Catalyst and catalyst production method

Abstract

Provided is a catalyst which is used to purify exhaust gas, said catalyst comprising high-entropy alloy particles, wherein: the high-entropy alloy particles each contain a first element group that is at least one element selected from the group consisting of Pd, Pt, Rh, Ir, Ru, and Os, a second element group that is at least one element selected from the group consisting of Ti, V, Cr, Mn, Fe, Co, Ni, and Zn, and a third element group that is at least one element selected from the group consisting of Sc, Cu, Y, Zr, Nb, Mo, Hf, Ta, W, Ag, and Au; and the content of the second element group near the surface of each high-entropy alloy particle is higher than the content of the second element group in the entirety of that high-entropy alloy particle.

Description

Catalysts and methods for producing catalysts

[0001] This invention relates to a catalyst used for purifying exhaust gases and a method for producing the catalyst.

[0002] Traditionally, efforts have been made to mitigate or reduce the impacts of climate change, and research and development are being conducted to reduce the emission of hazardous substances in order to achieve this.

[0003] Patent Document 1 describes a catalyst in which alloy nanoparticles are supported on a carrier. Here, the alloy nanoparticles include at least five types from the group consisting of platinum group elements (Ru, Rh, Pd, Os, Ir, Pt), Ag, Au, Cd, Hg, In, Tl, Sn, Pb, Sb, Bi, Mo, W, Tc, Re, D-block elements of the fourth period (Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn), Ga, Ge, As, H, B, Al, C, Si, N, P, Y, Zr, Nb, lanthanides, Hf, and Ta.

[0004] International Publication No. 2021 / 020377

[0005] However, the catalyst described in Patent Document 1 may experience a decrease in exhaust gas purification performance (durability) after prolonged use, for example.

[0006] The present invention aims to provide a catalyst capable of improving exhaust gas purification performance.

[0007] (1) A catalyst used for purifying exhaust gas, comprising high-entropy alloy particles, wherein the high-entropy alloy particles comprise a first element group consisting of one or more elements selected from the group consisting of Pd, Pt, Rh, Ir, Ru, and Os; a second element group consisting of one or more elements selected from the group consisting of Ti, V, Cr, Mn, Fe, Co, Ni, and Zn; and a third element group consisting of one or more elements selected from the group consisting of Sc, Cu, Y, Zr, Nb, Mo, Hf, Ta, W, Ag, and Au, wherein the content of the second element group near the surface of the high-entropy alloy particles is greater than the total content of the second element group in the high-entropy alloy particles.

[0008] (2) The catalyst according to (1), wherein the first element group contains one or two platinum group elements, and the second element group contains two iron group elements.

[0009] (3) The catalyst according to (2), wherein the first element group contains Pd and Pt, the second element group contains Ni and Fe or Co, and the third element group contains Cu.

[0010] (4) The catalyst according to (3), wherein the high-entropy alloy particles comprise a 5-element alloy.

[0011] (5) The 5-element alloy is represented by the general formula Pd ａ Fe ｂ Pt ｃ Cu ｄ Ni ｅ , or Pd ａ Co ｂ Pt ｃ Cu ｄ Ni ｅ (wherein the sum of a, b, c, d and e is 1, a and b are each independently 0.325 or more and 0.375 or less, c and d are each independently 0.045 or more and 0.055 or less, and e is 0.195 or more and 0.205 or less.), the catalyst according to (4).

[0012] (6) The catalyst according to any one of (1) to (5), wherein the high-entropy alloy particles are supported on a carrier containing a metal oxide.

[0013] (7) The catalyst according to (6), wherein the metal oxide is one or more selected from the group consisting of aluminum oxide, cerium oxide and zirconium oxide.

[0014] (8) A method for producing the catalyst according to any one of (1) to (7), comprising: a step of obtaining a colloidal solution in which colloidal particles containing the first element group, the second element group, and the third element group are dispersed; a step of removing a solvent from the colloidal solution to obtain a powder containing the colloidal particles; and a step of firing the powder in an oxygen-containing atmosphere to obtain a catalyst containing the high-entropy alloy particles.

[0015] According to the present invention, it is possible to provide a catalyst capable of improving exhaust gas purification performance.

[0016] Embodiments of the present invention will be described below.

[0017] [Catalyst] The catalyst of this embodiment is used for purifying exhaust gases. The catalyst of this embodiment is installed, for example, in the exhaust passage of an internal combustion engine to purify the exhaust gases discharged from the internal combustion engine. The internal combustion engine is not particularly limited, but examples include gasoline engines and diesel engines.

[0018] The catalyst of this embodiment includes high-entropy alloy particles. The high-entropy alloy particles include a first element group consisting of one or more elements selected from the group consisting of Pd, Pt, Rh, Ir, Ru, and Os; a second element group consisting of one or more elements selected from the group consisting of Ti, V, Cr, Mn, Fe, Co, Ni, and Zn; and a third element group consisting of one or more elements selected from the group consisting of Sc, Cu, Y, Zr, Nb, Mo, Hf, Ta, W, Ag, and Au. Here, the high-entropy alloy is an alloy composed of five or more elements with high content.

[0019] The content of the second element group near the surface of the high-entropy alloy particles is greater than the total content of the second element group in the high-entropy alloy particles. Therefore, the exhaust gas purification performance of the catalyst in this embodiment is improved. This is presumed to be because the presence of the second element group, along with the first element group, near the surface of the high-entropy alloy particles improves the exhaust gas purification performance of the high-entropy alloy particles.

[0020] The content of the second element group near the surface of the high-entropy alloy particles is measured by X-ray photoelectron spectroscopy (XPS). The overall content of the second element group in the high-entropy alloy particles is measured by inductively coupled plasma atomic emission spectroscopy (ICP-AES).

[0021] The first group of elements preferably includes one or two platinum group elements, and more preferably includes Pd and Pt. This further improves the exhaust gas purification performance of the catalyst in this embodiment.

[0022] The second group of elements preferably includes two iron group elements, and more preferably includes Ni and Fe or Co. This further improves the exhaust gas purification performance of the catalyst in this embodiment.

[0023] The third group of elements preferably includes Cu. This further improves the exhaust gas purification performance of the catalyst in this embodiment.

[0024] The high-entropy alloy particles preferably contain a pentagonal alloy consisting of Pd, Pt, Ni, Fe or Co, and Cu. This further improves the exhaust gas purification performance of the catalyst in this embodiment. In this case, the pentagonal alloy is of the general formula Pd ａ Fe ｂ Pt ｃ Cu ｄ Ni ｅ , or Pd ａ Co ｂ Pt ｃ Cu ｄ Ni ｅ (However, it is preferable that the sum of a, b, c, d, and e is 1, a and b are independently 0.325 or more and 0.375 or less, c and d are independently 0.045 or more and 0.055 or less, and e is 0.195 or more and 0.205 or less.)

[0025] The high-entropy alloy particles are preferably supported on a carrier containing a metal oxide. This further improves the exhaust gas purification performance of the catalyst in this embodiment. The carrier is not particularly limited, but examples include porous powder.

[0026] The metal oxide is preferably one or more selected from the group consisting of aluminum oxide, cerium oxide, and zirconium oxide. This further improves the exhaust gas purification performance of the catalyst in this embodiment.

[0027] The content of high-entropy alloy particles in the catalyst of this embodiment is not particularly limited, but for example, it is 0.1% by mass or more and 10% by mass or less.

[0028] [Method for Producing the Catalyst] The method for producing the catalyst of this embodiment includes the step of obtaining a colloidal solution in which colloidal particles containing a first element group, a second element group, and a third element group are dispersed. When obtaining the colloidal solution, for example, a liquid-phase reduction method is used. In this case, known compounds applicable to the liquid-phase reduction method can be used as precursors for the colloidal particles. Also, known reducing agents applicable to the liquid-phase reduction method can be used.

[0029] The catalyst production method of this embodiment further includes a step of removing the solvent from the colloidal solution to obtain a powder containing colloidal particles. In this case, the solvent may be removed after mixing the colloidal solution with a support containing a metal oxide.

[0030] The catalyst manufacturing method of this embodiment further includes the step of calcining powder in an oxygen-containing atmosphere to obtain a catalyst containing high-entropy alloy particles. At this time, since the second element group is more reactive with oxygen than the first and third element groups, it is presumed that the content of the second element group near the surface of the high-entropy alloy particles will be greater than the total content of the second element group in the high-entropy alloy particles. For this reason, the content of the second element group near the surface of the high-entropy alloy particles changes depending on the oxygen concentration in the atmosphere and the heating temperature.

[0031] The oxygen concentration in the atmosphere is not particularly limited, but for example, it is between 5% by volume and 80% by volume. The heating temperature is not particularly limited, as long as it is possible to form a solid solution, but for example, it is between 100°C and 1000°C.

[0032] Although embodiments of the present invention have been described above, the present invention is not limited to the above embodiments, and the above embodiments may be modified as appropriate within the scope of the spirit of the present invention.

[0033] The following describes embodiments of the present invention, but the present invention is not limited to these embodiments.

[0034] [Example 1] (Pd ０．３５ Fe ０．３５ Pt ０．０５ Cu ０．０５ Ni ０．２ / La-Al２ O ３ Catalyst production) PdCl as a precursor of colloidal particles ２ FeCl ２ 4H ２ O, H ２ PtCl ６ 6H ２ O, CuCl ２ ・2H ２ O and NiCl ２ 6H ２ O, polyvinylpyrrolidone as a protective agent, and pure water were mixed to obtain a mixture. At this time, a precursor of colloidal particles was added so that the composition [at%] of Pd, Fe, Pt, Cu, and Ni was 35:35:5:5:20. Next, NaBH was added as a reducing agent. ４ While adding the ethanol solution to the mixture, the precursor of colloidal particles was reduced in a microreactor to generate colloidal particles and obtain a colloidal solution.

[0035] La-Al in colloidal solution ２ O ３ After adding and mixing the porous powder, the solvent is removed from the mixture using an evaporator, and then La-Al ２ O ３ A powder was obtained in which colloidal particles were supported on a porous powder. Next, the powder was calcined in a muffle furnace at 500°C for 2 hours in an atmospheric atmosphere, and then reduced to Pd ０．３５ Fe ０．３５ Pt ０．０５ Cu ０．０５ Ni ０．２ / La-Al ２ O ３ A catalyst was obtained. At this time, Pd ０．３５ Fe ０．３５ Pt ０．０５ Cu ０．０５ Ni ０．２ / La-Al ２ O ３ The catalyst is Pd ０．３５ Fe ０．３５ Pt ０．０５ Cu ０．０５ Ni ０．２ The content was 3% by mass.

[0036] (Pd ０．３５ Fe０．３５ Pt ０．０５ Cu ０．０５ Ni ０．２ (Composition in the vicinity of the surface of alloy particles) Using an X-ray photoelectron spectrometer KRATOS ULTRA2 (manufactured by Shimadzu Corporation), Pd in the catalyst ０．３５ Fe ０．３５ Pt ０．０５ Cu ０．０５ Ni ０．２ The composition in the vicinity of the surface of the alloy particles was analyzed.

[0037] (Pd ０．３５ Fe ０．３５ Pt ０．０５ Cu ０．０５ Ni ０．２ (Overall composition of alloy particles) Using an emission spectrometer 5800 ICP-OES (manufactured by Agilent Technologies), Pd in the catalyst ０．３５ Fe ０．３５ Pt ０．０５ Cu ０．０５ Ni ０．２ The overall composition of the alloy particles was analyzed.

[0038] Table 1 shows Pd ０．３５ Fe ０．３５ Pt ０．０５ Cu ０．０５ Ni ０．２ The analysis results of the composition [at%] in the vicinity of the surface and the overall composition [at%] of the alloy particles are shown.

[0039]

[0040] From Table 1, it can be seen that the Pd ０．３５ Fe ０．３５ Pt ０．０５ Cu ０．０５ Ni ０．２ alloy particles of Example 1 have a content of the second element group (Fe and Ni) in the vicinity of the surface that is higher than the content of the second element group in the entire alloy particles. Also, it can be seen that the Pd ０．３５ Fe ０．３５ Pt ０．０５ Cu ０．０５ Ni ０．２ overall composition of the alloy particles of Example 1 is substantially the same as the composition of Pd, Fe, Pt, Cu and Ni when blending the colloid particle precursor.

[0041] [Comparative Example 1] (Pt / La-Al ２ O ３ Catalyst Production) H ２ PtCl ６ ·6H ２ O, polyvinylpyrrolidone as a protective agent, and pure water were mixed to obtain a mixed liquid. Next, while adding an ethanol solution of NaBH ４ as a reducing agent to the mixed liquid, the precursor of colloidal particles was reduced in a microreactor to generate colloidal particles, thereby obtaining a colloidal solution.

[0042] La-Al ２ O ３ porous powder was added to the colloidal solution and mixed, then the solvent was removed from the mixed liquid using an evaporator to obtain a powder in which colloidal particles are supported on La-Al ２ O ３ porous powder. Next, the powder was calcined in a muffle furnace at 500°C for 2 hours under an air atmosphere, and then reduced to obtain Pt / La-Al ２ O ３ catalyst. At this time, the Pt content of the Pt / La-Al ２ O ３ catalyst was 3% by mass.

[0043] [Comparative Example 2] (Pt ０．５ Fe ０．５ / La-Al ２ O ３ Catalyst Production) FeCl ２ ·4H ２ O, H ２ PtCl ６ ·6H ２ O, polyvinylpyrrolidone as a protective agent, and pure water were mixed to obtain a mixed liquid. At this time, the precursors of colloidal particles were blended such that the composition [at%] of Fe and Pt was 50:50. Next, while adding an ethanol solution of NaBH ４ as a reducing agent to the mixed liquid, the precursor of colloidal particles was reduced in a microreactor to generate colloidal particles, thereby obtaining a colloidal solution.

[0044] La-Al２ O ３ After adding and mixing the porous powder, the solvent is removed from the mixture using an evaporator, and then La-Al ２ O ３ A powder was obtained in which colloidal particles were supported on a porous powder. Next, the powder was calcined in a muffle furnace at 500°C for 2 hours in an atmospheric atmosphere, and then reduced to Pt ０．５ Fe ０．５ / La-Al ２ O ３ A catalyst was obtained. At this time, Pt ０．５ Fe ０．５ / La-Al ２ O ３ The catalyst is Pt ０．５ Fe ０．５ The content was 3% by mass.

[0045] [Endurance Treatment] The catalyst was subjected to an endurance treatment at 980°C for 32 hours, alternating between a lean atmosphere (20 seconds) and a rich atmosphere (80 seconds).

[0046] [Exhaust Gas Purification Performance] Using a BELREA catalytic reactor (manufactured by Microtrac-Bel), the exhaust gas purification performance (NO conversion rate) of the catalyst before and after durability treatment was evaluated by raising the ambient temperature from 100°C to 500°C. The amount of catalyst used for evaluating exhaust gas purification performance was 100 mg. The model gas composition used for evaluating exhaust gas purification performance was NO (500 ppm), CO (5000 ppm), propylene (400 ppm), H ２ O (10%), O ２ (4900ppm), H ２ (1700ppm), N ２ The residual gas was used, and the flow rate of the model gas was set to 400 mL / min. In addition, before evaluating the exhaust gas purification performance, the catalyst was subjected to a pretreatment in which it was oxidized at 500°C for 15 minutes under an oxygen atmosphere, and then reduced at 500°C for 15 minutes under a hydrogen atmosphere.

[0047] The conversion rate of NO at 350°C was calculated using the formula [(Concentration of NO at the inlet) - (Concentration of NO at the outlet)] / (Concentration of NO at the inlet) × 100.

[0048] Table 2 shows the evaluation results of the catalyst's exhaust gas purification performance at 350°C before and after durability treatment.

[0049]

[0050] Table 2 shows that the catalyst of Example 1 has high exhaust gas purification performance (durability) after durability treatment. In contrast, the catalyst of Comparative Example 1 does not contain the second and third element groups, and therefore has low exhaust gas purification performance (durability) after durability treatment. Similarly, the catalyst of Comparative Example 2 does not contain the third element group, and therefore has low exhaust gas purification performance (durability) after durability treatment.

Claims

1. A catalyst used for purifying exhaust gases, comprising high-entropy alloy particles, wherein the high-entropy alloy particles comprise a first element group consisting of one or more elements selected from the group consisting of Pd, Pt, Rh, Ir, Ru, and Os; a second element group consisting of one or more elements selected from the group consisting of Ti, V, Cr, Mn, Fe, Co, Ni, and Zn; and a third element group consisting of one or more elements selected from the group consisting of Sc, Cu, Y, Zr, Nb, Mo, Hf, Ta, W, Ag, and Au, wherein the content of the second element group near the surface of the high-entropy alloy particles is greater than the total content of the second element group in the high-entropy alloy particles.

2. The catalyst according to claim 1, wherein the first group of elements comprises one or two platinum group elements, and the second group of elements comprises two iron group elements.

3. The catalyst according to claim 2, wherein the first group of elements comprises Pd and Pt, the second group of elements comprises Ni and Fe or Co, and the third group of elements comprises Cu.

4. The catalyst according to claim 3, wherein the high-entropy alloy particles include a pentagonal alloy.

5. The 5-component alloy is represented by the general formula Pd ａ Fe ｂ Pt ｃ Cu ｄ Ni ｅ , or Pd ａ Co ｂ Pt ｃ Cu ｄ Ni ｅ (provided that the sum of a, b, c, d and e is 1, a and b are each independently 0.325 or more and 0.375 or less, c and d are each independently 0.045 or more and 0.055 or less, and e is 0.195 or more and 0.205 or less.) The catalyst according to claim 4, which is represented by 6. The catalyst according to any one of claims 1 to 5, wherein the high-entropy alloy particles are supported on a carrier containing a metal oxide.

7. The catalyst according to claim 6, wherein the metal oxide is one or more selected from the group consisting of aluminum oxide, cerium oxide, and zirconium oxide.

8. A method for producing a catalyst according to any one of claims 1 to 5, comprising the steps of: obtaining a colloidal solution in which colloidal particles comprising the first element group, the second element group, and the third element group are dispersed; removing a solvent from the colloidal solution to obtain a powder comprising the colloidal particles; and calcining the powder in an oxygen-containing atmosphere to obtain a catalyst comprising the high-entropy alloy particles.

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