Gold on carbon catalyst and method for its production

Abstract

[Problem] To provide a gold-supporting carbon catalyst in which gold fine particles are smaller in size and have high adhesion strength to carbon black, and in which the aggregation of the gold fine particles is suppressed. [Solution] A gold-supporting carbon catalyst in which gold fine particles having an average particle diameter of 1.0 to 1.5 nm are supported on carbon black in a coverage of 10 to 70% in the presence of an alkyl mercaptan.

Description

Technical Field

[0001] This invention relates to gold-supported carbon catalysts and their manufacturing methods. Background Technology

[0002] Gold particles with nanoscale particle size can be used, for example, as cathode catalysts for the reduction of carbon dioxide.

[0003] There are two methods for manufacturing these gold microparticles: gas-phase methods and liquid-phase methods. An example of a liquid-phase method is the method of reducing gold ions by adding a reducing agent to obtain gold microparticles.

[0004] Patent Document 1 discloses a method for controlling the particle size by controlling the reduction reaction rate in a method for manufacturing gold microparticles by reducing chloroaurate ions with sodium borohydride in the presence of alkyl thiols using a toluene / water two-phase system.

[0005] Existing technical documents

[0006] Patent documents

[0007] Patent Document 1: JP 2004-232017 Summary of the Invention

[0008] The problem the invention aims to solve

[0009] In catalysts where gold microparticles are supported on carbon black, small particle size is required for high activity, while the ability to suppress gold microparticle aggregation is necessary for high durability. However, further reducing the size of the gold microparticles leads to their tendency to aggregate during use, resulting in reduced activity.

[0010] The purpose of this invention is to provide a gold-loaded carbon catalyst with smaller gold particles and stronger adhesion to carbon black, which can inhibit the aggregation of gold particles.

[0011] Technical solutions for solving the problem

[0012] The inventors of this invention discovered that, in the gold microparticle processing step, by removing larger gold microparticles, the particle size of the gold microparticles becomes smaller. Furthermore, by loading alkathiol-coordinated gold microparticles onto carbon black in hexane, a gold-supported carbon catalyst capable of inhibiting gold microparticle aggregation can be obtained due to the strong adhesion strength and the steric hindrance effect of the coordinated alkathiols, thus completing this invention. Specifically, it is believed that if gold microparticles are loaded onto carbon black using the method of this invention, loading can be carried out under conditions where water is absent, which would adversely affect the bonding between the functional groups of carbon black and the gold microparticles. In addition, the adhesion strength is enhanced by the bonds (covalent and ionic) between the functional groups of carbon black and the alkathiols coordinated to the gold microparticles.

[0013] Furthermore, it is believed that the alkylthiols coordinated to the gold microparticles act as steric hindrances, inhibiting the aggregation of gold microparticles during catalyst use, suppressing the functional degradation of the catalyst, and contributing to high durability.

[0014] Invention Effects

[0015] According to the present invention, a gold-loaded carbon catalyst can be provided, wherein the gold particles are smaller in size and have a strong adhesion to carbon black, thereby inhibiting the aggregation of gold particles. Attached Figure Description

[0016] Figure 1 This is a TEM image of Example 1. Detailed Implementation

[0017] This invention relates to a gold-loaded carbon catalyst, wherein gold microparticles with an average particle size of 1.0 to 1.5 nm are supported on carbon black, with an alkylthiol coverage of 10% to 70%. The average particle size of the gold microparticles is preferably 1.2 to 1.5 nm.

[0018] Alkylthiols are derived from the general formula C n H (2n+1) SH indicates that it is a water-insoluble thiol composed of a sulfur-containing bonding group bonded to the gold surface, a methylene group as a spacer chain, and a methyl group as a head group. Examples include dodecanethiol, hexadecanethiol, and octadecanethiol.

[0019] Gold microparticles are loaded onto the carbon black surface in a highly dispersed state. The carbon black is electrically conductive and has a BET specific surface area of ​​80–1300 m². 2 / g. Carbon black typically possesses surface functional groups such as carboxyl groups, lactone groups, phenolic hydroxyl groups, and carbonyl groups. For example, a BET specific surface area of ​​approximately 800 m² can be used as carbon black. 2 The specific surface area of ​​Ketjen Black EC300J or BET is approximately 1270 m² / g. 2 / g Ketjen Black EC600JD.

[0020] The method for manufacturing the gold-loaded carbon catalyst of the present invention includes a gold particle generation step, a gold particle treatment step, and a gold particle loading step.

[0021] In the gold microparticle generation step, an aqueous solution of chloroauric acid and an organic solvent solution containing a phase transfer agent are mixed, and then the organic solvent solution phase is obtained by liquid phase separation. Alkyl thiols are mixed into the organic solvent solution phase, and an aqueous solution containing a reducing agent is mixed into the mixed solution to obtain alkyl thiols coordinated gold microparticles.

[0022] Specifically, for example, an aqueous solution of chloroauric acid dissolved in pure water and a solution of tetraoctylammonium bromide dissolved in toluene as an organic solvent are mixed to react chloroauric acid with tetraoctylammonium bromide as a phase transfer agent. The aqueous phase is then separated and removed. Dodecyl mercaptan is added to the resulting toluene solution phase (organic solvent solution phase), and the mixture is stirred and mixed to obtain a complex with gold-coordinated groups replaced by dodecyl mercaptan groups (C). 12 H 25 S) gold complex salt (C8H) 17 )4N[Au(C 12 H 25 S)4]. In the above steps, stirring is carried out at 30°C for at least 6 hours, preferably at least 12 hours.

[0023] Next, the toluene solution phase (organic solvent solution phase) containing the dodecanethiol and mixed with sodium borohydride dissolved in pure water is mixed and stirred at 30-60°C for 1-4 hours to reduce and precipitate the dodecanethiol-coordinated gold particles in the toluene solution phase (organic solvent solution phase). The toluene solution phase (organic solvent solution phase) is separated, and the toluene in the organic solvent is removed by an evaporator to obtain the dodecanethiol-coordinated gold particles as precipitate.

[0024] In the gold microparticle processing step, the following series of operations are repeated multiple times: the alkanthiol-coordinated gold microparticles are dispersed in hexane, then a polar organic solvent is added and mixed, and the alkanthiol-coordinated gold microparticles are separated by centrifugation.

[0025] Methanol or ethanol can be used as a polar organic solvent, for example.

[0026] Specifically, for example, gold microparticles coordinated with dodecylthiol are dispersed in hexane.

[0027] Next, ethanol, a polar organic solvent, was added and mixed. The mixture was then centrifuged to extract the precipitated gold microparticles coordinated with dodecylthiol and washed.

[0028] The above series of operations are repeated two or more times.

[0029] In the above steps, unreacted tetraoctylammonium bromide and dodecylthiol adhering to the gold microparticles coordinated with dodecylthiol can be removed (cleaned).

[0030] Through the above gold microparticle processing steps, gold microparticles with an average particle size of 1.0 to 1.5 nm, coordinated with dodecanethiol at a coverage of 10 to 70%, are obtained.

[0031] In this gold microparticle treatment step, the dodecyl mercaptan of larger gold microparticles has a lower coordination number per unit surface area and a relatively stronger polarity. It combines with ethanol, a polar organic solvent, and remains in the liquid without precipitation. Therefore, it is believed that larger gold microparticles can be removed.

[0032] In the gold microparticle loading step, a solution obtained by dispersing the above-mentioned alkathiol-coordinated gold microparticles after the gold microparticle treatment step in hexane and a solution obtained by dispersing carbon black in hexane are prepared separately. They are mixed and stirred for more than 6 hours to obtain carbon black loaded with the above-mentioned alkathiol-coordinated gold microparticles.

[0033] Specifically, for example, gold microparticles coordinated with dodecylthiol are dispersed in hexane by ultrasonic irradiation to obtain a gold colloidal hexane solution. Carbon black is then dispersed in the hexane solution by ultrasonic irradiation. In the above steps, for example, dispersion is achieved by irradiation with ultrasound at 33–40 kHz for 1 hour each time.

[0034] The two solutions are mixed and stirred at room temperature for, for example, 12 hours, to load dodecyl mercaptan-coordinated gold microparticles onto carbon black. This stirring process loads the gold microparticles onto the carbon. While mixing the two solutions, the mixture can be irradiated with ultrasound for 10 to 30 minutes.

[0035] Through the above steps, a gold-loaded carbon catalyst was obtained, wherein gold particles with an average particle size of 1.0–1.5 nm were supported on carbon black, with alkyl thiols coordinated at a coverage of 10–70%. By adjusting the carbon content relative to the gold content, gold-loaded carbon with a gold loading rate of 5–70% by weight can be prepared.

[0036] In addition, when the carbon black is irradiated with ultrasound in hexane, trace amounts of water that were absorbed by the carbon black during processing are removed.

[0037] When the coverage of alkylthiols is less than 10%, the adhesion strength with carbon black decreases. However, if the coverage of alkylthiols is greater than 70%, the gold surface, which functions as a catalyst, cannot be adequately obtained. The alkylthiols coverage is preferably 10–70%, more preferably 15–65%.

[0038] Example

[0039] The present invention will be described in more detail below through examples.

[0040] (Example 1)

[0041] The aqueous solution of chloroauric acid (HAuCl4·4H2O) obtained by dissolving 21g of chloroauric acid (HAuCl4·4H2O) in 10g of pure water and the solution obtained by dissolving 42.9g of tetraoctylammonium bromide (phase transfer agent) in 693g of toluene were mixed and stirred at room temperature.

[0042] Next, the aqueous solution phase was removed to obtain the toluene solution phase.

[0043] Add 31.2 mL of dodecyl mercaptan (protectant) to the obtained toluene solution phase and stir for 12 hours.

[0044] Then, an aqueous solution of sodium borohydride (reducing agent) and 255g of ultrapure water, which was mixed and added to a toluene solution phase maintained at 60°C, was added at a dropping rate of 10mL / min. After stirring for 30 minutes, the solution was stirred at 25°C for 3 hours.

[0045] Then, the aqueous phase was removed, and the toluene was evaporated using a rotary evaporator to obtain the precipitate.

[0046] Next, a gold microparticle treatment step is performed. This involves removing excess tetraoctylammonium bromide, dodecyl mercaptan, and larger gold microparticles from the gold-containing precipitate. As a first treatment, the precipitate (gold colloid) is redispersed by ultrasonic irradiation at 40 kHz for 10 minutes in 60 mL of hexane. Then, 500 mL of ethanol is added and mixed, followed by centrifugation at 8000 rpm at 10°C for 15 minutes to obtain the precipitate.

[0047] As a second treatment, the precipitate was irradiated with ultrasound at 40 kHz for 10 minutes in 24 mL of hexane to redisperse it. 500 mL of ethanol was added and mixed, and the mixture was centrifuged at 8000 rpm at 10 °C for 15 minutes. Then, the supernatant was removed, and the precipitate was redispersed in hexane. The hexane solution was evaporated using a rotary evaporator to obtain the precipitate (dodecanethiol coordinated gold microparticles).

[0048] The obtained gold microparticles coordinated with dodecylthiol were dispersed by irradiating 100 mL of hexane with ultrasound at 40 kHz for 30 minutes to obtain a gold colloidal hexane solution.

[0049] 90g of carbon black (EC300J) was dispersed in 6L of hexane solution. The solution, which had been irradiated with ultrasound at 40kHz for 1 hour, was mixed with the above gold colloidal hexane solution. After irradiating with ultrasound at 40kHz for 30 minutes, the mixture was stirred at room temperature for 12 hours, thereby loading dodecanethiol coordinated gold microparticles onto the carbon black.

[0050] The solution was filtered through a glass filter and dried at 60°C to obtain the gold-loaded carbon catalyst of Example 1 with a gold loading of 10.8% by weight.

[0051] The generated gold-supported carbon catalyst has an average gold particle size of 1.4 nm and a standard deviation of 0.60. The surface coverage of the coordinated dodecyl mercaptan gold particles is 17%.

[0052] (Method for determining the average particle diameter of gold)

[0053] TEM observations were performed (accelerating voltage 200kV, magnification 1 million times) to determine the particle size of the gold microparticles in the photographs, and the average particle size and standard deviation were calculated.

[0054] (Method for determining the surface coverage of gold particles in alkyl thiols)

[0055] The number of gold particles (A) with an average particle size and the number of alkathiol molecules (B) coordinated on the gold particles per 1g of gold-supported carbon catalyst are calculated using the following formulas. The number of alkathiol molecules per gold particle is then calculated (C = B / A). Using this value (C), the surface coverage of alkathiols on the gold particles (D) is calculated using Equation 3.

[0056] Formula 1A = (Gold loading per 1g catalyst) ÷ {(Volume of one gold particle with average diameter) ÷ (Volume of one gold atom) × 197 ÷ (6.02 × 10⁻⁶)} 23 )}

[0057] Equation 2B = X ÷ (mass of 1 mole of alkylthiol) × 6.02 × 10 23

[0058] X: Mass loss of 1g of gold-loaded carbon catalyst before and after heat treatment at 300℃

[0059] Equation 3D = π (atomic radius of sulfur) 2 ×C ÷ (Surface area of ​​a gold particle with an average particle size) ×100

[0060] (Example 2)

[0061] Except that the 31.2 mL dodecyl mercaptan in Example 1 was replaced with 39.4 mL hexadecyl mercaptan, the gold-supported carbon catalyst of Example 2 was obtained using the same manufacturing method as in Example 1. The gold-supported carbon catalyst produced had a gold loading of 10.5% by weight, an average gold particle size of 1.4 nm, and a standard deviation of 0.55. The gold particle surface coverage of the coordinated hexadecyl mercaptan was 58%.

[0062] (Comparative Example 1)

[0063] In Comparative Example 1, except that the gold microparticle treatment step was not performed, the method of Example 1 was used to load carbon black to obtain a gold-loaded carbon catalyst with a gold loading rate of 7.6% by weight.

[0064] (Comparative Example 2)

[0065] In Comparative Example 2, the gold-loaded carbon catalyst obtained in Example 2 was subjected to heat treatment at 200°C for 1 hour to evaporate hexadecyl mercaptan, resulting in a gold-loaded carbon catalyst with an average particle size of 1.6 nm.

[0066] The characteristics of the catalysts for Examples 1, 2, and Comparative Example 1 are shown in Table 1. Additionally, Figure 1 The image shows a TEM image of Example 1. The TEM image reveals a catalyst in which gold particles with a diameter of 1.0–1.5 nm are uniformly dispersed on carbon black without agglomeration.

[0067] The gold particle surface coverage of alkyl thiols in Comparative Example 1 of Table 1 was calculated using Equation 3, and a value of over 100% was obtained, but it is marked as 100%. This can be attributed to the fact that the gold particle treatment step was not performed, resulting in the remaining alkyl thiols becoming entangled with the alkyl thiols coordinated on the surface of the gold particles.

[0068] [Table 1]

[0069] Table 1

[0070]

[0071] (Seam strength evaluation)

[0072] The adhesion strength between gold microparticles and the carbon black support in the gold-loaded carbon catalyst was evaluated. The adhesion strength was assessed by irradiating the gold-loaded carbon in hexane with ultrasound at 40 kHz for 30 minutes, and comparing the gold loading rate before and after ultrasound irradiation. The gold-loaded carbon catalyst after ultrasound irradiation was recovered by filtration through a glass filter.

[0073] In addition, the gold loading rate of each sample was determined by the mass analysis value of gold and the mass of the gold-loaded carbon catalyst.

[0074] [Table 2]

[0075] Table 2

[0076]

[0077] In Example 1, no change in gold loading rate was observed before and after the ultrasonic test, indicating strong adhesion between the dodecylthiol-coordinated gold microparticles and the carbon black carrier. On the other hand, in Comparative Example 1, the loading rate decreased after the ultrasonic test, indicating insufficient adhesion. This is believed to be because the unreacted tetraoctylammonium bromide and dodecylthiol attached to the dodecylthiol-coordinated gold microparticles adversely affected the bonding between the functional groups of the carbon black and the alkanethiols coordinated to the gold microparticles.

[0078] Furthermore, compared to Comparative Example 1 without the gold microparticle treatment step, Example 1 with the gold microparticle treatment step had a higher gold loading rate before ultrasonic testing. Therefore, it is believed that by performing the gold microparticle treatment step, the loading rate of gold microparticles on carbon is increased.

[0079] (Accelerated Coagulation Experiment)

[0080] For Example 1 and Comparative Example 2, the aggregation of gold microparticles using a gold-supported carbon catalyst was evaluated by an accelerated test conducted at 300°C for 1 hour. The results are shown in Table 3.

[0081] In Comparative Example 2, the gold microparticles agglomerated, and the average particle size after accelerated testing increased significantly to 5.2 nm. In contrast, in Example 1 with dodecylthiol coordination, the average particle size was 2.8 nm, indicating that the agglomeration of gold microparticles was suppressed.

[0082] [Table 3]

[0083] Table 3

[0084]

Claims

1. A method for manufacturing a gold-supported carbon catalyst, wherein the gold-supported carbon catalyst comprises gold microparticles with an average particle size of 1.0 to 1.5 nm, coordinated on carbon black with dodecanethiol or hexadecanethiol at a coverage of 10-58% according to Formula 3. The method includes: The gold microparticle generation step includes: mixing an aqueous solution of chloroauric acid with an organic solvent solution containing a phase transfer agent, then obtaining an organic solvent solution phase by liquid phase separation, mixing dodecanethiol or hexadecanethiol in the organic solvent solution phase, and mixing an aqueous solution containing a reducing agent in the mixed solution to obtain gold microparticles coordinated with dodecanethiol or hexadecanethiol. The gold microparticle processing step involves repeatedly performing the following series of operations to obtain gold microparticles with a coverage of 10-58% and an average particle size of 1.0-1.5 nm, coordinated with dodecyl mercaptan or hexadecyl mercaptan: dispersing the gold microparticles coordinated with dodecyl mercaptan or hexadecyl mercaptan in hexane, adding a polar organic solvent and mixing, and then centrifuging the gold microparticles coordinated with dodecyl mercaptan or hexadecyl mercaptan; and The gold microparticle loading step includes: mixing a solution obtained by dispersing the dodecyl mercaptan or hexadecyl mercaptan-coordinated gold microparticles after the above-mentioned gold microparticle treatment step in hexane with a solution obtained by dispersing carbon black in hexane, thereby loading the dodecyl mercaptan or hexadecyl mercaptan-coordinated gold microparticles onto the carbon black. The surface coverage of gold particles in dodecyl mercaptan or hexadecyl mercaptan was determined as follows: The number of gold particles (A) with an average particle size per 1g of gold-supported carbon catalyst and the number of dodecyl mercaptan or hexadecyl mercaptan molecules coordinated on the gold particles are calculated using the following formulas. The number of dodecyl mercaptan or hexadecyl mercaptan molecules per gold particle, C, is then calculated, where C = B / A. Using this value C, the surface coverage of dodecyl mercaptan or hexadecyl mercaptan on the gold particles, D, is calculated using Equation 3. Formula 1 A = (Gold loading per 1g catalyst) ÷ {(Volume of one gold particle with average diameter) ÷ (Volume of one gold atom) × 197 ÷ (6.02 × 10⁻⁶)} 23 )} Equation 2: B = X ÷ (mass of 1 mole of dodecanethiol or hexadecanethiol) × 6.02 × 10 23 X: Mass loss of 1g of gold-loaded carbon catalyst before and after heat treatment at 300℃ Equation 3: D = π (atomic radius of sulfur) 2 ×C÷(Surface area of ​​a gold particle with an average particle size)×100%.

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