Deposition of Monodisperse Platinum Nanoparticles of Controlled Size on Different Supports

doi:10.4236/anp.2013.21007

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Advances in Nanoparticles, 2013, 2, 32-38

http://dx.doi.org/10.4236/anp.2013.21007 Published Online February 2013 (http://www.scirp.org/journal/anp)

Deposition of Monodisperse Platinum Nanoparticles of

Controlled Size on Different Supports

Zinaida Kaidanovych, Yevhen Kalishyn, Peter Strizhak

L.V. Pisarzhevsky Institute of Physical Chemistry, The National Academy of Sciences of Ukraine, Kyiv, Ukraine

Email : z.kaida n [email protected] om, kali s hyn.yevhen@gma il.com

Received December 18, 2012; revised January 20, 2013; accepted January 30, 2013

ABSTRACT

Monodisperse platinum nanoparticles with controlled size were synthesized by polyol synthesis and supported on

γ-Al2O3, SiO2 and carbon nanotubes (CNT) by the colloid deposition method. The average size of Pt nanoparticles in

colloidal solutions and on supports was determined by TEM images and from XRD patterns. The size of Pt nanoparti-

cles supported on SiO2 and CNT determined from XRD patterns is in a good agreement with size obtained from the

TEM analyses. There were shown that no agglomeration and size changing of Pt nanoparticles on these supports were

observed. All these findings illustrate that the method of colloid deposition allows one to obtain catalyst with monodis-

perse platinum nanoparticles of controlled size deposited on different supports without changing the nanoparticle’s size

and morphology.

Keywords: Platinum Nanoparticles; Pt/γ-Al2O3; Pt/SiO2; Pt/CNT

1. Introduction

The pure suppo rted Pt nanopar ticles catalysts are of great

interest owing to their specific features resulting from

their size and morphology that are exploited as efficient

catalysts in both homogeneous and heterogeneous cata-

lytic technologies [1,2]. In addition, these have led to

investigate the dependence of catalytic activity on the

size and shape of Pt nanoparticles as well as the sur-

face-to-volume ratio and quantum size effect because of

their potential applications in electronics, catalysis, and

biology [1-5]. Performance of Pt nanosized catalysts is

affected by numerous factors, one of which is the nature

and structure of the support materials. Mostly studies of

platinum catalysts have been performed with the metal

supported on SiO2, Al2O3, MgO, zeolites, and carbon

[1-6]. Materials with supported Pt nanoparticles are

known to have good catalytic characteristics. For exam-

ple, carbon nanotubes (CNT) supported platinum catalyst

shows superior activity in catalytic oxidation of various

organic compounds [7,8]. Also, the electrocatalytic ac-

tivity of Pt/CNT towards methanol oxidations was dis-

covered [9].

Silica supported nanoparticles have been used to cata-

lyze a wide variety of reactions such as hydrogenations,

oxidations, and other organic synthetic reactions. A wide

variety of transition metal nanoparticles have also been

adsorbed onto Pt/SiO2 shows selective hydrogenation of

acetophenone [10] and high catalytic activity in ethanol

electrooxidation [11].

Platinum supported on alumina catalyzes a variety of

chemical reactions, particularly, processes used in oil

refinery [12]. Cubic platinum nanoparticles supported on

alumina have been used to catalyze the NO reduction

reaction [13]. It was observed a conversion of the low

index facets of the cubic nanoparticles to higher index

planes that occurs during the reaction conditions, which

is attributed to substantial changes in the catalytic activ-

ity and selectivity to reaction products [13]. A large

morphological evolution of large platinum nanoparticles

is also observed during the NO reduction reaction [14].

Moreover, Pt/γ-Al2O3 shows catalytic activity in ethylene

glycol reforming [15].

Discovery of carbon nanotubes (CNTs), followed by

extensive studies of their properties, has also resulted in

highlighting their catalytic properties [16-20]. Particu-

larly, comparison of the catalytic activity of metal cata-

lysts supported on various oxides, amorphous carbon,

and CNTs showed that catalytic performance is generally

better for CNTs. For example, a CNT-supported plati-

num catalyst shows superior activity in catalytic oxida-

tion of vario us organic compo un ds [ 19] .

Many studies show that size- and shape-controlled

metallic nanoparticles supported onto mesoporous mate-

rials are responsible in changing catalytic activity and

selectivity [21-24]. The metal-support interaction, which

refers to support-induced changes in reaction selectivity

of metal nanoparticles, has been shown mostly on 2-di-

mensional nanoparticle arrays on oxide substrates, be-

Z. KAIDANOVYCH ET AL. 33

cause the oxide thin films and corresponding catalysts

are easily prepared and characterized providing kinetic

differences which invokes different mechanisms [25,26].

However, there are some studies abou t deposition of col-

loidal Pt nanoparticles on different supports [27]. There is

no information about size changing of nanoparticles after

their deposition. A choice of support is vitally important

to improve catalytic characteristics, because a nanoparti-

cle-based catalyst can induce reciprocal electronic or

chemical interactions.

The goal of this study is to show that the method of

deposition from colloid solution gives a reliable root to

prepare catalyst with monodisperse Pt nanoparticles with

controlled size.

2. Experimental

All chemicals and solvent were of the highest purity

available and were used as purchased without further

purification or distillation.

A solution o f 3 g of Poly(N-vin yl-2-pyrrolido ne) (PVP,

Mw = 40,000) and 0.06 g of sodium hydroxide in 300 ml

ethylene glycol were heated to 120˚C under stirring.

Varying amounts (40, 60, 160, 240 and 360 ml) of 1%

hexachloroplatinic acid in water solution were dosed

slowly to the hot ethylene glycol. Next, the solutions

were stirred for an additional 30 min and cooled to room

temperature. PVP-protected Pt nanoparticles were pre-

cipitated by adding acetone and then redispersed in

ethanol.

CNTs were synthesized by the catalytic decomposition

of ethylene according to procedure described elsewhere

[28]. γ-Al2O3 and SiO2 was grinded and the fraction of

0.25 - 0.5 mm was heat-treated at 300˚C in air. Deposi-

tion of Pt nanoparticles on supports was performed by

mixing appropriate amounts of SiO2, γ-Al2O3 or CNTs

and colloidal solution of nanoparticles in ethanol under

stirring. The obtained samples were dried in air. The ob-

tained samples contained 1.0% of platinum.

The average particle size was determined from trans-

mission electron spectroscopy (TEM) images. TEM stud-

ies were carried out using PEM-125K (Selmi, Ukraine).

The samples of colloidal solution of nanoparticles for

TEM analysis were dropped onto carbon-coated copper

grid. The samples of Pt/support previously were grinded

into powder and mixed with drop of water. At least 600

nanoparticles per sample were analyzed to determine

their size and distribution.

The samples of γ-Al2O3, SiO2, CNTs, and Pt/support

were grinded into powder and analyzed using the X-ray

diffractometer Bruker D8 Advance. The mean particle

size also was determinate using the Scherrer equation:



0.9 cosD





, (1)

where λ is the wavelength used (1.54184 Å), β is the line

broadening at half the maximum intensity in radians and

θ is the angle of diffraction.

3. Results and Discussion

Figures 1(a), (c), (e), (g) show a typical TEM images of

Pt nanoparticles in colloidal solutions prepared using

different amount of hexachloroplatinic acid. Figures 1(b),

(d), (f), (h) give corresponding size distributions of Pt

nanoparticles. The presented data indicate that the

nanoparticles are almost spherical. It was shown that the

average size of Pt nanoparticles depends on concentra-

tion of hexachloroplatinic acid. If the concentration of

hexachloroplatinic acid is 3.3 mmol/L than the average

size of Pt nanoparticles is 1.3 nm as it is shown in Figure

1(a). The 29.3 mmol/L of concentration of hexachloro-

platinic acid gives 3.1 nm of Pt nanoparticles. The av-

erage size of Pt nanoparticles in colloidal solution in-

creases from 1.3 to 3.1 nm with increasing of precursor

concentration. Corresponding size distribution of Pt nano-

particles is presented in Figures 1(b), (d), (f), (h) show-

ing that size distribution is almost Gaussian. All samples

are characterized by narrow width of particle size distri-

bution with typical standard deviations (SD) less than

15%. Therefore, the synthesized Pt nanoparticles are al-

most monodispersed.

Pt nanoparticles with average size in colloidal solutio n

2.8 nm (Figure 1(e)) were supported on γ-Al2O3, SiO2

and CNTs in order to determine their size changing after

deposition on different supports. Figures 2(a), (c), (e)

show typical TEM images of Pt nanoparticles supported

on γ-Al2O3, SiO2 and CNTs. The presented data indicate

that supported nanoparticles ar e not aggregating and stay

almost spherical. Figures 2(b)-(f) give corresponding

size distributions of supported Pt nanoparticles. The av-

erage size of supported Pt nanoparticles is nearly the

same as average size of those particles in solution –2.9

nm for Pt/γ-Al2O3 and 2.8 nm for Pt/SiO2 and Pt/CNTs.

Size distribution of supported Pt nanoparticles is almost

gaussian with nearly the same SD as for Pt nanoparticles

in solution 0.3 - 0.4 nm, what is amount less than 15% of

particles size. Therefore, the Pt nanoparticles on these

supports stay almost monodispersed as in solution. Com-

parison of data presented in Figures 1 and 2 allows one

to conclude that deposition of platinum nanoparticles on

γ-Al2O3, SiO2 and CNTs does not prod uce changing par-

ticles size and morphology.

In order to synthesis Pt/γ-Al2O3 with different size of

supported nanoparticles the concentration of hexachloro-

platinic acid in reaction solution was varying. The ob-

tained colloidal solutions of Pt nanoparticles with differ-

ent nanoparticles sizes were deposited on γ-Al2O3. The

mean sizes and standard deviations of supported nano-

particles were measured using their TEM images.

Z. KAIDANOVYCH ET AL.

(a) (b)

(e) (f)

(g) (h)

Figure 1. TEM image of Pt nanoparticles prepared from colloidal solution (a, c, e, g); their distribution by size (b, d, f, h).

Z. KAIDANOVYCH ET AL. 35

(a) (b)

(e) (f)

Figure 2. TEM image of Pt nanoparticles supported on γ-Al2O3 (a), SiO2 (c), CNT (e); their distribution by size (b), (d), (f)

respectively.

The obtained dependence presented in Figure 3. The

size of supported Pt nanoparticles increases non linear

with increasing the H2PtCl6 concentration, abruptly at

low amount of hexacloroplatinic acid and slightly at

higher precursor concentration. It is noticeable that for

larger particles the value of standard deviation is bigger,

but it is always less than 15% of mean size of the parti-

cles. Varying concentration of hexachloroplatinic acid in

reaction solution from 3.3 to 29.3 mmol/l allows one to

obtain Pt/γ-Al2O3 with average size of nanoparticles in

the range of 1. 3 - 3.3 nm.

The XRD patterns were obtained for all solids. Figure

4(a) gives the XRD pattern for γ-Al2O3 and Pt/γ-Al2O3.

The major features of Pt pattern overlaps with that for

Z. KAIDANOVYCH ET AL.

Figure 3. Dependence of average size of Pt nanoparticles

supported on γ-Al2O3 on concentration of hexachloroplatini c

acid in reaction solution.

γ-Al2O3, that is in agreement with data published in lit-

erature [29]. Figure 4(b) shows the XRD patterns for

SiO2 and Pt/SiO2. The XRD pattern for Pt/SiO2 shows a

presence of the crystalline Pt face centered cubic (fcc)

phase. The peaks belong to (111), (200), (220) faces cor-

responding to 2θ values of about 39.72˚, 46.08˚, 67.65˚.

The XRD peaks of Pt nanoparticles are broad and com-

parable comparing to those of the bulk Pt material. The

most intensive reflection (111) from the Pt nanoparticles

were used to calculate the average size of Pt nanocrystal-

lites on the basic of the width of the reflection according

to the Debye-Scherrer Equation (1). The crystallite size

of Pt particle was estimated about 4 nm, which is in a

good agreement with results of TEM analyses.

Figure 4(c) gives the results of XRD analysis of CNT

and Pt/CNT. The results represent the property of the

crystalline Pt face centered cubic (fcc) phase. Because of

the low concentration of Pt nanoparticles an d high inten-

sivity of CNTs reflections it is p ossible to determine on ly

the most intensive peak (111) of Pt, respective to 2θ

value of about 39.55˚. The estimated size of platinum

nanoparticles based on the Debye-Scherrer equation was

found about 4 nm, that is, again, in a good agreement

with results of TEM analyses.

4. Conclusions

In this study, nanoparticles with controlled size were

synthesized by reducing of hexachloroplatinic acid by

ethylene glycol, using PVP as protected agent. These

nanoparticles were deposited on γ-Al2O3, SiO2 and car-

bon nanotubes by the colloid deposition method. No ag-

glomeration of platinum nanoparticles on all of these

supports was observed. The average size determined by

TEM images of nanoparticles deposited on different

supports corresponds to their size in colloid solution be-

fore deposition. Deposition of platinum nanoparticles on

(a)

(b)

(c)

Figure 4. The XRD patterns of (a) γ-Al2O3 and Pt/γ-Al2O3;

(b) SiO2 and Pt/SiO2; (c) CNT and Pt/CNT.

γ-Al2O3, SiO2 and CNTs does not lead to changing of

particles size and morphology. The var ying of concentra-

tion of hexachloroplatinic acid in reaction solution allows

to obtain Pt/γ-Al2O3 with controlled size of monodisperse

Pt nanoparticles.

According to XRD analysis, supported platinum nano-

particles have the face centered cubic phase. The size of

Pt nanoparticles supported on SiO2 and CNT determined

from XRD patterns is in a good agreement with size ob-

tained from the TEM analyses.

Z. KAIDANOVYCH ET AL. 37

Therefore we show that the method of colloid deposi-

tion allows one to obtain catalyst with monodisperse

platinum nanoparticles of controlled size deposited on

different supports without changing the nanoparticle’s

size and morphology.

5. Acknowledgements

The work is supported by the grants of the National

Academy of Sciences of Ukraine and the Ministry of

Education and Science of Ukraine.

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