e-Journal of Surface Science and Nanotechnology

23 June 2012

Conference - IWAMN2009 -

e-J. Surf. Sci. Nanotech. Vol. 10 (2012) 263-267

Synthesis and Study on Catalytic Activity of Spinel Metallic Oxides in Styrene
Preparation from Ethylbenzene∗
Le Thanh Son,† Hoa Huu Thu, Nguyen Thanh Binh, Tran Thi Nhu Mai, and Nguyen Hong Vinh
Department of Petroleum Chemistry, Faculty of Chemistry,
Hanoi University of Science, 334 Nguyen Trai, Thanh Xuan, Hanoi, Vietnam
(Received 6 December 2009; Accepted 21 December 2011; Published 23 June 2012)
A series of spinel oxides AB2−x B’x O4 /γ-Al2 O3 (A: Ni, Cu; B: Cr; B’: Fe and x = 0, 0.5, 1, 1.5, 2) were synthesized
by two methods: solid-state reaction and coprecipitation. The oxides obtained were characterized by XRD, SEM
and BET to determinate their textural and structural properties. Their catalytic activity was evaluated by reaction
of oxidative dehydrogenation of ethylbenzene to styrene. The XRD showed the spinel phase formed for all oxides
synthesized by two methods. However, the coprecipitation method seems to be more favorable for formation
of spinel phase. All samples showed a high catalytic activity and selectivity for oxidative dehydrogenation of
ethylbenzene to styrene, especially, in the case of NiCr2−x Fex O4 obtained by coprecipitation method.
[DOI: 10.1380/ejssnt.2012.263]
Keywords: Nano spinel; Ethylbenzene; Dehydrogenation

I.

INTRODUCTION

Recent years, the styrene quantity consumed is increasing as start materials to synthesize the polymers and
copolymers. The worldwide capacity for production of
stryrene is approximately 15.106 t/year [9]. Stryrene is

II.

EXPERIMENTAL

A.

Spinel preparation

There have been a lot of methods to prepare spinel
materials. Here, we have used two methods of preparing
the spinels AB2−x B’x O4 (x = 0, 0.5, 1.0, 1.5, 2.0), which
are described in the following. Details of samples used in
the present study are summarized in Table II.

1.

Solid-state reaction method

In this method, iron (III) oxide, chromium (III)
nickel oxide all in PA, were used as sources of metallic irons in spinel ternary structure NiCr2−x Fex O4 (x =
0, 0.5, 1.0, 1.5, 2.0). Spinel NiCr2−x Fex O4 was prepared
as following: first, the quantities calculated in advance of
the oxides above were mixed carefully in a porcelain mortar for 30 minutes. Then, the powder mixture granulated
at pressure of 2.000 N/cm2 . Transfer the granules in a

c 2012 The Surface Science Society of Japan ( />ISSN 1348-0391 ⃝

263



V/Mg/O
Fe/K/Li/Cr/O

States
Industrial
Commercial
Research
Research
Research

scheme (fig.1)

TABLE II: Spinel samples obtained by different methods.
Sample
No.
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15

NiCrFeO4
NCF 3 (II)
NCF 4 (II)
NF 5(II)
CC 1 (I)
CCF 2 (II)
CuCrFeO4
CCF 3 (II)
CCF 4 (II)
CF 5(II)

cup and place this cup in a furnace, heat the electrical
furnace at 1300◦ C for 4 hours. We cooled the solid obtained in desiccators and cracked them into small grains
of 0.1-1.0 mm in diameter as catalyst grains.
The reaction of spinel formation at 1300◦ C is generally
represented after the following equation:
2NiO + xFe2 O3 + (2 − x)Cr2 O3 → 2NiCr2−x FeO4 (1)
In the case of x = 0, the reaction is as follows:
NiO + Cr2 O3 → NiCr2 O4

(2)

As a comparison, we also prepared two series of spinels:
NiCr2−x Fex O4 and CuCr2−x Fex O4 by coprecipitation
method, using the sources of respective metal nitrates.
2.

Figure 1: Scheme of formation of ternary spinels NiCr2-xFexO4 at high temperature

FIG. 1: Scheme of formation of ternary spinels NiCr2−x Fex O4

desired solid. The precipitate was filtered and washed
with distillated water until absence of NO−
3 ions. Then,
264

Characterization

Reaction system and analysis of liquid products
obtained

The reaction of oxidative dehydrogenation was carried
out in the vapor phase in a fixed bed flow type reactor
consisting of a quarts tube in which the catalyst bed was
placed in the middle of the tube. The reactor was heated
by electricity and controlled by digital temperature controller. The temperature was measured by thermocouple
placed in the center of the catalyst bed. The reactants
were fed into the catalyst bed by a syringe infusion pump
following the ethylbenzene flow rate desired. The liquid products collected for the first 30 min were discarded
and analyzed on Gas Chromatography-Mass spectroscopy
(GC-MS HP 6890).

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e-Journal of Surface Science and Nanotechnology





Volume 10 (2012)


RESULTS AND DISCUSSIONS

The solid solution of metallic oxides mixture having
spinel structure or the ceramic materials are often prepared to suit their applications. Generally, the spinel solid
solutions are formed at different temperatures according

to chemical precursors used for preparing spinels desired.
In the solid-state reaction method, the precursors are all
metallic oxides, the reaction temperature is used being
1300◦ C.
2NiO + xFe2 O3 + (2 − x)Cr2 O3 → 2NiCr2−x Fex O4
(x = 0, 0.5, 1.0, 1.5, 2.0)
(3)

In these reactions, NiO existing at solid state with
body-centered cubic structure coordination number of
Ni2+ , O2− ions being 6; Cr2 O3 and Fe2 O3 having hexadiTABLE III: Characteristic absorption bands in IR region of
rection structure, while the spinels NiCr2−x Fex O4 represpinel samples.
sented face-centered cubic structure. So, the formation
Absorption bands in the IR of samples (cm−1 )
of spinels is easy because of their structure being apSpinels
Vibration of Vibration of Presence Presence proachable although the reaction temperature 1300◦ C was
tetrahedral
octahedral of nitrate of water far from their fusion temperature. In the reaction prometal-oxygen metal-oxygen
NO−
∼1670 [3]
3
cess, the ions consisting of anion O2− and cation Ni2+ ,
bond ∼620 [3] bond ∼530 [3] ∼1390 [3]

610
517
—
1634
NCF 2 (I)
604
507
1378
1664
(x = 0, 0.5, 1.0, 1.5, 2.0) were formed.
NCF 3 (I)
664
554
1344
1638
This solid-state reaction process can be analogous to
NCF 4 (I)
621
514
1439
—
crystallization one of spinels through reorganization of
NF 5(II)
—
—
—
—
metallic cation Cr3+ and Fe3+ in the octagonal sites and
CC 1 (I)
630


Le, et al.

Volume 10 (2012)

TABLE IV: X-ray d-spacing for the series of samples: NiCr2−x Fex O4 and CuCr2−x Fex O4 obtained by coprecipitation method
compared with NiCr2−x Fex O4 obtained by solid-state reaction method and reference [3].
Plane
(hkl)
111
220
311
222
400
422
Plane
(hkl)
111
220
311
222
400
422
Plane
(hkl)
111
220
311
222
400

NC 1(II)
4.81
2.95
2.50
2.40
2.08
1.70

CC 1 (II)
4.81
2.95
2.51
2.41
2.08
1.70

NC 1(I)
4.80
2.95
2.51
2.41
2.08
1.70

d-spacing for NiCr2−x Fex O4 obtained by coprecipitation
NCF 2 (II)
NCF 3 (II)
NCF 4 (II)
4.80
4.80

2.31
2.42
2.06
2.07
2.09
—
—
—

d-spacing for NiCr2−x Fex O4 obtained by solid-state reaction
NCF 2 (I)
NCF 3 (I)
NCF 4 (I)
4.79
4.79
4.81
2.90
2.93
2.93
2.48
2.50
2.50
—
—
2.40
2.07
2.07
2.07
1.69
1.69

same time with the reaction, oxidative dehydrogenation
of ethylbenzene.
Basing on several publications in recent years and the
results represented in Table V, the main reaction and the
secondary reactions in the oxidative dehydrogenation of
ethylbenzene can be explained after the following steps:
First, oxygen that comes from the air was adsorbed on
the hole vacant catalyst surface to form oxygen adsorbed
(O−
ad ):
3+
1/2O2 + Me2+ → (O−
ad ) + Me

(4)

And then, the monomolecular reaction went on after
mechanism of Langmuir-Hinshelwood to form the reaction
products (see Fig. 3): (a) Process of splitting hydride on
metallic sites Fe3+ or Cr3+ (Me3+ ); (b) Breaking of C–C
bond; (c) Oxidative dehydrogenation of intermediate; (d)
Process repeated:
2OH− → H2 O + O2−
net
Me2+ + 1/2O2 → Me3+ + O−
ad ,

(5)

where O2−

NF 5(I)
NC 1 (II)
NCF 2 (II)
NCF 3 (II)
NCF 4 (II)
NCF 5(II)
CC 1 (I)*
CCF 2 (II)*
CCF 3 (II)*
CCF 4 (II)*
CF 5(II)*

350

400

450

Overall
Selectivity Toluene
Overall
Selectivity Toluene
Overall
Selectivity Toluene
conversion in styrene + benzene conversion in styrene + benzene conversion in styrene + benzene
of ethyl(%)
yield (%)
of ethyl(%)
yield (%)
of ethyl(%)

8.70
18.71
78.07
21.41
31.38
70.07
28.16
47.65
64.30
35.40
16.25
78.29
21.45
28.69
69.45
30.06
46.44
59.12
35.22
21.72
56.06
40.15
22.52
57.63
41.23
32.37
40.76
55.58
26.45
72.60

24.63
40.08
60.13
37.69
35.27
93.69
—
47.03
70.72
—
98.21
47.76
—
30.42
92.78
—
51.62
89.43
—
70.14
57.15
—
40.01
78.27
—
70.23
90.17
—
70.23
69.20


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spinels NiCr2−x Fex O4 (I) and (II) was complicated
beside the main product, styrene there was secondary reaction influencing quality of styrene obtained.

Acknowledgments

the authors gratefully acknowledge financial support
from the National Foundation for Science and Technology Development of Vietnam (NAFOSTED).

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