JPH1080637A - Composite ultrafine particles, method for producing the same, and catalyst for synthesizing and reforming methanol using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a remarkably fine super-fine particle having high catalytic activity as a catalyst for methanol synthesis and reformation, prevented from the formation of coarse particle due to the sintering phenomenon of the particles each other, capable of keeping high catalytic activity over a long period and excellent in durability and the producing method. SOLUTION: The Cu-Zn-Cr based multiple super-fine particle containing super fine particle of copper or the oxide, zinc or the oxide and chromium or the oxide is produced by arc-melting an alloy having a composition of 69-92.5atom% copper, 1-24.5atm% zinc and 6.5-30atom% chromium in an inert gas atmosphere containing a diatomic molecule gas and an oxidizing gas and allowing the vaporized material to react with the oxidizing gas in the atmosphere. The super-fine particle is used as the high activity, high selectivity and high durability catalyst for methanol synthesis and reformation.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to Cu-Zn-Cr-based composite ultrafine particles in which ultrafine particles of copper, zinc, chromium or their oxides are composited (mixed or bonded) at the nm level, and a method for producing the same. And a catalyst for synthesizing and reforming methanol using the same.

[0002]

2. Description of the Related Art 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 for fuel cells, fuels for power generation, etc. by separating hydrogen and as a raw material for the chemical industry. Also used as. On the other hand, a reaction opposite to the steam reforming reaction of methanol, that is, as shown by the following reaction formula (2), a methanol synthesis reaction for obtaining methanol from carbon dioxide and hydrogen (or a carbon dioxide fixing reaction) is It is attracting attention as one of the carbon recycling methods. 3H ₂ + CO ₂ → CH ₃ OH + H ₂ O (2) That is, with the recent economic activity, CO ₂ emissions tend to increase with the year, and global warming due to the accumulation of CO ₂ of recent serious reduction of CO ₂ emissions is an urgent need on a global scale. Various CO ₂ reduction methods are being studied as a solution to this problem. Among them, a prominent method is a method of reacting CO ₂ with H ₂ to convert it into an alcohol raw material such as methanol and recycling the same. Methanol obtained by this method can be used as an energy source, but it is also a key raw material in the synthesis of chemicals, so if this method can be established, not only can CO ₂ emissions be reduced, but also petroleum It can also contribute to resource saving.

As a catalyst for the methanol reforming reaction which is the steam reforming reaction of methanol or its reverse reaction, oxide catalysts (JP-A-6-178938 and JP-A-4-122) are used.
No. 450, Japanese Patent Publication No. 5-67336, etc.), metal-based catalysts (JP-A-3-25838, Japanese Patent Publication No. 4-30383).
And alloy catalysts are known, and among these, oxide catalysts are considered to have good performance. The oxide powder is generally manufactured by a liquid phase method (wet method) utilizing a coprecipitation method. However, since it is manufactured in a liquid phase, impurities remain in the powder, and it is difficult to obtain high-purity powder. 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.

[0004]

In view of the above problems, a method for producing an oxide catalyst by a gas phase method has recently been proposed. For example, Hayashi Tax, Ryoji Ueda, Akira Tazaki, "Ultra Fine Particles", published in 1988 by Mita Press, No. 115-
On page 122, there is disclosed a method for producing ultrafine particles by evaporating Cu and Zn by induction heating in a He gas atmosphere (a so-called gas evaporation method). In such a gas evaporation method, when the heating temperature of the evaporation source is estimated to be about 1500 ° C., the vapor pressure of Cu and Zn at this temperature becomes 5 ° C.
There is a digit difference. That is, while the vapor pressure of Cu at 1500 ° C. is 2 Torr, the vapor pressure of Zn is 10 ⁵ To
rr. When two components having greatly different vapor pressures are dissolved and evaporated in the same crucible as described above, an element having a high vapor pressure is selectively evaporated at an early stage of the evaporation, and Cu
Remains without being evaporated. As a result, the composition of the generated ultrafine particles is biased depending on the production time.
Therefore, in the above-mentioned gas evaporation method, a special device is used to melt Cu, which is a metal having a lower vapor pressure, in a crucible, and Zn rods are continuously supplied therein, so that the evaporation amount of Zn is reduced. The Cu—Zn-based ultrafine particles are produced while making corrections.

Generally, fine Cu-Zn catalyst particles are
Initially, it has a relatively large specific surface area, so it shows relatively good initial catalytic activity in a temperature environment up to, for example, about 300 ° C. However, if it is kept in that temperature environment for a long time, it will sinter between particles. Since a phenomenon occurs and particles are coarsened, there is a problem that the catalytic activity is significantly reduced. It has been reported that the gas evaporation method can provide ultrafine particles having a two-layer structure in which the surface of Cu particles having a diameter of several hundred angstroms is covered with ZnO particles having a diameter of 20 to 30 angstroms. See page 119). Regarding the generation process of such ultrafine particles, while the Cu particles are being carried by the flow of the He gas, Zn vapor condenses on the surfaces of the Cu particles to form a Zn layer on the surfaces of the Cu particles. It is presumed that ZnO is oxidized during the slow oxidation process. Here, the gradual oxidation treatment means that if the ultrafine particles generated in the evaporation chamber are exposed to the air as they are, they will burn, so oxygen is gradually supplied into the chamber to form an oxide film on the particle surface and stabilize. Processing.

[0006] As described above, ultrafine particles having a structure in which the surface of Cu particles is covered with finer ZnO particles than that of Cu particles have a particle size of 300 to
At the high temperature of about 400 ° C., the grain growth of the Cu particles hardly occurs, and the advantage that the coarsening of the particles is relatively suppressed is obtained. However, the amount of Cu having catalytic activity contained in the catalyst particles is apparent. Therefore, there is a problem that the catalytic activity is reduced. Further, in the above-described gas evaporation method, a special device having a mechanism for continuously introducing a Zn rod into a crucible disposed in an evaporation chamber is required, and expensive He is used as an atmosphere gas. There is a disadvantage that the cost increases due to the use.

On the other hand, JP-A-3-25838 and JP-B-4-30383 disclose inert gases such as He, Ar and N ₂ , hydrogen, carbon monoxide, carbon dioxide and oxygen.
Under the atmosphere of a mixed gas of two or more species or at a pressure of 10
Ultrafine catalyst having an average particle size of 1 nm to 1 μm produced by heating and evaporating catalyst reinforcing metals such as Cu, Zn, Cr, and Al at a pressure of ^-5 mmHg to atmospheric pressure as a catalyst for a methanol synthesis reaction. It is disclosed for use. However, when heating and evaporating Cu and Zn in a single boat, it is difficult to control the composition ratio because the vapor pressures of Cu and Zn are different as described above.
In order to control the composition, it is considered that a cumbersome operation such as placing each metal in a separate boat and heating or supplying Zn to the heated and molten Cu is required. Further, when heating and evaporating in an oxidizing gas atmosphere, an oxide film is formed on the surface of the molten metal, so that ultrafine particles are not gradually generated. Therefore, there is a problem that it is difficult to produce ultrafine oxide particles by this method.

Accordingly, an object of the present invention is to provide a composite ultrafine particle of high purity and extremely fine, which can be advantageously used as a catalyst for synthesizing and reforming methanol by a relatively simple method and at a low cost. It is in. Furthermore, an object of the present invention is to provide a catalyst which is extremely fine and has high catalytic activity as a catalyst for synthesizing and reforming methanol. It is an object of the present invention to provide composite ultrafine particles having excellent durability and capable of maintaining the same. Another object of the present invention is to provide a catalyst having higher catalytic activity than those obtained by a conventionally known liquid phase method such as a coprecipitation method or a gas phase method such as a gas evaporation method, as well as selectivity and catalyst durability. An object of the present invention is to provide a catalyst for synthesizing and reforming methanol which is excellent in performance.

[0009]

According to one aspect of the present invention, 69-92.5 at.% Copper, 1-24.5 at.% Zinc and 6.5-6.5 at.% Chromium. 30
Provided is a Cu-Zn-Cr-based composite ultrafine particle containing ultrafine particles of copper or its oxide, zinc or its oxide, and chromium or its oxide prepared from an alloy having an atomic percent composition by an arc plasma method. You. Such Cu-Zn-Cr-based composite ultrafine particles are generally obtained in the form of a mixture of particles bonded to individually separated particles of each metal or its oxide, but depending on the manufacturing conditions, Zn-Cr- O-based composite oxide and / or Cu-Cr
Containing -O-based composite oxide, or Cu-Zn alloy or intermetallic compound, and / or Zn ₁₇ Cr, and / or contain Zn ₁₃ Cr, or alternatively substantially spherical ultrafine particles of copper or an oxide thereof And ultrafine spherical or substantially columnar particles of zinc or oxide thereof, and ultrafine spherical or substantially plate-like particles of chromium or oxide thereof are integrally joined.

Such composite ultrafine particles can be used very advantageously as a catalyst for a methanol synthesis reaction and a steam reforming reaction. In particular, copper or its oxide (C
Cr oxide (Cr ₂ O ₃ ) between particles of uO, Cu ₂ O)
Presence prevents fusion or growth (coarsening) of Cu or Cu oxide particles at the temperature of the catalytic reaction, and can maintain high catalytic activity for a long period of time. The Cr oxide may be bonded to the Cu or Cu oxide particles, or may be interposed between the Cu or Cu oxide particles as individual independent particles.

According to another aspect of the invention, copper 69-9
5. 2.5 atomic%, zinc 1-24.5 atomic% and chromium 6.
Raw materials consisting of an alloy having a composition of 5 to 30 atomic%,
Arc melting in an inert gas atmosphere containing a diatomic molecular gas and an oxidizing gas, and reacting the evaporated material with the oxidizing gas in the atmosphere, copper or its oxide, zinc or its oxide and chromium or its There is provided a method for producing composite ultrafine particles, which comprises producing Cu-Zn-Cr-based composite ultrafine particles containing ultrafine oxide particles. In a preferred embodiment, nitrogen is used as the diatomic molecular gas and O ₂ , O ₃ and / or N ₂ O is used as the oxidizing gas.
Is used.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In general, since a catalytic reaction proceeds on the surface of a catalyst, if the catalyst particles are made highly pure and fine, the number of active points per unit mass is remarkably increased, and high activity can be expected. Further, if the catalyst particles are made into ultrafine particles and the composition ratio is controlled, it is considered that the catalyst becomes more active. However, when the ultrafine particles are generated simply by heating and evaporating Cu and Zn in an inert gas atmosphere, as described above, since the vapor pressures of Cu and Zn are different, the composition ratio of the generated composite ultrafine particles is different. Difficult to control. Also, when heating and evaporating in an atmosphere gas containing an oxidizing gas, an oxide film is formed on the surface of the molten metal, so that the amount of generated ultrafine particles is extremely small. In contrast, the production of the composite ultrafine particles according to the present invention uses a Cu—Zn—Cr ternary alloy having the above composition range as a starting material, uses an atmosphere gas containing a diatomic molecular gas and an oxidizing gas, and This is performed by an arc plasma method. As a result, the composition ratio between the starting material and the produced ultrafine particles is shifted, but the difference is a certain regularity, the composition can be easily controlled, and the forced evaporation by using a diatomic molecular gas. By the effect described above, oxide ultrafine particles can be easily obtained without being affected by the oxide film.

The composite ultrafine particles obtained according to the present invention contain ultrafine particles of copper and / or copper oxide, zinc and / or zinc oxide and chromium and / or chromium oxide, and are extremely fine on the order of nm. Particles, containing no impurities and having extremely high purity. 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 a methanol synthesis reaction and a reforming reaction. Such Cu-Zn-Cr-based composite ultrafine particles are generally obtained in the form of a mixture of particles bonded to individually separated particles of each metal or its oxide,
Depending on the production conditions, ultrafine particles of Zn—Cr—O-based composite oxide and / or Cu—Cr—O-based composite oxide and C
u-Zn alloy (including intermetallic compounds) and / or Zn ₁₇
Ultra-fine particles of Cr and / or Zn ₁₃ Cr or the like, or alternatively, approximately spherical ultra-fine particles of copper and / or copper oxide; approximately spherical or substantially columnar ultra-fine particles of zinc and / or zinc oxide; And / or composite ultrafine particles in which substantially spherical or substantially plate-like ultrafine particles of chromium oxide are integrally joined.

Further, the composite ultrafine particles of the present invention, by adding Cr, suppress the sintering of the Cu—Zn composite ultrafine particles, and maintain a high specific surface area.
Has better catalytic activity. That is, by adding Cr to the Cu-Zn-based ultrafine particles, the catalytic performance is improved as is clear from the examples described later. It is considered that the reason is that Cr oxide is interposed between Cu or Cu oxide particles. When Cu-Zn based ultrafine particles are used as a catalyst material, Cu is sintered (fused of Cu or Cu oxide particles) at the temperature of the catalytic reaction.
Alternatively, Cu oxide particles grow (coarse), and sufficient catalytic activity cannot be obtained as the reaction time elapses.
However, it is considered that the presence of the Cr oxide particles between the Cu or Cu oxide particles functions to prevent fusion or growth of the Cu or Cu oxide particles. As a result, even when the temperature is maintained at about 150 ° C. or higher, which is used as a catalyst in a methanol synthesis reaction or a steam reforming reaction, for a long time, a fine particle state can be stably maintained without causing coarsening of particles. . Therefore,
The composite ultrafine particles of the present invention exhibit excellent catalytic activity in the above reaction, exhibit stable catalytic activity over a long period of time, and can be advantageously used as a catalyst for synthesizing and reforming methanol having excellent durability.

The composite ultrafine particles of the present invention are produced by arc melting a ternary alloy comprising copper, zinc and chromium in an inert gas atmosphere containing a diatomic molecular gas and an oxidizing gas. Nitrogen gas is preferred as the diatomic molecular gas, and oxygen, ozone or nitrous oxide can be suitably used as the oxidizing gas. When nitrogen gas is used as the diatomic molecular gas, since nitrogen gas is also an inert gas, it is not necessary to use another inert gas such as He, Ar, or Kr. When a nitrogen-oxygen mixed gas is used, its composition may be an oxygen partial pressure of 5 to 50%,
The range of the partial pressure of nitrogen is preferably 50 to 95%. If the oxygen partial pressure is lower than the above range, the amount of oxygen is smaller than the amount of generated ultrafine particles, so that the ultrafine particles desired as an oxide are less likely to be sufficiently oxidized. On the other hand, when the oxygen partial pressure is higher than the above range, the carbon electrode is greatly consumed and the time for one production is limited. Also, if a gas containing high concentration of oxygen is used, there is a danger of explosion,
Operation and management become troublesome. Note that dry air can also be used as the nitrogen-oxygen mixed gas, whereby composite ultrafine particles can be produced at low cost.

The pressure (total pressure) of the atmosphere gas is 3 to 200 k
The range of Pa is appropriate. If the pressure is less than 3 kPa, the arc plasma becomes unstable, and it becomes difficult to generate ultrafine particles. On the other hand, if it exceeds 200 kPa, the amount of generated ultrafine particles hardly changes.

As the starting material alloy, copper 69-92.
5 atomic%, zinc 1-24.5 atomic% and chromium 6.5-
An alloy within a composition range of 30 atomic% is used. FIG. 1 shows the STY (g-CH ₃ OH / kg · hr) of methanol per unit time per kg of catalyst and the alloy composition of the starting material when the composite ultrafine particles of the present invention are used as a catalyst for a methanol synthesis reaction. It is a triangular chart showing the relationship with. In FIG. 1, the symbol STY-580 is 580 g-CH ₃ OH / k.
g / hr methanol composition range, STY
-620 is 620 g-CH ₃ OH / kg · hr, STY
-660 is 660 g-CH ₃ OH / kg · hr, STY
-700 indicates a composition range in which a methanol yield of 700 g-CH ₃ OH / kg · hr can be obtained. The respective composition ranges (expressed in atomic%) are as follows. STY-580 is (1) Cu: 69%, Z
n: 1%, Cr: 30%, (2) Cu: 92.5%, Z
n: 1%, Cr: 6.5%, (3) Cu: 69%, Z
A range surrounded by three points of n: 24.5% and Cr: 6.5%. STY-620 is (1) Cu: 71.5%, Zn:
7%, Cr: 21.5%, (2) Cu: 84.5%, Z
n: 7%, Cr: 8.5%, (3) Cu: 71.5%,
A range surrounded by three points of Zn: 20% and Cr: 8.5%.
STY-660 is (1) Cu: 74%, Zn: 9.5
%, Cr: 16.5%, (2) Cu: 81.5%, Z
n: 9.5%, Cr: 9%, (3) Cu: 74%, Z
A range surrounded by three points of n: 17% and Cr: 9%. STY
-700 is (1) Cu: 74.5%, Zn: 12%, C
r: 13.5%, (2) Cu: 78.5%, Zn: 12
%, Cr: 9.5%, (3) Cu: 76%, Zn: 1
A range surrounded by three points of 4.5% and Cr: 9.5%.

Hereinafter, the production of composite ultrafine particles according to the present invention will be described with reference to FIG. 2 showing a preferred apparatus for producing composite ultrafine particles. FIG. 2 shows an example of an apparatus suitable for producing composite ultrafine particles by arc melting according to the present invention, and is a schematic configuration diagram of an apparatus used in Examples described later. This apparatus 1 includes a dissolution chamber 2 and a glove box 3. In the melting chamber 2, a hearth 4 in which a raw material (master alloy) A is disposed is rotatably provided 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 dissolving chamber 2 and the glove box 3 are communicated with each other by a collection tube 6, and a filter 8 is detachably attached to a rear end 7 of the collection tube 6 located in the glove box 3. Reference numeral 9 denotes a gas mixer which supplies an inert gas containing a predetermined concentration of a diatomic molecular gas and an oxidizing gas into the melting chamber 2. Reference numeral 10 denotes a turbo molecular pump, 11 denotes a mechanical booster pump and a rotary pump, and these 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 a diatomic molecular gas and an oxidizing gas is supplied into the melting chamber 2 at a predetermined flow rate, and the gas pressure in the melting chamber 2 is set to a predetermined pressure. At this time, it is preferable that the inside of the apparatus is once evacuated, except when the atmosphere is used as the atmospheric gas. After that, as in ordinary 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 becomes high temperature, evaporates, and ultrafine particles B are generated. I do. The ultrafine particles B generated from the mother alloy A react with the oxidizing gas in the atmosphere, and are sucked into the collecting pipe 6 on the gas flow generated by the pressure difference between the melting chamber 2 and the glove box 3, It is collected by a filter 8 installed at the rear end.

There are two major problems in producing Cu-Zn-Cr-based oxide ultrafine particles. First, one is
In the arc plasma method using an inert gas such as argon or helium as an atmosphere gas, the amount of generation of ultrafine particles is very small, and the amount recovered even after performing arc discharge for several tens of minutes is determined by the method of the present invention. Only 1/10 to 1/4. Another problem is that the vapor pressures of Cu, Cr and Zn are very different (at 1500 ° C., Cu: 2 Torr).
In the arc plasma method in an atmosphere of Ar + O _{2 (} r, Zn: 10 ⁵ Torr), only Zn oxide is selectively generated at the beginning of evaporation, and Cu and Cr remain without being evaporated. As a result, the composition of the generated ultrafine particles is biased depending on the production time. In other words, when a mixed gas of an inert gas such as argon or helium and oxygen is used, the main cause of generation of ultrafine particles is evaporation by heat, so that only the difference between the vapor pressures of the respective metals constituting the master alloy is used. The amount of evaporation of each metal is determined.

In order to solve such a problem, the method according to the present invention utilizes the action of forced evaporation by diatomic molecular gas such as nitrogen gas. For example, when a mixed gas of nitrogen and oxygen is used as the atmosphere gas, the nitrogen gas has a property of forcibly evaporating the molten metal, and thus is not affected by the vapor pressure of the alloy element, and the Cu ultrafine particles, the Zn ultrafine particles,
The ultrafine particles can be evaporated together. Describing the mechanism of forced evaporation, first, nitrogen in the atmosphere becomes atomic in the arc C (see FIG. 2) and dissolves in the molten metal. The dissolved nitrogen atoms combine to form molecules, which fly off the molten metal. At this time, it is presumed that the molten metal is involved and generated like sputtered particles. The ultrafine particles of copper, zinc, and chromium thus generated react with oxygen in the atmosphere to become Cu oxide, Zn oxide, and Cr oxide. As described above, according to the method for producing composite ultrafine particles of the present invention, Cu-Zn-Cr-based oxide ultrafine particles can be obtained in high yield without being affected by a large difference in vapor pressure of alloy elements.

[0022]

EXAMPLES Hereinafter, the present invention will be described in detail with reference to Examples, but it goes without saying that the present invention is not limited to the following Examples.

EXAMPLE 1 76 at% copper, 14 at% zinc, and 10 at% chromium
Using a mother alloy consisting of Cu ₇₆ Zn ₁₄ Cr ₁₀ and performing an arc melting (arc current 200 A) in an N ₂ gas atmosphere (gas pressure 15 kPa) containing 10% oxygen gas by an apparatus as shown in FIG. Composite ultrafine particles were produced.

Examples 2 to 4 Composite ultrafine particles were produced in the same manner as in Example 1 except that the composition ratio of the mother alloy as a raw material was changed as shown in Table 1.

Incidentally, Cu: 81 at%, Zn: 9 at%
3 and 4 show two types of TEM (Transmission Electron Microscope) photographs of composite ultrafine particles prepared using a master alloy having a composition of 10% at% and Cr at 10% at different magnifications. In FIG. 4, the central particle body is a Cu particle, and the lower layered portion joined to the particle body is determined to be chromium oxide (Cr ₂ O ₃ ).

Catalytic Properties of Composite Ultrafine Particles: The composite ultrafine particles produced in each of the above examples were evaluated for characteristics as a catalyst for a methanol synthesis reaction. For comparison, Cu-Zn-based composite ultrafine particles (Comparative Example 1) prepared in the same manner as in Example 1 except that the composition of the mother alloy was changed as shown in Table 1, and a commercially available coprecipitation method Cu-Zn-
Investigations were also made on an Al-based catalyst (Comparative Example 2). The catalyst performance was evaluated using a fixed bed pressurized flow reactor packed with 0.1 g of ultrafine particles, using a reaction gas flow rate of 50 ml / min, a reaction pressure of 50 atm, and an STY (space-time yield) by methanol synthesis at 250 ° C. ) Was measured. Table 1 shows the results.

[0027]

[Table 1] As is clear from Table 1, when the catalysts of the Cu—Zn—Cr-based composite ultrafine particles of Examples 1 to 4 obtained according to the present invention were used, the results were both higher than those obtained using the catalyst of Comparative Example 1 or 2. A high methanol yield was obtained, and particularly when the catalyst of Example 1 was used, the methanol yield was improved by about 30 to 40% as compared with the case where the catalysts of Comparative Examples 1 and 2 were used.

FIG. 5 shows the change in the catalytic activity (catalytic activity ratio) of the catalysts of Example 1 and Comparative Examples 1 and 2 over the reaction time. As is clear from FIG. 5, the catalyst composed of the composite ultrafine particles of Example 1 showed less change in catalytic activity with time than the catalyst of Comparative Example 1 or 2, and retained high catalytic activity for a long period of time.

Further, Example 1 and Comparative Examples 1 and 2
With respect to the above catalyst, the change in the specific surface area and the decrease rate of the specific surface area with the passage of the reaction time were measured. The results are shown in Table 2 and FIG. 6, respectively.

[Table 2] As is clear from FIG. 6, the composite ultrafine particles of Example 1 showed less decrease in the specific surface area with the lapse of reaction time than the catalyst of Comparative Example 1 or 2, and particularly the Cu—Zn composite ultrafine particles of Comparative Example 1. While the specific surface area of the fine particle catalyst was remarkably reduced, the Cu-
The specific surface area of the Zn—Cr-based composite ultrafine particle catalyst is hardly reduced. As described above, since the catalytic reaction generally proceeds on the surface of the catalyst, when the specific surface area decreases as the reaction time elapses as in Comparative Example 1, the catalytic reaction, that is, the progress of the methanol synthesis reaction is shown in FIG. It will be lowered so that

[0030]

As described above, the Cu—Zn according to the present invention is
The addition of Cr suppresses sintering of the Cu-Zn-based ultrafine particles in the -Cr-based composite ultrafine particles, improves durability as a catalyst, and maintains a high specific surface area. Therefore, such composite ultrafine particles maintain stable catalytic activity even in a relatively high temperature range used as a catalyst.
Further, the composite ultrafine particles of the present invention, unlike oxide particles produced by a conventional liquid phase method, contain a large amount of composite ultrafine particles on the order of nm, the particles are extremely fine, and do not contain impurities, Extremely high purity. Therefore, the composite ultrafine particles according to the present invention exhibit high activity, high selectivity, and high durability as a catalyst for methanol synthesis and steam reforming. Further, according to the present invention, the composite ultrafine particles as described above can be produced at low cost and by a relatively simple method. In addition, the composite ultrafine particles of the present invention may be used in addition 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). Similar reactions, such as the reaction of synthesizing methanol from carbon monoxide and hydrogen, and vice versa, the reaction of synthesizing methanol from carbon dioxide + carbon monoxide + hydrogen (when carbon dioxide and carbon monoxide are mixed) and the like It can be advantageously used also as a catalyst for the reverse reaction.

[Brief description of the drawings]

FIG. 1 shows Cu—Zn—C produced by the method of the present invention.
4 is a triangular chart showing the relationship between the composition range of a mother alloy used as a raw material of r-based composite ultrafine particles and the yield of methanol when the mother alloy is used as a methanol synthesis catalyst.

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 transmission electron micrograph of composite ultrafine particles produced using a master alloy having a composition of Cu ₈₁ Zn ₉ Cr ₁₀ .

FIG. 4 is a transmission electron micrograph of composite ultrafine particles produced using a master alloy having a composition of Cu ₈₁ Zn ₉ Cr ₁₀ .

FIG. 5 is a graph showing the change in catalytic activity of the catalysts prepared in Example 1 and Comparative Examples 1 and 2 over the reaction time in the methanol synthesis reaction.

FIG. 6 is a graph showing a change in a specific surface area reduction rate with a lapse of reaction time in a methanol synthesis reaction of the catalysts prepared in Example 1 and Comparative Examples 1 and 2.

[Explanation of symbols]

 DESCRIPTION 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

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification number Agency reference number FI Technical indication location C07C 31/04 9155-4H C07C 31/04 C22C 9/04 C22C 9/04 C23C 14/24 C23C 14 / 24 F // C07B 61/00 300 C07B 61/00 300 (72) Inventor Hideo Fukui 4-15-19 Izumigaoka, Izumi-ku, Sendai, Miyagi Prefecture (72) Inventor Hironori Arakawa 1-3-3 Kasumigaseki, Chiyoda-ku, Tokyo No. 1 Inside the Industrial Technology Institute (72) Inventor Kiyomi Okabe 1-1 1-1 Higashi, Tsukuba City, Ibaraki Prefecture Inside the Institute for Materials Engineering Technology (72) Inventor Kazuhiro Sayama 1-1-1 East Higashi Tsukuba City, Ibaraki Prefecture Research on Material Engineering Industrial Technology In-house (72) Inventor Jin Kusama 1-1-1 Higashi, Tsukuba, Ibaraki Pref.

Claims (8)

[Claims] 1. 69-92.5 atomic% of copper, 1-2 of zinc
It contains copper or its oxide, zinc or its oxide, and ultrafine particles of chromium or its oxide produced by an arc plasma method from an alloy having a composition of 4.5 atomic% and chromium 6.5 to 30 atomic%. Cu-Zn-C
r-based composite ultrafine particles. 2. The Cu—Zn—Cr-based composite ultrafine particles according to claim 1, comprising a Zn—Cr—O-based composite oxide and / or a Cu—Cr—O-based composite oxide. 3. A Cu—Zn alloy or an intermetallic compound,
And / or Zn ₁₇ Cr, and / or Zn ₁₃ Cu-Zn-Cr-based composite ultrafine particles according to claim 1 or 2 containing Cr. 4. A substantially spherical ultrafine particle of copper or its oxide, a substantially spherical or substantially columnar ultrafine particle of zinc or its oxide, and a substantially spherical or substantially plate-like ultrafine particle of chromium or its oxide. Contains a composite ultrafine particle integrally bonded, Cu-Z according to any one of claims 1 to 3.
n-Cr-based composite ultrafine particles. 5. The Cu—Zn—Cr-based composite ultrafine particles according to claim 1, wherein a chromium oxide is interposed between copper or oxide particles thereof. 6. A catalyst for synthesizing and reforming methanol, comprising the Cu-Zn-Cr-based composite ultrafine particles according to any one of claims 1 to 5. 7. Copper of 9 to 92.5 atomic%, zinc of 1 to 2
A raw material comprising an alloy having a composition of 4.5 atomic% and chromium 6.5 to 30 atomic% is arc-melted in an inert gas atmosphere containing a diatomic molecular gas and an oxidizing gas, and the evaporated material is melted in the atmosphere. Cu-Zn-Cr containing copper or its oxide, zinc or its oxide and chromium or its oxide ultrafine particles by reacting with oxidizing gas therein
A method for producing composite ultrafine particles, comprising generating system-based composite ultrafine particles. 8. The method according to claim 7, wherein the diatomic molecular gas is nitrogen, and the oxidizing gas is O ₂ , O ₃ and / or N ₂ O.