WO2019187604A1 - Diesel oxidation catalyst powder and method for manufacturing same, and integrated structure-type exhaust gas purification catalyst - Google Patents

Abstract

Provided are a diesel oxidation catalyst powder and a method for manufacturing the same, and an integrated structure-type exhaust gas purification catalyst and the like, having excellent CO purification performance. This diesel oxidation catalyst powder is characterized by being provided with composite particles containing parent material particles including a ceria-zirconia based oxygen storing and releasing material, and a catalytic active component supported on the parent material particles, wherein the catalytic active component includes palladium having an oxidation number of 1 to 6, and the composite particles are subjected to surface modification using a reoxidant.

Description

Diesel oxidation catalyst powder, method for producing the same, and monolithic exhaust gas purification catalyst

The present invention relates to a diesel oxidation catalyst powder used for purifying exhaust gas discharged from a diesel engine, a method for producing the same, and an integral structure type exhaust gas purification catalyst.

Many proposals have been made on the purification technology of exhaust gas generated from an internal combustion engine. For example, as an exhaust gas purification device that purifies exhaust gas discharged from a diesel engine, diesel oxidation to purify harmful components such as carbon monoxide (CO), hydrocarbon (HC), and nitric oxide (NO) in the exhaust gas Diesel particulate filter (DPF: Diesel Particulate デ ィ ー ゼ ル Filler) for collecting catalyst (DOC: Diesel Oxidation Catalyst) and particulate matter (PM: Particulate matter) such as soot contained in exhaust gas Those arranged in the exhaust passage are widely known.

As the diesel oxidation catalyst, composite particles having base metal particles made of a metal oxide such as alumina, zirconia, and ceria, and a platinum group element (PGM: Platinum Group Metal) as a catalytic active component supported on this carrier are used. Commonly used.

As this type of exhaust gas purification catalyst, for example, Non-Patent Documents 1 and 2 disclose Pd-supported CeO ₂ . Non-Patent Document 3 discloses Pd-supported CeO ₂ —TiO ₂ .

Further, Patent Document 1 discloses an exhaust gas purifying oxidation catalyst containing a carrier made of AZ composite oxide or AZT composite oxide and a noble metal such as Pt or Pd. Patent Document 2 discloses a substrate B composed of a substrate A composed of an AZ composite oxide or an AZT composite oxide and an oxide containing at least one element selected from the group consisting of silicon, cerium, praseodymium and lanthanum. And an exhaust gas purifying oxidation catalyst containing noble metals such as Pt and Pd.

International Publication No. 2012/137930 International Publication No. 2014/129634

As represented by the exhaust gas regulation stage V enforced in the European Union (EU) from 2019, with the recent tightening of automobile exhaust gas regulations, further improvement in purification performance of exhaust gas purification catalysts is required. In addition, an idling stop mechanism has become widespread in response to requests for exhaust gas reduction and fuel efficiency improvement, and as a result, the exhaust gas temperature has been lowered. In particular, when the exhaust gas temperature is relatively low, such as when the engine is started or restarted, the amount of CO emission tends to increase compared to when the exhaust gas temperature is high. It has been. Further, in diesel engines, exhaust gas temperature tends to be lower than that of gasoline engines, and an exhaust gas purification catalyst having excellent CO purification performance in a low temperature region is strongly demanded.

The present invention has been made in view of the above problems. That is, an object of the present invention is to provide a diesel oxidation catalyst powder excellent in CO purification performance, a method for producing the same, and a monolithic exhaust gas purification catalyst.

In order to solve the above-mentioned problems, the present inventors diligently studied paying attention to the oxidation state of palladium which is a catalytically active component on the base material particles. As a result, it has been found that the surface of the composite particles can be modified with a reoxidant to suppress the deterioration of the oxidation catalyst performance with respect to CO, and the present invention has been completed.

That is, the present invention provides various specific modes shown below.
(1) It comprises composite particles containing base material particles containing a ceria zirconia-based oxygen storage / release material and a catalytically active component supported on the base material particle, wherein the catalytically active component is palladium having an oxidation number of 1 to 6 A diesel oxidation catalyst powder, wherein the composite particles are surface-modified with a reoxidant.
(2) The reoxidizer is at least one selected from the group consisting of clay minerals, zeolites, activated carbon, metal oxides, metal sulfides, metal salts, and metal composite oxides. Diesel oxidation catalyst powder.
(3) The diesel oxidation catalyst powder according to (1) or (2), wherein the reoxidant is contained in a total amount of 0.1 to 20% by mass with respect to the total amount of the powder.
(4) the re-oxidizing agent, the above has an average particle diameter _{D 50} of 1 ~ 200nm (1) ~ ( 3) diesel oxidation catalyst powder according to any one of.

(5) The diesel oxidation catalyst powder according to any one of (1) to (4), wherein a mass ratio of the palladium to the reoxidant is 1: 0.1 to 15.
(6) Any of the above (1) to (5), wherein the ratio of the average particle diameter D ₅₀ of the base material particles to the average particle diameter D ₅₀ of the reoxidant is 1: 0.00001 to 0.4 The diesel oxidation catalyst powder according to claim 1.
(7) The diesel oxidation catalyst powder according to any one of (1) to (6), wherein the palladium is contained in an amount of 0.1 to 10% by mass based on the total amount of the powder.
(8) the base particles is 0.5 above has an average particle diameter _{D 50} of ~ 100 [mu] m (1) ~ diesel oxidation catalyst powder according to any one of (7).
(9) The diesel oxidation catalyst powder according to any one of (1) to (8), wherein the base material particles have a BET specific surface area of 10 to 250 (m ² / g).

(10) Preparatory step of preparing base material particles containing ceria zirconia-based oxygen storage / release material, impregnating the surface of the base material particles with an aqueous solution containing at least palladium ions, and supporting palladium on the base material particles A composite particle forming step for producing composite particles, a surface modification step for impregnating the composite particles with an aqueous solution containing at least a reoxidant or a precursor thereof, and surface-modifying the composite particles with the reoxidant or a precursor thereof, And a method for producing a diesel oxidation catalyst powder, comprising at least a palladium forming step in which the composite particles are heat-treated or chemically treated to form palladium having an oxidation number of 1 to 6 on the surface of the base material particles.

(11) The method for producing diesel oxidation catalyst powder according to (10), wherein the palladium forming step is performed after the composite particle forming step and before the surface modification step.
(12) The method for producing a diesel oxidation catalyst powder according to (10) or (11), wherein the palladium formation step is performed after the surface modification step.
(13) The method for producing a diesel oxidation catalyst powder according to (10), wherein the surface modification step and the palladium formation step are performed simultaneously after the composite particle formation step.

(14) A diesel oxidation catalyst according to any one of (1) to (9), further comprising a catalyst carrier and a catalyst layer provided on at least one side of the catalyst carrier. A monolithic exhaust gas purifying catalyst comprising a powder.

ADVANTAGE OF THE INVENTION According to this invention, the diesel oxidation catalyst powder with improved CO purification performance, its manufacturing method, the integral structure type | mold exhaust gas purification catalyst using these, etc. are realizable. The diesel oxidation catalyst powder of the present invention is a catalyst particle having a composite structure in which a large number of minute catalytically active components are supported on base material particles, and is further surface-modified with a reoxidant, and the composition and Based on the structure and the like, it can be particularly suitably used as a catalyst material for reducing NOx, CO, HC, etc. in the exhaust gas. And since the diesel oxidation catalyst powder of the present invention has the same heat resistance as Al ₂ O ₃ particles and CZ particles, it can be mounted on an engine direct type catalytic converter, a direct type catalytic converter in a tandem arrangement, etc. Thereby, reduction of canning cost etc. can be aimed at.

It is a mimetic diagram showing a schematic structure of diesel oxidation catalyst powder 100 of one embodiment. It is explanatory drawing which shows the CO oxidation reaction mechanism in a prior art. It is explanatory drawing which shows the CO oxidation reaction mechanism in the diesel oxidation catalyst powder 100 of this embodiment. It is a timing chart which shows a DRIFTS analysis procedure. It is a graph which shows the DRIFTS analysis result of the comparative example 1. It is a graph which shows the DRIFTS analysis result of Example 1 and Comparative Example 1 (adsorption temperature 50 degreeC 30 minutes). It is a graph which shows the DRIFTS analysis result of Example 1 (temperature increase to 200 degreeC after adsorption temperature 50 degreeC 30 minutes). 3 is a graph showing CO purification performance of diesel oxidation catalyst powders of Example 1 and Comparative Example 1. It is a graph which shows COT50 of the diesel oxidation catalyst powder of Example 1 (calcination temperature 750 degreeC, calcination temperature 850 degreeC, calcination temperature 900 degreeC). 3 is a graph showing CO purification performance of the monolithic catalyst of Example 1 and Comparative Example 1.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. The positional relationship such as up, down, left, and right is based on the positional relationship shown in the drawings unless otherwise specified. Further, the dimensional ratios in the drawings are not limited to the illustrated ratios. However, the following embodiments are examples for explaining the present invention, and the present invention is not limited to these. In other words, the present invention can be implemented with any modifications without departing from the scope of the invention. In this specification, for example, the description of a numerical range of “1 to 100” includes both the upper limit value “100” and the lower limit value “1”. This also applies to other numerical range notations.

FIG. 1 is a schematic diagram showing a composite particle structure of a diesel oxidation catalyst powder 100 according to an embodiment of the present invention. The diesel oxidation catalyst powder 100 includes composite particles 31 containing base material particles 11 containing a ceria zirconia-based oxygen storage / release material, and catalytically active components 21 supported on the surfaces 11a of the base material particles 11, and a catalyst. The active component 21 contains palladium having an oxidation number of 1 to 6 (hereinafter sometimes simply referred to as “palladium”), and the composite particle 31 is surface-modified with a reoxidant 41 It is. Hereinafter, each component will be described in detail.

The base material particles 11 are carrier particles for supporting the catalytic active component 21 on the surface 11a. In the diesel oxidation catalyst powder 100 of the present embodiment, a ceria zirconia-based oxygen storage / release material that not only has excellent oxygen storage / capacity (Oxygen Storage Capacity) but also relatively excellent heat resistance is used as the base material particle 11. By using it, CO purification performance and heat resistance are improved.

Here, in this specification, the “ceria zirconia-based oxygen storage / release material” means a composite oxide containing ceria (CeO ₂ ) and zirconia (ZrO ₂ ) in terms of oxide. Specifically, it is used as a concept including ceria zirconia or a complex oxide or solid solution doped with other elements. More specifically, it means a composite oxide or solid solution containing ceria (CeO ₂ ) and zirconia (ZrO ₂ ), or a composite oxide or solid solution doped with elements other than cerium and zirconium. The ceria zirconia-based oxygen storage / release material is preferably ceria zirconia, which has an excellent balance between oxygen storage / release capability and heat resistance, and a ceria zirconia-based composite oxide in which a rare earth element other than cerium and zirconium is further dissolved is also preferably used. It is done. As the ceria zirconia-based oxygen storage / release material, a material in which the mass ratio of Ce and Zr is 50% by mass to 95% by mass in terms of oxide (CeO ₂ and ZrO ₂ ) is preferably used.

Here, the ceria zirconia-based oxygen storage / release materials are scandium, yttrium, lanthanum, praseodymium, neodymium, promethium, samarium, eurobium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, and lutetium. Other rare earth elements (hereinafter, may be referred to as “other rare earth elements”). Among these, yttrium, lanthanum, praseodymium, and neodymium are preferable. Other rare earth elements can be used singly or in appropriate combination of two or more. When other rare earth elements are included, the content ratio is not particularly limited, but the total amount of other rare earth elements described above in terms of oxide (for example, La ₂ O ₃ , Nd ₂₎ with respect to the total amount of the base material particles 11. O ₃ , Pr ₅ O _11, etc.) is preferably 0.1% by mass or more, more preferably 3% by mass or more, further preferably 5% by mass or more, preferably 50% by mass or less, and preferably 45% by mass or less. More preferred is 40% by mass or less.

The ceria zirconia-based oxygen storage / release material may contain transition elements such as chromium, cobalt, iron, nickel, titanium, manganese, and copper. A transition element can be used individually by 1 type or in combination of 2 or more types as appropriate. When the transition element is included, the content ratio is not particularly limited, but the total amount of the transition element described above in terms of oxide of the transition element (for example, the total sum of Fe ₂ O ₃ , TiO _2, etc.) 0.01 mass% or more is preferable, 0.1 mass% or more is more preferable, 0.5 mass% or more is more preferable, 10 mass% or less is preferable, 5 mass% or less is more preferable, and 3 mass% or less. Is more preferable.

In the above ceria zirconia-based oxygen storage / release material, some of cerium and zirconium are alkali metal elements such as lithium, sodium and potassium, and alkaline earth metal elements such as beryllium, magnesium, calcium, strontium and barium. May be substituted. Moreover, an alkali metal element and an alkaline-earth metal element can each be used individually by 1 type or in arbitrary combinations and ratios of 2 or more types. The ceria zirconia oxygen storage / release material may contain hafnium (Hf), which is usually contained in the zirconia ore in an amount of about 1 to 2% by mass, as an inevitable impurity.

The average particle diameter D ₅₀ of the base particles 11 may be appropriately set according to the desired performance, not particularly limited. From the viewpoint of maintaining a large specific surface area and increasing the number of the catalytically active sites by increasing the heat resistance, the average particle diameter D ₅₀ of the base material particles 11 is preferably 0.5 to 100 μm, and preferably 1 to 100 μm. Is more preferable, and 1 to 50 μm is more preferable. In the present specification, the average particle diameter D ₅₀ of the base material particle 11 is measured by a laser diffraction particle size distribution measuring device (for example, a laser diffraction particle size distribution measuring device SALD-3100 manufactured by Shimadzu Corporation). Means the median diameter. In this specification where the average particle diameter D ₅₀ of the base particles 11 may vary during the combined grain formation and surface modification during and palladium forming, aging the diesel oxidation catalyst powder 100 to be measured (durability It means a value measured using a sample subjected to treatment. This durability treatment is performed for the purpose of stabilizing the running performance of the catalyst powder.

The BET specific surface area of the base material particle 11 can be appropriately set according to the desired performance, and is not particularly limited. However, from the viewpoint of maintaining a large specific surface area and increasing the catalytic activity, the BET specific surface area by the BET single point method is used. Is preferably 10 to 250 m ² / g, more preferably 20 to 150 m ² / g, and still more preferably 30 to 120 m ² / g. Here, in this specification, the BET specific surface area of the diesel oxidation catalyst powder 100 may vary during composite particle formation, surface modification, or palladium formation, but is measured using the diesel oxidation catalyst powder 100 after endurance treatment as a sample. Means the value to be

As the base material particle 11, in addition to the above-described base material particle containing the ceria zirconia-based oxygen storage / release material, other base material particles, for example, metal oxide particles such as alumina, ceria, zirconia, and other rare earths are used. Metal composite oxide particles doped with elements and / or transition elements, perovskite oxide particles, and the like may be included.

The ceria zirconia oxygen storage / release materials described above are commercially available in various grades from domestic and foreign manufacturers, and various grades of commercially available products can be used as the base material particles 11 of the present embodiment according to the required performance. it can. The ceria zirconia oxygen storage / release material having the above-described composition can also be produced by a method known in the art. Although it does not specifically limit as a manufacturing method, A powder mixing method, a hydrothermal method, a coprecipitation method, an alkoxide method etc. are mentioned, Among these, a coprecipitation method and an alkoxide method are preferable.

As the coprecipitation method, for example, an alkaline substance is added to an aqueous solution in which a cerium salt and a zirconium salt and other rare earth metal elements and transition elements to be blended as necessary are mixed at a predetermined stoichiometric ratio. A production method in which hydrolysis or coprecipitation of the precursor is performed and the hydrolysis product or coprecipitate is fired is preferable. The kind of various salt used here is not specifically limited. In general, hydrochloride, oxyhydrochloride, nitrate, oxynitrate, carbonate, phosphate, acetate, oxalate, citrate and the like are preferable. Moreover, the kind of alkaline substance is not particularly limited. In general, an aqueous ammonia solution is preferred. As the alkoxide method, for example, a mixture obtained by mixing cerium alkoxide and zirconium alkoxide with other rare earth metal elements and transition elements to be blended as necessary at a predetermined stoichiometric ratio is hydrolyzed and then fired. A manufacturing method is preferable. The kind of alkoxide used here is not particularly limited. In general, methoxide, ethoxide, propoxide, isopropoxide, butoxide, and these ethylene oxide adducts are preferable. Further, the rare earth metal element may be blended as a metal alkoxide or as the various salts described above.

The firing conditions may be in accordance with conventional methods and are not particularly limited. The firing atmosphere may be any of an oxidizing atmosphere, a reducing atmosphere, and an air atmosphere. The firing temperature and treatment time vary depending on the desired composition and the stoichiometric ratio, but from the viewpoint of productivity, etc., generally, it is preferably 150 ° C. or more and 1300 ° C. or less and 1 to 12 hours, more preferably Is 350 to 800 ° C. for 2 to 4 hours. Prior to the high-temperature firing, it is preferable to perform drying under reduced pressure using a vacuum dryer or the like, and to perform a drying treatment at 50 to 200 ° C. for about 1 to 48 hours.

On the base material particle 11, palladium is supported in a highly dispersed manner as the catalytic active component 21. Palladium used here is indispensable as a catalytically active component from the viewpoint of excellent oxidation catalyst performance for carbon monoxide (CO) and hydrocarbons (HC). In addition, the oxidation number of palladium is currently known as 0, 1, 2, 4, and 6. However, the oxidation number is not particularly limited. Among these, monovalent palladium Pd (I) (Pd ₂ O) and divalent palladium Pd (II) (PdO) are preferable because they can be used relatively stably.

In addition, if necessary, a compound such as a platinum group element other than palladium (hereinafter, simply referred to as “other platinum group element”) or an oxide thereof is used as the catalytic active component 21 of the base material particle 11. It may be carried on the surface 11a. That is, at least one selected from the group consisting of Pt, Pd, Ir, Rh, Ru, and Os may be carried on the surface 11 a of the base material particle 11. Among these, as other platinum group elements, Pt and Rh are preferable from the viewpoint of excellent oxidation catalyst performance with respect to carbon monoxide (CO) and hydrocarbons (HC), and Pt is more in view of cost. preferable. Furthermore, you may contain noble metal elements (PM) other than the platinum group element mentioned above, ie, gold (Au), and silver (Ag) as needed. However, in consideration of economy, stable supply, use under high temperature conditions, and the like, it is preferable that the noble metal element other than the platinum group element described above is not substantially contained. Here, substantially not containing means that the total amount of gold and silver described above is in the range of 0% by mass or more and less than 1.0% by mass with respect to the total amount of the diesel oxidation catalyst powder 100. More preferably, it is 0 mass% or more and less than 0.5 mass%, More preferably, it is 0 mass% or more and less than 0.3 mass%.

Loading of palladium on base particles 11 (content), taking into account the materials and the average particle diameter D ₅₀ of the base particles 11 such as may be appropriately set depending on the desired performance, but are not limited to, catalyst From the viewpoint of balance between activity and cost, etc., in terms of the amount of Pd metal with respect to the total amount of the diesel oxidation catalyst powder 100, 0.1 to 10% by mass is preferable, 0.5 to 5% by mass is more preferable, and 0.8 to 3% by mass is more preferable.

Further, when other platinum group elements are contained, the content ratio of the other platinum group elements and palladium (other platinum group elements: palladium) may be appropriately set according to the desired performance.

The average particle diameter of the catalytically active particles on the base material particle 11 may be appropriately set according to the desired performance in consideration of the material, pore diameter, etc. of the base material particle 11 and is not particularly limited. From the viewpoints of further enhancing the catalytic activity and suppressing sintering and grain growth, the average particle diameter of palladium is preferably 20 nm or less, more preferably 15 nm or less, and even more preferably 10 nm or less. In addition, the minimum of the average particle diameter of palladium is not specifically limited, For example, 1 nm or more is preferable. By making the catalyst active component 21 having such a fine particle size exist on the surface 11a of the base material particle 11 in a highly dispersed state, high catalyst activity tends to be easily obtained. In the present specification, the average particle size of the catalytically active component 21 is an average value of 200 points randomly extracted from a STEM image with a magnification of 10,000. Further, the average particle diameter of palladium may vary during composite particle formation, surface modification, or palladium formation. The sample used at this time is the diesel oxidation catalyst powder 100 after the endurance treatment.

In the diesel oxidation catalyst powder 100 of the present embodiment, as described above, the structure of the composite particle 31 in which palladium having an oxidation number of 1 to 6 is supported on the surface 11a of the base material particle 11 as the catalytic active component 21 in a highly dispersed manner. In addition, the composite particle 31 is characterized by being surface-modified with a reoxidant 41 that oxidizes metallic palladium. The reason why the surface modification of the reoxidant 41 improves the oxidation catalyst performance of CO by palladium is not clear, but is presumed as follows.

As shown in FIG. 2, the oxidation reaction of CO on palladium supported on the base material particle 11 is as follows: (a) adsorption of CO on the surface of palladium such as Pd ₂ O and PdO; (b) on palladium. CO oxidation (CO ₂ production) and accompanying palladium reduction (metal palladium Pd ⁰ production), (c) oxygen adsorption to metal palladium Pd ⁰ by external oxygen supply, and metal palladium accompanying this There is a three-step reaction mechanism of oxidation of Pd ⁰ (production of palladium having an oxidation number of 1 to 6), and these steps (a) to (c) are considered to be repeated.

However, according to the findings of the present inventors, in the reaction mechanism of the (c), CO adsorption to metal palladium Pd ⁰ is competitively caused the oxygen adsorption, moreover CO adsorption kinetic advantage proceeded Turned out to be. In addition, it has been found that CO adsorption onto metallic palladium Pd includes, for example, linear adsorption of Pd ⁺ or Pd ²⁺ —CO and relatively stable (Pd ⁰ ) ₂ —CO bridge adsorption. Then, CO adsorption proceeds more preferentially than oxygen adsorption to metal palladium Pd ⁰ , and once the bridge-type adsorption of CO occurs on metal palladium Pd, the supply of oxygen to metal palladium Pd ⁰ is inhibited. It is considered that the return from the stage c) to the stage (a) is the rate-limiting stage in the oxidation reaction of CO on palladium.

On the other hand, in the diesel oxidation catalyst powder 100 of the present embodiment, since the surface is modified with the reoxidant 41 as well as having the composite particle structure described above, the reoxidant is used in the reaction mechanism (c). Oxidation by 41 allows the metal palladium Pd ⁰ to oxidize preferentially. That is, as shown in FIG. 3, in the diesel oxidation catalyst powder 100 of the present embodiment, the metal palladium Pd ⁰ is rapidly oxidized, and the generation of bridge type adsorption of (Pd ⁰ ) ₂ —CO is suppressed. It is presumed that the reduction in CO oxidation performance is suppressed. However, the action is not particularly limited to these.

The adsorption of CO can be detected based on Diffuse Reflectance Infrared Fourier Transform Spectroscopy (hereinafter referred to as DRIFTS). The linear adsorption of CO (Pd ⁰ —CO, Pd ⁺ —CO, Pd ²⁺ —CO) has a peak of 2080 to 2160 cm ⁻¹ , and the bridge adsorption of CO ((Pd ⁰ ) ₂ —CO) ranges from 1960 to 2000 cm ^−. Each peak can be identified as ^one peak. Specifically, linear type adsorption of Pd ²⁺ -CO has a peak of 2140 cm ⁻¹ , linear type adsorption of Pd ⁺ —CO has a peak of 2100 cm ⁻¹ , and bridge type adsorption of (Pd ⁰ ) ₂ —CO has a peak of 1980 cm. ^-1 peaks are observed.

The kind of reoxidant 41 described above is not particularly limited as long as it can oxidize metallic palladium. As the reoxidant 41, various inorganic compounds that function as a solid acid with respect to metallic palladium can be suitably used. Specifically, clay minerals such as kaolinite, montmorillonite, saponite; structures having structures such as FAU, BEA, MOR, MFI, MEL, CHA, FER, AEI, AFL, AFX, LEV, KFI, USY; Activated carbon; metal oxides such as ZnO, Al ₂ O ₃ , FeO, Fe ₂ O ₃ , CoO, Co ₃ O ₄ , Cr ₂ O ₃ , CuO, ZrO ₂ , and TiO ₂ ; metal sulfides such as CdS and ZnS; Examples thereof include metal salts such as MgSO ₄ , FeSO ₄ , AlPO ₄ , and AlCl ₃ , and metal composite oxides such as SiO ₂ —Al ₂ O ₃ , SiO ₂ —TiO ₂ , SiO ₂ —MgO, and TiO ₂ —ZrO _2. However, it is not particularly limited to these. Among these, zeolite, activated carbon, metal oxide, metal sulfide, metal salt, and metal composite oxide are preferable, and zeolite, metal oxide, metal salt, and metal composite oxide are more preferable. Each of these may be used alone or in any combination and proportion of two or more.

As described above, the reoxidant 41 used here is preferably in the form of a surface that can be highly dispersed with respect to the composite particles 31, specifically, solid fine particles at room temperature (25 ° C.). By using the reoxidant 41 that can be supported in a highly dispersed manner on the composite particles 31, the reoxidant 41 can be interposed between the catalytic active components 21 on the base material particles 11 of the composite particles 31. Thus, grain growth due to sintering between the catalytically active components 21 is suppressed, and as a result, deterioration of catalyst performance can also be suppressed. When the reoxidant 41 is fine particles that are solid at room temperature, the average particle diameter D ₅₀ may be appropriately set according to the desired performance, and is not particularly limited. From the viewpoint of obtaining high catalytic activity, it is preferably 1 to 200 nm, more preferably 5 to 180 nm, still more preferably 7 to 150 nm, and particularly preferably 10 to 70 nm. In the present specification, the average particle diameter D ₅₀ of the reoxidant 41 of the composite particles 31 of the diesel oxidation catalyst powder 100 is a dynamic light scattering / photon correlation method apparatus (for example, SZ-100 manufactured by HORIBA). Means the median diameter measured in The average particle diameter D ₅₀ of the re-oxidizing agent 41, may vary when the composite particles formed during or surface modification during or palladium formed, the sample used here is a diesel oxidation catalyst powder 100 after the durability treatment.

The ratio from the viewpoint of performing surface modification of the composite particles 31 due to the re-oxidizing agent 41 uniformly, the average particle diameter D ₅₀ of the average particle diameter D ₅₀ and the re-oxidizing agent 41 of the base particles 11, 1: 0 0.0001 to 0.4 is preferable, 1: 0.0005 to 0.035 is more preferable, and 1: 0.001 to 0.030 is more preferable. As described above, by using the extremely fine reoxidant 41 for the base material particles 11, the surface modification tends to be easily performed uniformly and uniformly. The average particle diameter D ₅₀ of the base particles 11 and re-oxidizing agent 41, may vary when the composite particles formed during or surface modification during or palladium formed, the sample used here, the diesel oxidation catalyst powder after the durability treatment 100.

Loading of reoxidation agent 41 (content), material and average particle diameter D ₅₀ and the specific surface area of the base particles 11, further it may be appropriately set depending on the desired performance in view of the palladium supporting amount or the like, Although not particularly limited, from the viewpoint of catalytic activity and the like, the total amount of the diesel oxidation catalyst powder 100 is preferably 0.1 to 20% by mass, more preferably 0.5 to 15% by mass, 0.8% More preferably, it is 12% by mass.

Here, the content ratio of the palladium and the reoxidant 41 may be appropriately set according to the desired performance, and is not particularly limited. However, the reoxidant 41 is supported in a highly dispersed manner near the palladium. From the viewpoint of promoting the oxidation reaction by 41, palladium (metal amount conversion): reoxidant is preferably 1: 0.1 to 15, more preferably 1: 0.3 to 13, and 1: 0.5 to 10 Further preferred.

The diesel oxidation catalyst powder 100 according to the present embodiment is manufactured by various known powders as long as the composite particles 31 in which palladium is supported on the base material particles 11 and surface-modified with the reoxidant 41 are obtained as described above. A manufacturing method can be applied, and the kind thereof is not particularly limited. From the viewpoint of producing the above-described diesel oxidation catalyst powder 100 having a composite particle structure with good reproducibility and at low cost, the evaporation to dryness method (impregnation method) or the like is preferable.

Hereinafter, the typical evaporative drying method will be described in detail. In this example, first, the base material particles 11 described above are impregnated with an aqueous solution containing at least palladium ions, and palladium is supported on the surfaces 11a of the base material particles 11 (composite particle forming step S1). By this first impregnation treatment, palladium is adsorbed (attached) to the surface 11a of the base material particle 11 in a highly dispersed state. At this time, the average particle diameter D ₅₀ of the base material particles 11 used as the raw material is not particularly limited, but is preferably 1 to 80 μm, more preferably 1 to 70 μm, and further preferably 1 to 60 μm. Here, palladium ion can be mix | blended with aqueous solution as various salts. The kind of various salt used here is not specifically limited. In general, sulfate, hydrochloride, oxyhydrochloride, nitrate, oxynitrate, carbonate, oxycarbonate, phosphate, acetate, oxalate, citrate, chloride, oxide, complex oxidation And a complex salt are preferable. Moreover, the content rate of the palladium ion in aqueous solution can be suitably adjusted so that it may become a desired content rate in the diesel oxidation catalyst powder 100 obtained, and it is not specifically limited.

After the impregnation treatment, if necessary, a solid-liquid separation treatment, a water washing treatment, for example, a drying treatment for removing moisture at a temperature of about 50 ° C. to 200 ° C. in the atmosphere for about 1 to 48 hours is performed according to a conventional method. be able to. The drying treatment may be natural drying, or a drying apparatus such as a drum dryer, a vacuum dryer, or spray drying may be used. The atmosphere during the drying treatment may be any of air, vacuum, and inert gas atmosphere such as nitrogen gas. In addition, you may perform a grinding | pulverization process, a classification process, etc. further before and after drying as needed.

Next, after the composite particle forming step S1, the obtained palladium-supporting base material particles (composite particles 31) are impregnated with an aqueous solution containing at least the reoxidant 41 or a precursor thereof, and the composite particles are used. Surface modification is performed with the reoxidant 41 or a precursor thereof (surface modification step S2). By this second impregnation treatment, the reoxidant 41 is adsorbed (attached) to the surfaces of the composite particles 31 (the surface of the base material particles 11 and the surface of palladium as the catalytically active component 21) in a highly dispersed state. At this time, when the reoxidant 41 itself is used as a raw material, the average particle diameter D ₅₀ is not particularly limited, but is preferably 1 to 150 nm, more preferably 1 to 120 nm, and further preferably 1 to 90 mn. Moreover, when using the precursor of the reoxidant 41 as a raw material, it can mix | blend with aqueous solution as various salt mentioned above. The kind of various salt used here is not specifically limited. In general, sulfate, hydrochloride, oxyhydrochloride, nitrate, oxynitrate, carbonate, oxycarbonate, phosphate, acetate, oxalate, citrate, chloride, oxide, complex oxidation And a complex salt are preferable. Moreover, the content rate of the reoxidant 41 or its precursor in aqueous solution can be suitably adjusted so that it may become a desired content rate in the diesel oxidation catalyst powder 100 obtained, and is not specifically limited.

After the impregnation treatment, if necessary, a solid-liquid separation treatment, a water washing treatment, for example, a drying treatment for removing moisture at a temperature of about 50 ° C. to 200 ° C. in the atmosphere for about 1 to 48 hours is performed according to a conventional method. be able to. The drying treatment may be natural drying, or a drying apparatus such as a drum dryer, a vacuum dryer, or spray drying may be used. The atmosphere during the drying treatment may be any of air, vacuum, and inert gas atmosphere such as nitrogen gas. In addition, you may perform a grinding | pulverization process, a classification process, etc. further before and after drying as needed.

Next, heat treatment or chemical treatment is performed to convert palladium adsorbed (attached) on the surface 11a of the base material particle 11 in a highly dispersed state into palladium having an oxidation number of 1 to 6, whereby the diesel oxidation catalyst powder 100 of the present embodiment is obtained. It can be obtained (palladium forming step S3). At this time, it is usually preferable to use relatively stable palladium oxide (Pd ₂ O, PdO). Further, when the precursor of the reoxidant 41 is used as a raw material, it is preferable to form the reoxidant 41 from the precursor of the reoxidant 41 in this palladium formation step S3.

The heat treatment conditions are not particularly limited as long as they follow a conventional method. A heating means is not specifically limited, For example, well-known apparatuses, such as an electric furnace and a gas furnace, can be used. The firing atmosphere may be any of an oxidizing atmosphere, an air atmosphere, and a reducing atmosphere, and an oxidizing atmosphere and an air atmosphere are preferable. The firing temperature and treatment time vary depending on the desired performance, but from the viewpoint of the production and productivity of the platinum group catalytically active component 21, it is generally from 0.1 to 12 at 500 ° C. to 1100 ° C. Time is preferred, more preferably 550 ° C. to 800 ° C. for 0.5 to 6 hours.

Also, chemical treatment can be performed instead of the heat treatment or together with the heat treatment. For example, palladium ions may be hydrolyzed on the surfaces 11 a of the base material particles 11 using a basic component after the impregnation treatment in the evaporation to dryness method. The basic component used here is preferably an amine such as ammonia or ethanolamine, an alkali metal hydroxide such as caustic soda or strontium hydroxide, or an alkaline earth metal hydroxide such as barium hydroxide. By these heat treatment and chemical treatment, palladium highly dispersed in nano-order size is generated on the surface 11 a of the base material particle 11.

In the above typical example, the composite particle forming step S1, the surface modifying step S2, and the palladium forming step S3 are performed in this order. However, the order of the steps is not limited to this. For example, the composite particle formation step S1, the palladium formation step S3, and the surface modification step S2 can be performed in this order. Moreover, it can also carry out in order of surface modification process S2, composite particle formation process S1, and palladium formation process S3. Furthermore, after performing composite particle formation process S1, surface modification process S2 and palladium formation process S3 can also be performed simultaneously.

The diesel oxidation catalyst powder 100 thus obtained can be used as a powder which is an aggregate of catalyst particles, and is mixed with a catalyst, a cocatalyst, a catalyst carrier known in the art, and an additive known in the art. Can be used. At this time, the diesel oxidation catalyst powder 100 can be used as a co-catalyst together with another catalyst (main catalyst), or another catalyst (co-catalyst) can be used in combination with the diesel oxidation catalyst powder 100. That is, the usage mode of the diesel oxidation catalyst powder 100 is not particularly limited, and can be used in a mode known in the art. Furthermore, the diesel oxidation catalyst powder 100 can be prepared as a composition containing the catalyst in advance and molded into an arbitrary predetermined shape, for example, to be used as a granular or pellet-shaped molded body (molded catalyst). Various known dispersing devices, kneading devices, and molding devices can be used for producing the molded body. When used as a compact here, the content of the diesel oxidation catalyst powder 100 in the compact is not particularly limited, but is preferably 10% by mass or more and 99% by mass or less, more preferably 20% by mass or more and 99% by mass with respect to the total amount. % Or less, more preferably 30% by mass or more and 99% by mass or less.

Furthermore, the diesel oxidation catalyst powder 100 can be held (supported) on a catalyst carrier and used as an integral structure type exhaust gas purification catalyst. As the catalyst carrier used here, those known in the art can be appropriately selected. Typical examples include ceramic monolith carriers such as cordierite, silicon carbide, silicon nitride, metal honeycomb carriers such as stainless steel, wire mesh carriers such as stainless steel, and steel wool knit wire carriers. There is no particular limitation. Further, the shape is not particularly limited, and any shape such as a prismatic shape, a cylindrical shape, a spherical shape, a honeycomb shape, or a sheet shape can be selected. These can be used individually by 1 type or in combination of 2 or more types as appropriate.

Known catalysts, promoters and catalyst carriers that can be used in combination include, for example, metal oxides or metal composite oxides such as silica, alumina, lanthanum oxide, neodymium oxide, praseodymium oxide, perovskite oxides, silica-alumina, Composite oxides containing alumina such as silica-alumina-zirconia, silica-alumina-boria; barium compounds, zeolites, and the like are exemplified, but not limited thereto. In addition, the use ratio of the catalyst, cocatalyst, and catalyst carrier used in combination can be appropriately set according to the required performance and the like, and is not particularly limited. The total is more preferably 0.05% by mass or more and 10% by mass or less, and the total is more preferably 0.1% by mass or more and 8% by mass or less.

Examples of additives that can be used in combination include various binders, dispersion stabilizers such as nonionic surfactants and anionic surfactants, pH adjusters, viscosity adjusters, and the like, but are not particularly limited thereto. . Examples of the binder include various sols such as alumina sol, titania sol, silica sol, and zirconia sol, but are not particularly limited thereto. Soluble salts such as aluminum nitrate, aluminum acetate, titanium nitrate, titanium acetate, zirconium nitrate, and zirconium acetate can also be used as the binder. In addition, acids such as acetic acid, nitric acid, hydrochloric acid, and sulfuric acid can also be used as the binder. In addition, the usage-amount of a binder is not specifically limited, What is necessary is just a quantity required for maintenance of a molded object. The use ratio of the above-mentioned additives can be appropriately set according to the required performance and is not particularly limited, but is preferably 0.01 to 20% by mass in total with respect to the total amount, and 0.05 to 10% by mass in total. %, More preferably 0.1 to 8% by mass in total.

The diesel oxidation catalyst powder 100 obtained as described above may further carry a noble metal element or a platinum group element as necessary. The method for supporting the noble metal element or the platinum group element is not particularly limited, and a known method can be applied. For example, by preparing a salt solution containing a noble metal element or a platinum group element, impregnating the diesel oxidation catalyst powder 100 with this salt-containing solution, performing a drying treatment as necessary, and then firing, a noble metal element or The platinum group element can be supported. The salt-containing solution is not particularly limited, but an aqueous nitrate solution, dinitrodiammine nitrate solution, aqueous chloride solution and the like are preferable. Further, the baking treatment is not particularly limited, but is preferably from 0.1 to 12 hours at from 500 ° C. to 1100 ° C., more preferably from 0.5 to 6 hours at from 550 ° C. to 800 ° C. The temperature is preferably 350 ° C. or more and 1000 ° C. or less for about 1 to 12 hours.

The diesel oxidation catalyst powder 100 of the present embodiment can be used by being blended with the catalyst layer of the monolithic exhaust gas purification catalyst. This monolithic exhaust gas purifying catalyst is a catalyst member having a laminated structure including at least a catalyst carrier and a catalyst layer provided on at least one surface side of the catalyst carrier. By adopting such a configuration, the applicability to various uses such as easy incorporation into the apparatus increases. For example, in exhaust gas purification applications, a honeycomb structure carrier or the like is used as a catalyst carrier, the monolithic laminated catalyst member is installed in a flow path through which the gas flow passes, and the gas flow is allowed to pass through the cells of the honeycomb structure carrier. Thus, exhaust gas purification can be performed with high efficiency.

Here, in this specification, “provided on at least one surface side of the catalyst carrier” means any other layer (for example, primer layer, adhesive layer) between the one surface of the catalyst carrier and the catalyst layer. Etc.) is included. That is, in this specification, “provided on one side” means an aspect in which the catalyst carrier and the catalyst layer are directly placed, and the catalyst carrier and the catalyst layer are separated via any other layer. It is used in the meaning including both arranged modes. Further, the catalyst layer may be provided on only one surface of the catalyst carrier, or may be provided on a plurality of surfaces (for example, one main surface and the other main surface).

Such an integral structure type exhaust gas purification catalyst can be implemented, for example, by providing a catalyst layer containing the diesel oxidation catalyst powder 100 of the present embodiment on a catalyst carrier such as the ceramic monolith carrier described above. In addition, the catalyst area of the monolithic exhaust gas purifying catalyst may be a single layer having only one catalyst layer or a laminate composed of two or more catalyst layers. Any of the laminates in combination with one or more other known layers may be used. For example, when the monolithic exhaust gas purification catalyst has a multilayer structure having at least an oxygen storage layer and a catalyst layer on a catalyst carrier, at least the catalyst layer contains the diesel oxidation catalyst powder 100 of the present embodiment. Therefore, it is possible to obtain an exhaust gas purification catalyst having an integral structure that is excellent in purification performance. Here, considering the trend of stricter exhaust gas regulations, the layer structure is preferably two or more layers.

The monolithic exhaust gas purifying catalyst having the layer structure described above can be manufactured according to a conventional method. For example, it can be obtained by coating (supporting) the above-described diesel oxidation catalyst powder 100 on the surface of the catalyst carrier. The method for applying the slurry-like mixture to the catalyst carrier may be performed according to a conventional method, and is not particularly limited. Various known coating methods, wash coating methods, and zone coating methods can be applied. Then, after the application of the slurry-like mixture, a monolithic exhaust gas purification catalyst having a catalyst layer containing the diesel oxidation catalyst powder of the present embodiment can be obtained by drying and firing according to a conventional method. .

Specific examples include, for example, the above-described diesel oxidation catalyst powder 100, an aqueous medium, and a binder, other catalyst, co-catalyst, OSC material, various base material particles, additives, and the like known in the art as required. A monolithic structure type having the above-mentioned layer structure by preparing a slurry-like mixture by mixing at a blending ratio of the above, applying the obtained slurry-like mixture to the surface of a catalyst carrier such as a honeycomb structure carrier, drying and firing. An exhaust gas purifying catalyst can be obtained.

The aqueous medium used for preparing the slurry mixture may be an amount that allows the exhaust gas purifying catalyst to be uniformly dispersed in the slurry. At this time, if necessary, an acid or a base for adjusting the pH can be blended, or a surfactant, a dispersing resin or the like can be blended for adjusting the viscosity or improving the slurry dispersibility. From the viewpoint of firmly attaching or bonding the diesel oxidation catalyst powder described above to the support, it is preferable to use the above-described binder or the like. Moreover, as a mixing method of a slurry, a well-known grinding | pulverization method or mixing methods, such as a grinding | pulverization mixing with a ball mill etc., are applicable.

After applying the slurry-like mixture on the catalyst carrier, drying and calcination can be performed according to conventional methods. The drying temperature is not particularly limited, but is preferably 70 to 200 ° C., for example, and more preferably 80 to 150 ° C. The firing temperature is not particularly limited, but is preferably 300 to 650 ° C., for example, and more preferably 400 to 600 ° C. About the heating means used at this time, it can carry out by well-known heating means, such as an electric furnace and a gas furnace, for example.

In the above-mentioned integrated structure type catalyst, the layer structure of the catalyst layer may be either a single layer or multiple layers. However, in the case of automotive exhaust gas applications, the catalyst performance is considered in consideration of the trend of stricter exhaust gas regulations. From the viewpoint of increasing the thickness, a laminated structure of two or more layers is preferable. At this time, the total coating amount of the diesel oxidation catalyst powder 100 described above is not particularly limited, but is preferably 20 to 350 g / L, more preferably 50 to 300 g / L, from the viewpoint of the catalyst performance and the balance of pressure loss.

The diesel oxidation catalyst powder 100 described above can be used as a catalyst for purifying exhaust gas of, for example, a diesel engine, gasoline engine, jet engine, boiler, gas turbine, etc. It is useful as an oxidation catalyst powder.

Also, the above-described monolithic exhaust gas purification catalyst can be disposed in the exhaust system of various engines. The number and location of the monolithic exhaust gas purification catalyst can be appropriately designed according to exhaust gas regulations. For example, when exhaust gas regulations are strict, the number of installation locations can be two or more, and the installation location can be arranged at the lower floor position behind the catalyst directly under the exhaust system. And according to the catalyst composition containing the diesel oxidation catalyst powder 100 and the monolithic exhaust gas purification catalyst of the present embodiment, various travel specifications including not only the start at low temperature but also the high speed travel at high temperature. Can exhibit an excellent effect on the purification reaction of CO, HC and NOx.

Hereinafter, the characteristics of the present invention will be described more specifically with reference to test examples, examples and comparative examples, but the present invention is not limited to these. That is, the materials, amounts used, ratios, processing details, processing procedures, and the like shown in the following examples can be changed as appropriate without departing from the spirit of the present invention. In addition, various production conditions and evaluation result values in the following examples have a meaning as a preferable upper limit value or a preferable lower limit value in the embodiment of the present invention, and a preferable range is the above-described upper limit or lower limit value. And a range defined by a combination of values of the following examples or values of the examples.

Average particle diameter _{D 50} of the base particles]
Using a laser diffraction type particle size distribution measuring device (manufactured by Shimadzu Corporation, laser diffraction type particle size distribution measuring device SALD-3100), the particle size distribution of the base material particles is measured, and the median diameter is the average particle size D of the base material particles. ₅₀ .

[Average particle diameter of reoxidant D ₅₀ ]
Dynamic light scattering, photon correlation spectroscopy apparatus (HORIBA Co., SZ-100) using a particle size distribution of the re-oxidizing agent were measured, and the average particle diameter D ₅₀ of the re-oxidizing agent the median diameter.

[Average particle diameter of palladium]
Using a transmission electron microscope (STEM; HD-2000, Hitachi High-Technologies), in the STEM image of the diesel oxidation catalyst powder after the endurance treatment at a magnification of 10,000 times, the average value of 200 randomly extracted points was calculated. The average particle diameter of palladium was used.

[Measurement of BET specific surface area]
The BET specific surface area uses a specific surface area / pore distribution measuring device (trade name: BELSORP-mini II, manufactured by Microtrack Bell) and analysis software (trade name: BEL_Master, manufactured by Microtrack Bell). The BET specific surface area of the base material particles was determined by the BET single point method.

Example 1
As the base material particles, ceria zirconia composite oxide (described as CZ base material particles, CeO ₂ : 30% by mass, ZrO ₂ : 55% by mass, remainder unavoidable impurities, D ₅₀ = 2 μm, BET specific surface area: 80 m ² / g) Was used.
Next, a palladium (II) nitrate solution (containing 25% by mass in terms of Pd) is prepared, and the palladium (II) nitrate solution is impregnated into the CZ base material particles, followed by sufficient drying treatment to obtain Pd Supported composite particles were obtained.
Separately, a reoxidant-containing liquid (solid content concentration in terms of TiO ₂ : 20% by mass) obtained by diluting a reoxidant (anatase type titanisol, average particle diameter D ₅₀ : 50 nm) was obtained, and the obtained Pd-supported composite particles 4.95 g of this reoxidant-containing liquid 0.25 g was impregnated, and then a drying treatment was sufficiently performed to obtain surface-modified Pd-supported composite particles.
Thereafter, the obtained surface-modified Pd-supported composite particles were subjected to a heat treatment at 600 ° C. for 30 minutes, so that the diesel oxidation catalyst powder of Example 1 (supported amount in terms of Pd: 1.0 mass%, reoxidant) (Supported amount: 1.0 mass%) was obtained.
Thereafter, the obtained powder catalyst was allowed to stand in a furnace and subjected to an endurance treatment at 800 ° C. for 20 hours in an air atmosphere to obtain a diesel oxidation catalyst powder of Example 1 after the endurance treatment.

(Example 2)
Except for changing the blending amount in the reoxidant-containing liquid to 5 times the same amount as in Example 1, the diesel oxidation catalyst powder of Example 2 (supported amount in terms of Pd: 1.0 mass%, The amount of the oxidant supported was 5.0% by mass).
Thereafter, the endurance treatment was performed in the same manner as in Example 1 to obtain the diesel oxidation catalyst powder of Example 2 after endurance treatment (supported amount in terms of Pd: 1.0 mass%, supported amount of reoxidant: 5.0). Mass%).

Example 3
Except for changing the blending amount in the reoxidant-containing liquid to 10 times the amount, the same procedure as in Example 1 was carried out, and the diesel oxidation catalyst powder of Example 3 (supported amount in terms of Pd: 1.0 mass%, The amount of oxidant supported was 10.0% by mass).
Thereafter, the endurance treatment was performed in the same manner as in Example 1 so that the diesel oxidation catalyst powder of Example 3 after endurance treatment (Pd equivalent loading: 1.0 mass%, reoxidant loading: 10.0) Mass%).

(Comparative Example 1)
A diesel oxidation catalyst powder of Comparative Example 1 (supported amount in terms of Pd: 1.0% by mass) was obtained in the same manner as in Example 1 except that the surface modification treatment with the reoxidant-containing liquid was omitted.
Then, the endurance treatment was performed in the same manner as in Example 1 to obtain a diesel oxidation catalyst powder (supported amount in terms of Pd: 1.0 mass%) of Comparative Example 1 after the endurance treatment.

<DRIFTS analysis>
FR-IR measurement was performed using the diesel oxidation catalyst powders of Example 1 and Comparative Example 1 after the durability treatment, and the CO adsorption state on palladium was observed. Here, measurement was performed using a Cary 600 Series FTIR Spectrometer manufactured by Agilent Technologies. FIG. 4 shows the DRIFTS analysis procedure and the gas used is shown below.
<Used gas>
CO gas: 0.2%
O ₂ gas: 5%
He gas: Balance

In FIG. 5, the DRIFTS measurement result of the comparative example 1 is shown. Figure 5 as shown, the CO adsorption treatment 20 minutes ^{after, Pd} 2+ Linear type peak is dominant in the 2100 cm ^-1 due to the Linear-type adsorption peak and ^Pd + -CO of 2140 cm ^-1 due to the adsorption of -CO However, after 30 minutes of CO adsorption treatment, these linear type adsorption peaks decreased, and instead, a peak of 1980 cm ⁻¹ due to bridge type adsorption of (Pd ⁰ ) ₂ —CO appeared. This is because the oxidation reaction from CO to CO ₂ starts to proceed remarkably, and as a result, Pd ²⁺ and Pd ⁺ are reduced to Pd ^0, and the bridge type adsorption of (Pd ⁰ ) ₂ —CO with time elapses. This is thought to be an increase.

In FIG. 6, the DRIFTS measurement result of Example 1 and Comparative Example 1 is shown. As shown in FIG. 6, in Example 1 was surface-modified with reoxidation agent, compared with Comparative Example 1 ^not, the peak of 2140 cm ^-1 attributable to the Linear-type adsorption ^Pd 2+ -CO and ^Pd + -CO It was confirmed that the peak at 2100 cm ⁻¹ due to the linear type adsorption was large. Further, in Example 1 where the surface was modified with a reoxidant, a peak of 1980 cm ⁻¹ due to the bridge type adsorption of (Pd ⁰ ) ₂ —CO was not observed. From these facts, in the Pd ⁰ produced by the oxidation reaction of CO by the surface modification with the reoxidant, the bridge type adsorption of (Pd ⁰ ) ₂ —CO occurs rather than the Pd ²⁺ and Pd ⁺ . Oxidation was performed kinetically, and as a result, it is considered that bridge type adsorption of (Pd ⁰ ) ₂ —CO hardly occurred.

FIG. 7 shows the DRIFTS measurement results when the temperature is increased to 200 ° C. at a temperature increase rate of 5 ° C./min after the CO adsorption treatment at 50 ° C. for 30 minutes. As apparent from FIG. ^7, the peak of 2100 cm ^-1 attributable to the Linear-type adsorption peak 2140 cm ^-1 due to the Linear-type adsorption ^Pd 2+ -CO and ^Pd + -CO may be reduced as the temperature rises confirmed. Further, even when the temperature was raised, a peak of 1980 cm ⁻¹ due to the bridge type adsorption of (Pd ⁰ ) ₂ —CO was not observed.

<Light off test of powder catalyst>
Using the powder catalysts of Examples 1 to 3 and Comparative Example 1, the light-off performance of the CO purification rate was confirmed. Here, each of the obtained powder catalysts was allowed to stand in a furnace and subjected to an endurance treatment at 800 ° C. for 20 hours in an air atmosphere, and Examples 1 to 3 and Comparative Example 1 after the endurance treatment were obtained. 50 mg of diesel oxidation catalyst powder was used as a sample. And after leaving each sample for 10 minutes in He flow at 500 ° C., supplying the following model gas, cooling to 80 ° C., then raising the temperature to 500 ° C. at a temperature rising rate of 15 ° C./min. CO and HC concentrations were measured using a model gas reactor (TPD Type-R, Rigaku). The measurement results are shown in FIG. Samples obtained by subjecting the powder catalyst of Example 1 to durability treatment at 750 ° C. for 20 hours, 850 ° C. for 20 hours, and 900 ° C. for 20 hours were prepared, and a light-off test was performed in the same manner. The temperature at which the purification rate reaches 50% was measured. Here, COT50 means the catalyst bed temperature when 50% of CO is purified. The measurement results are shown in FIG.

[Model gas]
CO gas: 1000ppm
C ₅ H ₁₂ gas: 300ppm
NO gas: 200ppm
O ₂ gas: 5%
H ₂ O: 2%
He gas: Balance model gas flow rate: 300 ml / min

[Model gas evaluation system]
Model gas evaluation system: TPD Type-R made by Rigaku
Analyzer: QUADRUPOLE MASS SPECTROMETER M-200QA manufactured by ANELVA

<Real machine test>
Using the powder catalysts of Example 1 and Comparative Example 1, the CO purification rate was measured. Here, diesel oxides of Example 1 and Comparative Example 1 after endurance treatment obtained by allowing each obtained powder catalyst to stand in a furnace and performing endurance treatment at 700 ° C. for 40 hours in an air atmosphere. Using the catalyst powder as a sample, each of the flow-through monolithic catalysts of Example 1 and Comparative Example 1 having the first catalyst layer and the second catalyst layer in this order on the honeycomb carrier in the following procedure was prepared. did.

First, 75 parts by mass and 25 parts by mass of platinum ammine salt aqueous solution and palladium nitrate aqueous solution are weighed in terms of Pt and Pd mass, and the average particle diameter (D ₅₀ ) is such that the mass ratio of platinum to palladium is 3: 1. 4,000 parts by mass of 30 μm γ-alumina powder (BET specific surface area 130 m ² / g, pore diameter 20 nm) are impregnated with platinum and palladium to form 1.8% by mass Pt and 0.005% for forming the first catalyst layer. A 6% by mass Pd-supported alumina powder was obtained. 1000 parts by mass of the obtained Pt and Pd supported alumina powder, 3 parts by mass of a surfactant, and 60 parts by mass of a pH adjuster were put into a ball mill, diluted with pure water, and the average particle diameter of the Pt and Pd supported alumina powder. Milling was performed until D ₅₀ became 7 μm to obtain slurry A (solid content concentration: 40% by mass) for forming the first catalyst layer.

Next, 1000 parts by mass of each of the above powder catalysts, 400 parts by mass of beta zeolite for HC trap, and 20 parts by mass of a pH adjuster are put into a ball mill, diluted with pure water, and the average particle diameter of each powder catalyst Milling was performed until D ₅₀ was 6 μm to obtain slurry B (solid content concentration: 30% by mass) for forming the second catalyst layer.

Next, a flow-through type honeycomb structure made of cordierite was prepared. The catalyst A was applied onto the honeycomb structure by a wash coat method, dried at 150 ° C. for 1 hour, and then fired at 450 ° C. in an air atmosphere to form a first catalyst layer. Next, the slurry B was applied onto the first catalyst layer of the honeycomb structure by a wash coat method, and dried and fired under the same conditions as the first catalyst layer to form a second catalyst layer. Thereafter, the obtained laminate is left in an endurance furnace, subjected to a high temperature exposure process (endurance process), and the first catalyst layer and the second catalyst layer are provided in this order on the honeycomb carrier. 1 unitary structure type catalyst was obtained. As the high temperature exposure treatment, heat treatment was performed at 700 ° C. for 40 hours in an air atmosphere.
[Honeycomb carrier]
Honeycomb carrier: Cordierite flow-through honeycomb substrate 2.0 L, 62 cells / cm ² , Wall thickness: 0.1 mm
Catalyst loading: 4.8 g / unit in terms of PGM metal relative to the honeycomb carrier

Using the engine dynamometer equipped with a turbocharged diesel engine (2.2L) equipped with HORIBA's gas analyzer and dual analyzer set, the purification performance of each of the monolithic structure catalysts obtained was NEDC) mode. The measurement results are shown in FIG.

As is apparent from FIGS. 8 to 10, the diesel oxidation catalyst powder and the monolithic catalyst of Example 1 surface-modified with a reoxidant have improved CO purification performance compared to Comparative Example 1 that is not. And excellent low-temperature purification performance.

The diesel oxidation catalyst powder and the monolithic exhaust gas purifying catalyst of the present invention can be widely and effectively used as a three-way catalyst for reducing NOx, CO, HC, etc. in the exhaust gas. In particular, the present invention can be effectively used in gasoline engine applications that require higher heat resistance than diesel engines. The diesel oxidation catalyst powder of the present invention can be effectively used as a TWC for an engine direct type catalytic converter, a direct type catalytic converter in a tandem arrangement, or the like.

DESCRIPTION OF SYMBOLS 100 ... Diesel oxidation catalyst powder 11 ... Base material particle 11a ... Surface 21 ... Catalytic active ingredient 31 ... Composite particle 41 ... Reoxidant

Claims (14)

1. Comprising composite particles containing base material particles containing ceria zirconia-based oxygen storage / release material and catalytically active components supported on the base material particles,
   The catalytically active component contains palladium having an oxidation number of 1 to 6,
   The composite particles are surface-modified with a reoxidant,
   Diesel oxidation catalyst powder.
2. The diesel oxidation catalyst according to claim 1, wherein the reoxidant is at least one selected from the group consisting of clay minerals, zeolites, activated carbon, metal oxides, metal sulfides, metal salts, and metal composite oxides. Powder.
3. The diesel oxidation catalyst powder according to claim 1 or 2, comprising the reoxidant in a total amount of 0.1 to 20% by mass based on the total amount of the powder.
4. The re-oxidizing agent, a diesel oxidation catalyst powder according to any one of claims 1 to 3 having an average particle diameter D ₅₀ of 1 ~ 200 nm.
5. The diesel oxidation catalyst powder according to any one of claims 1 to 4, wherein a mass ratio of the palladium to the reoxidant is 1: 0.1 to 15.
6. The ratio between the average particle diameter _{D 50} of the re-oxidizing agent and an average particle diameter _{D 50} of the base particles is 1: according to 0.00001 to any one of claims 1 to 5, which is a 0.4 Diesel oxidation catalyst powder.
7. The diesel oxidation catalyst powder according to any one of claims 1 to 6, wherein the palladium is contained in an amount of 0.1 to 10% by mass based on the total amount of the powder.
8. The base material particles, the diesel oxidation catalyst powder according to any one of claims 1 to 7 having an average particle diameter _{D 50} of 0.5 ~ 100 [mu] m.
9. The diesel oxidation catalyst powder according to any one of claims 1 to 8, wherein the base material particles have a BET specific surface area of 10 to 250 (m ² / g).
10. A preparation step of preparing base material particles containing a ceria zirconia-based oxygen storage / release material;
    A composite particle forming step of impregnating the surface of the base material particles with an aqueous solution containing at least palladium ions to produce composite particles in which palladium is supported on the base material particles;
    A surface modification step of impregnating the composite particles with an aqueous solution containing at least a reoxidant or a precursor thereof, and surface-modifying the composite particles with the reoxidant or a precursor thereof; and heat treating or chemically treating the composite particles. And at least a palladium forming step of forming palladium having an oxidation number of 1 to 6 on the surface of the base material particles,
    A method for producing diesel oxidation catalyst powder.
11. The manufacturing method of the diesel oxidation catalyst powder of Claim 10 which performs the said palladium formation process after the said composite particle formation process and before the said surface modification process.
12. The method for producing a diesel oxidation catalyst powder according to claim 10 or 11, wherein the palladium forming step is performed after the surface modification step.
13. The method for producing a diesel oxidation catalyst powder according to claim 10, wherein the surface modification step and the palladium formation step are performed simultaneously after the composite particle formation step.
14. A catalyst carrier, and a catalyst layer provided on at least one side of the catalyst carrier,
    The catalyst layer includes the diesel oxidation catalyst powder according to any one of claims 1 to 9,
    Monolithic exhaust gas purification catalyst.

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