JP2003020227A - Fine mixed oxide powder, production method thereor and catalyst - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce multiple oxide powder which has a large specific surface area and a large fine pore volume even after endurance at a high temperature, and in which, even when used as a catalyst carrying noble metals, the growth of the grains of the noble metals can be suppressed after endurance at a high temperature. SOLUTION: The powder consists of a multiple oxide of Zn oxide and the oxide of a metal M which is not allowed to enter into solid solution with the Zr oxide, and in which the Zr oxide and the oxide of metal M are uniformly dispersed on an nm scale. Since different oxides are acted as mutual barriers, sintering is suppressed. Further, fine pores formed between the oxides are made into mesofine pores on an nm scale, and a large specific surface area and a large fine pore volume can be realized.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a fine mixed oxide powder useful as a catalyst carrier, a method for producing the same, and a catalyst using the fine mixed oxide powder as a catalyst carrier. This catalyst can be used as a methane purification catalyst, an exhaust gas purification catalyst, a NO _x storage reduction catalyst, and the like.

[0002]

2. Description of the Related Art Conventionally, as a catalyst for purifying exhaust gas of automobiles, a three-way catalyst has been used which purifies the exhaust gas by simultaneously oxidizing CO and HC and reducing NO _x . As such a three-way catalyst, for example, a carrier layer made of γ-Al ₂ O ₃ is formed on a heat-resistant honeycomb substrate made of cordierite or the like, and platinum (Pt) or rhodium (Rh) is formed on the carrier layer. It is widely known that the above noble metal is supported.

The condition of the carrier used for the exhaust gas purifying catalyst is that it has a large specific surface area and high heat resistance, and in general, Al ₂ O ₃ , SiO ₂ , ZrO ₂ and TiO ₂ are often used. . Also, by using CeO ₂ which has an oxygen storage capacity together, it is possible to mitigate changes in the atmosphere of exhaust gas.

Further, Japanese Patent Application Laid-Open No. 9-024274 discloses a catalyst using a composite oxide composed of alumina and zirconia as a carrier. The composite oxide of alumina and zirconia, which is the carrier in this catalyst, is characterized in that Al and Zr are bonded via oxygen and alumina and zirconia are compounded at the atomic level. Exist adjacent to each other. Therefore, according to this catalyst, HC is activated at the acid site and NO is activated at the base site.
Are activated in an adjacent state to easily form an intermediate,
The reaction selectivity between HC and NO is improved. Further, it is described that this catalyst is also excellent in heat resistance.

On the other hand, from the viewpoint of protecting the global environment, the greenhouse effect of carbon dioxide (CO ₂ ) in exhaust gas has become a problem.
Therefore, in order to reduce the amount of CO ₂ emission, so-called lean burn in which lean combustion is performed in an oxygen excess atmosphere has been put into practical use. In this lean burn, the amount of fuel used can be reduced, and the amount of CO ₂ emitted as exhaust gas can be reduced.

[0006] Then as an exhaust gas purifying catalyst for lean-burn, JP-A-3-017652, composed of the _the NO _x storage material and the noble metals such as alkaline earth metal supported on a porous carrier such as alumina NO _x An occlusion reduction type catalyst is disclosed.
According to this NO _x storage reduction catalyst, the air-fuel ratio is controlled from the lean side to the stoichiometric or rich side (rich spike), so that the NO _x on the lean side is NO.
_Since it is stored in the _x storage material, which is released on the stoichiometric or rich side and reacts with reducing components such as HC and CO for reduction and purification, NO _x can be efficiently purified even in lean burn.

[0007]

By the way, in recent years, the temperature of exhaust gas from automobiles has risen to a high temperature of 600 to 700 ° C., against the backdrop of higher output of direct injection gasoline engines and increase in high speed running. However, the conventional catalyst has a problem that it has poor durability in actual exhaust gas, and the heat causes grain growth in the noble metal itself, resulting in a decrease in activity. In some cases, precious metal particles may grow due to sintering of the carrier. Therefore, it is required to prevent sintering of the carrier and suppress grain growth of the metal itself.

Further, Japanese Patent Application Laid-Open No. 9-024274 discloses that the heat resistance is high, but the reason therefor is not mentioned. And the composite oxide described in the publication is one in which Al atoms and Zr atoms are bonded via oxygen atoms, and since zirconia and alumina do not exist as particles, respectively, each characteristic is expressed. It is difficult to get it done. Further, there is no description about the specific surface area and the pores.

The conventional NO _x storage-reduction catalyst has a problem that the NO _x storage reduction ability is low in such a high temperature atmosphere.

In this NO _x storage reduction catalyst, NO in the exhaust gas is oxidized to NO 2 and is stored in the NO _x storage material as nitrate ions or nitrite ions. Therefore, it is considered that the higher the basicity of the carrier, the more effectively the basicity of the NO _x storage material is expressed, and the more the NO _x storage amount and storage rate are improved, the more the NO _x purification capacity in a high temperature atmosphere is improved. Therefore, it is considered that a highly basic carrier is preferable as the carrier for the NO _x storage reduction catalyst.

Therefore, "metal oxides and complex oxides" Tabe
As described in Shimizu and Fueki, p413, Kodansha (1978), since zirconia has a higher basicity than alumina, it has been conventionally used as a carrier for NO _x storage-reduction catalysts. It is more preferable to use zirconia.

However, the specific surface area of zirconia is lower than that of alumina, and when it is used as a catalyst carrier, the activity is lower than that of a catalyst using alumina as a carrier. It is also possible to synthesize zirconia having a high specific surface area, but there is a problem that the specific surface area and pore volume are reduced by sintering at a lower temperature than in the case of alumina.

The present invention has been made in view of the above circumstances, and has a large specific surface area and pore volume even after high temperature durability, and even when a precious metal is supported as a catalyst, noble metal particles after high temperature durability The purpose is to obtain a fine mixed oxide powder whose growth is suppressed.

[0014]

The fine mixed oxide powder of the present invention which solves the above-mentioned problems is characterized by a fine mixture of Zr oxide and an oxide of a metal M which does not form a solid solution with Zr oxide, The Zr oxide and the oxide of the metal M do not mix at the atomic level, but are dispersed uniformly on the nm scale while forming separate crystal grains.

In FE-STEM, Zr and metal M were ± 20% of the charged composition at 90% or more of each analysis point when EDX analysis was performed on a single particle without overlapping in the range of 0.5 nm in diameter.
It is desirable that the composition ratio be within the range. Also 800 ℃
It is particularly desirable to have the characteristic that the volume of pores having a pore diameter of 1 to 15 nm is 90% or more of the volume of pores having a pore diameter of 100 nm or less after firing for 5 hours. The oxide of the metal M is alumina, and it is desirable that the Zr oxide is contained in an amount of 50% by weight or more.

One of the features of the most suitable production method of the present invention for producing the above-mentioned fine mixed oxide powder is that it is prepared from an aqueous solution in which a Zr compound and a metal M compound in which the oxide does not form a solid solution with the Zr oxide are dissolved. This is to precipitate the Zr oxide precursor and the oxide precursor of the metal M, and to calcine the precipitate in a state where water is sufficiently present in the system.

Another characteristic of the production method most suitable for producing the fine mixed oxide powder of the present invention is that an aqueous solution in which a compound of Zr and a compound of the metal M in which the oxide does not form a solid solution with the Zr oxide are dissolved. To precipitate precipitates of the Zr oxide precursor and the oxide precursor of the metal M, ripen the precipitate in a suspension state using water as a dispersion medium, and then calcine.

The aging is preferably carried out at room temperature or higher.
It is more preferable to carry out at 00 to 200 ° C, more preferably 100 to 150 ° C.

The catalyst of the present invention is characterized in that the fine mixed oxide powder of the present invention carries a noble metal.
It is also preferable to use a NO _x storage reduction catalyst in which a noble metal and a NO _x storage material are supported.

[0020]

BEST MODE FOR CARRYING OUT THE INVENTION The fine mixed oxide powder of the present invention is
It is a mixture of a Zr oxide and an oxide of the metal M which does not form a solid solution with the Zr oxide, and the Zr oxide and the oxide of the metal M are uniformly dispersed on the nm scale. The state in which Zr and the metal M are evenly dispersed on the nm scale is 90% at each analysis point when EDX analysis with a diameter of 0.5 nm is performed on one particle without overlap in FE-STEM. %, It can be confirmed that Zr and metal M are detected at a composition ratio within ± 20% of the charged composition.

That is, the primary particles in the fine mixed oxide powder of the present invention are composed of Zr oxide and oxide of metal M, and the secondary particles obtained by aggregating the primary particles constitute the powder. In the primary particles, the oxide of Zr and the oxide of metal M are uniformly present in a very small size on the nm scale, so that the pores formed between the oxides also have fine mesoscales on the nm scale. It becomes pores and a high specific surface area can be realized. Mesopores have a diameter of 2 to 50 nm in IUPAC, but may also have a diameter of 1.5 to 100 nm due to the adsorption property of molecules. The mesopores referred to in the present invention have a measurable lower limit of 3.5 nm in principle using a mercury porosimeter.
Means pores in the 100 nm range.

And in the fine mixed oxide powder of the present invention,
Since the Zr oxide and the oxide of the metal M, which do not form a solid solution with each other, act as barriers to each other, sintering at high temperature is suppressed, and the pore volume of the mesopores can be kept high even after high temperature durability. . This fine mixed oxide powder is
After calcination at 0 ° C. for 5 hours, the pore volume having a pore diameter of 1 to 15 nm is 90% or more of the pore volume having a pore diameter of 100 nm or less. That is, it has a sharp pore distribution in an extremely narrow range. Since the sintering of each oxide is suppressed, the pore volume does not decrease, and there are many nm-scale pores even after high-temperature durability, and the pore volume remains extremely large. To do.

[0023] Thus, in the catalyst of the present invention in the fine mixed oxide powder obtained by supporting a noble metal or noble metal and _the NO _x storage material, having a catalyst component sharp pore distribution, such as precious metals and _the NO _x storage material Since it is stably supported in the mesopores in a highly dispersed state and the mesopores serve as a reaction field, the activity is extremely high. Further, even after high-temperature durability, the mesopores are sufficiently present in a large pore volume and the specific surface area is sufficiently large. And because the oxides that do not form a solid solution suppress sintering with each other,
The grain growth of the noble metal is also suppressed, and the decrease in activity after high temperature durability is greatly suppressed.

Then, the fine mixed oxide powder of the present invention is added to precious metal.
Genus and no_x NO with occlusion material_xWith an occlusion reduction type catalyst
In this case, since the carrier contains Zr oxide, it is highly basic.
No, no _x High storage capacity. Moreover, high ratio table even after high temperature durability
High NO due to its area and large pore volume_x Occlusion
Performance is maintained and durability is excellent.

That is, this fine mixed oxide powder is extremely useful as a carrier for a low temperature oxidation catalyst capable of removing HC in a low temperature range, a NO _x storage reduction type catalyst, a methane oxidation catalyst and the like.

The oxide of the metal M does not form a solid solution with the Zr oxide and includes Al ₂ O ₃ , MgAl ₂ O ₄ , ZrP ₂ O _7, etc. One or more of these should be used. You can
When used as a catalyst carrier, Al ₂ O ₃ having a large specific surface area and excellent heat resistance is particularly preferable.

The composition ratio of the Zr oxide and the oxide of the metal M in the metal oxide powder of the present invention is preferably Zr oxide: oxide of the metal M = 50/50 or more, by weight ratio, 80/20 or more. Is especially desirable. If this composition ratio is smaller than 50/50, the action of zirconia becomes small and the basicity of the carrier becomes small. The upper limit of this composition ratio is not particularly limited,
It is desirable to set it to 95/5 or less. If the amount of the oxide of the metal M is smaller than this, the effect of mutual suppression of sintering between the oxides cannot be obtained, and the high temperature durability becomes poor. For example, when the oxide of the metal M is alumina, the weight ratio is preferably ZrO ₂ / Al ₂ O ₃ = 90/10 to 60/40. When the amount of zirconia is less than this range, the basicity of the carrier becomes small, and the chemical stability when supporting an NO _x storage material such as an alkali metal or an alkaline earth metal also deteriorates. If the amount of zirconia exceeds this range, the high temperature durability will be poor, and the purifying performance of the catalyst will also deteriorate.

For example, when the oxide of the metal M is alumina, the fine mixed oxide powder of the present invention may have a characteristic that the average primary particle size after firing at 600 ° C. for 5 hours is 6 to 8 nm. desirable. With such a structure, grain growth is reduced even after being exposed to a high temperature, and after firing at 600 ° C. for 5 hours, the pore volume with a pore size of 1 to 15 nm is 0.09 cc / g or more, Further, after firing at 800 ° C. for 5 hours, the pore volume of pore diameters of 1 to 15 nm becomes 0.06 cc / g or more. This ensures a sufficient pore volume even after high temperature durability. Furthermore, the volume of pores having a pore size of 1 to 15 nm is 0.12 cc / g or more after firing at 600 ° C. for 5 hours,
It is more desirable to have the characteristic that the pore volume with a pore diameter of 1 to 15 nm is 0.09 cc / g or more after firing at 800 ° C. for 5 hours. The pore volume with a pore size of 1 to 15 nm is 0.18 cc / g or more after firing at 600 ° C for 5 hours, and the pore volume with a pore size of 1 to 15 nm is 0.12 cc / g after firing at 800 ° C for 5 hours. It is more desirable to have a characteristic of g or more.

Therefore, in the catalyst of the present invention in which the noble metal is supported on the fine mixed oxide powder, the pores which are the supporting sites of the noble metal are sufficiently present even after the high temperature durability, and the specific surface area is sufficiently large. This is ensured and the decrease in activity after high temperature durability is suppressed.

In the production method of the present invention capable of stably producing the fine mixed oxide powder of the present invention, first, the water-soluble compound of Zr and the water-soluble compound of the metal M whose oxide does not form a solid solution with the Zr oxide. A precipitate consisting of a Zr oxide precursor and a metal M oxide precursor is deposited from an aqueous solution in which and are dissolved. As the water-soluble compound of Zr and the water-soluble compound of metal M, a salt is generally used, and as the salt, sulfate, nitrate, hydrochloride,
Acetate can be used. Water and alcohols can be used as the solvent for uniformly dissolving the salt. Further, for example, aluminum hydroxide, nitric acid, and water may be mixed and used as a raw material of aluminum nitrate.

Then, by adding an alkaline solution to this solution, a precipitate of the oxide precursor is deposited. As the alkaline solution, an aqueous solution in which ammonia, ammonium carbonate, sodium hydroxide, potassium hydroxide, sodium carbonate or the like is dissolved, or an alcohol solution can be used. Ammonia and ammonium carbonate that volatilize during firing are particularly preferable. In addition, the pH of the alkaline solution is preferably 9 or more because it promotes the precipitation reaction of the precursor.

Then, the precipitate is calcined in a state where water is sufficiently present in the system. Alternatively, the precipitate is aged and then fired by performing an aging step of heating a mixture in a suspension state using water as a dispersion medium. Thereby, although the mechanism is unknown, a fine mixed oxide powder having a sharp pore distribution can be obtained.

In order to calcine the precipitate in a state where water is sufficiently present in the system, the solution containing the precipitate can be heated to evaporate the solvent and calcined as it is. Alternatively, the filtered precipitate may be calcined in the presence of steam. In this case, it is preferable to fire in a saturated steam atmosphere.

When the aging step is carried out, the heat of heating promotes the dissolution and reprecipitation and the growth of particles. This aging step is performed at room temperature or higher, preferably 100 to 2
It is desirable to carry out at 00 ° C, more preferably at 100 to 150 ° C. If the heating temperature is lower than 100 ° C, the aging-promoting effect is small and the aging time becomes long. On the other hand, if the temperature is higher than 200 ° C, the decomposition temperature of the oxide precursor may be high, which is not preferable because the firing temperature for forming the oxide is increased. Then, the obtained precipitate is fired to produce a fine mixed oxide powder having primary particles having a relatively small particle size.

The firing step may be carried out in the atmosphere, and the temperature is preferably in the range of 300 to 800 ° C. Firing temperature is 3
When it is lower than 00 ° C, the stability as a carrier is substantially lost. Further, firing at a temperature higher than 800 ° C causes a decrease in the specific surface area, and is unnecessary from the viewpoint of utilization as a carrier.

The catalyst of the present invention can be used as an exhaust gas purifying catalyst, a methane purifying catalyst and the like. This catalyst uses the fine mixed oxide powder of the present invention as a carrier and carries a noble metal thereon. In addition to the noble metal, it is also preferable to use a NO _x storage reduction type catalyst that supports a NO _x storage material such as an alkali metal or an alkaline earth metal. The shape of the catalyst is not particularly limited, such as pellet shape, foam shape or honeycomb shape.

The catalyst of the present invention forms a coat layer from the fine mixed oxide powder of the present invention on the surface of a substrate such as a honeycomb-shaped monolith substrate, pellet substrate or foam substrate, and a precious metal is formed on the coat layer. Alternatively, it is constituted by supporting a noble metal and a NO _x storage material. The material of the base material is only required to have heat resistance and required strength, and ceramics such as cordierite or metal foil can be used.

The coat layer can be formed by preparing a slurry containing the fine mixed oxide powder of the present invention and a binder component, and wet-coating and firing the slurry. Examples of the binder component include alumina sol, zirconia sol, silica sol and the like. In the case of NO _x storage reduction type catalyst,
For the purpose of occluding NO _x with a base, basic binders such as alumina sol and zirconia sol are preferable, and acidic silica sol is not preferable.

The noble metal supported on the coat layer is Pt, Rh,
It can be selected from Pd, Ru, Ir, etc. There is no difference in the degree of activity due to the noble metal species in the high temperature range of 550 ° C or higher, but it is desirable to use Pt because Pt has a particularly high oxidizing activity in the temperature range of 500 ° C or lower. Further, since Pt exhibits a high NO oxidation activity in the temperature range of 500 ° C. or lower, it is desirable to support Pt on the NO _x storage reduction catalyst. The amount of the noble metal supported can be arbitrarily selected within the range of 0.05 to 20% by weight, but it is preferably 2 g or more per liter of the catalyst. If the supported amount is smaller than this, the oxidation of NO will be insufficient and the NOx storage capacity will decrease.

As the NO _x storage material, alkali metals such as Li, Na, K and Cs, alkaline earth metals such as Ba, Be, Mg, Ca and Sr, Sc, Y, La, Ce, Pr and Nd, Examples are rare earth elements such as Hy and Yb. Among them, K, which has high alkalinity and is inexpensive,
Na is particularly preferred. The amount of this NO _x storage material supported is the amount of catalyst 1
It is preferable to use 0.2 to 2 mol per liter. If the supported amount is less than this range, the NO _x storage capacity becomes insufficient, and _{if the} supported amount exceeds this range, the activity may be reduced by covering the noble metal or accelerating grain growth of the noble metal.

[0041]

EXAMPLES The present invention will be specifically described below with reference to Examples and Comparative Examples.

(Example 1) 342.3 g of 18 wt% zirconium oxynitrate (0.5 mol as ZrO ₂ ) and 75.1 g of aluminum nitrate nonahydrate (0.2 mol as Al ₂ O ₃ ) were added to 2000
It was dissolved in g of ion-exchanged water, and 177 g of 25% ammonia water was added to the mixture while stirring to neutralize it, thereby coprecipitating the ZrO ₂ precursor and the Al ₂ O ₃ precursor.

Then, the precipitate and the supernatant liquid were aged without being separated, while being stirred under an atmosphere of 1.6 atm and 114 ° C. for hours. After that, the temperature was raised to 400 ° C. at a heating rate of 100 ° C./h, and the temperature was kept at 400 ° C. for 5 hours to evaporate to dryness. The obtained dried solid product was fired in the air at each temperature of 600 ° C., 700 ° C., 800 ° C. and 900 ° C. for 5 hours to prepare a fine mixed oxide powder of this example.

(Example 2) 342.3 g of 18 wt% zirconium oxynitrate (0.5 mol as ZrO ₂ ), 75.1 g (0.2 mol) of aluminum nitrate nonahydrate, and 0.02 mol of calcium nitrate were added to 2000 g of ion-exchanged water. Example 1
In the same manner as above, four kinds of fine mixed oxide powders having different firing temperatures were prepared.

(Example 3) Coprecipitation was carried out in the same manner as in Example 1, and thereafter 100% was obtained without separating the precipitate from the supernatant.
The temperature was raised to 400 ° C. at a temperature rising rate of ° C./h, and the mixture was kept at 400 ° C. for 5 hours and evaporated to dryness. The obtained dry solid is heated to 600 ° C, 700
The fine mixed oxide powder of this example was prepared by firing in the air for 5 hours at each temperature of 800C and 800C.

(Comparative Example 1) The same procedure as in Example 1 was carried out except that the oxide precursor was precipitated only from the aqueous zirconium oxynitrate solution without adding aluminum nitrate, and the same aging step was performed, followed by evaporation to dryness. The fine mixed oxide powder of Comparative Example 1 was prepared by firing in air at 600 ° C. for 5 hours.

Comparative Example 2 An oxide precursor was precipitated only from an aqueous zirconium oxynitrate solution without adding aluminum nitrate. After that, without separating the precipitate and the supernatant, the temperature was raised to 400 ° C at a heating rate of 100 ° C / h,
It was kept for 5 hours and evaporated to dryness. The obtained dried product is 600
The oxide powder of this comparative example was prepared by baking in the atmosphere at 5 ° C. for 5 hours. This oxide powder consists only of ZrO ₂ .

Comparative Example 3 Using commercially available ZrO ₂ powder containing 4% by weight of CaO, 600 ° C., 700 ° C., 800 ° C. and 900 ° C.
Each of these temperatures was fired for 5 hours in the air to obtain the oxide powder of this comparative example.

<Test / Evaluation> Using FE-STEM, Example 1
Of non-overlapping particles of fine mixed oxide powder
Elemental analysis was performed in the 0.5 nm range. The results are shown by white circles in FIG. As the analysis conditions, "HD-2000" manufactured by Hitachi, Ltd. was used, and the measurement was performed at an acceleration voltage of 200 kV. This device is equipped with an EDX detector (Vantage EDX system manufactured by NCRAN), and elemental analysis can be performed with high sensitivity by the characteristic X-ray generated from the sample.

As can be seen from FIG. 1, the composition distribution of Zr and Al is narrow within ± 10% around the theoretical atomic ratio (Zr: Al = 71: 29) even in a very small portion with a diameter of 0.5 nm. It is clear that they are concentrated on the range. If for example
If ZrO ₂ and Al ₂ O ₃ exist as particles of 0.5 nm or more, Zr is 100% or Al is 100% by the above measurement.
A large number of parts should be detected and should be dispersed in the range indicated by the black circles and arrows in FIG.

The X-ray diffraction (40 kV-350 mA) of each of the fine mixed oxide powders of the examples was measured. As a result, it was revealed that the diffraction line of ZrO ₂ was within the error range, no peak shift was observed, and it did not form a solid solution with Al ₂ O ₃ .

From the results of elemental analysis and X-ray diffraction, Al
It is considered that the surface of the ZrO ₂ particles is coated in the state of amorphous Al ₂ O ₃ or exists as fine crystals of γ-Al ₂ O ₃ .

Next, the specific surface areas of the oxide powders of Examples and Comparative Examples were measured, and the results are shown in Table 1.

[0054]

[Table 1]

From Table 1, comparing the ones calcined at 600 ° C., the fine mixed oxide powders of Examples 1 to 3 have a larger specific surface area than the comparative examples, and by mixing alumina to form a composite. It can be seen that the specific surface area has increased.
In addition, since the specific surface area of Comparative Example 1 is larger than that of Comparative Example 2, it can be seen that the specific surface area is also increased by performing the aging step.

Then, comparing the ones calcined at 800 ° C. or 900 ° C., the fine mixed oxide powders of the respective examples are
It is clear that the specific surface area is large and the heat resistance is remarkably improved as compared with Comparative Example 3 which is a commercially available CaO-stabilized zirconia powder.

Next, the pore distributions of the oxide powders of Examples 1 and 2 and Comparative Example 3 were measured using a mercury porosimeter, and the results are shown in FIG. For those baked at 800 ° C,
The pore volume of 3.5 to 15 nm was measured using a mercury porosimeter, and the results are shown in FIG.

As shown in FIG. 2, in the fine mixed oxide powders of Example 1 and Example 2, the pore distribution was highly concentrated in a narrow range of 15 nm or less, and the pore volume of 1-15 nm was the pore volume. Is 1
It can be seen that it occupies 95% or more of the pore volume of 00 nm or less and has an extremely sharp distribution.

Further, it can be seen from FIG. 3 that the fine mixed oxide powders of Examples 1 and 2 have a pore volume more than double that of Comparative Example 3 even after firing at 800 ° C.

That is, in the fine mixed oxide powder of the example,
Micropores with a pore diameter of 15 nm or less exist stably up to high temperatures. Such pores are useful as a support site for catalyst components such as precious metals and NO _x storage materials, and because they exist stably up to high temperatures, the catalyst components remain stable in a highly dispersed state up to high temperatures. Believed to be retained.

Example 4 Prepared in Example 1, 600 ° C.
Mix 30 parts by weight of finely mixed oxide powder calcined in, 30 parts by weight of commercially available heat-resistant alumina powder, and 40 parts by weight of CeO ₂ -ZrO ₂ solid solution powder (molar ratio CeO ₂ : ZrO ₂ = 45: 55) Then, aluminum nitrate, boehmite, and water were added to prepare a slurry.

Next, a honeycomb substrate of 1.3 liter 400 cells / in ² was prepared, and the above slurry was adhered and dried,
The coated layer was formed by baking at 500 ° C. for 3 hours. The coat layer was formed in an amount of 190 g per liter of the honeycomb substrate.

Then, Pt and Pd were respectively adsorbed and supported on the above-mentioned coat layer using an aqueous solution of dinitrodiammine platinum and an aqueous solution of palladium nitrate, and each was baked at 300 ° C. for 2 hours to prepare a catalyst of Example 4. 1.1 g of Pt and Pd are loaded per liter of the catalyst.

(Comparative Example 4) 60 parts by weight of commercially available heat-resistant alumina powder and CeO ₂ -ZrO ₂ solid solution powder (in molar ratio CeO ₂ : ZrO ₂ =
45:55) 40 parts by weight, aluminum nitrate, boehmite and water were added to prepare a slurry. A coat layer was formed in the same manner as in Example 4 except that this slurry was used,
After firing in air at 500 ° C. for 3 hours, as in Example 4.
The catalyst of Comparative Example 4 was prepared by loading Pt and Pd in the same amount.

<Test / Evaluation> The catalysts of Example 4 and Comparative Example 4 were mounted on the exhaust system of a D4 engine, respectively, and actual exhaust gas was flowed under the two conditions A and B shown in Table 2. Condition A is a condition for injecting fuel in the intake stroke and is a lean condition for A / F = 15.0. The B condition is a condition for injecting fuel in the compression stroke, and although A / F = 15.0, the CO concentration in the exhaust gas is relatively increased. Table 2 shows the exhaust gas composition under each condition.

[0066]

[Table 2]

HC is 50% from the time when the exhaust gas is introduced into the catalyst
The time required for purification was measured, and the results are shown in Table 3. The HC purification rate was measured 20 seconds after the introduction of the exhaust gas into the catalyst, and the results are shown in Table 3.

[0068]

[Table 3]

From Table 3, it can be seen that the catalyst of Example 4 can purify HC earlier than the catalyst of Comparative Example 4, and that it has a high low temperature purification activity. This difference is due to the presence or absence of the fine mixed oxide powder of Example 1, and it is clear that the use of the fine mixed oxide powder of Example 1 as a carrier improved the low temperature activity.

Example 5 20 g of the fine mixed oxide powder prepared in Example 1 and calcined at 600 ° C. was added to 300 g of ion-exchanged water.
g, and then a predetermined amount of a palladium nitrate aqueous solution having a predetermined concentration was mixed. This was evaporated to dryness, Pd was impregnated and supported at a ratio of 5 g with respect to 120 g of the fine mixed oxide powder, and the mixture was calcined in air at 300 ° C. for 2 hours. Compacting this
A 0.5-1.0 mm pellet catalyst was prepared.

Comparative Example 5 Comparative Example 5 was carried out in the same manner as in Example 5 except that the heat-resistant alumina powder made of alumina containing 1.5 mol% of lanthana was used in place of the fine mixed oxide powder of Example 1. Pellet catalyst was prepared.

<Test / Evaluation> The pellet catalysts of Example 5 and Comparative Example 5 were placed in a fixed bed flow reactor. Then, the model gas shown in Table 4 was added to 7 g per 1 g of catalyst
Room temperature to 600 ° C while flowing at liter / minute
The temperature was raised up to 10 ° C./minute until the methane purification rate was continuously measured. Then, the methane 50% purification temperature and the methane 90% purification temperature were calculated, and the results are shown in Table 5.

[0073]

[Table 4]

[0074]

[Table 5]

From Table 5, it can be seen that the catalyst of Example 5 has a higher methane purification activity than that of Comparative Example 5, and can purify methane from a lower temperature range.

Example 6 200 parts by weight of the fine mixed oxide powder prepared in Example 2 and calcined at 800 ° C. and Example 1
Finely mixed oxide powder prepared in and calcined at 800 ℃ 50
A slurry was prepared by mixing 10 parts by weight of Rh in advance by weight with a catalyst powder carrying 10% by weight of Rh and adding 10% by weight of zirconia binder (“NZS-30B” manufactured by Nissan Chemical Industries, Ltd.) as ZrO ₂ .

Next, a 35 cc, 400 cell / in ² cordierite honeycomb base material was prepared, and the above slurry was adhered and dried, followed by firing at 500 ° C. for 1 hour to form a coat layer. The coat layer was formed in an amount of 250 g per liter of the honeycomb substrate.

Then, 10 g / L of Pt was loaded on the above coating layer using an aqueous solution of dinitrodiamine platinum and baked at 300 ° C. for 1 hour, and then K was added at 0.6 mol / L using an aqueous solution of potassium acetate.
L was carried and calcined at 300 ° C. for 1 hour to prepare a NO _x storage reduction catalyst of Example 6.

Comparative Example 6 Instead of 200 parts by weight of the fine mixed oxide powder prepared in Example and calcined at 800 ° C., a commercially available alumina powder (“MI-386” manufactured by WD Grace) 200
A NO _x storage reduction catalyst of Comparative Example 6 was prepared in the same manner as in Example 6 except that 10 parts by weight of alumina sol (“Alumina sol 520” manufactured by Nissan Chemical Industries, Ltd.) was used in place of zirconia sol in an amount of 10 parts by weight. did.

<Test / Evaluation> NO of Example 6 and Comparative Example 6
_x Each of the storage reduction catalysts was placed in a fixed-bed flow reactor, and the lean gas in the model gas shown in Table 6 was passed through the catalyst for 10 minutes at an inlet gas temperature of 700 ° C. It was distributed in 3 seconds. Then, the NO _x concentration in the discharged gas after flowing the rich spike gas was measured with time, and a NO _x storage curve was created.

[0081]

[Table 6]

[0082] The _the NO _x storage curve is shown as in FIG. 4, for example, NO _x amount occluded by time t is represented by the area A, NO _x amount discharged without being occluded by the catalyst area B Therefore, the NO _x purification rate (%) is calculated by 100 × area A / (area A + area B). Therefore, the time t when the NO _x purification rate becomes 95% is obtained and corresponds to the area A at that time.
The NO _x storage amount was calculated to be 95% NO _x storage amount. The result is shown in FIG. 5 as an initial stage.

Next, the NO _x storage reduction catalysts of Example 6 and Comparative Example 6 were placed in a fixed bed flow reactor, and the model gases shown in Table 7 were alternately alternated between lean gas for 4 minutes and rich gas for 1 minute. A durability test was conducted in which the gas temperature was 750 ° C. for 5 hours. Then, the 95% NO _x storage amount of both catalysts after the durability test was measured in the same manner as above, and the result was 75%.
It is shown in FIG. 5 after the endurance at 0 ° C.

[0084]

[Table 7]

From FIG. 5, it can be seen that the catalyst of Example 6 exhibits a higher NO _x storage amount than the catalyst of Comparative Example 6 both in the initial stage and after the endurance. It is clear that this is due to the use of the fine mixed oxide powder of the present invention as the carrier.

[0086]

The fine mixed oxide powder of the present invention has an extremely small pore size with a large pore volume, has a sharp pore distribution in a narrow range, and suppresses sintering. . Therefore, according to the catalyst of the present invention in which a noble metal is supported on this fine mixed oxide powder,
The noble metal is supported in high dispersion, grain growth is suppressed, and the large pore volume improves gas diffusivity. As a result, high purification activity is exhibited even after high temperature durability.

Further, according to the NO _x storage reduction type catalyst of the present invention, in which the fine mixed oxide powder is loaded with the noble metal and the NO _x storage material,
It shows a high NO _x storage capacity even after high-temperature durability, and it is possible to efficiently purify NO _x in exhaust gas for a long time even in an engine in which the exhaust gas temperature becomes high.

[Brief description of drawings]

FIG. 1 shows the result of elemental analysis of a fine mixed oxide powder of Example 1 in a range of φ 0.5 nm, and is a distribution diagram of an atomic ratio of Zr and Al.

FIG. 2 is a graph showing pore distributions of oxide powders of Examples and Comparative Examples.

FIG. 3 is a graph showing pore volumes of oxide powders of Examples and Comparative Examples.

FIG. 4 shows an example of a NO _x occlusion curve, which shows that
6 is a graph showing the relationship with the NO _x concentration.

5 is a graph of 95 NO _x storage reduction type catalysts of Example 6 and Comparative example 6. FIG.
% Is a graph showing the _the NO _x storage amount.

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) B01J 23/58 F01N 3/08 A 23/63 3/10 A 35/10 301 Z F01N 3/08 3 / 28 Q 3/10 301C 301P 3/28 B01J 23/56 301A 301 B01D 53/36 103B ZAB 102H (72) Inventor Haruo Imagawa 1 41, Yokomichi Nagakute-cho, Aichi-gun, Aichi Prefecture Toyota Central Research Co., Ltd. In-house (72) Akira Morikawa Akira Prefecture, Aichi-gun, Nagakute-cho, Aichi Prefecture 41 41, Yokoshiro Yokouchi, Central Research Institute of Toyota Corporation (72) Inventor Shinichi Matsunaga, Aichi-gun, Aichi-gun, Nagakute-cho, 41 1 Toyota Central Research Institute Co., Ltd. (72) Inventor Toshio Yamamoto 1 of 41 Yokomichi Nagakute-cho, Aichi-gun, Aichi Prefecture Toyonaka Co., Ltd. In-lab (72) Inventor Masa Tadashi, Nagakute-cho, Aichi-gun, Aichi 1 1 41, Yokomichi Yokomichi Toyota Central Research Institute Co., Ltd. F-term (reference) 3G091 AA02 AA12 AA17 AA19 AA28 AB06 BA01 BA14 BA15 BA19 BA39 CB02 DA01 DA02 DA04 DB10 EA30 FB02 FB10 FB11 FB12 FC04 FC07 GA01 GA03 GA07 GA20 GB01X GB02W GB02Y GB03W GB03Y GB04W GB04Y GB05W GB06W GB07W GB10X GB16X GB17X 4D048 AA06 BA04XABAXBAAX BAAX BA30XBA08XBAAX BA08X BA30X AE05 AE07 4G069 AA01 AA03 AA08 BA01B BA05B BA16B BB06A BB06B BC03B BC32.

Claims (11)

[Claims] 1. A mixture of a Zr oxide and an oxide of a metal M which does not form a solid solution with the Zr oxide, wherein the Zr oxide and the metal M are mixed.
A fine mixed oxide powder characterized by being uniformly dispersed with the oxide of. 2. In the FE-STEM, Zr and the metal M account for 90% or more of each analysis point when EDX analysis with a diameter of 0.5 nm is performed on one particle without overlap. The fine mixed oxide powder according to claim 1, which is detected at a composition ratio within ± 20%. 3. The pore size is 1 to 5 after firing at 800 ° C. for 5 hours.
Pore volume of 15 nm is 90% of pore volume of 100 nm or less
The fine mixed oxide powder according to any one of claims 1 and 2, which has the above-mentioned characteristics. 4. The oxide of the metal M is alumina,
The fine mixed oxide powder according to claim 1, wherein the Zr oxide is contained in an amount of 50% by weight or more. 5. A Zr oxide precursor and a precipitate of the metal M oxide precursor are precipitated from an aqueous solution in which a compound of Zr and a compound of the metal M in which the oxide does not form a solid solution with the Zr oxide are dissolved to form a system. The method for producing a fine mixed oxide powder according to any one of claims 1 to 4, wherein the precipitate is calcined in a state where water is sufficiently present therein. 6. A Zr oxide precursor and a precipitate of the oxide precursor of the metal M are precipitated from an aqueous solution in which a compound of Zr and a compound of the metal M in which the oxide does not form a solid solution with the Zr oxide are dissolved, and water is added. The method for producing a fine mixed oxide powder according to any one of claims 1 to 4, wherein the precipitate is aged in a suspension state in which is used as a dispersion medium, and then calcined. 7. The method for producing a fine mixed oxide powder according to claim 6, wherein the aging is performed at room temperature or higher. 8. The method for producing a fine mixed oxide powder according to claim 6, wherein the aging is performed at 100 to 200 ° C. 9. The method for producing a fine mixed oxide powder according to claim 6, wherein the aging is performed at 100 to 150 ° C. 10. A catalyst comprising a carrier containing the fine mixed oxide powder according to claim 1 and a noble metal supported on the carrier. 11. A catalyst comprising a carrier containing the fine mixed oxide powder according to any one of claims 1 to 4, which carries a noble metal and a NO _x storage material.