Sulfated zirconia as a novel and recyclable catalyst for removal of olefins from aromatics

Article abstract of DOI:10.1016/j.catcom.2015.03.025

A novel sulfated zirconia (ZrO₂/SO₄^{2 -}) catalyst was prepared and the catalytic property of this catalyst was compared with active clay and zeolite (USY) in removing olefins from aromatics. Pyridine-FTIR indicated that the abundance of Lewis acid centers on sulfated zirconia is a vital factor for its excellent catalytic activity. N₂ adsorption analysis shows that sulfated zirconia is a promising mesopore catalyst material. The superior catalytic performance as well as efficient reusability demonstrated that sulfated zirconia possesses bright application prospects in industry.

Full text of DOI:10.1016/j.catcom.2015.03.025

Catalysis Communications 66 (2015) 126–129
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Catalysis Communications
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Short communication
Sulfated zirconia as a novel and recyclable catalyst for removal of olefins
from aromatics
⁎
Jiajia Yao, Naiwang Liu, Li Shi, Xin Wang
The State Key Laboratory of Chemical Engineering, East China University of Science and Technology, Shanghai 200237, People's Republic of China
a r t i c l e i n f o
a b s t r a c t
A novel sulfated zirconia (ZrO2/SO24−) catalyst was prepared and the catalytic property of this catalyst was
compared with active clay and zeolite (USY) in removing olefins from aromatics. Pyridine-FTIR indicated that
the abundance of Lewis acid centers on sulfated zirconia is a vital factor for its excellent catalytic activity. N2 ad-
sorption analysis shows that sulfated zirconia is a promising mesopore catalyst material. The superior catalytic
performance as well as efficient reusability demonstrated that sulfated zirconia possesses bright application
prospects in industry.
Article history:
Received 22 February 2015
Received in revised form 18 March 2015
Accepted 19 March 2015
Available online 20 March 2015
Keywords:
© 2015 Elsevier B.V. All rights reserved.
Sulfated zirconia
Removing olefins
Aromatics
1. Introduction
mentioned catalysts, modified zeolites such as USY is a considerable
material that may gradually replace the industrial application of clay
Benzene, toluene and xylene (BTX) are basic organic chemical raw
materials in the petrochemical process. Naphtha reforming and thermal
cracking are the main processes to obtain these aromatics [1]. However,
BTX streams produced by naphtha are accompanied by the formation
of undesirable non-aromatic olefinic impurities. Inevitably, these
impurities include styrene, diene, and hexene. These chemically active
contaminations will cause a series of adverse effects on subsequent
separation. In paraxylene (PX) adsorptive separation device, even
trace amount of olefins will lead to the deactivation of the adsorbent.
Because compared with PX, olefins are easier to adsorb in the adsorbent.
Therefore, it's quite necessary to remove these trace impurities from
aromatics.
As suggested by Liu [2] et al. and Pu [3] et al., these harmful olefins
can be removed via acid-catalyzed alkylation of specific aromatic hydro-
carbons. Conventionally, olefins are removed by acid-treated clay in
industrial plants [4]. However, as the lifetime of clay is quite limited,
the discharge of deactivated clay is a key problem for this method. In-
creasing demands from environmental protection and consequent
trend towards clean process force us to develop an eco-friendly catalyst
alternative. Effective catalysts can increase olefin removal rate and at
the time optimize products distribution without arene loss. In funda-
mental researches, novel catalysts have been continually studied and
developed for removing olefins from aromatics. Several relatively
green acid-catalyzed alkylation catalysts such as ionic liquids [5],
organic–inorganic hybrid silica [6] and modified zeolites [7] have
been studied in removal of olefins from aromatics. Among the above
in the future, as initial activity of USY is very high. Nevertheless, the
biggest disadvantage of zeolites is their rapid deactivation and the re-
generation is not satisfactory. So far, there has been no proper modifica-
tion method to overcome it.
As eco-friendly and promising catalysts, solid superacid catalysts by
incorporation of superacidity in solids have received considerable inter-
est in recent years, especially in the petroleum field. Solid superacid
catalysts like zeotypes, ion-exchange resins and metal oxides have
been extensively studied in many areas. Besides the strength of acidity,
the appropriate distribution of Lewis and Bronsted acid sites matter for
catalyzing kinds of industrial reactions with excellent activity and selec-
tivity [8]. Among these catalysts, sulphated zirconia (SZ) exhibits a great
application prospect in many industrially important reactions, which is
attributed to its distinctive surface acidic properties.
Despite several reports of Friedel-Crafts alkylation studies over SZ
catalysts [9,10], little available attention has been paid to the removal
of trace olefins from aromatics over SZ catalysts. In the present investi-
gation, a recyclable SZ catalyst was prepared and used to remove trace
olefins from aromatics in a fixed-bed micro reactor. The catalytic prop-
erty of SZ was compared with commercial clay and modified zeolites.
The physico-chemical properties of the catalysts were studied by N2 ad-
sorption analysis and py-IR measurements.
2. Experiment section
2.1. Materials
Aromatics used for experiment were industrial streams without
clay treatment. They were obtained from reforming p-xylene (PX)
⁎
Corresponding author.
http://dx.doi.org/10.1016/j.catcom.2015.03.025
1566-7367/© 2015 Elsevier B.V. All rights reserved.

J. Yao et al. / Catalysis Communications 66 (2015) 126–129
127
Table 1
below: X = [(n0 − ni) / n0] ∗ 100%, where n0 represents the content
of olefins of the feedstock and ni represents the content of olefins after
reaction. It's notable here that ASTM standard D2710-92 defined the
Bromine Index as the number of milligrams of bromine consumed by
100 g of hydrocarbon sample, so Bromine Index can be seen as an indi-
cator of olefins content.
Composition of the aromatic materials with a BI of 1109.
Component
Content (wt%)
Non-aromatics
Toluene
Ethylbenzene
p-Xylene
C9
0.238
0.238
7.885
52.207
32.622
6.81
2.4. Characterization of catalyst
C10+
Using pyridine as a probe molecule, surface acidity of the catalysts
was determined by Fourier transform infrared (FT-IR) spectroscopy.
The finely ground self-supported sample wafer (16.5–16.9 mg) loaded
into the in-situ cell was pretreated to eliminate the moisture at 653 K
under vacuum condition (under 0.1 Pa), followed by pyridine adsorp-
tion after cooling down to 353 K. Finally, the wafers were thermally
desorbed at 473 K and 723 K for 2 h. Fourier transform infrared
(FT-IR) spectra were collected using an FTIR (Nicolet-6700) spectrome-
ter (4000–400 cm−1) on sample wafers. The specific pore volume and
surface area were estimated by N2 adsorption–desorption at 77.3 K
(ASAP 2010 N, Micromeritics, America).
combination units of Sinopec Zhenhai Refining & Chemical Company.
USY zeolite modified with citric acid was obtained from XinNian
Petrochemical Additives Company (China). The commercial acid acti-
vated clay was produced in Anhui, China. The aromatics hydrocarbons
components (C8–C10) with a Bromine Index (BI) of 1109 mg Br/100 g
are listed in Table 1. All other reagents were commercially available
from the market, and they are of analytical grade without any further
purification.
2.2. Catalyst preparation and regeneration
Zirconium hydroxide was prepared by adding ammonia solution
(25%–28%) dropwise to dichlorooxozirconium (ZrOCl2·8H2O) solution
while stirring well at temperature of 60 °C until pH = 9.5. After aging
at room temperature for 12 h, the colloidal solution was filtered, washed
adequately to remove chloride ion and subsequently oven dried at
393 K for 24 h. The above dried Zr(OH)4 was sulfated by impregnating
in aqueous ammonium sulfate solution (1.0 mol/L) for 1 h. Then, the
suspension was filtrated, followed by drying for 12 h and calcined
in air at 650 °C for 3 h. The prepared catalyst is denoted as SZ. The
deactivated SZ catalyst was regenerated “in-situ” at 550 °C for 3 h
under air flow.
3. Results and discussion
3.1. Catalytic performance
Catalytic properties of different catalysts for removing olefins from
aromatics are presented in Fig. 1. As optional reaction temperature in in-
dustrial process is between 160 and 180 °C, the experimental tempera-
ture in Fig. 1I was set at 175 °C. As can been seen, the initial removal of
olefins catalyzed by active clay was appreciable, but the rapid inactiva-
tion rate made the whole performance unsatisfactory. More seriously,
the deactivated clay can't be regenerated, thus massive deactivated
clay has to be buried. This burning problem accounts for the dominant
motivation of this paper — to develop eco-friendly alternatives of active
clay.
2.3. Catalytic activity evaluation
The catalyst evaluation experiments were performed in a laboratory
fixed-bed micro-reactor system at a pressure of 1.0 MPa and a liquid
hourly space velocity (LHSV) of 30 h−1. The reaction system was
equipped with a metering pump to keep the flow rate and a temper-
ature control instrument to maintain the required temperature. The
constant temperature segment of the tubular micro-reactor was
charged with the catalyst (20–40 mesh) and spare spaces loaded
with quartz sand (40–60 mesh). The Bromine Index (BI) of the feed-
stock and products obtained was analyzed using a Bromine Index
Analyzer. Olefin removal rate X was determined using the equation
The initial activity of USY was also high, and the removal of olefins
for the first two points even reached 100%. However, there's a sharp
deactivation after 4 h. Herein it still needs further improvement for
USY to replace active clay. With regard to SZ, practically total olefins
were catalytically reacted at this temperature after running for 8 h,
which is nearly 3 times as long as that of USY. Even 12 h later, the re-
moval of olefins still remained as remarkable as 80%.
To obtain more comparable olefin removal rates on these catalysts, a
lower reaction temperature (125 °C) was set for SZ in comparison with
USY and active clay (Fig. 1II). It's noteworthy here that SZ exhibited a
125oC
175oC
100
100
80
60
40
20
80
60
40
20
I
II
0
0
0 1 2 3 4 5 6 7 8 9 10111213
0
1
2
3
4
5
6
7
8
9
Time (h)
Time (h)
Fig. 1. Olefin removal rates of different catalysts at 175 °C (I) and 125 °C (II). (■) SZ, ( ) USY zeolites, ( ) Active clay.

128
J. Yao et al. / Catalysis Communications 66 (2015) 126–129
100
90
80
70
60
50
40
30
20
10
0
Table 2
Amount of Lewis and Brønsted sites (×10−4 mol/g).
Samples
T
TB
3.5640
TL
SL
WL
SZ
USY
Clay
9.2746
5.7106
0.7124
1.2272
1.8016
0.0410
0.3655
3.9090
0.6714
0.8616
78.4472
3.1775
77.7348
1.9503
1540 cm−1 are characteristic of pyridine coordinated to Brønsted
(B) acid sites. Another strong band located at 1490 cm−1 is assigned
to the contribution of pyridine adsorbed on both L and B acidic centers.
There's no apparent wavenumber shift for the py adsorbate complexes,
indicating that the acidities of all samples are comparable. From mea-
surement of pyridine desorption at 473 K and 723 K, the total and strong
acidities can be monitored and calculated.
SZ
SZ-R1
SZ-R2
SZ-R3
0
2
4
6
8
10 12 14 16 18 20
Time (h)
The quantitative acid information from the py-IR spectral data of
was obtained by Lambert–Beer Law. The data is listed in Table 2. A sur-
prising point is that the concentrations of total acid sites were in the
order USY N SZ N clay. However, the amount of L sites, especially weak
L acid sites on the surface of SZ significantly exceeds those on USY and
clay, which is closely related to their catalytic behaviors. It can be
implied that the abundant quantity of L acid sites plays an important
role on the longer lifetime of catalysts. The excessive B acid sites on
USY may be responsible for dramatical catalytic activity decrease. As
suggested by Xin [7], the enrichment of the Lewis acidity and the
decrease of the Brønsted acidity in the catalysts are conducive to the
high catalytic activity and stability, because L acid sites have a promo-
tional effect on the resistance for coke formation. As for clay, the lack
of acidity leads to its poor catalytic performance from the beginning,
in spite of a relative slow deactivation rate.
Fig. 2. Regenerability performance of SZ for removal of trace olefins.
very high catalytic activity even at the temperature of 125 °C, while the
activities of USY and active clay were completely lost after a quite short
running time (2 and 4 h respectively). Comparing Fig. 1I and II, it is ob-
vious that the activity of SZ at 125 °C remained much higher than those
of USY and active clay at 175 °C. USY and active clay can only catalyze
this reaction at a higher temperature while SZ performed well even at
the low temperature. The evaluation for removing olefins from aro-
matics shows that SZ is a superior catalyst over USY and active clay. In
comparison with USY, SZ is a more outstanding and promising candi-
date to supersede active clay in industry.
The reusability of SZ is shown in Fig. 2. The SZ-Rn (n = 1, 2, 3) de-
notes the regenerated cycles of deactivated SZ. Remarkably, the removal
of olefins remained over 90% during the first 6 h of running time using
the recovered SZ for the third time.
Table 2 also suggests that SZ only reveals high acidity, but not super
acids, especially compared with USY. This phenomenon can be ex-
plained by some available publications [11,12].
In conclusion, the outstanding catalytic performance, available re-
covery and reuse of SZ are hopeful to facilitate development of favorable
and waste-free processes for removing olefins from aromatics.
The pore-size distribution of different samples was depicted in Fig. 4.
The peaks at 4 nm indicate that there are a certain amount of mesopores
on all catalysts. Comparatively, the mesopores on SZ and clay are con-
siderably more abundant than those on USY. It's worth noting that
there are even huger numbers of mesopores on clay than that on SZ.
3.2. Acidic properties
It's well known that pyridine is an excellent molecular probe for
characterization of surface acidity of solid catalysts. Fig. 3 shows seg-
ments of FTIR photoacoustic spectra (in the 1410–1580 cm−1 region)
of different samples adsorbed with pyridine. IR adsorption peaks
observed in the spectrum at approximately 1450 cm−1 are attributed
to pyridine interacting with Lewis (L) acid sites; bands at around
3.3. BET analysis
The isotherms of nitrogen adsorption on different catalysts (Fig. 5)
can be similarly classified into type IV. The occurrence of hysteresis
loop can be ascribed to the presence of mesopores influenced by the
capillary condensation of liquid nitrogen on the surface [13]. USY
A
A
B
B
C
C
1560 1540 1520 1500 1480 1460 1440 1420
1560 1540 1520 1500 1480 1460 1440 1420
Wavenumber (cm-1)
Wavenumber (cm-1)
Fig. 3. FTIR spectra of pyridine-clay (A), pyridine-USY (B) and pyridine-SZ (C).

J. Yao et al. / Catalysis Communications 66 (2015) 126–129
129
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0.0
Table 3
USY
SZ
Clay
Surface areas and pore volumes of different catalysts.
Samples
Surface area
(m2/g)
Mesopore area
(m2/g)
Pore volume
(cm3/g)
Mesopore volume
(cm3/g)
SZ
USY
Clay
118.34
509.14
150.13
117.93
59.21
131.57
0.157
0.191
0.262
0.157
0.060
0.248
deactivated soon. As demonstrated by the experiments, the BI of aro-
matics remained unchanged after being treated by SZ. It can be conclud-
ed that SZ has fairly weak adsorptivity. Asphaltene and polyaromatic
hydrocarbon are not easily adsorbed on the surface of SZ, so the activity
of SZ decreased far more slowly than that of clay. It can be concluded
that SZ treating was owing to the catalytic reaction, while that of clay
treatment was mainly by adsorption [15].
1
2
3
4
5
6
7
8
9
10 11 12 13 14 15 16 17 18
Pore Diameter (nm)
Fig. 4. Pore size distributions of different samples.
4. Conclusion
represented an isotherm with a plateau at a distinctly higher relative
pressure, which is typically characteristic of microporous materials. It
was also remarkable that the relative pressure (P/P0) of SZ and clay at
which the adsorption reaches the last plateau shifts to the right for a
sample with larger pore diameter [14]. This special relative pressure
(P/P0) is a well-known indicator for qualitatively comparing the pore di-
mensions and the higher value reveals a mesopore size. It is demon-
strated that SZ and clay exhibit larger pore volume than USY. The pore
size of SZ is over 50 Å, which is spacious enough for the molecules of
polycyclic aromatic hydrocarbons and other carbonaceous compounds
in aromatic hydro-carbons.
In summary, sulfated zirconia was synthesized and used here for the
first time as an outstanding catalyst for removing olefins from aro-
matics. The high catalytic activity and recoverability of SZ are promising
to promote the development of favorable and pollution-free processes
in industry. In comparison with conventional catalyst (active clay), the
unobvious adsorptive property for carbonaceous materials in SZ can
prevent the coke blocking the pore. In contrast to USY, the remarkable
L acidity and plenty of mesopores was contributed to the high activity.
Unlike USY, the reasonable distribution of B acid sites on SZ and the
abundance of mesopores can effectively decrease the deactivated ratio.
Table 3 summarized the result of surface area and pore volumes for
SZ, USY and clay. One can see that there's only mesopore without micro-
pore on SZ. The mesopore area and mesopore volume of SZ was greatly
larger than that of the USY sample.
The surprise is that the clay demonstrates more distinguished meso-
porous characteristic than SZ. Nevertheless, SZ exhibited a greater per-
formance in spite of lower surface areas than the clay. This indicates
that the excellent performance achieved by SZ can't be simply ascribed
to the difference in textural properties. Clay, with larger surface area,
can adsorb considerable amount of trace olefin from aromatic hydrocar-
bons. Once the clay is approaching adsorption equilibration, it will be
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USY
Clay
40
20
SZ
0
0.0
0.2
0.4
0.6
0.8
1.0
Relative Pressure (P/P0)
Fig. 5. N2 adsorption–desorption isotherms of different catalysts.