JPH09225317A - Nickel/noble metal binary metal cluster and catalyst made from the cluster and its preparation - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a catalyst which functions as an effective hydrogenation catalyst over a wide range of a Ni/noble metal mole ratio by protecting a binary cluster consisting of noble metal and nickel with water soluble polymer. SOLUTION: This nickel/noble metal cluster and its dispersion liquid is prepared by a method in which the water soluble and/or organic solvent soluble salt and/or complex of noble metal and the water soluble and/or organic solvent soluble salt and/or complex of Ni(II) and/or Ni(III) are mixed in a form of an organic solvent solution, the mixture is mixed with water soluble polymer, the pH of the mixture is adjusted at 9-11, and the mixture is heated and refluxed in an inactive atmosphere under normal pressure or increased pressure. A catalyst is prepared from the cluster or its dispersion liquid. As the noble metal, Pd, Pt, Rh, Ru, Ir, etc., can be named, and polyvinyl pyrrolidone, polyvinyl alcohol, polyacrylic acid, etc., can be named as the water soluble polymer.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a nickel / noble metal binary metal cluster, a dispersion thereof, a catalyst using the same,
In particular, it relates to a hydrogenation catalyst and a method for producing the same.

[0002]

2. Description of the Related Art In recent years, as a supported metal catalyst which has been widely used as a practical catalyst, attention has been paid to the catalytic action of bare metal particles that are not affected by an inorganic carrier, and ultrafine metal particle catalysts have been developed. Especially in what are called small metal clusters,
I am interested in the unique properties of a region that should be called a "metal molecule", which is different from both a bulk metal and a metal atom. Regarding this, research from the standpoint of theoretical physics such as quantum effect preceded, and it was not so easy to synthesize metal clusters of ultrafine particles with a uniform particle size. Recently, it has been revealed that polymers are useful for stabilizing such metal clusters. It is a metal cluster dispersion type catalyst using a polymer further developed from a conventional metal colloid catalyst protected by a polymer. This catalyst is apparently uniform, but since the polymer surrounds it, it is possible to further immobilize it on a cross-linked polymer, and it is expected to develop in various fields.

Recently, binary metal colloids containing two kinds of metals in one particle have been attracting attention. The activity and selectivity of metal catalysts often show dramatic improvements with the addition of second and third components. These are the "ligand effect" of added metals.
Or "ensemble effect". For example, a binary metal cluster colloidal dispersion can be prepared by simultaneously reducing two types of noble metal ions by the alcohol reduction method. Polyvinylpyrrolidone (P
When a mixed solution of palladium (II) chloride and platinum (IV) chloride is heated to reflux in the presence of VP) in ethanol / water (1/1, v / v), the polymer is dispersed well and becomes a stable polymer. A protected binary metal cluster colloidal dispersion is obtained. From the UV-VIS (ultraviolet / visible absorption) spectrum and electron microscope, it was revealed that the colloidal fine particles thus obtained have a uniform particle size, and that each particle contains palladium and platinum atoms. It was In the structure of the ultrafine metal particles, platinum forms a central nucleus (core),
Examination of catalytic activity and EXAFS (Ex
tended X-ray Absorption F
ine Structure, wide-range X-ray absorption fine structure) analysis results [N. Toshima
Outside two, J. Chem. Soc. Faraday
Trans. 84 , 2537 (1993), M.A.
3 people from Harada, J. Phys. Chem. 9
6 , 9730 (1992)].

A colloidal dispersion of Au / Pt binary metal clusters can be obtained by the same method [N. Toshima
Outside 1 person, Makromol. Chem. , Ma
cromol. Symp. , 59 , 281 (19
92), T.W. Yonezawa Outside 1 person, J. Mo
l. Catal. , 83 , 167 (1993)].
PVP not only protects the hydrophobic colloidal ultrafine particles in an aqueous solution, but also plays a role in determining the metal composition of the cluster surface. That is, since PVP is considered to have stronger interaction with platinum than gold, first, the gold atoms are reduced and aggregated, and then the platinum atoms are deposited around the gold clusters as nuclei. It was revealed from the change of the UV-VIS spectrum during the reaction. That is, a "gold core-platinum shell" structure. A similar binary metal colloid is Au / Pd [N. 3 people from Toshima, J. Phys, Chem. , 96 , 992
7 (1992)], Pt / Rh [M. 2 people from Harada, J. Phys. Chem. , 98 , 265
3 (1994)], Pd / Rh [the same, J. Phys,
Chem. , 97 , 10742 (1993)] and subjected to structural analysis by EXAFS.

Esaku et al. Prepared a bare Cu / Pd binary metal colloid without a protective agent by pyrolysis [K.
3 people from Esumi, Chem. Mater. , 2 , 56
4 (1990)]. Bradley et al. Improved the method of Esaku et al. To prepare a colloidal dispersion of polymer-protected Cu / Pd bimetallic clusters [J. S. Brad
4 people outside ley, Chem. Mater. , 5 , 254
(1993)]. By reducing palladium and copper acetate in 2-ethoxyethanol (bp 135 ° C.) in the presence of PVP, first, Pd (II) can be reduced to a metal. , Cu (II)
It is believed that can be reduced. The binary metal obtained by this method is monodisperse, and the average particle size of the Pd ₇₀ Cu ₃₀ clusters thus obtained is 4.0 ± 0.
4 nm.

On the other hand, the present inventors have also prepared PVP-protected Cu / Pd binary metal clusters [N. T
1 person outside of Shima, Adv. Mater. , 6 , 24
5 (1994)]. In this method, first, the pH of the solution is adjusted to 9 to 11 with sodium hydroxide, and Cu / P
By preparing a binary hydroxide colloid of d
The difference in redox potential between u and Pd was overcome. The reduction reaction is
It is carried out by the so-called polyol process, ie heating in ethylene glycol. The particle size distribution of this binary metal is 1 to 4 nm. PVP-protected palladium particle size distribution is 1 to 3.5 nm (average 1.2 nm)
On the other hand, the particle size distribution of copper protected by PVP is 3 ~
Compared to the wideness of 250 nm, this binary metal
It is not a mixture of Pd colloid and Cu colloid. The formation of binary metal clusters was also clear from the UV-VIS spectrum and X-ray diffraction, and it was also confirmed from XPS and Auger spectra that copper was zero-valent.

[0007]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a novel bimetallic cluster dispersion catalyst, namely nickel /
The point is to provide a noble metal bimetallic cluster dispersion catalyst and a method for producing the same.

[0008]

Means for Solving the Problems The first aspect of the present invention is that (A)
The present invention relates to a nickel / noble metal binary metal cluster obtained by protecting a binary metal cluster composed of a noble metal and (B) nickel with a water-soluble polymer, or a dispersion liquid thereof.

The second aspect of the present invention is (a) a water-soluble and / or organic solvent-soluble salt and / or complex of a noble metal,
(B) Ni (II) and / or Ni (III) water-soluble and / or organic solvent-soluble salts and / or complexes were mixed in the form of an aqueous solution or an organic solvent solution, to which a water-soluble polymer was added. After that, the pH of the system is adjusted to 9 to 11 and the mixture is heated to reflux under an inert atmosphere under normal pressure or pressure, and the nickel / noble metal binary metal cluster or a dispersion thereof is prepared. Regarding

A third aspect of the present invention relates to a catalyst comprising the nickel / noble metal binary metal cluster according to claim 1 or a dispersion thereof.

A fourth aspect of the present invention relates to a hydrogenation catalyst comprising the nickel / noble metal bimetallic cluster according to claim 1 or a dispersion thereof.

Ni in the binary metal cluster of the present invention
Most of the precious metals are presumed to be alloyed or solid solution.

As the noble metal (A), Pd, Pt,
Mention may be made of Rh, Ru, Ir, Ag and Au.

Examples of the water-soluble polymer include polyvinylpyrrolidone, polyvinylalcohol, polyacrylic acid, cyclodextrin, aminopectin, methylcellulose and the like. Vinyl polymers having a cyclic amide structure, especially polyvinylpyrrolidone, especially Poly N-vinyl-2-pyrrolidone is preferred because it is the most active catalyst. These water-soluble polymers are
It is surprising that not only does it have the ability to protect and stabilize metal colloids than surfactants, but it also shows higher catalytic activity than when only clusters containing no water-soluble polymer are used. .

The amount of the water-soluble polymer used in the nickel / noble metal binary metal cluster dispersion of the present invention is 0.1 to 1 in terms of the molar ratio of the monomer constituting the water-soluble polymer to the total metal.
00, preferably 1 to 20.

The particle size of the nickel / noble metal binary metal cluster of the present invention is 0.5-100 nm, preferably 1-1.
It is 0 nm, particularly preferably 1 to 5 nm.

The nickel / noble metal binary metal cluster of the present invention has no particular limitation on the nickel / noble metal ratio (element ratio), and all ratios can be used. If no precious metal is contained, oxidation will proceed in the air and become unstable. The stability is excellent when there are many noble metals. Generally, it is used at a ratio of 1/5 to 7/3.

Examples of the (a) water-soluble and / or organic solvent-soluble salt and / or complex of the noble metal include acetates, chlorides, sulfates, nitrates, sulfonates, phosphates and complexes thereof. be able to. Taking palladium as an example, palladium acetate, palladium sulfate, palladium nitrate, palladium chloride, palladium phosphate, palladic acid chloride, palladium benzotolyl complex, palladium acetylacetonate complex, palladium cyclooctadiene complex, palladium ethylenediamine complex, palladium trioxide. Examples thereof include a phenylphosphine complex.

(B) Ni (II) and / or Ni
Examples of the water-soluble and / or organic solvent-soluble salt and / or complex of (III) include nickel sulfate, nickel nitrate, nickel chloride, nickel phosphate, nickel ammine complex, nickel ethylenediamine complex, nickel acetylacetonate complex and the like. be able to.

Suitable solvents for dissolving the noble metal salt or complex (a) include water and organic solvents miscible with water and alcohol. Examples of these organic solvents include dioxane, tetrahydrofuran, N
-Methylpyrrolidone, acetone and the like can be mentioned.

As the solvent suitable for dissolving the above-mentioned nickel salt or complex (b), water and primary or secondary alcohols are preferable, and alcohols having a high boiling point are particularly preferable. For example, ethylene glycol, propylene glycol, isoamyl alcohol, n-amyl alcohol, sec-butyl alcohol, n-butyl alcohol, isobutyl alcohol, allyl alcohol,
Although n-propyl alcohol, 2-ethoxyethyl alcohol, etc. can be mentioned, even those having a low boiling point such as ethyl alcohol can be used if they are carried out under pressure. Depending on the selection of these solvents, the state in which the water-soluble polymer contains the binary metal cluster is slightly different,
This is related to changes in catalytic activity.

In the reduction reaction in the production method of the present invention, it is presumed that the metal ions in the system are reduced to metal atoms, and then the metal atoms aggregate to form metal colloid particles, which may be alloyed or solid solution. It is still unclear when will happen. When producing the nickel / noble metal binary cluster of the present invention or a dispersion thereof, when the solvent used has a low boiling point, the reaction can be carried out under pressure so that the solvent does not boil during heating. . Of course, when boiling at the temperature required for the reaction, the reaction can be carried out under normal pressure.

Next, a mode of using as a catalyst, especially as a hydrogenation catalyst will be explained.

The solvent used for the hydrogenation reaction is basically one that dissolves the substrate to be hydrogenated. Since the water-soluble polymer is polar, it is important that this catalyst also has some polarity. Is. Therefore, the solvent is preferably a polar organic solvent or a mixture of a non-polar solvent and a polar solvent. There are no special restrictions as long as this can be satisfied. Specific examples thereof include a mixture of water and alcohols, esters such as tetrahydrofuran, methyl acetate and ethyl acetate, and a mixture of hexane and butyl alcohol. In the case of hydrogenation of nitrobenzene, alcohols such as ethyl alcohol are preferred.

As the catalyst, the catalyst obtained by the method of claim 2 can also be used by adding it to the hydrogenation reaction system. If the solvent system convenient for use in the method of claim 2 and the solvent convenient for use in the hydrogenation reaction system are the same, of course, they are used as they are, but when the preferred solvent used for each process is different, The catalyst system obtained is vacuum dried, and the catalyst is redispersed using the same solvent as the solvent for the hydrogenation reaction system or a solvent that is compatible with the solvent, such as ethyl alcohol, and the dispersion is hydrogenated. It can also be added to the reaction system.

When used as a hydrogenation catalyst, the element ratio of Ni / noble metal, especially Ni / Pd, is preferably 1/5 to 7/3.

Substrate (raw material compound) / total metal is 1 to 10,000, preferably 3 to 100 on a molar basis.

The hydrogen pressure during hydrogenation is not particularly limited, but usually 1 to 5 atm can be adopted.

The substrate concentration in the reaction system is generally 0.0
It is carried out in the range of 01 to 10 M, preferably 0.01 to
It is 1.0M.

The reaction temperature during hydrogenation is usually 0 to 100 ° C.,
Preferably it is 20-50 degreeC.

Examples of the substrate include nitro group-containing hydrocarbon compounds and olefins.

[0032]

The present invention will be described below with reference to examples.
The present invention is not limited to this.

Examples 1 to 7 An ethylene glycol solution of nickel sulfate and a dioxane solution of palladium acetate were mixed at a predetermined ratio shown in Table 1 (total metal amount 2.5 mmol) to prepare poly (N-vinyl-2-).
Pyrrolidone) (PVP, K-30, average molecular weight 40,0)
00) 4.006 g, and adjusted to pH 9 with an alkaline aqueous solution.
After adjusting to -11, a stable nickel / palladium binary metal cluster dispersion (colloidal dispersion) was synthesized by heating and refluxing at 198 ° C for 2 hours under a nitrogen stream.

Comparative Examples 1 to 2 Examples 1 to 7 except that only an ethylene glycol solution of nickel sulfate (Comparative Example 2) or a palladium acetate dioxane solution (Comparative Example 1) was used in the amounts shown in Table 1.
A nickel single cluster dispersion liquid (Comparative Example 2) and a palladium single cluster dispersion liquid (Comparative Example 1) were synthesized in the same manner as in the above method.

[0035]

[Table 1] * ¹ : Nickel sulfate * ² : Palladium acetate * ³ : Poly (N-vinyl-2-pyrrolidone) Average molecular weight 40,000 * ⁴ : Ethylene glycol

Examples 8 to 14, Comparative Examples 3 to 4 The cluster dispersions prepared in Examples 1 to 7 and Comparative Examples 1 and 2 were evaporated to remove the solvent, completely dried in vacuum at 150 ° C. for 24 hours, and then ethanol. Was used to prepare an ethanol dispersion of each cluster having a concentration of 20 mM. Then, each dispersion was used as a catalyst for the hydrogenation reaction of nitrobenzene in a hydrogen atmosphere at 30 ° C. and 1 atm using a closed atmospheric pressure hydrogenation apparatus. The specific operation is as shown below. First, a 50 cm ³ flask is attached to a thermostat kept at 30 ° C., the inside of the flask is degassed several times, and then replaced with hydrogen. Using a syringe in this flask, 10 ml of hydrogenation reaction solvent ethanol and 10 m of nickel, palladium, bimetallic cluster or its morometallic cluster dispersion (20 mm)
1 is injected and the solvent is saturated with hydrogen (pre-adsorption) by stirring with a magnetic stirrer for several hours. Then, 0.1 ml of nitrobenzene as a substrate was injected with a syringe to start hydrogenation. In addition, the initial rate of hydrogen absorption and the total hydrogen absorption consumption were determined from a diagram in which the hydrogen absorption was plotted against time. Table 2 shows the results. The results are summarized in FIG.

[0037]

[Table 2]

From the above results, it was found that the Ni / Pd bimetallic cluster shows much higher catalytic activity than the single cluster of nickel or palladium alone. The initial hydrogenation rate depends on the Ni / Pd composition,
It was found that the highest catalytic activity was exhibited at i / Pd (1/4).

In addition, a small amount of the solution (2
μl) was collected using a microsyringe, and the reaction product was examined by gas chromatography. The measurement conditions are as shown below. Device: Shimadzu GC-14A Column: CBP-20-M25-025 (equivalent to PEG20) Injector / Temperature: 200 ° C DETECTOR / Temperature: 200 ° C Carrier gas: Helium (He) Detection port: FID Temperature rising file (column temperature): After holding at 50 ° C for 5 minutes,
The temperature is raised to 140 ° C. at a heating rate of 5 ° C./min, and at this temperature, 1
Hold for 5 minutes, then 200 ℃ at a heating rate of 10 ℃ / min.
The temperature was raised to 10 minutes and held at this temperature for 10 minutes.

As a result of the above measurement, regardless of the catalyst composition,
The product was found to be predominantly aniline. Therefore, it was found that the nickel / palladium bimetallic cluster dispersion effectively acts on the hydrogenation of nitrobenzene to aniline under mild conditions.

[0041]

【effect】

(1) The catalyst of the present invention functions as an effective hydrogenation catalyst over a wide range of Ni / noble metal molar ratio. (2) According to the production method of the present invention, it is presumed that Ni and the noble metal in the catalyst component are not merely a mixture, but most of them are in an alloy or solid solution state. (3) The action of the water-soluble polymer in the present invention is not only useful as a protective agent for stably dispersing nickel / noble metal clusters, but also significantly improves the efficiency as a catalyst. (4) Since the hydrogenation reaction using the catalyst of the present invention can be carried out under extremely mild conditions, the reaction is easy to control and the amount of impurities produced is small.

[Brief description of drawings]

FIG. 1 is a graph showing the relationship between the initial rate of hydrogen absorption and the Ni molar content (%).

Claims (7)

[Claims] 1. A nickel / noble metal binary metal cluster obtained by protecting a binary metal cluster consisting of (A) a noble metal and (B) nickel with a water-soluble polymer. 2. A water-soluble and / or organic solvent-soluble salt and / or complex of a noble metal, and (b) Ni (II).
And / or Ni (III) water-soluble and / or organic solvent-soluble salt and / or complex are mixed in the form of an aqueous solution or an organic solvent solution, and a water-soluble polymer is added thereto, and then the pH of the system is adjusted to 9 Nickel / Claim 1 according to claim 1, characterized in that it is adjusted to -11 and heated to reflux under an inert atmosphere.
Manufacturing method of precious metal binary metal clusters. 3. A nickel / noble metal binary metal cluster dispersion obtained by protecting a binary metal cluster consisting of (A) a noble metal and (B) nickel with a water-soluble polymer. 4. A catalyst comprising the nickel / noble metal binary metal cluster according to claim 1. 5. A catalyst comprising the nickel / noble metal binary metal cluster dispersion according to claim 3. 6. A hydrogenation catalyst comprising the nickel / noble metal bimetallic cluster according to claim 1. 7. A hydrogenation catalyst comprising the nickel / noble metal binary metal cluster dispersion according to claim 3.