JP2013233538A - Oxidation catalyst particle, exhaust gas cleaning filter, and exhaust gas cleaning device of internal-combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an oxidation catalyst particle which can improve combustion properties of the particulate matter (PM) contained in exhaust gas of an internal-combustion engine such as an engine without using a noble metal and to provide an exhaust gas cleaning filter, and the exhaust gas cleaning device of the internal combustion engine such as the engine.SOLUTION: In an oxidation catalyst particle 1, an oxide layer 3 comprising amorphous SiOC(wherein 0<x≤3 and 0≤y≤3) is formed on the surface of a silicon carbide particle 2 having average primary particle size of 0.005-5 μm, and oxygen is adsorbed on/desorbed from the surface of the oxide layer 3.

Description

  The present invention relates to oxidation catalyst particles, an exhaust gas purification filter, and an exhaust gas purification device for an internal combustion engine. More specifically, the present invention relates to particulate matter (PM) contained in the exhaust gas of an internal combustion engine such as an engine without using a noble metal element. The present invention relates to an oxidation catalyst particle capable of efficiently purifying matter), an exhaust gas purification filter containing the oxidation catalyst particle, and an exhaust gas purification device for an internal combustion engine.

  Substances such as carbon monoxide (CO), hydrocarbons (HC), nitrogen oxides (NOx), and particulate matter (PM) contained in the exhaust gas discharged from engines such as automobiles (internal combustion engines) are air pollution. Has caused various environmental problems. In particular, particulate matter (PM) contained in exhaust gas is also said to cause allergic diseases such as asthma and hay fever. Therefore, an exhaust gas purification apparatus is used to purify substances that cause air pollution contained in these exhaust gases.

In general, in a diesel engine for automobiles, a diesel particulate filter (DPF: Diesel Particulate Filter) having a plugged ceramic honeycomb structure is used as an exhaust gas purification filter for collecting PM. . This DPF is a ceramic structure made of a metal oxide such as alumina, ceria, zirconia, or a honeycomb structure made of a metal composite oxide having a perovskite structure represented by the general formula ABO ₃ (where A and B are metal elements). Both ends of the cell (gas flow path) are sealed in a checkered pattern, and a noble metal element having an oxidation catalyst function is supported on at least the surface of the cell on the inflow side gas flow path. When exhaust gas passes, PM is collected.
The collected PM is removed by combustion, but the noble metal element having an oxidation catalyst function carried on the DPF acts as a catalyst for combustion removal of the PM, thereby reducing the combustion temperature and the combustion time. (For example, refer to Patent Documents 1 and 2).

By the way, noble metal elements are essential in the above-described conventional catalysts for purifying exhaust gas, but on the other hand, the number of automobiles in emerging countries is increasing rapidly, and exhaust gas regulations in developed countries are further strengthened. Therefore, the demand for precious metal elements used in automobile exhaust gas purification devices is expected to increase further.
Therefore, as a catalyst for exhaust gas purification that can reduce the amount of noble metal element used, the surface area of the noble metal element is reduced by supporting the noble metal element on the surface of fine particles (supported particles) such as γ-alumina having a high specific surface area. There has been proposed a structure using, as a catalyst, composite particles that are expanded and have an increased catalytic activity (see, for example, Patent Document 3).

Japanese Patent Laid-Open No. 5-23512 JP-A-9-77573 JP 2006-7117 A

However, in a conventional catalyst in which a noble metal element is supported on the surface of fine particles such as γ-alumina, γ-alumina causes a crystal transition to α-alumina at a high temperature of 1000 ° C. or higher, so that the specific surface area is remarkably reduced. There was a problem.
Furthermore, the structural change due to the crystal transition from γ-alumina to α-alumina becomes a cause of promoting the sintering (grain growth) of the catalyst component. In addition, when these catalysts are formed in layers on a substrate, structural changes due to catalyst crystal transition also cause separation or dropping of the formation layer.
From the above, there is a problem that a catalyst in which a noble metal element is supported on the surface of fine particles such as γ-alumina cannot maintain catalytic activity at high temperatures.

  Furthermore, direct injection for the purpose of improving fuel efficiency and high output has been performed in gasoline engines, but in this direct injection gasoline engine, the generation of PM is unavoidable. There is an increasing need for a PM collection filter corresponding to the above.

  The present invention has been made in view of the above circumstances, and oxidation catalyst particles and exhaust gas capable of improving the combustibility of PM contained in exhaust gas of an internal combustion engine such as an engine without using a noble metal. It is an object of the present invention to provide a purification filter and an exhaust gas purification device for an internal combustion engine.

The present inventors include carbon monoxide (CO), hydrocarbon (HC), nitrogen oxide (NOx), particulate matter (PM), etc. contained in exhaust gas discharged from an engine (internal combustion engine) such as an automobile. As a result of intensive studies on a catalyst for efficiently purifying the above substances, amorphous SiO _x C _y (where 0 <x ≦ 3, 0 ≦ y ≦ 3) is formed on the surface of fine silicon carbide particles. By using the oxidation catalyst particles that form the oxide layer and adsorbing and desorbing oxygen on the surface of the oxide layer, the combustibility of PM contained in the exhaust gas can be improved without using noble metal elements. Therefore, the present inventors have found that this PM can be purified efficiently and have completed the present invention.

That is, the oxidation catalyst particle of the present invention has an amorphous SiO _x C _y (where 0 <x ≦ 3, 0 ≦ y) on the surface of silicon carbide particles having an average primary particle diameter of 0.005 μm or more and 5 μm or less. ≦ 3) is formed, and oxygen is adsorbed and desorbed on the surface of the oxide layer.

The content of the oxide layer is preferably 0.1% by mass or more and 50% by mass or less with respect to the total mass of the silicon carbide particles.
The oxygen is preferably adsorbed when the surface temperature of the oxide layer is 100 ° C. or higher and 1000 ° C. or lower.
The oxygen adsorbed on the surface of the oxide layer is preferably desorbed when the surface temperature of the oxide layer is 300 ° C. or higher and 1000 ° C. or lower.

  The exhaust gas purification filter of the present invention is an exhaust gas purification filter that traps particulate matter contained in exhaust gas by passing through a filter base made of a porous body and purifies the exhaust gas, and the filter base is porous Provided in a position different from the inflow side gas flow path of the filter base, and an inflow side gas flow path formed by the partition and having an inflow end portion of exhaust gas containing particulate matter opened. And an outflow side gas passage formed by the partition wall and having an outflow side end portion of the exhaust gas opened. The oxidation catalyst particles of the present invention are provided on at least the surface of the partition wall on the inflow side gas channel side. A porous film containing and having a pore size smaller than that of the partition wall is formed.

  An exhaust gas purification apparatus for an internal combustion engine according to the present invention is an exhaust gas purification apparatus that purifies exhaust gas from the internal combustion engine with a catalyst disposed in an exhaust gas path of the internal combustion engine, and the catalyst uses the oxidation catalyst particles of the present invention. It is characterized by comprising.

According to the oxidation catalyst particles of the present invention, amorphous SiO _x C _y (where 0 <x ≦ 3, 0 ≦ y) is formed on the surface of silicon carbide particles having an average primary particle diameter of 0.005 μm or more and 5 μm or less. ≦ 3) is formed, and oxygen is adsorbed / desorbed on the surface of this oxide layer, so that the combustibility of PM contained in exhaust gas is improved without using noble metal elements. Can do. Therefore, PM contained in the exhaust gas can be efficiently purified.
In addition, since the silicon carbide particles and the oxide layer are stable even at a high temperature of 1000 ° C. or higher, high durability can be maintained while maintaining high catalytic activity from the low temperature region to the high temperature region.

  According to the exhaust gas purification filter of the present invention, the porous membrane containing the oxidation catalyst particles of the present invention and having a pore size smaller than the partition wall is formed on at least the surface of the partition wall on the inflow side gas flow path side. The combustibility of contained PM can be improved, and this PM can be purified efficiently. Therefore, high durability can be maintained while maintaining high catalytic activity from the low temperature region to the high temperature region, and the reliability of the exhaust gas purification filter can be improved.

  According to the exhaust gas purification apparatus for an internal combustion engine of the present invention, since the catalyst disposed in the exhaust gas path of the internal combustion engine contains the oxidation catalyst particles of the present invention, the combustibility of PM contained in the exhaust gas of the internal combustion engine is improved. This PM can be purified efficiently. Therefore, high durability can be maintained while maintaining high catalytic activity from the low temperature region to the high temperature region, and the reliability of exhaust gas purification in the internal combustion engine can be improved.

It is sectional drawing which shows the oxidation catalyst particle | grains of one Embodiment of this invention. It is a partially broken perspective view which shows DPF which is an example of the exhaust gas purification filter of one Embodiment of this invention. It is sectional drawing which shows the partition structure of DPF which is an example of the exhaust gas purification filter of one Embodiment of this invention. It is a figure which shows the XPS spectrum of O1s of the oxide layer of the oxidation catalyst particle | grain of the Example of this invention. It is a figure which shows the XPS spectrum of Si2p of the oxide layer of the oxidation catalyst particle | grain of the Example of this invention. It is a diagram showing an H _2-TPR curve of the oxide layer of the oxidation catalyst particles of Example of the present invention.

The form for implementing the oxidation catalyst particle | grains and exhaust gas purification filter of this invention, and the exhaust gas purification apparatus of an internal combustion engine is demonstrated.
This embodiment is specifically described for better understanding of the gist of the invention, and does not limit the present invention unless otherwise specified.

[Oxidation catalyst particles]
The oxidation catalyst particles according to an embodiment of the present invention have amorphous SiO _x C _y (where 0 <x ≦ 3, 0) on the surface of silicon carbide particles having an average primary particle diameter of 0.005 μm or more and 5 μm or less. An oxide layer composed of ≦ y ≦ 3) is formed, and oxygen is adsorbed / desorbed on the surface of the oxide layer.
The oxidation catalyst particles of the present embodiment are suitably used for purifying PM contained in exhaust gas from an internal combustion engine such as a gasoline engine or a diesel engine, and can be used for automobiles such as gasoline cars and diesel cars, for example.

FIG. 1 is a cross-sectional view showing an oxidation catalyst particle 1 of the present embodiment. This oxidation catalyst particle 1 is amorphous on the surface of silicon carbide particles 2 having an average primary particle diameter of 0.005 μm or more and 5 μm or less. An oxide layer 3 made of SiO _x C _y (where 0 <x ≦ 3, 0 ≦ y ≦ 3) is formed.

The silicon carbide particles 2 preferably have an average primary particle size of 0.005 μm to 5 μm, more preferably 0.02 μm to 0.1 μm, and still more preferably 0.03 μm to 0.85 μm.
Here, when the average primary particle diameter of the silicon carbide particles 2 is less than 0.005 μm, the surface activity of the silicon carbide particles 2 becomes too high, and when the oxidation catalyst particles 1 are used at a high temperature, the oxidation catalyst Since sintering (grain growth) between the particles 1 progresses and the particle diameter becomes coarse, and the catalytic activity decreases, it is not preferable. On the other hand, when the average primary particle diameter exceeds 5 μm, the specific surface area of the silicon carbide particles 2 decreases, and as a result, the oxygen adsorption / desorption points on the surface of the oxide layer formed on the surface of the silicon carbide particles 2. Is decreased, and the catalytic activity is lowered, which is not preferable.

  As a method for obtaining such silicon carbide particles 2 having an average primary particle size of 0.005 μm or more and 5 μm or less, it has high temperature and high activity in a non-oxidizing atmosphere, and it is easy to introduce a high-speed cooling process. There is a thermal plasma method using a certain thermal plasma. This production method is useful as a method for producing silicon carbide nanoparticles having an average primary particle diameter of 0.005 μm or more and 5 μm or less and having excellent crystallinity. By selecting a high-purity raw material, the content of impurities It is possible to obtain silicon carbide nanoparticles with very little.

Moreover, the silica precursor baking method can also be mentioned. In this method, a mixture containing a silicon-containing substance such as an organosilicon compound, silicon sol, or silicic acid hydrogel, a carbon-containing substance such as a phenol resin, and a metal compound such as lithium that suppresses grain growth of silicon carbide is obtained. In this method, silicon carbide particles are obtained by firing in a non-oxidizing atmosphere.
If necessary, it can also be obtained by using the Atchison method, the silica reduction method, the silicon carbonization method or the like.

The oxide layer 3 is preferably an amorphous silicon carbide or silicon oxide represented by SiO _x C _y (where 0 <x ≦ 3, 0 ≦ y ≦ 3), particularly 1000 ° C. or more. In view of being stable even at a high temperature, it is preferably composed of one or more selected from the group of SiO ₂ , SiO, SiOC ₃ , SiO ₂ C ₂ , and SiO ₃ C. The silicon carbide oxide may contain silicon, carbon, and oxygen together, and may contain a composition other than the above three types (SiOC ₃ , SiO ₂ C ₂ , SiO ₃ C).

The content of the oxide layer 3 is preferably 0.1% by mass or more and 50% by mass or less, more preferably 1% by mass or more and 30% by mass or less, based on the total mass of the silicon carbide particles 2. More preferably, it is 5 mass% or more and 20 mass% or less.
Here, the reason for limiting the content of the oxide layer 3 to the above range is that this range is a range in which the combustibility of PM contained in the exhaust gas can be improved.
When the content of the oxide layer 3 is less than 0.1% by mass, the content of the oxide layer 3 is too small, so that the adsorption / desorption of oxygen on the surface of the oxide layer 3 is insufficient. As a result, the combustibility of PM contained in the exhaust gas is lowered, and this PM cannot be efficiently purified, which is not preferable. On the other hand, if the content of the oxide layer 3 exceeds 50% by mass, the catalytic activity itself of the oxidation catalyst particles 1 is not affected, but the thermal conductivity decreases because the content of the oxide layer 3 is too large. As a result, the thermal shock resistance of the porous film formed containing the oxidation catalyst particles 1 is lowered, which is not preferable.

The thickness (film thickness) of the oxide layer 3 is preferably 0.0005 μm (0.5 nm) or more and 1 μm or less, more preferably 0.001 μm (1 nm) or more and 0.5 μm or less, and further preferably 0.005 μm. (5 nm) or more and 0.1 μm or less.
Here, if the thickness of the oxide layer 3 is less than 0.0005 μm (0.5 nm), the film thickness becomes excessively thin, so that oxygen adsorption / desorption on the surface of the oxide layer 3 is insufficient. As a result, the combustibility of PM contained in the exhaust gas is lowered, and this PM cannot be efficiently purified, which is not preferable. On the other hand, if the thickness of the oxide layer 3 exceeds 1 μm, the catalytic activity itself of the oxidation catalyst particles 1 is not affected, but the film thickness becomes too thick and the thermal conductivity is lowered. This is not preferable because the thermal shock resistance of the porous film formed containing the catalyst particles 1 is lowered.

In this oxidation catalyst particle 1, amorphous SiO _x C _y (where 0 <x ≦ 3, 0 ≦ y ≦ 3) constituting the oxide layer 3 exhibits oxygen adsorption / desorption characteristics. This action, even in a low temperature region where the reaction rate of the catalytic reaction is dependent on the number of active sites, by oxygen desorbed from SiO _x C _y of the amorphous burning the PM contained in the exhaust gas, the result Therefore, it is considered that high combustion catalyst activity is obtained, and PM combustibility in a low temperature region is improved.

In the oxidation catalyst particle 1, oxygen easily adsorbs when the surface temperature of the oxide layer 3 is in the range of 100 ° C. or more and 1000 ° C. or less.
Here, when the surface temperature of the oxide layer 3 is less than 100 ° C., it becomes difficult to adsorb oxygen to the surface of the oxide layer 3, and it takes a long time to adsorb the desired amount of oxygen. On the other hand, when the surface temperature of the oxide layer 3 exceeds 1000 ° C., the oxygen once adsorbed on the surface of the oxide layer 3 is likely to be detached, and a desired amount of oxygen can be adsorbed. Since it becomes difficult, it is not preferable.
The temperature of exhaust gas from an internal combustion engine such as a gasoline engine or diesel engine is usually 150 ° C. or higher and 600 ° C. or lower. Therefore, in order for oxygen in the exhaust gas to be adsorbed on the surface of the oxide layer, the above temperature range It is more preferable to adsorb oxygen.

Further, oxygen adsorbed on the surface of the oxide layer 3 is easily desorbed when the surface temperature of the oxide layer 3 is in the range of 300 ° C. or higher and 1000 ° C. or lower.
Here, if the surface temperature of the oxide layer 3 is less than 300 ° C., sufficient thermal energy cannot be obtained for desorbing oxygen adsorbed on the surface of the oxide layer 3, and oxygen is desorbed. On the other hand, when the surface temperature of the oxide layer 3 exceeds 1000 ° C., there is a high possibility that oxygen once desorbed from the surface of the oxide layer 3 will be adsorbed again on this surface. Since it becomes difficult to desorb the amount of oxygen, it is not preferable.
Note that PM can react with oxygen in exhaust gas at 600 ° C. or higher to burn and remove. On the other hand, the temperature of the exhaust gas from the internal combustion engine is usually in the range of 150 ° C. to 600 ° C. as described above, and it is difficult to obtain the PM combustion removal effect only by the temperature of the exhaust gas. For these reasons, the desorption temperature is more preferably 600 ° C. or lower in order to obtain an effective catalytic effect using desorbed oxygen on the surface of the oxide layer.

[Production method of oxidation catalyst particles]
The method for producing oxidation catalyst particles of the present embodiment includes a silicon carbide particle preparation step for preparing silicon carbide particles 2 and SiO _x C _y (where 0 <x ≦ 3, 0 ≦ y) on the surface of silicon carbide particles 2. And an oxide layer forming step for forming the amorphous oxide layer 3 represented by 3).

Next, each step will be described in detail.
"Silicon carbide particle preparation process"
This is a step of preparing silicon carbide particles having an average primary particle diameter of 0.005 μm or more and 5 μm or less.
The average primary particle diameter of the silicon carbide particles to be prepared may be selected according to the required characteristics of the exhaust gas purification filter and the exhaust gas purification device, but is preferably in the range of 0.005 μm to 5 μm. The silicon carbide particles are sub-micron to micron (micrometer) size silicon carbide particles such as the thermal plasma method or the silica precursor firing method if the particles are nanometer-sized particles. It can be obtained using a method, a silica reduction method, a silicon carbonization method or the like.

"Oxide layer formation process"
In this step, the silicon carbide particles are oxidized to form an oxide layer on the surface of the silicon carbide particles.
The silicon carbide particles are placed in an oxidizing atmosphere such as air or oxygen at a temperature of 600 ° C. to 1000 ° C., preferably 650 ° C. to 900 ° C., preferably 0.5 hours to 36 hours, preferably Oxidation treatment is performed for 4 hours or more and 12 hours or less to form an oxide layer on the surface of the silicon carbide particles.

Thereby, an oxide layer having a uniform thickness can be formed on the surface of the silicon carbide particles. Thus, by oxidizing the silicon carbide particles in an oxidizing atmosphere such as air or oxygen, the surface of the silicon carbide particles 2 having an average primary particle diameter of 0.005 μm or more and 5 μm or less is amorphous. The oxidation catalyst particle 1 in which the oxide layer 3 made of SiO _x C _y (where 0 <x ≦ 3, 0 ≦ y ≦ 3) is formed can be obtained.

[Exhaust gas purification filter]
FIG. 2 is a partially broken perspective view showing a DPF which is an example of an exhaust gas purification filter using the oxidation catalyst particles 1 according to an embodiment of the present invention, and FIG. 3 is a DPF on the surface indicated by the symbol β in FIG. It is sectional drawing which shows this partition structure.
As shown in FIG. 2, the DPF 10 is contained in the exhaust gas G by allowing the exhaust gas G to pass through a filter base 11 made of a cylindrical porous ceramic (porous body) having a large number of pores (pores). An exhaust gas purification filter that collects PM and purifies the exhaust gas G. Note that the DPF does not have to be cylindrical, and may have a shape such as a prismatic shape or an elliptical column shape.

  A gas flow path 12 is formed in the filter base 11, and when viewed from the flow direction (longitudinal direction) of the exhaust gas G, the upstream end and the downstream end are alternately closed. An inflow cell (inflow side gas flow path) 12A in which an inflow end of exhaust gas G containing particulate matter on the inflow side of exhaust gas G is opened, and a position different from the inflow cell 12A are formed. And an outflow cell (outflow side gas flow path) 12B whose outflow side end of the exhaust gas G is opened, and an upstream end (inflow side end) of the exhaust gas G in the gas flow path 12 is opened. A porous membrane 13 containing the oxidation catalyst particles 1 of the present embodiment and having a pore diameter smaller than that of the filter base 11 is formed on the inner wall surface 12a of the inflow cell 12A.

The flow of exhaust gas in the DPF 10 is shown in FIG.
The exhaust gas G containing PM30 that has flowed in from the inflow surface side, that is, the end surface α side, flows into the DPF 10 from the inflow cell 12A that opens to the inflow surface, and flows in the inflow cell 12A from the end surface α side to the end surface γ side. In the process, it passes through the partition wall 14 of the filter base 11. At this time, the PM 30 contained in the exhaust gas G is collected and removed by the porous film 13 provided on the inner wall surface 12a of the inflow cell 12A (the surface of the partition wall 14 constituting the inflow cell 12A). The purified gas C from which 30 has been removed flows from the end surface α side to the end surface γ side in the outflow cell 12B, and is discharged out of the filter from the open end (end surface γ) of the outflow cell 12B.

The filter base 11 is a honeycomb structure made of heat-resistant porous ceramics such as silicon carbide, cordierite, aluminum titanate, silicon nitride. The filter base 11 is formed with a partition wall 14 extending along the axial direction, which is the flow direction of the exhaust gas G, and an axial hollow region surrounded by the partition wall 14 is formed from a large number of inflow cells 12A and outflow cells 12B. It is set as the cell-shaped gas flow path 12 which becomes.
Here, the “honeycomb structure” in the present embodiment is such that a plurality of inflow cells 12A and outflow cells 12B are parallel to the filter base 11, and one of the inflow cells 12A and the outflow cells 12B surrounds the other. In addition, one opening end and the other opening end are formed in opposite directions.

  The cross-sectional shape in the direction perpendicular to the axial direction of the inflow cell 12A and the outflow cell 12B, that is, the gas flow path 12, is a quadrangular shape here, but is not limited to a quadrangular shape, but a polygonal shape such as a hexagonal shape, a circular shape, an elliptical shape, etc. Various cross-sectional shapes such as a shape can be used. In addition, the gas flow path 12 formed near the outer periphery of the filter base 11 has an arc shape in a part of the cross-sectional shape. However, the gas flow path 12 is arranged without a gap to the vicinity of the outer periphery of the filter base 11. Therefore, the gas flow path 12 having a cross-sectional shape following the outer shape of the filter base 11 is used.

  The average pore diameter of the partition wall 14 made of porous ceramics is preferably 5 μm or more and 50 μm. If the average pore diameter is less than 5 μm, the pressure loss due to the partition wall 14 itself is increased, which is not preferable. On the other hand, if the average pore diameter exceeds 50 μm, the strength of the partition wall 14 may not be sufficient, and it becomes difficult to form the porous film 13 on the partition wall 14, which is not preferable.

  The porous film 13 is formed on the inner wall surface 12a of the inflow cell 12A and is a porous film having a pore diameter smaller than the pore diameter of the partition wall 14, and is made of fine porous ceramics constituting the partition wall 14 of the filter base 11. It is formed as an independent film on the inner wall surface 12a of the inflow cell 12A without entering the hole so much. That is, the porous film 13 is formed on the inner wall surface 12a of the inflow cell 12A in a state where it only penetrates to the entrance of the pores formed in the partition wall 14. And the porous membrane 13 has many pores, these pores communicate, and as a result, it becomes a filter-like porous which has a through-hole.

The porosity of the porous membrane 13 is preferably 50% or more and 90% or less, more preferably 60% or more and 85% or less.
If the porosity is less than 50%, sufficient gas diffusion is not performed in the porous membrane 13, and the oxidation catalyst particles 1 of the present embodiment may not function effectively. Further, if the porosity exceeds 90%, the mechanical strength of the porous membrane 13 is lowered, so that the porous membrane 13 itself is deformed or peeled off from the inner wall surface 12a, and the oxidation catalytic action may be lowered. There is.

  When the exhaust gas G flows into the porous film 13, PM contained in the exhaust gas is collected and deposited on the porous film 13 when the exhaust gas G passes through the pores of the porous film 13, and the PM is removed. Purified gas is discharged into the atmosphere. Here, since the pore diameter of the porous membrane 13 is smaller than the pore diameter of the partition wall 14, by providing the porous membrane 13, PM having a smaller particle diameter can also be collected, and thus the exhaust gas discharged into the atmosphere. The amount of PM inside is reduced, and the purifying property is improved.

Next, the PM deposited on the porous film 13 is burned, for example, by raising the temperature of the DPF, and the carbon constituting the PM is oxidized and removed as CO ₂ . Here, since the collected PM is in contact with the oxidation catalyst particles 1 contained in the porous film 13, the PM is burned and removed with high efficiency due to the catalytic effect of the oxidation catalyst particles 1. Furthermore, the combustion temperature can be reduced by the catalytic effect of the oxidation catalyst particles 1.
The PM removal method is a forced regeneration method in which the PM collected in the porous film 13 is deposited to some extent and then burned and removed by, for example, increasing the temperature of the DPF. A continuous regeneration system in which combustion is performed simultaneously may be used.

[Exhaust gas purification device for internal combustion engine]
An exhaust gas purification apparatus for an internal combustion engine according to an embodiment of the present invention is an exhaust gas purification apparatus that purifies exhaust gas from the internal combustion engine with a catalyst disposed in an exhaust gas path of the internal combustion engine, and the catalyst is the present embodiment. The oxidation catalyst particles 1 are contained.
The exhaust gas purification apparatus for an internal combustion engine according to the present embodiment is used for automobiles such as gasoline cars and diesel cars, for example. The exhaust gas purifying device may be disposed in the exhaust gas path, and the arrangement and structure of the exhaust gas purifying device are not particularly limited. For example, when used in an automobile (gasoline car, diesel car), the DPF 10 described above is used as a diesel engine. By disposing in the exhaust gas path of an automobile or the like, the combustibility of PM contained in the exhaust gas G can be improved, and this PM can be efficiently purified.

As described above, according to the oxidation catalyst particle 1 of the present embodiment, the surface of the silicon carbide particle 2 having an average primary particle diameter of 0.005 μm or more and 5 μm or less is formed of amorphous SiO _x C _y (however, 0 <x ≦ 3, 0 ≦ y ≦ 3) is formed, and oxygen is adsorbed / desorbed on the surface of the oxide layer, so that no exhaust gas is used in the exhaust gas without using noble metal elements. The combustibility of contained PM can be improved. Therefore, PM contained in the exhaust gas can be efficiently purified.
In addition, since the silicon carbide particles 2 and the oxide layer 3 are stable even at a high temperature of 1000 ° C. or higher, high durability can be maintained while maintaining high catalytic activity from the low temperature region to the high temperature region.

  According to the exhaust gas purification filter 10 of the present embodiment, the porous membrane 13 containing the oxidation catalyst particles 1 of the present embodiment on the inner wall surface 12a of the inflow cell 12A of the filter base 11 and having a pore diameter smaller than that of the filter base 11. Therefore, the combustibility of PM contained in the exhaust gas G can be improved, and this PM can be efficiently purified. Therefore, high durability can be maintained while maintaining high catalytic activity from the low temperature region to the high temperature region, and the reliability of exhaust gas purification can be improved.

  According to the exhaust gas purification apparatus for an internal combustion engine of the present embodiment, since the catalyst disposed in the exhaust gas path of the internal combustion engine contains the oxidation catalyst particles 1 of the present embodiment, combustion of PM contained in the exhaust gas of the internal combustion engine The PM can be purified efficiently. Therefore, high durability can be maintained while maintaining high catalytic activity from the low temperature region to the high temperature region, and the reliability of exhaust gas purification in the internal combustion engine can be improved.

  EXAMPLES Hereinafter, although an Example demonstrates this invention concretely, this invention is not limited by these Examples.

[Example]
The silicon carbide particles having an average primary particle size of 0.035 μm were oxidized in the atmosphere at 700 ° C. for 30 hours to form an oxide layer on the surface of the silicon carbide particles to obtain the oxidation catalyst particles of the examples. .
It was 5 nm when the thickness of the oxide layer of this oxidation catalyst particle was measured using the transmission electron microscope (TEM). X-ray photoelectron spectroscopy The composition of the oxide layer: was examined by (XPS X-ray Photoelectron Spectroscopy) , it was found to be composed of amorphous SiO ₂ and _SiO x _{C y.}

FIG. 4 is a diagram showing an XPS spectrum of O1s of the oxide layer of the oxidation catalyst particle of the example, and it can be seen that respective peaks of SiO ₂ and SiO _x C _y exist.
FIG. 5 is a diagram showing an XPS spectrum of Si2p of the oxide layer of the oxidation catalyst particle of the example, and it can be seen that respective peaks of SiO ₂ , SiO ₃ C, SiO ₂ C ₂ , and SiOC ₃ exist. .

The hydrogen consumption (oxygen desorption) temperature of the oxide layer of the oxidation catalyst particles was examined by a hydrogen temperature programmed desorption method (H ₂ -TPR). Here, in order to once adsorb oxygen to the oxide layer of the oxidation catalyst particles, pretreatment is performed at 800 ° C. for 1 hour in helium gas containing 5% by volume of oxygen, and then the temperature is lowered to room temperature (25 ° C.). Then, it is naturally cooled, and then heated up to 800 ° C. at a heating rate of 10 ° C./min in an argon gas containing 5% by volume of hydrogen, and the hydrogen consumption (oxygen desorption) temperature of the oxide layer is increased. Examined.
FIG. 6 is a diagram showing an H ₂ -TPR curve of the oxide layer of the oxidation catalyst particle of the example, in which oxygen adsorbed on the oxide layer starts desorption at 350 ° C. and 580 ° C. I understood.

The activation energy of the overall reaction in PM combustion of the oxidation catalyst particles was calculated from the Arrhenius plot of the reaction rate at each combustion temperature, and was 75 kJ / mol.
On the other hand, the activation energy of the overall reaction in PM combustion on a conventional DPF (SiC particle size: several tens of μm) substrate was calculated in the same manner as described above, and was 120 kJ / mol.

Thus, it was found that the activation energy of the overall reaction in PM combustion was greatly reduced from 120 kJ / mol to 75 kJ / mol in the oxidation catalyst particles of the Examples as compared with the conventional DPF.
The reduction of the activation energy in the oxidation catalyst particles of the example is considered because oxygen having a small binding energy desorbed at 450 ° C. contributed to the improvement of PM combustibility.

DESCRIPTION OF SYMBOLS 1 Oxidation catalyst particle 2 Silicon carbide particle 3 Oxide layer 10 Exhaust gas purification filter 11 Filter base 12 Gas flow path 12A Inflow cell 12B Outflow cell 13 Porous membrane 14 Partition 30 Particulate matter α, γ End face G Exhaust gas C Purified gas

Claims (6)

An oxide layer made of amorphous SiO _x C _y (where 0 <x ≦ 3, 0 ≦ y ≦ 3) is formed on the surface of silicon carbide particles having an average primary particle size of 0.005 μm or more and 5 μm or less. And oxidation catalyst particles, wherein oxygen is adsorbed and desorbed on the surface of the oxide layer.   The oxidation catalyst particle according to claim 1, wherein the content of the oxide layer is 0.1 mass% or more and 50 mass% or less with respect to the total mass of the silicon carbide particles.   3. The oxidation catalyst particle according to claim 1, wherein the oxygen is adsorbed at a surface temperature of the oxide layer of 100 ° C. or more and 1000 ° C. or less.   4. The oxidation according to claim 1, wherein oxygen adsorbed on the surface of the oxide layer is desorbed when the surface temperature of the oxide layer is 300 ° C. or more and 1000 ° C. or less. Catalyst particles. An exhaust gas purification filter that purifies the exhaust gas by collecting particulate matter contained in the exhaust gas by passing through a filter base made of a porous body,
The filter base includes a partition wall made of a porous body, an inflow side gas passage formed by the partition and having an inflow side end portion of an exhaust gas containing particulate matter, and the inflow side gas of the filter base. An outflow side gas flow path provided at a position different from the flow path, formed by the partition wall and having an outflow side end of the exhaust gas opened,
A porous membrane containing the oxidation catalyst particles according to any one of claims 1 to 4 and having a pore diameter smaller than that of the partition wall is formed on at least a surface of the partition wall on the inflow side gas flow path side. An exhaust gas purification filter characterized by. An exhaust gas purifying device for purifying exhaust gas from the internal combustion engine with a catalyst disposed in an exhaust gas path of the internal combustion engine,
An exhaust gas purification apparatus for an internal combustion engine, characterized in that the catalyst contains the oxidation catalyst particles according to any one of claims 1 to 4.

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