Supported metal catalyst

Abstract

To provide a supported metal catalyst enabling hydrogenolysis of a plastic to proceed even under mild conditions.SOLUTION: According to one aspect of the present invention, there is provided a supported metal catalyst 10 used for hydrogenolysis of plastics, comprising: a support 11 composed of a metal oxide; and catalyst metal particles 12 that are carried on the support 11 and comprise one or more ruthenium particles 12A composed of ruthenium and one or more metal particles 12B composed of a metal having a function of activating hydrogen, wherein the metal particles 12B are in contact with the ruthenium particles 12A.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to supported metal catalysts. [Background technology]

[0002] Currently, environmental pollution caused by waste plastics is a serious problem, and efficient recycling of waste plastics is an urgent issue. Hydrogenolysis using supported metal catalysts is attracting attention as one of the most promising methods for recycling waste plastics.

[0003] Hydrocracking is a technology that uses a supported metal catalyst to decompose plastics in a hydrogen stream under high temperature and / or pressure, converting them into lighter hydrocarbons. Currently, a ruthenium-supported catalyst (Ru / CeO2 catalyst), in which ruthenium is supported on ceria, is known as the supported metal catalyst used in hydrocracking (see Non-Patent Documents 1 to 3).

[0004] Non-Patent Document 1 discloses the hydrogenolysis of low-density polyethylene using a Ru / CeO2 catalyst in a hydrogen atmosphere at 240°C and 6 MPa. Non-Patent Document 2 discloses the hydrogenolysis of low-density polyethylene or polypropylene using a Ru / CeO2 catalyst in a hydrogen atmosphere at 260°C and 5 to 60 atmospheres. Non-Patent Document 3 discloses the hydrogenolysis of low-density polyethylene using a Ru / CeO2 catalyst in a hydrogen atmosphere at 240°C and 3 MPa. [Prior art documents] [Non-patent literature]

[0005] [Non-Patent Document 1] Y. Nakaji et al., Low temperature catalytic upgrading of waste polyolefinic plastics into liquid fuels and waxes, Applied Catalysis B: Environmental, 2021, 285, 119805 [Non-patent document 2] L. Chen et al., Disordered,Sub Nanometer Ru Structures on CeO2 are Highly Efficient and Selective Catalysts in Polymer Upcycling by Hydrogenolysis, ASC Catalysis, 2022, 12, 4618-4627 [Non-patent document 3] Shenglu Lu et al., Enhanced Production of Liquid Alkanes from Waste Polyethylene via the Electronic Effect Favored Csecondary Csecondary Bond Cleavage, ChemCatChem, 2023, 15, e202201375 Summary of the Invention [Problem to be solved by the invention]

[0006] However, due to the strength of the C-C bond in plastics, high temperature and / or high pressure conditions are required, and the hydrogenolysis process requires a large amount of energy in Non-Patent Documents 1 to 3. Therefore, there is currently a strong demand for the development of supported metal catalysts that enable the hydrogenolysis of plastics even under mild conditions.

[0007] The present invention has been made to solve the above problems, and its object is to provide a supported metal catalyst that enables the hydrogenolysis of plastics even under mild conditions. [Means for solving the problem]

[0008] [1] A supported metal catalyst used for the hydrolysis of plastics, comprising: a carrier made of a metal oxide; and catalytic metal particles supported on the carrier, the catalytic metal particles comprising one or more ruthenium particles made of ruthenium and one or more metal particles made of a metal having the function of activating hydrogen, wherein the metal particles are in contact with the ruthenium particles.

[0009] [2] The supported metal catalyst according to [1] above, wherein the catalytic metal particles are composed of a ruthenium-based alloy in which the metal is segregated relative to ruthenium.

[0010] [3] The supported metal catalyst according to [1] or [2] above, wherein the metal particles are exposed on the surface of the catalytic metal particles.

[0011] [4] The supported metal catalyst according to any one of [1] to [3] above, wherein the molar ratio of the amount of the supported metal to the amount of supported ruthenium is 0.1 or more and 10 or less.

[0012] [5] The supported metal catalyst according to any one of [1] to [4] above, wherein the metal is a platinum group metal.

[0013] [6] The supported metal catalyst according to any one of [1] to [5] above, wherein the metal oxide has a function of bringing the ruthenium particles and the metal particles into contact with each other.

[0014] [7] The supported metal catalyst according to any one of [1] to [6] above, wherein the metal oxide is ceria or silica. [Effects of the Invention]

[0015] According to the present invention, it is possible to provide a supported metal catalyst that enables the hydrogenolysis of plastics even under mild conditions. [Brief explanation of the drawings]

[0016] [Figure 1] FIG. 1 is a schematic diagram of a supported metal catalyst according to an embodiment. [Figure 2] FIG. 2 is a graph showing the component ratios of products obtained when low-density polyethylene was subjected to hydrolysis using the catalysts according to Examples 1 and 2 and Comparative Examples 1 to 3. [Figure 3] FIG. 3 is a graph showing the component ratios of products obtained when low-density polyethylene was hydrolyzed using the catalyst of Example 3. [Figure 4] FIG. 4 is a graph showing the component ratios of products obtained when polypropylene was hydrolyzed using the catalyst of Example 1. [Figure 5] FIG. 5A is an HAADF-STEM photograph of the catalyst according to Example 1, and FIG. 5B is a mapping photograph of each element in EDS elemental analysis of the catalyst according to Example 1. [Figure 6] FIG. 6A is an HAADF-STEM photograph of the catalyst according to Example 3, and FIG. 6B is a mapping photograph of each element in EDS elemental analysis of the catalyst according to Example 3. DETAILED DESCRIPTION OF THE INVENTION

[0017] BEST MODE FOR CARRYING OUT THE INVENTION The supported metal catalyst according to an embodiment of the present invention will be described below. Figure 1 is a schematic diagram showing the configuration of the supported metal catalyst according to this embodiment.

[0018] <<<Supported metal catalysts>>> The supported metal catalyst 10 shown in FIG. 1 is used for the hydrolysis of plastics, and includes a support 11 and catalytic metal particles 12 supported on the support 11 .

[0019] The plastics that can be hydrolyzed by the supported metal catalyst 10 are not particularly limited, but examples thereof include polyolefins such as polyethylene and polypropylene. The weight-average molecular weight of the polyolefin is not particularly limited, but may be, for example, 4,000 or more and 300,000 or less. From the viewpoint of decomposition performance, it is preferable that the plastic does not contain halogens such as chlorine.

[0020] <<Carrier>> The carrier 11 is made of a metal oxide. A preferred metal oxide is one that functions to bring ruthenium particles 12A and hydrogen-activated metal particles 12B, which will be described later, into contact with each other. Examples of such metal oxides include ceria (CeO), silica (SiO), alumina (AlO), titania (TiO), zirconia (ZrO), tungsten oxide (WO), and zeolite (e.g., ZSM-5). Among these, ceria (CeO) and silica (SiO) are preferred because of their excellent functionality.

[0021] <<Catalytic metal particles>> The catalytic metal particle 12 includes one or more ruthenium particles 12A made of ruthenium and one or more metal particles 12B made of a metal having the function of activating hydrogen (hereinafter, this metal may be referred to as a "hydrogen-activating metal particle"). The catalytic metal particle 12 preferably includes a plurality of ruthenium particles 12A and a plurality of hydrogen-activating metal particles 12B.

[0022] In the catalytic metal particles 12, the hydrogen-activating metal particles 12B are in contact with the ruthenium particles 12A as shown in Figure 1. When the hydrogen-activating metal particles 12B are in contact with the ruthenium particles 12A, the hydrogen adsorbed on the hydrogen-activating metal particles 12B moves to the ruthenium particles 12A and becomes more likely to bind to the reaction intermediates, which are decomposition products of plastic, thereby accelerating the hydrogenation of the reaction intermediates and the release of the products.

[0023] The catalytic metal particles 12 are preferably made of a ruthenium-based alloy in which the hydrogen-activating metal is segregated relative to the ruthenium. By using such an alloy, catalytic metal particles 12 in which the hydrogen-activating metal particles 12B are in contact with the ruthenium particles 12A can be easily obtained.

[0024] The average particle diameter (secondary particle diameter) of the catalytic metal particles 12 is preferably 0.5 nm or more and 10 nm or less. An average particle diameter within this range allows efficient hydrogen activation and C—C bond cleavage, both of which are key to the hydrogenolysis of plastics. The lower limit of the average particle diameter of the catalytic metal particles 12 is more preferably 1 nm or more, 1.5 nm or more, or 2 nm or more, and the upper limit is more preferably 8 nm or less, 5 nm or less, or 4 nm or less. For example, the average particle diameter of the catalytic metal particles 12 is more preferably 1 nm or more and 8 nm or less, 1.5 nm or more and 5 nm or less, or 2 nm or more and 4 nm or less. The average particle diameter of the catalytic metal particles 12 is the arithmetic mean value of the particle diameters of 124 catalytic metal particles 12 randomly measured using a transmission electron microscope.

[0025] The ruthenium particles 12A mainly have the function of breaking the C-C bonds of plastics, and the hydrogen-activating metal particles 12B have the function of activating hydrogen. Examples of the hydrogen-activating metal particles 12B include platinum group particles such as platinum particles, palladium particles, and iridium particles. Among platinum group particles, platinum particles are preferred because they exhibit superior decomposition performance even in a mild environment.

[0026] The hydrogen activation metal particles 12B are preferably exposed on the surface of the catalytic metal particles 12. When the hydrogen activation metal particles 12B are exposed on the surface of the catalytic metal particles 12, hydrogen is more easily adsorbed onto the hydrogen activation metal particles 12B, thereby increasing catalytic activity.

[0027] The molar ratio of the amount of hydrogen activation metal supported to the amount of ruthenium supported (amount of hydrogen activation metal supported (moles) / amount of ruthenium particles supported (moles)) is preferably 0.1 or more and 10 or less. If this molar ratio is within this range, plastics can be hydrolyzed more effectively even under mild conditions. The lower limit of this molar ratio is preferably 0.12 or more, 0.15 or more, or 0.2 or more, and the upper limit is preferably 9.5 or less, 9 or less, or 8 or less. For example, this molar ratio is more preferably 0.12 or more and 9.5 or less, 0.15 or more and 9 or less, or 0.2 or more and 8 or less. This molar ratio can be measured by inductively coupled plasma atomic emission spectroscopy.

[0028] <<Method for Hydrogenolysis of Plastics Using Supported Metal Catalysts>> When a plastic is hydrolyzed using the supported metal catalyst 10, the plastic and the supported metal catalyst 10 are mixed in a predetermined ratio in a hydrogen atmosphere of, for example, 0.1 MPa to 5 MPa, and the mixture is reacted at a temperature of 150°C to 350°C for 1 hour to 72 hours. This decomposes the plastic, producing products such as hydrocarbons. For example, if the plastic is polyolefin, alkanes are produced.

[0029] From the viewpoint of carrying out the hydrolysis of plastics under mild conditions, the upper limit of the pressure of the hydrogen atmosphere is preferably 4 MPa or less, 3 MPa or less, or 1 MPa or less. For example, the pressure of the hydrogen atmosphere is more preferably 0.1 MPa or more and 4 MPa or less, 0.1 MPa or more and 3 MPa or less, or 0.1 MPa or more and 1 MPa or less. Furthermore, from the viewpoint of carrying out the hydrolysis of plastics under mild conditions, the upper limit of the temperature during the hydrolysis of plastics is more preferably 300°C or less, 250°C or less, or 225°C or less. For example, this temperature is more preferably 150°C or more and 300°C or less, 150°C or more and 250°C or less, or 150°C or more and 225°C or less.

[0030] The mass ratio of the supported metal catalyst 10 to the plastic (mass of the supported metal catalyst / mass of the plastic) is preferably 0.1 or more and 0.5 or less. If this ratio is 0.1 or more, the plastic can be effectively hydrolyzed even under mild conditions, and if it is 0.5 or less, the hydrolysis can be performed with even higher efficiency. The lower limit of this ratio is more preferably 0.12 or more, 0.15 or more, or 0.2 or more, and the upper limit is more preferably 0.48 or less, 0.45 or less, or 0.4 or less. For example, this mass ratio is more preferably 0.12 or more and 0.48 or less, 0.15 or more and 0.45 or less, or 0.2 or more and 0.4 or less.

[0031] <<<Method of manufacturing supported metal catalysts>>> Such a supported metal catalyst 10 can be obtained, for example, by the following method: First, a ruthenium precursor such as ruthenium(III) chloride n-hydrate (RuCl3·nH2O) and a hydrogen-activated metal precursor such as hexachloroplatinic(IV) acid hexahydrate (H2PtCl6·6H2O) are prepared.

[0032] Next, the ruthenium precursor and the hydrogen-activated metal precursor are dissolved in water, and the support 11 is impregnated with this solution to support the ruthenium precursor and the hydrogen-activated metal precursor on the surface of the support 11.

[0033] The support carrying the ruthenium precursor and hydrogen-activated metal precursor is then solidified by evaporation and then subjected to hydrogen reduction for 1 to 5 hours at a temperature of 200° C. to 300° C. This results in catalytic metal particles 12 containing ruthenium particles 12A and hydrogen-activated metal particles 12B on the surface of support 11, with the hydrogen-activated metal particles 12B segregated relative to the ruthenium particles 12A.

[0034] The present inventors conducted extensive research into supported metal catalysts that enable the hydrolysis of plastics even under mild conditions. They discovered that the use of a supported metal catalyst, consisting of a metal oxide support carrying ruthenium particles and hydrogen-activated metal particles in contact with the ruthenium particles, enables the hydrolysis of plastics even under mild conditions. This is believed to be based on the following mechanism. The hydrolysis of plastics proceeds in the following order: (1) adsorption of the plastic onto the supported metal catalyst, accompanied by dehydrogenation; (2) cleavage of the C—C bonds in the plastic; and (3) hydrogenation of the reaction intermediate and elimination of the product. The presence of hydrogen-activated metal particles in the catalytic metal particles increases active hydrogen, and the contact of the hydrogen-activated metal particles with the ruthenium particles allows active hydrogen to be supplied to the reaction intermediate adsorbed on the ruthenium particles. This promotes hydrogenation of the reaction intermediate, enabling the hydrolysis of plastics to be carried out under mild conditions of relatively low temperature and / or relatively low pressure. According to this embodiment, ruthenium particles 12A and hydrogen-activated metal particles 12B in contact with the ruthenium particles 11 are supported on a carrier 11 made of a metal oxide, which promotes hydrogenation of the reaction intermediate, thereby enabling the hydrolysis of plastics even under mild conditions. [Example]

[0035] In order to explain the present invention in detail, the following examples are given, but the present invention is not limited to these. Fig. 2 is a graph showing the component ratios of the products obtained when low-density polyethylene was hydrolyzed using the catalysts of Examples 1 and 2 and Comparative Examples 1 to 3. Fig. 3 is a graph showing the component ratios of the products obtained when low-density polyethylene was hydrolyzed using the catalyst of Example 3. Fig. 4 is a graph showing the component ratios of the products obtained when polypropylene was hydrolyzed using the catalyst of Example 1. Fig. 5A is an HAADF-STEM photograph of the catalyst of Example 1, Fig. 5B is a mapping photograph of each element obtained by EDS elemental analysis of the catalyst of Example 1, Fig. 6A is an HAADF-STEM photograph of the catalyst of Example 3, and Fig. 6B is a mapping photograph of each element obtained by EDS elemental analysis of the catalyst of Example 3.

[0036] Example 1 First, a ruthenium precursor consisting of ruthenium(III) chloride n-hydrate (RuCl3·nH2O) and a platinum precursor consisting of hexachloroplatinic(IV) acid hexahydrate (H2PtCl6·6H2O) were prepared.

[0037] Next, the ruthenium precursor and the platinum precursor were dissolved in water, and the solution was impregnated into a support, ceria (CeO), to support the ruthenium precursor and the platinum precursor on the surface of the ceria.

[0038] The ceria carrying the ruthenium and platinum precursors was then solidified by evaporation and then subjected to hydrogen reduction at 300°C for 2 hours. This resulted in a catalyst (RuPt / CeO catalyst) having catalytic alloy particles composed of ruthenium particles and platinum particles as hydrogen-activated metal particles on the surface of the ceria. In the catalyst of Example 1, the ruthenium particles were 5 mass%, the molar ratio of the amount of platinum to the amount of ruthenium supported was 0.2, and the average particle size (secondary particle size) of the catalytic alloy particles was 2 nm.

[0039] <Example 2> In Example 2, a catalyst (RuPt / CeO2 catalyst) was obtained in the same manner as in Example 1, except that the molar ratio of the amount of supported platinum to the amount of supported ruthenium was set to 0.1.

[0040] Example 3 In Example 3, a catalyst (RuPt / SiO2 catalyst) was obtained in the same manner as in Example 1, except that silica (SiO2) was used as the support instead of ceria.

[0041] <Comparative Example 1> In Comparative Example 1, a catalyst (Ru / CeO catalyst) was obtained in the same manner as in Example 1, except that platinum particles were not included and the same number of moles of ruthenium particles as the ruthenium particles in the catalyst of Example 1 were supported on ceria.

[0042] <Comparative Example 2> In Comparative Example 2, a catalyst (Pt / CeO catalyst) was obtained in the same manner as in Example 1, except that ruthenium particles were not included and the same molar amount of platinum particles as the platinum particles in the catalyst of Example 1 was supported on ceria.

[0043] <Comparative Example 3> In Comparative Example 3, 0.1 g of the catalyst according to Comparative Example 1 and 0.1 g of the catalyst according to Comparative Example 2 were mixed together to obtain a catalyst (Ru / CeO2 catalyst+Pt / CeO2 catalyst).

[0044] <Hydrogenolysis test of low-density polyethylene> A hydrogenolysis test of low-density polyethylene (LDPE) was conducted using the catalysts of Examples 1 to 3 and Comparative Examples 1 to 3. Specifically, 0.5 g of LDPE (number-average molecular weight (Mn): 10,100, weight-average molecular weight (Mw): 105,600) and 0.1 g of catalyst were used to carry out a hydrogenolysis reaction at 200°C under a hydrogen atmosphere of 5 atmospheres (approximately 0.51 MPa) for 12 hours. After the hydrogenolysis reaction, the mixture was allowed to cool to room temperature, and the products were quantified using the following procedure. First, in the reaction system, alkane products with carbon numbers differing by one existed in the gaseous, liquid, and solid states at room temperature. First, the gaseous products were quantified using a gas chromatograph (GC-BID, Shimadzu Corporation's "GC-2010") equipped with a barrier discharge ionization detector (BID). Next, methylene chloride and biphenyl as an internal standard were added to the remaining liquid and solid products, and the soluble C5–C35 alkane products were quantified using a gas chromatograph equipped with a flame ionization detector (GC-FID, Shimadzu Corporation, GC-2014). The remaining solid product was dissolved in tetrachloroethane while heating, the stirrer was removed, and the dried product was weighed and quantified. Because methylene chloride-soluble products of C36 and above cannot be detected by gas chromatography, the total yield (mass%) of the gaseous product, solid product, and detectable liquid product was subtracted from 100%.

[0045] The results are shown in Figures 2 and 3. As shown in Figure 2, when the catalysts of Examples 1 and 2 were used, LPDE could be hydrolyzed under mild conditions, and the yield of the solid product containing unreacted LDPE was lower than when the catalysts of Comparative Examples 1 to 3 were used. This means that the catalysts of Examples 1 and 2 have higher catalytic activity for the hydrolysis of LDPE than the catalysts of Comparative Examples 1 to 3. Furthermore, the results of Example 1 and Comparative Example 3 indicate that in order to improve catalytic activity for the hydrolysis of LDPE, it is not enough to simply use a Ru / CeO2 catalyst and a Pt / CeO2 catalyst; it is also necessary to use a RuPt / CeO2 catalyst in which Ru and Pt are in contact. Furthermore, as shown in Figure 3, it was confirmed that LDPE could be hydrolyzed under mild conditions even when the catalyst of Example 3 was used.

[0046] <Polypropylene Hydrogenolysis Test> A hydrogenolysis test of polypropylene (PP) was carried out using the catalyst of Example 1. Specifically, using 0.5 g of PP (number average molecular weight (Mn): 55,300, weight average molecular weight (Mw): 268,100) and 0.1 g of catalyst, a hydrogenolysis reaction was carried out at 200°C under a hydrogen atmosphere of 20 atmospheres (approximately 2.03 MPa) for 48 hours. After the hydrogenolysis reaction, the mixture was allowed to cool to room temperature, and the product was quantified using the procedure described in the low-density polyethylene column.

[0047] The results are shown in Figure 4. As shown in Figure 4, when the catalyst according to Example 1 was used, PP could also be hydrolyzed under mild conditions.

[0048] <Confirming contact between ruthenium particles and platinum particles> The catalysts of Examples 1 and 3 were observed with a high-angle annular dark-field scanning transmission electron microscope (HAADF-STEM) and subjected to elemental analysis by energy dispersive X-ray spectroscopy (EDS elemental analysis). Specifically, the catalyst of Example 1 was observed at a magnification of 6,000,000 times using an HAADF-STEM (JEOL Ltd., "JEM-ARM200F Thermal FE STEM"), resulting in the image shown in FIG. 5A. Furthermore, EDS elemental analysis of the catalyst of Example 1 was performed using a detector attached to the HAADF-STEM, resulting in the image shown in FIG. 5B. In FIG. 5B, bright areas indicate the presence of each element. Furthermore, "Ru+Pt+Ce" is an image in which the three elements ruthenium, platinum, and cerium are superimposed. Ruthenium, shown in pink, and platinum, shown in yellow, overlap, indicating that nano-sized catalyst alloy particles in contact with platinum particles have been obtained.

[0049] Similarly, the catalyst of Example 3 was observed at a magnification of 6,000,000 times using the HAADF-STEM, and the image shown in FIG. 6A was obtained. Furthermore, EDS elemental analysis of the catalyst of Example 3 was performed using a detector attached to the HAADF-STEM, and the image shown in FIG. 6B was obtained. In FIG. 6B, bright areas indicate the presence of each element. Furthermore, "Ru+Pt+Si" is an image in which the three elements ruthenium, platinum, and silicon are superimposed. Since ruthenium, shown in pink, and platinum, shown in yellow, are superimposed, it can be seen that nano-sized catalyst alloy particles in contact with ruthenium particles and platinum particles have been obtained. [Explanation of symbols]

[0050] 10...Supported metal catalyst 11...Carrier 12...Catalytic metal particles 12A...Ruthenium particles 12B...Hydrogen activated metal particles

Claims

1. A supported metal catalyst for use in the hydrolysis of plastics, comprising: a support made of a metal oxide; catalytic metal particles supported on the carrier, the catalytic metal particles including one or more ruthenium particles made of ruthenium and one or more metal particles made of a metal having a function of activating hydrogen; A supported metal catalyst, wherein the metal particles are in contact with the ruthenium particles.

2. 2. The supported metal catalyst of claim 1, wherein said catalytic metal particles are comprised of a ruthenium-based alloy in which said metal is segregated relative to ruthenium.

3. 2. The supported metal catalyst of claim 1, wherein the metal particles are exposed on the surface of the catalytic metal particles.

4. 2. The supported metal catalyst according to claim 1, wherein the molar ratio of the amount of the supported metal to the amount of supported ruthenium is 0.1 or more and 10 or less.

5. 2. The supported metal catalyst of claim 1, wherein the metal is a platinum group metal.

6. 2. The supported metal catalyst according to claim 1, wherein the metal oxide has a function of bringing the ruthenium particles and the metal particles into contact with each other.

7. 2. The supported metal catalyst of claim 1, wherein the metal oxide is ceria or silica.

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