exhaust gas flowing into the honeycomb structure 10 moves from the cells 13 whose inlet side is not sealed to the cells 13 whose outlet side is not sealed through the partition walls 12 (see arrow a1 in fig. 3). At this time, the exhaust gas is oxidized by the metal oxide particles (i.e., oxidation catalyst) provided in the partition walls 12. The honeycomb structure 10 is preferably provided with one seal portion 14 at every 1 position along the arrangement direction of the cells 13 at each of the inlet-side end portion and the outlet-side end portion.

The main component of the honeycomb structure 10 is cordierite (2MgO · 2 Al)₂O₃·5SiO₂). The honeycomb structure 10 may be formed of only cordierite, or may include a material other than cordierite (for example, metal or ceramic other than cordierite). The cordierite content in the honeycomb structure 10 is, for example, 75 mass% or more, and preferably 80 mass% or more. This embodimentIn the formula, the honeycomb structural body 10 is substantially formed of only cordierite.

Fig. 4 is an enlarged view of a part of the partition walls 12 of the porous ceramic structure 1. The honeycomb structure 10 is provided with a plurality of pores (hereinafter also referred to as "pores 121"). The metal oxide particles 2 are fixed in the pores 121 (i.e., on the surfaces of the pores 121) of the honeycomb structure 10. Fine particles (hereinafter referred to as "additive fine particles") other than the metal oxide particles 2 may be fixed in the pores 121. The additive particles are, for example, particles containing cerium (Ce) and/or iron (Fe) elements. The additive particles being, for example, iron oxide (Fe)₂O₃) Particulate and/or ceria (CeO)₂) Particles. In fig. 4, the metal oxide particles 2 and the additive fine particles on the surface of the pores 121 are not distinguished from each other, but are schematically shown by oblique lines parallel to each other. The metal oxide particles 2 and the additive fine particles do not need to cover the entire surface of the pores 121.

The open porosity of the cell walls 12 of the honeycomb structure 10 is, for example, 25% or more, preferably 30% or more, and more preferably 35% or more, in order to reduce the pressure loss of the porous ceramic structure 1. From the viewpoint of ensuring the strength of the porous ceramic structure 1, the open porosity of the partition walls 12 is, for example, 70% or less, preferably 65% or less. For example, the open porosity can be measured by the archimedes method using pure water as a medium.

The average pore diameter of the partition walls 12 of the honeycomb structure 10 is, for example, 5 μm or more, preferably 8 μm or more. Similarly to the open porosity, the larger the average pore diameter of the partition walls 12, the lower the pressure loss of the porous ceramic structure 1. The average pore diameter of the honeycomb structure 10 is, for example, 40 μm or less, preferably 30 μm or less, and more preferably 25 μm or less in order to improve the oxidation performance of the porous ceramic structure 1. The average pore diameter can be measured by, for example, mercury intrusion method (according to JIS R1655). Depending on the design of the porous ceramic structure 1, the sealing part 14 may be omitted, and the metal oxide particles 2 may be held in a layer form on the surfaces of the cells 13.

Fig. 5 is an SEM (scanning electron microscope) image showing the surface of the fine pores 121 of the honeycomb structure 10. In the porous ceramic structure 1, a plurality of metal oxide particles 2 in a substantially granular or substantially fibrous form are fixed to the surfaces (i.e., the inner surfaces) of the pores 121 of the honeycomb structure 10. The metal oxide particles 2 are fixed to, for example, the grain boundaries of a large number of substantially rectangular parallelepiped cordierite crystals 3 forming the pores 121, and grow and protrude from the surfaces of the pores 121 toward the spaces in the pores 121.

The metal oxide particles 2 which are white at the substantially central portion of fig. 5 are manganese tungstate (MnWO)₄) The fine particles of (1). In the example shown in fig. 5, the metal oxide particles 2 have a substantially fibrous shape having anisotropy. MnWO₄The major axis of the fine particles (2) is preferably 50nm to 5000nm, more preferably 1000nm to 4000 nm. In addition, MnWO₄The short diameter of the fine particles (2) is preferably 50 to 1000nm, more preferably 150 to 500 nm. MnWO₄The aspect ratio of the fine particles of (3) is preferably 1.5 or more, more preferably 5.5 or more. The upper limit of the aspect ratio is not particularly limited, and is, for example, 100 or less, preferably 10 or less.

The major axis, minor axis, average particle diameter, and aspect ratio of the metal oxide particles 2 can be determined by the following methods. First, the porous ceramic structure 1 is processed by a cross-section polishing machine (CP) to expose a polished cross section, and the polished cross section is photographed by SEM at a predetermined magnification (for example, 10000 times). At this time, the field of view is set so that 5 or more metal oxide particles 2 are present in the field of view.

Next, focusing on 1 metal oxide particle 2 in the obtained SEM image, as shown in fig. 6, the lengths L1, L2, and L3 in the longitudinal direction of 3 points in the width direction of the metal oxide particle 2 were measured. The lengths L1, L2, and L3 were measured at arbitrary 3 points (for example, substantially the center and substantially both ends in the width direction) in the width direction of the metal oxide particle 2. Then, the arithmetic mean of the lengths L1, L2, and L3 is defined as the temporary major axis.

Further, widths L4, L5, and L6 in the width direction at any 3 points in the longitudinal direction of the metal oxide particle 2 were measured, and the arithmetic average of the widths L4, L5, and L6 was defined as a temporary short diameter. The measurement width of any 3 points of L4, L5, and L6 is measured, for example, at a point substantially at the center in the longitudinal direction of the metal oxide particle 2 and at 2 points 1/4 to 1/2 having the long diameter from the substantially center. These 2 points are located on the opposite side in the longitudinal direction with respect to the substantially central point in the longitudinal direction of the metal oxide particle 2.

In the same manner, the temporary major axis and the temporary minor axis are obtained for 5 metal oxide particles 2 in the SEM image, and the arithmetic mean of the 5 temporary major axes and the arithmetic mean of the 5 temporary minor axes are obtained as the major axis and the minor axis of the metal oxide particle 2, respectively. The arithmetic mean of the major axis and the minor axis is obtained as the average particle diameter of the metal oxide particles 2, and the value obtained by dividing the major axis by the minor axis is obtained as the aspect ratio of the metal oxide particles 2.

In the measurement of the major and minor diameters of the metal oxide particles 2, the longitudinal direction of the metal oxide particles 2 is determined as follows. First, in the SEM image, 2 parallel straight lines (hereinafter, referred to as "a pair of straight lines") sandwiching the metal oxide particles 2 are circumscribed with the metal oxide particles 2. Next, the orientation of the pair of straight lines is changed while maintaining the state in which the pair of straight lines are circumscribed with the metal oxide particles 2. Then, the direction in which the pair of straight lines extend with the interval between the pair of straight lines (i.e., the distance between the pair of straight lines in the direction perpendicular to the pair of straight lines) minimized is defined as the longitudinal direction. The direction perpendicular to the longitudinal direction is defined as the width direction.

MnWO in porous ceramic structure 1₄The content of (b) is preferably 0.2 mass% or more and 2.0 mass% or less. MnWO in porous ceramic structure 1₄The content of (b) is more preferably 0.4% by mass or more. The content is more preferably 1.8% by mass or less.

Fig. 7 is a sectional view of a portion near the metal oxide particle 2 on the surface of the pore 121. As shown in fig. 7, the metal oxide particles 2 partially protrude from the inside of the honeycomb structure 10 into the pores 121.

The metal oxide particles 2 include fixed portions 21 and protruding portions 22. The fixing portion 21 is located inside the honeycomb structure 10. The inside of the honeycomb structure 10 does not mean the inside of the pores 121 provided in the honeycomb structure 10 (i.e., the internal space of the pores 121), but means the inside of cordierite surrounding the pores 121. The fixed portion 21 is a bonded portion of the metal oxide particle 2 bonded to cordierite, which is a main material of the honeycomb structure 10, and fixed inside the cordierite. In other words, the fixed portion 21 is a portion of the metal oxide particle 2 that enters the cordierite from the surface of the pore 121 of the honeycomb structure 10 toward the side opposite to the pore 121 and enters the cordierite. In other words, the fixed portion 21 is a portion of the metal oxide particle 2 whose surface is coated with cordierite. Specifically, the fixed portions 21 are present at the grain boundaries of the cordierite crystals 3 of the honeycomb structure 10 and fixed to the grain boundaries.

The protruding portion 22 is a portion of the metal oxide particle 2 protruding from the surface of the pore 121 into the pore 121 in a granular or fibrous form. In other words, the protruding portion 22 is a granular or fibrous portion exposed from the surface of the cordierite. Specifically, the protruding portions 22 protrude from the grain boundaries of the cordierite crystals 3 into the pores 121 in a granular or fibrous form. The protruding portion 22 is connected to the fixing portion 21. The major axis, minor axis, average particle diameter, and aspect ratio of the metal oxide particles 2 are those of the projections 22 observed by SEM.

Among the large number of metal oxide particles 2 contained in the porous ceramic structure 1, for example, a part of the metal oxide particles 2 is fixed to the surface of the pores 121 in the pores 121 as described above, and the whole of the other metal oxide particles 2 is located in the honeycomb structure 10. Substantially all of the metal oxide particles 2 may be fixed to the surface of the pores 121 inside the pores 121.

In the porous ceramic structure 1, the honeycomb structure 10 is not subjected to a coating treatment (so-called wet coating) with γ -alumina or the like. Therefore, the coating film formed by the coating treatment is not formed on the surfaces of the pores 121, and the metal oxide particles 2 are not fixed to the honeycomb structure 10 through the coating film.

The large number of metal oxide particles 2 fixed to the honeycomb structure 10 may contain Mn and W as constituents, and does not necessarily need to contain MnWO₄May contain MnWO₄Other metal oxide particles different in fine particle of (A) in place of MnWO₄Or, in addition to comprising MnWO₄The fine particles of (2) further contain MnWO₄Different from the fine particles of the other metal oxide particles. In this case, the major axis, the minor axis, the average particle diameter, and the aspect ratio of the metal oxide particles 2 can be determined by the same method as described above.

The content of Mn in the porous ceramic structure 1 is represented by manganese oxide (Mn)₂O₃) The conversion is preferably 0.5 mass% or more and 3.0 mass% or less. Note that, according to Mn₂O₃The calculated Mn content means: assuming that Mn is contained in the porous ceramic structure 1 in its entirety₂O₃Mn when present in the form of₂O₃Is divided by the mass of the porous ceramic structure 1.

The content of W in the porous ceramic structure 1 is determined by tungsten oxide (WO)₃) The conversion is preferably 0.1 mass% or more and 1.5 mass% or less. The content of W in the porous ceramic structure 1 was set to WO₃More preferably 0.5% by mass or more. Further, the content ratio (i.e., according to WO)₃Calculated W content) according to WO₃The conversion is more preferably 1.4 mass% or less. To be noted, according to WO₃The content of W calculated by conversion means: it is assumed that all of the W components contained in the porous ceramic structure 1 are represented by WO₃In the form of (A) or (B)₃Is divided by the mass of the porous ceramic structure 1.

In the porous ceramic structure 1, the content of the metal oxide particles 2 in the porous ceramic structure 1 is, for example, 0.1 mass% or more in order to realize high catalytic performance by the metal oxide particles 2. The content of the metal oxide particles 2 in the porous ceramic structure 1 is, for example, 5.0 mass% or less so as to reduce the pressure loss of the porous ceramic structure 1.

In other words, the amount of the metal oxide particles 2 supported in the porous ceramic structure 1 is, for example, 3g/L (gram per liter) or more, preferably 5g/L or more, and more preferably 8g/L or more. The amount of the metal oxide particles 2 supported in the porous ceramic structure 1 is, for example, 50g/L or less, preferably 45g/L or less, and more preferably 40g/L or less. The supported amount (g/L) of the metal oxide particles 2 represents the amount (g) of the metal oxide particles 2 supported per unit volume (L) of the honeycomb structure 10.

Next, an example of a method for manufacturing the porous ceramic structure 1 will be described with reference to fig. 8. In the production of the porous ceramic structure 1, first, the material of the honeycomb structure 10, the material of the metal oxide particles 2, and the material of the additive fine particles are weighed and mixed to prepare a structure raw material. The main component of the material of the honeycomb structure 10 is a raw material of cordierite as an aggregate of the honeycomb structure 10, for example, magnesia (MgO) and alumina (Al)₂O₃) And silicon oxide (SiO)₂). The material of the honeycomb structure 10 further contains a pore-forming agent, a binder, and the like. The material of the metal oxide particles 2 is, for example, Mn₂O₃And WO₃. The material of the additive particles being, for example, Fe₂O₃And CeO₂. Next, the structural body raw material is dry-mixed by a kneader, and then, water is added, and further, kneaded by the kneader to prepare a clay (step S11).

The time required for the dry mixing and kneading is, for example, 15 minutes and 30 minutes. The dry mixing time and the kneading time may be variously changed. As the material of the metal oxide particles 2, for example, a salt such as manganese nitrate can be used in place of Mn₂O₃Instead of WO, ammonium salts of tungsten may be used₃. In addition, as the material of the additive fine particles, for example, salts such as iron nitrate and cerium nitrate may be used instead of Fe₂O₃And CeO₂。

In step S11, the raw material of the metal oxide particles 2 and the raw material of the additive fine particles are added to the aggregate or the like of the honeycomb structure 10, respectively, but the method of adding these materials may be variously modifiedFurthermore, the method is simple and convenient. For example, CeO may be impregnated with the raw material of the metal oxide particles 2₂The material produced by drying and firing is added to the aggregate of the honeycomb structure 10. In this material, a part of the raw material of the metal oxide particles 2 may be solid-dissolved or attached to CeO₂。

The clay prepared in step S11 is formed into a columnar shape by a vacuum pug mill or the like, and then extruded into a honeycomb-shaped honeycomb formed body by an extrusion molding machine (step S12). The honeycomb formed body includes lattice-shaped partition walls defining a plurality of cells, and fluid channels are formed in the plurality of cells. The honeycomb formed body had a honeycomb diameter of 30mm, a cell wall thickness of 12mil (about 0.3mm), and a cell density of 300cpsi (cell per square inches: 46.5 cells/cm)²) The peripheral wall thickness was about 0.6 mm. In step S12, the honeycomb formed body may be formed by a forming method other than extrusion molding.

About 70% of the water was evaporated by microwave drying and then dried by hot air (80 ℃ C.. times.12 hours) with respect to the honeycomb formed body produced in step S12. Next, the honeycomb formed body was put into a desolventizing furnace maintained at 450 ℃, and the organic matter component remaining in the honeycomb formed body was removed (i.e., degreased). Then, a firing treatment (main firing) of the honeycomb formed body is performed to obtain the porous ceramic structure 1 including the honeycomb structure 10, the metal oxide particles 2, and the additive fine particles (step S13). For example, the firing treatment of step S13 is performed at a firing temperature of 1300 to 1500 ℃ for 8 hours under atmospheric pressure. The firing temperature is preferably 1350 ℃ or higher, and more preferably 1370 ℃ or higher. The firing temperature is preferably 1450 ℃ or lower, more preferably 1430 ℃ or lower. The conditions of the firing treatment may be changed as appropriate. The porous ceramic structure 1 manufactured by the above-described manufacturing method does not contain a noble metal, and therefore can be manufactured at low cost.

Next, the relationship between the content of the metal oxide particles 2 in the porous ceramic structure 1, the pressure loss, and the catalytic ability will be described with reference to tables 1 to 3.

TABLE 1

TABLE 2

TABLE 3

The composition of the crystal phase (i.e., the mass ratio of the constituent components) of the porous ceramic structure 1 was identified and quantified as follows. The crystal phase of each particle was measured using an X-ray diffraction device (rotary anticathode X-ray diffraction device: RINT2500, manufactured by RINT2500) for the prepared sample. Here, the X-ray diffraction measurement conditions were CuK α source, 50kV, 300mA, and 2 θ were 10 ° to 60 °, and the obtained X-ray diffraction data was analyzed using commercially available X-ray data analysis software.

MnWO as metal oxide particles 2₄The major axis, minor axis and aspect ratio of (a) are determined by the above-mentioned method. The open porosity of the porous ceramic structure 1 was measured by the archimedes method using pure water as a medium. As described above, if the open porosity is increased, the pressure loss of the porous ceramic structure 1 is reduced.

The NO oxidation temperature of the porous ceramic structure 1 was determined as follows. First, NO of the porous ceramic structure 1 is determined₂Conversion versus temperature. NO₂The conversion was: introducing NO-containing gas at Space Velocity (SV)24400h^－1The derived gas supplied to and passed through the porous ceramic structure 1 is converted into NO₂NO of (c). The introduced gas contained 100ppm of NO, 1500ppm of CO, and 5% of CO₂450ppm propane (C)₃H₈) And 2% of H₂And O. Derivation was performed by Fourier transform Infrared Spectroscopy (FT-IR)And (4) analyzing the gas. NO₂The conversion rate was about 0% during the low temperature period, gradually increased and reached a maximum value as the temperature rose, and then gradually decreased. NO₂When the conversion rate is high, the catalytic ability of the porous ceramic structure 1 is high. If NO is found₂The relationship between the conversion and the temperature, in which NO is determined when the temperature is raised from the low temperature side₂The temperature of 1/2 at which the conversion reaches a maximum is taken as the NO oxidation temperature. When the NO oxidation temperature is low, the porous ceramic structure 1 has high catalytic performance.

The thermal expansion coefficient of the porous ceramic structure 1 is a value measured by a method in accordance with "JIS R1618". Specifically, the thermal expansion coefficient is: a test piece having a length of 3 cells in the vertical direction, 3 cells in the horizontal direction, and a length of 50mm was cut out from the honeycomb structure 10, and the value obtained by measuring the coefficient of thermal expansion in the a-axis direction (i.e., the direction parallel to the flow path of the honeycomb structure) at 40 to 800 ℃.