JP6815893B2 - Metal-containing nanoparticle-supported catalyst and carbon dioxide reduction device - Google Patents

Description

The present invention relates to a metal-containing nanoparticle-supporting catalyst and a carbon dioxide reduction device.

In general, a catalyst is a substance that changes the reaction rate of a substance system that causes a chemical reaction and does not chemically change by itself. Depending on the type of catalyst (material, form, etc.), the selectivity for a specific chemical reaction and the reaction efficiency can be determined. different.

Further, as a catalyst material, a metal material is widely used, and a noble metal material is particularly heavily used because of its good reactivity. For example, Patent Document 1 discloses a noble metal catalyst that is selective in a specific reaction. Further, in recent years, an oxide catalyst has also attracted attention, and Patent Document 2 discloses an oxide catalyst having excellent catalytic activity and selectivity.

JP-A-2007-090164 JP-A-2007-301470

However, in the carbon dioxide reduction reaction, the chemical reaction with selectivity has not yet been sufficiently controlled, and the target product has not been obtained with high reaction efficiency. Therefore, it is desired to develop a catalyst capable of satisfactorily promoting and controlling the reaction, particularly in the reduction reaction of carbon dioxide.

Therefore, the present invention has been made in view of the above problems, and has particularly good catalytic performance (for example, catalytic activity, selectivity, etc.) for the reduction reaction of carbon dioxide, and the reduction reaction of carbon dioxide is good. It is an object of the present invention to provide a metal-containing nanoparticle-supporting catalyst and a carbon dioxide reducing device that can be promoted and controlled.

As a result of diligent studies to solve the above problems, the present inventors have found that a catalyst in which metal-containing nanoparticles containing a specific metal are supported on semiconductor particles has particularly good catalytic performance for a carbon dioxide reduction reaction. It was found that can be expressed.

That is, the gist structure of the present invention is as follows.
[1] A metal-containing nanoparticle-supporting catalyst used for reducing carbon dioxide.
The metal-containing nanoparticles-supporting catalyst is formed by supporting metal-containing nanoparticles on semiconductor particles as a carrier.
The metal-containing nanoparticles contain at least one metal atom (M) selected from gold, silver, copper, platinum, rhodium, palladium, nickel, cobalt, iron, manganese, chromium, iridium, zinc, titanium and ruthenium. A metal-containing nanoparticle-supporting catalyst to be contained.
[2] The metal-containing nanoparticles-supporting catalyst according to the above [1], wherein the primary particle size of the metal-containing nanoparticles is 0.2 to 100 nm.
[3] The metal-containing nanoparticle-supporting catalyst according to the above [1] or [2], wherein the primary particle size of the semiconductor particles is 50 nm to 100 μm.
[4] The above [1] to [3], wherein the mass ratio of the metal-containing nanoparticles to the semiconductor particles [(mass of metal-containing nanoparticles / mass of semiconductor particles) × 100] is 0.001 to 1%. ], The metal-containing nanoparticles-supporting catalyst according to any one of the above items.
[5] The metal-containing nanoparticle-supporting catalyst according to any one of the above [1] to [4], wherein the metal atom (M) is copper.
[6] The metal-containing nanoparticle-supporting catalyst according to [5] above, wherein the average valence of copper is 0 to 1.5.
[7] A carbon dioxide reducing device comprising the metal-containing nanoparticle-supporting catalyst according to any one of the above [1] to [6].

The metal-containing nanoparticle-supporting catalyst of the present invention exhibits good catalytic performance particularly for the reduction reaction of carbon dioxide.

Embodiments of the metal-containing nanoparticle-supporting catalyst and the carbon dioxide reduction device according to the present invention will be described in detail below.

The metal-containing nanoparticles-supporting catalyst according to the present embodiment is formed by supporting metal-containing nanoparticles on semiconductor particles as a carrier, and the metal-containing nanoparticles are gold (Au), silver (Ag), copper (Cu). , Platinum (Pt), Rhodium (Rh), Palladium (Pd), Nickel (Ni), Cobalt (Co), Iron (Fe), Manganese (Mn), Chromium (Cr), Iridium (Ir), Zinc (Zn) , Titanium (Ti) and Rhodium (Ru) are characterized by containing at least one metal atom (M) selected from them.

Such a metal-containing nanoparticle-supporting catalyst exhibits excellent catalytic performance for the reduction reaction of carbon dioxide, and is therefore preferably used as a catalyst for reducing carbon dioxide.

The semiconductor particles serve as a carrier and are not limited as long as they can be used as a photocatalyst, and known materials can be used. For example, titanium oxide, tin oxide, zinc oxide, niobium oxide, calcium titanate, gallium oxide, tantalum oxide, strontium titanate, tungsten oxide, cerium oxide, gallium nitride, gallium aluminum nitride, gallium arsenide, gallium aluminum arsenide. Etc., and two or more of the above may be mixed and used. Of these, titanium oxide, calcium titanate, niobium oxide, gallium oxide, and tantalum oxide are preferable.

The primary particle size of the semiconductor particles is preferably 50 nm to 100 μm, more preferably 200 nm to 10 μm. Within the above range, a surface having high photocatalytic activity is formed on the surface of the semiconductor particles, a sufficient surface area is obtained, and the activity of the carbon dioxide reduction reaction is increased.

In the present specification, for the primary particle size, an image of primary particles (single particles that are not aggregated with other particles) is photographed by a transmission electron microscope (TEM), a scanning electron microscope (SEM), or the like. Then, this is used as a value calculated by image analysis. Specifically, for example, 100 particles (primary particles) are randomly selected from an image taken by TEM or the like, the projected area of each particle is obtained by an image processing device, and the total of the particles is calculated from the total of them. Calculate the occupied area of. Divide this total occupied area by the number of selected particles (100 particles) to calculate the average occupied area per particle, and calculate the diameter of the circle corresponding to this area (average circle equivalent diameter per particle). , The primary particle size (same below).

The metal atom (M) contained in the metal-containing nanoparticles is at least selected from Au, Ag, Cu, Pt, Rh, Pd, Ni, Co, Fe, Mn, Cr, Ir, Zn, Ti and Ru. It is one kind. Such metal-containing nanoparticles exhibit excellent performance in the reduction reaction of carbon dioxide. Among them, the metal atom (M) is preferably one selected from Cu, Ag, Au, Ni, Zn and Pd from the viewpoint of excellent reduction performance, and is particularly selectively selected in the reduction reaction of carbon dioxide. Cu is more preferable because it can generate hydrocarbons (methane, ethylene, etc.), and Ag is more preferable because it can selectively produce formic acid.

The metal-containing nanoparticles are not particularly limited as long as they contain the metal atom (M) as described above, and are a simple substance of the metal atom (M), an alloy containing the metal atom (M), and the metal atom (M). It may be a nanoparticle composed of either a metal oxide containing a metal oxide or a composite oxide containing a metal atom (M). The alloy or composite oxide containing the metal atom (M) is at least selected from Au, Ag, Cu, Pt, Rh, Pd, Ni, Co, Fe, Mn, Cr, Ir, Zn, Ti and Ru. It may be an alloy or composite oxide containing one kind of metal atom, and may be alloyed or composited with an alloy or composite oxide containing two or more kinds of metal atoms selected from the above, or a metal atom (M). It may be an alloy or a composite oxide containing a metal atom other than the above. Further, the metal-containing nanoparticles are particularly preferably made of a simple substance of a metal atom (M) or an alloy containing a metal atom (M).

Further, the metal-containing nanoparticles are at least one metal atom (M) selected from Au, Ag, Cu, Pt, Rh, Pd, Ni, Co, Fe, Mn, Cr, Ir, Zn, Ti and Ru. It is preferable that it is a cluster containing (hereinafter, simply referred to as “metal-containing cluster”). In addition, in this specification, a "cluster" means an atomic group in which a plurality of atoms are bonded. Such a metal-containing cluster is preferably, for example, a simple substance of a metal atom (M) or a metal oxide containing a metal atom (M) represented by the following general formula (1).
M _n O _m ... (1)
In the above equation (1), M represents the above-mentioned metal atom (M) and O represents oxygen.

Further, in the above equation (1), m preferably has a ratio of m / n of 0 to 2, more preferably 0.5 to 1.8, and further preferably 0.55 in relation to n. It is ~ 0.75, particularly preferably 0.6 to 0.7, and even more preferably 0.67. Within the above range, the reduction efficiency of carbon dioxide is enhanced. In the above equation (1), when m / n is 0, the metal-containing cluster is composed of a single metal atom (M).

Further, the metal-containing nanoparticles are more preferably clusters containing copper atoms or silver atoms. Such metal-containing nanoparticles exhibit excellent catalytic activity and selectivity in the reduction reaction of carbon dioxide, and if they are clusters containing copper atoms, they are excellent in producing hydrocarbons (methane, ethylene, etc.), and silver. Clusters containing atoms are excellent in producing hydrocarbons.

Further, in the metal-containing nanoparticles containing copper atoms such as the metal-containing clusters as described above, the average valence of copper is preferably 0 to 1.5, and 1.2 to 1.4. More preferably.

The primary particle size of the metal-containing nanoparticles is preferably 0.2 to 100 nm, more preferably 0.5 to 55 nm, and even more preferably 0.5 to 2.0 nm. Within the above range, the number of atoms constituting the metal-containing nanoparticles is changed from several to several tens, and it is possible to interact with carbon dioxide molecules different from the bulk crystal plane, reaction intermediates, and products. The activity is significantly improved.

Further, the mass ratio of the metal-containing nanoparticles to the semiconductor particles (mass of the metal-containing nanoparticles / mass of the semiconductor particles) × 100] is preferably 0.001 to 1%, more preferably 0.05 to 1%. It is 0.5%. Within the above range, the electrons generated by the photocatalyst can be efficiently used for the reduction of carbon dioxide, and the activity of the metal-containing nanoparticles per mass becomes the highest.

The method for producing such a metal-containing nanoparticle-supporting catalyst is not particularly limited and can be produced by a known method, but it is preferably performed by a heterogeneous precipitation method. According to the heterogeneous precipitation method, a specific metal can be deposited on the surface of the semiconductor particles.

Specifically, for example, a solution in which semiconductor particles and metal ions corresponding to the metal to be precipitated are dispersed is prepared, and (1) a reducing agent such as sodium boron hydride is added to this dispersion solution to reduce the metal ions. , A metal-containing nanoparticle-supporting catalyst is produced by a method of precipitating a metal on semiconductor particles, or (2) a method of heating this dispersion solution to remove a solvent and precipitating a metal or a salt thereof on the semiconductor particles. it can. Further, as the solution in which the metal ions are dissolved, for example, a solution in which a metal salt (for example, copper chloride, silver nitrate, etc.) corresponding to the metal to be precipitated is dissolved in a known solvent such as water or alcohol is used. be able to.

The metal-containing nanoparticle-supporting catalyst of the present invention exhibits good catalytic performance for the reduction reaction of carbon dioxide, and is therefore preferably used in a carbon dioxide reduction device for reducing carbon dioxide. The carbon dioxide reduction device includes, for example, a mechanism for bubbling a gas containing carbon dioxide in a sodium hydrogen carbonate solution in which the metal-containing nanoparticle-supporting catalyst of the present invention is dispersed, and a mechanism for recovering the generated gas. Examples include devices that are placed below to reduce carbon dioxide. As the sodium hydrogen carbonate solution, for example, an aqueous solution having a sodium hydrogen carbonate concentration of 10 to 500 mmol / L can be used. Further, as the bubbling gas, for example, a gas having a carbon dioxide concentration of 5% by mass or more can be used.

Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, but includes all aspects included in the concept of the present invention and the scope of claims, and varies within the scope of the present invention. Can be modified to.

Next, in order to further clarify the effect of the present invention, Examples and Comparative Examples will be described, but the present invention is not limited to these Examples.

(Example 1)
First, titanium oxide (TiO ₂ , manufactured by Ishihara Sangyo Co., Ltd.) having a primary particle size of 253 nm as semiconductor particles was dispersed in water so as to have a primary particle size of 5% by mass to obtain a solution in which the semiconductor particles were dispersed. Next, copper chloride (manufactured by Wako Pure Chemical Industries, Ltd.) was added to this dispersion solution and dissolved to bring the concentration of copper chloride to 0.004 mol / L. Further, sodium borohydride (manufactured by Sigma-Aldrich Japan GK) was added to this copper chloride solution and mixed to obtain a solution having a sodium borohydride concentration of 0.005 mol / L.

The resulting solution was stirred at room temperature for 1 hour. Subsequently, the reaction solution was centrifuged at a rotation speed of 5,000 rpm for 10 minutes to settle the product (catalyst in which copper nanoparticles were supported on TiO ₂ particles). Then, (1) the supernatant solution was discarded and water was added to redisperse the product. Further, (2) the dispersion solution was centrifuged at a rotation speed of 5,000 rpm for 10 minutes. The same procedure as (1) and (2) above was repeated twice more to wash the product. Finally, with the supernatant solution removed after centrifugation, the mixture was dried at 40 ° C. for 24 hours to obtain a catalyst in which copper nanoparticles were supported on TiO ₂ particles.

(Example 2)
The dried catalyst of Example 1 was further heat-treated at 150 ° C. for 30 minutes to oxidize the copper nanoparticles, and a catalyst in which the oxidized copper nanoparticles were supported on the TiO ₂ particles was obtained.

(Example 3)
A catalyst in which oxidized copper nanoparticles were supported on TiO ₂ particles was obtained by the same method as in Example 2 except that the heat treatment time was set to 1 hour.

(Example 4)
A catalyst in which silver nanoparticles were supported on TiO ₂ particles was prepared by the same method as in Example 1 except that silver nitrate (manufactured by Kishida Chemical Co., Ltd.) was used instead of copper chloride to prepare a 0.04% by mass solution of silver nitrate. Obtained.

(Example 5)
The dried catalyst of Example 4 was further heat-treated at 130 ° C. for 15 minutes to oxidize the silver nanoparticles, and a catalyst in which the oxidized silver nanoparticles were supported on TiO ₂ particles was obtained.

(Example 6)
A catalyst in which oxidized silver nanoparticles were supported on TiO ₂ particles was obtained by the same method as in Example 5 except that the heat treatment time was set to 30 minutes.

(Example 7)
First, copper chloride (manufactured by Wako Pure Chemical Industries, Ltd.) was dissolved in water to prepare a 0.21% by mass copper chloride aqueous solution. Next, gallium oxide (Ga ₂ O ₃ , manufactured by High Purity Chemical Laboratory Co., Ltd.) having a primary particle size of 2.5 μm was added to this copper chloride aqueous solution as semiconductor particles and dispersed to obtain a concentration of Ga ₂ O ₃ . Obtained a dispersion solution of 21% by mass. Next, this dispersion solution was heated under an argon atmosphere at 400 ° C. for 2 hours to remove the solvent to obtain a catalyst in which copper nanoparticles were supported on Ga ₂ O ₃ particles.

(Example 8)
And primary particle size in place of the TiO ₂ particles of 253 nm, niobium oxide primary particle diameter of the semiconductor particles is 1.7μm _(Nb 3 _{O 8,} Experiment synthetic: References Akatsuka, K .; Takanashi, G .; Ebina, Y .; Sakai, N .; Haga, M.-a .; Sasaki, T. Electrochemical and Photoelectrochemical Study on Exfoliated Nb ₃ O ₈ Nanosheet. J.Phys. Chem. Solids 2008, 69, 1288-1291) the same method as in example 1, except to obtain copper nanoparticles supported on Nb ₃ O ₈ particles catalyst.

(Example 9)
Calcium titanate with a primary particle size of 2.2 μm as a semiconductor particle instead of TiO ₂ particles with a primary particle size of 253 nm (CaTIO ₃ , experimental synthetic product: References H. Yoshida, L. Zhang, M. Sato, T. . Morikawa, T. Kajino, T. Sekito, S. Matsumoto and H. Hirata, Catal. Today, 2015, 251, 132.) By the same method as in Example 1, the copper nanoparticles are CaTIO ₃ particles. A catalyst carried on the surface was obtained.

(Example 10)
And primary particle size in place of the TiO ₂ particles of 253 nm, with use of the primary particle size of 250nm of TiO ₂ particles (manufactured by Ishihara Sangyo Kaisha, Ltd.) as the semiconductor particles and the concentration of sodium borohydride and 0.05 mol / L A catalyst in which copper nanoparticles were supported on TiO ₂ particles was obtained by the same method as in Example 1 except that.

(Example 11)
The copper nanoparticles were nitro by the same method as in Example 1 except that TiO ₂ particles having a primary particle size of 45 nm (manufactured by Ishihara Sangyo Co., Ltd.) were used as semiconductor particles instead of TiO ₂ particles having a primary particle size of 253 nm. A catalyst supported on _two particles was obtained.

(Example 12)
And primary particle size in place of the TiO ₂ particles of 253 nm, in the same manner as in Example 1 except for using the primary particle size of TiO ₂ particles 173Myuemu (manufactured by Ishihara Sangyo Kaisha, Ltd.) as the semiconductor particles, the copper nanoparticles TiO A catalyst supported on _two particles was obtained.

(Example 13)
A catalyst in which copper nanoparticles were supported on TiO ₂ particles was obtained by the same method as in Example 1 except that the concentration of the copper chloride solution was 0.4 mmol / L.

(Example 14)
A catalyst in which copper nanoparticles were supported on TiO ₂ particles was obtained by the same method as in Example 1 except that the concentration of the copper chloride solution was 0.2 mol / L.

(Example 15)
A catalyst in which oxidized copper nanoparticles were supported on TiO ₂ particles was obtained by the same method as in Example 2 except that the heat treatment time was set to 3 hours.

(Example 16)
A catalyst in which copper nanoparticles were supported on TiO ₂ particles was prepared by the same method as in Example 1 except that sodium cyanoborohydride (manufactured by Tokyo Chemical Industry Co., Ltd.) was used as a reducing agent instead of sodium borohydride. Obtained.

(Comparative Example 1)
Copper nanoparticles are silica particles by the same method as in Example 1 except that silica particles having a primary particle size of 200 nm (SiO ₂ , Sicastar silica particles, manufactured by Micromod) are used instead of TiO ₂ particles as semiconductor particles. A catalyst carried on the surface was obtained.

(Comparative Example 2)
Copper nanoparticles were produced by the same method as in Example 1 except that alumina particles (Al ₂ O ₃ , manufactured by Showa Denko Co., Ltd.) having a primary particle size of 1.6 μm were used instead of TiO ₂ particles as semiconductor particles. A catalyst supported on alumina particles was obtained.

[Evaluation]
The catalysts according to the above Examples and Comparative Examples were subjected to various measurements and characteristic evaluations shown below. The evaluation conditions for each characteristic are as follows. The results are shown in Table 1.

[1] Primary particle size of carrier With respect to various semiconductor particles, silica particles and alumina particles to be carriers, the contours of the primary particles are determined by using a scanning electron microscope (SEM, manufactured by Hitachi High-Technologies Co., Ltd.) before producing a catalyst. The primary particles were photographed at a clearly recognizable magnification. The obtained image was analyzed under the above conditions, and the primary particle size was calculated.

[2] Particle size of metal-containing nanoparticles With respect to the obtained catalyst, using a transmission electron microscope (TEM, manufactured by Nippon Denshi Co., Ltd.), the contours of the primary particles can be clearly recognized at a magnification of the metal-containing nanoparticles. The primary particles were photographed. The obtained image was analyzed under the above conditions, and the primary particle size was calculated.

[3] Average valence of metal (M) The average valence of copper and silver was measured for the metal-containing nanoparticles constituting the catalyst by using X-ray photoelectron spectroscopy.

[4] Mass ratio of metal-containing nanoparticles to carrier (%)
The obtained catalyst is analyzed by inductively coupled plasma (ICP, manufactured by Hitachi High-Tech Science Co., Ltd.), and the metal element (Cu or Ag) constituting the metal-containing nanoparticles and some elements (TiO ₂ ) constituting the carrier are analyzed. In the case of Ti, in the case of Ga ₂ O ₃ , Ga, in the case of Nb ₃ O ₈ , Nb, in the case of CaTIO ₃ , Ca in the case of CaTIO ₃ , Si in the case of SiO ₂ , and Al in the case of Al ₂ O ₃ ). did. Using these values, the mass concentration of the metal-containing nanoparticles and the mass concentration of the carrier were obtained, and from these ratios, the mass ratio of the metal-containing nanoparticles to the carrier [(mass of metal-containing nanoparticles / mass of carrier) × 100]. Was calculated.

[5] Reduction Test 100 mg of the catalyst obtained as described above was dispersed in 100 mL of a 0.05 mol / L KHCO ₃ aqueous solution to obtain a 1 g / L catalyst dispersion solution. This catalytic dispersion solution is irradiated with a pseudo-solar light source (Sora Mini USS-40, manufactured by Ushio Denki Co., Ltd.) for 10 hours while bubbling CO ₂ at 1 mL / min, and carbon monoxide (CO) and formic acid are produced as products. The amounts of (HCOOH), methane (CH ₄ ), ethylene (C ₂ H ₄ ) and ethane (C ₂ H ₆ ) produced were analyzed.
Of the products, carbon monoxide, methane, ethylene and ethane were analyzed using a gas chromatograph mass spectrometer (GCMS-QP2010, manufactured by Shimadzu Corporation). A SUPELCO CARBOXEN 1010PLOT 30 m × 032 mlD was used as the column, and a hydrogen flame ion detector (FID) was used as the detector.
For formic acid, the reaction solution after being irradiated with the above pseudo-substitute light source for 10 hours was analyzed by high performance liquid chromatography (HPLC, manufactured by Shimadzu Corporation).
In addition, the amount of carbon dioxide reduced to carbon monoxide, methane, ethylene, ethane, or formic acid was calculated from the total amount of these products.
In this example, a catalyst that has a reducing action on carbon dioxide is set as an acceptable level, and the amount of carbon dioxide reduced to carbon monoxide, methane, ethylene, ethane, or formic acid is set to 0.5 mmol or more, which is even better. evaluated.

From the results in Table 1, the metal-containing nanoparticles-supported catalyst according to Examples 1 to 16 of the present invention has good catalytic performance for the reduction reaction of carbon dioxide, and promotes and controls the reduction reaction of carbon dioxide satisfactorily. It was confirmed that it could be done. In particular, it was confirmed that the metal-containing nanoparticles-supported catalysts according to Examples 1 to 9 and 16 exhibited more excellent catalytic activity and selectivity for the reduction reaction of carbon dioxide.

On the other hand, in the catalysts of Comparative Examples 1 and 2, it was confirmed that the carrier supporting the metal-containing nanoparticles was not semiconductor particles and did not show a reducing action on carbon dioxide.

Claims (8)

A metal-containing nanoparticle-supported catalyst used to reduce carbon dioxide.
The metal-containing nanoparticle-supporting catalyst comprises supporting metal-containing nanoparticles on semiconductor particles as a carrier (excluding those selected from the group consisting of cadmium sulfide, cadmium selenide, gallium phosphate, and silicon). ,
The metal-containing nanoparticles contain at least one metal atom (M) selected from gold, silver, copper, platinum, rhodium, palladium, nickel, cobalt, iron, manganese, chromium, iridium, zinc, titanium and ruthenium. A metal-containing nanoparticle-supporting catalyst to be contained. The semiconductor particles are titanium oxide, tin oxide, zinc oxide, niobium oxide, calcium titanate, gallium oxide, tantalum oxide, strontium titanate, tungsten oxide, cerium oxide, gallium nitride, gallium aluminum nitride, gallium arsenide and arsenide. The metal-containing nanoparticle-supporting catalyst according to claim 1, which contains at least one material selected from aluminum gallium. The metal-containing nanoparticles-supporting catalyst according to claim 1 or 2 , wherein the primary particle size of the metal-containing nanoparticles is 0.2 to 100 nm. The metal-containing nanoparticle-supporting catalyst according to any one of claims 1 to 3, wherein the primary particle size of the semiconductor particles is 50 nm to 100 μm. Any one of claims 1 to 4 , wherein the mass ratio of the metal-containing nanoparticles to the semiconductor particles [(mass of metal-containing nanoparticles / mass of semiconductor particles) × 100] is 0.001 to 1%. The metal-containing nanoparticle-supporting catalyst according to. The metal-containing nanoparticle-supporting catalyst according to any one of claims 1 to 5 , wherein the metal atom (M) is copper. The metal-containing nanoparticle-supporting catalyst according to claim 6 , wherein the average valence of copper is 0 to 1.5. A carbon dioxide reducing device comprising the metal-containing nanoparticle-supporting catalyst according to any one of claims 1 to 7 .