JP2014000516A - Carrier for supporting catalyst, supported catalyst for exhaust gas purification, and filter for exhaust gas purification - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress an oxidation rate of an oxygen storage emission material, thereby to suppress atmosphere fluctuation of a catalyst vicinity, and to reduce a discharge amount of a nitrogen oxide.SOLUTION: A carrier for supporting an exhaust gas purification catalyst includes: an oxygen storage emission material having oxygen storage ejection ability; and a coating material that is made to cover a surface of the oxygen storage emission material, has oxygen storage ejection ability lower than the oxygen storage ejection ability of the oxygen storage emission material, and has a coat thickness of 50-500 μm.

Description

  The present invention relates to a carrier for supporting an exhaust gas purification catalyst, an exhaust gas purification support catalyst having an exhaust gas purification catalyst supported on the carrier, and an exhaust gas purification filter including the exhaust gas purification support catalyst. .

  Exhaust gas discharged from an internal combustion engine such as an engine contains harmful substances such as hydrocarbons (HC), carbon monoxide (CO), and nitrogen oxides (NOx). Since these substances cause air pollution, it is required to remove these substances from the exhaust gas.

  In general, a metal oxide is used as a catalyst in order to remove harmful substances contained in exhaust gas. For example, Patent Documents 1 to 3 disclose a perovskite type composite oxide containing Pd, a perovskite type composite oxide containing Rh, and a perovskite type composite oxide containing Pt. It is described that the exhaust gas is purified using the above catalyst.

  Patent Document 4 discloses a composite oxide-supported catalyst carrier in which cerium, aluminum, and zirconium are uniformly dispersed, and exhaust gas is purified using a supported catalyst in which a metal catalyst is supported on the carrier. It describes what to do. Patent Document 5 describes purifying exhaust gas using a metal catalyst supported on an activated alumina coating layer containing at least one of nickel oxide and cobalt oxide. Patent Document 6 describes that exhaust gas is purified using a metal catalyst supported on a catalyst support layer containing cerium oxide and zirconium oxide.

JP 2004-41866 A JP 2004-41867 A JP 2004-41868 A JP-A-10-202101 JP-A-1-242149 JP 63-1116741 A

  In order to efficiently purify the exhaust gas, it is necessary to control the amount of oxygen in the vicinity of the exhaust gas purifying catalyst within a certain range. Here, by using a material having oxygen storage / release ability such as cerium (hereinafter referred to as “oxygen storage / release material”) as a carrier for supporting the exhaust gas purifying catalyst, fluctuation in the atmosphere in the vicinity of the catalyst is suppressed. be able to. Specifically, oxygen is occluded by oxidizing cerium from trivalent to tetravalent under oxygen-excess conditions, and oxygen is released by reducing cerium from tetravalent to trivalent under oxygen-deficient conditions. Thereby, even in a situation where a large amount of exhaust gas is discharged, such as during rapid acceleration of an automobile, it is possible to suppress atmospheric fluctuations in the vicinity of the catalyst and efficiently purify the exhaust gas.

However, for example, when the fuel is cut during mode running, a large amount of oxygen flows, so that the oxygen storage / release material is completely oxidized, and oxygen cannot be stored any more. As a result, the amount of oxygen in the vicinity of the exhaust gas purification catalyst increases too much, so that nitrogen oxides in the exhaust gas cannot be reduced to harmless nitrogen (N ₂ ).

  Therefore, an object of the present invention is to suppress atmospheric fluctuation in the vicinity of the catalyst and reduce the discharge amount of nitrogen oxides by suppressing the oxidation rate of the oxygen storage / release material.

  As a result of intensive studies by the present inventors, the surface of the oxygen storage / release material is coated with a constant thickness using another material having a low oxygen storage / release capability, thereby supporting the catalyst with a reduced oxidation rate. It has been found that a carrier can be provided.

That is, the present invention includes the following.
[1] An oxygen storage / release material having an oxygen storage / release capability; and a coating material that is coated on the surface of the oxygen storage / release material and has an oxygen storage / release capability lower than the oxygen storage / release capability of the oxygen storage / release material. Including
A carrier for supporting an exhaust gas purification catalyst, wherein the coating material has a thickness of 50 to 500 µm.
[2] The carrier according to [1], wherein a coverage of the oxygen storage / release material by the coating material is 60 to 100%.
[3] The carrier according to [1] or [2], wherein the covering material has an oxygen storage / release capacity of 0.001 (O ₂ ) mol / (coating material) mol or less.
[4] An exhaust gas purifying supported catalyst comprising the carrier according to any one of [1] to [3] and an exhaust gas purifying catalyst supported on the carrier.
[5] An exhaust gas purifying supported catalyst according to [4] and a filter base material,
An exhaust gas purifying filter in which the exhaust gas purifying supported catalyst is supported on the filter base material.
[6] A method for purifying exhaust gas, comprising a step of bringing the exhaust gas purifying catalyst according to [4] or the exhaust gas purifying filter according to [5] into contact with the exhaust gas.

  By using the exhaust gas purifying supported catalyst in which the exhaust gas purifying catalyst is supported on the carrier of the present invention, the emission amount of nitrogen oxide can be reduced.

The relationship between the thickness of the coating of the coating material and the emission amount of nitrogen oxides is shown. The relationship between the coverage of the oxygen storage / release material by the coating material and the discharge amount of nitrogen oxides is shown. The relationship between the oxygen storage-release capability of a coating material and the discharge amount of nitrogen oxides is shown.

Hereinafter, the present invention will be described in detail.
<Catalyst carrier>
The present invention relates to an oxygen storage / release material having an oxygen storage / release capability, and a coating material coated on the surface of the oxygen storage / release material and having an oxygen storage / release capability lower than the oxygen storage / release capability of the oxygen storage / release material. And a carrier for supporting an exhaust gas purification catalyst. The carrier according to the present invention is characterized in that the film thickness of the coating material on the surface of the oxygen storage / release material is 50 to 500 μm.

  If the thickness of the coating material coating is too thin, oxygen easily moves to the oxygen storage / release material via the coating, so that the oxidation rate of the oxygen storage / release material cannot be sufficiently suppressed. On the other hand, if the coating material is too thick, oxygen cannot be stored and released, so the advantage of using the oxygen storage / release material is lost. From these viewpoints, in the carrier according to the present invention, the thickness of the coating material is 50 to 500 μm. By setting the thickness of the coating within this range, the oxidation rate can be suppressed while maintaining the oxygen storage / release capability.

  The thickness of the coating is not particularly limited as long as it is in the range of 50 to 500 μm, and examples thereof include 60 to 480 μm, 70 to 400 μm, 80 to 300 μm, 90 to 250 μm, and 100 to 200 μm. The thickness of the coating can be appropriately changed by adjusting the amount of the coating material to be used. In the present specification, the “film thickness” means an average of the film thicknesses of a plurality of randomly selected carrier particles. However, the standard deviation of the thickness of the coating is 15 μm or less.

  The thickness of the coating can be determined using a scanning electron microscope (SEM). Specifically, the carrier particles are fixed to a resin and polished to expose a cross section of the carrier particles, and the thickness of the coating is measured by analyzing the cross section using an SEM.

  In the carrier according to the present invention, the coverage of the oxygen storage / release material by the coating material is preferably 60 to 100%. Here, the “covering ratio” means the ratio of the surface of the oxygen storage / release material covered with the coating material.

  When the coverage is low, oxygen easily comes into contact with the oxygen storage / release material. From the viewpoint of suppressing the oxidation rate of the oxygen storage / release material, a higher coverage is preferable. Therefore, the coverage is more preferably 70 to 100%, still more preferably 80 to 100%, and particularly preferably 90 to 100%.

  The coverage can be determined using SEM. Specifically, the surface of the carrier particles is observed at a magnification of 2500 to 50000 times using SEM. Then, in the obtained observation view, the area S1 of the carrier particles is defined, and the area S2 covered with the coating material in the area S1 is determined. Next, the coverage at the observation location is determined according to the following equation.

  The above operation is performed at 100 randomly selected locations, and the determined coverage is averaged to determine the coverage in the present invention.

  The carrier according to the present invention is further characterized by coating the surface of the oxygen storage / release material with a coating material having an oxygen storage / release capability lower than that of the oxygen storage / release material. Here, the “oxygen storage / release ability” means the ability to store oxygen under an oxygen excess condition and to release oxygen under an oxygen deficiency condition. The oxygen storage / release capacity is generally called OSC (Oxygen Storage Capacity).

By coating the surface of the oxygen storage / release material with a coating material having a low oxygen storage / release capability, the oxidation rate of the oxygen storage / release material can be suppressed. The lower the oxygen storage / release capability of the coating material, the more the oxidation rate of the oxygen storage / release material can be suppressed. Therefore, the lower the oxygen storage / release capability of the coating material, the better. For example, the oxygen storage / release capacity of the coating material is preferably 0.001 (O ₂ ) mol / (coating material) mol or less, more preferably 0.0005 (O ₂ ) mol / (coating material) mol or less. Yes, and particularly preferably 0 (O ₂ ) mol / (coating material) mol.

The oxygen storage / release ability of the coating material can be determined by a temperature-reduction method (TPR). Specifically, the temperature of the coating material is raised from room temperature to 600 ° C. while flowing oxygen (O ₂ ), and the coating material is made to sufficiently store oxygen. Thereafter, the temperature of the coating material is lowered to room temperature, and the temperature is raised to 1000 ° C. while flowing hydrogen (H ₂ ) instead of oxygen. During this time, by measuring the amount of water (H ₂ O) released from the coating material, the oxygen storage / release capacity of the coating material (the amount of oxygen that can be stored in the coating material) is determined.

  Examples of the coating material used in the carrier according to the present invention include metal oxides whose valence does not change in the JC08 mode. Since the occlusion and release of oxygen occurs due to a change in the valence of the metal, a metal oxide whose valence does not change does not have the ability to occlude and release oxygen. Therefore, a metal oxide whose valence does not change can be used as the coating material. The “JC08 mode” is a method for measuring the energy consumption efficiency of an automobile determined by the Ministry of Land, Infrastructure, Transport and Tourism and the Ministry of Economy, Trade and Industry.

More specific coating materials include, for example, Al ₂ O ₃ , ZrO ₂ , Y ₂ O ₃ , Nd ₂ O ₃ , La ₂ O ₃ , MgO, CaO, SrO, BaO and the like.

The oxygen storage / release material used in the carrier according to the present invention is not particularly limited, and a wide variety of materials known to have oxygen storage / release ability can be used. It is preferable that the oxygen storage / release material has a high oxygen storage / release capacity. For example, the oxygen storage / release capability of the oxygen storage / release material is preferably 0.002 to 1.5 (O ₂ ) mol / (oxygen storage / release material) mol, more preferably 0.003 to 1.0 (O ₂ ) mol / (oxygen storage / release material) mol, and particularly preferably 0.005 to 0.5 (O ₂ ) mol / (oxygen storage / release material) mol.

The oxygen storage / release capability of the oxygen storage / release material can be determined by the temperature-reduction method (TPR), as with the coating material.
More specific oxygen storage material, for _example, a _{CeO 2 -ZrO 2, CeO 2,} MnO 2, PrO 4, NiO, Fe 2 O 3, CuO and the like. A material that does not have the ability to store and release oxygen can be added to the extent that the effects of the present invention are not impaired.

<Supported catalyst for exhaust gas purification>
The present invention further relates to an exhaust gas purifying supported catalyst comprising the carrier described above and an exhaust gas purifying catalyst supported on the carrier. By supporting the exhaust gas purifying catalyst on the carrier according to the present invention and using it, it is possible to suppress atmospheric fluctuation in the vicinity of the catalyst and efficiently purify nitrogen oxide in the exhaust gas.

In particular, as shown in FIG. 1, the use of a carrier having a thickness of 50 to 500 μm as the carrier in the exhaust gas purifying supported catalyst can significantly improve the purifying ability of nitrogen oxides. . Moreover, as shown in FIG. 2, the purification ability of nitrogen oxides can be remarkably improved by using a carrier having an oxygen storage / release material coverage of 60 to 100%. Furthermore, as shown in FIG. 3, by using a carrier coated with a coating material having an oxygen storage / release capacity of 0.001 (O ₂ ) mol / (coating material) mol or less, the purification ability of nitrogen oxides Can be significantly improved.

  The exhaust gas purifying catalyst used in the exhaust gas purifying supported catalyst according to the present invention is not particularly limited as long as it can purify (reducing) nitrogen oxides, and in the technical field to which the present invention belongs. Commonly used ones can be used. For example, examples of the exhaust gas purification catalyst include Pt, Pd, Rh, Ir, Ru, and the like.

<Exhaust gas purification filter>
The present invention further relates to an exhaust gas purification filter comprising the exhaust gas purification supported catalyst described above and a filter base material. By carrying the exhaust gas purifying supported catalyst according to the present invention on a filter base material, it can be advantageously used in actual applications. The exhaust gas purifying filter according to the present invention can be preferably used for a vehicle equipped with an internal combustion engine that discharges exhaust gas, particularly an automobile.

  The filter substrate used in the exhaust gas purification filter according to the present invention is not particularly limited, and those generally used in the technical field to which the present invention belongs can be used. For example, examples of the filter substrate include a honeycomb type, a corrugated type, and a monolith honeycomb type substrate.

<Exhaust gas purification method>
The present invention further relates to a method for purifying exhaust gas, which includes a contact step of contacting the exhaust gas with a supported catalyst for purifying exhaust gas described above, in particular, an exhaust gas purifying filter. By using the exhaust gas purifying supported catalyst or the exhaust gas purifying filter according to the present invention, it is possible to efficiently purify nitrogen oxides in the exhaust gas.

  In the purification method according to the present invention, the contacting step may be performed in any manner as long as the exhaust gas purifying supported catalyst or the exhaust gas purifying filter is in contact with the exhaust gas. However, in order to effectively exhibit the properties of the carrier according to the present invention, the contact step is performed under the condition that a large amount of oxygen flows and the oxygen concentration in the vicinity of the catalyst increases, such as when the fuel is cut during mode running. It is preferable to carry out.

  EXAMPLES Hereinafter, although this invention is demonstrated in detail using an Example and a comparative example, the technical scope of this invention is not limited to this.

<Manufacture of exhaust gas purification filter>
[Example 1]
20 g of cerium-zirconium composite oxide (CeO ₂ / ZrO ₂ = 5/95), 10 g of alumina, and 10 g of polyacrylamide were dispersed in 500 g of pure water. After removing moisture by heating, the support was coated with alumina on the oxide surface by firing at 500 ° C. for 1 hour in the air.

  The obtained support was dispersed in 500 g of pure water, and an aqueous palladium nitrate solution (Pg amount: 1 g) was added to obtain a supported catalyst having Pd supported on the surface of the support. The aqueous solution was subjected to suction filtration, and the filtrate was subjected to dielectric coupled plasma (ICP) emission analysis. As a result, the loading efficiency of Pd was 100%.

A slurry (dry weight 61 g, Pd amount 1 g) containing the obtained supported catalyst, 30 g of alumina, and pure water was prepared. The slurry was coated on a monolith honeycomb substrate (full length: 100 mm, volume: 1.0 L, number of cells: 900 cells / in ² ), dried at 250 ° C. for 1 hour, then fired at 500 ° C. for 1 hour, and exhaust gas A purification filter was obtained.

[Example 2]
The same as Example 1 except that the composite oxide (CeO ₂ / ZrO ₂ = 5/95) used in Example 1 was changed to a cerium-zirconium composite oxide (CeO ₂ / ZrO ₂ = 20/80). An exhaust gas purification filter was manufactured.

[Example 3]
Same as Example 1 except that the composite oxide (CeO ₂ / ZrO ₂ = 5/95) used in Example 1 was changed to a cerium-zirconium composite oxide (CeO ₂ / ZrO ₂ = 70/30). An exhaust gas purification filter was manufactured.

[Example 4]
Exhaust gas as in Example 1 except that the complex oxide (CeO ₂ / ZrO ₂ = 5/95) used in Example 1 was changed to cerium oxide (CeO ₂ / ZrO ₂ = 100/0) A purification filter was produced.

[Example 5]
The composite oxide (CeO ₂ / ZrO ₂ = 5/95) used in Example 1 was replaced with a cerium-zirconium-lanthanum-neodymium-praseodymium composite oxide (CeO ₂ / ZrO ₂ / La ₂ O ₃ / Nd ₂ O ₃ / Exhaust gas purifying filters were produced in the same manner as in Example 1 except that Pr ₆ O ₁₁ = 70/15/5/5/5).

[Example 6]
An exhaust gas purification filter was produced in the same manner as in Example 3 except that 20 g of cerium-zirconium composite oxide (CeO ₂ / ZrO ₂ = 20/80) was added to the slurry prepared in Example 3.

[Example 7]
An exhaust gas purification filter was produced in the same manner as in Example 1 except that the composite oxide (CeO ₂ / ZrO ₂ = 5/95) used in Example 1 was changed to MnO ₂ .

[Example 8]
An exhaust gas purifying filter was produced in the same manner as in Example 3 except that the alumina used in the preparation of the carrier in Example 3 was changed to ZrO ₂ .

[Example 9]
An exhaust gas purification filter was produced in the same manner as in Example 3 except that the amount of alumina used in the preparation of the carrier in Example 3 was changed from 10 g to 2 g.

[Example 10]
An exhaust gas purification filter was produced in the same manner as in Example 3 except that the amount of alumina used in the preparation of the carrier in Example 3 was changed from 10 g to 200 g.

[Example 11]
An exhaust gas purification filter was produced in the same manner as in Example 3 except that the amount of alumina used in the preparation of the carrier in Example 3 was changed from 10 g to 1 g.

[Example 12]
An exhaust gas purifying filter was produced in the same manner as in Example 3 except that the amount of alumina used in the preparation of the carrier in Example 3 was changed from 10 g to 250 g.

[Example 13]
An exhaust gas purifying filter was produced in the same manner as in Example 3 except that the amount of alumina used in the preparation of the carrier in Example 3 was changed from 10 g to 35 g.

[Example 14]
An exhaust gas purification filter was produced in the same manner as in Example 3 except that the amount of polyacrylamide used in the preparation of the carrier in Example 3 was changed from 10 g to 6 g.

[Example 15]
An exhaust gas purification filter was produced in the same manner as in Example 3 except that the amount of polyacrylamide used in the preparation of the carrier in Example 3 was changed from 10 g to 4 g.

[Example 16]
Exhaust gas purification as in Example 3, except that the alumina used in the preparation of the carrier in Example 3 was changed to cerium-zirconium composite oxide (CeO ₂ / ZrO ₂ = 0.5 / 99.5) A filter was manufactured.

[Comparative Example 1]
A filter for exhaust gas purification was produced in the same manner as in Example 3 except that the alumina used in the preparation of the support in Example 3 was changed to cerium-zirconium composite oxide (CeO ₂ / ZrO ₂ = 20/80). .

[Comparative Example 2]
An exhaust gas purification filter was produced in the same manner as in Example 3 except that the alumina used in the preparation of the carrier in Example 3 was not used.

[Comparative Example 3]
An exhaust gas purification filter was produced in the same manner as in Example 3 except that 20 g of MnO ₂ was used instead of 30 g of the carrier prepared in Example 3 to prepare the supported catalyst.

[Comparative Example 4]
An exhaust gas purification filter was produced in the same manner as in Example 3 except that the amount of alumina used in the preparation of the carrier in Example 3 was changed from 10 g to 0.5 g.

[Comparative Example 5]
An exhaust gas purification filter was produced in the same manner as in Example 3 except that the amount of alumina used in the preparation of the carrier in Example 3 was changed from 10 g to 300 g.

[Comparative Example 6]
An exhaust gas purification filter was produced in the same manner as in Example 3 except that the amount of polyacrylamide used in the preparation of the carrier in Example 3 was changed from 10 g to 3 g.

[Comparative Example 7]
An exhaust gas purification filter was produced in the same manner as in Example 3, except that the alumina used in the preparation of the support in Example 3 was changed to cerium-zirconium composite oxide (CeO ₂ / ZrO ₂ = 2/98). .

<Exhaust gas purification test>
The exhaust gas purifying filter manufactured in each of the examples and comparative examples was mounted on an actual vehicle having an engine with a displacement of 1.0 L after performing an endurance test equivalent to 80,000 km. Driving in JC08 mode, emissions of non-methane hydrocarbons (NMHC), carbon monoxide (CO), and nitrogen oxides (NOx) were measured. The results are shown in Tables 1 and 2. The results shown in Tables 1 and 2 are the combined values of Cold evaluation and Hot evaluation in JC08 mode.

  The relationship between the coating thickness of the coating material and the nitrogen oxide emission is shown in FIG. FIG. 1 shows the results of Examples 3 and 9 to 13 and Comparative Examples 4 and 5.

  FIG. 2 shows the relationship between the coverage of the oxygen storage / release material by the coating material and the discharge amount of nitrogen oxides. FIG. 2 shows the results of Examples 3, 14, and 15 and Comparative Example 6.

  FIG. 3 shows the relationship between the oxygen storage / release capacity of the coating material and the nitrogen oxide emission. FIG. 3 shows the results of Examples 3 and 16 and Comparative Examples 1 and 7.

Claims (6)

An oxygen storage / release material having an oxygen storage / release capability; and a coating material that is coated on the surface of the oxygen storage / release material and has an oxygen storage / release capability lower than the oxygen storage / release capability of the oxygen storage / release material;
A carrier for supporting an exhaust gas purification catalyst, wherein the coating material has a thickness of 50 to 500 µm.   The carrier according to claim 1, wherein a coverage of the oxygen storage / release material by the coating material is 60 to 100%. The carrier according to claim 1 or 2, wherein the covering material has an oxygen storage / release capacity of 0.001 (O ₂ ) mol / (coating material) mol or less.   A supported catalyst for purifying exhaust gas, comprising the carrier according to any one of claims 1 to 3 and a catalyst for purifying exhaust gas supported on the carrier. The exhaust gas purifying supported catalyst according to claim 4 and a filter base material,
An exhaust gas purifying filter in which the exhaust gas purifying supported catalyst is supported on the filter base material.   An exhaust gas purification method comprising the step of bringing the exhaust gas purification supported catalyst according to claim 4 or the exhaust gas purification filter according to claim 5 into contact with the exhaust gas.

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