Investigation of Structural, Thermal, and Dynamical Properties of Pd

Article pubs.acs.org/JPCC

Investigation of Structural, Thermal, and Dynamical Properties of Pd−Au−Pt Ternary Metal Nanoparticles Confined in Carbon Nanotubes Based on MD Simulation Hui Wei, Song Wei, Xiaolei Zhu,* and Xiaohua Lu* State Key Laboratory of Materials-Oriented Chemical Engineering, College of Chemical Engineering, Nanjing Tech University, Nanjing 210009, China S Supporting Information *

ABSTRACT: We apply molecular dynamics (MD) simulations to investigate structural, thermal, and dynamical properties of Pd−Au−Pt trimetallic nanoparticles confined in armchair single-walled carbon tubes ((n,n)-SWNTs). The metal−carbon interactions are described by a Lennard-Jones (LJ) potential, while the metal−metal interactions are represented by the second-moment approximation of the tight-binding (TB-SMA) potentials. Results illustrate that the confined Pd−Au−Pt metal nanoparticles appear to be of cylindrical multishelled structure, similar to those of gold (or Au−Pt) nanoparticles confined in SWNT and different from free Pd−Au−Pt nanoparticles or bulk gold. For each confined Pd−Au−Pt nanoparticle, gold atoms preferentially accumulate near the tube center, while Pt atoms preferentially distribute near the tube wall. These results are in qualitative agreement with previous observations on Au−Pt nanoparticles confined in SWNT. Importantly, Pd atoms disperse thorough the confined Pd− Au−Pt nanoparticle, which is consistent with caltalytic observations in experiment. The melting temperatures of the confined Pd−Au−Pt nanoparticles are controlled by platinum with greater cohesive energy. The melting temperatures of the confined Pd−Au−Pt nanoparticles are significantly higher than those of the free Pd−Au−Pt nanoparticles, which are caused by the confined interaction of SWNT. Some important dynamic results are obtained in terms of the classical nucleation theory. nanoparticles with the same cross area. Dong et al.34 observed the single-walled gold nanotubes grown in carbon nanotubes and found that their solidification temperatures depend on both the Au nanotube’s length and diameter. Cheng et al.35 used MD simulation to investigate the thermal behavior of Pd clusters confined in carbon nanotubes and found that the melting temperatures of palladium clusters decrease linearly with 1/N1/3 (N is the total atom number of a Pd cluster). Wang et al.36 investigated the thermal evolution of a platinum cluster encapsulated in carbon nanotube in terms of MD simulation, and the results revealed that SWNTs have a considerable effect on the structures of the confined Pt clusters. Subsequently, the MD simulation studies about the binary metal nanoparticles confined in carbon nanotubes have also been reported. For example, Zhang et al.37 investigated the structures and buckling behaviors under axial compression of Ni−Cu alloys confined in SWNT. Dong et al.38 used MD simulation to observe the growth of single-walled bimetallic Au−Ag, Au−Cu, and Ag−Cu alloy nanotubes (NTs) and nanowires (NWs) confined in carbon nanotubes (CNTs). They found that the freezing transition temperatures of the alloy nanotubes locate between

I. INTRODUCTION Binary and ternary metal nanoparticles1−22 have attracted plenty of attention due to the fact that the catalytic, magnetic, optical, and electrical properties23−26 can be adjusted via controlling their compositions, structures, and sizes. Because free metal nanoparticles are unstable due to their large specific surface area, usually metal nanoparticles are supported inside the holes of supports in experiment. How to improve the stability of supported metal catalysts has been a very challenging issue in recent years. Clearly, similar to graphene and graphene oxide (GO),27,28 carbon nanotubes (CNTs)29 have also been applied as supports to improve the stability of metal nanoparticles. For example, experimentally, some researchers synthesized supported binary and ternary metal nanoparticles1−3,14−20 and the filled metal (Pd, Au, Pt, Ni, Fe, and so on) carbon nanotube, and investigated their catalytic and magnetic properties.30,31 Li et al.32 investigated the structure, stability, and dynamic behavior of Al nanowires (NWS) confined in armchair single-wall carbon nanotube (SWNT) during the melting process based on molecular simulation and found some delicate phenomena for these systems. Poulikakos et al.33 studied the structure and freezing behavior of gold nanoparticles encapsulated in SWNT in terms of molecular dynamics (MD) simulation. The freezing temperature depends only on the length of the gold © 2017 American Chemical Society

Received: March 15, 2017 Revised: May 17, 2017 Published: May 30, 2017 12911

DOI: 10.1021/acs.jpcc.7b02434 J. Phys. Chem. C 2017, 121, 12911−12920

Article

The Journal of Physical Chemistry C Table 1. Composition of Systems Studied (PdxAuyPtz)m/(n,n)-SWNT x=y

y=z

x=z

(Pd0.1Au0.1Pt0.8)818/(19,19)-SWNT (Pd0.15Au0.15Pt0.7)818/(19,19)-SWNT (Pd0.2Au0.2Pt0.6)818/(19,19)-SWNT (Pd0.25Au0.25Pt0.5)818/(19,19)-SWNT (Pd0.3Au0.3Pt0.4)818/(19,19)-SWNT (Pd0.33Au0.33Pt0.33)818/(19,19)-SWNT (Pd0.4Au0.4Pt0.2)818/(19,19)-SWNT (Pd0.45Au0.45Pt0.1)818/(19,19)-SWNT (Pd0.1Au0.1Pt0.8)1522/(25,25)-SWNT (Pd0.15Au0.15Pt0.7)1522/(25,25)-SWNT (Pd0.2Au0.2Pt0.6)1522/(25,25)-SWNT (Pd0.25Au0.25Pt0.5)1522/(25,25)-SWNT (Pd0.3Au0.3Pt0.4)1522/(25,25)-SWNT (Pd0.33Au0.33Pt0.33)1522/(25,25)-SWNT (Pd0.4Au0.4Pt0.2)1522/(25,25)-SWNT (Pd0.45Au0.45Pt0.1)1522/(25,25)-SWNT (Pd0.1Au0.1Pt0.8)2230/(30,30)-SWNT (Pd0.15Au0.15Pt0.7)2230/(30,30)-SWNT (Pd0.2Au0.2Pt0.6)2230/(30,30)-SWNT (Pd0.25Au0.25Pt0.5)2230/(30,30)-SWNT (Pd0.3Au0.3Pt0.4)2230/(30,30)-SWNT (Pd0.33Au0.33Pt0.33)2230/(30,30)-SWNT (Pd0.4Au0.4Pt0.2)2230/(30,30)-SWNT (Pd0.45Au0.45Pt0.1)2230/(30,30)-SWNT



melting (or freezing) process of nanoparticles, the understanding of these processes is limited and not clear because of the size and complicated structure of confined nanoparticles.45 Moreover, experimental investigations on the effect of a SWNT on the properties of nanoparticles are very difficult and expensive. MD simulation32−42,46−48 is a unique technique used to solve the above problems. Therefore, in current work, the MD simulation method is used to investigate and reveal the thermodynamic and kinetic behaviors of the Pd−Au−Pt trimetallic nanoparticles confined in (n,n)-SWNT during melting and freezing processes. Results indicate that the confined Pd−Au−Pt nanoparticles possess cylindrical multishelled structures. The atom distribution and structure feature of the confined Pd−Au−Pt nanoparticles are examined and revealed during melting and freezing processes. Some important kinetic results are obtained via the classical nucleation theory. The current work provides a guide for controlling the size of supported metal catalysts in experiment.

those of the corresponding pure metal tubes. Akbarzadeh et al.39 studied the effects of chirality and diameter of nanotubes, and the size and composition of nanoclusters on the melting behavior of (PdxPt1−x)n nanoclusters confined in single-walled carbon nanotubes. On the other hand, Akbarzadeh et al.40 investigated the effect of the several kinds of different nanotubes on the thermodynamic properties of Pt−Cu bimetallic nanoclusters based on MD simulation. In our previous works,41,42 the melting and freezing behaviors of Au and Au−Pt nanoparticles confined in (n,n)-SWNT were investigated in terms of MD simulations. Recently, ternary metal nanoparticles have received much attention4,6−10,21,22 because of their multifunctional catalytic activities. In fact, for most supported metal catalysts, metal nanoparticles usually are supported inside the porous materials (also called supported metal catalysts)43 in the experiment. However, so far, the structural, thermal, and dynamical properties of the ternary metal nanoparticles confined in carbon nanotubes have not been reported. As compared to elemental and bimetallic nanoparticles, Au−Pd−Pt ternary metal nanoparticles have attracted considerable interest for their promising oxygen reduction reaction (ORR) performance.21 So far, although the Pd−Au−Pt nanoparticles confined in SWNTs have not been synthesized, some pure metals have been filled experimentally in carbon tubes.30 The Pd−Au−Pt nanoparticles confined in SWNTs can be synthesized in the future. In our opinion, the synthesis of the Pd−Au−Pt nanoparticles confined in SWNTs is not difficult, but the structural, thermal, and dynamical properties of the ternary metal nanoparticles confined in carbon nanotubes will be very difficult for experimental studies. On the other hand, the synthesis of nanoparticles will be considerably affected by the solid−liquid (or liquid−solid) phase transition.44 Although many experimental techniques can be used to investigate the

II. COMPUTATIONAL DETAILS The structural, thermal, and dynamical properties of Pd−Au− Pt trimetallic nanoparticles confined in armchair (n,n)-SWNTs are examined and investigated in terms of MD simulations. Each system includes a Pd−Au−Pt nanoparticle with the length of 3.567 nm filled in the carbon tube (22.017 nm). The diameters of the selected (19,19)-SWNT, (25,25)-SWNT, and (30,30)-SWNT are 25.76, 33.90, and 40.68 Å, respectively. Each SWNT is simulated by a box with length 22.017 nm using periodic boundary conditions along the tube axis. In current MD simulations, Pd−Au−Pt nanoparticles (PdxAuyPtz)N (y = z, x = 1 − y − z, z = 0.1, 0.15, 0.2, 0.25, 0.3, 0.33, 0.4, and 0.45), (PdxAuyPtz)N (x = z, y = 1 − x − z, y = 0.1, 0.15, 0.2, 0.25, 0.3, 0.33, 0.4, and 0.45), and (PdxAuyPtz)N (y = x, z = 1 − x − y, x = 0.1, 0.15, 0.2, 0.25, 0.3, 0.33, 0.4, and 0.45) with N = 818, 1522, 12912


Article

The Journal of Physical Chemistry C

During the phase transition simulation process, first, each Pd−Au−Pt trimetallic nanoparticle within the SWNT is heated to 1800 K for 1.2 ns to generate a melted Pd−Au−Pt nanoparticle. Next, a slow cooling run is carried out from 1800 to 300 K with temperature intervals of 20 K. The time step is set as 3 fs. Each system undergoes constant temperature simulation (NVT ensemble) for 40 000 time steps and constant energy simulation (NVE ensemble) for 40 000 time steps. The final structure at 300 K obtained from the cooling process is taken as the initial configuration for slow heating process. During the slow heating process, each confined Pd−Au−Pt nanoparticle is heated from 300 to 1800 K with temperature increments of 20 K. To obtain some important dynamic data, nucleation simulations are performed on three systems (181-25, 252-25, and 414-25). Each of the melted nanoparticles confined in SWNTs is put in a bath with the temperature of 1800 K. During the constant temperature (1800 K) simulation, a structure is extracted per running 3000 time steps, from which 30 melted nanoparticles can be generated. These melted nanoparticles have different thermal histories. After that, these melted nanoparticles confined in SWNTs are quenched to specified temperatures for 180 ps to obtain structures and energies with time for analyses of nucleation and crystallization.

and 2230 are encapsulated in (19,19)-, (25,25)-, and (30,30)SWNTs, respectively. For simplicity, if n = 19, N = 818, x = 0.15, y = 0.15, and z = 0.7, this system is marked as 117-19 and so on. The details about the studied systems are shown in Table 1. The reliability of the MD simulation is determined by the potential function of the studied systems, especially for the investigation on phase transition and nucleation. As compared to the EAM model only related to local electron density properties, the second-moment approximation of the tightbinding (TB-SMA) potential function, an empirical many-body potential represented by analytical form, includes bandstructure effects and can reproduce the structural and thermodynamic properties for most transition metals.49,50 Moreover, the TB-SMA potential function has also been proven to be effective49,50 for simulating the structures of ultrathin nanowires,51 nanoclusters,52 and confined gold nanoparticles. In addition, the TB-SMA potential for the investigation on phase transition has also been confirmed experimentally to be reliable.53−55 Therefore, in current MD simulations, the metal−metal interactions in confined Pd−Au− Pt trimetallic nanoparticle are described by the TB-SMA potential.50 The relevant TB-SMA potential parameters for metal−metal are displayed in Table 2. The interactions

III. RESULTS AND DISCUSSION To reveal the structural pattern of Pd−Au−Pt nanoparticle confined in SWNT, Figure 1 provides the images of (Pd0.15Au0.15Pt0.7)N, (Pd0.15Au0.7Pt0.15)N, and (Pd0.7Au0.15Pt0.15)N confined, respectively, in (n,n)-SWNTs (N = 818, 1522, and 2300, n = 19, 25, and 30) parallel to the tube axis at 300 K. It

Table 2. Potential Parameters of TB-SMA Potential for Transition Metals in MD Simulations M−M a

Pd−Pd Au−Aua Pt−Pta Pd−Aub Pd−Ptb Au−Ptb

A (eV)

ξ (eV)

p

q

r0

0.1746 0.2061 0.2975 0.1897 0.2279 0.2476

1.718 1.790 2.695 1.754 2.152 2.196

10.867 10.229 10.612 10.548 10.740 10.421

3.742 4.036 4.004 3.889 3.873 4.02

2.752 2.884 2.775 2.818 2.763 2.830

a

The parameters of TB-SMA potential obtained from ref 47. bAPd−Au = (A Pd−Pd A Au−Au ) 1/2 , A Pd−Pt = (A Pd−Pd A Pt−Pt ) 1/2 , A Au−Pt = (AAu−AuAPt−Pt)1/2, ξPd−Au = (ξPd−PdξAu−Au)1/2, ξPd−Pt = (ξPd−PdξPt−Pt)1/2, ξAu−Pt = (ξAu−AuξPt−Pt)1/2, pPd−Au = (1/2)(pPd−Pd + pAu−Au), pPd−Pt = (1/ 2)(pPd−Pd + pPt−Pt), pAu−Pt = (1/2)(pAu−Au + pPt−Pt), qPd−Au = (1/ 2)(qPd−Pd + qAu−Au), qPd−Pt = (1/2)(qPd−Pd + qPt−Pt), qAu−Pt = (1/ 2)(qAu−Au + qPt−Pt), r0Pd−Au = (1/2)(r0Pd−Pd + r0Au−Au), r0Pd−Pt = (1/ 2)(r0Pd−Pd + r0Pt−Pt), and r0Au−Pt = (1/2)(r0Au−Au + r0Pt−Pt).

between metals and SWNTs are represented by 12-6 Lennard-Jones (L-J) potentials,36,56−58 and relevant L-J parameters are illustrated in Table 3. In current MD Table 3. Relevant LJ Potential Parameters Applied in MD Simulations pairs

ε (eV)

σ (Å)

ref

C−Pd C−Au C−Pt

0.03444 0.01273 0.04092

3.0865 2.9943 2.936

50, 51 52 36

Figure 1. Images of (Pd0.15Au0.15Pt0.7)N, (Pd0.15Au0.7Pt0.15)N, and (Pd0.7Au0.15Pt0.15)N confined, respectively, in (n,n)-SWNTs (n = 19, 25, and 30) parallel to the tube axis of SWNTs at 300 K. (Pd0.15Au0.15Pt0.7)818 confined in (19,19)-SWNT is marked as 19117, and so on for simiplicity: (a) 117-19; (b) 171-19; (c) 711-19; (d) 117-25; (e) 171-25; (f) 711-25; (g) 117-30; (h) 30-171; and (i) 30711. The blue, green, yellow, and pink balls represent carbon, palladium, gold, and platinum atoms, respectively.

simulations, we suppose that the structures of SWNTs will not be considerably changed in the presence of transition metal;36 thus, the SWNTs are set as rigid as applied in previous studies.33,41,42,59 The initial crystal structure of the three metals is considered to be the same. The crystal structure slightly changes with composition, which has been ignored in the current work. 12913


Article


Figure 2. (A) The image of (Pd0.33Au0.33Pt0.33)1522 nanoparticle confined in (25,25)-SWNT parallel to the tube axis of SWNT at 300 K. The blue, green, yellow, and pink balls represent carbon, palladium, gold, and platinum atoms, respectively. (B) The image of (Pd0.33Au0.33Pt0.33)1522 nanoparticle confined in (25,25)-SWNT perpendicular to the tube axis of SWNT at 300 K. The blue, green, yellow, and pink balls represent carbon, palladium, gold, and platinum atoms, respectively. (C) Density distribution along the radial direction of the carbon tube for the (Pd0.33Au0.33Pt0.33)1522 nanoparticle confined in (25,25)-SWNT at 300 K. (D) The relationship between the Pt (or Pd or Au) probability in surface and subsurface layers and Pt (or Pd or Au) composition in the confined (PdxAuyPtz)1522 (z = 0.1, 0.2, 0.33, 0.4, 0.5, 0.6, 0.7, and 0.8; x = y = (1 − z)/2), (PdyAuxPtx)1522 (x = 0.1, 0.2, 0.33, 0.4, 0.5, 0.6, 0.7, and 0.8; y = z = (1 − x)/2), and (PdxAuyPtx)1522 (y = 0.1, 0.2, 0.33, 0.4, 0.5, 0.6, 0.7, and 0.8; x = z = (1 − y)/2). Green dash represents average distribution.

density peaks (blue lines) near the tube center reveal that Au atoms preferentially locate around the tube center. Similarly, the stronger density peaks (green lines) near the tube wall suggest that Pt atoms prefer to stay at the tube wall. Figure 2C also reveals that Pd atoms tend to uniformly distribute in the confined Pd−Au−Pt nanoparticles, which may be ascribed to the competitive result between the metal−SWNT and metal− metal interactions. Figure 2D represents the relationship between the Pt (or Pd or Au) probability in surface and subsurface layers and Pt (or Pd or Au) composition in the confined (PdxAuyPtz)1522 (z = 0.1, 0.2, 0.33, 0.4, 0.5, 0.6, 0.7, and 0.8; x = y = (1 − z)/2), (PdxAuyPtz)1522, (PdxAuyPtz)1522 (x = 0.1, 0.2, 0.33, 0.4, 0.5, 0.6, 0.7, and 0.8; y = z = (1 − x)/2), and (PdxAuyPtx)1522 (y = 0.1, 0.2, 0.33, 0.4, 0.5, 0.6, 0.7, and 0.8; x = z = (1 − y)/2). The green dashed line represents average distribution. It can be seen from Figure 2D that Pd probability in surface and subsurface layers (blue ■) is very close to average distribution (green dash line). Relatively, Pt probability in surface and subsurface layers (red ▲) is larger than average distribution (green dash line), and Au probability in surface and subsurface layers (pink ●) is significantly smaller than average distribution (green dash line), which confirm the results obtained from the panels A and C of Figure 2. In fact, the specific structures of the confined Pd−Au−Pt nanoparticles are caused by the competitive effect between the metal−SWNT and metal−metal interactions, which may affect the stability of supported metal catalysts. In fact, the above special structure includes the “mesoscale” structure of catalyst surface induced by the competition interaction; how the latter affects the stability of supported metal catalysts is an important

can be seen from Figure 1 that each solid Pd−Au−Pt nanoparticle confined in SWNT possesses cylindrical multishelled structure and the atoms of each layer are arranged into the hexagonal lattice, which are consistent with previous results about the structures of Au cluster/(n,0)-SWNT by Poulikakos et al.,33 Pt55/(n,n)-SWNT by Wang et al.,36 Au nanoparticle (or Au−Pt nanoparticle)/(n,n)-SWNT by our previous studies,41,42 and are different from those of free Pd−Au−Pt nanoparticles21,22 or bulk gold (fcc structure). In fact, the multishelled structures of the confined Pd−Au−Pt nanoparticles can be ascribed to the confined interaction of SWNT. To examine atomic distribution of each kind of noble metals in the confined Pd−Au−Pt nanoparticles, the density distributions of noble metals along the radial direction of carbon tube and tube axis direction are analyzed as shown in Figure 2. It is worthy to note from panels A and B of Figure 2 that the gold atoms preferentially distribute near the tube center, while Pt atoms preferentially distribute around the tube wall, similar to the previous observation on Au−Pt nanoparticles confined SWNT.42 It is due to that the interactions between Pt atoms and carbon tube are significantly stronger than those between gold atoms and SWNT. On the other hand, interestingly, Pd atoms scatter thorough the confined (Pd0.33Au0.33Pt0.33)1522 nanoparticle, consistent with catalytic observations.60,61 To further gain insight into the atomic arrangement of confined Pd−Au−Pt nanoparticles, the density distribution along the radial direction of the carbon tube for the (Pd0.33Au0.33Pt0.33)1522 nanoparticle confined in (25,25)-SWNT at 300 K is shown in panel C of Figure 2. Clearly, in the confined (Pd0.33Au0.33Pt0.33)1522 nanoparticle, the stronger 12914


Article


Figure 3. Images of (Pd0.33Au0.33Pt0.33)1522 confined in (25,25)-SWNT at different stages of cooling and heating processes. Cooling stages (top): (a) 1800 K; (b) 1200 K; (c) 700 K; (d) 300 K. Heating stages (bottom): (e) 700 K; (f) 1200 K; (g) 1800 K. The blue, green, yellow, and pink balls represent carbon, palladium, gold, and platinum atoms, respectively.

Figure 4. (A) Temperature dependence of tatal energy for PdxAuyPtz (y = 0.1, 0.2, 0.33, 0.4, 0.5, 0.6, 0.7, and 0.8; x = z = (1 − y)/2) confined in (25,25)-SWNT during the heating process. (B) The relationship between melting point and gold composition for PdxAuyPtz (y = 0.1, 0.2, 0.33, 0.4, 0.5, 0.6, 0.7, and 0.8; x = z = (1 − y)/2) confined in (25,25)-SWNT.

“mesoscale” issue or “mesoscale” phenomenon.62 Extended research is in progress. The structure and atomic distribution of a confined ternary Pd−Au−Pt nanoparticle are different from those of a free Pd−Au−Pt nanoparticle.21,22 Figure S1 shows the structure of the capping region for (Pd0.33Au0.33Pt0.33)818/ (19,19)-SWNT parallel to tube axis at 300 K. It is worth noting from Figure S1 that in the capping region, the atomic density near the tube wall is larger than that near the tube center, and the compositions of Pd, Au, and Pt are 31%, 46%, and 23%, respectively. The above results suggest that the surfaces of the two ends (capping regions) of each confined nanoparticle parallel to tube axis exhibit an inward concave. To examine and reveal the structure feature of Pd−Au−Pt nanoparticles during the phase transition processes, we represent the structures of (Pd0.33Au0.33Pt0.33)1522 confined in (25,25)-SWNT at different stages of cooling and heating as shown in Figure 3. Before melting, the confined (Pd0.33Au0.33Pt0.33)1522 nanoparticle exhibits ordered multishelled structures (Figure 3c−e). However, after melting, the (Pd0.33Au0.33Pt0.33)1522 has disordered structures (Figure 3a, b, f, and g). In fact, after quenching in nucleation MD simulations, the confined Pd−Au−Pt nanoparticles possess similar structures. To further explore how the confined interactions of the carbon nanotube influence the structures of Pd−Au−Pt nanoparticles during heating and cooling processes, the radial density distributions of the confined (Pd0.33Au0.33Pt0.33)1522 nanoparticle at different temperatures are examined as shown

in Figure S2. Clearly, before melting (Figure S2: (a) 300, 700 K and (b) 300, 700 K), the confined (Pd0.33Au0.33Pt0.33)1522 nanoparticle exhibits layering structure. Interestingly, after melting, there are layered structures near the tube wall in the melted (Pd0.33Au0.33Pt0.33)1522 nanoparticle (Figure S2: (a) 1200, 1800 K, and (b) 1200, 1900 K). It is worthy to note from Figure S2 that the surface layers first appear during the cooling process, which suggests that crystallization starts from the outer layers near the tube wall. To confirm the above inference, the time dependence of total energies and structures of (Pd0.45Au0.1Pt0.45)1522 nanoparticle confined in (25,25)-SWNT during the quenching process (from 1800 to 1050K) is shown in Figure S3. It is easy to note from Figure S3 that during nucleation and crystal growth, crystallization does start from the outer layers. The above results are similar to those of confined Au nanoparticles33 and confined Au−Pt nanoparticles.42 The solid−liquid structural transition of the confined gold nanoparticle as shown in Figure 3 and Figure S2 is naturally accompanied by an energy change. The solid−liquid transition temperature can be estimated from some physical properties (such as total energy, diffusion coefficient, and heat capacity) or structural properties (such as Lindemman index, bond order parameter, and so on). In the current work, the total energy curve is applied to determine melting temperatures for the confined Pd−Au−Pt nanoparticles. Figure 4 represents the temperature dependence of total energy for PdxAuyPtz (y = 0.1, 12915


Article

The Journal of Physical Chemistry C 0.2, 0.33, 0.4, 0.5, 0.6, 0.7, and 0.8; z = x = (1 − y)/2) confined in (25,25)-SWNT during the heating process. The “energy jump” in Figure 4A implies the solid−liquid melting transition of the confined PdxAuyPtz (z = x) nanoparticles. In the confined PdxAuyPtz (z = x) nanoparticles, the compositions of Pd and Pt are the same. As shown in Figure 4B, when the gold composition of the confined PdxAuyPtx nanoparticles increases, and Pd and Pt compositions equally decrease, the melting points linearly decrease as expected. It is due to the fact that interactions between Pd−Pd (or Pt−Pt) atoms are significantly larger than those between Au−Au atoms in the confined Pd− Au−Pt nanoparticles. In addition, the heats of fusion and heat capacities of the confined PdxAuyPtz (y = 0.1, 0.2, 0.33, 0.4, 0.5, 0.6, 0.7, and 0.8, z = x = (1 − y)/2) are estimated from Figure 4A and listed in Table 4. It is interesting to observe the

between the melting temperatures and Pt composition for (Pd(1−x)/2Au(1−x)/2Ptx)1522/(25,25)-SWNT (red curve) and (Au1−xPtx)1522/(25,25)-SWNT (blue curve). It is not difficult to see that the melting points of (Pd(1−x)/2Au(1−x)/2Ptx)1522/ (25,25)-SWNT are higher than those of (Au1−xPtx)1522/ (25,25)-SWNT. It can be ascribed to the fact that (Pd(1−x)/2Au(1−x)/2Ptx)1522/(25,25)-SWNT can be obtained by replacing one-half of the gold atoms in (Au1−xPtx)1522/(25,25)SWNT using Pd atoms with greater cohesive energy.64 On the other hand, when the Pt composition is smaller than 0.6, both Pd and Pt atoms with greater cohesive energies govern the melting points of (Pd(1−x)/2Au(1−x)/2Ptx)1522/SWNT, leading to that the melting points of (Pd(1−x)/2Au(1−x)/2Ptx)1522/SWNT are higher than that of (Au1−xPtx)1522/SWNT with increasing Pt composition. When Pt composition is greater than 0.6, Pt atoms with greater cohesive energy dominate the melting p o i n t s o f ( Pd ( 1 − x ) / 2 A u ( 1 − x ) / 2 P t x ) 1 5 2 2 / S W N T a n d (Au1−xPtx)1522/SWNT, resulting in that the melting points of the two systems with increasing Pt composition are similar. Figure 6 indicates the ternary contour plots of the melting temperature of Pd−Au−Pt/(19,19)-SWNT, Pd−Au−Pt/ (25,25)-SWNT, and Pd−Au−Pt /(30,30)-SWNT. Clearly, it can be seen from Figure 6 that the melting points change with the composition of Pd−Au−Pt nanoparticles as expected. All melting temperatures fall within a range of 820−1420 K, which are lower than that (2043 K)65 of free bulk platinum from experiment and that (2070 K)66 of free bulk platinum obtained from MD simulations. Because the characteristics of panels A, B, and C of Figure 6 are similar, subsequent discussion will focus on Figure 6 (panel A). It is interesting to note from Figure 6 (panel A) that the melting points in regions W, X, and Y of Figure 6 (panel A) subsequently decrease. It is due to the fact that the main ingredients of the regions T, U, and V of Figure 6 (panel A) are platinum, palladium, and gold, respectively, and the interactional rank of noble metal is Pt− Pt > Pd−Pd > Au−Au within SWNTs. On the other hand, the melting points in regions V, W, and T of Figure 6A progressively increase, revealing that platinum with greater cohesive energy governs the melting points of confined Pd− Au−Pt trimetallic nanoparticles. Figure S4 reveals how the confined effect of SWNT improves the stability of a Pd−Au−Pt nanoparticle (see the Supporting Information). The studied systems in the current work belong to heterogeneous systems. For our previous studied systems, that is, Au nanoparticles (or Au−Pt nanoparticles) confined in SWNT,41,42 because there are not other nucleation theories available for nucleation analysis of heterogeneous system, the classical nucleation theory67,68 is approximately used to estimate kinetic and thermodynamic data, and the obtained results are relatively reasonable.41,42 Therefore, in current work, the classical nucleation theory is approximately used to estimate kinetic and thermodynamic data. Usually, the empirical estimation of σsl developed by Turnbull69 can be described as

Table 4. Thermodynamic Data Obtained from This Work system 181-25 171-25 262-25 252-25 343-25 333-25 424-25 414-25 bulk Au (exp) bulk Pt (exp)

Tm (K)a

Cp(liquid) (J K−1 mol−1)

836 866 917 1004 1045 1092 1144 1191 1336b

33.98 36.20 36.81 36.82 37.18 37.44 37.42 37.37

2043b

± ± ± ± ± ± ± ±

0.30 0.29 0.43 0.14 0.58 0.68 0.92 0.73

Cp(solid) (J K−1 mol−1)

ΔHfus (kJ mol−1)

± ± ± ± ± ± ± ±

4.68 6.38 6.46 6.81 6.82 7.87 7.90 8.88 12.4c

27.53 27.24 27.21 26.97 27.01 27.27 27.22 27.12

0.20 0.31 0.22 0.15 0.16 0.28 0.18 0.15

19.7c

The average error of melting temperatures is about ±20 K. bBarin, I.; Knacke, O. Thermochemical Properties of Inorganic Substances; SpringerVerlag: Berlin, 1973. cFrom ref 64. a

hysteresis of freezing temperatures as compared to the corresponding melting temperatures. This hysteresis is a characteristic of finite-sized systems or nonbulk.63 Figure 5 demonstrates the relationship between melting point and Pt composition for the confined (Pd(1−x)/2Au(1−x)/2Ptx)1522 (x = 0.1, 0.2, 0.33, 0.4, 0.5, 0.6, 0.7, and 0.8) and (Au1−xPtx)1522 confined in (25,25)-SWNT.42 Figure 5 shows the relationship

σsl = k TΔHfus/(V 2/3NA1/3)

(1)

where NA is Avogadro’s number, and ΔHfus accounts for heat of fusion. In terms of eq 1 and ΔHfus values listed in Table 4, the computed σsl values for the confined Pd−Au−Pt nanoparticles are 0.031−0.078 J/m2 as displayed in Table 5. During the slow cooling process, a self-diffusion coefficient (D) is computed in terms of the slope of the mean-square displacement curve r2(t) according to the Einstein equation, that is:

Figure 5. Relationship between melting point and Pt composition for (Pd(1−x)/2Au(1−x)/2Ptx)1522 (x = 0.1, 0.2, 0.33, 0.4, 0.5, 0.6, 0.7, and 0.8) and (Au1−xPtx)1522 confined in (25,25)-SWNT. 12916


Article


Table 5. Solid−Liquid Interfacial Free Energies (mJ m−2) and Nucleation Rates (×10−35, m−3 s−1) for Pd−Au−Pt Nanoparticles Confined in SWNTs system

T (K)

σsla

J

414-25

850 900 950 1000 1050 1100 700 750 800 850 900 600 650 700 750

52.6 57.6 62.6 67.6 72.6 77.6 37.3 42.1 46.9 51.7 56.5 30.8 34.0 37.1 40.3

26.39(20) 19.51(17) 16.83(15) 14.01(12) 11.43(10) 8.93(7) 24.97(15) 16.63(13) 13.17(11) 8.96(8) 6.53(6) 16.79(14) 11.01(11) 8.73(5) 5.14(3)

252-25

181-25

a

(1 − y)/2) nanoparticles with the data from free bulk platinum.70 As expected, first, all D−T curves increase with temperature. Second, the diffusion coefficients decrease as the compositions of platinum and palladium increase by an equal amount, which can be ascribed to relatively stronger Pd-SWNT and Pt-SWNT interactions. Third, as shown in Figure S5, the computed diffusion coefficients of the confined PdxAuyPtz (y = 0.1, 0.2, 0.33, 0.4, 0.5, 0.6, 0.7, and 0.8, z = x = (1 − y)/2) are larger than those of free bulk Pt70 within 1600−1800 K. In fact, the size of confined PdxAuyPtz (y = 0.1, 0.2, 0.33, 0.4, 0.5, 0.6, 0.7, and 0.8, z = x = (1 − y)/2) nanoparticles is much smaller than that of the bulk Pt, and they have more dangling bonds than those of bulk Pt, resulting in that free bulk Pt has more cohesive energy than those of the confined PdxAuyPtz (y = 0.1, 0.2, 0.33, 0.4, 0.5, 0.6, 0.7, and 0.8, z = x = (1 − y)/2) nanoparticles, which makes larger diffusivity of the confined PdxAuyPtz (y = 0.1, 0.2, 0.33, 0.4, 0.5, 0.6, 0.7, and 0.8, z = x = (1 − y)/2) nanoparticles than that of free bulk Pt. The freezing of supercooled melts is an activated process, in which crystal nucleation and growth will occur. The nucleation time (tn) can be identified on the basis of the curve of total energy with time42 and the corresponding structure of the simulated system. The nucleation rate J can be derived from the fraction (Nn/N0) of unfrozen nanoparticles at time (tn) in terms of the first-order rate law, that is:

Figure 6. Ternary contour plots of melting temperature of Pd−Au−Pt nanoparticle/(19,19)-SWNT (A), Pd−Au−Pt nanoparticle/(25,25)SWNT (B), and Pd−Au−Pt nanoparticle/(30,30)-SWNT (C). All melting temperatures are in unit of kelvin.

D = (d⟨r 2(t )⟩/dt )/6

σsl values are obtained from the Turnbull relation.

Nn /N0 = exp[−JVc(tn − t0)]

(2)

(3)

where Vc is the volume of the cluster, N0 is the number of nanoparticles, and t0 is the nucleation time lag. Nn is set to be N0 − n + 1. Figure S6 presents plots of ln(Nn/N0) versus the time of nucleation for (Pd0.45Au0.1Pt0.45)1522/(25,25)-SWNT, (Pd0.25Au0.5Pt0.25)1522/(25,25)-SWNT, and (Pd0.10Au0.80Pt0.10)1522/(25,25)-SWNT. From the slopes of Figure S6, nucleation rates (J) can be obtained. According to the theory of homogeneous nucleation, the nucleation rate is represented by

The diffusion coefficient will be used for calculating the p r e f a c t o r o f t h e nu c l e a t i o n ra t e eq u a t i o n . F o r (Pd0.33Au0.33Pt0.33)1522 confined in (25,25)-SWNT, at 1050 K, the average atomic diffusion coefficient is 0.0939 × 10−8 m2/s, and the x, y, and z components of atomic diffusion coefficient (Dx, Dy, and Dz) are 0.0931 × 10−8, 0.0977 × 10−8, and 0.0909 × 10−8, respectively, which suggest that the atomic diffusion is indeed three-dimensional. Thus, even for the particles inside the nanotubes, we can use eq 2 to compute the atomic diffusion coefficients. The results of atomic diffusion coefficients are represented in Figure S5. Because the experimental values of the diffusion constants for Pd−Au−Pt trimetallic nanoparticles are unavailable, we compared our results of the confined PdxAuyPtz (y = 0.1, 0.2, 0.33, 0.4, 0.5, 0.6, 0.7, and 0.8, z = x =

J = A exp( −ΔG*/KBT )

(4)

where ΔG* is the free energy for formation of a critical nucleus and A is a prefactor. In the present analysis, the classical nucleation theory (CNT) developed by Turnbull and 12917


Article

The Journal of Physical Chemistry C colleagues67,68 is considered. The prefactor A can be expressed as A = 16(3/4π )1/3 σsl1/3D/(kBTV m4/3)

SWNT are examined and investigated in terms of MD simulation method. Results demonstrate that the confined Pd−Au−Pt nanoparticles possess a cylindrical multishelled structure, similar to those of gold (or Au−Pt) nanoparticles confined in SWNT and different from free Pd−Au−Pt nanoparticles or bulk gold. In each confined Pd−Au−Pt nanoparticle, the gold atoms preferentially accumulate near the tube center, while Pt atoms preferentially distribute near the tube wall, which are in accord with the previous observation on Au−Pt nanoparticles confined in SWNT. Interestingly and importantly, Pd atoms scatter through the confined Pd−Au−Pt nanoparticle, which is consistent with catalytic observations in experiment. This specific structure of the confined Pd−Au−Pt nanoparticles can be ascribed to the competitive effect between the metal−SWNT and metal−metal interactions, which may affect the stability of supported metal catalysts. The platinum with greater cohesive energy governs the melting points of confined Pd−Au−Pt trimetallic nanoparticles. The confined effect of SWNT considerably improves the stability of Pd−Au− Pt nanoparticles. Because the nucleation barrier increasing with temperature dominates nuclei formation, the nucleation rates significantly decrease with temperature. The calculated nucleation rates of confined Pd−Au−Pt nanoparticles are about 1036 m−1 s−1. On the other hand, for the confined Pd− Au−Pt nanoparticles, as gold composition increases, the nucleation barrier increases, resulting in that nucleation rate considerably decreases, suggesting that the size of supported metal nanoparticles can be controlled via adjusting the composition of metals with different cohesive energies. The current work will be helpful for controlling the size of supported metal catalysts in experiment.

(5)

where Vm represents the molecular volume in crystal and the self-diffusion (D) can be calculated on the basis of eq 2. Figure 7 displays the relationship between nucleation rate and

Figure 7. Relationship between nucleation rate and temperature for the confined (Pd0.45Au 0.1 Pt 0.45 )1522 , (Pd 0.25 Au 0.5Pt 0.25 ) 1522, and (Pd0.10Au0.80Pt0.10)1522 nanoparticle.

temperature for the confined (Pd 0.45 Au 0.1 Pt 0.45 ) 1522 , (Pd0.25Au0.5Pt0.25)1522, and (Pd0.10Au0.80Pt0.10)1522 nanoparticles. As shown in Figure 7, the nucleation rates significantly decrease with temperature, which may be due to the fact that the nucleation barrier increasing with temperature controls nuclei formation. On the other hand, as gold composition increases, nucleation rate significantly decreases, which can be attributed to the lower cohesive energy of gold. As shown in Table 5 and Figure 7, the calculated nucleation rates of confined Pd−Au−Pt nanoparticles are about 1036 m−1 s−1, consistent with those of the gold nanoparticles confined within SWNT.41 As illustrated in Figure S7, based on eqs 1−5, the computed nucleation energy barriers are about 10−16 J. As shown in Figure S7, the nucleation barrier considerably increases with temperature, resulting in that the nucleation rates considerably decrease with temperature as shown in Figure 7. On the other hand, as represented in Figure S7, the nucleation barrier increases with gold composition in the confined Pd−Au−Pt nanoparticles, leading to that nucleation rate decreases with gold composition; that is, during quenching processes of some confined Pd−Au− Pt nanoparticles, when the gold compositions increase, nucleation rates decrease, and thus these nanoparticles can grows into larger particles. The above results suggest that the size of supported metal nanoparticles can be controlled via adjusting the composition of metals with different cohesive energies. Because there is no report on the experimental study of the Pd−Au−Pt nanoparticles confined within SWNT so far, the simulated results in the current work remain to be confirmed by experiment in the future.

■

ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.jpcc.7b02434. Effect of SWNT on the stability of a Pd−Au−Pt nanoparticle, Figure S1 showing the structure of the capping region for (Pd0.33Au0.33Pt0.33)818/(19,19)-SWNT parallel to tube axis, Figure S2 representing the radial density distribution for (Pd0.33Au0.33Pt0.33)1522/(25,25)SWNT during the cooling and heating processes, Figure S3 indicating the time dependence of total energies and structures of (Pd0.45Au0.1Pt0.45)1522 nanoparticle confined in (25,25)-SWNT during the quenching process (from 1800 to 1050 K), Figure S4 accounting for total energy as a function of temperature for free and confined (Pd0.33Au0.33Pt0.33)1522 nanoparticles, Figure S5 illustrating the temperature dependence of diffusion coefficient for the confined PdxAuyPtz (y = 0.1, 0.2, 0.33, 0.4, 0.5, 0.6, 0.7, and 0.8, z = x = (1 − y)/2) nanoparticles and free bulk Pt, Figure S6 showing plots of ln(Nn/N0) against nucleation time for (Pd0.45Au0.1Pt0.45)1522/SWNT, (Pd0.25Au0.5Pt0.25)1522/SWNT, and (Pd0.10Au0.80Pt0.10)1522/SWNT, and Figure S7 representing temperature dependence of nucleation barrier for confined (Pd0.45Au0.1Pt0.45)1522, (Pd0.25Au0.5Pt0.25)1522, and (Pd0.10Au0.80Pt0.10)1522 (PDF)

■

IV. CONCLUSIONS In summary, the structural, thermal, and dynamical properties of Pd−Au−Pt trimetallic metal nanoparticles confined in (n,n)-

AUTHOR INFORMATION

Corresponding Authors

*E-mail: [email protected]. 12918


Article

The Journal of Physical Chemistry C *E-mail: [email protected].

(14) Ahmed, M.; Attard, G. A.; Wright, E.; Sharman, J. Methanol and Formic Acid Electrooxidation on Nafion Modified Pd/Pt{111}: The Role of Anion Specific Adsorption in Electrocatalytic Activity. Catal. Today 2013, 202, 128−134. (15) Li, L.; E, Y.; Yuan, J.; Luo, X.; Yang, Y.; Fan, L. Electrosynthesis of Pd/Au Hollow Cone-Like Microstructures for Electrocatalytic Formic Acid Oxidation. Electrochim. Acta 2011, 56, 6237−6244. (16) Lim, B.; Kobayashi, H.; Yu, T.; Wang, J. G.; Kim, M. J.; Li, Z. Y.; Rycenga, M.; Xia, Y. N. Synthesis of Pd-Au Bimetallic Nanocrystals via Controlled Overgrowth. J. Am. Chem. Soc. 2010, 132, 2506−2507. (17) Deng, Y. J.; Tian, N.; Zhou, Z. Y.; Huang, R.; Liu, Z. L.; Xiao, J.; Sun, S. G. Alloy Tetrahexahedral Pd-Pt Catalysts: Enhancing Significantly the Catalytic Activity by Synergy Effect of High-Index Facets and Electronic Structure. Chem. Sci. 2012, 3, 1157−1161. (18) Zhang, G. R.; Wu, J.; Xu, B. Q. Syntheses of Sub-30 nm Au@Pd Concave Nanocubes and Pt-on-(Au@Pd) Trimetallic Nanostructures as Highly Efficient Catalysts for Ethanol Oxidation. J. Phys. Chem. C 2012, 116, 20839−20847. (19) Wang, L.; Yamauchi, Y. Strategic Synthesis of Trimetallic Au@ Pd@Pt Core-Shell Nanoparticles from Poly(vinylpyrrolidone)- Based Aqueous Solution toward Highly Active Electrocatalysts. Chem. Mater. 2011, 23, 2457−2465. (20) Wang, L.; Yamauchi, Y. Autoprogrammed Synthesis of TripleLayered Au@Pd@Pt Core-Shell Nanoparticles Consisting of a Au@Pd Bimetallic Core and Nanoporous Pt Shell. J. Am. Chem. Soc. 2010, 132, 13636−13638. (21) Zhao, Z.; Li, M.; Cheng, D.; Zhu, J. Understanding the Structural Properties and Thermal Stabilities of Au−Pd−Pt Trimetallic Clusters. Chem. Phys. 2014, 441, 152−158. (22) Fan, T. E.; Liu, T. D.; Zheng, J. W.; Shao, G. F.; Wen, Y. H. Structural Optimization of Pt-Pd-Au Trimetallic Nanoparticles by Discrete Particle Swarm Algorithms. J. Mater. Sci. 2015, 50, 3308− 3319. (23) Ferrando, R.; Jellinek, J.; Johnston, R. L. Nanoalloys: From Theory to Applications of Alloy Clusters and Nanoparticles. Chem. Rev. 2008, 108, 845−910. (24) Alayoglu, S.; Nilekar, A. U.; Mavrikakis, M.; Eichhorn, B. Ru-Pt Core-Shell Nanoparticles for Preferential Oxidation of Carbon Monoxide in Hydrogen. Nat. Mater. 2008, 7, 333−338. (25) Kesavan, L.; Tiruvalam, R.; Ab Rahim, M. H.; bin Saiman, M. I.; Enache, D. I.; Jenkins, R. L.; Dimitratos, N.; Lopez-Sanchez, J. A.; Taylor, S. H.; Knight, D. W.; et al. Solvent-Free Oxidation of Primary Carbon-Hydrogen Bonds in Toluene Using Au-Pd Alloy Nanoparticles. Science 2011, 331, 195−199. (26) Khanal, S.; Bhattarai, N.; Velazquez-Salazar, J. J.; Bahena, D.; Soldano, G.; Ponce, A.; Mariscal, M. M.; Mejia-Rosalesc, S.; JoseYacaman, M. Trimetallic Nanostructures: The Case of AgPd-Pt Multiply Twinned Nanoparticles. Nanoscale 2013, 5, 12456−12463. (27) Si, Y. C.; Samulski, E. T. Exfoliated Graphene Separated by Platinum Nanoparticles. Chem. Mater. 2008, 20, 6792−6797. (28) Huang, J.; Zhang, L.; Chen, B.; Ji, N.; Chen, F.; Zhang, Y.; Zhang, Z. Nanocomposites of Size-Controlled Gold Nanoparticles and Graphene Oxide: Formation and Applications in SERS and Catalysis. Nanoscale 2010, 2, 2733−2738. (29) Koga, K.; Gao, G. T.; Tanaka, H.; Zeng, X. C. Formation of Ordered Ice Nanotubes inside Carbon Nanotubes. Nature 2001, 412, 802−805. (30) Nguyen, T. T.; Serp, P. Confinement of Metal Nanoparticles in Carbon Nanotubes. ChemCatChem 2013, 5, 3595−3603. (31) Guo, S. H.; Zhu, B. E.; Ou, X. D.; Pan, Z. Y.; Wang, Y. X. Deformation of Gold-Filled Single-Walled Carbon Nanotubes under Axial Compression. Carbon 2010, 48, 4129−4135. (32) Fang, R. R.; He, Y. Z.; Zhang, K.; Li, H. Melting Behavior of Aluminum Nanowires in Carbon Nanotubes. J. Phys. Chem. C 2014, 118, 7622−7629. (33) Arcidiacono, S.; Walther, J. H.; Poulikakos, D.; Passerone, D.; Koumoutsakos, P. Solidification of Gold Nanoparticles in Carbon Nanotubes. Phys. Rev. Lett. 2005, 94, 105502.

ORCID

Xiaohua Lu: 0000-0001-9244-6808 Notes

The authors declare no competing financial interest.

■

ACKNOWLEDGMENTS

■

REFERENCES

This work is supported by grants from the Major Research Plan of the National Natural Science Foundation of China (nos. 91434109 and 91334202), and the National Science Foundation of China (no. 21276122). We want to express our thanks for the reviewers’ valuable suggestions for this Article.

(1) Fan, F. R.; Liu, D. Y.; Wu, Y. F.; Duan, S.; Xie, Z. X.; Jiang, Z. Y.; Tian, Z. Q. Epitaxial Growth of Heterogeneous Metal Nanocrystals: From Gold Nano-octahedra to Palladium and Silver Nanocubes. J. Am. Chem. Soc. 2008, 130, 6949−6951. (2) Fernández, J. L.; Walsh, D. A.; Bard, A. J. Thermodynamic Guidelines for the Design of Bimetallic Catalysts for Oxygen Electroreduction and Rapid Screening by Scanning Electrochemical Microscopy. M-Co (M: Pd, Ag, Au). J. Am. Chem. Soc. 2005, 127, 357−365. (3) Zhang, X.; Zhang, F.; Chan, K. Y. Preparation of Pt-Ru-Co Trimetallic Nanoparticles and Their Electrocatalytic Properties. Catal. Commun. 2004, 5, 749−753. (4) You, L. J.; Hu, L. J.; Xie, Y. P.; Zhao, S. J. Influence of Cu Precipitation on Tensile Properties of Fe-Cu-Ni Ternary Alloy at Different Temperatures by Molecular Dynamics Simulation. Comput. Mater. Sci. 2016, 118, 236−244. (5) Wang, P.; Zhang, J.; Bai, Y.; Xiao, H.; Tian, S.; Xie, H.; Yang, G.; Tsubaki, N.; Han, Y.; Tan, Y. Ternary Copper-Cobalt-Cerium Catalyst for the Production of Ethanol and Higher Alcohols Through CO Hydrogenation. Appl. Catal., A 2016, 514, 14−23. (6) Liu, T. D.; Xu, L. Y.; Shao, G. F.; Tu, N. N.; Tao, J. P.; Wen, Y. H. Structural Optimization of Pt-Pd-Rh Trimetallic Nanoparticles Using Improved Genetic Algorithm. J. Alloys Compd. 2016, 663, 466− 473. (7) Akbarzadeh, H.; Abbaspour, M.; Mehrjouei, E. Investigation of Thermal, Structural and Dynamical Properties of (Au x -Cu yNiy)N=32,108,256 Ternary Nanosystems: Effect of Au Addition to CuNi Bimetallic Nanoclusters via MD Simulation. RSC Adv. 2016, 6, 67619−67629. (8) Yu, C. Y.; Liu, X. J.; Zheng, G. P.; Niu, X. R.; Liu, C. T. Atomistic Approach to Predict the Glass-Forming Ability in Zr-Cu-Al Ternary Metallic Glasses. J. Alloys Compd. 2015, 627, 48−53. (9) Zhu, L. S.; Zhao, S. J. Influence of Ni on Cu Precipitation in FeCu-Ni Ternary Alloy by an Atomic Study. Chin. Phys. B 2014, 23, 063601. (10) Huang, R.; Shao, G. F.; Wen, Y. H.; Sun, S. G. Tunable Thermodynamic Stability of Au-CuPt Core-Shell Trimetallic Nanoparticles by Controlling the Alloy Composition Insights from Atomistic Simulations. Phys. Chem. Chem. Phys. 2016, 16, 22754− 22761. (11) Zhao, S. Z.; Li, J. H.; Liu, B. X. Favored Composition Region for Metallic Glass Formation and Atomic Configurations in the Ternary Ni-Zr-Ti System Derived from n-Body Potential Through Molecular Dynamics Simulations. J. Mater. Res. 2011, 26, 2050−2064. (12) Liang, S. H.; Dai, Y.; Li, J. H.; Liu, B. X. Glass Forming Region of Cu-Ti-Hf Ternary Metal System Derived from the n-Body Potential Through Molecular Dynamics Simulation. J. Phys. Chem. B 2010, 114, 9540−9545. (13) Erkoc, S.; Oymak, H. AlTiNi Ternary Alloy Clusters: Molecular Dynamics Simulations and Density Functional Theory Calculations. J. Phys. Chem. B 2003, 107, 12118−12125. 12919


Article

The Journal of Physical Chemistry C (34) Ge, Y.; Fa, W.; Zhou, J.; Dong, J. Single-Walled Gold Nanotubes Grown in Carbon Nanotubes: Molecular Dynamics Simulations. Phys. Lett. A 2010, 374, 3258−3262. (35) Cheng, D. J.; Lan, J. H. Thermal Behaviour of Pd Clusters inside Carbon Nanotubes: Insights into the Cluster-Size, Tube-Size and Metal-Tube Interaction Effects. Mol. Simul. 2010, 36, 805−814. (36) Cheng, D. J.; Wang, W. C.; Huang, S. P. Thermal Evolution of a Platinum Cluster Encapsulated in Carbon Nanotubes. J. Phys. Chem. C 2007, 111, 1631−1637. (37) Wang, L.; Zhang, H. W.; Zheng, Y. G.; Wang, J. B.; Zhang, Z. Q. Single-Walled Carbon Nanotubes Filled with Bimetallic Alloys: Structures and Buckling Behaviors. J. Appl. Phys. 2008, 103, 083519. (38) Han, Y.; Zhou, J.; Dong, J.; Yoshiyuki, K. Formation of SingleWalled Bimetallic Coinage Alloy Nanotubes in Confined Carbon Nanotubes: Molecular Dynamics Simulations. Phys. Chem. Chem. Phys. 2013, 15, 17171−17178. (39) Akbarzadeh, H.; Shamkhali, A. N. Melting Behavior of (PdxPt1‑x)n Nanoclusters Confined in Single-Walled Carbon Nanotubes: A Molecular Dynamics Investigation on the Effects of Chirality and Diameter of Nanotubes, and Size and Composition of Nanoclusters. RSC Adv. 2015, 5, 23160−23173. (40) Akbarzadeh, H.; Shamkhali, A. N.; Abbaspour, M.; Salemi, S.; Attaran, Z. A Molecular Dynamics Study of the Effect of the Substrate on the Thermodynamic Properties of Bound Pt-Cu Bimetallic Nanoclusters. Phys. Chem. Chem. Phys. 2016, 18, 21730−21736. (41) Shao, J. L.; Yang, C.; Zhu, X. L.; Lu, X. H. Melting and Freezing of Au Nanoparticles Confined in Armchair Single-Walled Carbon Nanotubes. J. Phys. Chem. C 2010, 114, 2896−2902. (42) Shi, R. W.; Shao, J. L.; Zhu, X. L.; Lu, X. H. On the Melting and Freezing of Au-Pt Nanoparticles Confined in Single-Walled Carbon Nanotubes. J. Phys. Chem. C 2011, 115, 2961−2968. (43) Sanz-Navarro, C. F.; Astrand, P.; Chen, D.; Ronning, M.; van Duin, A. C. T. Molecular Dynamics Simulations of Metal Clusters Supported on Fishbone Carbon Nanofibers. J. Phys. Chem. C 2010, 114, 3522−3530. (44) Johnston, R. L. Atomic and Molecular Clusters; Taylor and Francis: London, 2002. (45) Baletto, F.; Ferrando, R. Structural Properties of Nanoclusters: Energetic, Thermodynamic, and Kinetic Effects. Rev. Mod. Phys. 2005, 77, 371−423. (46) Fernández-Navarro, C.; Mejía-Rosales, S. Molecular Dynamics of Free and Graphite-Supported Pt-Pd Nanoparticles. Adv. Nanopart. 2013, 2, 323−328. (47) Sankaranarayanan, S. K. R. S.; Bhethanabotla, V. R.; Joseph, B. Molecular Dynamics Simulations of the Structural and Dynamic Properties of Graphite-Supported Bimetallic Transition Metal Clusters. Phys. Rev. B: Condens. Matter Mater. Phys. 2005, 72, 195405. (48) Morrow, B. H.; Striolo, A. Supported Bimetallic Pt-Au Nanoparticles: Structural Features Predicted by Molecular Dynamics Simulations. Phys. Rev. B: Condens. Matter Mater. Phys. 2010, 81, 155437. (49) Kang, J. W.; Hwang, H. J. J. Korean Phys. Soc. 2001, 38, 695. (50) Cleri, F.; Rosato, V. Tight-Binding Potentials for Transition Metals and Alloys. Phys. Rev. B: Condens. Matter Mater. Phys. 1993, 48, 22−33. (51) Wang, B. L.; Yin, S. Y.; Wang, G. H.; Zhao, J. J. Structures and Electronic Properties of Ultrathin Titanium Nanowires. J. Phys.: Condens. Matter 2001, 13, L403−L408. (52) Lei, H. Melting of Free Copper Clusters. J. Phys.: Condens. Matter 2001, 13, 3023−3030. (53) Celtek, M.; Sengul, S.; Domekeli, U.; Canan, C. Molecular Dynamics Study of Structure and Glass Forming Ability of Zr70Pd30 alloy. Eur. Phys. J. B 2016, 89, 65. (54) Wang, J.; Seifert, S.; Winans, R. E.; Tolmacho, E.; Xin, Y. X.; Chen, D. P.; Wang, H.; Anderson, S. L. In situ X-ray Scattering and Dynamical Modeling of Pd Catalyst Nanoparticles Formed in Flames. J. Phys. Chem. C 2015, 119, 19073−19082.

(55) Zhang, B. L.; Wang, B. W.; Liu, Q. X. Melting Curves of Cu, Pt, Pd and Au under High Pressures. Int. J. Mod. Phys. B 2016, 30, 1650013. (56) Heinz, H.; Vaia, R. A.; Farmer, B. L. Accurate Simulation of Surfaces and Interfaces of Face-Centered Cubic Metals Using 12−6 and 9−6 Lennard-Jones Potentials. J. Phys. Chem. C 2008, 112, 17281−17290. (57) David, M.; Tim, J.; Leanne, C. Potential Energy Distributions within and on Single-Walled and Double-Walled Carbon Nanotubes. J. Nanopart. Res. 2005, 7, 59−73. (58) Luedtke, W. D.; Landman, U. Slip Diffusion and Levy Flights of an Adsorbed Gold Nanocluster. Phys. Rev. Lett. 1999, 82, 3835−3838. (59) Hwang, H. J.; Kwon, O. K.; Kang, J. W. Copper Nanocluster Diffusion in Carbon Nanotube. Solid State Commun. 2004, 129, 687− 690. (60) Zribi, S.; Albela, B.; Bonneviot, L.; Zina, M. S. Surface Engineering and Palladium Dispersion in MCM-41 for Methane Oxidation. Appl. Catal., A 2015, 502, 195−203. (61) Hu, C. Y.; Wang, X. Highly Dispersed Palladium Nanoparticles on Commercial Carbon Black with Significantly High Electro-Catalytic Activity for Methanol and Ethanol Oxidation. Int. J. Hydrogen Energy 2015, 40, 12382−12391. (62) Li, J. H. Exploring the Logic and Landscape of the Knowledge System:Multilevel Structures, Each Multiscaled with Complexity at the Mesoscale. Engineering 2016, 2, 276−285. (63) Subbaraman, R.; Sankaranarayanan, S. K. R. S. Effect of Ag addition on the thermal characteristics and structural evolution of AgCu-Ni ternary alloy nanoclusters: Atomistic simulation study. Phys. Rev. B: Condens. Matter Mater. Phys. 2011, 84, 075434. (64) Sun, C. Q.; Shi, Y.; Li, C. M.; Li, S.; Yeung, T. C. A. SizeInduced Undercooling and Overheating in Phase Transitions in Bare and Embedded Clusters. Phys. Rev. B: Condens. Matter Mater. Phys. 2006, 73, 075408−075409. (65) Weast, R. C. CRC Handbook of Chemistry and Physics, 63rd ed.; CRC Press: Boca Raton, FL, 1982. (66) Akbarzadeh, H.; Parsafar, G. A. A Molecular-Dynamics Study of Thermal and Physical Properties of Platinum Nanoclusters. Fluid Phase Equilib. 2009, 280, 16−21. (67) Turnbull, D. Kinetics of Solidification of Supercooled Liquid Mercury Droplets. J. Chem. Phys. 1954, 20, 411−424. (68) Turnbull, D.; Fisher, J. C. Rate of Nucleation in Condensed Systems. J. Chem. Phys. 1949, 17, 71−73. (69) Turnbull, D. Formation of Crystal Nuclei in Liquid Metals. J. Appl. Phys. 1950, 21, 1022. (70) Peterson, N. L. WADD technical report, 1960; pp 60−793.

12920


Investigation of Structural, Thermal, and Dynamical Properties of Pd

Recommend Documents