KR102661332B1 - Method for preparation of platinum nanoparticle-metal oxide composite - Google Patents

Abstract

The present invention introduces an atomic layer-level manganese oxide or iron oxide coating layer and can simply manufacture a platinum nanoparticle-metal oxide complex through oxidation heat treatment. The manufacturing method is economical because it is easy to apply on a large scale. Additionally, platinum nanoparticles introduced with an oxide coating layer such as the manganese oxide or iron oxide coating layer have improved thermal and chemical stability, and can further maintain or improve the chemical properties of the platinum nanoparticles.

Description

Method for preparation of platinum nanoparticle-metal oxide composite}

The present invention is intended to provide a method for producing a platinum nanoparticle-metal oxide complex with excellent thermal and chemical durability, and a platinum nanoparticle-metal oxide complex prepared thereby.

Metal nanoparticle catalysts containing platinum are widely used in various fields, such as chemically removing harmful substances such as carbon monoxide, formaldehyde, and nitrogen oxides, or manufacturing useful high value-added chemicals. In addition, in addition to the above, it plays an important role in promoting the production and utilization of new and renewable energy, such as hydrogen production and hydrogen utilization.

Metal nanoparticles have unique properties that are inherently different from bulk materials. For example, they exhibit characteristics such as increased surface energy, lower melting point, and low-temperature sinterability, resulting in lower durability than bulk materials. On the other hand, since the majority of industrial catalytic reactions operate at high temperatures and in environments containing various chemical species, when metal nanoparticles are used here as catalysts, performance degradation due to low durability is inevitably accompanied. Therefore, metal nanoparticles are used as industrial catalysts. In order to use it as a catalyst, it is important to go beyond simple nanoparticle catalyst production and improve its thermal and chemical durability.

Conventionally, in order to ensure the durability of metal nanoparticles, many metal-oxide core-shell structures have been proposed in which the surface of the nanoparticle is physically protected by a metal oxide film. For example, nanoparticle stabilization strategies using various types of metal oxides such as SiO ₂ , TiO ₂ , ZrO ₂ , and CeO ₂ have been introduced. However, this method of stabilizing metal nanoparticles using metal oxides requires a complex manufacturing process including organic functional groups, which entails low process yield, high process cost and time, so it has the disadvantage of being difficult to apply in actual industry due to poor economic feasibility. there is.

Accordingly, the present invention seeks to provide a method for producing a platinum nanoparticle-metal oxide complex with excellent thermal and chemical durability.

Additionally, the present invention seeks to provide a platinum nanoparticle-metal oxide complex prepared by the above production method.

Additionally, the present invention seeks to provide a catalyst using the platinum nanoparticle-metal oxide complex.

In order to solve the above problems, the present invention provides a method for producing a platinum nanoparticle-metal oxide complex comprising the following steps:

Forming a manganese oxide or iron oxide coating layer on the surface of the platinum nanoparticles by atomic layer deposition (step 1); and

Heat treating the platinum nanoparticles on which the coating layer is formed under an oxidizing atmosphere (step 2).

The present invention is to coat the surface of platinum nanoparticles with a metal oxide in order to improve the thermal and chemical durability of the platinum nanoparticles. To this end, the metal oxide is coated on the surface of the platinum nanoparticles by atomic layer deposition and then heat treated in an oxidizing atmosphere. It is characterized by:

Because the atomic layer deposition method is used, a metal oxide coating layer can be first formed on the surface of platinum nanoparticles with an Angstrom-level thickness, and then heat-treated in an oxidizing atmosphere to form a spontaneous epitaxial metal oxide coating layer. You can.

Through this, a very thin metal oxide coating layer can be formed on the surface of the platinum nanoparticles, and this metal oxide coating layer prevents the surface of the platinum nanoparticles from being exposed to the external environment and provides a channel for the platinum nanoparticles to participate in the reaction. It has a duality that provides. As a result, the platinum nanoparticle-metal oxide complex according to the present invention exhibits excellent thermal and chemical stability in terms of durability, and at the same time can exhibit improved reaction characteristics in terms of catalytic reactivity compared to platinum nanoparticles not coated with metal oxide. These improved reaction characteristics are due to the excellent durability of the catalyst, the interaction between the platinum nanoparticles and the metal oxide coating layer (metal-support interaction, MSI), or the two effects acting simultaneously.

Hereinafter, the present invention will be described in detail for each step.

(Step 1)

Step 1 of the present invention is a step of forming a manganese oxide or iron oxide coating layer on the surface of the platinum nanoparticle by atomic layer deposition.

Preferably, the platinum nanoparticles have a diameter of 1 nm to 20 nm. Additionally, the platinum nanoparticles may be supported on a support, in which case a portion of the surface of the platinum nanoparticles is exposed on the support, and a coating layer is formed on the exposed surface.

Step 1 uses atomic layer deposition, through which manganese oxide or iron oxide can be formed on the surface of platinum nanoparticles to an angstrom-level thickness.

Specifically, the atomic layer deposition method can be performed repeatedly in one cycle by sequentially exposing the surface of the platinum nanoparticles to manganese oxide or iron oxide, purging gas, oxidizing gas, and purging gas, and the manganese The thickness of the manganese oxide or iron oxide coating layer can be formed by adjusting the concentration of the oxide or iron oxide, the exposure time of the reaction gas, or the number of cycles performed.

Meanwhile, each precursor can be used to form a manganese oxide or iron oxide coating layer. For example, Mn(TMHD) ₃ ((tetrakis(2,2,6,6-tetramethyl-3,5-heptanedionato)manganese(III)) for manganese and Ferrocene(Fe(Cp) ₂ ) for iron. can be used, but is not limited to this.

Preferably, step 1 is performed so that the thickness of the manganese oxide or iron oxide coating layer is 0.3 nm to 1.0 nm. If the thickness of the coating layer exceeds 1.0 nm, it is difficult to provide a channel through which platinum nanoparticles can participate in the reaction in the finally produced platinum nanoparticle-metal complex because the thickness of the coating layer is too thick. Conversely, if the thickness of the coating layer is less than 0.3 nm, it is difficult to improve the thermal and chemical durability of the platinum nanoparticles in the finally manufactured platinum nanoparticle-metal composite because the thickness of the coating layer is too thin.

Meanwhile, the purging gas used in the atomic layer deposition method is not particularly limited as long as it is widely used in the art, and for example, an inert gas such as argon gas, nitrogen gas, or helium gas can be used.

Meanwhile, Step 1 is preferably performed at 25 to 300°C.

(Step 2)

Step 2 of the present invention is a step of heat treating the platinum nanoparticles with the coating layer prepared in Step 1 under an oxidizing atmosphere.

By Step 1, an angstrom-level manganese oxide or iron oxide coating layer is formed on the surface of the platinum nanoparticles, and when heat treated in an oxidizing atmosphere, a spontaneous epitaxial metal oxide coating layer is formed. This is also called heteroepitaxy because it is lattice matching between different materials. The lattice structure and lattice constant between platinum and manganese oxide or platinum and iron oxide are rearranged in a similar form, resulting in an epitaxial structure in which the lattice is matched. is formed Through this structure, the interaction between the metal and the oxide can be maximized, and thus improved reaction performance and stability can be achieved.

The heat treatment temperature is preferably 400 to 900°C, more preferably 500 to 800°C.

Preferably, the oxidizing atmosphere is an atmospheric atmosphere containing oxygen gas. At this time, the atmosphere containing oxygen gas contains 0.1% to 100% oxygen.

Additionally, step 2 is performed for 30 minutes to 2 hours.

(Platinum nanoparticle-metal oxide complex)

The present invention provides a platinum nanoparticle-metal oxide complex prepared by the production method according to the present invention described above.

According to the present invention, an angstrom-level manganese oxide or iron oxide coating layer can be formed on the surface of the platinum nanoparticles, and the platinum nanoparticle-metal oxide complex according to the present invention is used to prevent the surface of the platinum nanoparticles from being exposed to the external environment. This prevents damage and improves thermal and chemical durability.

In addition, the manganese oxide or iron oxide coating layer is a crystalline coating layer that prevents the surface of the platinum nanoparticles from being exposed to the external environment and at the same time allows the platinum nanoparticles to form through metal-oxide interaction (metal-support interaction, MSI). Provides a channel to participate in the response. As in the examples to be described later, in the platinum nanoparticle-metal oxide composite according to the present invention, catalytic performance due to platinum is exhibited even though platinum is not exposed to the outside, thereby improving the thermal and chemical durability of platinum nanoparticles. At the same time, the chemical properties of platinum nanoparticles can be maintained or improved.

Therefore, since the platinum nanoparticle-metal oxide complex according to the present invention has the chemical properties of platinum nanoparticles, it can be used in fields where platinum nanoparticles are used, such as a chemical catalyst.

As described above, the present invention introduces an atomic layer-level manganese oxide or iron oxide coating layer and can simply manufacture a platinum nanoparticle-metal oxide complex through oxidation heat treatment. The manufacturing method is economical because it is easy to apply on a large scale. am. Additionally, platinum nanoparticles introduced with an oxide coating layer such as the manganese oxide or iron oxide coating layer have improved thermal and chemical stability, and can further maintain or improve the chemical properties of the platinum nanoparticles.

Figure 1 _shows transmission _electron microscopy (TEM _{) images} of the _surfaces of _MnO It was observed and the results were shown.
_{Figure 2 shows the} results of _{DRFITS analysis for MnO}
Figure 3 shows the results of thermal durability evaluation according to Experimental Example 3.
Figure 4 shows the results of chemical durability evaluation according to Experimental Example 4.
Figure 5 shows the results of evaluating catalyst properties according to Experimental Example 5.

Hereinafter, examples and experimental examples of the present invention will be described in detail. These examples and experimental examples are for illustrating the present invention in more detail, and the scope of the present invention is not limited to these examples and experimental examples.

Example 1: Platinum nanoparticle-metal oxide complex (MnO _x /Pt/Al ₂ O ₃ )Manufacture of

In order to use aluminum oxide for carrying platinum and manganese oxide as a support, commercial Al ₂ O ₃ powder was stabilized by heat treatment in air at 900°C for 24 hours. In the case of platinum, Pt(acac) ₂ was used as a precursor and was prepared by performing an ALD 1 cycle process and then heat treating it at 500°C for 10 minutes in an atmospheric environment. Afterwards, an ALD 55 cycle process was performed at a temperature of 250°C using Mn(TMHD) ₃ ((tetrakis(2,2,6,6-tetramethyl-3,5-heptanedionato)manganese(III)) as a precursor to produce Pt. /Al ₂ O ₃ After depositing the manganese oxide, heat treatment was performed in an air atmosphere at 500°C for 1 hour or 800°C for 1 hour to produce two types of platinum nanoparticle-metal oxide complexes (MnO _x) . /Pt/Al ₂ O ₃ ) was prepared.

Example 2: Platinum nanoparticle-metal oxide complex (FeO _x /Pt/Al ₂ O ₃ )Manufacture of

In order to use aluminum oxide for supporting platinum and iron oxides as a support, commercial Al ₂ O ₃ powder was stabilized by heat treatment in air at 900°C for 24 hours. In the case of platinum, Pt(acac) ₂ was used as a precursor and was prepared by performing an ALD 1 cycle process and then heat treating it at 500°C for 10 minutes in an atmospheric environment. Afterwards, using Ferrocene (Fe(Cp) ₂ ) as a precursor, an ALD 50 cycle process was performed at a temperature of 250 ^o C to deposit iron oxide on Pt/Al ₂ O ₃ . After iron oxide deposition, heat treatment was performed in an air atmosphere at 500°C for 1 hour or 800°C for 1 hour to prepare two types of platinum nanoparticle-metal oxide complexes (FeO _x /Pt/Al ₂ O ₃ ).

Comparative example: Platinum nanoparticles (Pt/Al ₂ O ₃ )

A platinum nanoparticle catalyst (Pt/Al ₂ O ₃ ) supported on aluminum oxide used as a starting material in Examples 1 and 2 was used as a comparative example.

Experimental Example 1

_{The surfaces of MnO ​ ​} The results are shown in Figure 1.

As shown in Figure 1, it was confirmed that a crystalline metal oxide atomic layer was formed on the surfaces of MnO _x /Pt/Al ₂ O ₃ and FeO _x /Pt/Al ₂ O ₃ with a thickness of angstrom level.

Experimental Example 2

Diffuse _{reflection infrared Fourier} transform _{spectroscopy was performed on MnO} Gas adsorption characteristics were analyzed by performing infrared Fourier transform spectroscopy (hereinafter 'DRFITS') analysis.

Specifically, DRFITS proceeded as follows. First, each sample was prepared by heat treatment at 200°C for 10 minutes in a mixed gas atmosphere consisting of 10% oxygen and 90% helium. Afterwards, the temperature was lowered to 25°C, exposed to a mixed gas consisting of 10% carbon monoxide and 90% helium for 5 minutes, purged with 100% helium gas for 10 minutes, and the IR spectrum was observed. The adsorption characteristics of CO were analyzed using this method, and the results are shown in Figure 2.

_{As shown in Figure 2 ,} MnO After heat treatment, CO gas adsorption was significantly reduced. This indicates that the surface of the platinum nanoparticles is not exposed to the external environment after oxidation heat treatment at each temperature, considering the transmission electron microscope observation results showing the formation _{of MnO}

Experimental Example 3

Thermal and chemical durability evaluations were performed on MnO _x /Pt/Al ₂ O ₃ prepared in Example 1 and Pt/Al ₂ O ₃ in Comparative Example.

First, in the case of thermal durability, the degree to which the radius of platinum nanoparticles increases was evaluated after exposing the composite to the atmosphere at 800°C for 1 hour. The results are shown in Table 1 and Figure 3 below, respectively.

Particle radius after heat treatment at 800℃ Particle radius increase Example 1 (MnO _x /Pt/Al ₂ O ₃ ) 6.7nm 223% Comparative Example (Pt/Al ₂ O ₃ ) 14.0nm 460%

As shown in Table 1, the comparative example showed an increase of 460% compared to the initial particle radius, and Example 1 to which the MnO _x coating was applied showed an increase of 233%, and the thermal durability of the platinum nanoparticles was improved after coating. showed.

Additionally, a noticeable difference in particle radius could be confirmed in Figure 3.

Next, in the case of chemical durability, the amount of carbon coking formed after exposing the composite to a 4% propane (C ₃ H ₈ ) atmosphere at 700°C for 12 hours was quantitatively evaluated. The results are shown in Table 2 and Figure 4 below.

Carbon deposition amount Example 1 (MnO _x /Pt/Al ₂ O ₃ ) 375 μmol Comparative Example (Pt/Al ₂ O ₃ ) 1,234 μmol

As shown in Table 2, Comparative Example showed 1,234 μmol of carbon deposition, and Example 1 using _MnO (70% = {(1,234 - 375)/(1,234)} × 100).

In addition, as shown in Figure 4, after the carbon deposition experiment, it was confirmed that black carbon powder was generated on the quartz cotton, and it was confirmed that carbon deposition was suppressed through the introduction of a coating layer compared to the control group.

Experimental Example 5

_{MnO x} /Pt/Al ₂ O _{3 (} 800 _{° C} heat treatment ₎ and FeO ℃ heat treatment), the catalyst reactivity was confirmed by applying it to the carbon monoxide removal reaction.

Specifically, carbon monoxide removal reactivity was measured by injecting CO:O ₂ mixed gas (28.6 Torr CO, 14.3 Torr O ₂ ) at a ratio of 2:1 using 0.1 g of each composite as a catalyst. Helium was used as the carrier gas, and the total flow rate was controlled at 106 mL/min. The results are shown in Figure 5.

Figure 5 shows an Arrhenius plot showing the CO oxidation reaction rate, and as shown in Figure 5, compared to the comparative example catalyst, the platinum nanoparticles with the MnO _x coating layer introduced showed catalytic properties about 20 times higher. , the sample with the FeO _x coating layer showed catalytic properties about 100 times higher.

Such high reaction characteristics are believed to result from the excellent durability of the catalyst, the interaction between platinum nanoparticles and the oxide coating layer (metal-support interaction, MSI), or the two effects acting simultaneously.

Claims (10)

Forming a manganese oxide or iron oxide coating layer on the surface of the platinum nanoparticles by atomic layer deposition (step 1); and
Comprising the step (step 2) of heat treating the platinum nanoparticles on which the coating layer is formed at 400 to 900° C. for 30 minutes to 2 hours in an oxidizing atmosphere.
Method for producing platinum nanoparticle-metal oxide complex.
According to paragraph 1,
The platinum nanoparticles have a diameter of 1 nm to 20 nm,
Manufacturing method.
According to paragraph 1,
The thickness of the manganese oxide or iron oxide coating layer is 0.3 nm to 1.0 nm,
Manufacturing method.
According to paragraph 1,
Step 1 is performed at 25 to 300°C,
Manufacturing method.
delete According to paragraph 1,
The oxidizing atmosphere is an atmospheric atmosphere containing oxygen gas,
Manufacturing method.
According to clause 6,
The atmosphere containing oxygen gas contains 0.1% to 100% oxygen,
Manufacturing method.
delete A platinum nanoparticle-metal oxide complex manufactured by the production method of any one of claims 1 to 4, 6, and 7.
A catalyst comprising the platinum nanoparticle-metal oxide complex of claim 9.