WO2023198617A2

WO2023198617A2 - Multimetallic alloy transition metal nanoparticles and methods for their production

Info

Publication number: WO2023198617A2
Application number: PCT/EP2023/059220
Authority: WO
Inventors: Carlos Lizandara Pueyo; Knut WITTICH; Nils-Olof Joachim BORN; Oliver Pikhard; Stefan Guenter RESCH; Stephan A Schunk; Matthew T CAUDLE; Fabian Seeler; Andreas Sundermann; Olga Gerlach; Ivana JEVTOVIKJ; Lars Matthes; Sandip DE
Original assignee: Basf Se
Priority date: 2022-04-11
Filing date: 2023-04-06
Publication date: 2023-10-19
Also published as: WO2023198617A3

Abstract

The present invention relates to multimetallic alloy nanoparticles and to processes for its preparation, and in particular to multimetallic alloy nanoparticles, comprising a solid solution comprising three or more transition metals, wherein the three or more transition metals comprise one or more metals M1 selected from the group consisting of Pt, Pd, Au, Ag, Rh, Ir, Os, Ru, and Re, and one or more metals M2 selected from the group consisting of Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Zr, Nb, Mo, Cd, Hf, Ta, and W, wherein the nanoparticles display a mean hydrodynamic particle size DZ in the range of from 10 ± 1 to 1,000 ± 50 nm. Furthermore, the present invention relates to the use of the multimetallic alloy nanoparticles as a catalyst or a precursor thereof, as well as to catalytic conversion methods respectively employing the multimetallic alloy nanoparticles of the invention.

Description

Multimetallic alloy transition metal nanoparticles and methods for their production

TECHNICAL FIELD

The present invention relates to multimetallic alloy nanoparticles and to processes for its preparation, and in particular to multimetallic alloy nanoparticles comprising a solid solution comprising three or more transition metals. Furthermore, the present invention relates to the use of the multimetallic alloy nanoparticles as a catalyst or a precursor thereof, as well as to catalytic conversion methods respectively employing the multimetallic alloy nanoparticles of the invention.

INTRODUCTION

High entropy alloys (HEAs) were theoretically described early in the 80s and 90s. Significant research interest started 10-15 years ago when the world's first high-entropy alloys of metals that can withstand the highest temperatures and pressures for use in industrial and technological applications were discovered. Multimetallic alloys, like HEAs exhibit compelling mechanical properties for structural applications, such as outstanding fracture resistance, ultrahigh ductility and strength, and desirable thermal and physiochemical stabilities. Thus, Z. Li et al. in Nature 2016, 534, pages 227-230 describes metastable high-entropy dual-phase alloys which are able to overcome the strength-ductility trade-off.

However, one of the major challenges for these materials is their synthesis/production at the nanoscale. This step is crucial for the performance and applicability of this class of materials as catalytic materials, and to this date, only few examples are presented in the literature. Thus, Y. Sun and S. Dai in Sci. Adv. 2021 ; 7 : eabg1600 provide an overview of high-entropy materials for catalysis.

Thus, there remains a need for processes which may afford new multimetallic alloys displaying unique properties, in particular relative to their use as catalysts.

DETAILED DESCRIPTION

It was therefore the object of the present invention to provide new ways for synthesizing multimetallic alloys which would lead to new materials displaying new and unique properties, in particular with regard to their use in catalysis. Said object is solved by the inventive processes for the production of multimetallic alloys and the multimetallic alloy materials obtained therefrom. Thus it has quite surprisingly been found that multimetallic alloy nanoparticles may be provided which combine the properties of platinum group metals with those of non-platinum group transition metals in a synergistic manner, such as to obtain highly efficient catalysts both with regard to their catalytic performance as well as with regard to their production and material costs, in particular as supported catalyst materials. In particular, it has unexpectedly found that such multimetallic alloy nanoparticles are highly resistant to hydrothermal aging, in particular with regard to sintering effects and incurring deactivation normally observed in conventional catalyst materials. This applies in particular with regard to conventional platinum group metal catalysts, which are known to suffer reduced activity and/or selectivity in catalysis as a result of sintering due to hydrothermal aging.

Therefore, the present invention relates to a process for the preparation of multimetallic alloy nanoparticles comprising

(i) preparing a multimetallic alloy target comprising, preferably consisting of, a solid solution comprising three or more transition metals, wherein the three or more transition metals comprise, preferably consist of, one or more metals M1 selected from the group consisting of Pt, Pd, Au, Ag, Rh, Ir, Os, Ru, and Re, and one or more metals M2 selected from the group consisting of Ti, V, Or, Mn, Fe, Co, Ni, Cu, Zn, Zr, Nb, Mo, Cd, Hf, Ta, and W;

(ii) submerging the multimetallic alloy target prepared in (i) in an organic solvent system;

(iii) irradiating the surface of the submerged multimetallic alloy target with a laser beam for ablating multimetallic alloy nanoparticles from the surface of the target;

(iv) obtaining a colloidal solution of multimetallic alloy nanoparticles from irradiation in (iii).

In this regard, it is preferred that the one or more metals M1 are selected from the group consisting of Pt, Pd, Ag, Rh, Ir, and Ru, more preferably from the group consisting of Pt, Pd, Ag, and Rh, and more preferably from the group consisting of Pt, Pd, and Rh, wherein more preferably the one or more metals M1 comprise, preferably consist of, Pd and Pt.

It is equally particularly preferred that the one or more metals M1 comprise, preferably consist of, Ru.

It is preferred that the one or more metals M2 are selected from the group consisting of Mn, Fe, Co, Ni, Cu, Zn, and Mo, more preferably from the group consisting of Fe, Co, Ni, and Cu, and more preferably from the group consisting of Fe, Co, and Ni, wherein more preferably the one or more metals M2 comprise, preferably consist of, Fe, Co, and Ni.

It is preferred that the multimetallic alloy target provided in (i) comprises, preferably consists of, a solid solution comprising 4 to 6 transition metals, more preferably comprising 5 transition metals. In particular, it is preferred that the multimetallic alloy target provided in (i) comprises, more preferably consists of, a solid solution consisting of 4 to 6 transition metals, preferably of 5 transition metals.

It is preferred that the transition metals contained in the multimetallic alloy target provided in (i) consist of the metals M1 and M2. It is preferred that the multimetallic alloy target comprises from 1 to 5 transition metals M1 , more preferably from 2 to 5, more preferably from 2 to 4, and more preferably 2 or 3, wherein more preferably the multimetallic alloy target comprises 3 transition metals M1 .

It is preferred that the multimetallic alloy target comprises from 1 to 5 transition metals M2, more preferably from 2 to 5, more preferably from 2 to 4, and more preferably 2 or 3, wherein more preferably the multimetallic alloy target comprises 2 transition metals M1 .

It is preferred that the multimetallic alloy target comprises each of the three or more transition metals in an amount ranging from 100/n ± (100/n)/x mole-% based on 100 mole-% of the transition metals contained in the multimetallic alloy target, wherein n is the total number of the transition metals contained in the multimetallic alloy target, and wherein x is in the range of from 1.01 to 100, more preferably of from 1 .05 to 50, more preferably of from 1 .1 to 10, more preferably of from 1 .5 to 5, and more preferably of from 2 to 3. In this regard, it is particularly preferred that n stands for the total number of the transition metals contained in the multimetallic alloy in an amount of 10 wt.-% or more, calculated as the element and based on 100 wt.-% of the total amount of the transition metals, calculated as the respective element, contained in the multimetallic alloy target, more preferably of 5 wt.-% or more, more preferably of 3 wt.-% or more, more preferably of 2 wt.-% or more, more preferably of 1 wt.-% or more, more preferably of 0.5 wt.-% or more, and more preferably of 0.1 wt.-% or more.

It is preferred that each of the three or more transition metals are contained in the multimetallic alloy target in an amount of 0.1 wt.-% or more, calculated as the element and based on 100 wt.- % of the total amount of the transition metals, calculated as the respective element, contained in the multimetallic alloy target, more preferably of 0.5 wt.-% or more, more preferably of 1 wt.-% or more, more preferably of 2 wt.-% or more, more preferably of 3 wt.-% or more, more preferably of 5 wt.-% or more, and more preferably of 10 wt.-% or more.

It is preferred that in (i) the multimetallic alloy is prepared by melting powders of the three or more transition metals at a temperature in the range of from 800 to 2,500 °C, more preferably from 1 ,000 to 2,200 °C, more preferably from 1 ,200 to 2,000 °C, and more preferably from 1 ,500 to 2,000 °C. In this regard, it is particularly preferred that melting is performed in a furnace, more preferably in an electric arc furnace. Furthermore, and independently thereof, it is particularly preferred that after the cooling of the melted powders, melting is repeated one or more times with the alloy obtained, preferably 3 or more times, more preferably 5 or more times, more preferably 5 to 10 times, more preferably 5 to 8 times, and more preferably 5 or 6 times.

It is preferred that the organic solvent system in (ii) comprises, preferably consists of, one or more organic solvents selected from the group consisting of protic organic solvents, more preferably from the group consisting of C1-C6 alkanols and mixtures thereof, more preferably from the group consisting of C1-C4 alkanols and mixtures thereof, more preferably from the group consisting of C2-C3 alkanols and mixtures thereof, wherein more preferably the organic solvent system comprises, preferably consists of, ethanol. It is preferred that in (ii) one or more stabilizing agents for nanoparticles are dissolved in the organic solvent system, wherein the one or more stabilizing agents comprise, more preferably consist of, one or more polymers, wherein preferably the one or more polymers comprise, preferably consist of, one or more polymers functionalized with pyrrolidone groups, wherein more preferably the one or more polymers comprise, preferably consist of, polyvinylpyrrolidone. In this regard, it is particularly preferred that in (ii) the one or more polymers are dissolved in the organic solvent system in an amount in the range of from 0.01 to 20 g/L, more preferably of from 0.05 to 10 g/L, more preferably of from 0.1 to 5 g/L, more preferably of from 0.3 to 2 g/L, more preferably of from 0.5 to 1.5 g/L, more preferably of from 0.8 to 1.3 g/L, and more preferably of from 0.9 to 1.1 g/L.

It is preferred that in (iii) the laser beam displays a wavelength in the range of from 50 to 5000 nm, more preferably of from 100 to 3000 nm, more preferably of from 300 to 2000 nm, more preferably of from 500 to 1800 nm, more preferably of from 800 to 1500 nm, more preferably of from 1000 to 1200 nm, and more preferably of from 1050 to 1100 nm.

It is preferred that in (iii) the laser beam displays an average laser power in the range of from 5 to 500 W, more preferably of from 10 to 250 W, more preferably of from 20 to 150 W, more preferably of from 40 to 100 W, and more preferably of from 60 to 70 W.

It is preferred that in (iii) the laser beam displays an intensity of from 2 to 50 J/cm² at the surface of the multimetallic alloy target, J/cm², more preferably of from 4 to 25 J/cm², more preferably of from 6 to 20 J/cm², more preferably of from 8 to 18 J/cm², more preferably of from 10 to 16 J/cm², and more preferably of from 12 to 14 J/cm². In this regard, it is particularly preferred that the spot diameter of the layer beam at the surface of the multimetallic alloy target is in the range of from 50 to 2,000 pm, more preferably of from 200 to 1 ,500 pm, more preferably of from 400 to 1 ,200 pm, more preferably of from 500 to 900 pm, and more preferably of from 600 to 800 pm.

It is preferred that in (iii) the laser beam is pulsed, wherein preferably the pulse duration is in the range of from 0.5 to 50 ns, more preferably of from 1 to 30 ns, more preferably of from 2 to 25 ns, more preferably of from 3 to 15 ns, more preferably of from 5 to 11 ns, and more preferably of from 7 to 9 ns. In this regard, it is particularly preferred that in (iii) the repetition rate of the pulse is in the range of from 0.1 to 200 kHz, more preferably of from 0.5 to 150 kHz, more preferably of from 1 to 100 kHz, more preferably of from 2 to 50 kHz, more preferably of from 3 to 15 kHz, and more preferably of from 4 to 6 kHz. Furthermore and independently thereof, it is particularly preferred that in (iii) the pulse power is in the range of from 5 to 120 mJ/pulse, more preferably of from 10 to 80 mJ/pulse, more preferably of from 12 to 50 mJ/pulse, more preferably of from 15 to 30 mJ/pulse, and more preferably of from 18 to 22 mJ/pulse.

It is preferred that in (iii) the organic solvent is circulated, preferably by pumping of the organic solvent. It is preferred that the process further comprises

(v) removing at least a portion of the organic solvent system from the colloidal solution obtained in (iv).

In case where the process further comprises

(v), it is preferred that removal in (v) is achieved by evaporation of the organic solvent system, more preferably by evaporation of the organic solvent system under reduced pressure.

It is preferred that the process further comprises

(vi) impregnation of the colloidal solution obtained in (iv) or (v) onto a support material.

In case where the process further comprises (vi), it is preferred that the support material comprises a metal oxide and/or a metalloid oxide, more preferably a metal oxide, wherein more preferably the support material comprises one or more metal oxides and/or metalloid oxides selected from the group consisting of alumina, silica, silica-alumina, zirconia, ceria, ceriazirconia, and titania, including mixtures and mixed oxides of two or more thereof, preferably from the group consisting of alumina, silica, silica-alumina, zirconia, ceria, and ceria-zirconia, including mixtures and mixed oxides of two or more thereof, more preferably from the group consisting of alumina, silica, and silica-alumina, including mixtures of two or more thereof, wherein more preferably the support material comprises, preferably consists of, alumina and/or silica-alumina, preferably alumina. Furthermore and independently thereof, it is particularly preferred that the support material is a particulate or monolithic support, wherein more preferably the support material is a particulate support material.

In case where the support material is a particulate or monolithic support, it is preferred that the particulate support material displays an average particle size D50 in the range of from 1 to 200 pm, more preferably of from 3 to 120 pm, more preferably of from 5 to 80 pm, more preferably of from 10 to 60 pm, more preferably of from 20 to 50 pm, more preferably of from 25 to 45 pm, and more preferably of from 30 to 40 pm, wherein the average particle size D50 is preferably determined according to ISO 13320:2020. Furthermore and independently thereof, it is particularly preferred that the support material displays a pore volume in the range of from 0.1 to 5.0 ml/g, more preferably of from 0.3 to 3.0 ml/g, more preferably of from 0.5 to 2.0 ml/g, more preferably of from 0.6 to 1 .5 ml/g, more preferably of from 0.7 to 1 .0 ml/g, and more preferably of from 0.8 to 0.9 ml/g, wherein the pore volume is preferably determined according to ISO 15901- 2:2022. Furthermore and independently thereof, it is particularly preferred that the support material displays an average pore diameter in the range of from 1 to 50 nm, more preferably of from 3 to 30 nm, more preferably of from 5 to 20 nm, more preferably of from 8 to 15 nm, and more preferably of from 10 to 12 nm, wherein the average pore diameter is preferably determined according to ISO 15901-2:2022.

Furthermore and independently thereof, it is particularly preferred that the loading of the multi- metallic alloy nanoparticles on the support material is in the range of from 0.005 to 10 based on 100 wt.-% of the loaded support material, more preferably of from 0.01 to 5 wt.-%, more prefer- ably of from 0.015 to 1.0 wt.-%, more preferably of from 0.02 to 0.5 wt.-%, more preferably of from 0.025 to 0.1 wt.-%, and more preferably of from 0.03 to 0.05 wt.-%.

Furthermore and independently thereof, it is particularly preferred that impregnation in (vi) is performed as an impregnation by incipient wetness or as a wet impregnation, more preferably as a wet impregnation.

Furthermore and independently thereof, it is particularly preferred that during the impregnation in (vi) the organic solvent system is continuously removed, more preferably by evaporation of the organic solvent, more preferably by evaporation of the organic solvent under reduced pressure.

The present invention also relates to a process for the preparation of multimetallic alloy nanoparticles comprising

(1) preparing a solution comprising, preferably consisting of, one or more surfactants and three or more transition metal compounds dissolved in an organic solvent system, wherein the three or more transition metal compounds comprise, preferably consist of, one or more compounds of one or more metals M1 selected from the group consisting of Pt, Pd, Au, Ag, Rh, Ir, Os, Ru, and Re, and one or more compounds of one or more metals M2 selected from the group consisting of Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Zr, Nb, Mo, Cd, Hf, Ta, and W;

(2) adding a reducing agent to the solution prepared in (1 );

(3) heating the reaction mixture obtained in (2) for obtaining a colloidal solution of multimetallic alloy nanoparticles;

(4) cooling the mixture obtained in (3);

(5) isolating the colloidal fraction obtained in (4).

It is equally preferred that the one or more metals M1 comprise, preferably consist of, Ru.

It is preferred that the solution prepared in (1) comprises from 4 to 6 transition metals, and more preferably comprises 5 transition metals. It is preferred that the transition metals contained in the solution prepared in (1) consist of the metals M1 and M2.

It is preferred that the solution prepared in (1) comprises from 1 to 5 transition metals M1 , more preferably from 2 to 5, more preferably from 2 to 4, and more preferably 2 or 3, wherein more preferably the solution prepared in (1 ) comprises 3 transition metals M1 .

It is preferred that the solution prepared in (1) comprises from 1 to 5 transition metals M2, more preferably from 2 to 5, more preferably from 2 to 4, and more preferably 2 or 3, wherein more preferably the solution prepared in (1 ) comprises 2 transition metals M 1.

It is preferred that the solution prepared in (1) comprises each of the three or more transition metals in an amount ranging from 100/n ± (100/n)/x mole-% based on 100 mole-% of the transition metals contained in the solution prepared in (1 ), wherein n is the total number of the transition metals contained in the solution prepared in (1 ), and wherein x is in the range of from 1.01 to 100, more preferably of from 1.05 to 50, more preferably of from 1.1 to 10, more preferably of from 1 .5 to 5, and more preferably of from 2 to 3. In this regard, it is particularly preferred that n stands for the total number of the transition metals contained in the solution prepared in (1) in an amount of 10 wt.-% or more, calculated as the element and based on 100 wt.-% of the total amount of the transition metals, calculated as the respective element, contained in the solution prepared in (1 ), more preferably of 5 wt.-% or more, more preferably of 3 wt.-% or more, more preferably of 2 wt.-% or more, more preferably of 1 wt.-% or more, more preferably of 0.5 wt.-% or more, and more preferably of 0.1 wt.-% or more.

It is preferred that each of the three or more transition metals are contained in the solution prepared in (1) in an amount of 0.1 wt.-% or more, calculated as the element and based on 100 wt.-% of the total amount of the transition metals, calculated as the respective element, contained in the solution prepared in (1), more preferably of 0.5 wt.-% or more, more preferably of 1 wt.-% or more, more preferably of 2 wt.-% or more, more preferably of 3 wt.-% or more, more preferably of 5 wt.-% or more, and more preferably of 10 wt.-% or more.

It is preferred that the one or more transition metal compounds are provided as salts, more preferably as halides and/or complex salts, more preferably as chlorides and/or chlorometalate complexes and/or as metal acetylacetonates, wherein more preferably the one or more transition metal compounds are provided as metal acetylacetonates.

It is preferred that the organic solvent system in (1 ) comprises, preferably consists of, one or more non-polar solvents, wherein preferably the one or more non-polar solvents are selected from the group consisting of diphenyl ether, n-hexane, benzene, toluene, and 1 ,4-dioxane, including mixtures of two or more thereof, wherein more preferably the organic solvent system in (1 ) comprises, preferably consists of, diphenyl ether. It is preferred that the organic solvent in 1 comprises 0.1 wt.-% or less of H2O based on 100 wt.- % of the organic solvent system, more preferably 0.05 wt.-% or less, more preferably 0.01 wt.-% or less, more preferably 0.005 wt.-% or less, more preferably 0.001 wt.-% or less, more preferably 0.0005 wt.-% or less, and more preferably 0.0001 wt.-% or less.

It is preferred that in (1) the one or more surfactants are selected from nonionic surfactants, more preferably from the group consisting of (Cs-C22)fatty acids, (Cs-C22)fatty amines, (Cs- C22)alcohols, (C6-C2o)alcohol ethoxylates with 1 to 8 ethylene oxide units, (Ce-C2o)alkyl polyglycosides, polyoxyethylene glycol alkyl ethers, polyoxypropylene glycol alkyl ethers, glucoside alkyl ethers, polyoxyethylene glycol alkylphenol ethers, glycerol alkyl esters, sorbitan alkyl esters, polyoxyethylene glycol sorbitan alkyl esters, cocamide monoethanolamine, cocamide diethanolamine, dodecyldimethylamine oxide, block copolymers of polyethylene glycol and polypropylene glycol, polyethoxylated tallow amine, and mixtures of two or more thereof, wherein more preferably the one or more nonionic surfactants are selected from the group consisting of (Ci4-C2o)fatty acids, (Ci4-C2o)fatty amines, (Ci4-C2o)alcohols, (C8-Cis)alcohol ethoxylates with 2 to 6 ethylene oxide units, (Cs-Ci8)alkyl polyglycosides, octaethylene glycol monododecyl ether and/or pentaethylene glycol monododecyl ether, polyoxypropylene glycol alkyl ethers, decyl glucoside, lauryl glucoside, myristil glucoside, octyl glucoside, polyoxyethylene glycol octylphenol ethers, preferably triton X-100, nonoxynol-9, glyceryl laurate, polyglycerol polyricinoleate, sorbitan monolaurate, sorbitan monopalmitate, sorbitan monostearate, sorbitan monooleate, polyoxyethylene sorbitan monolaurate, polyoxyethylene sorbitan monopalmitate, polyoxyethylene sorbitan monostearate, polyoxyethylene sorbitan monooleate, cocamide monoethanolamine, cocamide diethanolamine, dodecyldimethylamine oxide, block copolymers of polyethylene glycol and polypropylene glycol, polyethoxylated tallow amine, and mixtures of two or more thereof, wherein more preferably the one or more nonionic surfactants are selected from the group consisting of (Ci6-Cis)fatty acids, (Ci6-Cis)fatty amines, (Ci6-Ci8)alcohols, (Ci6-Ci8)alcohol ethoxylates with 2 to 6 ethylene oxide units, (Cs-Ci4)alkyl polyglycosides, preferably cetyl alcohol, stearyl alcohol, oleyl alcohol, and mixtures of two or more thereof, octaethylene glycol monododecyl ether and/or pentaethylene glycol monododecyl ether, polyoxypropylene glycol alkyl ethers, decyl glucoside, lauryl glucoside, myristil glucoside, octyl glucoside, polyoxyethylene glycol octylphenol ethers, nonoxynol-9, glyceryl laurate, polyglycerol polyricinoleate, sorbitan monolaurate, sorbitan monopalmitate, sorbitan monostearate, sorbitan oleate, polyoxyethylene (20) sorbitan monolaurate, polyoxyethylene (20) sorbitan monopalmitate, polyoxyethylene (20) sorbitan monostearate, polyoxyethylene (20) sorbitan monooleate, cocamide monoethanolamine, cocamide diethanolamine, dodecyldimethylamine oxide, block copolymers of polyethylene glycol and polypropylene glycol, polyethoxylated tallow amine, Stearyl-EC>2, poly- glyceryl-2-dipolyhydroxystearate, polyglyceryl-distearate, C13/15 - PEG3, C13 - PEG2, glyceryl monooleate, C16/18 - PEG2, oleyl - PEG2, PEG20 - sorbitan monooleate, functionalized polyisobutene, C16/18 - PEG9, and mixtures of two or more thereof, more preferably from the group consisting of (Cis)fatty acids, (Cis)fatty amines, polyglyceryl-2-dipolyhydroxystearate, diglycer- yl-distearate, triglyceryl-distearate, C13/15 - PEG3, C13 - PEG2, glyceryl monooleate, sorbitan monooleate, polyglycerol-3-polyricinoleate, C16/18 - PEG2, oleyl - PEG2, PEG20 - sorbitan monooleate, functionalized polyisobutene, C16/18 - PEG9, and mixtures of two or more thereof, more preferably from the group consisting of oleic acid, oleylamine, polyglyceryl-2- dipolyhydroxystearate, diglyceryl-distearate, triglyceryl-distearate, and mixtures of two or more thereof, wherein more preferably the one or more surfactants in (1 ) comprise, preferably consist of, oleic acid and/or oleylamine, wherein more preferably the one or more surfactants in (1 ) comprise, preferably consist of, oleic acid and oleylamine.

In case where in (1) the one or more surfactants are selected from nonionic surfactants, it is preferred that the one or more surfactants in (1) comprise, preferably consist of, oleic acid and oleylamine, wherein the oleic acid : oleylamine molar ratio of oleic acid to oleylamine in the solution prepared in (1 ) is in the range of from 5:95 to 95:5, more preferably of from 10:90 to 90:10, more preferably of from 30:70 to 70:30, more preferably of from 40:60 to 60:40, and more preferably of from 45:55 to 55:45.

It is preferred that in (1) the one or more surfactants are dissolved in the organic solvent system in an amount in the range of from 5 to 500 g/L, more preferably of from 5 to 500 g/L, more preferably of from 10 to 300 g/L, more preferably of from 30 to 250 g/L, more preferably of from 50 to 200 g/L, more preferably of from 80 to 150 g/L, more preferably of from 100 to 130 g/L, and more preferably of from 115 to 120 g/L.

It is preferred that in (2) the one or more reducing agents comprise, more preferably consist of, one or more hydrides, preferably one or more ionic hydrides, more preferably one or more hydrides selected from the group consisting of alkali metal hydrides, more preferably one or more hydrides selected from the group consisting of sodium borohydride, lithium aluminum hydride, lithium triethylborohydride, wherein more preferably the one or more hydrides comprise, preferably consist of, lithium triethylborohydride.

It is preferred that in (2) the solution is heated to a temperature in the range of from 50 to 200 °C, more preferably of from 80 to 160 °C, more preferably of from 100 to 140 °C, and more preferably of from 115 to 125 °C.

It is preferred that in (3) the reaction mixture obtained in (2) is heated to a maximum temperature in the range of from 120 to 350 °C, more preferably of from 150 to 300 °C, more preferably of from 180 to 280 °C, more preferably of from 220 to 270 °C, and more preferably of from 240 to 260 °C. In particular, it is preferred that in (3) the reaction mixture obtained in (2) is heated to the maximum temperature at a rate comprised in the range of from 5 to 360 °C/h, more preferably of from 10 to 240 °C/h, more preferably of from 20 to 180 °C/h, more preferably of from 30 to 120 °C/h, more preferably of from 35 to 60 °C/h, and more preferably of from 40 to 45 °C/h. Furthermore and independently thereof, it is particularly preferred that in (3) heating is stopped when having reached the maximum temperature.

It is preferred that in (4) the mixture obtained in (3) is cooled to a temperature in the range of from 0 to 50 °C, more preferably of from 5 to 40 °C, more preferably of from 10 to 35 °C, more preferably of from 15 to 30 °C, and more preferably of from 20 to 25 °C. It is preferred that isolating in (5) is achieved by centrifugation.

It is preferred that the process further comprises

(6) suspending the colloidal fraction obtained in (5) in an organic solvent system.

It is preferred that the organic solvent system in (ii) comprises, more preferably consists of, one or more organic solvents selected from the group consisting of protic organic solvents, preferably from the group consisting of C1-C6 alkanols and mixtures thereof, more preferably from the group consisting of C1-C4 alkanols and mixtures thereof, more preferably from the group consisting of C2-C3 alkanols and mixtures thereof, wherein more preferably the organic solvent system comprises, preferably consists of, ethanol.

It is preferred that the process further comprises

(7) impregnation of the colloidal solution obtained in (6) onto a support material.

In case where the process further comprises (7), it is preferred that the support material comprises a metal oxide and/or a metalloid oxide, more preferably a metal oxide, wherein more preferably the support material comprises one or more metal oxides and/or metalloid oxides selected from the group consisting of alumina, silica, silica-alumina, zirconia, ceria, ceriazirconia, and titania, including mixtures and mixed oxides of two or more thereof, preferably from the group consisting of alumina, silica, silica-alumina, zirconia, ceria, and ceria-zirconia, including mixtures and mixed oxides of two or more thereof, more preferably from the group consisting of alumina, silica, and silica-alumina, including mixtures of two or more thereof, wherein more preferably the porous support material comprises, preferably consists of, alumina and/or silica-alumina, preferably alumina. Furthermore and independently thereof, it is particularly preferred that the support material is a particulate or monolithic support, wherein preferably the support material is a particulate support material. In this regard, it is particularly preferred that the particulate support material displays an average particle size D50 in the range of from 1 to 200 pm, more preferably of from 3 to 120 pm, more preferably of from 5 to 80 pm, more preferably of from 10 to 60 pm, more preferably of from 20 to 50 pm, more preferably of from 25 to 45 pm, and more preferably of from 30 to 40 pm, wherein the average particle size D50 is preferably determined according to ISO 13320:2020.

Furthermore and independently thereof, it is preferred that the support material displays a pore volume in the range of from 0.1 to 5.0 ml/g, more preferably of from 0.3 to 3.0 ml/g, more preferably of from 0.5 to 2.0 ml/g, more preferably of from 0.6 to 1 .5 ml/g, more preferably of from 0.7 to 1 .0 ml/g, and more preferably of from 0.8 to 0.9 ml/g, wherein the pore volume is preferably determined according to ISO 15901-2:2022.

Furthermore and independently thereof, it is preferred that the support material displays an average pore diameter in the range of from 1 to 50 nm, more preferably of from 3 to 30 nm, more preferably of from 5 to 20 nm, more preferably of from 8 to 15 nm, and more preferably of from 10 to 12 nm, wherein the average pore diameter is preferably determined according to ISO 15901-2:2022.

Furthermore and independently thereof, it is preferred that the loading of the multimetallic alloy nanoparticles on the support material is in the range of from 0.005 to 10 based on 100 wt.-% of the loaded support material, more preferably of from 0.01 to 5 wt.-%, more preferably of from 0.015 to 1.0 wt.-%, more preferably of from 0.02 to 0.5 wt.-%, more preferably of from 0.025 to 0.1 wt.-%, and more preferably of from 0.03 to 0.05 wt.-%.

Furthermore and independently thereof, it is preferred that impregnation in (7) is performed as an impregnation by incipient wetness or as a wet impregnation, more preferably as a wet impregnation.

Furthermore and independently thereof, it is preferred that during the impregnation in (7) the organic solvent system is continuously removed, more preferably by evaporation of the organic solvent, more preferably by evaporation of the organic solvent under reduced pressure.

The present invention also relates to multimetallic alloy nanoparticles obtainable or obtained according to the process of any one of the particular and preferred embodiments of the inventive processes for the preparation of multimetallic alloy nanoparticles.

Furthermore, the present invention relates to multimetallic alloy nanoparticles, preferably obtainable or obtained according to the process of any one of the particular and preferred embodiments of the inventive processes for the preparation of multimetallic alloy nanoparticles , comprising, preferably consisting of, a solid solution comprising three or more transition metals, wherein the three or more transition metals comprise, preferably consist of, one or more metals M1 selected from the group consisting of Pt, Pd, Au, Ag, Rh, Ir, Os, Ru, and Re, and one or more metals M2 selected from the group consisting of Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Zr, Nb, Mo, Cd, Hf, Ta, and W, wherein the nanoparticles display a mean hydrodynamic particle size Dz in the range of from 10 ± 1 to 1 ,000 ± 50 nm, preferably of from 30 ± 2 to 500 ± 30 nm, more preferably of from 50 ± 5 to 300 ± 20 nm, more preferably of from 80 to 250 ± 10 nm, more preferably of from 100 to 220 ± 10 nm, more preferably of from 125 to 200 ± 10 nm, more preferably of from 130 to 180 ± 10 nm, and more preferably of from 140 to 160 ± 10 nm, wherein the mean hydrodynamic particle size Dz of the nanoparticles is preferably determined by dynamic light scattering, more preferably according to ISO 22412:2017.

In this regard, it is preferred that the multimetallic alloy nanoparticles display a mean hydrodynamic particle size Dz in the range of from 10 ± 1 to 150 ± 10 nm, more preferably of from 20 ± 2 to 100 ± 10 nm, more preferably of from 25 ± 2 to 80 ± 10 nm, more preferably of from 30 ± 2 to 60 ± 5 nm, more preferably of from 35 to 50 ± 5 nm, and more preferably of from 40 to 45 ± 5 nm. It is preferred that the multimetallic alloy nanoparticles display a mean particle size in the range of from 0.5 to 50 nm, more preferably of from 1 to 20 nm, more preferably of from 1.2 to 10 nm, more preferably of from 1.5 to 5.0 nm, more preferably of from 1.8 to 3.0 nm, more preferably of from 2.0 to 2.5 nm, and more preferably of from 2.1 to 2.3 nm, wherein the mean particle size is preferably determined by transmission electron microscopy (TEM), more preferably according to ISO 21363:2020.

It is preferred that one or more metals M1 are selected from the group consisting of Pt, Pd, Ag, Rh, Ir, and Ru, more preferably from the group consisting of Pt, Pd, Ag, and Rh, and more preferably from the group consisting of Pt, Pd, and Rh, wherein more preferably the one or more metals M1 comprise, preferably consist of, Pd and Rh.

It is preferred that the multimetallic alloy nanoparticles comprise, preferably consist of, a solid solution comprising 4 to 6 transition metals, more preferably comprising 5 transition metals. In particular, it is preferred that the multimetallic nanoparticles comprise, preferably consists of, a solid solution consisting of 4 to 6 transition metals, more preferably of 5 transition metals.

It is preferred that the transition metals contained in the multimetallic alloy nanoparticles consist of the metals M1 and M2.

It is preferred that the multimetallic alloy nanoparticles comprise from 1 to 5 transition metals M1 , more preferably from 2 to 5, more preferably from 2 to 4, and more preferably 2 or 3, wherein more preferably the multimetallic alloy nanoparticles comprise 3 transition metals M1.

It is preferred that the multimetallic alloy nanoparticles comprise from 1 to 5 transition metals M2, more preferably from 2 to 5, more preferably from 2 to 4, and more preferably 2 or 3, wherein more preferably the multimetallic alloy nanoparticles comprise 2 transition metals M1 .

It is preferred that the multimetallic alloy nanoparticles comprise each of the three or more transition metals in an amount ranging from 100/n ± (100/n)/x mole-%, wherein n is the total number of the transition metals contained in the multimetallic alloy nanoparticles, and wherein x is in the range of from 1.01 to 100, more preferably of from 1.05 to 50, more preferably of from 1 .1 to 10, more preferably of from 1 .5 to 5, and more preferably of from 2 to 3. In this regard, it is particularly preferred that n stands for the total number of the transition metals contained in the multimetallic alloy nanoparticles in an amount of 10 wt.-% or more, calculated as the element and based on 100 wt.-% of the total amount of the transition metals, calculated as the respective element, contained in the multimetallic alloy nanoparticles, more preferably of 5 wt.-% or more, more preferably of 3 wt.-% or more, more preferably of 2 wt.-% or more, more preferably of 1 wt.-% or more, more preferably of 0.5 wt.-% or more, and more preferably of 0.1 wt.-% or more.

It is preferred that each of the three or more transition metals are contained in the multimetallic alloy nanoparticles in an amount of 0.1 wt.-% or more, calculated as the element and based on 100 wt.-% of the total amount of the transition metals, calculated as the respective element, contained in the multimetallic alloy nanoparticles, more preferably of 0.5 wt.-% or more, more preferably of 1 wt.-% or more, more preferably of 2 wt.-% or more, more preferably of 3 wt.-% or more, more preferably of 5 wt.-% or more, and more preferably of 10 wt.-% or more.

It is preferred that the multimetallic alloy nanoparticles are supported on a support material. In this regard, it is preferred that the support material comprises a metal oxide and/or a metalloid oxide, more preferably a metal oxide, wherein more preferably the support material comprises one or more metal oxides and/or metalloid oxides selected from the group consisting of alumina, silica, silica-alumina, zirconia, ceria, ceria-zirconia, and titania, including mixtures and mixed oxides of two or more thereof, preferably from the group consisting of alumina, silica, silica- alumina, zirconia, ceria, and ceria-zirconia, including mixtures and mixed oxides of two or more thereof, more preferably from the group consisting of alumina, silica, and silica-alumina, including mixtures of two or more thereof, wherein more preferably the support material comprises, preferably consists of, alumina and/or silica-alumina, preferably alumina. Furthermore and independently thereof, it is preferred that the support material is a particulate support material or a monolithic support, wherein more preferably the support material is a particulate support material.

Furthermore and independently thereof, it is preferred that the loading of the multimetallic alloy nanoparticles on the support material is in the range of from 0.005 to 10 based on 100 wt.-% of the loaded support material, more preferably of from 0.01 to 5 wt.-%, more preferably of from 0.015 to 1.0 wt.-%, more preferably of from 0.02 to 0.5 wt.-%, more preferably of from 0.025 to 0.1 wt.-%, and more preferably of from 0.03 to 0.05 wt.-%. The present invention also relates to a method for the treatment of an exhaust gas comprising CO, NO_X, and hydrocarbons, said method comprising

(A) providing a gas stream comprising CO, NO_X, and hydrocarbons;

(B) contacting the gas stream provided in (A) with a catalyst comprising multimetallic alloy nanoparticles according to any one of the particular and preferred embodiments of the present invention.

Furthermore, the present invention relates to a method for the treatment of an exhaust gas comprising NH3 and oxygen, said method comprising

(A’) providing a gas stream comprising NH3 and oxygen;

(B’) contacting the gas stream provided in (A’) with a catalyst comprising multimetallic alloy nanoparticles according to any one of the particular and preferred embodiments of the present invention.

Furthermore and independently thereof, it is preferred that the exhaust has stream provided in (A) or (A’) is from an internal combustion engine, more preferably from a lean burn combustion engine, and more preferably from a diesel engine or lean burn gasoline engine.

In addition thereto, the present invention relates to a method for the reforming of ammonia, wherein the process comprises

(A”) providing a reactor containing a catalyst comprising multimetallic alloy nanoparticles according to any one of the particular and preferred embodiments of the present invention;

(B”) preparing a feed gas stream comprising NH3;

(C”) feeding the feed gas stream prepared in (B”) into the reactor provided in (A”) and contacting the feed gas stream with the catalyst;

(D”) removing an effluent gas stream from the reactor, the effluent gas stream comprising H2 and N2.

The present invention also relates to the use of multimetallic alloy nanoparticles according to any one of the particular and preferred embodiments of the present invention as a catalyst or a precursor thereof, preferably as a catalyst for the conversion of NO, CO, and/or hydrocarbons; for the selective catalytic reduction (SCR) of nitrogen oxides NO_X; for the oxidation of NH3, in particular for the oxidation of NH3 slip; for the decomposition of N2O; as a catalyst in fluid catalytic cracking (FCC) processes; for NH3 reforming; and/or as a catalyst in organic conversion reactions, preferably in the conversion of alcohols to olefins, and more preferably in methanol to olefin (MTO) catalysis; and more preferably as a three-way catalyst for the conversion of NO, CO, and hydrocarbons.

The present invention is further illustrated by the following set of embodiments and combinations of embodiments resulting from the dependencies and back-references as indicated. In particular, it is noted that in each instance where a range of embodiments is mentioned, for example in the context of a term such as "The process of any one of embodiments 1 to 4", every embodiment in this range is meant to be explicitly disclosed for the skilled person, i.e. the word- ing of this term is to be understood by the skilled person as being synonymous to "The process of any one of embodiments 1 , 2, 3, and 4". Further, it is explicitly noted that the following set of embodiments is not the set of claims determining the extent of protection, but represents a suitably structured part of the description directed to general and preferred aspects of the present invention.

1 . A process for the preparation of multimetallic alloy nanoparticles comprising

(i) preparing a multimetallic alloy target comprising, preferably consisting of, a solid solution comprising three or more transition metals, wherein the three or more transition metals comprise, preferably consist of, one or more metals M1 selected from the group consisting of Pt, Pd, Au, Ag, Rh, Ir, Os, Ru, and Re, and one or more metals M2 selected from the group consisting of Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Zr, Nb, Mo, Cd, Hf, Ta, and W;

2. The process of embodiment 1 , wherein the one or more metals M1 are selected from the group consisting of Pt, Pd, Ag, Rh, Ir, and Ru, preferably from the group consisting of Pt, Pd, Ag, and Rh, and more preferably from the group consisting of Pt, Pd, and Rh, wherein more preferably the one or more metals M1 comprise, preferably consist of, Pd and Pt.

3. The process of embodiment 1 or 2, wherein the one or more metals M 1 comprise, preferably consist of, Ru.

4. The process of any of embodiments 1 to 3, wherein the one or more metals M2 are selected from the group consisting of Mn, Fe, Co, Ni, Cu, Zn, and Mo, preferably from the group consisting of Fe, Co, Ni, and Cu, and more preferably from the group consisting of Fe, Co, and Ni, wherein more preferably the one or more metals M2 comprise, preferably consist of, Fe, Co, and Ni.

5. The process of any of embodiments 1 to 4, wherein the multimetallic alloy target provided in (i) comprises, preferably consists of, a solid solution comprising 4 to 6 transition metals, preferably comprising 5 transition metals.

6. The process of embodiment 5, wherein the multimetallic alloy target provided in (i) comprises, preferably consists of, a solid solution consisting of 4 to 6 transition metals, preferably of 5 transition metals. 7. The process of any of embodiments 1 to 6, wherein the transition metals contained in the multimetallic alloy target provided in (i) consist of the metals M1 and M2.

8. The process of any of embodiments 1 to 7, wherein the multimetallic alloy target comprises from 1 to 5 transition metals M 1 , preferably from 2 to 5, more preferably from 2 to 4, and more preferably 2 or 3, wherein more preferably the multimetallic alloy target comprises 3 transition metals M1.

9. The process of any of embodiments 1 to 8, wherein the multimetallic alloy target comprises from 1 to 5 transition metals M2, preferably from 2 to 5, more preferably from 2 to 4, and more preferably 2 or 3, wherein more preferably the multimetallic alloy target comprises 2 transition metals M1.

10. The process of any of embodiments 1 to 9, wherein the multimetallic alloy target comprises each of the three or more transition metals in an amount ranging from 100/n ± (100/n)/x mole-% based on 100 mole-% of the transition metals contained in the multimetallic alloy target, wherein n is the total number of the transition metals contained in the multimetallic alloy target, and wherein x is in the range of from 1.01 to 100, preferably of from 1.05 to 50, more preferably of from 1.1 to 10, more preferably of from 1 .5 to 5, and more preferably of from 2 to 3.

11 . The process of embodiment 10, wherein n stands for the total number of the transition metals contained in the multimetallic alloy in an amount of 10 wt.-% or more, calculated as the element and based on 100 wt.-% of the total amount of the transition metals, calculated as the respective element, contained in the multimetallic alloy target, preferably of 5 wt.-% or more, more preferably of 3 wt.-% or more, more preferably of 2 wt.-% or more, more preferably of 1 wt.-% or more, more preferably of 0.5 wt.-% or more, and more preferably of 0.1 wt.-% or more.

12. The process of any of embodiments 1 to 11 , wherein each of the three or more transition metals are contained in the multimetallic alloy target in an amount of 0.1 wt.-% or more, calculated as the element and based on 100 wt.-% of the total amount of the transition metals, calculated as the respective element, contained in the multimetallic alloy target, preferably of 0.5 wt.-% or more, more preferably of 1 wt.-% or more, more preferably of 2 wt.-% or more, more preferably of 3 wt.-% or more, more preferably of 5 wt.-% or more, and more preferably of 10 wt.-% or more.

13. The process of any of embodiments 1 to 12, wherein in (i) the multimetallic alloy is prepared by melting powders of the three or more transition metals at a temperature in the range of from 800 to 2,500 °C, preferably from 1 ,000 to 2,200 °C, more preferably from 1 ,200 to 2,000 °C, and more preferably from 1 ,500 to 2,000 °C. 14. The process of embodiment 13, wherein melting is performed in a furnace, preferably in an electric arc furnace.

15. The process of embodiment 13 or 14, wherein after the cooling of the melted powders, melting is repeated one or more times with the alloy obtained, preferably 3 or more times, preferably 5 or more times, more preferably 5 to 10 times, more preferably 5 to 8 times, and more preferably 5 or 6 times.

16. The process of any of embodiments 1 to 15, wherein the organic solvent system in (ii) comprises, preferably consists of, one or more organic solvents selected from the group consisting of protic organic solvents, preferably from the group consisting of C1-C6 alkanols and mixtures thereof, more preferably from the group consisting of C1-C4 alkanols and mixtures thereof, more preferably from the group consisting of C2-C3 alkanols and mixtures thereof, wherein more preferably the organic solvent system comprises, preferably consists of, ethanol.

17. The process of any of embodiments 1 to 16, wherein in (ii) one or more stabilizing agents for nanoparticles are dissolved in the organic solvent system, wherein the one or more stabilizing agents comprise, preferably consist of, one or more polymers, wherein preferably the one or more polymers comprise, preferably consist of, one or more polymers functionalized with pyrrolidone groups, wherein more preferably the one or more polymers comprise, preferably consist of, polyvinylpyrrolidone.

18. The process of embodiment 17, wherein in (ii) the one or more polymers are dissolved in the organic solvent system in an amount in the range of from 0.01 to 20 g/L, preferably of from 0.05 to 10 g/L, more preferably of from 0.1 to 5 g/L, more preferably of from 0.3 to 2 g/L, more preferably of from 0.5 to 1 .5 g/L, more preferably of from 0.8 to 1 .3 g/L, and more preferably of from 0.9 to 1.1 g/L.

19. The process of any of embodiments 1 to 18, wherein in (iii) the laser beam displays a wavelength in the range of from 50 to 5000 nm, preferably of from 100 to 3000 nm, more preferably of from 300 to 2000 nm, more preferably of from 500 to 1800 nm, more preferably of from 800 to 1500 nm, more preferably of from 1000 to 1200 nm, and more preferably of from 1050 to 1100 nm.

20. The process of any of embodiments 1 to 19, wherein in (iii) the laser beam displays an average laser power in the range of from 5 to 500 W, preferably of from 10 to 250 W, more preferably of from 20 to 150 W, more preferably of from 40 to 100 W, and more preferably of from 60 to 70 W.

21 . The process of any of embodiments 1 to 20, wherein in (iii) the laser beam displays an intensity of from 2 to 50 J/cm² at the surface of the multimetallic alloy target, J/cm², preferably of from 4 to 25 J/cm², more preferably of from 6 to 20 J/cm², more preferably of from 8 to 18 J/cm², more preferably of from 10 to 16 J/cm², and more preferably of from 12 to 14 J/cm². The process of embodiment 21 , wherein the spot diameter of the layer beam at the surface of the multimetallic alloy target Is in the range of from 50 to 2,000 pm, preferably of from 200 to 1 ,500 pm, more preferably of from 400 to 1 ,200 pm, more preferably of from 500 to 900 pm, and more preferably of from 600 to 800 pm. The process of any of embodiments 1 to 22, wherein in (iii) the laser beam is pulsed, wherein preferably the pulse duration is in the range of from 0.5 to 50 ns, preferably of from 1 to 30 ns, more preferably of from 2 to 25 ns, more preferably of from 3 to 15 ns, more preferably of from 5 to 11 ns, and more preferably of from 7 to 9 ns. The process of embodiment 23, wherein in (iii) the repetition rate of the pulse is in the range of from 0.1 to 200 kHz, preferably of from 0.5 to 150 kHz, more preferably of from 1 to 100 kHz, more preferably of from 2 to 50 kHz, more preferably of from 3 to 15 kHz, and more preferably of from 4 to 6 kHz. The process of embodiment 23 or 24, wherein in (iii) the pulse power is in the range of from 5 to 120 mJ/pulse, preferably of from 10 to 80 mJ/pulse, more preferably of from 12 to 50 mJ/pulse, more preferably of from 15 to 30 mJ/pulse, and more preferably of from 18 to 22 mJ/pulse. The process of any of embodiments 1 to 25, wherein in (iii) the organic solvent is circulated, preferably by pumping of the organic solvent. The process of any of embodiments 1 to 26, wherein the process further comprises

(v) removing at least a portion of the organic solvent system from the colloidal solution obtained in (iv). The process of embodiment 27, wherein removal in (v) is achieved by evaporation of the organic solvent system, preferably by evaporation of the organic solvent system under reduced pressure. The process of any of embodiments 1 to 28, wherein the process further comprises

(vi) impregnation of the colloidal solution obtained in (iv) or (v) onto a support material. The process of embodiment 29, wherein the support material comprises a metal oxide and/or a metalloid oxide, preferably a metal oxide, wherein more preferably the support material comprises one or more metal oxides and/or metalloid oxides selected from the group consisting of alumina, silica, silica-alumina, zirconia, ceria, ceria-zirconia, and titania, including mixtures and mixed oxides of two or more thereof, preferably from the group consisting of alumina, silica, silica-alumina, zirconia, ceria, and ceria-zirconia, including mixtures and mixed oxides of two or more thereof, more preferably from the group consisting of alumina, silica, and silica-alumina, including mixtures of two or more thereof, wherein more preferably the support material comprises, preferably consists of, alumina and/or silica-alumina, preferably alumina. The process of embodiment 29 or 30, wherein the support material is a particulate or monolithic support, wherein preferably the support material is a particulate support material. The process of embodiment 31 , wherein the particulate support material displays an average particle size D50 in the range of from 1 to 200 pm, preferably of from 3 to 120 pm, more preferably of from 5 to 80 pm, more preferably of from 10 to 60 pm, more preferably of from 20 to 50 pm, more preferably of from 25 to 45 pm, and more preferably of from 30 to 40 pm, wherein the average particle size D50 is preferably determined according to ISO 13320:2020. The process of any of embodiment 29 to 32, wherein the support material displays a pore volume in the range of from 0.1 to 5.0 ml/g, preferably of from 0.3 to 3.0 ml/g, more preferably of from 0.5 to 2.0 ml/g, more preferably of from 0.6 to 1 .5 ml/g, more preferably of from 0.7 to 1.0 ml/g, and more preferably of from 0.8 to 0.9 ml/g, wherein the pore volume is preferably determined according to ISO 15901-2:2022. The process of any of embodiment 29 to 33, wherein the support material displays an average pore diameter in the range of from 1 to 50 nm, preferably of from 3 to 30 nm, more preferably of from 5 to 20 nm, more preferably of from 8 to 15 nm, and more preferably of from 10 to 12 nm, wherein the average pore diameter is preferably determined according to ISO 15901- 2:2022. The process of any of embodiments 29 to 34, wherein the loading of the multimetallic alloy nanoparticles on the support material is in the range of from 0.005 to 10 based on 100 wt.- % of the loaded support material, preferably of from 0.01 to 5 wt.-%, more preferably of from 0.015 to 1 .0 wt.-%, more preferably of from 0.02 to 0.5 wt.-%, more preferably of from 0.025 to 0.1 wt.-%, and more preferably of from 0.03 to 0.05 wt.-%. The process of any of embodiments 29 to 35, wherein impregnation in (vi) is performed as an impregnation by incipient wetness or as a wet impregnation, preferably as a wet impregnation. 37. The process of any of embodiments 29 to 36, wherein during the impregnation in (vi) the organic solvent system is continuously removed, preferably by evaporation of the organic solvent, more preferably by evaporation of the organic solvent under reduced pressure.

38. A process for the preparation of multimetallic alloy nanoparticles comprising

(2) adding a reducing agent to the solution prepared in (1);

(4) cooling the mixture obtained in (3);

(5) isolating the colloidal fraction obtained in (4).

39. The process of embodiment 38, wherein the one or more metals M1 are selected from the group consisting of Pt, Pd, Ag, Rh, Ir, and Ru, preferably from the group consisting of Pt, Pd, Ag, and Rh, and more preferably from the group consisting of Pt, Pd, and Rh, wherein more preferably the one or more metals M1 comprise, preferably consist of, Pd and Pt.

40. The process of embodiment 38, wherein the one or more metals M1 comprise, preferably consist of, Ru.

41 . The process of any of embodiments 38 to 40, wherein the one or more metals M2 are selected from the group consisting of Mn, Fe, Co, Ni, Cu, Zn, and Mo, preferably from the group consisting of Fe, Co, Ni, and Cu, and more preferably from the group consisting of Fe, Co, and Ni, wherein more preferably the one or more metals M2 comprise, preferably consist of, Fe, Co, and Ni.

42. The process of any of embodiments 38 to 41 , wherein the solution prepared in (1) comprises from 4 to 6 transition metals, and preferably comprises 5 transition metals.

43. The process of any of embodiments 38 to 42, wherein the transition metals contained in the solution prepared in (1) consist of the metals M1 and M2.

44. The process of any of embodiments 38 to 43, wherein the solution prepared in (1 ) comprises from 1 to 5 transition metals M1 , preferably from 2 to 5, more preferably from 2 to 4, and more preferably 2 or 3, wherein more preferably the solution prepared in (1) comprises 3 transition metals M 1. 45. The process of any of embodiments 38 to 44, wherein the solution prepared in (1 ) comprises from 1 to 5 transition metals M2, preferably from 2 to 5, more preferably from 2 to 4, and more preferably 2 or 3, wherein more preferably the solution prepared in (1) comprises 2 transition metals M 1.

46. The process of any of embodiments 38 to 45, wherein the solution prepared in (1 ) comprises each of the three or more transition metals in an amount ranging from 100/n ± (100/n)/x mole-% based on 100 mole-% of the transition metals contained in the solution prepared in (1), wherein n is the total number of the transition metals contained in the solution prepared in (1), and wherein x is in the range of from 1 .01 to 100, preferably of from 1 .05 to 50, more preferably of from 1.1 to 10, more preferably of from 1 .5 to 5, and more preferably of from 2 to 3.

47. The process of embodiment 46, wherein n stands for the total number of the transition metals contained in the solution prepared in (1) in an amount of 10 wt.-% or more, calculated as the element and based on 100 wt.-% of the total amount of the transition metals, calculated as the respective element, contained in the solution prepared in (1), preferably of 5 wt.-% or more, more preferably of 3 wt.-% or more, more preferably of 2 wt.-% or more, more preferably of 1 wt.-% or more, more preferably of 0.5 wt.-% or more, and more preferably of 0.1 wt.-% or more.

48. The process of any of embodiments 38 to 47, wherein each of the three or more transition metals are contained in the solution prepared in (1) in an amount of 0.1 wt.-% or more, calculated as the element and based on 100 wt.-% of the total amount of the transition metals, calculated as the respective element, contained in the solution prepared in (1), preferably of 0.5 wt.-% or more, more preferably of 1 wt.-% or more, more preferably of 2 wt.-% or more, more preferably of 3 wt.-% or more, more preferably of 5 wt.-% or more, and more preferably of 10 wt.-% or more.

49. The process of any of embodiments 38 to 48, wherein the one or more transition metal compounds are provided as salts, preferably as halides and/or complex salts, more preferably as chlorides and/or chlorometalate complexes and/or as metal acetylacetonates, wherein more preferably the one or more transition metal compounds are provided as metal acetylacetonates.

50. The process of any of embodiments 38 to 49, wherein the organic solvent system in (1 ) comprises, preferably consists of, one or more non-polar solvents, wherein preferably the one or more non-polar solvents are selected from the group consisting of diphenyl ether, n-hexane, benzene, toluene, and 1 ,4-dioxane, including mixtures of two or more thereof, wherein more preferably the organic solvent system in (1) comprises, preferably consists of, diphenyl ether. The process of any of embodiments 38 to 50, wherein the organic solvent in 1 comprises 0.1 wt.-% or less of H2O based on 100 wt.-% of the organic solvent system, preferably 0.05 wt.-% or less, more preferably 0.01 wt.-% or less, more preferably 0.005 wt.-% or less, more preferably 0.001 wt.-% or less, more preferably 0.0005 wt.-% or less, and more preferably 0.0001 wt.-% or less. The process of any of embodiments 38 to 51 , wherein in (1 ) the one or more surfactants are selected from nonionic surfactants, preferably from the group consisting of (Cs- C22)fatty acids, (Cs-C22)fatty amines, (C8-C22)alcohols, (C6-C2o)alcohol ethoxylates with 1 to 8 ethylene oxide units, (Ce-C2o)alkyl polyglycosides, polyoxyethylene glycol alkyl ethers, polyoxypropylene glycol alkyl ethers, glucoside alkyl ethers, polyoxyethylene glycol alkylphenol ethers, glycerol alkyl esters, sorbitan alkyl esters, polyoxyethylene glycol sorbi- tan alkyl esters, cocamide monoethanolamine, cocamide diethanolamine, dodecyldimethylamine oxide, block copolymers of polyethylene glycol and polypropylene glycol, polyethoxylated tallow amine, and mixtures of two or more thereof, wherein more preferably the one or more nonionic surfactants are selected from the group consisting of (Ci4-C2o)fatty acids, (Ci4-C2o)fatty amines, (Ci4-C2o)alcohols, (Cs- Cis)alcohol ethoxylates with 2 to 6 ethylene oxide units, (Cs-Ci8)alkyl polyglycosides, octaethylene glycol monododecyl ether and/or pentaethylene glycol monododecyl ether, polyoxypropylene glycol alkyl ethers, decyl glucoside, lauryl glucoside, myristil glucoside, octyl glucoside, polyoxyethylene glycol octylphenol ethers, preferably triton X-100, nonox- ynol-9, glyceryl laurate, polyglycerol polyricinoleate, sorbitan monolaurate, sorbitan monopalmitate, sorbitan monostearate, sorbitan monooleate, polyoxyethylene sorbitan monolaurate, polyoxyethylene sorbitan monopalmitate, polyoxyethylene sorbitan monostearate, polyoxyethylene sorbitan monooleate, cocamide monoethanolamine, cocamide diethanolamine, dodecyldimethylamine oxide, block copolymers of polyethylene glycol and polypropylene glycol, polyethoxylated tallow amine, and mixtures of two or more thereof, wherein more preferably the one or more nonionic surfactants are selected from the group consisting of (Ci6-Cis)fatty acids, (Ci6-Cis)fatty amines, (Ci6-Ci8)alcohols, (C16- Cis)alcohol ethoxylates with 2 to 6 ethylene oxide units, (Cs-Ci4)alkyl polyglycosides, preferably cetyl alcohol, stearyl alcohol, oleyl alcohol, and mixtures of two or more thereof, octaethylene glycol monododecyl ether and/or pentaethylene glycol monododecyl ether, polyoxypropylene glycol alkyl ethers, decyl glucoside, lauryl glucoside, myristil glucoside, octyl glucoside, polyoxyethylene glycol octylphenol ethers, nonoxynol-9, glyceryl laurate, polyglycerol polyricinoleate, sorbitan monolaurate, sorbitan monopalmitate, sorbitan monostearate, sorbitan oleate, polyoxyethylene (20) sorbitan monolaurate, polyoxyethylene (20) sorbitan monopalmitate, polyoxyethylene (20) sorbitan monostearate, polyoxyethylene (20) sorbitan monooleate, cocamide monoethanolamine, cocamide diethanolamine, dodecyldimethylamine oxide, block copolymers of polyethylene glycol and polypropylene glycol, polyethoxylated tallow amine, Stearyl-EC>2, polyglyceryl-2- dipolyhydroxystearate, polyglyceryl-distearate, C13/15 - PEG3, C13 - PEG2, glyceryl monooleate, C16/18 - PEG2, oleyl - PEG2, PEG20 - sorbitan monooleate, functionalized polyisobutene, C16/18 - PEGg, and mixtures of two or more thereof, more preferably from the group consisting of (Cis)fatty acids, (Cis)fatty amines, polyglyc- eryl-2-dipolyhydroxystearate, diglyceryl-distearate, triglyceryl-distearate, C13/15 - PEG3, C13 - PEG2, glyceryl monooleate, sorbitan monooleate, polyglycerol-3-polyricinoleate, C16/18 - PEG2, oleyl - PEG2, PEG20 - sorbitan monooleate, functionalized polyisobutene, C16/18 - PEGg, and mixtures of two or more thereof, more preferably from the group consisting of oleic acid, oleylamine, polyglyceryl-2- dipolyhydroxystearate, diglyceryl-distearate, triglyceryl-distearate, and mixtures of two or more thereof, wherein more preferably the one or more surfactants in (1 ) comprise, preferably consist of, oleic acid and/or oleylamine, wherein more preferably the one or more surfactants in (1 ) comprise, preferably consist of, oleic acid and oleylamine. The process of embodiment 52, wherein the one or more surfactants in (1) comprise, preferably consist of, oleic acid and oleylamine, wherein the oleic acid : oleylamine molar ratio of oleic acid to oleylamine in the solution prepared in (1 ) is in the range of from 5:95 to 95:5, preferably of from 10:90 to 90:10, more preferably of from 30:70 to 70:30, more preferably of from 40:60 to 60:40, and more preferably of from 45:55 to 55:45. The process of any of embodiments 38 to 53, wherein in (1 ) the one or more surfactants are dissolved in the organic solvent system in an amount in the range of from 5 to 500 g/L, preferably of from 5 to 500 g/L, more preferably of from 10 to 300 g/L, more preferably of from 30 to 250 g/L, more preferably of from 50 to 200 g/L, more preferably of from 80 to

150 g/L, more preferably of from 100 to 130 g/L, and more preferably of from 115 to 120 g/L. The process of any of embodiments 38 to 54, wherein in (2) the one or more reducing agents comprise, preferably consist of, one or more hydrides, preferably one or more ionic hydrides, more preferably one or more hydrides selected from the group consisting of alkali metal hydrides, more preferably one or more hydrides selected from the group consisting of sodium borohydride, lithium aluminum hydride, lithium triethylborohydride, wherein more preferably the one or more hydrides comprise, preferably consist of, lithium triethylborohydride. The process of any of embodiments 38 to 55, wherein in (2) the solution is heated to a temperature in the range of from 50 to 200 °C, preferably of from 80 to 160 °C, more preferably of from 100 to 140 °C, and more preferably of from 115 to 125 °C. The process of any of embodiments 38 to 56, wherein in (3) the reaction mixture obtained in (2) is heated to a maximum temperature in the range of from 120 to 350 °C, preferably of from 150 to 300 °C, more preferably of from 180 to 280 °C, more preferably of from 220 to 270 °C, and more preferably of from 240 to 260 °C. The process of embodiment 57, wherein in (3) the reaction mixture obtained in (2) is heated to the maximum temperature at a rate comprised in the range of from 5 to 360 °C/h, preferably of from 10 to 240 °C/h, more preferably of from 20 to 180 °C/h, more preferably of from 30 to 120 °C/h, more preferably of from 35 to 60 °C/h, and more preferably of from 40 to 45 °C/h. The process of embodiment 57 or 58, wherein in (3) heating is stopped when having reached the maximum temperature. The process of any of embodiments 38 to 59, wherein in (4) the mixture obtained in (3) is cooled to a temperature in the range of from 0 to 50 °C, preferably of from 5 to 40 °C, more preferably of from 10 to 35 °C, more preferably of from 15 to 30 °C, and more preferably of from 20 to 25 °C. The process of any of embodiments 38 to 60, wherein isolating in (5) is achieved by centrifugation. The process of any of embodiments 38 to 61 , wherein the process further comprises

(6) suspending the colloidal fraction obtained in (5) in an organic solvent system. The process of any of embodiments 38 to 62, wherein the organic solvent system in (ii) comprises, preferably consists of, one or more organic solvents selected from the group consisting of protic organic solvents, preferably from the group consisting of C1-C6 alkanols and mixtures thereof, more preferably from the group consisting of C1-C4 alkanols and mixtures thereof, more preferably from the group consisting of C2-C3 alkanols and mixtures thereof, wherein more preferably the organic solvent system comprises, preferably consists of, ethanol. The process of any of embodiments 38 to 63, wherein the process further comprises

(7) impregnation of the colloidal solution obtained in (6) onto a support material. The process of embodiment 64, wherein the support material comprises a metal oxide and/or a metalloid oxide, preferably a metal oxide, wherein more preferably the support material comprises one or more metal oxides and/or metalloid oxides selected from the group consisting of alumina, silica, silica-alumina, zirconia, ceria, ceria-zirconia, and titania, including mixtures and mixed oxides of two or more thereof, preferably from the group consisting of alumina, silica, silica-alumina, zirconia, ceria, and ceria-zirconia, including mixtures and mixed oxides of two or more thereof, more preferably from the group consisting of alumina, silica, and silica-alumina, including mixtures of two or more thereof, wherein more preferably the porous support material comprises, preferably consists of, alumina and/or silica-alumina, preferably alumina. 66. The process of embodiment 64 or 65, wherein the support material is a particulate or monolithic support, wherein preferably the support material is a particulate support material.

67. The process of embodiment 66, wherein the particulate support material displays an average particle size D50 in the range of from 1 to 200 pm, preferably of from 3 to 120 pm, more preferably of from 5 to 80 pm, more preferably of from 10 to 60 pm, more preferably of from 20 to 50 pm, more preferably of from 25 to 45 pm, and more preferably of from 30 to 40 pm, wherein the average particle size D50 is preferably determined according to ISO 13320:2020.

68. The process of any of embodiments 64 to 67, wherein the support material displays a pore volume in the range of from 0.1 to 5.0 ml/g, preferably of from 0.3 to 3.0 ml/g, more preferably of from 0.5 to 2.0 ml/g, more preferably of from 0.6 to 1 .5 ml/g, more preferably of from 0.7 to 1.0 ml/g, and more preferably of from 0.8 to 0.9 ml/g, wherein the pore volume is preferably determined according to ISO 15901-2:2022.

69. The process of any of embodiments 64 to 68, wherein the support material displays an average pore diameter in the range of from 1 to 50 nm, preferably of from 3 to 30 nm, more preferably of from 5 to 20 nm, more preferably of from 8 to 15 nm, and more preferably of from 10 to 12 nm, wherein the average pore diameter is preferably determined according to ISO 15901- 2:2022.

70. The process of any of embodiments 64 to 69, wherein the loading of the multimetallic alloy nanoparticles on the support material is in the range of from 0.005 to 10 based on 100 wt.- % of the loaded support material, preferably of from 0.01 to 5 wt.-%, more preferably of from 0.015 to 1 .0 wt.-%, more preferably of from 0.02 to 0.5 wt.-%, more preferably of from 0.025 to 0.1 wt.-%, and more preferably of from 0.03 to 0.05 wt.-%.

71 . The process of any of embodiments 64 to 70, wherein impregnation in (7) is performed as an impregnation by incipient wetness or as a wet impregnation, preferably as a wet impregnation.

72. The process of any of embodiments 64 to 71 , wherein during the impregnation in (7) the organic solvent system is continuously removed, preferably by evaporation of the organic solvent, more preferably by evaporation of the organic solvent under reduced pressure.

73. Multimetallic alloy nanoparticles obtainable or obtained according to the process of any of embodiments 1 to 72. Multimetallic alloy nanoparticles, preferably obtainable or obtained according to the process of any of embodiments 1 to 72, comprising, preferably consisting of, a solid solution comprising three or more transition metals, wherein the three or more transition metals comprise, preferably consist of, one or more metals M1 selected from the group consisting of Pt, Pd, Au, Ag, Rh, Ir, Os, Ru, and Re, and one or more metals M2 selected from the group consisting of Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Zr, Nb, Mo, Cd, Hf, Ta, and W wherein the nanoparticles display a mean hydrodynamic particle size Dz in the range of from 10 ± 1 to 1 ,000 ± 50 nm, preferably of from 30 ± 2 to 500 ± 30 nm, more preferably of from 50 ± 5 to 300 ± 20 nm, more preferably of from 80 to 250 ± 10 nm, more preferably of from 100 to 220 ± 10 nm, more preferably of from 125 to 200 ± 10 nm, more preferably of from 130 to 180 ± 10 nm, and more preferably of from 140 to 160 ± 10 nm, wherein the mean hydrodynamic particle size Dz of the nanoparticles is preferably determined by dynamic light scattering, more preferably according to ISO 22412:2017. The multimetallic alloy nanoparticles of embodiment 74, wherein the multimetallic alloy nanoparticles display a mean hydrodynamic particle size Dz in the range of from 10 ± 1 to 150 ± 10 nm, preferably of from 20 ± 2 to 100 ± 10 nm, more preferably of from 25 ± 2 to 80 ± 10 nm, more preferably of from 30 ± 2 to 60 ± 5 nm, more preferably of from 35 to 50 ± 5 nm, and more preferably of from 40 to 45 ± 5 nm. The multimetallic alloy nanoparticles of embodiment 74 or 75, wherein the multimetallic alloy nanoparticles display a mean particle size in the range of from 0.5 to 50 nm, preferably of from 1 to 20 nm, more preferably of from 1.2 to 10 nm, more preferably of from 1 .5 to 5.0 nm, more preferably of from 1.8 to 3.0 nm, more preferably of from 2.0 to 2.5 nm, and more preferably of from 2.1 to 2.3 nm, wherein the mean particle size is preferably determined by transmission electron microscopy (TEM), more preferably according to ISO 21363:2020. The multimetallic alloy nanoparticles of any of embodiments 74 to 76, wherein the one or more metals M1 are selected from the group consisting of Pt, Pd, Ag, Rh, Ir, and Ru, preferably from the group consisting of Pt, Pd, Ag, and Rh, and more preferably from the group consisting of Pt, Pd, and Rh, wherein more preferably the one or more metals M1 comprise, preferably consist of, Pd and Rh. The multimetallic alloy nanoparticles of embodiment 74 to 77, wherein the one or more metals M2 are selected from the group consisting of Mn, Fe, Co, Ni, Cu, Zn, and Mo, preferably from the group consisting of Fe, Co, Ni, and Cu, and more preferably from the group consisting of Fe, Co, and Ni, wherein more preferably the one or more metals M2 comprise, preferably consist of, Fe, Co, and Ni. The multimetallic alloy nanoparticles of any of embodiments 74 to 78, wherein the multimetallic alloy nanoparticles comprise, preferably consist of, a solid solution comprising 4 to 6 transition metals, preferably comprising 5 transition metals. 80. The multimetallic alloy nanoparticles of embodiment 79, wherein the multimetallic nanoparticles comprise, preferably consists of, a solid solution consisting of 4 to 6 transition metals, preferably of 5 transition metals.

81 . The multimetallic alloy nanoparticles of any of embodiments 74 to 80, wherein the transition metals contained in the multimetallic alloy nanoparticles consist of the metals M 1 and M2.

82. The multimetallic alloy nanoparticles of any of embodiments 74 to 81 , wherein the multimetallic alloy nanoparticles comprise from 1 to 5 transition metals M1 , preferably from 2 to 5, more preferably from 2 to 4, and more preferably 2 or 3, wherein more preferably the multimetallic alloy nanoparticles comprise 3 transition metals M 1.

83. The multimetallic alloy nanoparticles of any of embodiments 74 to 82, wherein the multimetallic alloy nanoparticles comprise from 1 to 5 transition metals M2, preferably from 2 to 5, more preferably from 2 to 4, and more preferably 2 or 3, wherein more preferably the multimetallic alloy nanoparticles comprise 2 transition metals M 1.

84. The multimetallic alloy nanoparticles of any of embodiments 74 to 83, wherein the multimetallic alloy nanoparticles comprise each of the three or more transition metals in an amount ranging from 100/n ± (100/n)/x mole-%, wherein n is the total number of the transition metals contained in the multimetallic alloy nanoparticles, and wherein x is in the range of from 1 .01 to 100, preferably of from 1 .05 to 50, more preferably of from 1 .1 to 10, more preferably of from 1 .5 to 5, and more preferably of from 2 to 3.

85. The multimetallic alloy nanoparticles of embodiment 84, wherein n stands for the total number of the transition metals contained in the multimetallic alloy nanoparticles in an amount of 10 wt.-% or more, calculated as the element and based on 100 wt.-% of the total amount of the transition metals, calculated as the respective element, contained in the multimetallic alloy nanoparticles, preferably of 5 wt.-% or more, more preferably of 3 wt.-% or more, more preferably of 2 wt.-% or more, more preferably of 1 wt.-% or more, more preferably of 0.5 wt.-% or more, and more preferably of 0.1 wt.-% or more.

86. The multimetallic alloy nanoparticles of any of embodiments 74 to 85, wherein each of the three or more transition metals are contained in the multimetallic alloy nanoparticles in an amount of 0.1 wt.-% or more, calculated as the element and based on 100 wt.-% of the total amount of the transition metals, calculated as the respective element, contained in the multimetallic alloy nanoparticles, preferably of 0.5 wt.-% or more, more preferably of 1 wt.- % or more, more preferably of 2 wt.-% or more, more preferably of 3 wt.-% or more, more preferably of 5 wt.-% or more, and more preferably of 10 wt.-% or more.

87. The multimetallic alloy nanoparticles of any of embodiments 74 to 86, wherein the multimetallic alloy nanoparticles are supported on a support material. 88. The multimetallic alloy nanoparticles of embodiment 87, wherein the support material comprises a metal oxide and/or a metalloid oxide, preferably a metal oxide, wherein more preferably the support material comprises one or more metal oxides and/or metalloid oxides selected from the group consisting of alumina, silica, silica-alumina, zirconia, ceria, ceria-zirconia, and titania, including mixtures and mixed oxides of two or more thereof, preferably from the group consisting of alumina, silica, silica-alumina, zirconia, ceria, and ceria-zirconia, including mixtures and mixed oxides of two or more thereof, more preferably from the group consisting of alumina, silica, and silica-alumina, including mixtures of two or more thereof, wherein more preferably the support material comprises, preferably consists of, alumina and/or silica-alumina, preferably alumina.

89. The multimetallic alloy nanoparticles of embodiment 87 or 88, wherein the support material is a particulate support material or a monolithic support, wherein preferably the support material is a particulate support material.

90. The multimetallic alloy nanoparticles of any of embodiments 87 to 89, wherein the support material displays a pore volume in the range of from 0.1 to 5.0 ml/g, preferably of from 0.3 to 3.0 ml/g, more preferably of from 0.5 to 2.0 ml/g, more preferably of from 0.6 to 1 .5 ml/g, more preferably of from 0.7 to 1.0 ml/g, and more preferably of from 0.8 to 0.9 ml/g, wherein the pore volume is preferably determined according to ISO 15901-2:2022.

91 . The multimetallic alloy nanoparticles of any of embodiments 87 to 90, wherein the support material displays an average pore diameter in the range of from 1 to 50 nm, preferably of from 3 to 30 nm, more preferably of from 5 to 20 nm, more preferably of from 8 to 15 nm, and more preferably of from 10 to 12 nm, wherein the average pore diameter is preferably determined according to ISO 15901- 2:2022.

92. The multimetallic alloy nanoparticles of any of embodiments 87 to 91 , wherein the loading of the multimetallic alloy nanoparticles on the support material is in the range of from 0.005 to 10 based on 100 wt.-% of the loaded support material, preferably of from 0.01 to 5 wt.-%, more preferably of from 0.015 to 1.0 wt.-%, more preferably of from 0.02 to 0.5 wt.-%, more preferably of from 0.025 to 0.1 wt.-%, and more preferably of from 0.03 to 0.05 wt.-%.

93. A method for the treatment of an exhaust gas comprising CO, NO_X, and hydrocarbons, said method comprising

(A) providing a gas stream comprising CO, NO_X, and hydrocarbons;

(B) contacting the gas stream provided in (A) with a catalyst comprising multimetallic alloy nanoparticles according to any of embodiments 73 to 92.

94. A method for the treatment of an exhaust gas comprising NH3 and oxygen, said method comprising (A’) providing a gas stream comprising NH3 and oxygen;

(B’) contacting the gas stream provided in (A’) with a catalyst comprising multimetallic alloy nanoparticles according to any of embodiments 73 to 92.

95. The method of embodiment 93 or 94, wherein the exhaust has stream provided in (A) or (A’) is from an internal combustion engine, preferably from a lean burn combustion engine, and more preferably from a diesel engine or lean burn gasoline engine.

96. A method for the reforming of ammonia, wherein the process comprises

(A”) providing a reactor containing a catalyst comprising multimetallic alloy nanoparticles according to any of embodiments 73 to 92;

(B”) preparing a feed gas stream comprising NH3;

97. Use of multimetallic alloy nanoparticles according to any of embodiments 73 to 92 as a catalyst or a precursor thereof, preferably as a catalyst for the conversion of NO, CO, and/or hydrocarbons; for the selective catalytic reduction (SCR) of nitrogen oxides NO_X; for the oxidation of NH3, in particular for the oxidation of NH3 slip; for the decomposition of N2O; as a catalyst in fluid catalytic cracking (FCC) processes; for NH3 reforming; and/or as a catalyst in organic conversion reactions, preferably in the conversion of alcohols to olefins, and more preferably in methanol to olefin (MTO) catalysis; and more preferably as a three-way catalyst for the conversion of NO, CO, and hydrocarbons.

DESCRIPTION OF THE FIGURES

Figure 1 a displays the XRD pattern of the as-cast (black) and subsequent thermally treated (grey) PdPtRhCoFe ingot according to Example 8.

Figure 1 b displays an enlarged area of the XRD pattern of an as-cast (black) and subsequent thermally treated (grey) PdPtRhCoFe ingot from Example 8 (see Figure 1 ).

Figure 2a displays the SEM image (backscattering) of the PdPtRhCoFe ingot of Example 8.

Figure 2b displays the SEM image (backscattering) of the PdPtRhCoNi ingot of Example 8.

Figure 2c displays the SEM image (backscattering) of the PdPtRhCuNi ingot of Example 8. Figure 3 displays the SEM image (backscattering) of the PdPtRhCoFe ingot from Example 8 with EDX measurement spots and measured composition for the spots expressed in both weight and atom percentage.

Figure 4a displays the particle size distribution obtained from HR-TEM images of PdPtRhCoFe (520 particles) and PdPtRhCoNi (1274 particles) nanoparticles as obtained from Example 8.

Figure 4b displays Particle size distribution based on HR-TEM images of PdPtRhCoFe (520 particles) and PdPtRhCoNi (1274 particles) nanoparticles as obtained from Example 8.

EXPERIMENTAL SECTION

The present invention is further illustrated by the following examples.

Example 1 : Preparation of multimetallic alloy nanoparticles via pulsed laser ablation in liquid (PLAL)

Alloy ingots were prepared by arc melting of powder mixtures in a MAM-1 arc furnace from Edmund Buhler with 0.7 bara argon atmosphere. Melting of the powders was carried out at least 5 times for every sample. The power of the arc furnace and the duration of the treatment was varied stepwise without a significant impact on the resulting ingots. The so obtained ingots have a spherical form, which is not suitable for the nanoparticle production via PLAL, where a flat f is needed.

Two shaping approaches were pursued during or after the ingot preparation. The first generation of ingots was shaped during the melting process utilizing flat graphite molds to obtain the targets. Several graphite mold geometries were evaluated, in the end resulting in molds for flatround targets, rectangular-rods and round wires of different size.

The second generation of ingots was shaped after the melting process. The spherical ingots were cold pressed with up to 10 kN to obtain flat targets. The latter was only possible for alloys with a certain ductility, since otherwise the spherical ingots cracked. A high ductility is reported in literature for fcc-HEAs and was especially observed for ingots containing cobalt.

For laser ablation, a 220 W nanosecond-pulsed laser system (InnoSlab Laser IS400-1 , Edgewave, Wurselen) and a SCAN LAB scanning system (SCAN cube III 14) was used at the following parameters:

The different (equimolar) multimetallic alloy targets were then placed in ethanol containing 1 g/l poly vinyl pyrrolidone for subsequent laser ablation. The solvent was pumped in the circuit to increase the concentration of the product. The following ten samples were produced in total:

The size distribution of the nanoparticles obtained from laser ablation were measured by dynamic light scattering (Malvern Zetasizer Nano ZS ZEN3600) before centrifugation. The average hydrodynamic size and the standard deviation as obtained from dynamic light scattering are shown in the following table:

Impregnation on AI2O3 (Puralox®TM 100/150) was done with colloidal solutions of PdPtRhCoFe and PdPtRhCoNi nanoparticles, using a modified wet impregnation method in a moved bed. The colloidal ethanol solution was dosed while simultaneously removing the ethanol under reduced pressure (600 mbar).

Comparative Example 2: Preparation of bimetallic alloy nanoparticles via laser ablation

The procedure of Example 1 was repeated with a (equimolar) bimetallic target of Pd and Pt for affording a supported catalyst with Pt/Pd bimetallic nanoparticles. The sample thus obtained was designated as NP20.

Example 3: Preparation of multimetallic alloy nanoparticles in a non-aqueous solvent system via reduction of transition metal compounds

A four-neck flask was used with a cooler, a stirrer, and a thermo-couple. Diphenyl ether and the metal salts were added to the flask and stirred at 300 rpm. A low Ar stream was used for inertization throughout the experiment. The mixture was heated to 60°C and the oleic acid and oleyl amine were added through a septum using a syringe. The mixture was than heated to 120°C and the super hydride LiB(Et3)H was added using a drip funnel. After the addition the temperature was slowly increased to 250°C within 3 h. After reaching 250°C the experiment was stopped, and the mixture was quickly cooled to room temperature.

After cooling down, the mixture was separated into four centrifuge tubes (each containing -15 g of dispersion). The dispersions were mixed with roughly the same amount of Ethanol and centrifuged at 4000 rpm for 10 min and another 15 min at 5000 rpm. The supernatants were decanted, and each residue was mixed with 15 g Ethanol. The mixtures were shaken and centrifuged at 5000 rpm for 10 min. The supernatants were decanted, and the residue mixed with -15 g of Ethanol for further use.

Impregnation on AI2O3 (Puralox®TM 100/150) was done with colloidal solutions of colloidal nanoparticles, with a modified wet impregnation method in a moved bed. The colloidal ethanol solution was dosed while simultaneously removing the ethanol under reduced pressure (600 mbar). The sample thus obtained was designated as N13.

Reference Example 4: Preparation of platinum group metal multimetallic alloy nanoparticles in a non-aqueous solvent system via reduction or platinum group metal compounds

A four-neck flask was used with a cooler, a stirrer and a thermo-couple. Diphenyl ether and the metal salts were added to the flask and stirred at 300 rpm. A low Ar stream was used for inertization throughout the experiment. The mixture was heated to 60°C and the oleic acid and oleyl amine were added through a septum using a syringe. The mixture was than heated to 120°C and the super hydride was added using a drip funnel. After the addition the temperature was slowly increased to 240°C within 1 h. After reaching 240°C the experiment was stopped, and the mixture was cooled to room temperature quickly.

After cooling down the mixture was separated into four centrifuge tubes (each containing -13 g of dispersion). The dispersions were mixed with 15g of Ethanol and ultrasonicated for 2 min. Mixtures were centrifuged at 5000 rpm for 30 min twice. The supernatants were decanted. Each residue was mixed with -10 g Ethanol for further use.

Impregnation on AI2O3 (Puralox®TM 100/150) was done with colloidal solutions of colloidal nanoparticles, with a modified wet impregnation method in a moved bed. The colloidal ethanol solution was dosed while simultaneously removing the ethanol under reduced pressure (600 mbar). The sample thus obtained was designated as N10.

Comparative Example 5: Preparation of a supported platinum group multimetal catalyst by metal impregnation

In a first step, 5g of the carrier (AI2O3, Puralox®TM 100/150) were doped with Ir at 0.95 wt% on carrier using Ir(lll) chloride solution (14996-61-3, Umicore AG) by incipient wetness impregnation. After careful mixing the sample was dried at 110°C in a thin layer, followed by calcination at 500°C for 2h in air. To remove Cl ions, the sample was washed with CO2 saturated water until no Cl was detected in the washing water (using Ag nitrate solution as indicator). Afterwards the sample was dried again at 110°C in a thin layer.

In a second step, the Ir impregnated sample was doped with Ru (0.5 wt% on carrier) using a trinitratonitrosyl-ruthenium(ll) solution (Umicore AG, CAS 34513-98-9) by incipient wetness impregnation, followed by drying at 110°C in a thin layer. The resulting powder was finally coimpregnated with Pd (0.525 wt% on carrier, Pt (0.965 wt% on carrier) and Rh (0.509 wt% on carrier) using a solution of metal nitrates (Umicore AG). After drying at 110°C in a thin layer, the sample was calcined at 500°C for 2h in air.

Comparative Example 6: Preparation of a supported platinum group bimetal catalyst by metal impregnation

In a first step, 5g of the carrier (AI2O3, Puralox®TM 100/150) were doped with 1 wt% on carrier Pd nitrate solution by incipient wetness impregnation. After careful mixing, the sample was dried at 110°C in a thin layer. Afterwards the powder was doped with 1 wt% on carrier Pt using a colloidal Pt solution (BASF AG). Due to the low concentration, two incipient wetness impregnation steps with intermediate drying at 110°C were required. After final drying at 110°C in a thin layer, the sample was calcined for 2h at 500°C in air.

Example 7: Catalytic testing

The impregnated samples (0.028 wt.-% nanoparticles) were dried at 80 °C and tested in the fresh and aged states. For aging, the samples were submitted to hydrothermal aging at 800°C for 16h in 10% FhO/air.

The samples were tested in the conversion of NO, CO, and HC in exhaust gas emission, wherein the average conversion for the window 0.98 < A < 1 .02 is respectively displayed. The testing conditions were as follows:

- GHSV: 45000 hr¹

- Feed: 100 ppm NO, 800 ppm CO, 400 ppm-Ci HC (CsHe/toluene/ decane= 1/1/2 on Ci basis), 10% 02,10% CO2, 5% H2O Table 1 : Comparison of avg. NO, CO, and HC conversions in %.

(*) Reference Example

(**) Comparative Example

As may be taken from the results displayed in Table 1 , it has quite surprisingly been found that the multimetallic alloy nanoparticle catalysts according to the present invention which combine the properties of platinum group metals with those of non-platinum group metals afford superior results in catalysis compared to platinum group multimetal catalysts obtained by conventional impregnation methods. Thus, as may be taken from the comparison of comparative sample N22 and inventive sample N1 , the inventive sample displays comparable fresh conversion rates, yet superior conversion rates after aging with regard to CO and HC conversion. NO conversion, on the other hand, is comparable to the conversion of the comparative sample N22 after aging. These results are highly unexpected considering the high activity of platinum group metals compared to non-platinum group metals. Furthermore, it has quite surprisingly been found that a highly cost-efficient catalyst may be provided according to the present invention compared to the catalysts of the prior art which only contain platinum group metals in view of the far higher costs of the latter.

Furthermore, it has quite unexpectedly been found that these surprising results are due to a combination of the specific use of multimetallic alloy nanoparticles and the combined use of platinum and non-platinum group metals. Thus, as may be taken from a comparison of reference sample N10 with comparative sample N22, providing the platinum group metals of N22 as multimetallic alloy nanoparticles does not afford a catalyst with superior, or even comparable performance to the inventive sample N1. Rather, as may be taken from the results in Table 1 , the performance of the reference sample N 10 are far inferior than the performance of comparative sample N22 containing the same platinum group metals both in the fresh state and after aging. Said finding is particularly unexpected, since it is observed only for the multimetallic samples. Thus, as may be taken from a comparison of the bimetallic samples of comparative samples NP20 and N23, the nanoparticles of NP20 which were obtained according to the same method as inventive sample N1 displays worse results in conversion of CO, HC, and NO in the fresh state, and worse results in the conversion of HC and NO after aging as well.

EDX mappings in HR-TEM images of the inventive sample N3 in the fresh state reveal a highly homogeneous distribution of all of the elements in the multimetallic alloy nanoparticles. On the other hand, EDX mappings in HR-TEM images of the hydrothermally aged inventive sample N5 reveal a comparatively homogeneous distribution of all of the non-platinum group metal elements in the multimetallic alloy nanoparticles, whereas the platinum group metals contained therein form areas of increased concentration, especially as far as Pt is concerned. The HR- TEM images of the hydrothermally aged sample however reveals that the multimetallic alloy nanoparticles as such are considerably stable after hydrothermal aging and show only minor sintering. Consequently, although a concentration of the platinum group metals in the multimetallic nanoparticles is observed due to hydrothermal aging, it has quite surprisingly been found that this does not lead to a sintering of the multimetallic nanoparticles themselves.

Example 8: Preparation of multimetallic alloy nanoparticles via pulsed laser ablation in liquid (PLAL)

Alloy ingots were prepared by cold pressing and a thermal treatment under forming gas (5 vol% H2/N2) at Tamman temperature. For ingots containing Co a high ductility was observed. Higher ductility is reported for fcc-HEAs, on the other hand dendrite formation normally leads to a hardening of an ingot. Therefore, the high ductility of these samples may already be an indication that no dendrites formed.

Thus, thermal treatment of a PdPtRhCoFe ingot obtained according to Example 1 was performed at 1000 °C, for 7 days under 5 vol% H2/N2. The full width at half maximum (FWHM) of the reflexions in the XRD of the material is reduced by a factor of 6 through thermal treatment. In particular, as may be taken from Figures 1a and 1 b, the XRD powder diffractogram of the as- cast and thermally treated PdPtRhCoFe ingot, show both a simple fee pattern with lattice constants of a_as.cast = 3.80 A and a_therm. = 3.79 A and 6-fold smaller FWHMs for the thermally treated ingot. The smaller FWHM indicate lager crystalline domain sizes and therefore crystallite growth due to the thermal treatment. The lack of additional reflections points towards homogenization of the sample without segregation.

As may be taken from the SEM images of thermally treated PdPtRhCoFe, PdPtRhCoNi, and PdPtRhCuNi ingots respectively displayed in Figures 2a to 2c, show for the Co containing ingots (see Figures 2a and 2b) larger crystalline domains of up to 30 pm and no dendritic structure for PdPtRhCuNi (see Figure 2c). The difference in light intensity for the Co samples derives from different orientations of the crystallites rather than from differences in element distribution. This could be shown from EDX measurement of the thermally treated PdPtRhCoFe, which con- firmed identical compositions, that did exactly match (±1 .5 at.-%) the theoretical compositions (see Figure 3).

PLAL of the thermally treated PdPtRhCoFe and PdPtRhCoNi ingots was then performed in accordance with the procedure described in Example 1. Dynamic light scattering (DLS) measurements of the nanoparticles obtained from PLAL of the thermally treated PdPtRhCoFe and PdPtRhCoNi ingots average particle sizes of dpjptRhcoFe = 43 nm and dpdPtRhc<M = 42 nm were determined. Particle size distributions from HR-TEM images afforded an average particle size of 2.17 nm (see Figure 4a) and 2.25 nm (see Figure 4b), respectively. The value from DLS does not discriminate between agglomerates and an organic shell (stabilizer), however particles of up to 270 nm, respective 1 pm, were also seen in TEM which account for less than 1 % of the measured particles.

Results from EDX analysis of the nanoparticles obtained from PLAL using the PdPtRhCoFe and PdPtRhCoNi ingots showed that the nanoparticles contain the five elements in near equimolar ratios. Therefore, it can be concluded that the nanoparticles derived from the thermally treated ingots are indeed HEAs.

Cited prior art:

- Z. Li et al. in Nature 2016, 534, pages 227-230

- Y. Sun and S. Dai in Sci. Adv. 2021 ; 7 : eabg1600

Claims

(i) preparing a multimetallic alloy target comprising a solid solution comprising three or more transition metals, wherein the three or more transition metals comprise one or more metals M1 selected from the group consisting of Pt, Pd, Au, Ag, Rh, Ir, Os, Ru, and Re, and one or more metals M2 selected from the group consisting of Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Zr, Nb, Mo, Cd, Hf, Ta, and W;

2. The process of claim 1 , wherein the process further comprises

3. The process of claim 1 or 2, wherein the process further comprises

4. A process for the preparation of multimetallic alloy nanoparticles comprising

(1 ) preparing a solution comprising one or more surfactants and three or more transition metal compounds dissolved in an organic solvent system, wherein the three or more transition metal compounds comprise one or more compounds of one or more metals M1 selected from the group consisting of Pt, Pd, Au, Ag, Rh, Ir, Os, Ru, and Re, and one or more compounds of one or more metals M2 selected from the group consisting of Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Zr, Nb, Mo, Cd, Hf, Ta, and W;

(2) adding a reducing agent to the solution prepared in (1);

(4) cooling the mixture obtained in (3);

(5) isolating the colloidal fraction obtained in (4).

5. The process of claim 4, wherein the process further comprises

6. The process of claim 5, wherein the process further comprises

(7) impregnation of the colloidal solution obtained in (6) onto a support material. Multimetallic alloy nanoparticles obtainable or obtained according to the process of any of claims 1 to 6. Multimetallic alloy nanoparticles, comprising a solid solution comprising three or more transition metals, wherein the three or more transition metals comprise one or more metals M1 selected from the group consisting of Pt, Pd, Au, Ag, Rh, Ir, Os, Ru, and Re, and one or more metals M2 selected from the group consisting of Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Zr, Nb, Mo, Cd, Hf, Ta, and W, wherein the nanoparticles display a mean hydrodynamic particle size Dz in the range of from 10 ± 1 to 1 ,000 ± 50 nm. The multimetallic alloy nanoparticles of claim 8, wherein the multimetallic alloy nanoparticles display a mean hydrodynamic particle size Dz in the range of from 10 ± 1 to 150 ± 10 nm. The multimetallic alloy nanoparticles of claim 8 or 9, wherein the multimetallic alloy nanoparticles display a mean particle size in the range of from 0.5 to 50 nm. The multimetallic alloy nanoparticles of any of claims 8 to 10, wherein the multimetallic alloy nanoparticles are supported on a support material. A method for the treatment of an exhaust gas comprising CO, NO_X, and hydrocarbons, said method comprising

(A) providing a gas stream comprising CO, NO_X, and hydrocarbons;

(B) contacting the gas stream provided in (A) with a catalyst comprising multimetallic alloy nanoparticles according to any of claims 7 to 11 . A method for the treatment of an exhaust gas comprising N H3 and oxygen, said method comprising

(A’) providing a gas stream comprising NH3 and oxygen;

(B’) contacting the gas stream provided in (A’) with a catalyst comprising multimetallic alloy nanoparticles according to any of claims 7 to 11 . A method for the reforming of ammonia, wherein the process comprises

(A”) providing a reactor containing a catalyst comprising multimetallic alloy nanoparticles according to any of claims 7 to 11 ;

(B”) preparing a feed gas stream comprising NH3;

15. Use of multimetallic alloy nanoparticles according to any of claims 7 to 11 as a catalyst or a precursor thereof.