Catalyst having surface-modified metal nanoparticles immobilized in stationary phase in which a polymer electrolyte membrane is formed, and preparation method thereof

Abstract

The present invention relates to a catalyst having surface-modified metal nanoparticles immobilized in a stationary phase in which a polymer electrolyte membrane is formed, and a preparation method thereof. The catalyst of the present invention may be used in a process for producing hydrogen peroxide by direct synthesis from oxygen and hydrogen.

Claims

1. A method of preparing hydrogen peroxide from hydrogen and oxygen using a catalyst comprising: (i) introducing a catalyst into a reactor wherein the catalyst has been prepared by the following steps comprising; (a) alternately mixing a stationary phase with a first polymer electrolyte solution and a second polymer electrolyte solution, thus forming a polymer membrane on the stationary phase, in which the first polymer electrolyte solution and the second polymer electrolyte solution are cationic or anionic electrolyte solutions having different polarities, and the stationary phase is an ionic exchange resin; (b) surface-modifying metal nanoparticle by the following steps comprising: providing a metal precursor having a metal ion and a first ligand having hydrophobic property, thermally decompositing the metal precursor to form uniform hydrophobic metal nanoparticles, and substituting a terminal of the first ligand of the metal nanoparticles with a second ligand having a functional group which dissociates into negative or positive charge to obtain cationic or anionic metal nanoparticles, wherein the metal ion is palladium, platinum, ruthenium, rhodium, iridium, silver, osmium, nickel, copper, cobalt, titanium or mixtures thereof, wherein the first ligand is dodecyl sulfide, TOP (Trioctyl phosphine), PVP (Poly(vinylpyrrolidone)), or poly(4-vinylpyridine), and the second ligand includes negatively charged material or positively charged material; and (c) adding the stationary phase haying the polymer electrolyte membrane formed in (a) to a solution of the surface-modified metal nanoparticles obtained in (b), thus obtaining the catalyst having the surface modified metal nanoparticles immobilized on the stationary phase on which the polymer electrolyte membrane is formed; (ii) supplying hydrogen, oxygen and nitrogen into the reactor to which the catalyst has been introduced; and (iii) recovering hydrogen peroxide.

2. The method of preparing hydrogen peroxide of claim 1, wherein the polymer electrolyte membrane comprises cationic and anionic polymer electrolytes.

3. The method of preparing hydrogen peroxide of claim 1, wherein the surface-modified metal nanoparticles are negatively or positively charged.

4. The method of preparing hydrogen peroxide of claim 2, wherein the cationic polymer electrolyte is PAH (Poly(allylamine hydrochloride)), PDDA (Polydiallyldimethylammonium)), PEI(Poly(ethyleneimine)), or PAMPDDA (Poly-(acrylamide-co-diallyldimethylammonium).

5. The method of preparing hydrogen peroxide of claim 2, wherein the anionic polymer electrolyte is PSS (Poly(4-styrenesulfonate), PAA (Poly(acrylic acid)), PAM (Poly(acryl amide)), poly(vinylphosphonic acid), PAAMP (Poly(2-acrylamido-2-methyl-1-propanesulfonic acid), PATS (Poly(anetholesulfonic acid)), or PVS(Poly(vinyl sulfate)).

6. The method of preparing hydrogen peroxide of claim 1, wherein a number of layers of the polymer electrolyte membrane is 1˜9.

7. The method of preparing hydrogen peroxide of claim 1, wherein the polymer electrolyte has a weight average molecular weight of 1,000˜1,000,000 g/mol.

Description

DESCRIPTION OF DRAWINGS

(1) FIG. 1 illustrates a process of preparing a catalyst having surface-modified metal nanoparticles immobilized on a stationary phase on which a polymer electrolyte membrane is formed;

(2) FIG. 2 illustrates a process of preparing uniform metal nanoparticles via reaction between a metal precursor and a ligand;

(3) FIG. 3 illustrates a process of substituting the ligand of the metal nanoparticles so that the surface of the metal nanoparticles is modified to be negatively charged;

(4) FIG. 4 illustrates a process of repeating sequential formation of a cationic polymer electrolyte and an anionic polymer electrolyte on an anionic exchange resin stationary phase so that the cationic polymer electrolyte is formed on the outer surface, thus forming a multilayer polymer membrane, and then immobilizing negatively charged surface-modified metal nanoparticles thereon;

(5) FIG. 5 illustrates the uniformly prepared metal nanoparticles analyzed using a transmission electron microscope (2.1±0.2 nm);

(6) FIG. 6 illustrates the surface-modified metal nanoparticles analyzed using a transmission electron microscope (2.4±0.1 nm);

(7) FIG. 7 illustrates the surface-modified metal nanoparticles analyzed using a zeta potential meter (−33.09 mV); and

(8) FIG. 8 illustrates the catalyst having surface-modified metal nanoparticles immobilized on a stationary phase on which a polymer electrolyte membrane is formed, which is manufactured in the form of a specimen using a cryo-microtome and then analyzed using a cryo-electron microscope.

BEST MODE

(9) Hereinafter, a detailed description will be given of the present invention.

(10) An embodiment of the present invention is directed to a catalyst having surface-modified metal nanoparticles immobilized on a stationary phase on which a polymer electrolyte membrane is formed.

(11) As used in the detailed description of the specification and the claims, the term “polymer electrolyte membrane” means a polymer electrolyte layer as a membrane formed via a layer-by-layer (LBL) deposition technique using a polymer electrolyte material, and the membrane includes not only a monolayer but also a multilayer unless otherwise mentioned.

(12) The metal particles include palladium, platinum, ruthenium, rhodium, iridium, silver, osmium, nickel, copper, cobalt, titanium or mixtures thereof, and the surface-modified metal nanoparticles are negatively or positively charged.

(13) In the catalyst having the surface-modified metal nanoparticles immobilized on a stationary phase on which a polymer electrolyte membrane is formed, bonding between the stationary phase and the multilayer polymer electrolyte membrane and bonding between individual layers of the multilayer polymer electrolyte membrane are formed via electrostatic interaction, hydrogen bonding, Van der Waals interaction or covalent bonding, thus forming a structure that is very physically and chemically stable.

(14) Thus, the catalyst of the invention may fundamentally suppress the dissolution of metal particles during reaction, which is regarded as the major problem of conventionally prepared metal-supported catalysts, and thereby may prevent the activity of the catalyst from decreasing thus achieving a catalyst system having very high profitability.

(15) The stationary phase may have a predetermined charge so that the cationic or anionic polymer electrolyte may be easily adsorbed thereon. The stationary phase may include acidic, neutral, or basic inorganic materials, and particularly useful is an anionic or cationic resin.

(16) The stationary phase has a predetermined charge so that the cationic or anionic polymer electrolyte may be easily adsorbed thereon. According to a specific embodiment of the invention, the cationic resin used as the stationary phase may include a polymer resin having, at a side chain thereof, a cationic functional group selected from the group consisting of a sulfonic acid group, a carboxylic acid group, a phosphoric acid group, and a phosphonic acid group. An example of the ionic resin having such a cationic functional group may include one or more selected from among fluorine-based polymers, benzimidazole-based polymers, polyimide-based polymers, polyetherimide-based polymers, polyphenylenesulfide-based polymers, polysulfone-based polymers, polyethersulfone-based polymers, polyetherketone-based polymers, polyether-etherketone-based polymers and polyphenylquinoxaline-based polymers. Particularly useful are one or more selected from among poly(perfluorosulfonic acid), poly(perfluorocarboxylic acid), copolymers of fluorovinylether and tetrafluoroethylene having a sulfonic acid group, defluorinated polyetherketone sulfide, aryl ketone, poly[2,2′-(m-phenylene)-5,5′-bibenzimidazole] and poly(2,5-benzimidazole).

(17) The anionic resin used as the stationary phase includes a halogen compound and/or a bicarbonate type anionic resin and a carbonate and a hydroxide type resin or mixtures thereof.

(18) For example, the case where an anionic exchange resin having a sulfonic acid group (SO.sub.3.sup.−) is used as the stationary phase in the present invention enables strong bonding with the polymer electrolyte membrane. The metal nanoparticles immobilized on such a polymer electrolyte membrane may be very strongly bound to a ligand which stabilizes the polymer electrolyte membrane and the metal nanoparticles via electrostatic interaction, hydrogen bonding, Van der Waals interaction or covalent bonding.

(19) The polymer electrolyte membrane is composed of cationic and anionic polymer electrolytes, and a variety of kinds of cationic or anionic polymer electrolytes may be used, thus adjusting ionic bond strength of the polymer electrolyte.

(20) The cationic polymer electrolyte may include but is particularly not limited to PAH (Poly(allylamine hydrochloride)), PDDA (Polydiallyldimethylammonium), PEI (Poly(ethyleneimine)), or PAMPDDA (Poly(acrylamide-co-diallyldimethylammonium).

(21) The anionic polymer electrolyte may include PSS (Poly(4-styrenesulfonate), PAA (Poly(acrylic acid)), PAM (Poly(acryl amide)), poly(vinylphosphonic acid), PAAMP (Poly(2-acrylamido-2-methyl-1-propanesulfonic acid), PATS (Poly(anetholesulfonic acid)), or PVS (Poly(vinyl sulfate)).

(22) Because the hydrogen ion concentration varies depending on the number of layers of the anionic polymer electrolyte solution, the acid strength and the acid amount may be controlled by adjusting the number of layers. Particularly in the case of a halogen anion, it may form ionic bonding with the cationic polymer, and thus the number of layers is adjusted thus controlling the amount of halogen.

(23) The amount of the immobilized metal nanoparticles may vary depending on the number of layers of the polymer electrolyte membrane, and the number of layers of the polymer electrolyte membrane may be 1˜9 but the present invention is not particularly limited thereto. The polymer electrolyte may have a weight average molecular weight of 1,000˜1,000,000.

(24) Another embodiment of the present invention is directed to a method of preparing the catalyst having surface-modified metal nanoparticles immobilized on a stationary phase on which a polymer electrolyte membrane is formed, including (a) alternately mixing a stationary phase with a first polymer electrolyte solution and a second polymer electrolyte solution thus forming a polymer membrane on the stationary phase, in which the first polymer electrolyte solution and the second polymer electrolyte solution are cationic or anionic electrolyte solutions having different polarities; (b) forming uniform metal nanoparticles and then modifying the surface of the formed metal nanoparticles so as to be cationic or anionic; and (c) adding the stationary phase having the polymer electrolyte membrane formed in (a) to the solution of the surface-modified metal nanoparticles obtained in (b), thus preparing a catalyst having the surface-modified metal nanoparticles immobilized on the stationary phase on which the polymer electrolyte membrane is formed.

(25) In (a), the cationic polymer electrolyte and the anionic polymer electrolyte solution having different polarities are mixed so that the polymer electrolyte solutions are alternately formed on the stationary phase. The cationic and anionic polymer electrolytes used may be the same as the polymer electrolyte which constitutes the catalyst of the invention as mentioned above.

(26) In (b), the metal nanoparticles are uniformly formed, and then the surface thereof is modified so that the metal nanoparticles are cationic or anionic. When the cationic or anionic surface-modified metal nanoparticles are formed in this way, they may be easily immobilized on the polymer electrolyte membrane.

(27) FIG. 1 schematically shows the process of preparing the catalyst having the surface-modified metal nanoparticles immobilized on the stationary phase on which the polymer electrolyte membrane is formed, and FIG. 4 illustratively shows the preparation of the above catalyst in detail.

(28) The formation of the uniform nanoparticles in (b) is performed by subjecting a metal precursor to pyrolysis to form and grow a nucleus, and binding a ligand around the nucleus to enclose the nanoparticles so that these particles are stabilized.

(29) For example, as shown in FIG. 2, when the metal precursor including the metal ion and the ligand having a thiol functional group bound thereto is pyrolyzed, the metal ion is formed into nanoparticles via reduction, and the ligand stabilizes the procedure of forming the nanoparticles and suppresses the aggregation of the formed nanoparticles.

(30) The pyrolysis and reaction time and temperature and the ratio of the metal precursor and the ligand are adjusted, making it possible to control the size of the nanoparticles and to form uniform nanoparticles. The ratio of the metal precursor and the ligand may be appropriately adjusted but is not particularly limited.

(31) The ligand may include dodecyl sulfide, TOP (Trioctyl phosphine), PVP (Poly(vinylpyrrolidone)), poly(4-vinylpyridine), etc. Such a ligand forms a strong bond with a metal to thereby form nanoparticles and increase stability. Because the ligand is hydrophobic, it is dispersed in a hydrophobic organic solvent such as toluene and maintained in a solution state.

(32) Because the surface of the formed metal nanoparticles is hydrophobic, the terminal of the ligand is substituted with a functional group which easily dissociates into negative or positive charges while stabilizing the metal nanoparticles, as shown in FIG. 3, in order to immobilize them on a stationary phase such as a support. The ligand for surface modification may include a negatively charged material or a positively charged material. Particularly, the terminal of the ligand is substituted with a carboxylic functional group using MAA (Mercaptoacetic acid), MPA (Mercaptopropionic acid) or PEI (polyethyleneimine), thus forming a negatively charged surface.

(33) Upon surface-modifying the metal nanoparticles, the ratio of the metal nanoparticle solution and the ligand to be substituted is not particularly limited and may be adjusted.

(34) The substitution of the ligand is carried out via spontaneous bonding of a ligand around the nanoparticles and place-exchange reaction. Also, because the surface-modified nanoparticles are obtained via simple ligand substitution, the size and properties of the formed nanoparticles may be maintained, thereby retaining the intrinsic properties of the nanoparticles to thus have no influence on the effect of the catalyst.

(35) The surface-modified metal nanoparticles have a positively or negatively charged functional group at the terminal thereof, and are thus dispersed in an aqueous solution.

(36) In the case where a catalyst is conventionally prepared by directly binding the particles using a typical process, it is difficult to adjust the size of the metal particles and to maintain the properties of the uniform catalyst. However, the present invention adopts a method of immobilizing the uniform metal nanoparticles on the stationary phase via surface modification of the uniform metal nanoparticles and the formation of the polymer electrolyte membrane on the stationary phase, whereby the metal nanoparticles exist in the form of hanging on the polymer electrolyte membrane, making it possible to maintain the properties of the uniform catalyst and eliminating the dissolution of the metal nanoparticles.

(37) Also according to the method of the invention, upon layering the polymer membrane, the combination of cationic polymer membrane/surface-modified metal nanoparticles, or the combination of anionic polymer membrane/surface-modified metal nanoparticles is applied, so that the metal nanoparticles having an anionic surface or the metal nanoparticles having a cationic surface may be provided in the form of a single membrane, making it possible to prepare a catalyst. Because the ionic density of the surface varies depending on the number of layers, the amount of the immobilized metal nanoparticles may be adjusted.

(38) In the method of the invention, because the hydrogen ion concentration varies depending on the number of layers of the acidic polymer electrolyte, the acid strength and the acid amount may be controlled by adjusting the number of layers, or the amount of halogen may be controlled by adjusting the number of layers of the polymer electrolyte which forms a salt with the halogen anion.

(39) A further embodiment of the invention is directed to a method of preparing hydrogen peroxide via direct reaction of oxygen and hydrogen using the catalyst having surface-modified metal nanoparticles immobilized on a stationary phase on which a polymer electrolyte membrane is formed.

(40) The synthesis of hydrogen peroxide may be carried out via liquid reaction using methanol, ethanol or water as a solvent (a reaction medium).

(41) For the reaction, the oxygen and hydrogen reactants are provided in the form of a gas mixture diluted with nitrogen to decrease an explosion hazard, and the volume ratio of hydrogen to oxygen to nitrogen is 3:40:57, and the ratio of the total amount of gas used in the reaction and the rate of the solvent is set to about 3200, and a tubular reactor equipped with a cooling water jacket is used, and a reaction pressure of 50 bar and a reaction temperature of 25˜40° C. are applied.

(42) In the reaction for preparing hydrogen peroxide from oxygen and hydrogen, only a very small amount of halogen additive is used without the addition of a strong acid to prevent corrosion of the reactor. The halogen additive may include hydrobromic acid, sodium bromide (NaBr), potassium bromide (KBr), etc. The concentration of the halogen additive is 100 ppm or less, particularly 15 ppm, based on the mass of methanol used as the solvent.

(43) A better understanding of the present invention may be obtained through the following preparation example of a catalyst and examples and comparative examples of using the above catalyst to directly prepare hydrogen peroxide from oxygen and hydrogen reactants.

EXAMPLE 1

Synthesis of Uniform Metal Nanoparticles

(44) A metal precursor and a ligand were reacted to form uniform palladium nanoparticles as described below.

(45) Specifically, 45 ml of a toluene solvent was placed in a flask, and the temperature was increased to 95° C. in an argon gas environment. 0.20 g of palladium acetate as a metal precursor and 1.65 g of dodecyl sulfide as a ligand were dissolved in 5 ml of toluene and this solution was then placed in the flask, after which the reaction was carried out for 1 hr. Thereafter, the temperature of the solution was decreased to room temperature and the solvent was removed therefrom using a rotary concentrator. The reaction product was dispersed in 30 ml of acetone, divided into Eppendorf tubes, washed three times with acetone, and finally dispersed in 30 ml of toluene, thus obtaining formed metal nanoparticles. FIG. 5 shows the uniformly prepared metal nanoparticles analyzed using a transmission electron microscope (2.1±0.2 nm).

EXAMPLE 2

Surface Modification of Metal Nanoparticles

(46) The hydrophobic ligand of the above-prepared uniform metal nanoparticles was substituted with a ligand having a functional group at the terminal thereof to modify the surface of the nanoparticles.

(47) 10 ml of the metal nanoparticle solution of Example 1 and 10 ml of MAA (Mercaptoacetic acid) as a ligand to be substituted were placed in a vial. The reaction was carried out at 60° C. for 12 hr with vigorous stirring. After the reaction, 2 ml of toluene and 3 ml of distilled water were placed in the vial so that the phases were separated, and the toluene supernatant was removed.

(48) The remaining surface-modified metal nanoparticle solution was divided into Eppendorf tubes and washed three times with distilled water. Subsequently, MAA which was left behind in the surface-modified metal nanoparticle solution obtained after washing was removed using a filter, followed by dispersion in distilled water, yielding surface-modified metal nanoparticles. FIG. 6 shows the surface-modified metal nanoparticles analyzed using a transmission electron microscope (2.4±0.1 nm), and FIG. 7 shows the surface-modified metal nanoparticles analyzed using a zeta potential meter (−33.09 mV).

EXAMPLE 3

Formation of Polymer Electrolyte Membrane on Stationary Phase

(49) A polymer electrolyte membrane was formed on an anionic exchange resin having a sulfonic acid group (SO.sub.3.sup.−) as follows. The entire procedure was carried out at room temperature.

(50) Specifically, a 20 mM PAH (Poly(allylamine hydrochloride)), weight average molecular weight 200,000) aqueous solution and a 60 mM PSS (Poly(4-styrene sulfonic acid), weight average molecular weight 70,000) aqueous solution were prepared, and the pH thereof was adjusted to 9 using hydrochloric acid and sodium hydroxide.

(51) 10 g of the anionic exchange resin having a sulfonic acid group (SO.sub.3.sup.−) was added to 100 ml of distilled water and washing for 1 hr was repeated three times. The distilled water was removed, and 100 ml of a 20 mM PAH aqueous solution was placed in the flask containing the anionic exchange resin having a sulfonic acid group (SO.sub.3.sup.−), and stirred for 20 min. The solution remaining in the beaker was removed, and 100 ml of distilled water was further added and washing for 5 min was repeated three times. The number of layers of the polymer electrolyte membrane formed on the stationary phase was 1.

(52) A material including the anionic exchange resin having a sulfonic acid group (SO.sub.3.sup.−) and the PAH layer formed thereon was mixed with 100 ml of a 60 mM PSS aqueous solution and stirred for 20 min. The solution remaining behind in the beaker was removed, and 100 ml of distilled water was further added and washing for 5 min was repeated three times.

EXAMPLE 4

Formation of Multilayer Polymer Electrolyte Membrane on Stationary Phase

(53) This example was conducted in the same manner as in Example 3, with the exception that the same procedure as in Example 3 was repeated so that the number of layers of the polymer electrolyte membrane was 9.

EXAMPLE 5

Immobilization of Surface-Modified Metal Nanoparticles on Stationary Phase Having Polymer Electrolyte Membrane Formed Thereon

(54) Immobilizing the surface-modified metal nanoparticles on the anionic exchange resin having the polymer electrolyte membrane formed thereon was performed via the following to procedure. The entire procedure was carried out at room temperature.

(55) Into a flask containing the stationary phase having the anionic exchange resin having a sulfonic acid group (SO.sub.3.sup.−) on which the polymer electrolyte membrane was formed, 600 mg of surface-modified metal nanoparticles was added and stirred for 24 hr to react. The solution remaining in the beaker was removed, after which 100 ml of distilled water was further added and washing for 5 min was repeated three times.

EXAMPLE 6

Immobilization of Surface-Modified Metal Nanoparticles on Stationary Phase Having Multilayer Polymer Electrolyte Membrane Formed Thereon

(56) An immobilization process was conducted in the same manner as in Example 5, with the exception that the stationary phase having a 9-layer polymer electrolyte membrane instead of the monolayer polymer electrolyte membrane of Example 5 was used. FIG. 8 illustrates the surface-modified metal nanoparticles immobilized on the stationary phase on which the polymer electrolyte membrane was formed, which were manufactured in the form of a specimen using a cryo-microtome and then analyzed using a cryo-electron microscope.

TEST EXAMPLE 1

Efficiency of Catalyst Having Monolayer Polymer Electrolyte Membrane

(57) Hydrogen peroxide was prepared from oxygen and hydrogen using the catalyst prepared in Example 5, and the efficiency of the catalyst was evaluated.

(58) Into a tubular reactor equipped with a cooling water jacket, 10 cc of the catalyst was placed, and methanol was added for 3 hr under conditions of 1 bar and 30° C. and washing was conducted. Then, the solvent was replaced with methanol containing 15 ppm HBr, instead of methanol, and the reaction pressure was increased to 50 bar, and the volume ratio of hydrogen to oxygen to nitrogen was 3:40:57, and the ratio of the total amount of gas used in the reaction to the rate of the solvent was set to about 3200. In this state, the reaction was carried out. Thereafter, the yield of hydrogen peroxide was calculated via titration. The results are shown in Table 1 below.

TEST EXAMPLE 2

Efficiency of Catalyst Having 9-Layer Polymer Electrolyte Membrane

(59) Hydrogen peroxide was prepared from oxygen and hydrogen using the catalyst prepared in Example 6, and the efficiency of the catalyst was evaluated.

(60) TABLE-US-00001 TABLE 1 Cationic Polymer Anionic Polymer H.sub.2O.sub.2 Test Electrolyte Electrolyte Number of Layers Pd Yield Productivity (g Ex. Kind Conc. pH Kind Conc. pH of Membrane (wt %) (wt %) H.sub.2O.sub.2/g Pd .Math. hr) 1 PAH 20 mM 9 PSS 60 mM 9 1 0.154 8.03 105 2 PAH 20 mM 9 PSS 60 mM 9 9 0.009 1.11 249