JPH08215576A - Composite superfine particle, its production and catalyst for synthesis and refining of methanol using the same - Google Patents

Abstract

PURPOSE: To provide composite superfine particles which are very minute, has high catalytic activity as a catalyst for synthesis and refining of methanol, and can maintain high catalytic activity and selectivity even at high temp. CONSTITUTION: The composite superfine particles are produced by heating and melting the source material comprising aluminum and M<1> element (M<1> is at least one element selected from Fe, Co, Ni, Cu, Ru, Rh, Pd, Ag, Pt and Au) in an inert gas atmosphere containing oxygen to allow the evaporated material react with the oxygen so that first superfine particles comprising Al and/or Al oxide and second superfine particles comprising M<1> element or/and oxide are joined. The obtd. superfine particles contain a large amt. of composite superfine particles each having such a structure that minute superfine particles S of M<1> metal or M<1> oxide having catalytic activity is carried on a large-size superfine particle L comprising Al or γ-Al2 O3 . The composite superfine particle is useful as a catalyst for synthesis and refining of methanol having high activity and high selectivity.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a composite ultrafine particle in which an oxide and an oxide, or / and an oxide and a metal are very finely combined, and a method for producing the same, more specifically, a metal or a metal having a catalytic property. / And / or its oxide ultrafine particles and aluminum or / and aluminum oxide ultrafine particles are nm
TECHNICAL FIELD The present invention relates to ultrafine particles compounded at a level and a method for producing the same.
The present invention also relates to the use of such composite ultrafine particles as a catalyst for methanol synthesis / reforming.

[0002]

Methanol is relatively easily reformed into a gas having a high hydrogen content in the presence of a catalyst and steam, as shown in the following reaction formula (1). CH ₃ OH + H ₂ O → 3H ₂ + CO ₂ (1) The obtained reformed gas is used as an energy source such as a fuel for fuel cell power generation by separating hydrogen, and also as a raw material for the chemical industry. Is also used. On the other hand, the reverse reaction of the steam reforming reaction of methanol, that is, the methanol synthesis reaction (or carbon dioxide immobilization reaction) of obtaining methanol from carbon dioxide and hydrogen as shown in the following reaction formula (2), It is attracting attention as a powerful means of carbon recycling and global warming prevention. 3H ₂ + CO ₂ → CH ₃ OH + H ₂ O (2) That is, CO ₂ emissions tend to increase with the increase in economic activity in recent years, and global warming due to the accumulation of CO ₂ In recent years, the reduction of CO ₂ emissions has become an urgent task on a global scale. Various CO ₂ reduction methods have been studied as a solution to this problem. Among them, the most effective method is a method of reacting CO ₂ and H ₂ to convert it into an alcohol raw material such as methanol and recycling it. Methanol obtained by this method can be used as an energy source, but since it is also a basic raw material when synthesizing chemicals, if this method can be established, not only CO ₂ emission can be reduced, but also petroleum It can also contribute to resource saving.

As catalysts for the methanol synthesis reaction which is the steam reforming reaction of methanol and its reverse reaction, oxide type catalysts (JP-A-6-178938 and JP-A-4-122) are used.
450, Japanese Examined Patent Publication No. 5-67336, etc.), metal catalysts (JP-A-3-258738, JP-A-60-9493).
No. 1, etc.) and alloy-based catalysts are known, and among them, the performance of oxide-based catalysts is considered to be good. The oxide powder is generally produced by a liquid phase method using a metal salt as a starting material and a coprecipitation method. However,
Since it is produced in the liquid phase, impurities remain in the powder, which makes it difficult to obtain a highly pure powder. Further, when the oxide powder produced by this liquid phase method is used as a catalyst material, the obtained oxide is a catalyst precursor, so it is necessary to activate the catalyst by a reduction treatment prior to use, There is also a problem that it is difficult to obtain sufficient catalytic activity due to the influence of impurities.

As a steam reforming reaction catalyst for methanol, a CuO--ZnO--Al ₂ O ₃ -based catalyst is generally used. However, at a low temperature of 200 ° C., the catalytic activity is low and sufficient catalytic performance is not obtained. Also, 40
At a high temperature of 0 ° C., the catalytic activity is lowered, and further the selectivity is rapidly lowered. As another catalyst for reforming methanol steam, Cu-obtained by a liquid phase method is used.
Ni-Al-O powder has been proposed (Japanese Patent Publication No. 5-6).
7336 catalyst for methanol reforming). However, this powder is not suitable because it has a low catalytic activity at low temperatures and has a very low selectivity of about 30 to 70% over the entire temperature range. On the other hand, in the reaction for obtaining methanol from CO ₂ and H ₂ which is the reverse reaction of the steam reforming reaction of methanol, the same equilibrium reaction as in the methanol steam reforming is obtained as is clear from the above formulas (1) and (2). The same catalyst, CuO—ZnO—Al ₂ O ₃ type catalyst, is considered promising. However, in the reaction using this catalyst, both the catalytic activity and the selectivity are low, and the overall methanol yield is increased by passing an unreacted gas through the catalyst many times, such as by improving the system and recycling method. . However, it has been pointed out that this recycling method requires a large amount of electric power, and thus is not a method for reducing CO ₂ . For these reasons, a high-performance catalytic material having higher activity and higher selectivity is expected in the methanol steam reforming reaction and the synthetic reaction which is the reverse reaction thereof.

[0005]

Therefore, an object of the present invention is to provide a composite ultrafine particle which is highly pure and extremely fine and which can be advantageously used as a catalyst for synthesizing and reforming methanol, etc. It is to make in. A further object of the present invention is to provide nanometer-order composite ultrafine particles in which fine ultrafine particles of a metal having a catalytic property or / and its oxide are bonded onto ultrafine particles of Al or / and Al oxide. It is to provide the manufacturing method. Another object of the present invention is higher in catalytic activity and selectivity in both low temperature range and high temperature range than those obtained by a liquid phase method such as a conventionally known coprecipitation method,
It is to provide a catalyst for synthesizing and reforming methanol having excellent durability.

[0006]

In order to achieve the above object, according to one aspect of the present invention, Al or / and Al
Ultrafine particles of the oxide of M ¹ and M ¹ element (provided that M ^1
1 is Fe, Co, Ni, Cu, Ru, Rh, Pd, A
at least 1 selected from the group consisting of g, Pt and Au
It is a seed element. The present invention provides composite ultrafine particles, characterized in that they are joined to the second ultrafine particles made of a metal or / and an oxide. Part of the Al or / and Al oxide of the first ultrafine particles is an element of M ² element (provided that M ²
Is Ti, Zr, Hf, V, Cr, Mn, Zn, Ga, M
It is at least one element selected from the group consisting of g, Si, Ca, Y, La and Ce. It may be replaced with the metal or / and the oxide). Such composite ultrafine particles can be extremely advantageously used as a catalyst for a methanol synthesis reaction and a steam reforming reaction.

According to another aspect of the present invention, in order to provide the composite ultrafine particles as described above, aluminum and M ¹ element (wherein M ¹ is Fe, Co, Ni, Cu, Ru, R).
It is at least one element selected from the group consisting of h, Pd, Ag, Pt, and Au. ) The raw material consisting of
By heating and melting in an inert gas atmosphere containing oxygen, the evaporated material is reacted with oxygen in the atmosphere, and Al or / and Al
Of composite ultrafine particles, characterized in that the composite ultrafine particles are produced by bonding the first ultrafine particles composed of the oxide of 1) and the second ultrafine particles composed of the metal or / and the oxide of the M ¹ element. A method is provided. In a preferred embodiment, aluminum is 5 to 95 atom%, and M ¹ element is 5 to 9 atom%.
Using a raw material having a composition of 5 atomic%, arc melting is performed in an atmosphere of a mixed gas of 50 to 99% of an inert gas of Ar, He or N ₂ and 1 to 50% of an oxygen gas. In addition, 50 atomic% or less of Al is an M ² element (provided that M ² is T
i, Zr, Hf, V, Cr, Mn, Zn, Ga, Mg,
It is at least one element selected from the group consisting of Si, Ca, Y, La, and Ce. It is also possible to use a raw material obtained by substituting a).

[0008]

The present inventors have conducted extensive studies to achieve the above object, and as a result, when an alloy is melted by an arc or the like to produce ultrafine particles, an atmosphere containing oxygen is used as a reaction gas, and the arc is used. As a master alloy that dissolves due to, for example, M ¹ metal (M ¹ =
Fe, Co, Ni, Cu, Ru, Rh, Pd, Ag, P
When using an alloy containing t or Au), Al or / and A
1 nm nano-scale fine composite ultrafine particles in which ultrafine particles of oxide and a metal (M ¹ ) having catalytic properties or / and its oxide (M ¹ -O) are bonded are produced, and such shape and size are obtained. It was found that the obtained composite ultrafine particles exhibit extremely high catalytic activity as a catalyst for the synthesis reaction of methanol and the steam reforming reaction, by virtue of having a certain degree.

Since the catalytic reaction generally proceeds on the surface of the catalyst, if the catalyst particles are made highly pure and fine, the number of active sites per unit mass is remarkably increased, and high activity can be expected. Further, it is considered that if the catalyst particles are made into ultrafine particles and are combined with an oxide carrier having a good compatibility to control the interaction between the catalyst particles and the oxide carrier, a catalyst with higher activity will be obtained. The ultrafine particles produced by the method of the present invention are, as shown in FIG. 1, large particles L made of Al or γ-Al ₂ O ₃ and M ¹ having catalytic activity attached thereon.
It contains a large amount of composite ultrafine particles composed of small particles S made of metal or M ¹ oxide. For example, when an Al-Cu alloy is used as the raw material, the generated phase is A
l, at least one type of γ-Al ₂ O ₃ and Cu, Cu
₂ O, CuO, at least one kind, but a large amount of composite ultrafine particles composed of large particles L made of Al or γ-Al ₂ O ₃ and small particles made of Cu, Cu ₂ O, or CuO attached to them. The ultrafine particles contained are generated.
However, not all ultrafine particles are compounded in such a state. As described above, in the ultrafine particles obtained by the present invention, finer ultrafine particles made of M ¹ metal or M ¹ oxide exhibiting catalytic activity are larger than Al or γ-Al ₂
It contains a large amount of composite ultrafine particles of a structure supported on O ₃ ultrafine particles, and unlike oxide particles produced by a conventional liquid phase method, the particles are extremely fine and contain no impurities. , The purity is extremely high. Therefore, the ultrafine particles obtained by the method of the present invention have high catalytic activity and can be advantageously used as a catalyst for methanol synthesis reaction and reforming reaction.

According to the method of the present invention, the composite ultrafine particles constituting the catalyst particles are obtained in which the large particles L made of Al or γ-Al ₂ O ₃ are distributed in the size range of 5 to 500 nm. In particular, there are many ultrafine particles distributed in the range of 10 to 100 nm. On the other hand, small particles S made of M ¹ metal or its oxide supported on the large particles S
The size distribution range is 0.5 to 200 nm, but in most cases, the range is 1 to 50 nm. Considering the characteristics as a catalyst material, it is considered that the particle size of M ¹ metal or its oxide exhibiting catalytic activity is preferably 30 nm or less. Further, when the particle size of the M ¹ metal or its oxide is 10 nm or less, the catalytic effect is remarkably improved, and the particle size of 5 nm or less is particularly preferable.

The composition of the raw material used is preferably in the range of 5 to 95 atom% of aluminum and 5 to 95 atom% of M ¹ element. By using the raw material in this range,
Ultrafine particles containing the composite ultrafine particles having the above-mentioned structure and high catalytic activity can be produced. When the amount of aluminum in the raw material is less than 5 atomic%, the ratio of M ¹ metal or its oxide contained in the produced ultrafine particles becomes too large, and the ultrafine particles are used as a catalyst material as shown in FIG. Since it is difficult to form the composite ultrafine particles in an ideal form, the catalytic activity decreases. On the other hand, when the amount of aluminum exceeds 95 atomic%, the ratio of M ¹ metal or its oxide exhibiting catalytic activity decreases, and the overall catalytic activity decreases. In addition, if the ratio of M ¹ element in the raw material becomes too large, M
The grain growth of the ¹ metal or its oxide is likely to occur, the particle size is reversed from the above state, and the particle size of the M ¹ metal or its oxide is bonded to Al or γ.
-Al ₂ O ₃ composite ultrafine particles becomes larger than the particle will be generated. Therefore, as shown in FIG.
Or, small particles S made of M ¹ metal or its oxide showing catalytic activity by large particles L made of γ-Al ₂ O _3.
In order to produce a large amount of composite ultrafine particles in the form of an ideal catalyst material in which is supported, the composition range of the raw material is 40
˜95 at% Al-5 to 60 at% M ¹ is more preferable.

In the method of the present invention, a part of the Al, preferably 50 atomic% or less, is M ² element (provided that M ²
Is Ti, Zr, Hf, V, Cr, Mn, Zn, Ga, M
It is at least one element selected from the group consisting of g, Si, Ca, Y, La and Ce. It is also possible to use a raw material obtained by substituting a). These M ² elements are Al
A complex oxide or mixed oxide (hereinafter collectively referred to as an Al-M ² oxide) is formed together with the complex oxide or mixed oxide to carry ultrafine particles of a metal or an oxide composed of the M ¹ element. Contributes to the formation of catalyst particles. Thus, Al
By substituting a part of M ² with the M ² element, the interaction between the Al—M ² oxide and the M ¹ metal or its oxide is strengthened, and the catalytic activity is improved. However, when the ultrafine particles of M ¹ metal or its oxide exhibiting catalytic activity are larger than the ultrafine particles of Al-M ² oxide, the M ¹ metal or its oxide is likely to cause grain growth, and as a result, The catalytic activity will decrease. Therefore, it is preferable that the particle size of the Al-M ² oxide ultrafine particles is larger than the particle size of the M ¹ metal or its oxide ultrafine particles, and it is preferable that the ultrafine particles have a particle size twice or more. desirable. In this way, in order to obtain a catalyst particle in an ideal form in which ultrafine particles of M ¹ metal or its oxide having a finer particle diameter are supported by ultrafine particles of Al-M ² oxide having a relatively large particle diameter. In the raw material A
It is desirable to substitute 50 atomic% or less, more preferably 5 to 50 atomic% of 1 with M ² element.

The composition of the atmosphere gas is Ar, H
e, N ₂ or other inert gas 50 to 99%, oxygen gas 1 to 5
The range of 0% is preferable. The ratio of oxygen gas in the atmosphere is 1
If it is less than 0.1%, the effect of oxygen plasma is almost eliminated, oxides are hard to be generated, and it becomes difficult to produce catalyst particles in an ideal form as shown in FIG. On the other hand, the proportion of oxygen gas is 5
If it exceeds 0%, the effect of oxygen plasma becomes strong, the surface of the mother alloy of the raw material is covered with an oxide film, the arc becomes unstable, or in the worst case it does not occur, and ultrafine particles are not produced. There is a fear. In order to make it difficult for the surface of the raw material master alloy to be covered with an oxide film and to facilitate the production of ideal oxide ultrafine particles as shown in FIG. The ratio is more preferably in the range of 1 to 20%. Atmospheric gas pressure is 30 Torr
Or more, preferably 50 Torr or more, 1500 Torr
The following ranges are suitable. If it is less than 30 Torr, the arc plasma becomes unstable and it becomes difficult to generate ultrafine particles.
On the other hand, when it exceeds 1500 Torr, the amount of ultrafine particles generated hardly changes.

The mother alloy is preferably melted in an inert gas atmosphere before being melted in an inert gas atmosphere containing oxygen gas, but this mother alloy is melted in an inert gas atmosphere containing oxygen gas. Before melting, the same may be melted in a vacuum in the same container, or may be melted in another vacuum container. Further, as the heating melting method in the present invention, in addition to the arc melting method, a high frequency heating melting method, a plasma jet heating method, a high frequency induction heating method (high frequency plasma heating), an electron beam heating method, a laser beam heating method, etc. may be used. Is possible. The composite ultrafine particles of the present invention are not limited to the steam reforming reaction of methanol represented by the reaction formula (1) and the reaction of synthesizing methanol from carbon dioxide and hydrogen represented by the reaction formula (2). A similar reaction,
For example, it can be advantageously used as a catalyst for a reaction for synthesizing methanol from carbon monoxide and hydrogen and its reverse reaction.

[0015]

EXAMPLES The present invention will be specifically described below with reference to examples, but it goes without saying that the present invention is not limited to the following examples.

FIG. 2 shows an example of an apparatus suitable for producing composite ultrafine particles by arc melting according to the present invention,
It is a schematic block diagram of the apparatus used in the Example mentioned later. This apparatus 1 comprises a melting chamber 2 and a glove box 3. In the melting chamber 2, a hearth 4 for arranging the raw material (mother alloy) A is rotatably arranged by a motor 12. An arc electrode 5 is arranged above the hearth 4 in the melting chamber 2 so as to be accessible to the mother alloy A arranged in the hearth 4. The melting chamber 2 and the glove box 3 are communicated with each other by a collecting pipe 6, and a filter 8 is detachably attached to a rear end 7 of the collecting pipe 6 located inside the glove box 3. Reference numeral 9 is a gas mixer,
An inert gas containing a predetermined concentration of oxygen gas is supplied into the melting chamber 2. Reference numeral 10 is a turbo molecular pump, and 11 is a mechanical booster pump and a rotary pump, which control the differential pressure between the melting chamber 2 and the glove box 3.

Next, the operation procedure will be described. First,
An inert gas containing a predetermined concentration of oxygen gas is supplied into the dissolution chamber 2 at a predetermined flow rate, and the gas pressure in the dissolution chamber 2 is set to a predetermined pressure. At this time, it is preferable to evacuate the inside of the apparatus once, except when the atmosphere is used as the atmospheric gas. After that, as in the case of normal arc melting, an arc discharge is generated between the mother alloy A and the arc electrode 5 to generate an arc plasma C, so that the mother alloy A is heated to a high temperature and evaporated to generate ultrafine particles B. To do. The ultrafine particles B generated from the mother alloy A react with oxygen in the atmosphere and are sucked by the collecting pipe 6 along with the gas flow generated by the pressure difference between the melting chamber 2 and the glove box 3, and the rear end It is collected by the filter 8 installed at.

Example 1 Using aluminum and iron, each having a purity of 99.9 mass% or more, as raw materials, arc melting was performed in an Ar atmosphere, and A
An alloy button ingot having a composition of l ₇₀ Fe ₃₀ was prepared. Using this button-shaped ingot, arc melting was carried out in an atmosphere of He gas containing 10% oxygen gas (gas pressure 50 Torr) using a device as shown in FIG. 2 to produce composite ultrafine particles.

Examples 2 to 10 In Example 1, the raw material iron was replaced with Co, Ni, Cu, R.
Composite ultrafine particles were produced by the same operation and conditions as in Example 1, except that u, Rh, Pd, Ag, Pt, or Au was used instead. Ultrafine S particles (Cu or Cu oxide) produced using a mother alloy having a composition of Al ₇₀ Cu ₃₀
The particle size distribution of is shown in FIG.

Catalytic properties of composite ultrafine particles: The composite ultrafine particles produced in each of the above examples were investigated as a steam reforming catalyst for methanol. Further, as a comparison, it was also investigated for commercial CuO-ZnO-Al ₂ O ₃ catalyst. The catalyst performance evaluation was carried out at 200 ° C. and 4 ° C. using a normal pressure fixed bed flow reactor filled with 0.1 g of ultrafine particles.
The amount of hydrogen generated by the methanol steam reforming reaction at 00 ° C and the carbon dioxide selectivity were measured. The results are shown in Table 1.
And shown in Table 2.

[Table 1]

[0021]

[Table 2] As is clear from Tables 1 and 2, the composite ultrafine particles obtained by the present invention have characteristics that the hydrogen generation amount greatly exceeds the commercially available products at low temperatures, and the hydrogen generation amount and carbon dioxide at high temperatures are high. In terms of the selectivity of, the characteristics far exceeding the commercial products were obtained. The selectivity is the rate at which the desired reaction (CH ₃ OH + H ₂ O → 3H ₂ + CO ₂ ) occurs, which is also an important characteristic of the catalyst. The commercial catalyst showed a high selectivity at low temperature (200 ° C), but showed a sharp drop to 75% at high temperature (400 ° C). In contrast, the composite ultrafine particle catalyst of the present invention was able to maintain a high selectivity even at high temperatures. From the above results, the composite ultrafine particles of the present invention is a highly active and highly selective catalyst as compared with a conventional catalyst used for a methanol synthesis reaction which is a methanol steam reforming reaction and its reverse reaction, By industrially putting this material to practical use, it can be used as an inexpensive hydrogen production method or an inexpensive CO ₂ resource recycling method.

[0022]

INDUSTRIAL APPLICABILITY As described above, the ultrafine particles obtained by the present invention are finer ultrafine particles made of M ¹ metal or M ¹ oxide exhibiting catalytic activity.
It contains a large amount of composite ultrafine particles having a structure of being carried on ultrafine particles of ₂ O ₃ or Al-M ² oxide, and unlike the oxide particles produced by the conventional liquid phase method, the particles are It is extremely fine, contains no impurities, and has extremely high purity. Therefore, the composite ultrafine particles according to the present invention exhibit high catalytic activity as a catalyst for synthesizing methanol and steam reforming, and particularly exhibit high activity, high selectivity and high durability even in a high temperature range. Further, according to the method of the present invention,
The above-mentioned composite ultrafine particles exhibiting high catalytic activity as a catalyst for synthesizing and reforming methanol can be prepared by a relatively inexpensive and simple method. Since air can be used, composite ultrafine particles can be produced at low cost.

[Brief description of drawings]

FIG. 1 is a schematic view schematically showing the structure of composite ultrafine particles produced by the method of the present invention.

FIG. 2 is a schematic configuration diagram of an example of an apparatus for producing composite ultrafine particles by arc melting according to the present invention.

FIG. 3 is a graph showing the particle size distribution of ultrafine S particles (Cu or Cu oxide) produced using a mother alloy having a composition of Al ₇₀ Cu ₃₀ .

[Explanation of symbols] 1 Ultrafine particle production apparatus 2 Melting chamber 3 Glove box 5 Arc electrode 6 Collection tube 8 Filter 9 Gas mixer 10 Turbo molecular pump 11 Mechanical booster pump, rotary pump A Mother alloy B Ultrafine particle C Arc plasma

Continuation of front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical display location B01J 23/63 B01J 23/58 M 23/58 23/60 M 23/60 23/62 M 23/62 23 / 66 M 23/648 23/68 M 23/652 23/72 M 23/656 23/76 M 23/66 23/78 M 23/68 23/80 M 23/72 23/86 M 23/745 B22F 9 / 14 Z 23/75 C01B 3/40 23/755 C01F 7/02 D 23/76 9155-4H C07C 29/154 23/78 29/156 23/80 29/157 23/835 29/158 23/847 9155- 4H 31/04 23/889 C07B 61/00 300 23/86 B01J 23/56 301M B22F 9/14 23/64 102M C01B 3/40 103M C01F 7/02 104M C07C 29/154 23/74 301M 29/156 311M 29/157 321M 29/158 23/82 M 31/04 23/84 301M // C07B 61/00 300 311M

Claims (9)

[Claims] 1. First ultrafine particles made of Al or / and an oxide of Al and M ¹ element (wherein M ¹ is Fe, Co, N
It is at least one element selected from the group consisting of i, Cu, Ru, Rh, Pd, Ag, Pt, and Au. And a second ultrafine particle made of a metal and / or an oxide of the above). 2. A part of Al or / and an oxide of Al of the first ultrafine particles is an element of M ² (wherein M ² is Ti, Zr or H).
f, V, Cr, Mn, Zn, Ga, Mg, Si, Ca,
At least one selected from the group consisting of Y, La and Ce
It is a seed element. 3. The composite ultrafine particles according to claim 1, wherein the composite ultrafine particles are substituted with the metal or / and the oxide). 3. The composite ultrafine particles according to claim 1, wherein the first ultrafine particles have a particle size of 5 to 500 nm, and the second ultrafine particles have a particle size of 0.5 to 200 nm. 4. The first ultrafine particles are Al or / and γ-Al.
₂ O ₃ , the second ultrafine particles are Cu, Cu ₂ O or / and Cu
The composite ultrafine particles according to claim 1 or 3, which is O. 5. A catalyst for synthesizing and reforming methanol, which comprises the composite ultrafine particles according to any one of claims 1 to 4. 6. Aluminum and M ¹ element (provided that M ¹ is Fe, Co, Ni, Cu, Ru, Rh, Pd, Ag, P)
It is at least one element selected from the group consisting of t and Au. ) Is melted by heating in an atmosphere of an inert gas containing oxygen, and the evaporated material is reacted with oxygen in the atmosphere to form first ultrafine particles of Al or / and an oxide of Al and M ¹ A method for producing composite ultrafine particles, which comprises producing composite ultrafine particles obtained by bonding second ultrafine particles made of metal or / and oxide made of an element. 7. Aluminum 5 to 95 atomic%, The method of claim 6, M ¹ element is used raw materials 5-95 atomic% of the composition, for arc melting. 8. Al of 50 atomic% or less M ² element (where, M ² is Ti, Zr, Hf, V, Cr, Mn, Zn,
It is at least one element selected from the group consisting of Ga, Mg, Si, Ca, Y, La and Ce. The method according to claim 6 or 7, wherein a raw material obtained by substituting in (4) is used. 9. The atmosphere according to claim 6, wherein the inert gas is Ar, He or N ₂ and an atmosphere composed of a mixed gas of 50 to 99% of inert gas and 1 to 50% of oxygen gas is used. The method described in.