Rhenium-based highly concentrated hydrated hydrazine decomposition catalyst for highly efficient hydrogen production and method for preparing same

Abstract

An embodiment of the present invention provides a rhenium-based highly concentrated hydrated hydrazine decomposition catalyst for highly efficient hydrogen production and a method for preparing same. According to an embodiment of the present invention, there is an effect of providing a high-performance hydrated hydrazine decomposition catalyst having up to 100% hydrogen selectivity for concentrated hydrated hydrazine while generating only hydrogen (H2) and nitrogen (N2) molecules as a result of a reaction.

Description

Rhenium-based highly concentrated hydrated hydrazine decomposition catalyst for high-efficiency hydrogen production and method for manufacturing the same

[0001] The present invention relates to a hydrated hydrazine decomposition catalyst, and specifically, to a rhenium-based highly concentrated hydrated hydrazine decomposition catalyst, which is a highly efficient and highly stable catalyst having up to 100% hydrogen molecule selectivity.

[0002] Hydrogen is an important energy source capable of replacing fossil fuels. Unlike conventional fossil fuels, hydrogen produces water rather than carbon compounds when the reaction proceeds, making it the most representative eco-friendly energy source. However, currently, more than 95% of hydrogen produced globally is generated through the reforming of fossil fuels. Paradoxically, this means that carbon-based byproducts are emitted when hydrogen fuel is produced.

[0003] In this regard, hydrazine (N2H4) is attracting attention as a promising hydrogen storage material due to its high hydrogen storage capacity of 12.5 wt%. However, anhydrous hydrazine poses a serious safety risk due to its high explosiveness during the hydrogen extraction process. On the other hand, hydrazine monohydrate ((N2H4·H2O)) is considerably safe and contains a significant amount of hydrogen (8.0 wt%), which far exceeds the hydrogen content of the most promising liquid organic hydrogen carriers (LOHCs), such as toluene (6.2 wt%), phenazine (6.2 wt%), naphthalene (7.3 wt%), N-ethylcarbazole (5.8 wt%), and formic acid (4.4 wt%). Furthermore, this value exceeds the 5.5 wt% target set by the U.S. Department of Energy (DOE) for in-vehicle hydrogen production systems.

[0004] In particular, unlike other LOHCs, hydrated hydrazine (HH) is a technically more attractive alternative hydrogen source because it can be catalytically decomposed at temperatures (< 100 ℃) that are much lower than the temperatures (> 200 ℃) required to dehydrogenate the most promising LOHCs. Additionally, hydrazine monohydrate is an excellent candidate for hydrogen energy transport due to its liquid stability at room temperature and atmospheric pressure, low freezing point (-50 ℃), and lower volatility than gasoline.

[0005] In addition, the complete decomposition of hydrated hydrazine (N2H4·H2O → 2H2+ N2+ H2O) generally produces environmentally friendly products such as hydrogen (H2(g)), nitrogen (N2(g)), and water, in contrast to other storage materials that typically produce carbon-based gases or solid waste.

[0006] Despite the advantages of hydrated hydrazine as a hydrogen storage material, several challenges remain regarding its practicality. The most significant challenge is related to rapid and efficient hydrogen production, where the competitive hydrazine decomposition reaction (HHDR) (3N2H4 → 4NH3 + N2), an unwanted ammonia-generating reaction, poses a major obstacle. The initial decomposition step involving the cleavage of NN bonds is thermodynamically more favorable than the cleavage of NH bonds because the bond dissociation energy of NN bonds is lower. These unwanted reactions (the generation of N2 and NH3) are the primary cause of the slow reaction rates associated with HHDR in producing H2.

[0007] However, recently, various catalysts that selectively provide 100% H₂ production during HH decomposition have been reported. These catalysts often correspond to a configuration in which transition metals such as Ni, Pt, Pd, Cu, Fe, and Zn are combined in the form of two metals and three metals and supported on a catalyst support.

[0008] Although the catalyst reported above can decompose hydrated hydrazine with 100% hydrogen selectivity, most current HHDRs use diluted aqueous HH solutions, which naturally leads to low practical H2 productivity and hinders the commercial use of the technology for H2 supply. The preference for diluted HH is due to the fact that most previously reported catalysts are observed to degrade at high hydrazine concentrations. This degradation is caused by poisoning of the active site by decomposition intermediates, which results in reduced catalyst durability.

[0009] Therefore, there is a need to develop a new catalyst that has 100% hydrogen selectivity and can rapidly and continuously decompose undiluted HH (analysis > 98%).

[0010] The present invention aims to solve the problems of the aforementioned prior art and to provide a hydrated hydrazine decomposition reaction catalyst having up to 100% hydrogen selectivity even for undiluted hydrated hydrazine.

[0011] The technical problems that the present invention aims to solve are not limited to those mentioned above, and other unmentioned technical problems will be clearly understood by those skilled in the art to which the present invention belongs from the description below.

[0012] To achieve the above technical problem, one embodiment of the present invention provides a hydrated hydrazine decomposition catalyst.

[0013] A hydrated hydrazine decomposition catalyst according to one embodiment of the present invention is characterized by comprising rhenium nanoparticles doped with nickel and platinum elements.

[0014] In an embodiment of the present invention, the ratio of each element in the nanoparticle may be 0.65 to 0.95 rhenium element; 0.05 to 0.25 nickel element; and 0.05 to 0.15 platinum element, and the hydrated hydrazine decomposition catalyst may be characterized in that.

[0015] In an embodiment of the present invention, the rhenium nanoparticles may be a hydrated hydrazine decomposition catalyst characterized by being crystalline metal nanoparticles.

[0016] In an embodiment of the present invention, the catalyst may be a hydrated hydrazine decomposition catalyst characterized by the nanoparticles having a structure in which they are interconnected with amorphous carbon.

[0017] Another embodiment of the present invention for achieving the above technical problem provides a method for manufacturing a hydrated hydrazine decomposition catalyst.

[0018] A method for preparing a hydrazine decomposition catalyst according to one embodiment of the present invention comprises the steps of: forming a rhenium oxide polytetrahydrofuran complex; adding platinum and nickel precursors to the complex and heating to produce a nanoparticle oxide; and annealing the nanoparticle oxide at a temperature of 500°C or higher and 800°C or lower to obtain rhenium nanoparticles doped with nickel and platinum elements.

[0019] In an embodiment of the present invention, the heating in the step of preparing the nanoparticle oxide may be performed at 200°C to 300°C, and the method for preparing a hydrated hydrazine decomposition catalyst may be characterized in that.

[0020] In an embodiment of the present invention, the platinum and nickel precursors may be acetylacetonate platinum (II) and acetylacetonate nickel (II), respectively, and the method for preparing a hydrated hydrazine decomposition catalyst may be characterized in that.

[0021] In an embodiment of the present invention, the annealing may be a method for preparing a hydrated hydrazine decomposition catalyst characterized by being performed in a temperature range of 570 to 650 ℃.

[0022] In an embodiment of the present invention, the method for preparing a hydrated hydrazine decomposition catalyst may be characterized in that the platinum and nickel precursors are each added in an amount of 5 to 15 mol%.

[0023] According to an embodiment of the present invention, there is an effect of providing a hydrated hydrazine decomposition catalyst of excellent performance that has up to 100% hydrogen selectivity for concentrated hydrated hydrazine while producing only hydrogen (H2) and nitrogen (N2) molecules as a result of the reaction.

[0024] Specifically, the catalyst according to an embodiment of the present invention at a reaction temperature of 80°C for 10,115 h -1 It can provide a high TOF and a mass activity of 28,840 mL / (min·g), and has excellent effects, such as maintaining 100% H2 selectivity during the catalytic dehydrogenation of nearly pure HH between room temperature and 80°C, and also effectively regenerating catalytic activity.

[0025] The effects of the present invention are not limited to the effects described above, and should be understood to include all effects that can be inferred from the configuration of the invention described in the detailed description of the invention or the claims.

[0026] FIG. 1 shows a hydrated hydrazine decomposition catalyst according to one embodiment of the present invention.

[0027] FIG. 2 is a diagram showing an SEM image of a hydrated hydrazine decomposition catalyst according to one embodiment of the present invention.

[0028] FIG. 3 is a diagram showing the powder X-ray diffraction pattern (PXRD) of a hydrated hydrazine decomposition catalyst prepared by a manufacturing method according to one embodiment of the present invention.

[0029] Figure 4 is a diagram showing a TEM image and size distribution of a hydrated hydrazine decomposition catalyst according to one embodiment of the present invention.

[0030] FIG. 5 is a CS-HR-TEM image showing the lattice of individual nanoparticles in the (0001) symmetry plane of a hydrated hydrazine decomposition catalyst according to one embodiment of the present invention.

[0031] Figure 6 is an HAADF-STEM image of a hydrated hydrazine decomposition catalyst according to one embodiment of the present invention.

[0032] Figure 7 is an EDS map of a hydrated hydrazine decomposition catalyst according to one embodiment of the present invention.

[0033] FIG. 8 is a figure showing the XPS spectrum of a hydrated hydrazine decomposition catalyst according to one embodiment of the present invention.

[0034] FIG. 9 is an image showing a system for a hydrogen generation reaction for evaluating the activity of a hydrated hydrazine catalyst according to one embodiment of the present invention.

[0035] Figure 10 is a diagram showing the performance of hydrated hydrazine decomposition catalysts annealed at 600 °C according to Pt and Ni content relative to Re.

[0036] Figure 11 is a diagram showing the performance of hydrated hydrazine decomposition catalysts annealed at 500 ℃, 600 ℃, and 700 ℃, respectively.

[0037] FIG. 12 is a diagram showing the performance of a hydrated hydrazine decomposition catalyst according to one embodiment of the present invention as a function of temperature.

[0038] Figure 13 shows the performance of a hydrated hydrazine decomposition catalyst according to one embodiment of the present invention as an Arrhenius plot according to temperature.

[0039] Figure 14 shows Pt according to various NaOH concentrations. 0.1 -Ni 0.2 This is a diagram showing the catalytic performance of @Re / C NPCs.

[0040] FIG. 15 is a diagram showing the results of comparing the catalytic performance of one embodiment and comparative examples of the present invention.

[0041] Figure 16 is a diagram showing the catalytic performance of M-Ni@Re / C NPCs annealed at 600°C.

[0042] Figure 17 shows Pt according to the repetitive HHDR response caused by the continuous injection of HH. 0.1 -Ni 0.2 This is a diagram showing the results of the reusability experiment of the @Re / C NPC catalyst.

[0043] Fig. 18 shows Pt annealed at 600 °C under an Ar / H2 atmosphere. 0.1 -Ni 0.2 This is a diagram showing the results of a reusability experiment over 8 cycles using the @Re / C NPC catalyst.

[0044] The present invention will be described below with reference to the attached drawings. However, the present invention may be implemented in various different forms and is therefore not limited to the embodiments described herein. Furthermore, in order to clearly explain the present invention in the drawings, parts unrelated to the explanation have been omitted, and similar parts throughout the specification have been given similar reference numerals.

[0045] Throughout the specification, when it is stated that a part is "connected (connected, in contact, combined)" with another part, this includes not only cases where they are "directly connected," but also cases where they are "indirectly connected" with other members interposed between them. Furthermore, when it is stated that a part "includes" a certain component, this means that, unless specifically stated otherwise, it does not exclude other components but rather allows for the inclusion of additional components.

[0046] The terms used herein are merely for describing specific embodiments and are not intended to limit the invention. Singular expressions include plural expressions unless the context clearly indicates otherwise. In this specification, terms such as “comprising” or “having” are intended to indicate the presence of the features, numbers, steps, actions, components, parts, or combinations thereof described in the specification, and should be understood as not precluding the existence or addition of one or more other features, numbers, steps, actions, components, parts, or combinations thereof.

[0047] Embodiments of the present invention will be described in detail below with reference to the attached drawings.

[0048]

[0049] First, a hydrated hydrazine decomposition catalyst according to one embodiment of the present invention will be described.

[0050] A hydrazine decomposition catalyst according to one embodiment of the present invention is characterized by comprising rhenium (Re) nanoparticles doped with nickel (Ni) and platinum (Pt) elements.

[0051] FIG. 1 shows a hydrated hydrazine decomposition catalyst according to one embodiment of the present invention. Referring to FIG. 1, it can be seen that small amounts of nickel and platinum particles are doped into rhenium-based nanoparticles.

[0052] Generally, many transition metals have been considered as catalysts for the decomposition of hydrated hydrazine, but rhenium (Re) has not generally been selected as a catalytic material for the decomposition of hydrated hydrazine.

[0053] Accordingly, the inventors of the present invention discovered that rhenium can possess excellent catalytic potential in the hydrogen evolution reaction (HER) and invented the catalyst of the present invention comprising rhenium-based nanoparticles. In particular, since rhenium (Re) is much more economical than the precious platinum group metals, the rhenium-based nanoparticle catalyst of the present invention is characterized by high marketability.

[0054] However, as with previous research results, it is difficult to decompose hydrated hydrazine with metallic rhenium alone. Accordingly, the catalyst corresponding to the embodiment of the present invention effectively lowers the NH bond dissociation energy by doping small amounts of nickel and platinum into rhenium nanoparticles, thereby promoting the partial decomposition of N2H4 into N2H2 and H adatoms (H*) on the catalyst surface.

[0055] Furthermore, trimetallic rhenium-based catalysts exhibit excellent durability even in high pH (alkaline) environments, which is an essential condition for achieving 100% hydrogen selectivity in the decomposition reaction of hydrated hydrazine. High pH environments involve OH - N2H5 that is not wanted + (N2H5 + + OH - It is advantageous because it reduces the concentration of (→ N2H4 + H2O) to prevent the formation of NH3, and at the same time promotes the deprotonation step (N2H4 → N2H3* + H*; where * represents a chemical species adsorbed on the catalyst surface), which is the rate-determining step for 100% H2 selectivity.

[0056] In an embodiment of the present invention, the nanoparticle may contain rhenium element at a ratio of 0.65 molar ratio or more relative to the total nanoparticle.

[0057] Specifically, the ratio of each element in the nanoparticles may be 0.65 to 0.95 rhenium element, 0.05 to 0.25 nickel element, and 0.05 to 0.15 platinum element with respect to 1 total, preferably 0.7 to 0.91 rhenium element, 0.05 to 0.2 nickel element, and 0.05 to 0.13 platinum element, and most preferably 0.84 to 0.9 rhenium element, 0.05 to 0.09 nickel element, and 0.05 to 0.08 platinum element.

[0058] In addition, the nanoparticles may have a Pt / Re ratio of 0.05 to 0.2 and a Ni / Re ratio of 0.05 to 0.4 on the surface of the nanoparticles. The ratio of doped platinum and nickel elements within the rhenium nanoparticles described above, i.e., the ratio of dopants, can be adjusted by controlling the annealing temperature during the doping process of the nanoparticles. If the molar ratio of the dopants deviates from the range described above, the catalyst may not have 100% H2 selectivity, and side reactions may occur, which may be undesirable. In particular, considering that the catalytic reaction occurs on the surface of the nanoparticles, it may be preferable for the surface of the nanoparticles, which are a component of the present invention, to be formed within the range of elemental content ratios described above.

[0059] In an embodiment of the present invention, the rhenium nanoparticles of the catalyst may be crystalline metal nanoparticles, and the surroundings of the nanoparticles may have a structure interconnected by amorphous carbon. For example, in one embodiment of a method for preparing a rhenium nanocatalyst to be described later, if Re2O7 is dissolved in tetrahydrofuran (THF) at a concentration of 0.1 M or higher and stored at room temperature for 24 hours or more, rhenium oxide (ReO2) x )-Polytetrahydrofuran (PTHF) is formed. The ReO thus formed xDuring the heat treatment process of the PTHF composite, the PTHF is transformed into amorphous carbon, and ReOx is reduced to rhenium metal, thereby forming Re nanoparticle clusters in which rhenium nanoparticles are interconnected with amorphous carbon.

[0060] The hydrazine decomposition catalyst according to an embodiment of the present invention can be used in the decomposition process of hydrazine. Hydrogen can be produced by the decomposition process, and as previously described, 100% hydrogen selectivity without side reactions can be achieved by the catalyst.

[0061] Although the above hydrogen production can be carried out under normal atmospheric conditions, in order to maintain the durability of the catalyst and increase reaction stability, it can be performed under an inert gas atmosphere, such as Ar gas, for example, and can be carried out by supplying hydrated hydrazine to the container containing the catalyst.

[0062] In particular, the hydrazine decomposition catalyst according to the embodiment of the present invention has the excellent effect of being able to decompose even under low temperature conditions from room temperature to 80°C and rapidly produce a large amount of hydrogen, thus having high marketability and commercial potential.

[0063]

[0064] Next, a method for preparing a hydrated hydrazine decomposition catalyst according to one embodiment of the present invention will be described.

[0065] In describing the above method for preparing the hydrated hydrazine decomposition catalyst, descriptions that overlap with the previously described hydrated hydrazine decomposition catalyst are omitted.

[0066] A method for preparing a hydrazine decomposition catalyst according to one embodiment of the present invention comprises the steps of: forming a rhenium oxide polytetrahydrofuran composite gel (S100); adding platinum and nickel precursors to the composite gel and heating to produce a nanoparticle oxide (S200); and annealing the nanoparticle oxide at a temperature of 500°C or higher and 800°C or lower to obtain rhenium nanoparticles doped with nickel and platinum elements (S300).

[0067] First, rhenium oxide polytetrahydrofuran (hereinafter, ReO x -PTHF) forms a complex gel (S100).

[0068] In the above S100 step, a complex gel may be formed by polymerizing a monomer THF solution containing a rhenium precursor. In this case, the rhenium precursor may be, for example, Re2O7, and the above S100 step may be a step of dissolving Re2O7 in a THF solvent at a concentration of 0.1M or higher and then performing polymerization. In this case, rhenium oxide-polytetrahydrofuran is formed when the tetrahydrofuran is dissolved and stored for about 24 hours or more.

[0069] Next, a dopant precursor material is added to the composite gel and heated to form a nano powder (S200).

[0070] The above precursors may be platinum and nickel precursors, for example, platinum(II) acetylacetonate (Pt(acac)2) and nickel(II) acetylacetonate (Ni(acac)2), respectively.

[0071] At this time, it is preferable to add 5 to 15 mol%, most preferably 10 mol%, of each of the platinum and nickel precursors to the composite gel. A catalyst prepared by adding a dopant precursor outside the range described above may have low catalytic activity and may not be desirable.

[0072] The heating is preferably performed, for example, at 200°C to 300°C for 2 to 3 hours. By solvothermizing the composite gel described above, a platinum and nickel-doped rhenium-based nanoparticle oxide (Pt-Ni@ReOx / C) is formed.

[0073] Finally, the nanoparticle oxide is reduced (S300).

[0074] The above reduction includes a process of annealing the nanoparticle oxide prepared in step S200 at a temperature of 500°C or higher and 800°C or lower, and after the annealing process is completed, rhenium nanoparticles doped with nickel and platinum elements can be obtained.

[0075] At this time, the annealing is performed at a temperature range of 500°C to 800°C, preferably 550°C to 700°C, and most preferably 570°C to 650°C. When annealing is performed within the above range, the hydrated hydrazine decomposition catalyst obtained as in the experimental example to be described later can have 100% hydrogen selectivity and have an excellent effect.

[0076] Previously manufactured ReO x In the PTHF composite, during the heat treatment process of the S300 step below, PTHF is transformed into amorphous carbon and ReOx is reduced to rhenium metal, forming Re nanoparticle clusters in which rhenium nanoparticles are interconnected by amorphous carbon.

[0077] The present invention will be explained in more detail below through manufacturing examples, comparative examples, and experimental examples. However, the present invention is not limited to the following manufacturing examples and experimental examples.

[0078]

[0079] Example 1: Preparation of Pt-Ni@Re / C nanoparticle cluster catalyst

[0080] Crystalline rhenium metal nanoparticle clusters doped with rhenium and nickel (hereinafter, Pt-Ni@Re / C NPCs) were synthesized through the following three-step process.

[0081] First, rhenium oxide-polytetrahydrofuran (ReO₂) was produced under ambient conditions through the spontaneous cationic ring-opening polymerization of the monomer THF. x A -PTHF) complex gel was formed. At this time, 0.4 mmol of Re2O7 was dissolved in 1 mL of THF.

[0082] Subsequently, 10 mol% (each) of platinum(II) acetylacetonate (Pt(acac)2) and nickel(II) acetylacetonate (Ni(acac)2) were added and dissolved to form trimetallic Re-based nanoparticles (NPs) having excellent catalytic activity against HHDR.

[0083] Then, the above ReO x - The PTHF complex gel was placed in a Teflon autoclave and solvothermally treated by heating in an oven at 250°C for 2.5 hours to obtain Pt-Ni@ReO x / C formed NPCs into black powder.

[0084] In the final step, Pt-Ni@ReO x / C NPCs were annealed under H2 / Ar at a temperature of 500 °C or higher to reduce the oxide and obtain crystalline Re metal nanoparticles doped with Pt and Ni (i.e., Pt-Ni@Re / C NPC catalysts composed of nanoparticles interconnected by amorphous carbon).

[0085] Figure 2 is a diagram showing an SEM image of a hydrated hydrazine decomposition catalyst according to one embodiment of the present invention, and can be seen in the appearance of a catalyst in which crystalline Re metal nanoparticles are interconnected with amorphous carbon.

[0086]

[0087] Experimental Example 1: Observation of Structural Characteristics

[0088] FIG. 3 is a diagram showing the powder X-ray diffraction pattern (PXRD) of a hydrated hydrazine decomposition catalyst prepared by a manufacturing method according to one embodiment of the present invention.

[0089] The formation of crystalline metallic Re was confirmed by the Powder X-ray Diffraction (PXRD) pattern of these NPCs, which matches the typical pattern of metallic Re (space group: P63 / mmc, hcp, a = b = 2.76 Å, c = 4.458 Å, α = β˚= 90˚, γ= 120˚), as can be seen in Fig. 3 above. Meanwhile, the expected peaks associated with Pt and Ni dopants are not distinguished, which is likely because these elements are randomly dispersed.

[0090]

[0091] The method for preparing the nanoparticle cluster catalyst of Example 1 described above is characterized by a high annealing temperature and the addition of a transition metal dopant, and the higher annealing temperature can help to successfully prepare a material having Re NPs with smaller particles, a larger surface area, and more stably incorporated dopants that can effectively catalyze the thermal dissociation of molecular hydrazine.

[0092] Figure 4 is a diagram showing a TEM image and size distribution of a hydrated hydrazine decomposition catalyst according to one embodiment of the present invention.

[0093] FIG. 5 is a CS-HR-TEM image showing the lattice of individual nanoparticles in the (0001) symmetry plane of a hydrated hydrazine decomposition catalyst according to one embodiment of the present invention.

[0094] The high-resolution transmission electron microscope (HR-TEM) image of Pt-Ni@Re / C NPCs annealed at 600°C shown in Fig. 4 clearly shows interconnected nanoparticles with an average diameter of 2.69 ± 0.12 nm and a spacing of 2.40 Å in the (1000) plane, and as shown in Fig. 5, it can be confirmed that they are consistent with a crystalline structure in the (0001) plane of symmetry. In addition, the nanoparticles of Pt-Ni@Re / C NPCs are much smaller than those of NPCs annealed at 500°C.

[0095]

[0096] Figure 6 is an HAADF-STEM image of a hydrated hydrazine decomposition catalyst according to one embodiment of the present invention.

[0097] Figure 7 is an EDS map of a hydrated hydrazine decomposition catalyst according to one embodiment of the present invention.

[0098] In addition, the high-angle annular dark-field scanning transmission electron microscope (HAADF-STEM) image of Fig. 6 and the energy-dispersive X-ray spectroscopy (EDS) map of Fig. 7 show that Pt and Ni dopants are well dispersed in Re nanoparticles.

[0099]

[0100] Smaller particles obtained at higher temperatures may be due to the removal of oxygen atoms from the Re oxide used to synthesize Re NPCs. Re oxide is known to be thermally reduced during annealing in the absence of an external reducing agent, and this reduction can cause the pulverization of Re NPs due to the rupture of the Re oxide.

[0101] In fact, it was observed that increasingly smaller Re particles were formed as the annealing temperature increased, and consequently, the nanoparticle size in Pt-Ni@Re / C NPC was observed to be 3 nm in the sample annealed at 500°C and 2 nm in the sample annealed at 700°C. In addition, the particle size distribution improved as the annealing temperature increased.

[0102] Similarly, X-ray photoelectron spectroscopy (XPS) confirmed that the concentrations of Pt and Ni dopants on the surface of Re NPs increased with increasing annealing temperature. On the surface of Pt-Ni@Re / C NPCs prepared at 500°C, the Pt / Re and Ni / Re ratios were 0.11 and 0.08, respectively (Pt 0.1 -Ni 0.08 @Re / C).

[0103] On the other hand, when annealing at 600°C, 0.12 and 0.21 (Pt 0.1 -Ni 0.2 @Re / C) and at 700°C are 0.12 and 0.35 (Pt 0.1 -Ni 0.3 @Re / C).

[0104] Relative atomic ratioSamplePt / ReNi / ReSample namePt-Ni@Re / C NPCs annealed at 500 o C0.110.08Pt 0.1 -Ni 0.08 @Re / CPt-Ni@Re / C NPCs annealed at 600 o C0.120.21Pt 0.1 -Ni 0.2 @Re / CPt-Ni@Re / C NPCs annealed at 700 o C0.120.35Pt 0.1 -Ni 0.3 @Re / C

[0105] The difference in behavior between Pt and Ni during annealing can be attributed to their different physical and chemical properties. Ni, having a smaller atomic radius than Pt, allows for higher diffusion, enabling more active interactions with Re. Notably, XPS results showed that the atomic ratios of Pt and Ni on the Re surface were greater than the amount of initially added metal (relative to Re) (10 mol%) during the synthesis of Pt-Ni@Re / C NPCs. This was particularly true when annealing at temperatures above 600°C. Conversely, inductively coupled plasma (ICP) analysis revealed that catalysts annealed at 500 and 600°C exhibited a Re:Ni:Pt atomic ratio of approximately 86.7:5.6:7.7, while catalysts annealed at 700°C showed a ratio of 83.4:9.9:6.7, indicating that most of the Pt and Ni dopants were incorporated into the surface of the Pt-Ni@Re / C NPCs.

[0106] samplewt%at%RePtNiReNiPtPt-Ni@Re / C NPCs annealed at 500 o C74.966.851.5386.80455.62117.5744Pt-Ni@Re / C NPCs annealed at 600 o C75.297.021.5386.69645.58987.7137Pt-Ni@Re / C NPCs annealed at 700 o C83.777.053.1383.40889.88806.7032

[0107] FIG. 8 is a figure showing the XPS spectrum of a hydrated hydrazine decomposition catalyst according to an embodiment of the present invention. In FIG. 8 (a), Pt 0.1 -Ni 0.2 The XPS spectrum of @Re / C shows a distinct peak of Re at 38–50 eV, which is the fully reduced metallic Re (Re 4f 7 / 2 and Re 4f 5 / 2It was deconvolved into peaks at 40.56 and 42.98 eV corresponding to ), and peaks at 41.43, 43.85, 45.68, and 48.1 eV consistent with the presence of Re(IV) and Re(VI) due to surface oxidation. The Re in NPCs is approximately 75% metallic Re. 0 It consists of 25% Re oxide composed of Re(IV) and Re(VI).

[0108] In addition, in Fig. 8(b) above, the Pt 4f peak was observed at 64–80 eV, which is Pt 0 It is attributed to (71.1 and 74.43 eV) and Pt(II) (71.8 and 75.13 eV). The NPC's Pt is approximately 60% of Pt 0 It consists of 40% Pt(II).

[0109] In Fig. 8(c) above, the Ni incorporated into the Pt-Ni@Re / C NPC is in two oxidation states, namely Ni at 852.8 and 870 eV. 0 and Ni at 855.74 and 873.07 eV 2+ It represents a peak for and includes satellite peaks at 861.4 and 878.9 eV. The Ni in NPCs consists of 15.6% Ni0 and 84.4% Ni(II).

[0110] Table 3 below is a table listing the elemental content of the examples that vary depending on the annealing temperature as described above.

[0111] AnnealingReNiPt Example 1500 ℃ 86.85.67.6 Example 2600 ℃ 86.75.67.7 Example 3700 ℃ 83.49.96.7

[0112]

[0113] Experimental Example 2: Optimization of Pt-Ni@Re / C NPC Catalyst Activity

[0114] FIG. 9 is an image showing a system for a hydrogen generation reaction for evaluating the activity of a hydrated hydrazine catalyst according to one embodiment of the present invention.

[0115] As shown in Figure 9 above, a laboratory-fabricated stainless steel reaction vessel was used to evaluate the catalytic activity of Pt-Ni@Re / C NPCs for HHDR. The vessel contained a vial with 5 mg of Pt-Ni@Re / C NPCs and was equipped with an Ar gas inlet line, a generated gas outlet line, and a line for injecting 0.1 mL of undiluted HH (98%) containing 0.25 mmol of NaOH. The gases (hydrogen and nitrogen) emitted during catalytic HHDR were quantified using the water-displacement method. An Ar atmosphere was established before injecting the hydrazine to prevent nanocatalytic degradation through the potent reaction of the undiluted hydrazine and to ensure safety.

[0116] The optimal Pt and Ni content in Re NPs was determined by adjusting the amounts of Pt(acac)2 and Ni(acac)2 and the annealing temperature of the trimetallic Re-based NPCs. These variables, particularly the dopant content on the surface of Re metal nanoparticles, are critical factors as previously explained. In other words, the amount of each transition metal component in the NPC determines the catalytic HHDR activity.

[0117] Figure 10 is a diagram showing the performance of hydrated hydrazine decomposition catalysts annealed at 600 °C according to Pt and Ni content relative to Re.

[0118] Figure 11 is a diagram showing the performance of hydrated hydrazine decomposition catalysts annealed at 500 ℃, 600 ℃, and 700 ℃, respectively.

[0119] In FIGS. 10 and 11 above, finally, Pt-Ni@Re / C NPCs were synthesized using 10 mol% of Pt(acac)2 and Ni(acac)2 at an annealing temperature of 600°C to Pt that most effectively decomposes HH in the temperature range of 25–80°C. 0.1 -Ni 0.2 @Re / C I got NPCs.

[0120] FIG. 12 is a diagram showing the performance of a hydrated hydrazine decomposition catalyst according to one embodiment of the present invention as a function of temperature.

[0121] Optimal Pt 0.1 -Ni 0.2 As shown in Fig. 12 above, it can be confirmed that the @Re / C NPC catalyst completely decomposes hydrazine with 100% selectivity for hydrogen production at all temperatures within the aforementioned range.

[0122]

[0123] Hydrogen selectivity (x) can be calculated using the following Equation 1, which combines the complete reaction (N2H4→ 2H2+ N2) and the incomplete reaction (3N2H4→ 4NH3+ N2) during hydrazine decomposition.

[0124] (Equation 1)

[0125] 3N2H4(l)→ 6xH2(g) + (1 + 2x) N2(g) + 4(1 - x) NH3(g)

[0126]

[0127] Pt 0.1 -Ni 0.2 The HHDR on @Re / C NPCs has an activation energy of 39.96 kJ / mol. In the reaction vessel, 5 mg of NPCs completely decomposed 0.1 mL of undiluted hydrazine (2 mmol) to produce a gas volume of 146 mL at 25°C. This corresponds to an expected theoretical volume (6 mmol) with no side reactions releasing gaseous ammonia, with hydrogen and nitrogen as the only products.

[0128] The observed 100% H2 selectivity implies that since hydrazine can decompose to produce 1 mol of N2 and 2 mol of H2, there is a molar ratio of 3 (n(N2+H2) / n(N2H4)) between the total generated gas and hydrazine. Dissolved NH3 was detected using the indolephenol blue method, which involves passing the gas generated in the HHDR reactor through a 1 M HCl solution and then adding NaOCl and phenol to the solution.

[0129] No significant color change was observed in the 630–655 nm range, and no UV-vis absorbance peak was recorded, indicating that only N2 and H2 were generated by complete HHDR on the Pt-Ni@Re / C NPC catalyst. In addition, 100% H2 selectivity was confirmed using gas chromatography equipped with a thermal conductivity detector (TCD).

[0130]

[0131] Experimental Example 3: Pt-Ni@Re / C NPC Performance Indicators, Catalytic Activity, and the Role of pH

[0132] In the above Experimental Example 2, 5 mg of Pt 0.1 -Ni 0.2 @Re / C released gas at a rate of 10 mL / min even at room temperature and completely decomposed hydrazine with 100% H2 selectivity, which resulted in a mass activity of 2040 mL / min·g and 716 h -1 It corresponds to the TOF. This is the value obtained at the point of 50% HHDR completion. The TOF was calculated using Equation 2 below.

[0133] (Equation 2)

[0134] TOF = (n(H2) 50% ) / (n(metal)×t 50% )

[0135] In Equation 2 above, n(H2) 50% is the amount of H2 gas generated, and t 50%ε is the reaction time at the point of 50% dehydrogenation, and n(metal) is the number of moles of metal in the catalyst. Mass activity was calculated using the total mass of the loaded catalyst.

[0136] As shown in Fig. 12 above, the decomposition rate increased rapidly as the reaction temperature increased from room temperature to 80 °C. 0.1 mL of undiluted HH was completely decomposed with 100% H2 selectivity within 80 seconds at 80 °C, and the TOF was 10115 h -1 The mass activity was 28840 mL / (min·g). The TOF and mass activity values ​​determined here are the highest values ​​reported to date and correspond to the first values ​​obtained using undiluted HH.

[0137] In conclusion, Pt 0.1 -Ni 0.2 @Re / C catalysts have excellent characteristics in that they provide 100% H2 selectivity even at relatively high temperatures such as 80°C. This is because higher temperatures generally accelerate multiple reaction pathways in a way that prevents most catalysts from providing 100% H2 selectivity.

[0138] On the other hand, Pt-Ni@Re / C catalyst annealed at 500 ℃ (Pt 0.1 -Ni 0.08 @Re / C) did not provide 100% H2 selectivity, and the catalyst (Pt) annealed at 700 ℃ 0.1 -Ni 0.3 @Re / C) provided 100% H2 selectivity but exhibited lower catalytic activity than the catalyst annealed at 600 °C, and TOF was 6467 h -1 The mass activity was 18,440 mL / (min·g).

[0139] In addition, Pt-Ni@Re NPCs prepared using 5 and 15 mol% dopant precursors were annealed at 600 °C, and these catalysts exhibited lower catalytic activity than the catalyst prepared using 10 mol% dopant precursor, but both provided 100% H2 selectivity.

[0140] Figure 13 shows the performance of a hydrated hydrazine decomposition catalyst according to one embodiment of the present invention as an Arrhenius plot according to temperature.

[0141] Referring to Fig. 13 above, Pt 0.1 -Ni 0.2 The Arrhenius relationship constructed by considering the catalytic HHDR at various temperatures performed with @Re / C showed a low activation energy (Ea) of 39.96 kJ / mol, which is consistent with previously reported efficient hydrogen production from diluted HH despite the presence of numerous intermediates that significantly hinder catalytic activity during the dissociation of concentrated HH.

[0142]

[0143] A high pH environment is favorable for excellent HHDR-based H2 production facilitated by Pt-Ni@Re / C NPCs, and NaOH concentration plays a crucial role in ensuring 100% H2 selectivity and enhancing the reaction rate. - The presence of [something] in equilibrium according to Le Chatelier's principle (N2H4+ H2O ↔ N2H4·H2O ↔ N2H5+ ·OH - ) moves to the left, and this movement is an unwanted N2H5 + It lowers the concentration of and promotes the sequential cleavage of NH bonds. Consequently, only N2 is produced as a byproduct during the decomposition of N2H4. The pathway is as follows.

[0144] N2H4·H2O→N2H4→N2H3→N2H2→N2H→N2

[0145]

[0146] Figure 14 shows Pt according to various NaOH concentrations.0.1 -Ni 0.2 This is a diagram showing the catalytic performance of @Re / C NPCs.

[0147] Figure 14 above shows Pt at a reaction temperature of 80 ℃. 0.1 -Ni 0.2 @Re / C shows how the rate of the HH thermal decomposition reaction on NPCs varies with NaOH concentration (0-3 M).

[0148] Surprisingly, the NPC catalyst exhibited high H2 selectivity (> 95%) and high TOF (> 2000 h⁻¹) even at low NaOH concentrations (0.5 M) and in the absence of NaOH. -1 It provides ), but 100% H2 selectivity was not observed under these conditions.

[0149] Complete HH decomposition was observed at NaOH concentrations of 1 M or higher, and TOF at 2.5 M NaOH was 10115 h -1 It was recorded as such. However, as the NaOH concentration increased further, the reaction rate decreased sharply, and TOF in 3 M NaOH was 4924 h -1 It was recorded as such, which is believed to be due to catalyst decomposition or clogging caused by a large amount of hydroxide attached to the catalyst surface.

[0150]

[0151] Experimental Example 4: Pt-Ni@Re / C NPC Catalytic Mechanism

[0152] FIG. 15 is a diagram showing the results of comparing the catalytic performance of an embodiment and comparative examples of the present invention. Specifically, FIG. 15 shows Re powder, synthesized Re / C, Ni@Re / C, Pt@Re / C, and a corresponding Pt 0.1 -Ni 0.2 It is a graph showing the comparative catalyst performance of @Re / C NPCs.

[0153] The excellent H2 production capability of Pt-Ni@Re / C NPCs on HHDR is considered to be due to the synergistic effect of the trimetallic catalyst system, and to clarify the effect of this system, a single metal (Re 0 HHDR catalyst performance was evaluated using ) and bimetallic (Ni@Re and Pt@Re) catalysts. The results are shown in Fig. 15 above.

[0154] Commercially available single metal Re 0 The powder was nearly inactive for HHDR, just as most single metal NPs exhibit low catalytic activity for HDR. Synthesized Re / C NPCs without dopants showed some catalytic activity, but Pt 0.1 -Ni 0.2 @Re / C Much lower TOF than trimetallic systems (1445 h -1 It showed mass activity (4120 mL / (min·g)) and H2 selectivity (56%).

[0155] The difference in activity between commercial Re metal powder and Re / C NPCs is attributed to the much larger surface area of ​​Re / C NPCs and the catalyst support (aC). In bimetallic NPCs such as Ni@Re and Pt@Re, Re particles were individually doped with Ni and Pt, respectively. Although these catalysts exhibited superior catalytic performance compared to single-metal systems, they still failed to achieve 100% H2 selectivity and showed significantly inferior catalytic performance compared to trimetallic Pt-Ni@Re / C NPCs. This implies that when Pt and Ni are incorporated together, each transition metal plays a harmonious role with Re to form a trimetallic system that provides the most significant catalytic activity.

[0156] The decomposition of concentrated HH is likely to provide a much greater opportunity for the formation of intermediates than that of diluted HH, suggesting that more NH3 may be produced. The formation of NH3 corresponds to an unwanted side reaction that lowers catalytic activity for H2 production. However, the Pt-Ni@Re / C of the present invention has been shown to completely and rapidly decompose undiluted HH while producing 0 NH3.

[0157] FIG. 16 is a diagram showing the catalytic performance of M-Ni@Re / C NPCs annealed at 600°C. Here, M refers to another transition metal dopant.

[0158] In particular, the electronegativity of each transition metal in trimetallic Pt-Ni@Re / C NPCs is expected to play a crucial role in achieving such highly efficient catalytic activity.

[0159] The electronegativity of Re, Ni, and Pt are 1.9, 1.91, and 2.28, respectively. The electronegativity difference is due to the more positively charged (δ) electrons as electron density is attracted by the more electronegative Pt and Ni dopants. + ) Induces the Re surface. Notably, in the spectrum of Pt-Ni@Re / C, the Pt 4f and Ni 2p XPS peaks are shifted in the negative direction compared to the peaks of commercial Pt / C, PtNi / SWNT, and metal-doped Pt3Ni / C nanoparticles.

[0160] This negative shift suggests strong electron transfer to Pt and Ni particles because the electronegativity of Re is lower than that of Pt and Ni, indicating that Pt and Ni have been incorporated into the surface of Re in Pt-Ni@Re / C NPCs.

[0161] Consequently, Pt-Ni@Re / C NPCs provide 100% H2 selectivity without generating NH3. Referring to Figure 16 above, in the control experiment, Fe-Ni@Re / C, Co-Ni@Re / C, and Cu-Ni@Re / C NPCs doped with Fe, Co, and Cu instead of Pt exhibited much lower catalytic activity for HHDR than Pt-Ni@Re / C NPCs.

[0162] The electronegativity of Fe (1.8) and Co (1.88) is somewhat lower and more similar than that of Re, which can inhibit stable nitrogen atom bonding to the surface compared to Pt-Ni@Re / C NPCs. Additionally, the much lower H2 selectivity observed in Cu-Ni@Re / C NPCs implies that, despite the electronegativity of Cu being similar to that of Re (i.e., 1.9), Pt plays a significant role in promoting efficient NH bond cleavage by interacting with adsorbed H atoms.

[0163]

[0164] Experimental Example 5: Pt-Ni@Re / C NPC Catalyst Reusability Experiment

[0165] Figure 17 shows Pt according to the repetitive HHDR response caused by the continuous injection of HH. 0.1 -Ni 0.2 This is a diagram showing the results of the reusability experiment of the @Re / C NPC catalyst.

[0166] Fig. 18 shows Pt annealed at 600 °C under an Ar / H2 atmosphere. 0.1 -Ni 0.2 This is a diagram showing the results of a reusability experiment over 8 cycles using the @Re / C NPC catalyst.

[0167] The sustainability and reusability of nanocatalysts are very important aspects in practical applications.

[0168] Accordingly, the catalytic sustainability of Pt-Ni@Re / C NPCs was evaluated by repeatedly injecting 0.1 mL of undiluted HH at the end of each HHDR. This is illustrated in Fig. 17 above. This process was repeated while the HHDR continuously provided 100% H2 selectivity. The Pt-Ni@Re / C NPCs successfully degraded undiluted HH over seven consecutive injections. However, a 50% decrease in TOF was observed.

[0169] This significant decrease in TOF is due to the blockage of the catalytic active sites of Pt-Ni@Re / C NPCs caused by the accumulation of water and intermediates. However, the poisoned surfaces of Pt-Ni@Re / C NPCs were regenerated by thermal annealing at 600 °C under Ar / H2, which effectively removed water and other intermediate species.

[0170] As a result, as shown in Figure 18 above, the regenerated NPCs exhibited a TOF reduction of less than about 5% over 8 cycles. After 10 cycles, the TOF decreased by about 13% compared to the initial HHDR, but the reaction still provided 100% H₂ selectivity and high TOF.

[0171]

[0172] According to the embodiments of the present invention described above, it can be seen that the hydrazine decomposition catalyst of the present invention exhibited excellent catalytic performance for the dehydrogenation of concentrated HH while generating only H2 and N2.

[0173] Specifically, the catalyst according to one embodiment of the present invention at a reaction temperature of 80°C for 10,115 h -1It provided a high TOF and a mass activity of 28,840 mL / (min·g). In particular, Pt-Ni@Re / C NPCs maintained 100% H2 selectivity during the catalytic dehydrogenation of nearly pure HH between room temperature and 80 °C. Furthermore, catalytic activity was effectively regenerated by thermal annealing at 600 °C under Ar / H2, resulting in a TOF reduction of less than 5% over 8 cycles and about 13% over 10 cycles, which remained the same even when using high concentrations of HH.

[0174] Through the excellent performance of the present invention described above, the potential for using Pt-Ni@Re / C NPCs can be seen, for example, in hydrogen generation systems within vehicles driving fuel cells; in particular, the sustained and high H2 selectivity and catalytic efficiency confirm that the Pt-Ni@Re / C NPCs of the present invention can be used in various industrial fields.

[0175]

[0176] The foregoing description of the present invention is for illustrative purposes only, and those skilled in the art will understand that other specific forms can be easily modified without altering the technical spirit or essential features of the present invention. Therefore, the embodiments described above should be understood as illustrative in all respects and not restrictive. For example, each component described as a single unit may be implemented in a distributed manner, and components described as distributed may likewise be implemented in a combined form.

[0177] The scope of the present invention is defined by the claims set forth below, and all modifications or variations derived from the meaning and scope of the claims and equivalent concepts thereof should be interpreted as being included within the scope of the present invention.

Claims

1. A hydrated hydrazine decomposition catalyst characterized by comprising rhenium nanoparticles doped with nickel and platinum elements.

2. In Paragraph 1, The elemental ratio on the surface of the above nanoparticles is, The Pt / Re ratio is 0.05 to 0.2, and A hydrated hydrazine decomposition catalyst characterized by a Ni / Re ratio of 0.05 to 0.

4.

3. In Paragraph 1, The above nanoparticles are, Rhenium element 0.65 ~ 0.95; Nickel element 0.05 ~ 0.25; A hydrated hydrazine decomposition catalyst characterized by being composed of 0.05 to 0.15 platinum elements.

4. In Paragraph 1, The above rhenium nanoparticles are a hydrazine decomposition catalyst characterized by being crystalline metal nanoparticles.

5. In Paragraph 1, The above catalyst is a hydrazine decomposition catalyst characterized by the fact that the nanoparticles have a nanoparticle cluster structure in which the nanoparticles are interconnected with amorphous carbon.

6. Step of forming a rhenium oxide-polytetrahydrofuran complex; A step of adding platinum and nickel precursors to the above composite and heating to produce nanoparticle oxides; and A method for preparing a hydrated hydrazine decomposition catalyst, characterized by including the step of annealing the above-mentioned nanoparticle oxide at a temperature of 500°C or higher and 800°C or lower to obtain rhenium nanoparticles doped with nickel and platinum elements.

7. In Paragraph 6, A method for preparing a hydrated hydrazine decomposition catalyst, characterized in that the heating in the step of preparing the nanoparticle oxide is performed at 200 ℃ to 300 ℃.

8. In Paragraph 6, A method for preparing a hydrated hydrazine decomposition catalyst, characterized in that the platinum and nickel precursors are acetylacetonate platinum (II) and acetylacetonate nickel (II), respectively.

9. In Paragraph 6, A method for preparing a hydrated hydrazine decomposition catalyst, characterized in that the annealing is performed in a temperature range of 570 to 650 ℃.

10. In Paragraph 6, A method for preparing a hydrated hydrazine decomposition catalyst, characterized in that the platinum and nickel precursors are each added in an amount of 5 to 15 mol%.

11. A method for producing hydrogen characterized by using the catalyst of claim 1, supplying hydrated hydrazine to the catalyst under an inert gas atmosphere to decompose the hydrated hydrazine.

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