Patent Application
20240301534
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The present invention generally relates to synthesis of intermetallic nanoparticles. More specifically the present invention relates to controllable synthesis of noble-metal based intermetallic nanoparticles with hollow or solid architectures.
Noble metals have been intensively explored as promising candidates for versatile applications, especially in catalysis, owing to their unique physicochemical properties, while their practical application still suffers from the high cost and scarcity. Therefore, numerous research efforts have been devoted to developing high-performance catalysts with reduced content and increased utilization efficiency of noble metals. Specifically, alloying noble metals with high-abundance non-noble metals has been regarded as an appealing route, which not only reduces the usage of noble metals but also enhances their catalytic performances due to the synergistic effect of different metal atoms. Besides, the construction of hollow architectures in noble metal catalysts offers another promising approach to achieving this goal. Benefiting from the large specific surface area and open architecture, hollow noble metal catalysts could provide more exposed surface sites compared with their solid counterparts, thus enhancing the noble-metal utilization efficiency. To date, preparing noble metal-based alloys with hollow architectures has attracted extensive research attention for achieving high catalytic performance. However, the current studies are mainly limited to hollow noble metal-based alloys with conventional thermodynamically stable crystal phases.
Recently, phase engineering of nanomaterials (PEN) has been proven as a compelling strategy to modulate the intrinsic properties of noble metal-based nanomaterials and boost their catalytic performances by precisely tuning the atomic arrangements, which stimulates the synthesis of noble metal-based alloys with unconventional phases and allows the exploration of their phase-dependent properties and applications. In particular, noble metal-based intermetallic alloys with ordered atomic arrangements of component atoms represent a novel class of nanomaterials, exhibiting excellent performances towards various catalytic applications, e.g., carbon dioxide reduction reaction, oxygen reduction reaction, ethanol reduction reaction, and hydrogenation reaction. Although tremendous efforts have been devoted to the synthesis of noble metal-based intermetallic alloys with distinct crystal phases or architectures, most of the developed synthetic strategies can only yield intermetallic alloys with solid architectures and are not capable of tuning the crystal phase of products. The general and controlled preparation of hollow noble metal-based intermetallic alloys with different phases is highly desirable for the development of advanced catalysts and exploration of their structure-dependent performances.
In accordance with a first aspect of the present invention, a method for synthesizing intermetallic nanoparticles is provided. The method comprises: preparing noble-metal nanoparticle seeds; dispersing a metal precursor into the noble-metal nanoparticle seeds to form a first mixture; adding the first mixture into an organic solvent to form a first solution; sonicating the first solution at room temperature; subjecting the first solution to a heat treatment under N2 atmosphere to render a second solution; cooling the second solution naturally to room temperature; adding ethanol to the second solution to form a third solution; and collecting the intermetallic nanoparticle from the third solution by centrifugation.
In accordance with one embodiment, a heating temperature of the heat treatment ranges from 200° C. to 300° C.; and a heating time of the heat treatment is longer than 1 hour.
In accordance with another embodiment, the heating temperature is 250° C.; and the heating time is 3 hours.
In accordance with another embodiment, the noble-metal nanoparticle seeds are made of noble-metal nanoparticles with hexagonal close-packed phase such that the synthesized intermetallic nanoparticles are hollow intermetallic nanoparticles.
In accordance with another embodiment, the noble-metal nanoparticles with hexagonal close-packed phase are Pd nanoparticles and the metal precursor is a Sn precursor such that the synthesized intermetallic nanoparticles are hollow Pd—Sn intermetallic nanoparticles.
In accordance with another embodiment, a weight ratio of the Sn precursor to the Pd nanoparticles ranges from 3:2 to 4:1 such that the synthesized Pd—Sn intermetallic nanoparticles are hollow orthorhombic Pd2Sn alloy nanoparticles.
In accordance with another embodiment, the weight ratio of the Sn precursor to the Pd nanoparticles is 12:7.
In accordance with another embodiment, the synthesized hollow orthorhombic Pd2Sn alloy nanoparticles have an average particle size of 10.2±1.8 nm and an average void size of 5.2=1.1 nm.
In accordance with another embodiment, a weight ratio of the Sn precursor to the Pd nanoparticles ranges from 7:1 to 10:1 such that the synthesized Pd—Sn intermetallic nanoparticles are hollow monoclinic Pd3Sn2 alloy nanoparticles.
In accordance with another embodiment, the weight ratio of the Sn precursor to the Pd nanoparticles is 60:7.
In accordance with another embodiment, the synthesized hollow monoclinic Pd3Sn2 alloy nanoparticles have an average particle size of 11.5±2.9 nm and an average void size of 5.5±2.9 nm.
In accordance with another embodiment, the noble-metal nanoparticle seeds are made of noble-metal nanoparticles with face-centred cubic phase such that the synthesized intermetallic nanoparticles are solid intermetallic nanoparticles.
In accordance with another embodiment, the noble-metal nanoparticles with face-centred cubic (fcc) phase are Pd nanoparticles and the metal precursor is a Sn precursor such that the synthesized intermetallic nanoparticles are solid Pd—Sn intermetallic nanoparticles.
In accordance with another embodiment, a weight ratio of the Sn precursor to the Pd nanoparticles ranges from 3:2 to 4:1 such that the synthesized Pd—Sn intermetallic nanoparticles are solid orthorhombic Pd2Sn alloy nanoparticles.
In accordance with another embodiment, the weight ratio of the Sn precursor to the Pd nanoparticles is 12:7.
In accordance with another embodiment, the synthesized solid orthorhombic Pd2Sn alloy nanoparticles have an average particle size of 7.4±0.7 nm.
In accordance with a second aspect of the present invention, a method of using intermetallic nanoparticles made by the afore-said synthesis method as catalysts for an electrochemical glycerol oxidation reaction is provided.
The present invention provides a controllable and general seeded method for synthesizing distinct intermetallic alloy nanoparticles with hollow or solid architectures. The as-synthesized hollow orthorhombic Pd2Sn (o-Pd2Sn) alloy nanoparticles displays excellent glycerol oxidation reaction (GOR) performance with a high mass activity of 12.9 A·mgPd−1, which is 14.3 times that of commercial Pd/C and among the best of reported Pd-based GOR catalysts. The superior catalytic performance of hollow o-Pd2Sn compared to those of hollow monoclinic Pd3Sn2 (m-Pd3Sn2) and solid o-Pd2Sn counterparts demonstrates the importance of simultaneously regulating the crystal phase and architecture of nanomaterials in enhancing their catalytic performance. Operando infrared reflection absorption spectroscopy (IRRAS) results suggest that hollow o-Pd2Sn could accelerate the cleavage of C—C bond when compared with commercial Pd/C. Such delicate control over both the phase and architecture of alloys could provide important guidance for the development of advanced nanomaterials for promising applications.
Embodiments of the invention are described in more details hereinafter with reference to the drawings, in which:
In the following description, embodiments of the present invention are set forth as preferred examples. It will be apparent to those skilled in the art that modifications, including additions and/or substitutions may be made without departing from the scope and spirit of the invention. Specific details may be omitted so as not to obscure the invention; however, the disclosure is written to enable one skilled in the art to practice the teachings herein without undue experimentation.
In one aspect of the present invention, a controlled and general method is provided for synthesizing distinct intermetallic alloy nanoparticles with hollow or solid architectures through wet-chemical reduction of a metal precursor and subsequent diffusion of the metal atoms into noble-metal nanoparticle NP seeds.
The controlled and general method comprises: preparing noble-metal nanoparticle NP seeds; dispersing a metal precursor into the noble-metal nanoparticle NP seeds to form a first mixture; adding the first mixture into an organic solvent (such as an amine, an alkene or a mixture thereof) to form a first solution; sonicating the first solution at room temperature; subjecting the first solution to a heat treatment under N2 atmosphere to render a second solution; cooling the second solution naturally to room temperature; adding ethanol to the second solution to form a third solution; and collecting the hollow intermetallic nanomaterial from the third solution by centrifugation.
In some embodiments, hollow intermetallic alloy NPs may be synthesized by wet-chemical reduction of a metal precursor and subsequent diffusion of the metal atoms into seeds made of noble-metal NPs with 2H phase. For example, hollow PdSn intermetallic alloy NPs, such as orthorhombic Pd2Sn (o-Pd2Sn) NPs or monoclinic Pd3Sn2 (m-Pd3Sn2) NPs may be synthesized by wet-chemical reduction of Sn precursor and subsequent diffusion of Sn atoms into seeds made of Pd NPs with 2H phase (2H—Pd NPs).
2H—Pd nanoparticles may be prepared by heating the amorphous Pd (a-Pd) nanoparticles in an amine (e.g., oleylamine) in the absence of air. Typically, 1 mL of a-Pd nanoparticles in an organic solvent (e.g., toluene) was added to 12 mL of oleylamine in a 50 mL Schlenk tube under magnetic stirring. After stirring for 10 min at room temperature, the tube was evacuated for 10 min and then sealed to keep the high vacuum. Subsequently, the tube was placed into an oil bath at 180° C. and kept for 24 h, followed by natural cooling down to room temperature. After adding 20 mL of ethanol, the product was collected by centrifugation at 12,000 rpm for 10 min.
After the as-obtained 2H—Pd nanoparticles were dispersed into 5 mL of toluene and sonicated, 20 mL of ethanol were added to precipitate them. The 2H—Pd nanoparticles were then collected by centrifugation at 12,000 rpm for 10 min. The aforementioned washing process was repeated for twice.
The 2H—Pd nanoparticles were then re-dispersed in 1 mL of toluene. Subsequently, the aforementioned 2H—Pd nanoparticles were heated in oleylamine in air to remove the excess S-containing ligands capped on the surface. Typically, 1 mL of aforementioned 2H—Pd nanoparticles in toluene was added to 6 mL of oleylamine in a 20 mL vial under magnetic stirring. After stirring for 10 min at room temperature, the vial was placed into an oil bath at 130° C. and then kept for 6 h, followed by natural cooling down to room temperature. The final product was collected by centrifugation at 12,000 rpm for 10 min after adding 30 mL of ethanol.
After the 2H—Pd nanoparticles were dispersed into 5 mL of toluene and sonicated, 20 mL of ethanol were added to precipitate them. The washed 2H—Pd nanoparticles were then collected by centrifugation at 12,000 rpm for 10 min. Preferably, the aforementioned washing process was repeated for twice.
The TEM observation (
Synthesis of Hollow o-Pd2Sn NPs
In a typical synthesis of hollow o-Pd2Sn NPs, 70 μg of the 2H—Pd NPs (determined by the ICP-OES) and 120 μg of SnCl2 were dispersed into 2 mL of oleylamine in a 50 mL Schlenk tube and sonicated at room temperature to ensure the complete dissolution. Subsequently, the Schlenk tube was evacuated for 20 min at room temperature and purged with N2 flow. After being sealed tightly, the Schlenk tube was heated by a metal bath at 250° C. under magnetic stirring for 3 hours, followed by natural cooling down to room temperature. The produced hollow o-Pd2Sn NPs was collected by centrifugation at 10,000 rpm for 2 min after adding 2 mL of ethanol. Then the as-obtained hollow o-Pd2Sn NPs were re-dispersed into 2 mL of organic solvent (e.g., toluene) and sonicated for 1 min, followed by adding 2 mL of ethanol to precipitate them. The hollow o-Pd2Sn NPs was then collected by centrifugation at 10,000 rpm for 2 min. The aforementioned washing process was repeated twice. The washed hollow o-Pd2Sn NPs were finally re-dispersed in toluene.
Characterization of Hollow o-Pd2Sn NPs
The hollow architecture of the synthesized o-Pd2Sn NPs can be confirmed by TEM (
The atomic ratio of Pd/Sn in the hollow o-Pd2Sn NPs is about 64/36 as determined by EDS spectrum and ICP-OES result (
The HAADF-STEM image of a representative hollow o-Pd2Sn NP (
In addition, XPS spectra were measured to study the valence states of Pd and Sn in hollow o-Pd2Sn NPs. The Pd 3d spectrum suggests the predominant metallic state of Pd element since the ratio of Pd0 is much higher than that of Pd2 (
Synthesis of Hollow m-Pd3Sn2 NPs
Typically, hollow m-Pd3Sn2 NPs may be synthesized by following the aforementioned method for the typical synthesis of hollow o-Pd2Sn NPs except for except for increasing the amount of SnCl2 from 120 μg to 600 μg.
Characterization of Hollow m-Pd3Sn2 NPs
TEM (
The hollow architecture of m-Pd3Sn2 NPs can be further verified by the obvious decrease of Pd and Sn signals in the middle part of EDS line scan profiles (
The Pd/Sn atomic ratio determined from the EDS spectrum is about 55/45, which is consistent with the ICP-OES result (
HADDF-STEM image (
The valance states of Pd and Sn in hollow m-Pd3Sn2 NPs were also studied by XPS characterization. As revealed by the Pd 3d spectrum (
In some other embodiments, solid intermetallic alloy may be synthesized by the wet-chemical reduction of a metal precursor and subsequent diffusion of the metal atoms into seeds made of noble-metal NPs with fcc phase. For example, solid PdSn intermetallic alloy NPs, such as, solid o-Pd2Sn NPs, may be synthesized by wet-chemical reduction of Sn precursor and subsequent diffusion of Sn atoms into seeds made of Pd NPs with fcc phase (fcc-Pd NPs).
Synthesis of fcc-Pd NPs
In a typical synthesis of the fcc-Pd NPs, 0.25 mmol of palladium (II) acetylacetonate were dissolved in 15 mL of an amine (e.g., oleylamine) and subsequently heated to 60° C. under nitrogen gas flow and magnetic stirring. Then, 3 mL of oleylamine containing 0.2 g of borane morpholine complex were injected into the aforementioned solution. The temperature was slowly increased to 90° C. and kept for 30 min before cooling to room temperature. The fcc-Pd NPs were collected by centrifugation at 10,000 rpm for 10 min after adding 30 mL of ethanol. Preferably, the synthesized fcc-Pd NPs was washed twice with mixed solution of organic solvents (e.g., toluene and ethanol (v:v=1:6)) and finally dispersed in toluene.
Characterization of fcc-Pd NPs
TEM image (
Synthesis of Solid o-Pd2Sn NPs
Typically, solid o-Pd2Sn NPs may be synthesized by following the aforementioned method for the typical synthesis of hollow o-Pd2Sn NPs except for replacing the seeds made of 70 μg of 2H—Pd NPs to seeds made of 70 μg of fcc-Pd NPs.
Characterization of Solid o-Pd2Sn NPs
The solid o-Pd2Sn NPs synthesized by using fcc-Pd NPs as seeds possess a sphere-like shape without the formation of voids (
It should be appreciated that the provided method can be used to other types of Pd-based intermetallic alloy nanoparticles with hollow or solid architectures, including, but not limited to, binary or ternary intermetallic Pd-based nanoparticles. More particularly, the intermetallic Pd-based nanoparticles may be any one of Pd—Bi, Pd—Pb, Pd—Cd, Pd—Zn, Pd—Cu, Pd—Sn—Cu, or Pd—Sn—Co nanoparticles.
In another aspect of the present invention, the as-prepared PdSn intermetallic alloys, including hollow o-Pd2Sn, solid o-Pd2Sn, and hollow m-Pd3Sn2, may be applied respectively as catalysts toward the electrochemical GOR in alkaline media.
Typically, 10 mg of Vulcan XC-72R carbon black were first dispersed in 10 mL of ethanol and sonicated in an ice bath for 1 h to obtain a homogeneous solution. Subsequently, a catalyst solution containing 150 μg of one of the abovementioned as-prepared PdSn intermetallic alloy, determined by ICP-OES, was dropwise added into 1.35 mL of as-obtained carbon solution in a 4 mL glass vial, followed by sonication for another 1 h in an ice bath. Subsequently, the obtained catalyst on carbon (catalyst/C, 10 wt %) was collected by centrifugation at 14,800 rpm for 5 min, followed by washing five times with a mixed solvent of chloroform and ethanol (v:v=1:1). The obtained catalyst/C was finally dispersed in 1 mL of the mixture of Milli-Q water and isopropanol (v:v=3:7), and the concentration of Pd in catalyst/C was further determined by ICP-OES. Then, 100 μL of Nafion alcohol solution (5 wt %) were added in the catalyst/C solution, followed by sonication for another 30 min.
All electrochemical measurements were carried out in a standard three-electrode cell system using an electrochemical workstation (CHI 760E, CH Instrument, Inc.) at room temperature (˜25° C.). Glassy carbon electrode (GCE, 5 mm) coated with the prepared catalyst was used as the working electrode. Pt wire and Hg/HgO electrode were used as counter and reference electrodes, respectively. All potentials were converted into the values in reference to RHE, by using this formula: F(RHE)=F(Hg/HgO)+0.097+0.059×pH. Before each test, GCE was sequentially polished by Al2O3 slurry with particle sizes of 300 and 50 nm, followed by washing with Milli-Q water and ethanol to ensure a clean surface. Subsequently, the catalyst ink with 3 μg of catalysts/C was dropped onto the GCE surface and dried under ambient conditions. CV measurements of the working electrodes in N2-saturated aqueous solution containing 1.0 M KOH were first carried out in a potential range from 0.1 to 1.3 V (vs. RHE) at a scan rate of 50 m V·s−1 for 50 cycles to remove the ligands on catalyst surfaces and get stable CV curves. The ECSAs were calculated based on the charge required for oxygen desorption, that is, from the area of the reduction peak of PdO in the as-obtained CV curves.
The ECSA values (in terms of m2·gPd−1) of the catalysts were estimated based on the equation, ECSA=Q/(0.405×mPd), where Q is the coulombic charge by integrating peak areas of the reduction of PdO (mC), mPd is the Pd loading (mg·cm−2), and the constant (0.405) represents the charge required for the reduction of PdO monolayer (mC·cm−2Pd).
Then, the activity of the catalysts towards GOR was evaluated by CV measurements in a mixed N2-saturated solution containing 1.0 M KOH and 1.0 M glycerol between 0.1 and 1.3 V (vs. RHE) at 50 mV·s−1. Current transients were carried out by stepping the potential from 0.5 to 0.9 V (vs. RHE) and holding the potential for 30 s. The Tafel slopes of these catalysts were carried out in the mixed solution containing 1.0 M KOH and 1.0 M glycerol at a scan rate of 50 mV·s−1. The stability of the catalysts was evaluated by chronoamperometric measurements at 0.9 V (vs. RHE) for 3,600 s in the mixed solution containing 1.0 M KOH and 1.0 M glycerol.
The mass currents of these catalysts were further normalized to their corresponding ECSAs for better comparison of their intrinsic activities, and the specific currents were shown in
To further compare the GOR activities, the current transients of these catalysts were performed using chronoamperometric measurements by instantaneously stepping from the potential of 0.5 V (vs. RHE) where the GOR was negligible to the potential of 0.9 V (vs. RHE) (typical potential for GOR). As shown in
The Tafel analysis was conducted to further investigate the reaction kinetics on these catalysts (
The stability of catalysts was also evaluated by the chronoamperometric measurements at 0.9 V (vs. RHE). After the durability tests of GOR process for 3,600 s, hollow o-Pd2Sn can still deliver the highest mass activity among these catalysts. Moreover, the morphology and phase of hollow o-Pd2Sn were well maintained after the durability test (
The aforementioned results demonstrate that the hollow o-Pd2Sn catalyst shows better GOR performance than its solid counterpart, which could be attributed to the intrinsic advantages of hollow architecture. Furthermore, hollow o-Pd2Sn and solid o-Pd2Sn both exhibit superior GOR performances, including higher activity and better stability, to the hollow m-Pd3Sn2, suggesting the decisive role of the crystal phase of catalyst in modulating its catalytic performance.
The excellent GOR performance of hollow o-Pd2Sn could be originated from the following aspects. First, it is commonly accepted that alloying Pd with other transition metals like Sn could modify the electronic band structure of Pd-based nanomaterials, which contributes to the enhanced performance towards GOR. In this work, the change of electronic band structure of Pd in hollow o-Pd2Sn can be verified by the positive shift of binding energies in Pd 3d XPS spectrum as compared to those of pure Pd. Secondly, previous studies have revealed that noble metal-based intermetallic alloys could exhibit excellent catalytic performance because of their ordered atomic arrangements and unique electronic structures. In this work, the outstanding GOR performance of hollow o-Pd2Sn could also be originated from the unconventional orthorhombic intermetallic phase, which endows it with higher intrinsic catalytic activity, abundant active sites, and favorable reaction kinetics, as revealed by the highest specific activity, largest ECSA area, and lowest Tafel slope among all the as-prepared catalysts, respectively. Thirdly, catalysts with hollow architectures are featured with large specific surface area and enhanced utilization of noble metals, endowing them with promising catalytic performance, which also explains the better GOR activity of hollow o-Pd2Sn than that of solid o-Pd2Sn. Therefore, the alloying effect of Pd and Sn, ordered intermetallic structure, and hollow architecture simultaneously contribute to the excellent GOR performance of the hollow o-Pd2Sn catalyst.
Operando IRRAS measurements
To provide deeper insight into the reaction mechanism during GOR on the hollow o-Pd2Sn catalyst, operando IRRAS studies were performed. Specifically, we conducted operando IRRAS measurements on the hollow o-Pd2Sn and Pd/C catalysts with potentials varying from 0.1 to 1.3 V (vs. RHE) in Ar-saturated aqueous solution containing 0.1 M KOH and 0.1 M glycerol.
As displayed in
In addition, hollow o-Pd2Sn catalyst shows much weaker signals of triply bonded CO (COT) at 1873-1867 cm−1 as compared to Pd/C (located at 1888-1878 cm−1) from 0.3 to 1.3 V (vs. RHE), suggesting a better anti-poisoning ability to *CO. Notably, the signal of CO2 is also detected at 2342 cm−1 on both catalysts (
These results indicate that hollow o-Pd2Sn is more capable of breaking the C—C bond for complete oxidation of glycerol to generate CO2 compared with Pd/C. Moreover, two bands at around 1390 and 1360 cm−1 are corresponding to the existence of CO32− and HCO3−, respectively, which are sequentially generated from the continuous reaction between produced CO2 and the alkaline electrolyte. As shown in
The products after GOR process over hollow o-Pd2Sn were further analyzed by 1H NMR to clarify the reaction pathway. The co-existence of formate, acetic acid, lactic acid, glycolic acid, glycerate, and the remaining glycerol was detected in the products (
The embodiments may be chosen and described in order to best explain the principles of the invention and its practical application, thereby enabling others skilled in the art to understand the invention for various embodiments and with various modifications that are suited to the particular use contemplated. While the methods disclosed herein have been described with reference to particular operations performed in a particular order, it will be understood that these operations may be combined, sub-divided, or re-ordered to form an equivalent method without departing from the teachings of the present disclosure. Accordingly, unless specifically indicated herein, the order and grouping of the operations are not limitations. While the apparatuses disclosed herein have been described with reference to particular structures, shapes, materials, composition of matter and relationships . . . etc., these descriptions and illustrations are not limiting. Modifications may be made to adapt a particular situation to the objective, spirit and scope of the present disclosure. All such modifications are intended to be within the scope of the claims appended hereto.
