WO2015083590A1

WO2015083590A1 - Exhaust-gas purifying catalyst and method for producing same

Info

Publication number: WO2015083590A1
Application number: PCT/JP2014/081205
Authority: WO
Inventors: 明生立見; 勝香川; 和人板谷; 和剛武田
Original assignee: 田中貴金属工業株式会社
Priority date: 2013-12-02
Filing date: 2014-11-26
Publication date: 2015-06-11
Also published as: JP2015104715A; CN105792929A; CN105792929B; JP5777690B2

Abstract

The purpose of the present invention is to provide an exhaust-gas purifying catalyst containing a plurality of catalyst metals, with the catalyst layer thereof comprising a single layer, wherein the degree of dispersion of the catalyst metals is high and the catalyst performance thereof is also high. An additional purpose of the present invention is to provide a method for producing this catalyst, which can be definitively supported, without using an alkali solution. The present invention pertains to an exhaust-gas purifying catalyst obtained by forming a single catalyst layer on a support body, wherein: the catalyst layer is obtained by supporting palladium and rhodium on a carrier obtained by mixing an inorganic oxide such as alumina and a ceria-zirconia composite oxide with one another; and the ratio (S_Zr/S_Ce) of the zirconium concentration to the cerium concentration in the surface of the catalyst layer is 1.05-6.0 times the ratio (C_Zr/C_Ce) of the zirconium concentration to the cerium concentration at the interface between the catalyst layer and the support body.

Description

Exhaust gas purification catalyst and method for producing the same

The present invention relates to an exhaust gas purification catalyst and a method for producing the same, and more particularly to a catalyst suitable as a three-way catalyst for purifying carbon monoxide, hydrocarbons and nitrogen oxides in exhaust gas.

As the exhaust gas purification catalyst, a three-way catalyst is used that simultaneously purifies by oxidizing or reducing carbon monoxide (CO), hydrocarbon (HC), and nitrogen oxide (NOx), which are harmful substances contained in the exhaust gas. . As the structure of this catalyst, an oxygen storage material such as a ceria-zirconia composite oxide is used in addition to a general metal oxide support such as alumina as a support for supporting a catalyst metal. In the catalyst containing the oxygen storage material (OSM), it is easy to efficiently proceed the oxidation-reduction reaction of the three kinds of harmful substances (CO, HC, and NOx) by using the ability of oxygen absorption / extraction by the OSM. Many three-way catalysts contain two or more kinds of noble metals such as platinum, palladium, rhodium, etc. as catalyst metals. Since these noble metals are different in harmful substances that are easy to purify, a plurality of different noble metals can be combined to efficiently remove three kinds of harmful substances.

Here, a problem with a catalyst containing a plurality of noble metals as a catalyst metal is that when the catalyst metal is alloyed with each other, the intended catalyst performance is not sufficiently exhibited. For this reason, when a plurality of catalyst metals are applied, an exhaust gas purification catalyst in which a catalyst layer has a structure composed of a plurality of layers and separate catalyst metals are arranged in each catalyst layer is generally used. For example, Patent Document 1 describes an exhaust gas purification catalyst in which palladium is disposed in a first coating layer and platinum and rhodium are disposed in a second coating layer.

However, the catalyst in which a plurality of catalyst layers are formed in this way needs to be individually manufactured for each catalyst layer to be formed, such as preparation of the slurry, application to the support, and firing in preparation of the catalyst. Compared with a catalyst composed of a single catalyst layer, the number of manufacturing steps is increased, resulting in an expensive catalyst.

Against this background, as a catalyst using a plurality of catalyst metals and a single catalyst layer, Patent Document 2 discloses that rhodium and palladium are used as catalyst metals and two types of ceria-zirconia composite oxidation as a support. The catalyst using the product is described. In such a catalyst, the catalyst metal alloying is suppressed by carrying different catalyst metals on the two types of carriers.

As a method for producing the exhaust gas purification catalyst described above, generally, after adding a catalyst metal salt to a slurry containing a support, the pH of the slurry is increased with an alkaline solution to precipitate the catalyst metal as an insoluble compound. The method is applied. The catalyst metal is immobilized on the support by raising the pH of the slurry that has become acidic by addition of the catalyst metal salt with an alkaline solution. In this regard, Patent Document 2 describes a method for supporting a catalytic metal using tetraethylammonium hydroxide (TEAH) as an alkaline solution. Specifically, in order to support different catalyst metals on each of the two types of carriers, when rhodium salt is first added to the slurry containing the first type of carrier and becomes strongly acidic, TEAH is added to raise the pH. Rhodium is deposited. Next, the second type carrier is suspended in the slurry, and TEAH is added to the slurry that has become acidic again by adding a palladium salt to raise the pH again, thereby precipitating palladium.

Japanese Patent Laid-Open No. 11-151439 Special table 2010-521302 gazette

However, the catalyst of Patent Document 2 does not have sufficient purification performance when put to practical use as an exhaust gas purification catalyst, and further improvement in catalytic activity is expected. In particular, as a method for producing such a catalyst, a catalyst in which a catalytic metal is deposited using an alkaline solution is difficult to have a high catalytic activity.

Therefore, an object of the present invention is to provide a catalyst having higher purification performance in an exhaust gas purification catalyst containing a plurality of catalyst metals and having a single catalyst layer. Another object of the present invention is to provide a production method capable of reliably depositing a catalyst metal on a support without using an alkaline solution.

For this reason, the present inventors diligently studied an exhaust gas purification catalyst with good catalytic performance and focused on the state of catalyst metal supported on the support. At this time, in the catalyst of Patent Document 2 described above, it was assumed that the catalyst metal deposited was dropped or rearranged by stepwise loading of the catalyst metal, pH adjustment with an alkaline solution, or the like. Specifically, in the stage of adding a catalyst metal salt for depositing the second type of catalyst metal or adding an alkaline solution, the first type of catalyst metal once deposited on the carrier elutes and is deposited on another carrier. It is thought to rearrange. Moreover, the catalyst metal deposited using an alkaline solution precipitates as a hydroxide, and is easily bonded and coarsened. Therefore, the present inventors can realize further improvement in catalyst performance by reliably supporting the catalyst metal while suppressing the rearrangement of the catalyst metal and precipitation as a hydroxide. As a result, the exhaust gas purifying catalyst of the present invention was obtained. As a result, the obtained catalyst was analyzed in detail. When the ratio of zirconium concentration to cerium concentration (zirconium concentration / cerium concentration) was high on the catalyst layer surface, the supported state of the catalyst metal on the support was certain. As a result, the inventors have conceived the exhaust gas purifying catalyst of the present invention.

That is, the present invention is an exhaust gas purification catalyst in which a single catalyst layer is formed on a support, the catalyst layer comprising an inorganic oxide composed of at least one of alumina, ceria, and zirconia, and ceria- the carrier comprising a mixture of a zirconia composite oxide, which palladium and rhodium are supported, furthermore, the ratio of the zirconium concentration in the surface of the catalyst layer (S _Zr) and cerium concentration (S _Ce) (S _Zr / S _Ce ) is 1.05 to 6.0 with respect to the ratio (C _Zr / C _Ce ) of zirconium concentration (C _Zr ) to cerium concentration (C _Ce ) at the interface of the catalyst layer with the support. The present invention relates to an exhaust gas purification catalyst.

The exhaust gas purifying catalyst of the present invention is one in which two layers of palladium and rhodium are supported on a carrier as a catalyst metal while the catalyst layer is a single layer. The catalyst of the present invention is characterized in that the ratio of zirconium concentration to cerium concentration (zirconium concentration / cerium concentration) is higher near the surface of the catalyst layer than near the interface with the support. Such a catalyst of the present invention has a high degree of dispersion of the catalyst metal and high catalyst performance (particularly, CO oxidation and NOx reduction ability).

The zirconium / cerium concentration (S _Zr / S _Ce , C _Zr / C _Ce ) is the value at the surface of the catalyst layer (S _Zr / S _Ce ) and the value at the interface with the support of the catalyst layer (C _Zr / C _Ce). ) ((S _Zr / S _Ce ) / (C _Zr / C _Ce )), 1.05 to 6.0, preferably 1.1 to 5.0, and preferably 1.1 to 3.5 Particularly preferred. If it is less than 1.05, the durability of the catalyst metal tends to be insufficient, and if it exceeds 6.0, the degree of dispersion of the catalyst metal tends to be low.

Zirconium / cerium concentration ratio (S _Zr / S _Ce ) on the surface of the catalyst layer is measured from the outermost surface of the catalyst layer to the support side at the measurement position in the depth direction of the catalyst layer from the catalyst layer surface to the interface with the support. In addition, the analysis result at a measurement position having a depth of 5 to 10 μm can be applied. As the zirconium / cerium concentration (C _Zr / C _Ce ) at the interface with the support of the catalyst layer, the analysis result at a measurement position having a depth of 5 to 10 μm on the surface side from the interface with the support can be applied. The above zirconium concentration / cerium concentration (S _Zr / S _Ce , C _Zr / C _Ce ) can be measured by an electron beam microanalyzer (EPMA).

Hereinafter, each configuration of the exhaust gas purification catalyst of the present invention will be described in detail.
As a carrier, an oxygen storage material, ceria-zirconia composite oxide (CZ) is used together with an inorganic oxide such as alumina. CZ is preferably such that the ratio of zirconium oxide to cerium oxide (zirconia / ceria) is 95/5 to 5/95 in terms of mass ratio. Further, as an additive, one or more of oxides of rare earth elements such as yttrium, lanthanum, and praseodymium, and oxides of alkaline earth elements such as magnesium and calcium may be included. The content of CZ is preferably 20 to 80% by mass with respect to the total mass of the catalyst.

As the inorganic oxide, one or more of alumina, ceria, zirconia and the like can be used, and alumina is particularly preferable. As the alumina, γ-alumina is suitable, and it may be doped with rare earth elements such as yttrium, lanthanum, and praseodymium. The content of the inorganic oxide is preferably 20 to 80% by mass with respect to the total mass of the catalyst layer.

Catalyst metals include both palladium and rhodium. The amount of the catalyst metal supported is preferably 0.1 to 2.5% by mass relative to the support. If it is less than 0.1% by mass, sufficient catalyst performance is difficult to obtain, and if it exceeds 2.5% by mass, it is not economical and the catalyst metal tends to aggregate.

The catalyst layer preferably contains a barium compound in addition to the carrier and the catalyst metal. In addition to the zirconium / cerium ratio being in the above range, a catalyst containing barium is likely to have a higher CO oxidizing power and NOx reducing power. As the barium compound, any of barium sulfate, barium carbonate, and barium oxide is preferable. These barium salts are present as barium sulfate or barium carbonate in unused exhaust gas purification catalysts, and are often present in the catalyst layer as barium carbonate or barium oxide after the catalyst is used.

The content of the barium compound is preferably 0.1 to 10% by mass, more preferably 1.0 to 6.0% by mass in terms of barium oxide with respect to the mass in which all components in the catalyst layer are converted as oxides. %. If it is less than 0.1% by mass, it is difficult to obtain the effect of adding a barium compound. The upper limit of the content is not particularly limited, but the addition effect of the barium compound is hardly improved even when added in an amount of 10% by mass or more. The particle diameter of the barium compound is preferably 0.01 μm or more and less than 2.0 μm. Even when the particle size is less than 0.01 μm, it is difficult to expect further improvement in the addition effect, and barium compound aggregates are easily formed in the catalyst layer. When such an aggregate is formed, the adhesion of the catalyst layer is lowered. When the particle size of the barium compound is 2.0 μm or more, the catalyst performance is difficult to improve. The particle shape is preferably spherical or plate-like.

The exhaust gas purification catalyst of the present invention is provided with the catalyst layer described above on a support made of a structural body such as a ceramic honeycomb, a metal honeycomb, or a nonwoven fabric.

As a method for producing the exhaust gas purification catalyst of the present invention described above, a palladium salt and a rhodium salt are added to a carrier slurry in which a ceria-zirconia composite oxide and an inorganic oxide are suspended to form a catalyst layer precursor. Adding the palladium salt and the rhodium salt in the step of adjusting the mixed slurry, the step of adjusting the mixed slurry, and the step of applying the mixed slurry to the support to form a single catalyst precursor layer. A manufacturing method in which a zirconium compound is contained in the carrier slurry can be applied.

In the production method of the present invention, a zirconium compound is added as an additive in a slurry in which a support is suspended in a step of adding a palladium salt and a rhodium salt, which are catalytic metal salts. The catalyst obtained by the production method of the present invention is a catalyst having high catalytic activity, and is particularly effective for lowering the temperature (T ₅₀ ) at which the purification rate of the purification components (CO, HC, NOx) reaches 50%. This is presumably because palladium and rhodium are not easily rearranged on the carrier and are reliably supported. As described above, the catalyst metal is surely supported in a supported state because the catalyst metal can be prevented from precipitating as a hydroxide as in the case where the catalyst metal is supported using an alkaline solution, and the catalyst metal is supported on the carrier as ions. It is thought to be for this purpose. Further, as in the case where the catalyst metal is precipitated as a hydroxide, the catalyst metal is hardly coarsened due to the bond between the hydroxides.

Hereinafter, the production method of the present invention will be described in detail. The carrier, ceria-zirconia composite oxide and inorganic oxide, are suspended in water to prepare a carrier slurry. The amount of each carrier added is preferably 20 to 70% by mass of the inorganic oxide and 20 to 70% by mass of the ceria-zirconia composite oxide with respect to the entire catalyst layer obtained. When preparing the carrier slurry, it is preferable to pulverize and mix to obtain a uniform and predetermined particle size distribution. The particle size distribution is preferably 0.1 to 20 μm. As the ceria-zirconia composite oxide and the inorganic oxide, those having the same types and particle sizes as described above can be applied as the exhaust gas purification catalyst.

In preparing the carrier slurry, it is preferable to make a slurry by mixing an insoluble barium compound as an additive together with the ceria-zirconia composite oxide and the inorganic oxide. By adding an insoluble barium compound in addition to the zirconium compound, a catalyst with higher catalytic performance can be easily obtained. The insoluble barium compound may be added at any time before or after the preparation of the catalyst slurry as long as it is before the addition of the catalyst metal, but is added together with the ceria-zirconia composite oxide or inorganic oxide as the support at the time of preparation of the support slurry. It is preferable to do. Since the insoluble barium compound is in a particulate form, it is easy to adjust a mixed slurry having a uniform particle size distribution by pulverizing and mixing together with a particulate carrier to form a slurry.

As the insoluble barium compound, barium sulfate or barium carbonate is preferable, and barium sulfate is particularly preferable. The amount of the insoluble barium compound added is preferably 1.0 to 10% by mass in terms of barium oxide with respect to the mass of all components in the resulting catalyst layer as oxides. Here, in the present invention, an insoluble compound is applied as the barium compound. The soluble barium compound is finely dispersed on the surface of the ceria-zirconia composite oxide, tends to inhibit the oxygen absorption / release ability, is easily segregated, and is not easily dispersed uniformly in the catalyst layer. On the other hand, when an insoluble barium compound is applied as in the present invention, the particle shape can be maintained in the carrier slurry, so that the oxygen absorption / release capability is not inhibited on the surface of the ceria-zirconia composite oxide, and the barium is not contained in the catalyst layer. It is also possible to disperse the components uniformly. In addition, as an insoluble barium compound, the thing similar to the above-mentioned particle diameter as a structure of an exhaust gas purification catalyst is applicable.

Then, a palladium salt and a rhodium salt are added as catalyst metal salts to the carrier slurry to prepare a mixed slurry that becomes a precursor of the catalyst layer. As the catalyst metal salt, a general water-soluble compound such as nitrate and acetate can be used, and nitrate is preferred. The amount of each catalyst metal salt added is preferably 0.1 to 2.5% by mass of palladium and 0.1 to 0.5% by mass of rhodium with respect to the support.

The timing for adding the zirconium compound is preferably before adding the palladium salt and the rhodium salt when adjusting the mixed slurry. The zirconium compound is preferably at least one of zirconium oxynitrate, zirconium acetate, and zirconia sol, and particularly preferably zirconium oxynitrate. The added amount of the zirconium compound is preferably 0.5 to 5.0% by mass in terms of zirconium oxide relative to the mass of all components in the resulting catalyst layer as oxide. With this addition amount, it becomes possible to obtain a catalyst having the above-mentioned Zr / Ce ratio, and the resulting catalyst has a high degree of dispersion of the catalyst metal and tends to have high catalyst performance.

In the production method of the present invention, by adding a zirconium salt, the catalyst metal can be immobilized on the support without using an alkaline solution as in the production method described in Patent Document 2, so that the catalyst metal is water. Precipitation as an oxide can be suppressed. The pH of the mixed slurry after the addition of the catalyst metal salt is a value that varies depending on the amount of addition of the catalyst metal salt, but in the implementation conditions of the present invention, it is often within the range of about 2.5 to 6.0, It is particularly often about 3.0 to 5.0. According to the present invention, after the addition of the catalyst metal salt, the catalyst metal can be reliably deposited on the support without adding an alkaline solution. If the catalyst metal is not surely deposited, the catalyst metal may fall off in the step of drying and firing the mixed slurry to which the catalyst metal is added, but the catalyst metal deposited by the production method of the present invention is dried and fired. In such cases, the catalyst metal is unlikely to fall off.

The mixed slurry prepared above is preferably prepared such that the solid content of all catalyst components in the slurry is 20 to 50% by mass with respect to the mixed slurry. The obtained mixed slurry is applied to a support to form a single catalyst precursor layer, and then fired to form a catalyst layer to produce an exhaust gas purification catalyst. The firing temperature of the support is preferably 400 to 700 ° C. When the mixed slurry is applied to the support, the viscosity of the slurry may be adjusted using a regulator such as acetic acid or water. However, addition of an alkaline solution that tends to reduce the dispersibility of the catalyst metal is also avoided when adjusting the viscosity. The support coated with the mixed slurry is preferably dried before firing. The drying temperature is preferably 90 to 200 ° C.

The exhaust gas purification catalyst of the present invention is particularly excellent in catalyst performance while utilizing the characteristics of a plurality of catalyst metals.

The EPMA analysis figure of the exhaust gas purification catalyst in 1st embodiment.

Hereinafter, the best embodiment of the present invention will be described.

First embodiment : 100 g of activated alumina (lanthanum-doped γ-alumina) which is an inorganic oxide, 60 g of ceria-zirconia composite oxide (CeZrLaY, zirconia / ceria ratio 65/35), and barium acetate (purity 99% or more) 7.0 g was added to a mixed solution of 1.8 g of acetic acid and 0.17 L of pure water, and pulverized and mixed with an alumina media mill to prepare a carrier slurry. In the case of adding a zirconium salt, zirconium oxynitrate (purity 99.0% or more) or the like is added to and mixed with this carrier slurry, and further 8.3 g of palladium nitrate (Tanaka Kikinzoku Kogyo Co., Ltd.) and rhodium nitrate (Tanaka Kikinzoku Kogyo). 1.7 g was added and mixed to prepare a mixed slurry. The slurry had a pH of about 4.4. Acetic acid and water were added to the slurry to adjust the viscosity, and the slurry was applied to a support (monolith manufactured by cordierite, volume 1 L, cell number 600 cpsi, wall thickness 4.3 mil). No alkali solution was added in the stage from the mixed slurry adjustment described above to the application to the support. After drying at 95 ° C. for 30 minutes, it was calcined at 500 ° C. for 2 hours to obtain an exhaust gas purification catalyst (Test No. 1-2).

As shown in Table 1 below, a catalyst to which no barium salt or zirconium salt was added (Test No. 1-1), a catalyst in which the amount of zirconium salt added was changed (Test Nos. 1-3 to 1-5), Catalysts (test Nos. 1-6 to 1-8) using zirconium acetate, zirconium hydroxide, and zirconia sol instead of zirconium oxynitrate were also produced in the same manner as described above. Further, a catalyst (Test No. 1-9) containing zirconium oxynitrate and using barium sulfate as the barium salt instead of barium acetate was also produced.

For the catalyst obtained above, the zirconium / cerium concentration ratio in the catalyst layer was analyzed, and the supported state of the catalyst metal on the carrier was also confirmed. Moreover, the exhaust gas purification ability of CO, NO, and HC was evaluated as catalyst performance.

Test No. above. For the catalysts 1-3 to 1-5, the zirconium / cerium concentration ratio in the catalyst layer was analyzed using an electron beam microanalyzer (EPMA). The electron beam irradiation conditions were an acceleration voltage of 20 kV and an irradiation current of 1.0 × 10 ⁻⁸ A, and the irradiation position of the electron beam on the catalyst layer was moved every 0.2 μm from the vicinity of the center of the support toward the surface of the catalyst layer. Line analysis was performed. Zirconium / cerium concentration ratio average (X ₁ ) at a measurement position at a depth of 5 to 10 μm from the catalyst layer surface to the support side, and a measurement position at a depth of 5 to 10 μm from the interface between the support and the catalyst layer to the surface layer side The average (X ₂ ) of the zirconium / cerium concentration ratio was determined. In this test, the measurement position where the X-ray intensity of Zr was 10 or less was defined as the outermost surface of the catalyst layer. The ratio of the obtained surface layer side zirconium / cerium ratio (X ₁ ) and the support side zirconium / cerium ratio (X ₂ ) was determined to obtain the zirconium concentration ratio (X ₁ / X ₂ ) of the catalyst layer surface layer side and the support side. . No. The EPMA measurement results for 1-5 are shown in FIG.

1 and Table 2, it was confirmed that the catalyst produced by adding the Zr salt had higher Zr / Ce near the surface of the catalyst layer than near the interface with the support.

Next, the supported state of the catalyst metal on the support depending on the presence or absence of addition of Ba salt and Zr salt was confirmed. In this confirmation test, Test No. In the steps of producing the respective catalysts 1-1, 1-2, and 1-9, the mixed slurry after addition of the catalyst metal salt was used. Specifically, the concentration of noble metals (Pd and Rh) contained in the supernatant of the supernatant obtained by centrifuging the mixed slurry after the addition of palladium nitrate and rhodium nitrate and filter filtration is determined by the high frequency inductively coupled plasma method ( ICP). From the noble metal concentration in the supernatant, the proportion of the noble metal added to the slurry fixed on the inorganic oxide support was determined.

As a result, in the mixed slurry in the production process of the catalyst to which no zirconium salt or barium salt was added (Test No. 1-1), the ratio of palladium and rhodium immobilized on the support was 87%. On the other hand, in the catalyst to which barium salt was added (Test No. 1-2), the ratio of immobilized palladium and rhodium was 70%. Further, in the catalyst (Test No. 1-9) to which both the zirconium salt and the barium salt were added, almost 100% of palladium and rhodium were immobilized.

And the above test No. The exhaust gas purification performance (T ₅₀ ) of the catalysts 1-1 to 1-9 was evaluated. A catalyst cored in a cylindrical shape from the support was used for performance evaluation. The cored catalyst was subjected to deterioration treatment at 900 ° C. for 10 hours using an atmospheric furnace before performance evaluation. Since the reaction gas for performance evaluation simulates engine exhaust gas, as Rich gas, CO ₂ 10%, CO 0.77%, H ₂ 0.2%, C ₃ H ₈ 100 ppm, C ₃ H ₆ 300 ppm, NO 800 ppm, Using O ₂ 0.4% and H ₂ O 10.0%, as Lean gas, CO ₂ 10%, CO 0.77%, H ₂ 0.2%, C ₃ H ₈ 100 ppm, C ₃ H ₆ 300 ppm , NO 800 ppm, O ₂ 0.4%, H ₂ O 10.0%. Any of the atmospheric gas even balance was N _2. The reaction gas supplied to the catalyst was a space velocity (SV) of 90,000 h ⁻¹ and Rich / Lean was continuously switched every second. In a temperature rising reaction test in which the temperature at the catalyst inlet is increased from 100 to 600 ° C at 40 ° C / min, the reaction gas composition at the catalyst inlet and outlet is analyzed to measure the purification rate of carbon monoxide, hydrocarbons, and nitrogen oxides. did. The temperature at which the purification rate reached 50% was evaluated purifying ability as T _50. More T ₅₀ is low, indicating that high catalytic purification ability.

From the above, it was shown that the catalyst containing the zirconium salt (Test Nos. 1-3 to 1-9) had a low T _{50 and} a high catalytic activity in any purification performance of CO, NO, and HC. Further, when both barium and zirconia were contained (Test No. 1-9), T ₅₀ was particularly low, and good catalytic activity was exhibited.

From the above, the catalyst to which the zirconium salt was added had a larger amount of catalytic metal immobilized on the carrier and the catalytic activity was better than the catalyst to which the zirconium salt was not added. In the catalyst to which both barium and zirconia were added, most of the catalyst metal used was immobilized, and the catalytic activity was particularly high.

Second embodiment : A catalyst was produced using barium sulfate having a particle size shown in Table 4 below. Other manufacturing conditions and performance evaluation were performed in the same manner as in the first embodiment.

From the above, when the particle size of the barium compound was 0.01 μm or more and less than 2 μm, T ₅₀ was particularly low, and good catalytic activity was shown.

Third Embodiment : The degree of dispersion of the catalyst metal in the catalyst layer was evaluated by a CO adsorption method. Moreover, the catalyst which performed the deterioration process was also evaluated.

Catalysts were produced using barium salts and zirconium salts shown in Table 5 below. Test No. 3-1, after adding palladium nitrate and rhodium nitrate to the carrier slurry, TEAH was added as an alkaline solution to raise the pH to 7.0. Test No. The catalysts 3-3 to 3-5 were subjected to a aging treatment at 950 ° C. for 10 hours after the production of the catalyst. Other catalyst production conditions were the same as in the first embodiment, and the catalyst was produced.

For the catalyst obtained above, the unit dispersion and average particle size of the catalyst metal were measured by the CO pulse adsorption method. Specifically, the catalyst is held at 400 ° C. for 15 minutes in an oxygen atmosphere, then held at 400 ° C. for 15 minutes in a hydrogen atmosphere, and further cooled to 50 ° C. in a helium atmosphere. Was measured. By this measurement, the number of atoms of the catalyst metal exposed on the catalyst layer surface can be measured. The unit dispersity indicates the ratio (%) of the amount of the catalyst metal supported on the carrier that is exposed on the surface of the catalyst layer, and was calculated from the CO adsorption amount. The larger the unit dispersion, the larger the surface area of the exposed portion of the catalyst metal on the surface of the catalyst layer, and thus the better the performance of the catalyst. The average particle diameter was calculated from the surface area of the catalyst metal calculated from the CO adsorption amount, assuming that the shape of the catalyst metal was spherical.

As for the catalyst not subjected to the deterioration treatment (Test Nos. 3-1, 3-2), the catalyst added with the zirconium salt and not using the alkaline solution (Test No. 3-2) was adjusted to pH in the alkaline solution. The catalyst metal unit dispersion was higher and the average particle size was smaller than that of the catalyst with adjusted (Test No. 3-1). In the catalyst to which the alkaline solution was added, it is considered that the catalyst metal was increased in particle size because the catalyst metal was precipitated as a hydroxide.

In the catalyst (test Nos. 3-3 to 3-5) subjected to deterioration treatment at 900 ° C. for 10 hours, large-scale aggregation of the catalyst metal was observed in the catalyst to which no zirconium salt was added (test No. 3-3). As a result, the degree of dispersion and particle size could not be calculated by the CO pulse method. On the other hand, the catalysts added with zirconium salts (Test Nos. 3-4 and 3-5) showed lower dispersibility and increased particle size compared to catalysts not subjected to deterioration treatment. It was shown that the agglomeration of the catalyst metal was suppressed as compared with the catalyst to which no salt was added. From this, the catalyst added with a zirconium salt can be expected to suppress the aggregation of the catalyst metal even when the catalyst is deteriorated due to the use of the catalyst or the like.

According to the present invention, it is possible to provide a catalyst having high catalytic performance and low manufacturing cost as an exhaust gas purification catalyst. The exhaust gas purification catalyst of the present invention is particularly suitable as a three-way catalyst.

Claims

An exhaust gas purification catalyst in which a single catalyst layer is formed on a support,
The catalyst layer is one in which palladium and rhodium are supported on a support formed by mixing an inorganic oxide composed of at least one of alumina, ceria, and zirconia, and a ceria-zirconia composite oxide,
Furthermore, the ratio (S Zr / S Ce ) between the zirconium concentration (S Zr ) and the cerium concentration (S Ce ) on the surface of the catalyst layer is such that the zirconium concentration (C Zr ) and cerium at the interface with the support of the catalyst layer. An exhaust gas purification catalyst having a ratio (C Zr / C Ce ) to the concentration (C Ce ) of 1.05 to 6.0.
The exhaust gas purification catalyst according to claim 1, wherein the catalyst layer further contains a barium compound.
The exhaust gas purifying catalyst according to claim 2, wherein the barium compound is any one of barium sulfate, barium carbonate, and barium oxide.
The exhaust gas purification catalyst according to claim 2 or 3, wherein the barium compound has a particle size of 0.01 µm or more and less than 2.0 µm.
A method for producing an exhaust gas purifying catalyst according to any one of claims 1 to 4,
Adding a palladium salt and a rhodium salt to a carrier slurry in which an inorganic oxide and a ceria-zirconia composite oxide are suspended, and adjusting a mixed slurry to be a precursor of a catalyst layer;
Applying the mixed slurry to a support to form a single catalyst precursor layer, and
A method for producing an exhaust gas purifying catalyst, comprising a zirconium compound in a carrier slurry in a step of adding a palladium salt and a rhodium salt in the step of preparing the mixed slurry.
6. The production method according to claim 5, further comprising an insoluble barium compound in the carrier slurry in the step of adding the palladium salt and rhodium salt in the step of adjusting the mixed slurry.
The production method according to claim 6, wherein the insoluble barium compound is barium sulfate or barium carbonate.
The production method according to claim 6 or 7, wherein the addition amount of the insoluble barium compound is 1.0 to 10% by mass in terms of the mass converted as barium oxide with respect to the mass converted as an oxide of all components in the catalyst layer. .
The production method according to any one of claims 5 to 8, wherein the zirconium compound is at least one of zirconium oxynitrate, zirconium acetate, and zirconia sol.
The addition amount of the zirconium compound is 0.5 to 5.0% by mass in terms of zirconium oxide with respect to the mass in which all components in the catalyst layer are converted as oxides. The manufacturing method as described.
The production method according to any one of claims 6 to 10, wherein the carrier slurry is prepared by mixing an insoluble barium compound together with a ceria-zirconia composite oxide and an inorganic oxide and then forming a slurry.
The addition of the zirconium compound is performed after mixing the ceria-zirconia composite oxide and the inorganic oxide, forming a slurry to prepare a support slurry, and before adding the palladium salt and rhodium salt. The manufacturing method as described.
The production method according to any one of claims 5 to 12, wherein the catalyst layer is formed by calcining the support at 400 to 700 ° C after the step of forming the catalyst precursor layer.