WO2005085137A1

WO2005085137A1 - Complex oxide

Info

Publication number: WO2005085137A1
Application number: PCT/JP2005/003994
Authority: WO
Inventors: Eisaku Suda; Naotaka Otake; Bernard Pacaud; Lianxin Dai
Original assignee: Anan Kasei Co., Ltd.
Priority date: 2004-03-08
Filing date: 2005-03-08
Publication date: 2005-09-15
Also published as: JP4974674B2; JPWO2005085137A1

Abstract

Disclosed is a complex oxide represented by the general formula: (Ce1-xZrx)1-z(A1-yBy)zOδ (wherein x, y, z and δ represent numbers respectively satisfying 0.05 ≤ x ≤ 0.95, 0.01 ≤ y ≤ 0.99, 0.01 ≤ z ≤ 0.3 and 1.365 ≤ δ ≤ 1.995), wherein A contains at least one metal element selected from the group consisting of Bi, V, Ti, Nb, W, Fe, Pr, Tb and Eu, and B contains at least one element selected from the group consisting of Ba, Sr, Ca, Mg and La.

Description

Complex oxide

Technical field

The present invention relates to an exhaust gas purifying apparatus for purifying an exhaust gas discharged from an engine, for example, an internal combustion engine of an automobile or the like, in which energy supplied by combustion of a complex oxide, particularly gasoline or light oil, serves as a driving force. It relates to a co-catalyst for a dani catalyst.

Background art

[0002] Exhaust gas emitted from internal combustion engines such as automobiles contains hydrocarbons, carbon monoxide, and nitrogen oxides that are harmful to the human body or the environment. At present, so-called three-way catalysts, which oxidize carbon monoxide and hydrocarbons to carbon dioxide and water and reduce nitrogen oxides to nitrogen and water, are used as exhaust gas purifying catalysts. The three-way catalyst has, for example, a structure in which an oxide or composite oxide containing a noble metal of platinum, palladium, or rhodium as a main catalyst and cerium oxide as a co-catalyst is supported on a catalyst carrier such as alumina or cordierite. Has become. The co-catalyst states that the contained cerium absorbs oxygen by changing its valence from trivalent to tetravalent under an oxidizing atmosphere, and releases oxygen by changing its valence from tetravalent to trivalent under a reducing atmosphere. It has properties, so-called redox ability. This oxidation-reduction capability can mitigate sudden changes in the atmosphere of exhaust gas due to acceleration and deceleration of the engine, and the main catalyst can purify exhaust gas with high efficiency. As a co-catalyst, a complex iris containing cerium and zirconium (hereinafter referred to as "Ce-Zr-based complex iris") is widely used. The Ce-Zr-based composite oxides currently used do not have sufficient oxidation reduction ability at low temperatures of 300 ° C or lower, so when the engine temperature is low, such as when starting an engine, The exhaust gas purification efficiency of the main catalyst, which does not have the effect of mitigating the above-mentioned change in atmosphere, is low. The oxidation-reduction ability of the Ce-Zr-based composite oxide is determined by the reaction between the gas-phase exhaust gas and the solid-gas interface of the co-catalyst as the solid phase. Surface area has a significant effect. Therefore, it is important for the Ce-Zr-based composite oxide to maintain a high specific surface area even after being exposed to a high temperature of 900 ° C or more.

[0003] On the other hand, Patent Document 1 discloses that cerium oxide and zirconium oxide are used as co-catalysts of a three-way catalyst. It is disclosed to use a composite oxidized product composed of oxidized bismuth. The composite oxide has a high oxidation reduction ability in a low temperature range of 300 ° C or less even after being used as a promoter of an exhaust gas purification catalyst at 1000 ° C or more. It is described that it can purify the exhaust gas discharged from the catalyst and is suitable as a promoter having excellent heat resistance.

Patent Document 1: Japanese Patent Application Laid-Open No. 2003-238159

Disclosure of the invention

Problems to be solved by the invention

[0004] However, the composite oxide disclosed in Patent Document 1 certainly has an oxidizing and reducing ability at a temperature of 300 ° C or lower, but has a small specific surface area, so that the activity of the oxidation-reduction reaction is low. There are few points, and there is a possibility that sufficient performance as a promoter of a three-way catalyst cannot be exhibited.

[0005] The present invention has been made in view of its power, and an object of the present invention is to provide an exhaust gas purifying catalyst that has a large ratio even after being exposed to a high temperature of around 900 ° C. An object of the present invention is to provide a composite oxide having a surface area and exhibiting excellent oxidation-reduction ability in a low-temperature region of 300 ° C. or lower and having excellent heat resistance and low-temperature activity.

Means for solving the problem

[0006] The composite oxide of the present invention has the general formula (CeZr) (AB) O (where x, y, z, and δ are

δ

0,05≤x≤0.95, 0.011≤y≤0.99, 0.011≤z≤0.3, 1.365≤δ≤1, respectively

Where A includes at least one metal element selected from the group consisting of Bi, V, Ti, Nb, W, Fe, Pr, Tb, and Eu. Ba, Sr, Ca, Mg,

Including at least one selected from the group consisting of La.

Here, A is a metal element that activates an oxidation-reduction reaction in a low temperature range of 300 ° C. or less. B is a metal element that can increase the heat resistance of the composite oxidized product.

Further, the composite oxide of the present invention has a peak at a temperature of 300 ° C. or lower in a temperature-reduction spectrum, and has a specific surface area of 20 m ² Zg or more after calcining at 900 ° C. for 4 hours. Is preferred.

[0009] The composite oxide of the present invention further comprises at least one selected from the group consisting of rare earth elements (excluding Ce, Tb, Eu, La and Pr), Ni, Cu, Al, Si and Be. May be included Yes.

[0010] Further, in the composite oxide of the present invention, A preferably contains at least Bi, and B preferably contains at least Ba! /.

The invention's effect

[0011] The composite oxide of the present invention has a large specific surface area even after being exposed to a high temperature of around 900 ° C as a cocatalyst of an exhaust gas purifying catalyst, and has excellent oxidation even in a low temperature region of 300 ° C or less. It can exhibit a reducing ability.

Brief Description of Drawings

FIG. 1 is a temperature-reduction spectrum diagram of a composite oxidized product in Example 1.

[FIG. 2] FIG. 2 is a temperature-reduction spectrum diagram of a complex oxidized product in Example 2.

[FIG. 3] FIG. 3 is a temperature-reduction spectrum diagram of a composite oxidized product in Comparative Example 1.

FIG. 4 is a temperature-reduction spectrum chart of a composite oxidized product in Comparative Example 2.

FIG. 5 is a temperature-reduction spectrum diagram of a composite oxidized product in Comparative Example 3.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, as an embodiment, a method of evaluating the composition of a composite oxide and the performance of the composite oxide as a promoter of an exhaust gas purifying catalyst will be described.

[0014] In the present embodiment, the complex oxidized product is represented by the general formula (CeZr) (AB) O (where x, yl-χx1z1-yyz δ

, z, and δ are numbers that satisfy 0.055 x ≤ 0.95, 0.01 ≤ y ≤ 0.99, 0.01 ≤ z ≤ 0.3, 1.3 65 ≤ δ ≤ 1.995, respectively ).

The element A is selected from Bi, V, Ti, Nb, W, Fe, Pr, Tb, and Eu, and these can be used alone or as a mixture of two or more. Then, by adding the element A to the composite oxide, both the ionic conductivity and the electronic conductivity are exhibited in the composite oxide, and the oxidizing and reducing ability of Ce at a low temperature is improved. In some cases, the element A itself has a redox ability. And, as the element A, it is preferable that the complex oxidized product contains Bi, V, Ti, and Nb.

[0016] The element B is a basic element that can be a cation having a valence of 2 or more, and is selected from Ba, Sr, Ca, Mg, and La. These can be used alone or in combination of two or more. The composite oxide according to the present embodiment includes the element A and the element described above. Since it contains element B, it has a large specific surface area even after being exposed to a high temperature of around 900 ° C, and exhibits excellent oxidation reduction ability even in a low temperature region of 300 ° C or less.

[0017] It is not clear why adding the element B can suppress a decrease in the heat resistance of the composite oxidized product produced by the addition of the element A. It is believed that the element B acts as an impurity in the composite oxide in the embodiment, and therefore may prevent the growth of particles at a high temperature of around 900 ° C. In addition, among the elements B listed as specific examples, there are elements that function to further enhance the action of the element A to activate the redox reaction at low temperatures.

[0018] Further, in the general formula (Ce Zr) (A B) O, x force ^). 05≤x≤0.95 is satisfied.

δ

The composite oxides indicated by the numbers have practically sufficient heat resistance and oxidation-reduction ability. In the case of a composite oxide in which X satisfies 0.25≤χ≤0.75, its heat resistance and oxidation-reduction ability are improved, and in the case of a composite oxide in which X satisfies 0.4≤χ≤0.6, Its heat resistance and reducing ability are further improved. In the general formula (Ce Zr) (A B) O, y force ^). 01≤y≤0.

δ

A composite oxide satisfying 99 has practically sufficient heat resistance and low-temperature activity. And, the heat resistance and low-temperature activity are improved in the composite oxide where y satisfies 0.l≤y≤0.9, and in the composite oxide where y satisfies 0.2≤y≤0.8. The properties and low temperature activity are better. In the general formula (Ce Zr) (A B) O, z satisfies 0.01 ≤ z ≤ 0.3.

δ

The composite oxide has low-temperature activity, oxidation-reduction ability and heat resistance sufficiently high for practical use. In the case of a composite oxide where ζ satisfies 0.01 ≤ ζ ≤ 0.2, its low-temperature activity, redox activity and heat resistance are improved, and ζ is a number satisfying 0.01 ≤ ζ ≤ 0.1. In the case of the composite oxide, its low-temperature activity, oxidation reduction ability, and heat resistance are further improved.

Further, the composite oxide in the present embodiment is at least one selected from the group consisting of rare earth elements (excluding Ce, Tb, Eu, La and Pr), Ni, Cu, Al, Si and Be. They may also be included. These metal elements are appropriately selected depending on the characteristics required for the composite oxide. For example, the addition of rare earth elements (except Ce, Tb, Eu, La and Pr), Al, Si and Be further improves the heat resistance of the composite oxide, and the addition of Ni and Cu adds the composite oxide. This further enhances the exhaust gas purifying effect.

[0020] The composite oxide of the present embodiment remains large even after being exposed to a high temperature of around 900 ° C. As long as it has a high specific surface area and exhibits excellent oxidation-reduction performance even in a low temperature range of 300 ° C. or lower, it may contain an element other than the above-mentioned metal elements as long as it exhibits an effect.

[0021] The composite oxide in the present embodiment can be produced by a known synthesis method, but is preferably produced by a coprecipitation method in order to achieve the purpose of increasing the specific surface area. More preferably, a coprecipitation method including a step of heat-treating a raw salt aqueous solution is used as described in Examples below.

The heat resistance of the composite oxide in the present embodiment is evaluated based on the specific surface area after firing at 900 ° C. for 4 hours, and the specific surface area is measured using the BET method. This method of evaluating heat resistance is a method generally performed to evaluate the heat resistance of a promoter material. And, at 900 ° C., the specific surface area after firing for 4 hours at 900 ° C. is 20 m ² / g or more, preferably 25 m ² / g or more, more preferably 30 m ² / g or more. ^A composite oxide of ² / g or more can maintain excellent oxidation-reduction ability as a promoter of an exhaust gas purification catalyst. The details of the method for measuring the specific surface area will be described later in Examples.

The oxidation-reduction reaction of the composite oxide as a cocatalyst of the exhaust gas purifying catalyst in the present embodiment can be estimated by using a Temperature Programmed Reduction Spectra. The temperature-reduced reduction spectrum is a method in which the sample is heated at a constant rate while flowing a reducing gas such as hydrogen gas to the sample, and the amount of reducing gas used for reduction at each temperature is measured. Therefore, the temperature-reduced reduction spectrum is a spectrum showing the temperature dependence of the reducing ability of the test substance, and the reducing ability at a lower temperature than that of the substance whose peak appears on the lower temperature side. It can act as a co-catalyst of the exhaust gas purification catalyst at a lower temperature.Specifically, if a peak appears below 300 ° C. in the temperature-reduction reduction spectrum, 300 ° C. It will be able to act as a co-catalyst of the exhaust gas purifying catalyst at temperatures below C. The method of measuring the temperature-reduction spectrum will be described in detail in Examples below.

Example

In this example, specific surface area (unit: mVg) and temperature-reduction spectrum were measured using composite oxides having the composition formulas shown in Tables 1 to 3, and the composition formula or composition ratio of each composite oxide was measured. With (S (002

[] 0025 Specific surface area [m ² / g] Peak temperature [° C] s §3¾ Example 3 ^e 0.6 '0.4) 0.95 ( ^Dl 0.5 ^ ^a 0.5) 0.05〇1.962 ^.; 25.0 260 Example 4 25' 0.75) 0.95 (Β ¹ ^ 5 ^ ³ 0.5) 0. 5_Rei_1.9625 35.5 266施例5 (tooth θ _{_0.} ₅ ^ Γ ₀ .5

^{^{0.95 (Dl 0.5 ^ Γ 0.5)}} 0.05 ^ 1.9625 30.0 265施例6 (to _{_{_{_{e 0. 5 Zr 0 _ Γ}}}} ) 5 ο.5) 0.05 ^ 1.962i 25.7 276施例_{_{_{7 (Ce 0. 5 Zr 0}}} . R _{_{) o.95 (Nb 0. r,}} Ba 0 5) 0. 05 O L g625 31.2 290施例_{_{_{8 (Ce 0. 5 Zr 0}}} . 5 0.95 ^ O.5 ^ a 0.5) 0.05 ^ 1.9875 28.0 288施例_{_{_{9 (Ce 0. 5 Zr 0}}} . 5 Sr) 0

0.95 ^{i U} 0.5 ^± 0.5 no 0.05 ^v l. 9875 26.3 294

O CO

LO LO CM CM

Degree [] Table area [V] ° Temperature ratio c-mg

(( ₎ ) Actual ₍ Example _ΐΝΐ9 10) 160060S00000

O''1 (('.

00

CM CO

_施 ₍₎ () Example _τ0aTg 1 _ν 1 _B s "6esso 6oe: oοοοo · ·---

1

Here, as shown in Tables 1 to 3, in Examples 1 to 11, a composite oxide containing element A and element B was used. In Comparative Example 1, a composite oxide containing only Bi was used. In Comparative Example 2, a composite oxide containing only Ba was used. In Comparative Example 3, a composite oxide containing neither Bi nor Ba was used. The composite oxide of Comparative Example 1 corresponds to the composite oxide described in Example 1 of Patent Document 1. <Synthesis method of each composite oxide>

In measuring the specific surface area (unit: m ² / g) and the temperature-reduced reduction spectrum, the composite oxidized products used in Examples 1 to 11 and Comparative Examples 1 to 3 were synthesized by the following method.

—Example 1—

A cerium (IV) salt, a zirconium salt, a bismuth salt and a barium salt are mixed with Ce, Zr, Bi, and Ba monoliths 6:21 ::: 6: 6 & = 0.475: 0.475: 0.025: It was adjusted to be 0.025, and the acid-converted concentration was adjusted to 50 gZL to prepare 3 L of an acidic aqueous solution. Note that, in general, the dimethyl salt may contain several weight percent of hafnium (Hf), and the molar amount of the dimethyl includes the molar amount of hafnium. . The prepared aqueous solution was subjected to a heat treatment at 100 ° C. for 15 hours using a flask with a reflux condenser. After the heat treatment, the temperature of the aqueous solution was cooled to room temperature by water cooling. Then, the aqueous solution was neutralized with 5 L of an aqueous solution of 1 OOgZL of hydrogencarbonate. Then, the suspended neutralized aqueous solution was subjected to solid-liquid separation using a Nutsche. The obtained solid is washed by repeating decantation and filtration 10 times with pure water, then placed in a box-type electric furnace, baked in air at 500 ° C for 10 hours, and then mortared. Crushed. Thus, a composite oxide of the composition formula (CeZr) (BiBa) O shown in Table 1 was obtained.

0.50 0.50 0.95 0.50 0.50 0.05 1.9625

—Example 2—

A cerium (IV) salt, a zirconium salt, a bismuth salt and a barium salt are mixed with Ce, Zr, Bi, and Ba monoliths 6:21 ::: 6: 6 & = 0.475: 0.475: 0.0125: 0.0375, and 3 L of an acidic aqueous solution was prepared by adjusting so that the conversion concentration of the acid solution was 50 gZL. Then, according to the method for synthesizing the complex acidified product used in Example 1, the composition formula (Ce Zr) (Bi

0.50 0.50 0.95

A composite oxide of Ba) O was obtained.

0.25 0.75 0.05 1.95625

—Example 3—

The cerium (IV) salt, zirconium salt, bismuth salt and barium salt were mixed with Ce, Zr, Bi and Ba monoliths 6:21 ::: 61 :: 6 & = 0.57: 0.38: 0.25 : 0.025, and 3 L of an acidic aqueous solution was prepared by adjusting the concentration in terms of acid chloride to 50 gZL. Thereafter, according to the method for synthesizing the composite oxide used in Example 1, the composition formula (Ce Zr) (Bi Ba) shown in Table 2 was used.

0.6 0.4 0.95 0.5 0.5

A composite oxide of O 2 was obtained. —Example 4—

The cerium (IV) salt, zirconium salt, bismuth salt and barium salt were mixed with Ce, Zr, Bi and Ba in the form of 6:21 ::: 6: 6 & 0.2375: 0.7125: 0.025: 0.025. 3 L of an acidic aqueous solution was prepared by adjusting the conversion concentration of the dagger to 50 gZL. Then, according to the method for synthesizing the complex acidified product used in Example 1, the composition formula (Ce Zr) (Bi

0.25 0.75 0.95

A composite oxide of Ba) O was obtained.

0.5 0.5 0.05 1.9625

—Example 5—

Cerium (IV) salt, zirconium salt, bismuth salt and strontium salt are converted into mono-ktt force of Ce, Zr, Bi and Sr SCe: Zr: Bi: Sr = 0.475: 0.475: 0.025: 0.025, 3 L of an acidic aqueous solution was prepared by adjusting the reduced concentration to 50 gZL. Then, according to the method for synthesizing the composite oxidized product used in Example 1, the composition formula (Ce Zr) (Bi

0.5 0.5 0.95

A composite oxide of Sr 2 O 3 was obtained.

0.5 0.5 0.05 1.9625

—Example 6—

The cerium (IV) salt, zirconium salt, bismuth salt and calcium salt are converted to Ce, Zr, Bi and Ji & 6:21 ::: 61: J & 0.475: 0.475: 0.025: 0.025, 3 L of an acidic aqueous solution was prepared by adjusting so that the conversion concentration of the acid solution was 50 gZL. Then, according to the method for synthesizing the complex acidified product used in Example 1, the composition formula (Ce Zr) (Bi

0.5 0.5 0.95 0.5

A composite oxide of Ca) O was obtained.

0.5 0.05 1.9625

—Example 7—

The cerium (IV) salt, zirconium salt, niobium salt and barium salt are converted from Ce, Zr, Nb, and Ba in a monolayer (6:21 ::? «) :: 6 & = 0.475: 0.475: 0.025: 0.025, 3 L of an acidic aqueous solution was prepared by adjusting the concentration to 50 gZL in terms of acid dandelion. Then, according to the method for synthesizing the complex acidified product used in Example 1, the composition formula (Ce Zr) (Nb

0.5 0.5 0.95 0.5

A composite oxide of Ba) O was obtained.

0.5 0.05 1.9625

—Example 8—

Cerium (IV) salt, zirconium salt, vanadium salt and barium salt are converted into mono-ktt force of Ce, Zr, V and Ba SCe: Zr: V: Ba = 0.475: 0.475: 0.025: 0.025, 3 L of an acidic aqueous solution was prepared by adjusting the calculated concentration to 50 gZL. Then the example According to the method for synthesizing the complex acidified product used in 1, the composition formula (Ce Zr) (V

0.5 0.5 0.95 0.5

A composite oxide of Ba) O was obtained.

0.5 0.05 1.9875

—Example 9—

The cerium (IV) salt, zirconium salt, niobium salt and strontium salt were converted to Ce, Zr, Nb and Sr mono-ktt forces SCe: Zr: Nb: Sr = 0.475: 0.475: 0.025: 0.025. 3 L of an acidic aqueous solution was prepared by adjusting the reduced concentration to 50 gZL. Thereafter, according to the method for synthesizing the composite oxidized product used in Example 1, the composition formula (Ce Zr) (N

A composite oxide of 0.5 0.5 0.95 b Sr) O was obtained.

0.5 0.5 0.05 1.9875

—Example 10—

Cerium (IV) salt, zirconium salt, bismuth salt, barium salt and nickel salt are converted into mono ktt force of Ce, Zr, Bi, Ba and Ni Ce: Zr: Bi: Ba: Ni = 0.45: 0.45: 0.025: 0.025 : 0.05, and 3 L of an acidic aqueous solution was prepared by adjusting so as to have a concentration of 50 gZL. After that, according to the method for synthesizing the composite oxide used in Example 1, a composite oxide of the composition formula (CeZr) (BiBa) NiO shown in Table 3 was obtained.

0.5 0.5 0.9 0.5 0.5 0.05 0.05 1.9125

—Example 11—

A cerium (IV) salt, a zirconium salt, a bismuth salt, a barium salt and an aluminum salt are converted into a mono ktt force of Ce, Zr, Bi, Ba and A1 Ce: Zr: Bi: Ba: Al = 0.45: 0.45: 0.025: 0.025: It was adjusted to 0.05, and the acid-converted concentration was adjusted to 50 gZL to prepare 3 L of an acidic aqueous solution. After that, according to the method for synthesizing the composite oxide used in Example 1, a composite oxide of the composition formula (Ce Zr) (Bi Ba) Al O shown in Table 3 was obtained.

0.5 0.5 0.9 0.5 0.5 0.05 0.05 1.9375

Comparative Example 1

The cerium (IV) salt, zirconium salt and bismuth salt are mixed so that the molar ratio of Ce, Zr and Bi is Ce: Zr: Bi = 0.475: 0.475: 0.05 and the concentration power in terms of oxidized substance is 50 g / L. It was adjusted to prepare 3 L of an acidic aqueous solution. The prepared aqueous solution was subjected to a heat treatment at 100 ° C. for 15 hours using a flask with a reflux condenser. After the heat treatment, the temperature of the aqueous solution was cooled to room temperature by water cooling. Then, the cooled aqueous solution was neutralized with an aqueous ammonia solution, and the pH of the mixed aqueous solution was adjusted to pH = 8.5. Then, the suspended neutralized aqueous solution was subjected to solid-liquid separation using a Nutsche. The obtained solid is decanted with pure water. After washing was repeated 10 times, the mixture was placed in a box-type electric furnace, baked in air at 500 ° C. for 10 hours, and pulverized using a mortar. Thus, a composite oxide of the composition formula (Ce Zr) Bi 2 O shown in Table 1 was obtained.

0.50 0.50 0.95 0.05 1.975

-Comparative Example 2-A cerium (IV) salt, a zirconium salt and a barium salt were mixed with Ce, Zr and Ba at a molar ratio of Ce: Zr: Ba = 0.475: 0.475: 0.05, and 3 L of an acidic aqueous solution was prepared by adjusting the concentration in terms of a substance to 50 gZL. Thereafter, according to the method for synthesizing the composite oxide used in Example 1, a composite oxide of the composition formula (Ce Zr) Ba O 2 shown in Table 1 was obtained.

0.50 0.50 0.95 0.05 1.95

Comparative Example 3-A cerium (IV) salt and a zirconium salt were adjusted so that the molar ratio of Ce and Zr was Ce: Zr = 0.5: 0.5, and the concentration in terms of oxidized product was 50 gZL. Thus, 3 L of an acidic aqueous solution was prepared. Then, according to the method of synthesizing the composite oxidized product used in Comparative Example 1, the composition formula Ce Z shown in Table 1 was used.

A composite oxide of 0.50 rO was obtained.

0.50 2

After synthesizing the composite oxide by the above method, the specific surface area and the temperature-reduction spectrum of each composite oxide were measured.

5 g of each composite oxide was placed in a magnetic crucible with a maximum volume of 30 ml. At this time, only one kind of the composite iris was placed in one magnetic crucible. Then, a magnetic crucible containing 5 g of each composite oxide was placed in an electric furnace previously set to a temperature of 900 ° C. Four hours later, the electric crucible was taken out of the electric furnace and cooled to room temperature. After cooling, 200 mg of each complex oxide was squeezed out, and the specific surface area was measured by BET method (Brunauer-Emmett-Teller method) using Flow Soap # 2300 (manufactured by Micrometrics).

An automatic thermal desorption spectrometer TP5000 (manufactured by Oshoku Riken) was used for measurement of the thermal reduction spectrum. Specifically, 500 mg of each composite oxide heated in air at 900 ° C for 4 hours is filled into a U-shaped quartz tube, and the quartz tube is filled with 90% Ar gas and 10% H gas.

2

The measurement was performed from a temperature range of 50 ° C. to 1000 ° C. at a heating rate of 10 ° C./min. While flowing a mixed gas composed of 30 ml Zmin. <Measurement results>

Tables 1 to 3 show the values of the specific surface area (unit: m ² / g) of each composite oxidized product and the value of the temperature at the peak appearing on the lowest temperature side in the heating-up reduction spectrum (hereinafter, referred to as the following). , “Peak temperature”!). 1 to 5 show the temperature-reduction spectra of the composite oxidized products shown in Table 1, respectively.

First, the following can be said from the measurement results of the specific surface area.

[0030] As shown in Table 1, the value of the specific surface area of the composite oxides of Examples 1 and 2 is about 3.5 times larger than the value of the specific surface area of the composite oxide of Comparative Example 1. Further, the value of the specific surface area of the composite oxide of Example 2 is larger than that of the composite oxide of Example 1. Then, the specific surface area of each composite oxidized product after firing at 900 ° C. for 4 hours is measured. As described above, the heat resistance of the composite oxidized product is enhanced by adding Ba.

Further, since the specific surface area of the composite oxidized product of Example 1 is 30.8 m ² Zg, the molar ratio is Bi:

The complex oxide containing Ba, in which Ba = 1: 1, can sufficiently prevent a decrease in the specific surface area at a high temperature due to the addition of Bi to the extent practically possible. Further, from Table 1, the specific surface area of the composite oxidized product of Example 2 and the specific surface area of the composite oxidized product of Comparative Example 2 show values, for example. Since the composite oxidized product of Comparative Example 2 does not contain Bi, even if the composite oxidized product of Comparative Example 2 is baked at 900 ° C for 4 hours, the specific surface area may not be reduced by Bi. Absent. On the other hand, since the composite oxide of Example 2 contains Bi, firing the composite oxide of Example 2 at 900 ° C. for 4 hours results in a decrease in specific surface area. However, since the specific surface area of the composite oxidized product of Example 2 and the specific surface area of the composite oxidized product of Comparative Example 2 show the same value, the molar ratio is Bi: Ba = 1: 3. The complex oxide containing Ba can completely prevent the specific surface area from decreasing at high temperatures due to the Bi-added mash, and as a result, the specific surface area has a practically useful size. .

[0032] Note that, as a promoter of an exhaust gas purifying catalyst for an engine, if the specific surface area after calcining at 900 ° C for 4 hours is 20 m ² / g or more, it is generally sufficiently practical.

[0033] Further, as shown in Table 2, the specific surface areas of the composite oxidized products of Examples 3 to 9 are 20 m ² Zg or more, which are practically very useful. In other words, Nb or V Even if Sr or Ca is used as the element B, the specific surface area can be made a practically useful size. Furthermore, since any of the composite oxides shown in Table 2 has a specific surface area of 20 m ² / g or more, the combination of the elements A and B is not particularly limited.

[0034] Further, as shown in Table 3, the specific surface area of each of the composite oxidized products of Examples 10 and 11 is 20 m ² / g or more, which is a very useful size for practical use. Therefore, even in the case of a composite acid product to which Ni or A1 is added, the specific surface area of the composite acid product can be made a very useful size for practical use.

From the results of Examples 1 to 4, even if the molar ratio between Ce and Zr in the composite oxide is different, the specific surface area of the composite oxide is 20 m ² Zg or more, which is very practical. It is a useful size for

From the measurement results of the temperature-reduction spectrum, the following can be obtained.

As shown in Table 1 and FIGS. 1, 2, 3, 4, and 5, it can be seen that the peak shifts to the lower temperature side due to the inclusion of Bi. Furthermore, since the peak temperatures of the composite oxides of Examples 1 and 2 are lower than the peak temperature of the composite oxide of Comparative Example 1, the reduction of the composite oxide on the low-temperature side due to the inclusion of Ba is included. Noh increases. Since the composite oxidized products of Examples 1 and 2 have a peak at 300 ° C. or less, the composite oxidized products of Examples 1 and 2 exhibit an exhaust gas purification catalyst even at 300 ° C. or less. Can act as a co-catalyst.

[0038] Further, as shown in Table 2, the peak temperatures of the temperature-reduced reduction sprouts of the composite oxides of Examples 3 to 9 are 300 ° C or lower. Therefore, the composite oxides of Examples 3 to 9 also act as cocatalysts of the exhaust gas purification catalyst even at 300 ° C or lower. In other words, regardless of whether Nb or V is used as the element A or Sr or Ca is used as the element B, the composite oxide acts as a cocatalyst of the exhaust gas purification catalyst even at 300 ° C. or lower. Further, since any of the composite oxides shown in Table 2 shows a peak temperature of 300 ° C. or lower, the combination of element A and element B is not particularly limited.

Further, as shown in Table 3, the peak temperature of the temperature-reduced reduction spectrum of the composite oxidized products of Examples 10 and 11 is 300 ° C. or lower. Therefore, even a composite oxide to which Ni or A1 has been added acts as a co-catalyst for an exhaust gas purification catalyst even at 300 ° C or lower. [0040] The results of Examples 1 to 4 show that even if the molar ratio between Ce and Zr in the composite oxidized product is different, the value of the peak temperature of the temperature-reduction reduction spectrum does not change so much at 300 ° C. In the following, it also acts as a promoter of the exhaust gas purification catalyst.

The following can be said in the measurement results of the temperature-reduction spectrum and the measurement result of the specific surface area.

[0042] Comparing Example 1 with Comparative Example 1, the peak specific temperatures were all 300 ° C or less. The specific surface area of the composite oxidized product of Comparative Example 1 contained Ba. It shows a remarkably small value of 2m ² Zg. In addition, comparing the measurement results of Example 1 with the measurement results of Comparative Example 2, the specific surface area was 30 m ² / g or more even in the case of deviation. Because it does not contain, it shows extremely high temperature of 550 ° C. The above measurement results also correspond to a case where the measurement results of Example 2 are compared with the measurement results of Comparative Example 1 or Comparative Example 2. As described above, the composite oxide which has Ce, Zr and Bi and does not contain Ba like the composite oxidized product of Comparative Example 1 has a small specific surface area! Therefore, it cannot be used practically as a promoter for exhaust gas purification catalysts. Therefore, as in the composite oxidation catalyst of Comparative Example 2, the composite oxidation containing Ce, Zr, and Ba but not Bi. It is practically used as an exhaust gas purifying catalyst because it does not exhibit the catalytic ability of an exhaust gas purifying catalyst in a low temperature range below 300 ° C. Cannot be used for That is, for the first time, by adding both bismuth oxide and barium oxide to the Ce—Zr-based composite oxide, even when the specific surface area is 20 m ² / g or more and 300 ° C. or less, the exhaust gas purification catalyst can be used. The catalyst exhibits a very useful catalytic ability as a promoter.

Further, as described above, the composite oxides described in Table 2 exhibit substantially the same effects as those of the composite oxides of Examples 1 and 2. Therefore, even if niobium oxide or vanadium oxide is added to the Ce—Zr-based composite oxide instead of bismuth oxide, and calcium oxide or strontium oxide is added instead of barium oxide, the composite oxide does not have a specific ratio. Even when the surface area is not less than 20 m ² Zg and not more than 300 ° C., the catalyst exhibits practically very useful catalytic ability as a promoter of an exhaust gas purification catalyst.

Further, as described above, the composite oxides shown in Table 3 exhibit substantially the same effects as those of the composite oxides of Examples 1 and 2. Therefore, even in the case of a complex oxidized product to which Ni or A1 is added, Even when the surface area is not less than 20 m ² Zg and not more than 300 ° C., the catalyst exhibits practically very useful catalytic ability as a catalyst for an exhaust gas purification catalyst.

When the specific surface area is 25 m ² Zg or more, it has more active sites for oxidation-reduction reaction, so that the specific surface area is preferably 25 m ² / g or more. Further, if the peak temperature is lower than 280 ° C, it can act as a promoter of the exhaust gas purification catalyst at a lower temperature.

In this example, Bi, V, and Nb are used as examples of the element A, and Ba, Ca, and Sr are used as examples of the element B. The elements A and B are not limited thereto. Never. The element A may include at least one metal element selected from the group consisting of Bi, V, Ti, Nb, W, Fe, Pr, Tb, and Eu. Ba, Sr, Ca, Mg, and La may include at least one selected from the group consisting of the forces. Therefore, for example, a composite iris made of Ce, Zr, Bi, V, Ba, and Sr may be used as the composite iris in this embodiment. In addition, the composition formula of the composite oxide is (Ce Zr) (AB) O (where x, y, z, and δ are, respectively, 0.05 ≤ x ≤ 0.95 and 0.01 ≤ y ≤ 0.99, 0.01 ≤ z ≤ 0.3, 1. 365 ≤ δ ≤ 1.995) can be used. In addition, even when the specific surface area is 20 m ² Zg or more and 300 ° C. or less, the composite oxide exhibits practically very useful catalytic activity as a cocatalyst of an exhaust gas purification catalyst. On the other hand, an element other than the above metal element may be added.

The cerium (IV) salt, zirconium salt, bismuth salt, barium salt, and the like used in synthesizing the composite oxidized product in the present example are not particularly limited, and are not particularly limited. It may be an inorganic salt such as salt chloride, nitrate or the like, or may be an organic salt such as acetyl acetonato complex.

[0048] Further, when synthesizing the composite oxide in the present example, the composite oxide was synthesized using a coprecipitation method including a step of heat-treating the raw salt aqueous solution. However, the present invention is not limited thereto. Known synthesis methods such as a reaction method and a hydrolysis method can be used. In order to achieve the purpose of increasing the specific surface area, it is preferable to synthesize using a coprecipitation method including a step of heating the raw material salt aqueous solution, as described in this example.

[0049] Further, the firing step for synthesizing the composite oxide may be performed in a reducing atmosphere even in an oxidizing atmosphere. The atmosphere may be changed, or the atmosphere may be changed alternately and repeatedly. Industrial applicability

As described above, the present invention is intended to purify exhaust gas discharged from the power of an engine, for example, an internal combustion engine of an automobile or the like, which is driven by energy supplied by the combustion of complex oxides, particularly gasoline and light oil. It can be used as a cocatalyst for an exhaust gas purifying catalyst, etc.

Claims

The scope of the claims

[1] General formula (Ce Zr) (A B) O

l-χ x 1 z 1-y y z ό

(Where x, y, z, and δ are respectively 0.055≤χ≤0.95, 0.011≤y≤0.99, 0.011≤z≤0.3, 1.365≤δ≤ 1. A number that satisfies 995)

A contains at least one metal element selected from the group consisting of Bi, V, Ti, Nb, W, Fe, Pr, Tb and Eu,

B is a complex oxide containing at least one selected from the group consisting of Ba, Sr, Ca, Mg, and La.

[2] The composite oxide according to claim 1, which has a peak at 300 ° C or less in a temperature-reduction reduction spectrum and has a specific surface area of 20 m ² Zg or more after calcining at 900 ° C for 4 hours. object

[3] The method according to claim 1 or 2, further comprising at least one selected from the group consisting of rare earth elements (excluding Ce, Tb, Eu, La and Pr), Ni, Cu, Al, Si and Be. The composite oxide described.

[4] A contains at least Bi,

2. The composite oxide according to claim 1, wherein B contains at least Ba.