Core-shell structured composite particles and their manufacturing method

Abstract

The present invention relates to composite particles having a core-shell structure and a method for producing the same. The present invention relates to a core-shell composite particle comprising a core containing inorganic particles, a porous support having mesopores located on the core, and a composite catalyst shell containing gold nanoparticles contained in the pores of the porous support, and a method for producing the same.

Description

[Technical Field]

[0001] The present invention relates to composite particles having a core-shell structure and a method for producing the same. [Background technology]

[0002] Transition metal nanoparticles can exhibit catalytic activity due to their high specific surface area. However, transition metal nanoparticles typically have an average particle size of 20 nm or less as primary particles. Therefore, mesoporous supports with pore sizes of 2 nm to 50 nm are considered preferable for supporting such nanoparticles. The mesoporous support may be made of a metal oxide material, and typically silica, aluminosilicate, titania, or the like is known. Depending on the manufacturing method, mesopores of various sizes and shapes can be formed. The mesoporous support has the advantage that the acid site concentration and ion exchange capacity can be adjusted by adjusting the content of the metal or metalloid forming the framework. Therefore, mesoporous supports are used as supports for transition metal nanoparticles, and have the advantage of lower diffusion resistance of materials compared to microporous supports, resulting in faster reaction rates due to the mesoporous characteristics.

[0003] However, mesoporous supports loaded with transition metal nanoparticles are manufactured from powders, and when such powders are used as catalysts, pressure differentials occur as the catalytic reaction proceeds. Therefore, to mitigate the pressure differentials and apply them to commercial catalytic reaction processes, they must be coated on substrates of a certain size or larger. Even if a highly active catalyst is developed, its final commercialization requires a scale-up step suited to the application environment. To achieve this, catalyst design involves the manufacture of structural catalysts in the form of pellets, beads, or honeycomb monoliths. However, while these methods can reduce the differential pressure, they have the drawback of reducing the contact area between the catalytic reactant, harmful gas, and the catalyst, thereby reducing the harmful gas removal efficiency.

[0004] Therefore, there is a need to develop a composite catalyst that can effectively remove harmful gases contained in the air while reducing the differential pressure. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] US 2019-0255520 A1(2019.08.22) [Patent Document 2] KR 10-2017-0119051 A(2017.10.26) Summary of the Invention [Problem to be solved by the invention]

[0006] One object of the present invention is to provide a core-shell structured composite particle that has remarkably excellent catalytic activity at room temperature and, at the same time, can significantly alleviate the problem of differential pressure that occurs at high flow rates when using existing powder catalysts.

[0007] Another object of the present invention is to provide a core-shell structured composite particle that can organically combine adsorption and desorption reactions with catalytic oxidation reactions, thereby substantially completely removing harmful gases that have not been removed solely by oxidation reactions due to contact between harmful gases and catalysts, even at high flow rates. [Means for solving the problem]

[0008] In order to solve the above-mentioned problems, the present invention provides a core-shell structured composite particle including a core containing inorganic particles, and a composite catalyst shell located on the core and including a porous support having mesopores and gold nanoparticles contained in the pores of the porous support.

[0009] In one embodiment, the inorganic particles are porous beads or non-porous beads, and the material of the beads may be any one or a combination of two or more selected from the group consisting of glass, carbon, silica, silver-containing inorganic materials, alumina-silicate, and alumina.

[0010] In one embodiment, the inorganic particles may be porous inorganic particles.

[0011] Specifically, the porous inorganic particles may be particles containing any one or a combination of two or more selected from the group consisting of zeolite, activated carbon, porous silica, and porous alumina.

[0012] In one embodiment, the porous support may be a metal oxide or metalloid oxide porous support.

[0013] In one embodiment, the porous support may further include macropores.

[0014] In one embodiment, the diameter of the nanoparticles may be 1 nm to 20 nm.

[0015] In one embodiment, the nanoparticles may be incorporated into some of the mesopores of the porous support, and the mesopores not incorporating the nanoparticles may be interconnected by open pores.

[0016] In one embodiment, the pores of the composite catalyst shell may be connected to the pores of the core by open pores.

[0017] In one embodiment, the radial distribution function obtained by Fourier transforming the EXAFS (Extended X-ray absorption fine structure) spectrum of the composite catalyst shell can satisfy the following formula 1: [Formula 1] (DH2 / DH1)<0.3 In the above formula 1, DH1 is the height of the peak at interatomic distance D1, DH2 is the height of the peak at interatomic distance D2, and D1 and D2 satisfy the following formulas 2 and 3, respectively. [Formula 2] 0.8≦(D1 / D3)≦0.95 [Formula 3] 0.6≦(D2 / D3)≦0.7 In the above formulas 2 and 3, D3 means the interatomic distance of the Au-Au bond in the bulk phase, which is present in the range of 2.8 to 3.0 Å.

[0018] In one embodiment, the composite catalyst shell can satisfy the following formula 4: [Formula 4] (DA2 / DA1)<0.25 In the above formula 4, DA1 is the area of ​​the peak at interatomic distance D1, DA2 is the area of ​​the peak at interatomic distance D2, and D1 and D2 satisfy the above formulas 2 and 3, respectively.

[0019] In one embodiment, the composite catalyst shell may have a bimodal peak in the interatomic distance range of 2.2 Å to 3.0 Å of the radial distribution function.

[0020] In one embodiment, the diameter of the core may be 100 μm to 50 mm.

[0021] In one embodiment, the ratio of the core diameter D to the shell thickness T (T / D) is 2×10 -4 It can be ∼0.2.

[0022] In one embodiment, the composite particles may be used for the oxidation of carbon monoxide, aldehyde compounds, or hydrocarbon compounds.

[0023] In addition, another embodiment of the present invention provides an air purification filter comprising: a reactive filter part having an internal space and filled with a plurality of the above-mentioned composite particles; an inlet port provided on one side of the reactive filter part through which gas containing harmful gases flows in; and an outlet port provided on the other side of the reactive filter part through which gas from which harmful gases have been removed is discharged.

[0024] Furthermore, another embodiment of the present invention provides a method for producing core-shell structured composite particles, including: (S1) preparing inorganic particles; (S2) preparing a dispersion containing a composite catalyst and a binder, the composite catalyst including a porous support having mesopores and gold nanoparticles contained in the pores of the porous support; (S3) applying the dispersion to surfaces of the inorganic particles; and (S4) drying the dispersion.

[0025] In one embodiment, the binder may include an inorganic sol binder and a water-soluble polymer binder. [Effects of the Invention]

[0026] The core-shell structured composite particles according to the present invention have excellent catalytic activity at room temperature, and at the same time, can significantly alleviate the problem of differential pressure that occurs at high flow rates when using existing powder catalysts.

[0027] The core-shell structured composite particles according to the present invention organically combine adsorption and desorption reactions with catalytic oxidation reactions, thereby enabling the removal of substantially all harmful gases that have not been removed solely through oxidation reactions caused by contact between harmful gases and catalysts, even at high flow rates. [Brief explanation of the drawings]

[0028] [Figure 1] 1 is a schematic diagram of a core-shell structured composite particle and a composite catalyst contained therein according to an embodiment. [Figure 2] 1 is a schematic diagram of an air purification filter including the composite particles according to one embodiment. [Figure 3]1 is an image of a core-shell structured composite particle 1 according to Example 1. [Figure 4] 1 shows a radial distribution function obtained by Fourier transforming an EXAFS spectrum of a composite catalyst according to one example. [Figure 5] 1 shows a radial distribution function obtained by Fourier transforming an EXAFS spectrum of a composite catalyst according to one example. [Figure 6] 1 shows a radial distribution function obtained by Fourier transforming an EXAFS spectrum of a composite catalyst according to one example. DETAILED DESCRIPTION OF THE INVENTION

[0029] Unless otherwise defined, technical and scientific terms used in this specification have the meanings commonly understood by a person of ordinary skill in the art to which the present invention belongs, and descriptions of known functions and configurations that may obscure the gist of the present invention in the following description and accompanying drawings are omitted.

[0030] Furthermore, as used herein, the singular forms "a," "an," and "the" may be intended to include the plural forms as well, unless the context clearly indicates otherwise.

[0031] In addition, units used in this specification without any particular mention are based on weight, and as an example, the unit of % or ratio means % by weight or weight ratio, and unless otherwise defined, % by weight means the weight % of any one component of the total composition within the composition.

[0032] Furthermore, numerical ranges used herein include lower and upper limits and all values ​​within that range, increments logically derived from the shape and width of the defined range, all doubly limited values, and all possible combinations of upper and lower limits of numerical ranges defined in different ways. Unless otherwise specified in the specification of the present invention, values ​​outside the numerical range that may occur due to experimental error or rounding of values ​​are also included in the defined numerical range.

[0033] As used herein, the term "comprising" is an open-ended term that has the same meaning as expressions such as "comprising," "containing," "having," or "characterized by," and does not exclude further unrecited elements, materials, or steps.

[0034] The inventors recognized that even if a catalyst has high catalytic activity, when it is in powder form, a differential pressure problem occurs at high flow rates, making it difficult to commercialize a highly active catalyst. Furthermore, as a solution to this problem, when composite catalyst particles coated on a substrate are used, the differential pressure can be reduced, but the contact area between the catalytic reactant, harmful gas, and the catalyst is reduced, resulting in a decrease in harmful gas removal efficiency. They conducted extensive research to solve this problem. The present inventors have discovered that a core-shell structured composite particle, in which a composite catalyst shell containing a porous support and gold nanoparticles is located on a core containing inorganic particles, can solve the above-mentioned problems, and have completed the present invention.

[0035] FIG. 1 is a schematic diagram of a core-shell structured composite particle and a composite catalyst contained therein according to one embodiment.

[0036] Hereinafter, the core-shell structured composite particles according to the present disclosure will be described in detail with reference to the accompanying drawings. The accompanying drawings are provided for illustrative purposes only to fully convey the technical concept of the present invention to those skilled in the art, and the present invention is not limited to the drawings presented below and may be embodied in various other forms.

[0037] Referring to FIG. 1, a core-shell structured composite particle 100 according to the present disclosure is characterized by comprising a core 110 containing inorganic particles, and a composite catalyst shell 120 located on the core and including a porous support 121 containing mesopores and gold nanoparticles 122 contained within the pores of the porous support.

[0038] The composite particles have the core-shell structure described above, and therefore have excellent catalytic activity due to the composite catalyst located on the surface of the core. Furthermore, the particle size can be increased by supporting the composite catalyst on the core, thereby improving the differential pressure problem, which is one of the causes of reduced filter lifespan. Furthermore, when applied to an air purification filter that needs to fill a certain volume, conventional powder-type catalysts need to be filled with more catalyst than necessary, whereas the composite particles can be filled with only the amount of catalyst necessary for air purification, thereby reducing the amount of catalyst used and providing an economical advantage.

[0039] According to an embodiment, the inorganic particles may be porous beads or non-porous beads. Specifically, the material of the beads may be any one or a combination of two or more selected from the group consisting of glass, carbon, silica, silver-containing inorganic material, alumina-silicate, and alumina, and more specifically, alumina.

[0040] According to one embodiment, the inorganic particles may be porous inorganic particles, and the composite particles may contain porous inorganic particles as cores, thereby significantly reducing the pressure differential generated at high flow rates and substantially removing all harmful gases contained in air even at high flow rates. In particular, harmful gases may be oxidized when they come into contact with the surface of the composite catalyst shell or when they pass through the shell from the outside to the inside, but such contact between the harmful gas and the catalyst alone may not oxidize all of the harmful gases in the air. Harmful gases that are not removed solely through contact oxidation are rapidly and massively adsorbed into the core through the pores of the porous inorganic particles, and the adsorbed harmful gases are then desorbed and oxidized as they pass from the interior to the exterior of the composite catalyst shell again, allowing for substantially all harmful gas removal even at high flow rates.On the other hand, if the inorganic particles are non-porous, the above-mentioned adsorption / desorption oxidation reaction of harmful gases cannot occur, and they are only oxidized through contact on the surface of the composite catalyst shell, making it impossible to remove all harmful gases.

[0041] A non-limiting example of the porous inorganic particles may be particles containing any one or a combination of two or more selected from the group consisting of zeolite, activated carbon, porous silica, and porous alumina. Preferably, the inorganic particles may be activated carbon or zeolite.

[0042] According to one embodiment, the porous inorganic particles may be activated carbon particles. The composite particles contain activated carbon particles as cores, which increases the adsorption capacity of harmful substances into the pores of the porous inorganic particles, allowing the oxidation reaction of harmful gases through adsorption and desorption to occur at a faster rate, thereby effectively removing substantially all of the harmful gases.

[0043] According to one embodiment, the porous inorganic particles may be zeolite particles, and the composite particles may contain zeolite particles as cores, thereby increasing the adsorption capacity and thereby more effectively removing harmful gases, and further providing deodorizing and moisture absorbing functions due to the moisture desorption properties of zeolite.

[0044] According to one embodiment, the porous support may be a metal oxide or metalloid oxide porous support. The metal or metalloid of the metal oxide or metalloid oxide may be selected from Groups 2 to 5, 7 to 9, and 11 to 14, specifically, a metal or metalloid selected from Groups 2 to 4, 13, and 14, more specifically, Al, Ti, Zr, or Si.

[0045] The porous support includes mesopores and may optionally further include micropores. In the present disclosure, micropores refer to pores having an average internal pore diameter of less than 2 nm, and mesopores refer to pores having an average internal pore diameter of 2 nm to 50 nm. The mesopore volume of the porous support may be 50% by volume or more, 60% by volume or more, or 70% by volume or more. There is no upper limit, but the mesopore volume may be, for example, 100% by volume or less, 95% by volume or less, or 90% by volume or less, or may be 50 to 100% by volume, specifically 60 to 90% by volume, but this is merely an example and is not limited thereto.

[0046] According to a non-limiting example, the porous support may have a hierarchical porous structure, and may include a structure in which micropores are regularly present and interconnected between mesopores.

[0047] According to a non-limiting embodiment, the porous support may further include macropores, and it is preferable that the porous support includes macropores at a certain volume fraction or more, since the gas diffusion resistance can be significantly reduced.

[0048] The gold nanoparticles can be prepared by methods known in the art or commercially available materials. Specifically, gold nanoparticles can be prepared by reducing a gold precursor present in a solution to gold using a known method (Natan et al., Anal. Chem. 67, 735 (1995)). Examples of gold precursors include, but are not limited to, gold-containing halides, nitrates, acetates, acetylacetonates, and ammonium salts. Specifically, the gold precursor may be, but is not limited to, HAuCl4 or HAuBr4.

[0049] The diameter of the gold nanoparticles can be 1 nm to 20 nm, specifically 1 nm to 15 nm, and more specifically 1 nm to 12 nm. The diameter of the gold nanoparticles is preferably 1 nm to 10 nm, and more preferably 1 nm to 8 nm.

[0050] According to one embodiment, the average diameter of the nanoparticles may be larger than the average diameter of the mesopores of the porous support, thereby generating a deformation in the crystal lattice of the gold nanoparticles contained in the mesopores of the porous support, which may lead to improved catalytic activity at room temperature.

[0051] According to one embodiment, the nanoparticles may be contained in all or some of the mesopores of the porous support, more specifically, in some of the mesopores of the porous support, and more specifically, in some of the mesopores of the porous support, irregularly. In this case, the structure in which nanoparticles are contained in all of the mesopores of the porous support refers to a superlattice structure, specifically a highly ordered superlattice structure having face-centered cubic (FCC) symmetry. The morphology in which nanoparticles are irregularly contained in some of the mesopores has the advantage that gas diffusion can be more effective than in the superlattice structure.

[0052] According to one embodiment, the nanoparticles may be incorporated into some of the mesopores of the porous support, and the mesopores not incorporating the nanoparticles may be interconnected by open pores. In the composite particles, the nanoparticles are contained only in some of the pores of the porous support, which allows for more effective diffusion of harmful gases through the open pores that are interconnected and do not contain nanoparticles, thereby increasing the catalytic reaction rate of harmful gases within the composite catalyst shell.

[0053] According to one embodiment, the pores of the composite catalyst shell may be connected to the pores of the core through open pores. If the pores of the core and the pores of the shell are not connected to each other, material permeation may not proceed well or, if it does occur, the rate may be significantly reduced, and harmful gases may not be properly adsorbed to the core, resulting in a reduced rate of removal of harmful gases. The composite particles have interconnected pores in the core and shell, which increases the material diffusion rate, allowing harmful gases to diffuse into the core and be rapidly adsorbed in large amounts. As the adsorbed gases are desorbed, they pass from the interior to the exterior of the composite catalyst shell and are oxidized, allowing for the removal of substantially all harmful gases even at higher flow rates.

[0054] According to one embodiment, the composite catalyst may have an average particle size of 0.01 μm to 10 μm, specifically 0.05 μm to 5 μm, more specifically 0.1 μm to 5 μm. By satisfying this range, the composite catalyst can be more tightly bound to the core, thereby improving durability.

[0055] According to one embodiment, the composite catalyst has a specific surface area of ​​300 m 2 / g or more, 400m 2 / g or more, 500m 2 / g or more 600m 2 / g or more, 2,000m 2 / g or less or 1,500m 2 / g or less, for example, 300m 2 / g~2,000m 2 / g, 400m 2 / g~2,000m 2 / g or 600m 2 / g~1,500m 2 / g. The preferred specific surface area of ​​the composite catalyst is 640 m 2 / g~1,500m 2 / g, more preferably 700m 2 / g~1,500m 2 / g.

[0056] According to one embodiment, the composite catalyst has a total pore volume of 0.08 cm 3 / g~2.0cm 3 / g, 0.08cm 3 / g~1.5cm 3 / g, or 0.1cm 3 / g~1.0cm 3 / g. The total pore volume of the preferred composite catalyst is 0.12 cm 3 / g~1.0cm 3 / g, more preferably 0.15 cm 3 / g~1.0cm 3 / g or 0.2cm 3 / g~1.0cm 3 / g.

[0057] According to an embodiment, the composite catalyst may have an average pore diameter that is smaller than the average diameter of the nanoparticles, and may be 1.3 nm or more, 1.5 nm or more, or 2 nm or more.

[0058] The composite catalyst satisfies the above-mentioned ranges of specific surface area, pore volume, and pore diameter, so that harmful gases can be more effectively diffused through the pores, thereby increasing the catalytic reaction rate of harmful gases within the composite catalyst shell.

[0059] According to one embodiment, the composite catalyst shell includes a porous support having mesopores and gold nanoparticles contained in the pores of the porous support, and a radial distribution function obtained by Fourier transforming an EXAFS (Extended X-ray absorption fine structure) spectrum may satisfy the following Equation 1: [Formula 1] (DH2 / DH1)<0.3 In the above formula 1, DH1 is the height of the peak at interatomic distance D1, DH2 is the height of the peak at interatomic distance D2, and D1 and D2 satisfy the following formulas 2 and 3, respectively. Specifically, the above D1 and D2 are the interatomic distances of the maximum peaks found in the ranges that satisfy the following formulas 2 and 3, respectively. [Formula 2] 0.8≦(D1 / D3)≦0.95 [Formula 3] 0.6≦(D2 / D3)≦0.7 In the above formulas 2 and 3, D3 means the interatomic distance of the Au-Au bond in the bulk phase, which is 2.8 to 3.0 Å, specifically, it can be 2.88 to 2.98 Å, and more specifically, it can mean the standard interatomic distance of 2.90 Å. Specifically, D3 can refer to the interatomic distance of the Au-Au bond in the bulk phase, which is between 2.8 and 3.0 Å, obtained by peak deconvolution when the peak appears as a single asymmetric peak or has a bimodal peak. The asymmetry means that the peak has a shape of a single peak (unimodal peak), but as the two peaks overlap, there is asymmetry between the left and right sides of the center of the peak.

[0060] Specifically, (D1 / D3) in the above formula 2 can be 0.85 to 0.92, and (D2 / D3) in the above formula 3 can be 0.63 to 0.66.

[0061] According to a specific embodiment, in the above formula 1, DH1 may represent the height of the peak at an interatomic distance of 2.57±0.2 Å, and DH2 may represent the height of the peak at an interatomic distance of 1.85±0.2 Å. Specifically, DH1 may refer to the height of the peak at an interatomic distance of 2.57±0.1 Å, and DH2 may refer to the height of the peak at an interatomic distance of 1.85±0.1 Å.

[0062] When the composite catalyst satisfies the ratio of the height of the peak at the interatomic distance D1 to the height of the peak at the interatomic distance D2 of less than 0.3, the catalytic activity can be improved to a great extent.

[0063] EXAFS stands for Extended X-ray Absorption Fine Structure, which can analyze the radial distribution and coordination number of gold nanoparticles. For example, when high-energy X-rays are irradiated onto gold atoms, the gold atoms in the gold nanoparticles emit electrons. This generates a radial scattered wave centered on the gold atom that absorbed the X-ray, and when the electrons emitted from the gold atom that absorbed the X-ray reach neighboring atoms (gold or oxygen atoms), electrons are emitted from the neighboring atoms, generating a radial scattered wave centered on the neighboring atoms.

[0064] The scattered wave generated around the gold atom that absorbed the X-ray interferes with the scattered wave generated around the other adjacent atoms (gold or oxygen atoms). At this time, a standing wave is generated according to the distance between the gold atom that absorbed the X-ray and the other atoms (gold or oxygen atoms) adjacent to the gold atom. When the standing wave is Fourier transformed, a radial distribution with a peak corresponding to the distance between the gold atom and the other atoms (gold or oxygen atoms) adjacent to the gold atom is obtained. That is, a radial distribution can be obtained that has not only a peak corresponding to the distance between gold (Au) atoms but also a peak corresponding to the distance between a gold (Au) atom and an oxygen atom having an Au-O bond, if the gold (Au) atom has a bond with an oxygen atom.

[0065] According to one embodiment, (DH2 / DH1) in Equation 1 above may be 0.25 or less, more specifically 0.24 or less, and may be, without limitation, 0 or more. When the value falls within this range, the catalytic activity of the composite catalyst shell is significantly improved, which is preferable in that substantially all of the reactant gas contained in the gas stream can be converted to product gas significantly more quickly.

[0066] According to an embodiment, the composite catalyst shell may have a radial distribution function obtained by Fourier transforming an EXAFS (Extended X-ray absorption fine structure) spectrum that satisfies the following Equation 4: [Formula 4] (DA2 / DA1)<0.25 In the above formula 4, DA1 is the area of ​​the peak at interatomic distance D1, DA2 is the area of ​​the peak at interatomic distance D2, and D1 and D2 satisfy the above formulas 2 and 3, respectively.

[0067] According to a specific embodiment, in the above formula 4, DA1 may be the area of ​​the peak at an interatomic distance of 2.57±0.2 Å, and DA2 may be the area of ​​the peak at an interatomic distance of 1.85±0.2 Å. Specifically, DA1 may be the area of ​​the peak at an interatomic distance of 2.57±0.1 Å, and DA2 may be the area of ​​the peak at an interatomic distance of 1.85±0.1 Å.

[0068] When the area ratio of the peak at the interatomic distance D1 to the peak at the interatomic distance D2 of the composite catalyst is less than 0.25, the catalytic activity can be improved to a great extent.

[0069] According to one embodiment, (DA2 / DA1) in Equation 4 above may be 0.2 or less, specifically 0.18 or less, more specifically 0.15 or less, and may be, but is not limited to, 0 or more. By having this numerical range, the catalytic activity of the composite catalyst shell is significantly improved, which is preferable in that reactant gases contained in the gas stream can be substantially completely converted to product gases at a significantly faster rate.

[0070] The numerical ranges of Formula 1 and Formula 4 obtained from the EXAFS (Extended X-ray absorption fine structure) spectrum may be derived from the manufacturing process of the improved composite catalyst according to the present invention and may be implemented through one embodiment of the present disclosure, but the numerical ranges of Formula 1 and Formula 4 are not limited to one embodiment.

[0071] According to one embodiment, the radial distribution function obtained by Fourier transforming the EXAFS (Extended X-ray absorption fine structure) spectrum may have a bimodal peak in an interatomic distance range of 2.2 to 3.0 Å, and the bimodal peak appears due to gold (Au)-gold (Au) interatomic bonds. Specifically, the interatomic distance range of 2.2 to 3.0 Å may be a range in which the distance between gold (Au) atoms is located, and represents the distribution of Au-Au interatomic distances in the crystal lattice.

[0072] Typical gold nanoparticles can exhibit a single peak in the interatomic distance range of 2.2 to 3.0 Å, and the presence of a single peak means that the gold (Au)-gold (Au) atomic distance is constant within the crystal lattice of the nanoparticles. However, the presence of a bimodal peak may mean that there are different interatomic distances between gold (Au)-gold (Au) atoms in the crystal lattice. Although this has not been clearly determined, it is presumed that the two different interatomic distances between gold (Au)-gold (Au) atoms are generated by deformation of the crystal lattice due to compressive stress. The presence of a bimodal peak in the interatomic distance range of 2.2 to 3.0 Å is advantageous in that it can exhibit excellent catalytic activity even at low temperatures and can convert substantially all of the reactant gas contained in a high flow rate gas stream into product gas very quickly.

[0073] According to one embodiment, the composite catalyst shell may be included in an amount of 1 to 50 parts by weight, specifically 5 to 20 parts by weight, based on 100 parts by weight of the core containing the inorganic particles. The composite catalyst shell may be coated on the surface of the core to form a uniform surface coating layer.

[0074] According to an embodiment, the diameter of the core is not particularly limited, but may be, for example, 100 μm to 50 mm, specifically 0.5 mm to 50 mm, and more specifically 1 mm to 25 mm. When the core satisfies the above range, the size of the composite particles can be increased, thereby improving the differential pressure problem, which is one of the causes of reduced filter lifespan. At the same time, unlike conventional powder catalysts, there is no need to fill more catalyst than necessary, and it is possible to fill the air purification filter with just the amount of catalyst required, which reduces the amount of catalyst used and is economically advantageous.

[0075] According to one embodiment, the ratio of the diameter D of the core to the thickness T of the shell (T / D) is 1×10 -4 can be ∼0.2, specifically 1×10 -3 When the T / D value satisfies the above range, the catalyst has significantly excellent catalytic activity at room temperature, and at the same time, the pressure difference problem that occurs when using existing powder catalysts can be significantly alleviated.

[0076] According to an embodiment, the thickness of the shell is not particularly limited, but may be, for example, 1 μm to 1 mm, and specifically, 2 μm to 500 μm.

[0077] According to one embodiment, the core-shell structured composite particles may be used in the oxidation reaction of carbon monoxide, aldehyde-based compounds, or hydrocarbon-based compounds. Thus, the core-shell structured composite particles according to the present disclosure may be preferably used as a solid-phase oxidant for carbon monoxide, aldehyde-based compounds, or hydrocarbon-based compounds. The oxidation reaction may be carried out at a temperature of, but is not limited to, 0° C. to 60° C., specifically 10° C. to 50° C., more specifically 20° C. to 40° C. The aldehyde compound may be, but is not limited to, acetaldehyde or formaldehyde. The hydrocarbon-based compound may be an aliphatic or aromatic compound or a volatile organic compound (VOC), and examples thereof include, but are not limited to, methane, ethane, propane, butane, benzene, toluene, or xylene.

[0078] According to one embodiment, the composite particles can convert a 4% carbon monoxide-containing gas into carbon dioxide at a conversion efficiency of 80% or more, specifically 85% or more, and more specifically 90% or more at room temperature and at a flow rate of 100 ml / min. In addition, under the condition of a flow rate of 140 ml / min, conversion to carbon dioxide can be achieved at room temperature with a conversion efficiency of 80% or more, specifically 85% or more, and more specifically 90% or more. The carbon monoxide-containing gas may contain a certain amount of oxygen for oxidation, for example, 2% or more, 4% or more, 10% or more, or, but not limited to, 30% or less. For example, the carbon monoxide-containing gas may be air, but is not limited thereto as long as it contains a certain amount of oxygen or more.

[0079] FIG. 2 is a schematic diagram of an air purification filter including the composite particles according to one embodiment.

[0080] The air purification filter according to the present disclosure includes a reactive filter section 200 having an internal space filled with a plurality of composite particles, an inlet 300 provided on one side of the reactive filter section through which a gas 10 containing harmful gases flows in, and an outlet 400 provided on the other side of the reactive filter section through which a gas 20 from which harmful gases have been removed is discharged, and the composite particles are the composite particles 100 described above.

[0081] According to an embodiment, the harmful gas may be one or a combination of two or more selected from the group consisting of carbon monoxide, aldehyde-based compounds, and hydrocarbon-based compounds. The aldehyde-based compounds may be, but are not limited to, acetaldehyde or formaldehyde. The hydrocarbon-based compound may be an aliphatic or aromatic compound, and examples thereof include, but are not limited to, methane, ethane, propane, butane, benzene, toluene, or xylene.

[0082] Referring to FIGS. 1 and 2, harmful gases introduced through the inlet 300 are substantially completely removed even at a high flow rate through adsorption and desorption reactions and catalytic oxidation reactions in addition to contact with the composite particles 100 filled in the reactive filter unit 200, and can be discharged through the outlet 400.

[0083] More specifically, harmful gases that are not removed solely through the oxidation reaction due to contact are rapidly adsorbed in large quantities into the core through the pores of the porous inorganic particles, and the harmful gases adsorbed inside the core are desorbed again and can be oxidized while passing again from the inside to the outside of the composite catalyst shell, so that substantially all harmful gases can be removed even at high flow rates.

[0084] In addition, since the composite particles 100 filled in the reaction filter unit 200 have a core-shell structure and the particle size increases, the pressure difference problem that occurs at high flow rates when using existing powder catalysts can be significantly alleviated. Furthermore, when applied to an air purification filter that needs to fill a certain volume, conventional powder-type catalysts need to be filled with more catalyst than necessary, whereas the composite particles can be filled with just the amount of catalyst required for air purification, thereby reducing the amount of catalyst used and providing an economical advantage.

[0085] 2, the air purification filter may further include a particle filter unit for removing fine particles between the reactive filter unit 200 and the inlet 300. As a result, the air purification filter can remove some of the harmful gases contained in the gas before the gas passes through the reactive filter unit 200, so that the harmful gases contained in the gas can be completely removed even at a higher flow rate.

[0086] The method for producing core-shell composite particles according to the present disclosure includes the steps of: (S1) preparing inorganic particles; (S2) preparing a dispersion containing a composite catalyst and a binder, the composite catalyst including a porous support having mesopores and gold nanoparticles contained in the pores of the porous support; (S3) applying the dispersion to the surfaces of the inorganic particles; and (S4) drying the dispersion.

[0087] In the method for preparing the composite particles, the order of steps S1 and S2 is not limited, and the same as described above can be applied to the inorganic particles, porous support, and nanoparticles.

[0088] In step S2, the binder may include an inorganic binder, an organic binder, or a combination thereof, and preferably, an inorganic binder and an organic binder may be used in combination. More preferably, the binder may include an inorganic sol binder and / or a water-soluble polymer binder. The inorganic sol binder may be, for example, silica sol, but is not limited thereto. The inorganic sol binder may have an average particle size of 1 to 50 nm and may be contained in an amount of 0.5 to 3 wt % in the dispersion. The water-soluble polymer binder may be one or more selected from the group consisting of polyethylene glycol, polyvinyl alcohol, and poly(N-vinylpyrrolidone). The water-soluble polymer binder may be contained in an amount of 1 to 5 wt % in the dispersion. The weight-average molecular weight of the water-soluble polymer binder may be, but is not limited to, 10,000 to 1,000,000 g / mol. Specifically, the binder may be a combination of silica sol and polyvinyl alcohol, and this combination allows the composite catalyst to be firmly bound to the inorganic particles, thereby exhibiting excellent durability.

[0089] The dispersion liquid may have a weak acidity of pH 2 to 6 or pH 3 to 5. The solvent for the dispersion liquid is not particularly limited, and may be, for example, water, alcohol, or a combination thereof.

[0090] In step S3, the dispersion liquid may be applied to the surface of the inorganic particles by a coating method known in the art, such as spin coating, spray coating, knife coating, roll coating, inkjet printing, or dip coating.

[0091] According to an embodiment, the core-shell structured composite particles prepared in steps S1 to S4 may be further calcined after step S4. The calcination temperature may be, but is not limited to, 200°C to 600°C, specifically 300°C to 500°C. [Example]

[0092] Examples and experimental examples will be specifically illustrated below. However, the examples and experimental examples described below are merely illustrative of a portion of the technology described in this specification, and the technology described in this specification is not limited thereto.

[0093] <Production Example 1> Production of Composite Catalyst 1 [Step 1]: Preparation of polymer-functionalized gold nanoparticles [Step 1-1]: Oleylamine-stabilized gold nanoparticles are synthesized according to the following procedure. First, oleylamine was selected as the stabilizer. A solution consisting of 60 ml of tetralin, 60 ml of oleylamine, and 0.6 g of HAuCl H2O was prepared by stirring at room temperature for 10 minutes. 6 mmol of TBAB (tetrabutylammonium bromide), 6 ml of tetralin, and 6 ml of oleylamine were mixed by ultrasonic pulverization and quickly added to the above solution. The solution was stirred at room temperature for an additional hour, ethanol was added, and the mixture was centrifuged to precipitate gold nanoparticles. The gold nanoparticle precipitate was redispersed in hexane, and ethanol was added and centrifuged. The resulting gold nanoparticles had an average particle size of 4 nm, and were dispersed in 100 ml of toluene as they were.

[0094] [Step 1-2]: The surface of gold nanoparticles is functionalized with thiolated PEG via the following method. The gold nanoparticles dispersed in toluene in step 1-1 were further diluted with 100 ml of tetrahydrofuran, and 1 g of a monofunctional polyethylene glycol (aSH-PEG, weight-average molecular weight: 1 kDa) substituted at the end with a thiol group was added to functionalize the surface of the gold nanoparticles by binding the polymer to the surface of the gold nanoparticles. After stirring, hexane was added and the mixture was centrifuged to precipitate PEG-functionalized gold nanoparticles (4-Au-PEG). The 4-Au-PEG obtained by precipitation was dried and then dispersed in water.

[0095] [Step 2]: Preparation of PEG-functionalized gold nanoparticle-encapsulated porous silica 0.088 g of 4-Au-PEG prepared in step 1-2 above was mixed with 0.396 g of Pluronic F127 as an activator and uniformly dispersed in 10 ml of 1.6 M HCl aqueous solution, and then 1.49 g of tetraethyl orthosilicate (TEOS) was added to the dispersion. The resulting dispersion was stirred for 15 minutes and then left at room temperature for 40 hours without stirring to produce a red precipitate, which corresponds to the porous silica containing PEG-functionalized gold nanoparticles.

[0096] [Step 3]: Preparation of composite catalyst The red precipitate produced in the previous step was washed with water and dried, and then calcined in stages at 250°C for 3 hours, 400°C for 2 hours, and 500°C for 2 hours to remove the PEG and Pluronic F127 polymer, producing a composite catalyst, which is porous silica entrapping gold nanoparticles.

[0097] <Production Example 2> Production of Composite Catalyst 2 Composite catalyst 2, which is porous silica encapsulating gold nanoparticles, was prepared by performing the same steps as in Step 1-1 of Preparation Example 1, except that gold nanoparticles with an average particle size of 10 nm were prepared by adjusting the molar ratio of oleic amine and HAuCl HO in Step 1-1.

[0098] <Production Example 3> Production of Composite Catalyst 3 Steps 1 and 2 were repeated in the same manner as in Preparation Example 1, except that gold nanoparticles with an average particle size of 12 nm were prepared by adjusting the molar ratio of oleic amine and HAuCl HO in Step 1-1. In Step 3, the red precipitate prepared in the previous step was washed with water, dried, and then calcined at 450°C to remove PEG and Pluronic F127 polymer, thereby preparing composite catalyst 3, which is porous silica with gold nanoparticles entrapping therein.

[0099] <Production Example 4> Production of Composite Catalyst 4 Composite catalyst 4, which is porous silica in which gold nanoparticles are trapped in a superlattice structure, was prepared by repeating the same steps as in Step 2 of Preparation Example 1, except that 0.396 g of Pluronic F127 was not used.

[0100] <Production Example 5> Production of Composite Catalyst 5 The same steps as in Step 2 of Preparation Example 2 were carried out, except that 0.396 g of Pluronic F127 was not used, to prepare Composite Catalyst 5, which is porous silica in which gold nanoparticles are trapped in a superlattice structure.

[0101] <Production Example 6> Production of Composite Catalyst 6 The same steps as in Step 2 of Preparation Example 3 were carried out, except that 0.396 g of Pluronic F127 was not used, to prepare composite catalyst 6, which is porous silica in which gold nanoparticles are trapped in a superlattice structure.

[0102] Example 1: Preparation of composite particles 1 with core-shell structure The composite catalyst 1 prepared in Preparation Example 1 was mixed with an aqueous solution to a concentration of 10 wt % and milled to prepare a dispersion. The average particle size of the milled composite catalyst powder was 0.8 μm. An inorganic binder silica sol with an average particle size of 32 nm, which had been adjusted to a pH of 4 by adding acetic acid to the dispersion, was mixed into the dispersion to account for 1 wt % of the dispersion. An organic binder, polyvinyl alcohol, was then mixed into the dispersion to account for 2 wt % of the dispersion to produce a coating slurry.

[0103] The coating slurry was dip-coated onto the surface of zeolite with an average diameter of 2 mm for 5 minutes, and then excess slurry was removed by blowing air into the surface, followed by thorough drying. The immersion and drying process was repeated 10 times, and the coated zeolite was placed in a high-temperature furnace and fired at 450° C. for 4 hours to finally prepare composite particles 1 having a core-shell structure. FIG. 3 is an image of a composite particle 1 having a core-shell structure.

[0104] Example 2: Preparation of core-shell structured composite particles 2 The same procedure as in Example 1 was carried out, except that Composite Catalyst 2 prepared in Preparation Example 2 was used instead of Composite Catalyst 1 prepared in Preparation Example 1, to prepare composite particles 2 having a core-shell structure.

[0105] Example 3: Preparation of core-shell structured composite particles 3 The same procedure as in Example 1 was carried out, except that composite catalyst 3 prepared in Preparation Example 3 was used instead of composite catalyst 1 prepared in Preparation Example 1, to prepare composite particles 3 having a core-shell structure.

[0106] Example 4: Preparation of core-shell structured composite particles 4 The same procedure as in Example 1 was carried out, except that composite catalyst 4 prepared in Preparation Example 4 was used instead of composite catalyst 1 prepared in Preparation Example 1, to prepare composite particles 4 having a core-shell structure.

[0107] Example 5: Preparation of core-shell structured composite particles 5 The same procedure as in Example 1 was carried out, except that Composite Catalyst 5 prepared in Preparation Example 5 was used instead of Composite Catalyst 1 prepared in Preparation Example 1, to prepare composite particles 5 having a core-shell structure.

[0108] Example 6: Preparation of core-shell structured composite particles 6 The same procedure as in Example 1 was carried out, except that composite catalyst 6 prepared in Preparation Example 6 was used instead of composite catalyst 1 prepared in Preparation Example 1, to prepare composite particles 6 having a core-shell structure.

[0109] <Comparative Example 1> The following experimental example was carried out using the same amount of powdered composite catalyst 1 produced in the above Production Example 1 as in Example 1.

[0110] <Comparative Example 2> The following experimental example was carried out using zeolite with an average diameter of 2 mm.

[0111] <Experimental Example 1> EXAFS (Extended X-ray absorption fine structure) analysis Extended X-ray absorption fine structure (EXAFS) measurements were performed using the 4C and 10C beamlines at the Pohang Accelerator System (PLS-II). The EXAFS spectra were Fourier transformed to obtain the radial distribution function. Figure 4 shows the radial distribution function of a composite catalyst supporting gold particles with an average particle size of 4 nm (Production Example 1), Figure 5 shows the radial distribution function of a composite catalyst supporting gold particles with an average particle size of 10 nm (Production Example 2), and Figure 6 shows the radial distribution function of a composite catalyst supporting gold particles with an average particle size of 12 nm (Production Example 3).

[0112] Analysis of the radial distribution functions of the composite particles of Preparation Examples 1 to 6 revealed that a peak due to the Au-O bond was observed in the range of 1.4 to 1.7 Å in all cases. This confirms that the proximity between the gold nanoparticle surface and the porous silica capturing them provides the conditions for the formation of a stable Au-O bond at the interface between the gold nanoparticles and the porous silica, resulting in the formation of Au-O-Si.

[0113] In addition, in all of Figures 1 to 5, a peak due to bulk Au-Au bonds was observed in the range of 2.8 to 3.0 Å, and when the interatomic distance of such a peak is defined as D3, the peak of the radial distribution function was defined based on D3. Specifically, D1 and D2 are the interatomic distances of the maximum peaks found in the ranges that satisfy the following formulas 2 and 3, respectively, and the positions of D1, D2, and D3 are shown in Table 1. In addition, the ratios of the height (DH1) and area (DA1) of the peak with interatomic distance D1 to the height (DH2) and area (DA2) of the peak with interatomic distance D2 were calculated and shown in Table 1. [Formula 2] 0.8≦(D1 / D3)≦0.95 [Formula 3] 0.6≦(D2 / D3)≦0.7

[0114] [Table 1]

[0115] <Experimental Example 2> Pore characteristic analysis After degassing from 473 K to 20 μTorr for 12 hours, a nitrogen (N2) adsorption-desorption test was performed using a 3Flex adsorption analyzer (Micromeritics) at 77 K. The specific surface area and pore characteristics of the composite catalysts of Preparation Examples 1 to 6 were measured using the volume of adsorbed nitrogen gas molecules and the Brunauer-Emmett-Teller (BET) equation, and the results are shown in Table 2 below. Referring to Table 2, the composite catalyst according to Preparation Example 1 has larger specific surface area, pore volume, and pore diameter than the composite catalyst according to Preparation Example 4, and the composite catalysts according to Preparation Examples 2 and 3 have larger specific surface area, pore volume, and pore diameter than the composite catalysts according to Preparation Examples 5 and 6, respectively. This difference appears to be due to the fact that the composite catalysts of Preparation Examples 1 to 3 contain gold nanoparticles in only a portion of the surface of the porous silica, whereas the composite catalysts of Preparation Examples 4 to 6 have a superlattice structure in which gold nanoparticles are contained over the entire surface of the porous silica.

[0116] [Table 2]

[0117] <Experimental Example 3> Evaluation of catalytic activity and differential pressure The catalytic activity and differential pressure evaluation were carried out in a tubular reactor with both ends open. Composite particles according to the examples and comparative examples of the present disclosure were installed in the middle of the tubular reactor, a carbon monoxide-containing gas was supplied to one side of the reactor, and the other side of the reactor was connected to a gas chromatograph (DS Science) to measure the carbon monoxide concentration with a TCD detector (Carboxen 1000). Pressure sensors were installed on both sides of the reactor. A commercially available pressure sensor was used. The carbon monoxide-containing gas was 4% CO, 20% O, and 76% He. The carbon monoxide concentration discharged from the other side of the reactor was measured while adjusting the supply flow rate at room temperature (25°C). The carbon monoxide conversion rate (%) and differential pressure (mbar) according to the supply flow rate are shown in Tables 3 and 4 below, respectively.

[0118] [Table 3]

[0119] [Table 4]

[0120] Referring to Table 3, all examples showed a conversion rate of around 90% at a flow rate of 80 ml / min. Examples 1 to 3, which contain composite catalysts in which gold nanoparticles are impregnated on only a portion of the surface of porous silica, were shown to have superior catalytic activity compared to Examples 4 to 6, which contain composite catalysts in which gold nanoparticles are impregnated on the entire surface of porous silica. This is thought to be because gold nanoparticles are incorporated into some of the pores of the porous support, and are connected to each other by open pores between the pores of the porous support and / or between the pores of the core and shell, improving catalytic activity.

[0121] In particular, in the case of Example 1, a carbon monoxide conversion rate close to 100% was observed even at high flow rates of 140 ml / min or more, 160 ml / min or more, or 180 ml / min or more. In Example 2, although the conversion rate was shown to decrease partially at high flow rates, a conversion rate of 90% or more was still observed even under the condition of a flow rate of 140 ml / min.

[0122] Furthermore, referring to Table 4, it was confirmed that the Example had a significantly lower differential pressure than Comparative Example 1, which was in powder form, due to having a core-shell structure, and that the differential pressure was particularly low even at high flow rates of 140 ml / min or more, 160 ml / min or more, or 180 ml / min or more.

[0123] As mentioned above, the present disclosure has been described in this specification using specific matters and limited examples, but these are provided to help a more general understanding of the present disclosure. The present disclosure is not limited to the above examples, and various modifications and variations can be made from such a base material by a person having ordinary knowledge in the field to which the present disclosure pertains.

[0124] Therefore, the ideas described in this specification should not be limited to the described embodiments, and all variations that are equivalent to or equivalent to the scope of the claims, as well as the scope of the following claims, can be said to fall within the scope of the ideas described in this specification. [Explanation of symbols]

[0125] 10 Gases containing harmful gases 20 Gas from which harmful gases have been removed 100 Core-shell structured composite particles 110 Core containing inorganic particles 120 Composite catalyst shell 121 Porous support 122 Gold Nanoparticles 200 Reaction filter section 300 Inlet 400 Outlet

Claims

1. a core comprising inorganic particles; a composite catalyst shell located on the core and comprising a porous support containing mesopores and gold nanoparticles contained within the pores of the porous support;

2. The composite particle according to claim 1, wherein the inorganic particles are porous beads or non-porous beads, and the material of the beads is any one or a combination of two or more selected from the group consisting of glass, carbon, silica, silver-containing inorganic substances, alumina-silicate, and alumina.

3. The composite particles of claim 1 , wherein the inorganic particles are porous inorganic particles.

4. 4. The core-shell composite particles according to claim 3, wherein the porous inorganic particles are particles containing any one or a combination of two or more selected from the group consisting of zeolite, activated carbon, porous silica, and porous alumina.

5. The composite particle of claim 1 , wherein the porous support is a metal oxide or metalloid oxide porous support.

6. The composite particle of claim 1 , wherein the porous support further comprises macropores.

7. 2. The composite particle according to claim 1, wherein the nanoparticles have a diameter of 1 nm to 20 nm.

8. 2. The composite particle according to claim 1, wherein the nanoparticles are contained in a portion of the mesopores of the porous support, and the mesopores not containing the nanoparticles are interconnected by open pores.

9. 9. The composite particle of claim 8, wherein the pores of said composite catalyst shell are connected to the pores of said core by open porosity.

10. The composite particle according to claim 1, wherein a radial distribution function obtained by Fourier transforming an EXAFS (Extended X-ray absorption fine structure) spectrum of the composite catalyst shell satisfies the following formula 1: [Formula 1] (DH2 / DH1)<0.3 In the formula 1, DH1 is the height of the peak at the interatomic distance D1, DH2 is the height of the peak at the interatomic distance D2, and D1 and D2 satisfy the following formulas 2 and 3, respectively: [Formula 2] 0.8≦(D1 / D3)≦0.95 [Formula 3] 0.6≦(D2 / D3)≦0.7 D3 in the formulas 2 and 3 means the interatomic distance of the Au-Au bond in the bulk phase, which is between 2.8 and 3.0 Å.

11. The composite catalyst shell of claim 10 satisfies the following formula 4: [Formula 4] (DA2 / DA1)<0.25 In the formula 4, DA1 is the area of ​​the peak at the interatomic distance D1, DA2 is the area of ​​the peak at the interatomic distance D2, and D1 and D2 satisfy the formulas 2 and 3, respectively.

12. 11. The composite particle according to claim 10, wherein the radial distribution function has a bimodal peak in an interatomic distance range of 2.2 Å to 3.0 Å.

13. 2. The composite particle according to claim 1, wherein the core has a diameter of 100 μm to 50 mm.

14. The ratio (T / D) of the core diameter D to the shell thickness T is 2×10 －４ The composite particle according to claim 1, wherein the ρ is 0.2 or less.

15. The composite particles according to claim 1 , which are used for the oxidation reaction of carbon monoxide, aldehyde compounds, or hydrocarbon compounds.

16. a reaction filter unit having an internal space filled with a plurality of composite particles; an inlet provided on one side of the reaction filter unit through which gas containing harmful gas flows; an outlet provided on the other side of the reaction filter unit, through which gas from which harmful gases have been removed is discharged; Including, An air purification filter, wherein the composite particles are the composite particles according to any one of claims 1 to 15.

17. The air purification filter according to claim 16, further comprising a particle filter section between the reactive filter section and the inlet for removing fine particles.

18. (S1) preparing inorganic particles; (S2) preparing a dispersion containing a composite catalyst including a porous support having mesopores and gold nanoparticles contained in the pores of the porous support, and a binder; (S3) applying the dispersion liquid to the surface of the inorganic particles; (S4) drying the dispersion.

19. The method for producing core-shell structured composite particles according to claim 18, wherein the binder comprises an inorganic sol binder and a water-soluble polymer binder.

Images