Prosiding SKAM-17, 24 – 26 Ogos 2004, Kuantan
INFLUENCE OF SULFATE ION ON THE TEXTURAL PROPERTIES OF PT/SO42--ZRO2
Sugeng T.1*, M. Faizal R.2, Zalizawati A.2, Aishah A.J.2, Hadi Nur1,
M. Nazlan M.M.1, Mustaffa S.1, Halimaton H.1,
1
Ibnu Sina Institute for Fundamental Science Studies UTM, 81310 UTM Skudai, Johor, Malaysia.
2
Fac. of Chemical & Natural Resources Eng. UTM, 81310 UTM Skudai, Johor, Malaysia.
Tel: 07-5536071 Fax: 07-5536080 E-mail: [email protected]
Abstract
The influence of sulfate ion on the textural properties of Pt/SO42--ZrO2 (PSZ) has been studied. PSZ samples were
prepared by impregnation of Zr(OH)4 with 0.5N, 1.0N, 2.0N and 4.0N of sulfate ion and calcined at 873 K, followed
by addition of 0.5 wt% Pt. XRD and nitrogen physisorption have been used to monitor the physical structure of
catalysts. It has been found that the presence of sulfate ion preserves a great part of the small diameter pores and
stabilizes the tetragonal phase of zirconia. The surface area, volume of pore and tetragonal phase of zirconia are
directly related to the amount of sulfate ion incorporated into catalyst. The addition of sulfate ion up to 1.0N
increased the surface area, small diameter pores of particle and tetragonal phase of zirconia, but excessive amount of
sulfate ion covered or blocked pore of catalyst which lead to decrease the surface area, small diameter pores of
particle, volume of pore and crystallographic phase of zirconia.
Keywords: Pt/SO42--ZrO2; Tetragonal phase of zirconia; Monoclinic phase of zirconia
Introduction
The addition of zirconium oxide with metallic oxoanions such as sulfate ion, tungsten ion and
molybdenum ion has widely explored by several research groups in the study and development of
catalytic materials for the carbocationic reactions [1,2]. In particular, sulfate ion added zirconium oxide
has become an active area of research because of the high catalytic activity for alkylation,
hydroisomerization and oligomerization. Although the effects of precursor catalyst, preparation method,
activation method, the nature of metal-ion added and reaction mechanism are now better understood for
the carbocationic reactions, however, the source of activity and its relation to the crystallographic phase of
the sulfate ion added zirconia catalyst is not clear yet. Corma et al. [3] and Vera et al. [4] considered that
the higher activity of sulfate ion added zirconium oxide is associated with the presence of tetragonal
phase of zirconia. However, Stichert et al. reported that the monoclinic phase of zirconia active in the
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Prosiding SKAM-17, 24 – 26 Ogos 2004, Kuantan
hydroisomerization of alkane [5]. As can be seen, the role play of crystallographic phase of zirconia in
the catalytic reaction is still a matter of debate.
ZrOCl2 8H2O
In this study, the influence of sulfate ion
2.5% NH4OH
(final pH=10)
concentration has been studied for the purpose
of finding out the relation between the
concentration of sulfate ion, surface area,
Zr(OH)4
volume of pore and crystallographic phase of
H2SO4
Calc. at 873K
zirconia.
SO42--ZrO2 (SZ)
Experimental
H2PtCl6 6H2O
Calc. at 873K
The PSZ samples were prepared as follows.
Zirconium
hydroxide
was
prepared
Pt/SO42--ZrO2 (PSZ)
from
aqueous solution of ZrOCl2·8H2O by hydrolysis
Scheme 1 Preparation of PSZ Catalyst
with 2.5 wt % NH4OH aqueous solution. The
precipitate was filtered and washed with
deionized water.
The obtained gel was dried
at 383 K to form Zr(OH)4.
The sulfate ion-
treated Zr(OH)4, was prepared by impregnation
of the Zr(OH)4 with H2SO4 aqueous solution.
0.5N PSZ
The concentration of H2SO4 aqueous solution
was varied from 0.5 N to 4.0 N. The SO42-ZrO2 (SZ) was obtained by calcination of the
1.0N PSZ
sulfate ion-treated Zr(OH)4 at 873 K in air.
The PSZ was prepared by impregnation of the
SZ with H2PtCl6 aqueous solution. The content
2.0N PSZ
of Pt was adjusted to be 0.5 wt %.
4.0N PSZ
X-Ray powder diffraction pattern of the sample
20
30
40
50
60
70
80
was recorded on a JEOL X-Ray Diffractometer
2θ
JDX-3500 with a Cu-Kα radiation sources.
Fig. 1 XRD pattern of Pt/SO -ZrO
90
2-
4
2
The specific surface area was determined for
the samples outgassed at 573 K by BET method
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Prosiding SKAM-17, 24 – 26 Ogos 2004, Kuantan
with Coulter SA 3100.
Results and Discussion
0.04
0.5N-PSZ
1.0N-PSZ
2.0N-PSZ
4.0N-PSZ
Fig 1 shows the XRD patterns of prepared
samples having different concentration of sulfate
zirconia transforms into a monoclinic phase
(2θ=28.3º and 31.4º) from a tetragonal phase
(2θ=30.2º) of zirconia. However, the addition of
metal oxide such as sulfate ion stabilizes the
tetragonal
phase
of
zirconia
[5].
sulfate ion up to 1.0N increased the tetragonal
and
suppressed
the
formation
monoclinic phase of zirconia.
0.02
0.01
Our
experimental results showed that the addition of
phase
dV/dD / ml/g*nm
ion loading. In the calcination above 873K, pure
0.03
of
The further
0
0
5
10
15
20
Pore Diameter / nm
Fig. 2 Pore size distribution of PSZ.
addition of sulfate ion up to 4.0 decreased both
of the tetragonal phase and monoclinic phase of
zirconia.
Fig 2 shows the pore size distribution of prepared samples having different concentration of sulfate ion
loading. The addition of sulfate ion produced material with small pore size distribution. For all samples
presented maximum peaks centered at ca. 4nm. The intensity of peaks decreased in the increasing of the
concentration of sulfate ion. The BET measurement results also indicated that the addition of sulfate ion
decreased the specific surface area of samples.
Based on the above results, we concluded that the presence of sulfate ions is required to preserve the
zirconia with high surface area, volume of pore and tetragonal phase of zirconia. However, the addition
of sulfate ions of more than 1.0N leads to decrease the surface area, volume of pore and tetragonal phase
of zirconia. It may caused by the excessive amount of sulfate ion over the surface of catalyst which may
cover and/or block pores of catalyst.
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Prosiding SKAM-17, 24 – 26 Ogos 2004, Kuantan
References
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[3] A Corma, M.J. Rajadell, J.L. Nieto, A. Martinez, C. Martinez, Appl Catal. A: Gen. 111 (1994) 175.
[4] C.R. Vera, C.L. Pieck, K. Shimizu, J.M. Parera, Appl Catal. A: Gen. 230 (2002) 137.
[5] W. Stichert, F. Schuth, S. Kuba, H. Knozinger, J.Catal. 1998 (2001) 277.
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