TWI500574B - Confining device of metal nanoparticles and method of fabricating the same - Google Patents

Description

Confined metal nanoparticle structure and forming method thereof

The invention relates to a special three-dimensional distribution structure of metal nano particles, in particular to a cavity cavity containing a plurality of mesoporous channel inlets of about 3 nm±20%, and a plurality of entrances are formed at all entrances of the cavity. a metal nanoparticle having a thickness greater than 1 nm, and limiting the maximum width of any entrance of the cavity to 1 nm or less, and forming a structure of a plurality of high catalytic activity metal secondary nanoparticles inside the cavity Instead of forming a method.

Metal nanoparticles often exhibit different physical and chemical properties than metal blocks due to the high proportion of surface atoms per unit volume. The industrial application of nano metal particles is a catalyst whose main function is to change the chemical reaction path to reduce the activation energy of the reaction and increase the reaction rate. The chemical reactivity of the catalyst is closely related to the size of the catalyst particles, and the smaller the particles, the higher the activity. However, since the chemical reaction easily causes a change in the structure of the catalyst, the stability of the catalyst particles decreases as the particles become smaller. In consideration of increasing the chemical reaction activity and maintaining the stability, the catalyst particles usually have a size of about 5 nm to 100 nm and are supported on a porous substrate such as porous carbon materials or bubbles. Zeolites, or porous silicates.

As a general matter, as a porous substrate carrying catalytic particles, the main purpose is to increase the contact area of the catalyst particles, and the substrate itself does not participate in the chemical reaction. However, when the catalyst particles are less than 1 nm, if each atom on the catalyst particles is not directly bonded to the substrate, at least one adjacent atom is in contact with the substrate, so this sub-nano ( Subnano) The chemical reactivity of the catalyst particles is closely related to the structure of the catalyst particles on the substrate and the chemical properties of the substrate itself. In the commonly used substrate, the lattice structure of the pore carbon material has a bond-switching property of sp2–sp3, so that a so-called double-catalytic effect can be formed at the junction of the catalyst and the carbon material: one of the catalytic effects The carbon radicals are formed on the carbon material adjacent to the catalyst and the carbon material, and the decomposition efficiency of the reactants is improved by the ultra-high reactivity of the carbon radicals; the other effect is by sp3–sp2 The bond-conversion mechanism converts the sp3 carbon material lattice structure of the carbon material interface with the reactants into a stable sp2 (C=C, π) bond, and effectively removes the adsorption between the catalyst and the carbon material. The reactants in the vicinity of the surface enhance the progress of the subsequent catalyst reaction.

In addition to the double-catalytic effect of secondary nanocatalysts on carbon materials, another way to enhance the catalytic reaction path is to place the nanocatalyst in a closed nanospace, with the reactants continuing and touching in a confined space. The characteristics of the collision of the media particles enhance the probability of the catalyst reaction producing the most stable reactants. Generally, the method of placing the catalyst in the sealed nano space includes forming a template first, then forming nano particles on the template, and then partially removing the template, and then forming a complicated process program such as a closed catalyst reactor.

The invention provides a three-dimensional distribution structure of a special metal nanoparticle and a method for forming the same, which combines a limited catalytic effect with a high catalytic activity of a secondary nanoparticle. Its structural part contains:
a cavity having a plurality of mesoporous passages communicating with the outside and having a diameter of up to about 3 nm ± 20%;
A plurality of metal particles having a thickness greater than 1 nm are formed at the entrance of each mesoporous channel, and the maximum width of any inlet is limited to 1 nm or less; and a plurality of metal sub-nano particles are formed inside the cavity .

The manufacturing method includes the following steps:
Step 1: taking a mesoporous substrate, the substrate comprises a plurality of macropores having a diameter greater than 50 nm and communicating with each other, each macropores being further connected with a plurality of mesoporous channels having a diameter greater than 20 nm and communicating with each other, each diameter being larger than The 20 nm mesoporous channel is more connected to a plurality of mesoporous channels having a diameter of about 3 nm ± 20%, and all of the macropores and mesopores are connected to a plurality of micropores having a diameter of less than 2 nm.
Step 2: The metal precursor ion layer is adsorbed by the chemical immersion method at the entrance of the mesoporous channel having a diameter of about 3 nm±20%, and the maximum width of the inlet is limited to about 1 nm to form a hindrance diffusion effect. The metal precursor ion concentration inside the mesoporous channel is much smaller than the outside of the mesoporous channel.
Step 3: reducing metal precursor ions into metal nanoparticles by chemical reduction, and forming metal sub-nano particles of less than 1 nm in a mesoporous channel having a diameter of about 3 nm ± 20% by hindering diffusion, but More than 3 nm ± 20% of metal nanoparticles are formed outside the mesoporous channel.

10. . . Hole cavity

11. . . Hole cavity inlet

20. . . Confined inlet metal nanoparticles

twenty one. . . Metal sub-nanoparticle

30. . . Hole substrate

31. . . Giant holes larger than 50 nm in diameter

32. . . Mesoporous channels larger than 20 nm in diameter

33. . . Mesoporous channel with a diameter of about 3 nm ± 20%

34. . . Mesoporous channel inlet

35. . . Microporous

40. . . Metal precursor ion

41. . . Impeding diffusion metal precursor ion layer

50. . . Metal nanoparticles larger than 3 nm ± 20%

51. . . Metal nanoparticles with a thickness greater than 1 nm

52. . . Metal sub-nanoparticle

60. . . Mesoporous channel with a diameter of about 3 nm ± 20%

61. . . Mesoporous channel inlet

70. . . Metal nanoparticles larger than 5 nm

71. . . 2~3nm±20% grade metal nanoparticles

72. . . Metal sub-nanoparticle

Fig. 1 is a schematic view showing the structure of the present invention.
Fig. 2 is a schematic view showing the mesoporous substrate of the first embodiment of the present invention.
Fig. 3 is a schematic view showing the adsorption of metal precursor ions in the second step of the first embodiment of the present invention.
Fig. 4 is a schematic view showing the spatial distribution of the metal nanoparticles of the third step of the first embodiment of the present invention.
Fig. 5 is a schematic view showing the adsorption of metal precursor ions in the second step of the second embodiment of the present invention.
Figure 6 is a schematic view showing the spatial distribution of the metal nanoparticles of the third step of the second embodiment of the present invention.
Fig. 7 is a schematic view showing the pore characteristics of the carbon material according to the 77K nitrogen gas adsorption analysis of the first and second embodiments of the present invention and the platinum crystal nano-catalyst particles carried by the X-ray diffraction analysis.
Fig. 8 is a view showing the X-ray diffraction (XRD) of the first and second embodiments of the present invention.
Fig. 9 is a schematic view showing X-ray photoelectron spectroscopy (XPS) of the first and second embodiments of the present invention.

Please refer to FIG. 1 to FIG. 9 , which are schematic diagrams of the structure of the present invention, a schematic diagram of the mesoporous structure of the first embodiment of the present invention, and a schematic diagram of the second step of the first embodiment of the present invention. A schematic diagram of the third step of the first embodiment of the invention, a schematic diagram of the second step of the second embodiment of the present invention, a schematic diagram of the third step of the second embodiment of the present invention, and the carbon materials of the first and second embodiments of the present invention are based on 77K nitrogen. X-ray diffraction (XRD) schematic diagram of the first and second embodiments of the present invention and the first embodiment of the present invention, the pore characteristics of the adsorption analysis and the size of the platinum crystal nano-catalyst particles to be supported according to the X-ray diffraction analysis An X-ray photoelectron spectroscopy (XPS) schematic of the second embodiment.

Referring to the drawings, the present invention is a confined metal nanoparticle structure comprising at least the following structure:
a hole cavity 10, comprising a plurality of mesoporous passage inlets 11 communicating with the outside, having a diameter of up to about 3 nm ± 20%;
A plurality of metal particles 20 having a thickness greater than 1 nm are formed at the entrance 11 of each mesoporous channel, and the maximum width of the inlet is limited to 1 nm or less; and a plurality of metal sub-nano particles 21 of less than 1 nm are Formed inside the cavity 10 .

The method of forming includes the following steps:
Step 1: Referring to FIG. 2, a mesoporous substrate 30 is obtained. The mesoporous substrate 30 may be a mesoporous carbon material, or a similarly structured zeolite and porous silicates, and the mesoporous substrate 30 is The plurality of macropores 31 each having a diameter greater than 50 nm and connected to each other are connected, and each of the macropores is further connected with a plurality of mesoporous channels 32 having a diameter greater than 20 nm and communicating with each other, and each mesoporous channel 32 having a diameter greater than 20 nm is more connected. There are a plurality of mesoporous channels 33 having a diameter of about 3 nm ± 20%. The intersection of the mesoporous channels 32 and the mesoporous channels 33 having a diameter of about 3 nm ± 20% is also referred to as a mesoporous channel inlet 34, and all the macropores and mesopores. A plurality of micropores 35 having a diameter of less than 2 nm are connected to each other on the channel.
Step 2: Referring to FIG. 3, which is an enlarged view of FIG. 2, the metal precursor ion 40 is uniformly distributed in the mesoporous channel 32 by chemical immersion method, and adsorbed at the inlet 34 of the mesoporous channel having a diameter of about 3 nm±20%. There is a metal precursor ion layer 41, and the maximum width of the mesoporous channel inlet 34 is limited to about 1 nm to form a barrier diffusion effect, resulting in a metal precursor ion concentration inside the mesoporous channel inlet 34 being much smaller than the mesoporous channel inlet. 34 external concentration.
Step 3: As shown in FIG. 4, a metal nanoparticle 50 larger than 3 nm±20% is formed in the mesoporous channel 30 by a chemical reduction method, and a thickness greater than 1 is formed at the mesoporous inlet 34 by hindering the diffusion effect. The metal nanoparticle 51 of nm forms a metal nanoparticle 52 of less than 1 nm in the mesoporous channel 33 having a diameter of about 3 nm ± 20%.

The main principle of forming a metal nanoparticle structure by chemical immersion in the present invention is shown in Figures 3 and 4, and is adsorbed to a diameter of about 3 nm by a metal precursor ion 40 having a size of about 1 nm ± 20%. At the entrance of the 20% mesoporous channel 34, a metal precursor ion layer 41 which hinders the diffusion of the metal precursor ions 40 into the interior of the mesoporous channel 33 is easily formed, resulting in a far-reaching concentration of metal precursor ions inside the mesoporous inlet 34. It is smaller than the outside of the mesoporous passage inlet 34. Due to this effect of impeding the diffusion effect, the residual metal ion concentration inside the mesoporous channel inlet 34 is exhausted during the pregnancy phase of forming the metal particles, and therefore, the mesoporous channel inlet 34 can only generate less than 1 nm inside. Metal sub-nanoparticles 52.

Conversely, the position at the mesoporous channel inlet 34 is not limited by the effect of the diffusion effect, and under the supply of sufficient metal precursor ions 40, the metal naphthalene having a thickness greater than 1 nm is formed only by the limitation of the inlet width. The rice particles 51, while reducing the inlet width of about 3 nm ± 20% in diameter to a confinement inlet structure having a maximum width of less than 1 nm. Since the diameter of the mesoporous channel 32 is larger than 20 nm, the size of the metal nanoparticle 51 generated in the mesoporous channel 32 is 3 nm ± 20% or more without being hindered by the effect of diffusion and geometrical constraints.

The following is a description of the method for forming the above-mentioned confined metal nanoparticle structure, and the difference in the structure of the confined metal nanoparticle formed by the carbon material pore structure of the second and second embodiments respectively; the first embodiment and the first embodiment The pore structure analysis of the mesoporous substrate 30 of the second embodiment is as shown in Fig. 7, wherein the main mesoporous structure of the mesoporous substrate 30 of the first embodiment is composed of about 3 nm ± 20% mesoporous channels, and the second The main mesoporous structure of the mesoporous substrate 30 of the embodiment consists of a mesoporous channel of about 5 nm. Since the limitation of the metal nanoparticle structure of the present invention (see FIG. ㄧ) and its formation method is that the maximum inlet diameter of the pore cavity inlet 11 is about 3 nm±20%, the diffusion effect can be hindered, and thus it can be expected that The result of this second embodiment does not form the structure of the present invention. The main use of the second embodiment is to verify that the maximum diameter of the cavity inlet 11 is 3 nm ± 20%, which is a key condition for forming the confined metal nanoparticle structure of the present invention.

First embodiment:
The mesoporous substrate 30 used in this embodiment is a commercial carbon material (Jingming Chemical), and its pore structure is based on the result of 77K nitrogen adsorption analysis, as shown in the example of Figure 7, the specific area is 1886 m ² /g. The micropore volume was 0.275 cm ³ /g, the total pore volume was 0.976 cm ³ /g, and the mesoporous channel diameter was 3.07 nm. It is known that the mesopore volume is 0.701 cm ³ /g from the total volume of the pores, which means that 70% of the pore structure of the carbon material is mainly composed of mesoporous channels having a diameter of about 3 nm ± 20%. Taking the chemical immersion method of the platinum nanoparticle of the present invention as an example, the original carbon material is first placed in a solution of 8M HNO ₃ and 2M H ₂ SO ₄ , and oxidized at ~95 ° C for 40 minutes to The impurities are removed and an oxygen functional group is formed on the surface of the carbon material as an anchor point for subsequent formation of platinum atoms. The oxidized carbon material was first washed with deionized water and then dried in a vacuum at 95 ° C for 12 hours. Next, mix 1 g of the oxidized carbon material with 50 ml of ethylene glycol (EG) reducing agent, then slowly add 0.5 ml of the electrochemical metal precursor solution with continuous stirring (from 265.5 mg H ₂ PtCl ₆ ‧6H ₂ O is mixed with 1 ml EG). In order to adjust the reducing ability of EG, additional 1 ml of 1M NaHSO _{3 was} added to reduce tetravalent [Pt ^IV Cl ₆ ] ^2- to divalent [Pt ^II (SO ₃ ) ₄ ] ^{6 -} to form a more stable and uniform Dispersed platinum ion-displaced compounds. To adjust the growth of the platinum nanoparticles, add 1 ml of 4N NaOH to adjust the pH of the solution to ~4. Finally, the entire mixed solution was placed on a heated plate at 120 ° C and heated for 120 minutes to reduce the platinum ion-dissolving compound in the solution to platinum nanoparticle.

The test piece prepared in the first embodiment was analyzed by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS), as shown in the examples of Figs. 8 and 9 to find pore carbon. The platinum nanoparticles on the material are composed of platinum atoms in a reduced state, but the chemical structure of the platinum nanoparticles on the surface is similar to that of the platinum block, so the main lattice structure is 3 nm ± 20% of platinum nanoparticles. While the inner platinum nanoparticles show a strong platinum-carbon bond, the main lattice structure is amorphous platinum sub-nanoparticles (less than 1 nm). That is, in the case of the spatial distribution of the platinum nanoparticles of the first embodiment, as shown in FIG. 4, metal particles 52 having a thickness greater than 1 nm are formed at the mesopial channel inlet 34 having a diameter of about 3 nm ± 20%, and A metal particle 51 having an amorphous form and less than 1 nm is formed inside the mesoporous channel 33, and the metal particles 52 located at the inlet 34 of the mesoporous channel shrink the maximum width line of the mesoporous channel inlet 34 to less than 1 nm. Limits the structure of metal sub-nanoparticles.

Second embodiment:
The mesoporous substrate 30 used in this embodiment is a commercial carbon material (Jingming Chemical), and its pore structure is based on the result of 77K nitrogen adsorption analysis, and the specific area is 900 m ² /g as shown in the second example of FIG. The micropore volume was 0.234 cm ³ /g, the total pore volume was 0.567 cm ³ /g, and the mesoporous channel diameter was 4.99 nm. It is known that the mesopore volume is 0.333 cm ³ /g from the total volume of the pores, which means that 60% of the pore structure of the carbon material is mainly composed of mesoporous channels having a diameter of about 5 nm. The chemical immersion preparation step of the platinum catalyst nanoparticle is the same as that of the first embodiment, but the test piece produced by the second embodiment is X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). As shown in Example 2 of Figure 8 and Figure 9, the results of in-depth analysis show that the platinum nanoparticles on the pore carbon material are also composed of platinum atoms in the reduced state, but the surface and the inner platinum nanoparticles. Each contains a chemical structure similar to that of a platinum block. That is to say, the spatial distribution of the platinum nanoparticles of the second embodiment contains metal nanoparticles having a crystal form of more than 3 nm ± 20% from the inside to the outside, and cannot be formed as in the example (see FIG. 4). The crystalline metal nanoparticle 51 and the metal secondary nanoparticle 52 are respectively distributed in a distinct spatial difference distribution structure outside and inside the confinement inlet channel.

The main principle of the structure of the crystalline metal nanoparticle formed in a uniform distribution form in the second embodiment is as shown in Fig. 5, and the adsorption layer is about 1 nm ± 20 at the entrance 62 of the mesoporous channel 61 having a diameter of about 5 nm. The metal precursor ion 40 of % still leaves about 3 nm ± 20% of the gap entrance and therefore does not interfere with the diffusion effect. Therefore, as shown in Fig. 5, under the supply of sufficient metal precursor ions, the growth of the metal nanoparticles is mainly affected by the channel geometry. Therefore, the metal nanoparticle 70 formed on the outside of the mesoporous channel inlet 62 is in a crystalline form and has a size of about 5 nm, and a crystalline metal nanoparticle 71 having a size of about 2 to 3 nm ± 20% in the interior of the channel is formed. And amorphous metal sub-nanoparticles 72 having an ankle portion of less than 1 nm.

In summary, the limited metal nanoparticle structure of the present invention and its formation method utilize a three-dimensional distribution structure of a special metal nanoparticle which combines a limited catalytic effect with a high catalytic activity of a secondary nanoparticle. The formation method can achieve high catalytic activity and cost saving effect by selecting a carbon material of a specific pore structure and then using a simple chemical immersion method. The invention can improve the more advanced catalyst structure of the catalyst industry and the more economical process method, and has indeed met the requirements of the invention patent application, and filed a patent application according to law.

However, the above is only the preferred embodiment of the present invention, and the scope of the present invention is not limited thereto; therefore, the simple equivalent changes and modifications made in accordance with the scope of the present invention and the contents of the invention are modified. All should remain within the scope of the invention patent.

10. . . Hole cavity

11. . . Inlet channel with a diameter of about 3 nm ± 20%

20. . . Metal nanoparticles with a thickness greater than 1 nm

twenty one. . . Metal sub-nanoparticles less than 1 nm in diameter

Claims (10)

A confined metal nanoparticle structure comprising:
a cavity having a plurality of cavity inlets communicating with the outside;
a metal nanoparticle layer formed at the entrance of all of the pore cavities to limit the maximum width of the entrance of the cavities to a maximum width of 1 nm; and a plurality of metal sub-nanoparticles, the sub-nano scale Formed inside the cavity of the cavity. The limited metal nanoparticle structure according to the first aspect of the patent application, wherein the maximum diameter of the entrance of the cavity is 3 nm±20%. According to the limited metal nanoparticle structure described in claim 1, wherein at least the entrance diameter of the entrance of all the cavity is about 3 nm±20%. The limited metal nanoparticle structure according to claim 1, wherein the thickness of the metal nanoparticle layer is greater than 1 nm. The limited metal nanoparticle structure according to claim 1, wherein the metal sub-nanoparticles have a size range of less than 1 nm. A method for forming a localized metal nanoparticle structure, comprising the steps of:
Step 1: taking a mesoporous substrate, the mesoporous substrate comprising macropores, mesopores, and micropores that communicate with each other;
Step 2: adsorbing the metal precursor ion layer at the entrance of each mesoporous channel by chemical immersion method, and limiting the inlet width to form a diffusion preventing effect, so that the metal precursor ion concentration inside the mesoporous channel inlet is much smaller than the a concentration outside the inlet of the mesoporous channel; and step 3: forming a metal nanoparticle larger than 3 nm ± 20% outside the inlet of the mesoporous channel by a chemical reduction method, and forming an entrance at the entrance of the mesoporous channel by the diffusion preventing effect Metal nanoparticles having a thickness greater than 1 nm and forming metal sub-nano particles of less than 1 nm inside the entrance of the mesoporous channel. The method for forming a limited metal nanoparticle structure according to claim 6 , wherein the mesoporous substrate is a mesoporous carbon material or a structurally similar zeolite and porous silicate (porous) Silicates). According to the method for forming a limited metal nanoparticle structure according to Item 6 of the patent application scope, wherein the diameter of each macropore is greater than 50 nm, and the diameter of each mesoporous channel is between 2 nm and 50 nm, and each The microporous system is less than 2 nm. The method for forming a limited metal nanoparticle structure according to the sixth aspect of the patent application, wherein the mesoporous substrate has a main mesoporous channel diameter of about 3 nm ± 20%. The method for forming a limited metal nanoparticle structure according to claim 6, wherein the mesoporous channel has a total volume of at least 50% of the total pore volume of the mesoporous substrate.