Catalyst and method for producing catalyst

Abstract

Provided is a catalyst used for purification of exhaust gas, the catalyst containing high-entropy alloy particles, wherein the high-entropy alloy particles include a first element group that is one or more elements selected from the group consisting of Pd, Pt, Rh, Ir, Ru, and Os, a second element group that is one or more elements selected from the group consisting of Ti, V, Cr, Mn, Fe, Co, Ni, and Zn, and a third element group that is one or more elements selected from the group consisting of Sc, Cu, Y, Zr, Nb, Mo, Hf, Ta, W, Ag, and Au; and the content ratio of the second element group in the vicinity of surfaces of the high-entropy alloy particles is greater than the content ratio of the second element group in the entirety of the high-entropy alloy particles.

Description

Catalyst and method for producing catalyst

[0001] The present invention relates to a catalyst used for exhaust gas purification and a method for producing the catalyst.

[0002] Conventionally, efforts aimed at mitigating or reducing the impact of climate change have been continued, and research and development concerning reduction of harmful substance emissions have been carried out toward achieving this goal.

[0003] Patent Document 1 describes a catalyst in which alloy nanoparticles are supported on a carrier. The alloy nanoparticles include platinum group elements (Ru, Rh, Pd, Os, Ir, Pt), Ag, Au, Cd, Hg, In, Tl, Sn, Pb, Sb, Bi, Mo, W, Tc, Re, 4th period D-block elements (Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn), Ga, Ge, As, H, B, Al, C, Si, N, P, Y, Zr, Nb, lanthanoids, Hf and Ta, and contain at least five elements selected from the group consisting of the above.

[0004] International Publication No. 2021 / 020377

[0005] However, the catalyst described in Patent Document 1 may have insufficient exhaust purification performance in some cases.

[0006] An object of the present invention is to provide a catalyst capable of improving exhaust purification performance.

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

[0028] The catalyst manufacturing 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.

[0029] 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.

[0030] 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.

[0031] 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.

[0032] The following describes embodiments of the present invention, but the present invention is not limited to these embodiments.

[0033] [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.

[0034] 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.

[0035] (Pd ０．３５ Fe ０．３５ Pt ０．０５ Cu ０．０５ Ni ０．２ (Composition near the surface of alloy particles) Using the X-ray photoelectron analyzer KRATOS ULTRA2 (manufactured by Shimadzu Corporation), Pd in ​​the catalyst was analyzed. ０．３５ Fe ０．３５ Pt ０．０５ Cu ０．０５ Ni ０．２ The composition of the alloy particles near their surface was analyzed.

[0036] (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 was analyzed. ０．３５ Fe ０．３５ Pt ０．０５ Cu ０．０５ Ni ０．２ The overall composition of the alloy particles was analyzed.

[0037] Table 1 shows Pd ０．３５ Fe ０．３５ Pt ０．０５ Cu ０．０５ Ni ０．２ The analysis results for the composition [at%] near the surface of the alloy particles and the overall composition [at%] are shown.

[0038]

[0039] From Table 1, Pd of Example 1 ０．３５ Fe ０．３５ Pt ０．０５ Cu ０．０５ Ni ０．２ It can be seen that the alloy particles have a higher content of the second element group (Fe and Ni) near the surface than the overall content of the second element group. Also, Pd in ​​Example 1 ０．３５ Fe ０．３５ Pt ０．０５ Cu ０．０５ Ni ０．２ The overall composition of the alloy particles is found to be approximately the same as the composition of Pd, Fe, Pt, Cu, and Ni when blending the colloidal particle precursors.

[0040] [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).

[0041] [Exhaust Gas Purification Performance] Using a BELREA catalytic reactor (manufactured by Microtrac-Bel), the exhaust gas purification performance (NO conversion rate) of the durable catalyst was evaluated by lowering the ambient temperature from 500°C to 200°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.

[0042] Furthermore, the NO conversion rate was calculated using the formula [(NO concentration at the inlet) - (NO concentration at the outlet)] / (NO concentration at the inlet) × 100, and was found to be 35%.

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 five-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 (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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