JP4696299B2 - Composites of porous carbon and metal nanoparticles with sharp pore size distribution - Google Patents

Description

  The invention of this application relates to a composite of porous carbon and metal nanoparticles having a sharp pore size distribution. More specifically, the invention of this application relates to a composite of porous carbon and metal nanoparticles having a sharp pore size distribution that is excellent in sulfur resistance and useful as a hydrogenation catalyst.

  In recent years, composites composed of metal nanoparticle catalysts / supports such as platinum / zeolite, platinum / alumina, platinum / silica / alumina, etc. have been actively used as hydrogenation catalysts in petroleum refining processes.

  The sulfur resistance of platinum as a catalyst strongly depends on the solid acidity of the carrier carrying platinum. For example, when electron transfer from platinum to the carrier is likely to occur, the platinum is in an electron-deficient state, so that the affinity with an electron-withdrawing compound is weakened and sulfur resistance is improved. Therefore, it can be said that the use of a solid acid as a carrier is effective in improving the sulfur resistance of platinum. However, the solid acid also has a drawback that the catalytic activity of platinum is likely to be lowered due to adsorption poisoning or carbonaceous precipitation by a basic nitrogen compound. It has been reported that this decrease in catalytic activity is suppressed by improving the basicity of the carrier (Non-patent Document 1).

  In the hydrogenation of petroleum fractions containing highly polymerizable components such as olefins and diolefins, when the hydrogenation ability is not sufficient, olefins and the like are thermally polymerized, and carbonaceous matter is deposited on the surface of the carrier. For this reason, the influence of the pore size distribution of the support on the hydrogenation catalyst activity is widely recognized. That is, it is pointed out that when a broad carrier having a pore size distribution is used, olefins and the like are easily thermally polymerized in the pores, so that these polymers may be deposited on the pore surface ( For example, refer nonpatent literature 2). In addition, since poisonous substances such as nitrogen compounds are likely to enter the pores, it is said that hydrogenation activity is likely to be reduced by platinum being poisoned (Non-patent Document 3).

On the other hand, a method for producing a composite in which nanosized platinum fine particles are supported in a pore structure on a carbon aerogel, which is a carbon-based carrier whose pore diameter can be easily controlled, has been reported so far (non-patent) References 4-6). The existence of porous carbon cryogel particles having a sharp pore size distribution is also known (Non-patent Document 7).
"Properties of porous materials and their applied technologies", Fuji Techno System, P.576 (1999) Catalyst, vol. 28, No. 4, p.256 (1986) "Properties of porous materials and their applied technologies", Fuji Techno System, P.544 (1999) "Highly dispersed platinum on carbon aerogels as supportedcatalysts for PEM fuel cell-electrodes: comparison of two different synthesispaths," J. Non-Cryst. Solids, 350 (2004) 88-96. "Preparation of platinum / carbon aerogel nanocomposites usinga supercritical deposition method," J. Phys. Chem. B, 108 (2004) 7716-7722. "Invention of the supercritical deposition of platinum nanoparticles into carbon aerogels," Micropor. Mesopor. Mat., 80 (2005) 11-23. "Preparation and characterization of carbon cryogelmicrospheres," Carbon, 40 (2002) 1345-1351

  However, since the composites disclosed in Non-Patent Documents 4 to 6 all use a carbon-based support having a broad pore size distribution, they do not have sufficient sulfur resistance, and the hydrogenation catalyst It could not be used as effectively.

  In addition, with respect to porous carbon gel particles having a sharp pore size distribution, it has not been realized yet to support catalyst fine particles having a uniform size in nano size or a composite thereof. As described above, carbon-based materials, such as activated carbon, having a sharp pore distribution and a high specific surface area in a region of 2 nm or less are known, but they are useful as hydrogenation catalyst carriers 2. At present, a composite comprising a metal nanoparticle catalyst / support using a carbon-based material having a sharp pore system distribution and a high specific surface area in a region of ˜20 nm as a support has not been realized.

  For this reason, the sulfur resistance of a catalyst such as platinum can be improved, and a non-acidic porous carbon material having a sharp pore size distribution with less carbonaceous precipitation and adsorption poisoning by nitrogen compounds is used as a carrier. There is a need for the realization of sulfur-resistant catalyst / support composites.

  Accordingly, the invention of this application has been made in view of the circumstances as described above, which eliminates the problems of the prior art and is useful as a hydrogenation catalyst having excellent sulfur resistance, such as a sharp pore size distribution. It is an object of the present invention to provide a composite of porous carbon having metal and metal nano-particles.

  The inventors of this application have made various attempts to improve the sulfur resistance of metal nanoparticles supported on a carrier, and as a result, the metal nanoparticles are supported on porous carbon having a sharp pore size distribution. The present inventors have found that the problem can be solved, and have completed the invention of this application.

  That is, the invention of this application is, first of all, to provide a composite of porous carbon and metal nanoparticles, wherein metal nanoparticles are supported on porous carbon having a sharp pore size distribution. provide.

  Further, according to the invention of this application, secondly, the porous carbon has a sharp pore diameter of 90% or more of the total pore volume belonging to a range of 2 to 20 nm and a distribution width of 6 nm. Provided is a composite of porous carbon and metal nanoparticles, characterized by having a fine pore size distribution.

  Third, the porous carbon has a sharp pore size distribution in which the pore diameter of 90% or more of the total pore volume is in the range of 3 to 10 nm and the distribution width is 6 nm. A composite of porous carbon and metal nanoparticles is provided.

  Fourth, the present invention provides a composite of porous carbon and metal nanoparticles, wherein the porous carbon is spherical or substantially spherical.

  Fifth, the present invention provides a composite of porous carbon and metal nanoparticles, wherein the porous carbon has a particle size of 50 nm to 2 mm.

  Sixth, the present invention provides a composite of porous carbon and metal nanoparticles, wherein the porous carbon has a particle size of 100 nm to 1 mm.

  Seventh, the porous metal and the metal are characterized in that the metal nanoparticle is any one of group 8 element or group 6A element of the periodic table, or a combination of two or more kinds of nanoparticle. A composite of nanoparticles is provided.

  Eighth, the present invention provides a composite of porous carbon and metal nanoparticles, wherein the metal nanoparticles are any one of group 8 elements.

  Ninth, a porous carbon and metal nanoparticle, wherein the metal nanoparticle is supported on the inner surface of the pore of the porous carbon by the same size as the pore Provide a complex of

  Tenth, the present invention provides a composite of porous carbon and metal nanoparticles, wherein the metal nanoparticles have a particle size of 2 to 20 nm.

  Eleventh, the present invention provides a composite of porous carbon and metal nanoparticles, wherein the metal nanoparticles have a particle size of 3 to 10 nm.

12thly, the composite of the porous carbon and metal nanoparticle characterized by the weight ratio of the said metal nanoparticle and porous carbon being 0.5 to 50% is provided.

  13thly provides the composite of the porous carbon and metal nanoparticle of Claim 12 whose weight ratio of the said metal nanoparticle and porous carbon is 1.0 to 30%.

  Fourteenth, an aqueous solution containing phenols, aldehydes and a catalyst is subjected to a sol-gel polymerization reaction, and the aqueous solution in progress of the sol-gel polymerization reaction is dispersed in an organic solvent to which a surfactant has been added. A porous carbon precursor is produced by phase emulsion polymerization, and after removing the organic solvent from the porous carbon precursor, the metal precursor solution is impregnated to support the metal on the porous carbon precursor. A composite of porous carbon and metal nanoparticles is provided, which is a particulate composition obtained by removing and then heat-treating a porous carbon precursor carrying a metal.

  Fifteenth, the present invention provides a composite of porous carbon and metal nanoparticles, wherein the metal precursor is any one of the metal ammine complexes, nitrates, acetates, sulfates, and chlorides. .

  Sixteenth, the present invention provides a composite of porous carbon and metal nanoparticles, wherein the metal precursor is any one of the metal ammine complexes, nitrates, and chlorides.

  Seventeenth, the porous carbon precursor carrying the metal is heat-treated in an inert atmosphere to form metal nanoparticles on the inner surface of the pores of the porous carbon. A composite of carbonaceous and metal nanoparticles is provided.

  In addition, 18thly, the hydrogenation catalyst characterized by comprising the composite of any one of the above-mentioned porous carbon and metal nanoparticles is also provided.

  The invention of this application provides a composite of porous carbon and metal nanoparticles having a sharp pore size distribution. Since this composite has remarkable sulfur resistance, a hydrogenation catalyst useful for, for example, hydrodesulfurization treatment of a gasoline fraction is also provided.

  The invention of this application has the features as described above, and an embodiment thereof will be described below.

  The composite of porous carbon and metal nanoparticles (hereinafter also simply referred to as a composite) of the present invention of this application is characterized in that metal nanoparticles are composited with porous carbon having a sharp pore size distribution. It is said. In the invention of this application, the sharp pore size distribution means that the pore diameter distribution in which the horizontal axis represents the pore diameter of porous carbon and the vertical axis represents the integrated value of the pore volume, This means that 90% or more of the total pore volume is distributed in the range of width 6 nm. More specifically, it can be assumed that the pore diameters of 90% or more of the total pore volume are distributed in a range of ± 3 nm with respect to the peak value of the pore system distribution. That is, the pore diameters are extremely uniform, and the pore diameter distribution curve draws a very sharp peak at the pore diameter.

  The basic structure of the composite of porous carbon and metal nanoparticles according to the invention of this application will be described based on the enlarged schematic diagram of FIG. In FIG. 1, the spherical or substantially spherical substance is porous carbon (1), and porous carbon (1) is formed as secondary particles having a network structure in which a number of primary particles (2) are three-dimensionally bonded. Has been. The gaps in such a network structure form mesopores (2 to 50 nm), and the metal nanoparticles (3) are supported in these gaps.

  In the invention of this application, the shape of the porous carbon is not particularly limited, but in general use, it is preferably spherical or substantially spherical. Further, the particle diameter and pore diameter of the porous carbon are not particularly limited, and the particle diameter is preferably about 50 nm to 2 mm because it is easy to use. If the particle size of the porous carbon is too small, for example, when used as a hydrogenation catalyst, the pressure loss when the petroleum fraction is circulated increases, which is not preferable. On the other hand, if the particle size is too large, the voids between the particles also increase, which is not preferable because the residence time necessary for sufficiently refining the petroleum fraction cannot be obtained. Therefore, the particle diameter of porous carbon particularly preferable when this composite is used as a hydrogenation catalyst can be about 100 nm to 1 mm.

  Also, the pore diameter can be set as desired. For example, when this composite is used as a hydrogenation catalyst for refining petroleum oil, the pore diameter is 2 depending on the oil type. It can be set as a desired pore diameter within a range of about ˜50 nm, and further about 2-20 nm. More specifically, for example, when used as a hydrogenation catalyst for hydrodesulfurization treatment of a gasoline fraction, an average pore diameter of 3 to 10 nm is shown as a preferred example.

  As described above, the metal nanoparticles are supported in a highly dispersed manner in the gap in the porous carbon network structure having a sharp pore size distribution. As the metal nanoparticle, any one kind or two kinds or more of group 8 elements including platinum, nickel and cobalt or group 6A elements including chromium and molybdenum in the periodic table may be used. Nanoparticles can be used in combination. For the purpose of enhancing the performance as a hydrogenation catalyst, it is preferable to use any one kind of metal among group 8 elements including platinum, nickel and cobalt.

  In addition, the particle size of the metal nanoparticle is not particularly limited, but can be about 2 to 50 nm. In the composite of the invention of this application, the one having a relatively uniform particle size is supported. Can be a feature. In order for this complex to obtain sufficient activity as, for example, a hydrogenation catalyst, the particle size is preferably in the range of 2 to 20 nm, and more preferably in the range of 3 to 10 nm. In the invention of this application, the nano fine particles can include nano-sized particles having a particle size of about 100 nm or less, typically about 50 nm or less, more specifically, about 20 nm or less. To do.

  The preferred mass ratio (support rate) between the metal nanoparticles and the porous carbon of the composite according to the invention of this application is 0.5 to 50% by mass. Depending on the relationship between the particle size of the metal nanoparticle and the pore diameter of the porous carbon, etc., it is not possible to say unconditionally. However, when used as a hydrogenation catalyst, sufficient space for the reactants to enter is secured. Taking this into consideration, it is shown as a particularly preferred example that the supporting rate of the metal nanoparticles is 1.0 to 30% by mass.

  Such a composite of porous carbon and metal nanoparticles according to the invention of this application has a very sharp pore size distribution compared to a conventional composite of porous carbon and metal nanoparticles, for example, hydrogenation. When used as a catalyst or the like, it is preferably used in that the sulfur resistance is remarkably improved.

  The composite of porous carbon and metal nanoparticles according to the invention of the application described above can also be characterized as obtained by the following method, for example. That is, the composite of porous carbon and metal nanoparticles is prepared by subjecting an aqueous solution containing <A> phenols, aldehydes and a catalyst to a sol-gel polymerization reaction, and <B> an aqueous solution in progress of the sol-gel polymerization reaction. Is dispersed in an organic solvent to which a surfactant is added and subjected to reverse phase emulsion polymerization to form a porous carbon precursor. After removing the organic solvent from the porous carbon precursor, <C> metal precursor It is a particulate composition obtained by impregnating a solution to support a metal on a porous carbon precursor, removing the solution, and then heat-treating the porous carbon precursor supporting <D> metal.

  More specifically, first, an aqueous solution containing <A> phenols, aldehydes and a reverse phase emulsion polymerization catalyst is subjected to a sol-gel polymerization reaction.

  The phenols used here are not particularly limited, and various monovalent or polyvalent phenols can be used. Examples include using monohydric phenols such as phenol, cresol, thymol, naphthol, dihydric phenol catechol, resorcinol, hydroquinone, dihydroxynaphthalene, trihydric phenol pyrogallol, phloroglucinol, and the like. . Among these, dihydric phenol is exemplified as a preferable one because it is easy to prepare a uniform aqueous alkali solution.

  The use of aldehydes is not particularly limited, and the use of formaldehyde and acetaldehyde is a preferable example in terms of good solubility in a sol-gel polymerization reaction solvent (such as water). Of these, formaldehyde is even more preferable.

  Moreover, as a catalyst suitable for reverse phase emulsion polymerization, the substance which makes the aqueous solution containing the said phenols and aldehydes alkaline can be used, For example, the compound of an alkali metal or an alkaline-earth metal can be mention | raise | lifted. Particularly preferred are alkali metal carbonates, alkali metal bicarbonates, and alkali metal hydroxides.

Here, by adjusting the composition of the aqueous solution, the pore diameter of the obtained porous carbon can be controlled. For example, the molar ratio of phenols to catalyst is 50 to 1500, preferably in the range of about 100 to 1000, and the ratio of phenols to water (g / cm ³ ) is 0.05 to 1.
Preferably, by controlling in the range of about 0.1 to 0.5, it is possible to have a sharp pore size distribution in the range of the pore diameter of 2 to 20 nm, more preferably 3 to 10 nm.

  <B> An aqueous solution containing phenols, aldehydes, and a catalyst starts a sol-gel polymerization reaction at the same time as the preparation, and is poured into an organic solvent containing a surfactant during the reaction, and stirred. Reverse phase emulsion polymerization is performed.

  As the organic solvent, an organic solvent having low solubility in a sol-gel polymerization reaction solvent, such as cyclohexane or hexane, can be used.

  As the surfactant, those having a function of stably dispersing the aqueous phase in the oil phase can be used. For example, a W / O having an HLB value of about 3.5 to 7 indicating a balance between hydrophilicity and hydrophobicity can be used. The use of a mold having an emulsifying action is exemplified. More specifically, for example, sorbitan monooleate (SPAN80, HLB = 4.3), glycerin monostearate (HLB = 3.8), sorbitan monopalmitate (HLB = 6.7) and the like are suitable. Can be used.

  The stirring speed at the time of reverse phase emulsion polymerization is a point to be noted in obtaining the composite of the invention of this application. This is because the precursor of the porous carbon formed in the liquid can be adjusted to a spherical shape or a substantially spherical shape by stirring, and the particle size is influenced by the stirring speed. When the stirring speed is high, the shear stress acting on the emulsion is large, so that reagglomeration of droplets in the emulsion is suppressed, and the porous carbon precursor, that is, the particle size of the porous carbon becomes small. On the other hand, when the stirring speed is low, the shear stress is small and the droplets are likely to reaggregate, so the particle size of the porous carbon increases. Thus, it is necessary to pay sufficient attention to the stirring speed. The preferred stirring speed varies depending on the viscosity of the aqueous solution, the volume and shape of the reaction vessel, etc., so it is difficult to uniquely determine, and the optimum stirring speed depends on the desired porous carbon particle size and the reaction system used. The speed can be determined.

  The temperature during reverse phase emulsion polymerization can be set from 0 ° C. to a temperature range below the boiling point of the organic solvent used as the dispersion medium, but the temperature of reverse phase emulsion polymerization is the porous carbon finally obtained. It has been newly clarified by the present inventor's recent research that it has a great influence on the pore characteristics of the present invention. In the composite of the invention of this application, the porous carbon is preferably one in which mesopores are developed on the outer surface of the porous carbon particle as a supporting site for the metal nanoparticle. However, if the inverse emulsion polymerization temperature is too low, moisture is dehydrated from the droplet surface to the organic solvent phase in the emulsion, and the pores shrink and a dense layer is formed on the surface. It is difficult to produce porous carbon that is preferable as a site for supporting metal nanoparticles in the invention. On the other hand, when the reverse-phase emulsion polymerization temperature is appropriate, the dehydration effect is suppressed and pore shrinkage does not occur, and porous carbon with developed mesopores is obtained. This reverse phase emulsion polymerization temperature can be adjusted according to the pore state required for the target porous carbon particles. For example, it is particularly preferable to set the reverse emulsion polymerization temperature in the range of 40 ° C. or more and less than 60 ° C. Indicated.

  By removing the solvent from the gel product thus produced, a precursor of porous carbon having a sharp pore size distribution can be obtained. The removal of the solvent is not particularly limited as long as it is a technique that does not impair the structure having a sharp pore size distribution formed in the porous carbon precursor. Generally, as a suitable drying method for obtaining a porous body having developed pores, techniques such as supercritical drying and freeze drying are known, and the gels obtained by these are distinguished from aerogels and cryogels, respectively. In the invention of this application, for the removal (drying) of the solvent, various drying methods such as supercritical drying, freeze drying, vacuum drying, hot air drying, and microwave drying can be used.

  Next, after impregnating the precursor of <C> porous carbon with the aqueous metal precursor solution, the aqueous solution is removed and <D> heat treatment is performed.

  The metal precursor is preferably an ammine complex, nitrate, acetate, sulfate, or any one of two or more group 8 elements or group 6A elements in the periodic table as described above. Any of chlorides, more preferably ammine complexes, nitrates, and chlorides.

  When the porous carbon precursor is immersed in the metal precursor aqueous solution, the metal precursor aqueous solution is impregnated in the gaps in the network structure formed inside the porous carbon, and the metal precursor is supported. The mass ratio (support rate) between the metal nanoparticles and the porous carbon in the composite of the invention of this application can be easily controlled by adjusting the concentration of the metal precursor solution. If the concentration of the metal precursor solution is too low, the amount of supported metal nanoparticles will be small, so that sufficient catalytic activity as a hydrogenation catalyst is not exhibited, which is not preferable. On the other hand, if the concentration is too high, the inside of the pores is blocked by the formed metal nanoparticles, which is not preferable because a sufficient space for the reactants to enter cannot be secured when used as a hydrogenation catalyst. . Therefore, the concentration of the metal precursor solution can be appropriately determined in consideration of the weight ratio of the metal nanoparticles and the porous carbon in the finally obtained composite.

  Further, the means for removing the aqueous metal precursor solution is not particularly limited, and a technique such as vacuum suction or heating can be employed.

  The heat treatment is performed for the purpose of carbonizing the porous carbon precursor to form porous carbon and thermally decomposing the metal precursor supported on the porous carbon precursor to form metal nanoparticles. This heat treatment is preferably performed at a treatment temperature of 300 to 1300 ° C. in an inert atmosphere such as argon or nitrogen. If the treatment temperature is too low, the metal precursor is not sufficiently thermally decomposed, which is not preferable. On the other hand, if the treatment temperature is too high, metal nanoparticles are sintered (aggregated) and coarsened during carbonization of the porous carbon precursor, and metal nanoparticles having a uniform particle size are not formed. For these reasons, it is particularly preferable to set the heat treatment temperature to 400 to 700 ° C. in order to control the particle size of the metal nanoparticle within a suitable range. The metal nanoparticles are mainly formed in the pores of the porous carbon, and the space in which the metal nanoparticles can grow is limited by the pore diameter. That is, in the composite of the invention of this application, the pore diameter distribution of porous carbon and the particle size distribution of metal nanoparticles are similar, and the metal nanoparticles also have a sharp particle size distribution. It is supposed to be. In addition, controlling the diameter of the pores of the porous carbon in order to support the metal nanoparticles having a desired particle diameter is also an effective method.

  Thereby, the composite of the porous carbon and metal nanoparticle of the invention of this application can be obtained as the particulate composition.

  The composite of porous carbon and metal nanoparticles having a sharp pore size distribution of the invention of this application can be produced in a large amount by a single adjustment, and metal nanoparticles having catalytic action on porous carbon Can be used as a catalyst. And it is preferably used as a catalyst or the like for which sulfur resistance is required in that the sulfur resistance is remarkably improved as compared with the conventional composite of porous carbon and metal nanoparticles. Therefore, the hydrogenation catalyst comprising the composite of porous carbon and metal nanoparticles according to the invention of this application is extremely suitable as a hydrogenation catalyst used for hydrodesulfurization treatment of gasoline fractions.

  The composite of the invention of this application is not limited to a hydrogenation catalyst, and is widely used as a polymer electrolyte membrane fuel cell, a water treatment catalyst for decomposing organic substances in wastewater, and the like. Be expected.

  Examples will be shown below, and the embodiment of the invention of this application will be described in more detail. Of course, the present invention is not limited to the following examples, and it goes without saying that various aspects are possible in detail.

Example <A> Resorcinol (R) (manufactured by Wako Pure Chemical Industries, Ltd.) and formaldehyde (F) (manufactured by Wako Pure Chemical Industries, Ltd.) as raw materials, sodium carbonate (C) (manufactured by Wako Pure Chemical Industries, Ltd.) And distilled water (W) as a sol-gel reaction catalyst and diluent, respectively, an aqueous solution of resorcinol-formaldehyde (RF) was prepared and allowed to stand at 25 ° C. to advance the sol-gel reaction. The molar ratio of resorcinol to formaldehyde (R / F [mol / mol]) and the ratio of resorcinol to distilled water (R / W [g / cm ³ ]) are fixed at 0.5 and 0.25, respectively.
The molar ratio of resorcinol to sodium carbonate (R / C [mol / mol]) was 200.
<B> When about 80% of the time required for the RF aqueous solution to gel has elapsed from the start of the reaction, the RF aqueous solution is made up of a 5% by volume surfactant (SPAN80) (Wako Pure Chemical). "Reverse Phase Emulsion Polymerization" in which an emulsion is formed by injecting into dissolved cyclohexane (manufactured by Kogyo Co., Ltd.) and stirring at a rate of 400 rpm at 60 ° C.
Thus, porous carbon precursor particles were synthesized.

  The obtained porous carbon precursor particles are quickly filtered while being careful not to dry, and separated from cyclohexane, and then the solvent containing water as a main component in the pores is replaced with 10 times the wet gel volume. It was immersed in the above t-butyl alcohol and washed for 1 day with stirring. This washing operation was repeated three times or more.

The porous carbon precursor particles were frozen at −30 ° C. for 1 day, and then kept under a reduced pressure of −10 ° C. for 4 days to sublimate and remove t-butyl alcohol in the pores. Carbonaceous precursor particles a were obtained. The drying of the porous carbon precursor particles is not performed by such a freeze-drying method.
<C> Next, an aqueous metal precursor solution was supported on the porous carbon precursor particles a by an impregnation method. That is, 2 g of porous carbon precursor particles (dry basis) was converted into platinum precursor [Pt (NH ₃ ) ₄ ] Cl ₂ .nH ₂ O (manufactured by N.E. Chemcat Co., Ltd., platinum content purity 55.07 mass). %) 0.363 g was dissolved in 2 ml of pure water and immersed in an aqueous solution prepared. Next, this was put together with the aqueous solution into an insulator-type flask, pressure reduction was started at room temperature using an evaporator, the temperature was gradually raised and kept at 60 ° C. for 2 hours to evaporate the water, and further using a rotary pump A high vacuum was drawn at 60 ° C. to sufficiently evaporate water.
<D> The obtained platinum precursor-supporting porous carbon precursor particles are held under reduced pressure for 24 hours, and then heat-treated at 500 ° C. in an argon atmosphere to carbonize the porous carbon precursor particles and be supported. The platinum precursor was pyrolyzed. Subsequently, it is calcined in an oxygen stream (12 L / min) at 200 ° C. for 3 hours (temperature increase rate until reaching 200 ° C .: 0.5 ° C./min) to obtain porous carbon (RF A composite A of carbon gel particles) and metal nanoparticles was prepared.

Comparative Example <A> Resorcinol (R), formaldehyde (F), and sodium carbonate (C) were dissolved in distilled water (W) to prepare a resorcinol-formaldehyde (RF) aqueous solution at 25 ° C. The sol-gel reaction was allowed to proceed by allowing to stand. The molar ratio of resorcinol to formaldehyde (R / F [mol / mol]) and the ratio of resorcinol to distilled water (R / W [g / cm ³ ]) were fixed at 0.5 and 0.25, respectively. The molar ratio of sodium carbonate (R / C [mol / mol]) was 200.
<B ′> The RF aqueous solution was put into a glass bottle vial, sealed so as not to come into contact with air, and kept for 1 day to gel. The obtained porous carbon precursor was immersed in t-butyl alcohol having a volume of 10 times or more of its volume, and left still for one day for washing in order to replace the solvent mainly composed of water in the pores. This washing operation was repeated three times or more. Furthermore, after maintaining the porous carbon precursor at −30 ° C. for 1 day to freeze the t-butyl alcohol in the pores, the porous carbon precursor is maintained at −10 ° C. under reduced pressure for 4 days to thereby maintain the t-butyl in the pores. Alcohol was sublimated and removed to obtain a porous carbon precursor b.
<C> Next, an aqueous metal precursor solution was supported on the porous carbon precursor b by an impregnation method. That is, 2 g of porous carbon precursor was prepared by dissolving 0.363 g of platinum precursor [Pt (NH ₃ ) ₄ ] Cl ₂ .nH ₂ O (platinum content purity 55.07 mass%) in 2 ml of pure water. Soaked in an aqueous solution. Next, this was put together with the aqueous solution into an insulator-type flask, pressure reduction was started at room temperature using an evaporator, the temperature was gradually raised and kept at 60 ° C. for 2 hours to evaporate the water, and further using a rotary pump A high vacuum was drawn at 60 ° C. to sufficiently evaporate water.
<D> The obtained platinum precursor-supporting porous carbon precursor was held under reduced pressure for 24 hours, and then heat treated at 500 ° C. in an argon atmosphere to carbonize the porous carbon precursor, and the supported platinum The precursor was pyrolyzed. Subsequently, it is calcined in an oxygen stream (12 L / min) at 200 ° C. for 3 hours (temperature increase rate until reaching 200 ° C .: 0.5 ° C./min), and porous carbon having a broad pore size distribution (RF Carbon gel) and metal nanoparticle composite B were prepared.

Comparison of pore characteristics of composites A and B About composites A and B obtained in the above examples and comparative examples, the pores were measured using a fully automatic nitrogen gas adsorption amount measuring device (manufactured by Nippon Bell Co., Ltd.). The characteristics were determined. That is, 0.05 g of a sample was collected in a dedicated cell, pretreated under reduced pressure at 250 ° C. for 4 hours to remove adsorbate on the pore surface in advance, and nitrogen adsorption / desorption on the carbon gel at −196 ° C. The isotherm was measured. The pore size distribution was obtained by analyzing this adsorption / desorption isotherm by the Dollimore-Heal method. FIG. 2 shows the results of examining the pore size distribution of composites A and B, respectively. (A) shows the pore diameter on the horizontal axis, frequency on the vertical axis, and (B) shows the pore diameter on the horizontal axis and the integrated value of the pore volume on the vertical axis. As can be seen from FIG. 2A, the composite B made of RF carbon gel has a broad pore size distribution in which the pore diameter is widely distributed over a range of pore diameters of 20 nm or more, whereas the RF carbon gel The pore width distribution width of the composite A composed of particles was within 6 nm, and it was confirmed that it had a sharp pore size distribution.

  Further, in FIG. 2B, when a region in which 90% or more of the total pore volume of the composite B is distributed is confirmed, the region having a pore diameter of 2 to 24 nm covers a wide range of 20 nm or more. In A, it was found that most of the pore volume was concentrated in a narrow range having a pore diameter of 2 to 6 nm. From this, it was confirmed that the pore size distribution of the composite A was extremely sharp compared to the composite B in which the pore diameter was distributed in a monolithic form.

TEM Observation of Metal Nanoparticles of Composite A For the composite A obtained in the above examples and comparative examples, a bright-field image and a dark-field image of platinum fine particles supported in the pores are transmitted with a high-resolution transmission electron microscope. (TEM) and the result is shown in FIG. As can be seen from FIG. 3, it was confirmed that the platinum fine particles supported on the composite A had a uniform particle diameter and were uniformly dispersed on the surface of the porous carbon.

  Further, the photographed TEM photograph was subjected to image processing to determine the particle size distribution of the platinum nanoparticle, and the result is shown in FIG. 4 together with the pore size distribution of the porous carbon. It can be seen that the pore diameter distribution of the porous carbon and the particle size distribution of the metal nanoparticles are almost the same, and the particle diameter of the metal nanoparticles is determined according to the pore diameter distribution of the porous carbon.

Comparison of degree of dispersion and sulfur resistance of metal nanoparticles of composites A and B With respect to composites A and B obtained in the above examples and comparative examples, the dispersion degree of platinum supported on the surface of the carrier was changed to gas. Determined by adsorption method. Using a fully automatic catalyst gas adsorption amount measuring device (manufactured by Nippon Bell Co., Ltd.), 0.06 g of the composite sample is collected in a dedicated cell, hydroreduced at 300 ° C. for 1 hour, and then chemically adsorbed CO. The degree of dispersion was determined from the number of surface atoms determined from The degree of dispersion of the metal nanoparticles is defined as the ratio of the number of atoms exposed on the surface to the total number of atoms of the supported metal, and the adsorption ratio of CO molecules to platinum atoms is 1.

  In addition, the dispersion degree of the metal nanoparticles was measured in the same manner for the composites A and B that were subjected to sulfurization treatment at 280 ° C. for 1 hour under the flow of 500 ppm of hydrogen sulfide.

  Table 1 shows the metal dispersion degree before and after the sulfiding treatment of the platinum nanoparticles supported on the composites A and B.

  The platinum nanoparticle carried on the composite A having a sharp pore size distribution had a metal dispersion degree as large as 7.0%, which was 6.9 nm in terms of particle size. On the other hand, the metal dispersity of the platinum nanoparticles supported on the composite B having a broad pore size distribution was relatively small at 5.3%, which was 9.3 nm in terms of particle size.

  From these results, it is shown that the composite of porous carbon and metal nanoparticles of the invention of this application has a sharp pore size distribution and the metal nanoparticles are supported with a smaller particle size. It was.

  Further, the metal dispersion degree of the composite B is reduced to 0.6% after the sulfidation treatment. This means that 90% or more of the surface of the supported platinum nanoparticle was sulfided. On the other hand, in the case of the composite A, the metal dispersion after the sulfidation treatment is 1.9%, and 27% or more of the metal surface is maintained without being sulfidized as compared with that before the sulfidation treatment. From this, it was confirmed that the composite of porous carbon and metal nanoparticles having a sharp pore size distribution of the invention of this application has high resistance to hydrogen sulfide.

Regarding the residual chlorine of the composites A and B, the chlorine contained in the raw materials of the composites A and B adversely affects the catalytic activity, so it is desirable that the residual chlorine is decomposed by the final heat treatment. For this reason, the composition analysis before and behind heat processing of the composites A and B before and after heat processing was performed using the X-ray analyzer (made by Horiba Seisakusho). As a result, the peak of chlorine derived from the platinum precursor was detected before the heat treatment, but no chlorine was detected after the heat treatment, so it was confirmed that the chlorine was almost completely decomposed.

It is the figure which illustrated typically the basic structure of the composite_body | complex of the porous carbon which has sharp pore diameter distribution of this invention, and a metal nanoparticle. It is the figure which illustrated pore diameter distribution of the composites A and B produced in the Example. It is the figure which illustrated the TEM observation result of the composite A produced in the Example. It is the figure which illustrated the particle diameter distribution of the platinum nanoparticle in the composite A, and the pore diameter distribution of porous carbon.

Explanation of symbols

1 Porous carbon 2 Primary particles 3 Nano metal fine particles

Claims (17)

  Metal nanoparticles are supported on porous carbon having a sharp pore size distribution in which the pore diameter of 90% or more of the total pore volume is in the range of 2 to 20 nm and the distribution width is 6 nm. A composite of porous carbon and metal nanoparticles, characterized in that The porous carbon has a sharp pore size distribution in which a pore diameter of 90% or more of the total pore volume falls within a range of 3 to 10 nm and a distribution width of 6 nm. Item 2. A composite of porous carbon and metal nanoparticles according to Item 1 .   The composite of porous carbon and metal nanoparticles according to claim 1 or 2, wherein the porous carbon is spherical or substantially spherical.   4. The composite of porous carbon and metal nanoparticles according to claim 1, wherein the porous carbon has a particle size of 50 nm to 2 mm.   5. The composite of porous carbon and metal nanoparticles according to claim 4, wherein a particle size of the porous carbon is 100 nm to 1 mm.   6. The metal nanoparticle according to any one of claims 1 to 5, wherein the metal nanoparticle is any one of group 8 element or group 6A element of the periodic table, or a combination of two or more metal nanoparticles. A composite of porous carbon and metal nanoparticles as described in 1.   The composite of porous carbon and metal nanoparticles according to claim 6, wherein the metal nanoparticles are nanoparticles of any one of the group 8 elements.   The porous metal according to any one of claims 1 to 7, wherein the metal nano-particles are supported on the inner surface of the pores of the porous carbon in the same size as the pores. Of carbonaceous and metal nanoparticles. 2. The composite of porous carbon and metal nanoparticles according to claim 1 , wherein a particle diameter of the metal nanoparticles is 2 to 20 nm. The composite of porous carbon and metal nanoparticles according to claim 2 , wherein the metal nanoparticles have a particle size of 3 to 10 nm.   The composite of porous carbon and metal nanoparticles according to any one of claims 1 to 10, wherein a loading ratio of the metal nanoparticles to the porous carbon is 0.5 to 50% by mass.   The composite of porous carbon and metal nanoparticles according to claim 11, wherein the loading ratio of the metal nanoparticles to the porous carbon is 1.0 to 30% by mass.   An aqueous solution containing phenols, aldehydes, and a catalyst for reverse-phase emulsion polymerization is subjected to a sol-gel polymerization reaction, and the aqueous solution in progress of the sol-gel polymerization reaction is dispersed in an organic solvent to which a surfactant is added and reversed. A porous carbon precursor is produced by phase emulsion polymerization, and after removing the organic solvent from the porous carbon precursor, the metal precursor solution is impregnated to support the metal on the porous carbon precursor. The composite of porous carbon and metal nanoparticles according to claim 1, which is a particulate composition obtained by removing and then heat-treating a porous carbon precursor carrying a metal.   The composite of porous carbon and metal nanoparticles according to claim 13, wherein the metal precursor is any one of the metal ammine complex, nitrate, acetate, sulfate, and chloride.   The composite of porous carbon and metal nanoparticles according to claim 14, wherein the metal precursor is any one of the metal ammine complex, nitrate, and chloride.   16. The metal nano-particles are formed on the inner surfaces of the pores of the porous carbon by heat-treating the porous carbon precursor supporting the metal in an inert atmosphere. A composite of porous carbon and metal nanoparticles according to any one of the above. The composite of porous carbon and metal nanoparticles according to any one of claims 13 to 16, wherein the heat treatment temperature is 400 to 700 ° C.