Effect of sulfation of zirconia on catalytic performance in the dehydration of aliphatic alcohols

Article abstract of DOI:10.1002/jccs.200900046

Catalytic dehydration of 2-propanol and that of 1-butanol were performed at atmospheric pressure and 150-300 °C over ZrO₂ and sulfated ZrO₂ (S/ZrO₂) in a fixed-bed, tubular reactor. The catalysts were characterized with XRD, elemental analysis, FT-IR, N₂ physisorption, TG/DTA, TPD, and TPR. Themain structures of ZrO₂ and S/ZrO₂ were monoclinic and tetragonal, respectively. As ZrO ₂ was modified with sulfuric acid, its surface area and acid amount were greatly increased, whereas the pore volume, the pore diameter, and the particle size were reduced. Both samples owned weak basicity. For both reactions, only dehydration products of alkene and ether were obtained. The alcohol conversion enhanced remarkably with the catalyst acid amount and the surface area as well as the reaction temperature. In addition, the ether selectivity on S/ZrO₂ decreased with raising the reaction temperature. The activation energy was 81.0 kJ/mol in the propene formation from 2-propanol over S/ZrO₂. The corresponding value was 94.4 kJ/mol for the dehydration of 1-butanol.

Full text of DOI:10.1002/jccs.200900046

314
Journal of the Chinese Chemical Society, 2009, 56, 314-322
Effect of Sulfation of Zirconia on Catalytic Performance in the Dehydration
of Aliphatic Alcohols
Ya-Sun Hsu (
), Yin-Lan Wang (
Department of Chemistry, Tunghai University, Taichung, Taiwan, R.O.C.
) and An-Nan Ko* (
)
Catalytic dehydration of 2-propanol and that of 1-butanol were performed at atmospheric pressure
and 150-300 °C over ZrO2 and sulfated ZrO2 (S/ZrO2) in a fixed-bed, tubular reactor. The catalysts were
characterized with XRD, elemental analysis, FT-IR, N2 physisorption, TG/DTA, TPD, and TPR. The main
structures of ZrO2 and S/ZrO2 were monoclinic and tetragonal, respectively. As ZrO2 was modified with
sulfuric acid, its surface area and acid amount were greatly increased, whereas the pore volume, the pore
diameter, and the particle size were reduced. Both samples owned weak basicity. For both reactions, only
dehydration products of alkene and ether were obtained. The alcohol conversion enhanced remarkably
with the catalyst acid amount and the surface area as well as the reaction temperature. In addition, the ether
selectivity on S/ZrO2 decreased with raising the reaction temperature. The activation energy was 81.0
kJ/mol in the propene formation from 2-propanol over S/ZrO2. The corresponding value was 94.4 kJ/mol
for the dehydration of 1-butanol.
Keywords: Zirconia; Sulfated zirconia; Dehydration; Catalyst characterization; 2-Propanol;
1-Butanol.
INTRODUCTION
Solid acid catalysis has drawn much attention due to
The catalytic conversion of aliphatic alcohols has
been carried out using a variety of catalysts possessing
acidic and/or basic sites, i.e., metal oxides, mixed metal ox-
ides, clays, pillared clays and molecular sieves.4,13-16 Pure
zirconia, sulfated zirconia, zirconia based binary and ter-
nary oxides were prepared and applied to the reactions of
ethanol,17 2-propanol,18-22 2-butanol,23 4-methyl-pentan-
2-ol,24 and 2-octanol.25 Among theses alcohols studied, the
conversion of 2-propanol was often used as a model reac-
tion to probe catalyst acid-base properties. For this reaction
over TiO2, ZrO2 and CeO2 at 473-623 K, higher activity
and acetone selectivity were observed in flowing air than in
helium or hydrogen.18 Sulfated ZrO2-TiO2 containing Ti
mole fraction 0.4 possessed the largest amount of sulfur,
the highest acidity and also the best activity.19 A new solid
superacid catalyst was prepared by doping sulfated ZrO2
with Ce that greatly enhanced the surface area and stabi-
lized the tetragonal phase. The catalytic activity was in line
with the catalyst acidity.22 The dehydration of 2-butanol
over a sulfated zirconia/g-alumina catalyst was performed
in the injection port of a gas chromatograph. The kinetics
were found to be a pseudo-first-order reaction mecha-
nism.23
its great potential for both academic research and industrial
applications.1 Up to now, zirconia has been intensively
studied for its ultilization as a solid support and a catalyst
since it exhibits acidic, basic, oxidizing and reducing sur-
face properties.2,3 Zirconia possesses three different crys-
talline structures, viz monoclinic, tetragonal and cubic
phase, depending on the treatment conditions.4 After modi-
fication with sulfate anions, the sulfated zirconia mainly
has a tetragonal structure at high calcined temperature.5
According to the results obtained from various tech-
niques such as IR, Raman spectroscopy, XPS, thermal anal-
ysis and XRD, many models were proposed to describe the
formation mechanism and the structure of sulfated zirco-
nia.6-10 Despite much efforts were done on the characteriza-
tion of physical properties of sulfated zirconia, the exact
structure and the nature of acid sites still remain a subject of
large debate. However, it is widely accepted that the ad-
sorption of sulfate anions on the zirconia surface generates
highly acidic or superacidic properties. Consequently, this
materical has been utilized to catalyze a variety of reactions
such as isomerization, dehydration, alkylation, acylation,
esterification, condensation, nitration, cyclization, etc. as
reported in the review papers.11,12
Recently the dehydration of 1-butanol has attracted
increasing interest using various solid catalysts, viz sil-

Dehydration of Aliphatic Alcohols over Sulfated Zirconia
J. Chin. Chem. Soc., Vol. 56, No. 2, 2009 315
ica-alumina,26 AlPO4 and modifized AlPO4,27,28 pillared
clays29-31 and nitrided aluminophosphate.32 The acidity-ba-
sicity of silica-alumina depended on the alumina content
which affected the catalytic activity and product selectiv-
ity.26 Modification of AlPO4 with SO42- ions caused an in-
crease of the number of strong acid sties, whereas opposite
trend occurred with Na+ ions. The butenes selectivity en-
hanced with the catalyst strong acidity.27 With phospho-
rus-modified aluminum pillared montmorillonite, the 1-
butanol conversion was well associated with Lewis acid-
ity.29 So far, to the best of our knowledge no report has been
found for the 1-butanol dehydration over sulfated zirconia
catalysts. In this study, zirconia and sulfated zirconia were
prepared. Both catalysts were characterized with various
techniques to determine their physico-chemical properties.
The reaction of 2-propanol and that of 1-butanol were uti-
lized as test reactions to compare the catalytic performance
among these catalysts. The kinetic parameters for both
reactions were estimated; the apparent rate constants were
correlated with the catalyst properties.
spectively, according to the Debye-Schererr equation.
D = Kl/bcosq
where K is the crystallite shape constant (~1), l is the X-ray
wavelength (nm), b is the width of half height peak (ra-
dian), and q is the Bragg angle (degree).
The N2 physisorption was conducted at 77 K with a
Micromeretics system ASAP 2020 to obtain the specific
surface area, the N2 adsorption/desorption isotherm, the
pore volume, and the pore size distribution. Prior to each
run, the sample was pre-treated at 110° under a pressure of
1 ´ 10-4 torr for 2 h.
FT-IR spectra of ZrO2 and S/ZrO2 samples were taken
for the pellets of these samples mixed with KBr at room
temperature in the transmission mode with resolution of 2
cm-1 by a Perkin-Elmer system 2000 spectrometer.
The TG/DTAanalysis was performed with an EXSTAR
6000 series instrument. A 0.01 g of sample was heated in
the air (20 °C/min) from 50 to 900 °C. The weight loss and
heat flow were measured as a function of temperature.
The catalyst acidity and basicity were determined by
a self-designed temperature programmed desorption (TPD)
apparatus, containing a quartz reactor (i.d. = 4 mm) and a
T.C.D. detector. In a typical run, 0.1 g of catalyst was heated
up to 500 °C under helium flow (40 mL/min) with a rate of
10 °C/min and then cooled to room temperature. Then sev-
eral pulses of ammonia or carbon dioxide were injected
into the reactor until saturated adsorption. The temperature
was increased to 100 °C and kept there for 2 h to remove the
physisorbed ammonia. Finally the system was heated from
110 to 600 °C at a rate of 10 °C/min and the desorbed gas
was monitored with a T.C.D. detector.
EXPERIMENTAL SECTION
Catalyst preparation
Zirconium oxide was prepared by dissolving 25 g of
zirconyl (IV) chloride octahydrate (ZrOCl2·8H2O, Acros)
in 200 mL de-ionized water. The solution was stirred at 98
°C for 2 h into which was added dropwise aqueous ammo-
nia solution until a pH value of 9.3 with subsequent filtra-
tion and washing to obtain Zr(OH)4. This compound was
dried at 100 °C for 24 h, heated at 1 °C/min up to 600 °C
and calcined for 3 h to produce ZrO2.
To prepare sulfated ZrO2, 1 g of Zr(OH)4 was mixed
with 15 mL of 1 M sulfuric acid and stirred for 0.5 h. After
filtration, the sample was dried at 100 °C for 24 h, heated at
1 °C/min to 600 °C and calcined for 3 h to form sulfated
ZrO2 (S/ZrO2).
For the analysis of temperature programmed reduc-
tion (TPR) the same apparatus as that of TPD was ultilized.
A gaseous mixture of hydrogen and argon (1:10) with a
flow rate of 30 mL/min passed through the reactor at 110
°C for 0.5 h and then the temperature was raised to 750 °C
at a rate of 10 °C/min.
Catalyst characterization
The content of sulfur in S/ZrO2 was measured with an
elemental analyzer (elementar vario EL III) and was found
to be 2.3 wt.%.
Catalytic reaction
The powder X-ray diffraction patterns of various
samples were recorded using a Shimadzu XRD-6000 dif-
fractometer with Ni filtered CuKa radiation (l = 0.154 nm)
in the range of 2q = 20-70° at a scanning speed of 2°/min.
The mean particle sizes D (nm) of ZrO2 and S/ZrO2 were
calculated from the (111) reflex of the monoclinic form at
2q = 28.19° and that of tetragonal form at 2q = 30.63°, re-
The catalytic dehydration of 2-propanol and that of
1-butanol were performed at atmospheric pressure and
150-300 °C in a fixed-bed, integral flow reactor (2 cm i.d. ´
49 cm) with down flow mode. The reactor was placed in a
vertical furnance and the catalyst sample (0.02~0.5 g) di-
luted with glass particles of similar sizes was loaded in the
middle part of the reactor. A thermocouple was situated

316 J. Chin. Chem. Soc., Vol. 56, No. 2, 2009
Hsu et al.
near the catalyst in order to measure the reaction tempera-
ture. Prior to the reaction, the catalyst was activated at 400
°C with flowing air (60 mL/min) for 1 h to remove water
vapor and carbon dioxide, followed by cooling to the reac-
tion temperature with flowing N2 gas (60 mL/min). Then
the reactant was fed into the reactor via a microfeeder
(Stoelting). The unconverted alcohol and the products were
condensed, collected periodically and analyzed by a HP
5890 gas chromatograph fitted with a FFAP capillary col-
umn (50 m ´ 0.2 mm) and a flame-ionization detector.
consistent with other studies.17,33,34 Based on the Debye-
Schererr formula, the calculated mean particle sizes are
12.4 and 9.5 nm for ZrO2 and S/ZrO2, respectively. Conse-
quently, the size of ZrO2 particles is reduced after sulfation
of ZrO2 due to phase transformation and suppression of
particle aggregation. Similar results were reported else-
where.21,24,35
Textural properties
The N2 adsorption-desorption isotherm and the pore
size distribution of various catalysts are illustrated in Fig.
2. The ZrO2 sample exhibits a type IV isotherm, indicating
the monolayer adsorption at low relative pressure (P/Po).
The degree of adsorption enhanced greatly with an hyster-
esis loop occurring at P/Po in the range of 0.7~0.9, which
implys capillary condensation in the mesopores. For the
S/ZrO2 sample the adsorption also belongs to the type IV
isotherm and the hysteresis loop appears at P/Po > 0.4.36
Based on the BJH method, the calculated average
pore diameters are 12.2 and 3.3 nm for ZrO2 and S/ZrO2,
respectively. Table 1 lists the textural properties of these
RESULTS AND DICUSSION
XRD results
The dependence of ZrO2 crystalline structure on the
calcination temperature was studied previously; ZrO2 was
amorphous up to 300 °C, tetragonal phase at 350 °C, a mix-
ture of tetragonal and monoclinic form at 400-800 °C and a
pure monoclinic phase at 900 °C.22 Fig. 1 displays the XRD
patterns of Zr(OH)4, ZrO2, and S/ZrO2. The Zr(OH)4 sam-
ple belongs to an amorphous solid whereas ZrO2 and
S/ZrO2 reveal well crystalline structure. In addition, ZrO2,
being calcined at 600 °C, contains mainly the monoclinic
phase and partly the tetragonal phase. The peaks of mono-
clinic phase appear at 2q = 24.0, 28.2, 31.5, 49.3, and
50.1°. After modification with sulfuric acid, the mono-
clinic phase transforms to the tetragonal phase at 2q = 30.6,
34.0, 35.2, 49.5, and 60.1° in the sample of S/ZrO2 that is
Fig. 2. N2 physisorption: (A) adsorption-desorption
isotherms; (B) pore size distribution. (a) ZrO2;
(b) S/ZrO2.
Fig. 1. Powder XRD patterns of various samples: (a)
Zr(OH)4; (b) ZrO2; (c) S/ZrO2; (n) monoclinic
phase of ZrO2; (o) tetragonal phase of ZrO2.

Dehydration of Aliphatic Alcohols over Sulfated Zirconia
Table 1. The physico-chemical properties of various catalysts
J. Chin. Chem. Soc., Vol. 56, No. 2, 2009 317
supported 3Ce-ZrO2/SO42- after evacuation (³ 200 °C) for
1 h, which indicates the asymmetric S=O stretching fre-
quency of sulfate ion bonded to ZrO2. However, this band
was not detected in this study because the S/ZrO2 sample
was not evacuated prior to FT-IR measurements and water
molecules were adsorbed on the surface.4,6
Catalyst
ZrO2
S/ZrO2
Sulfur content (%)
Surface area (m2/g)
Pore diameter (nm)
Pore volume (cm3/g)
Particle size (nm)
---
2.3
132
3.3
42.3
12.2
0.13
12.4
0.21
0.056
0.12
9.5
Acid amount (mmol/g)
Base amount (mmol/g)
0.40
0.042
Thermal analysis
Fig. 4 dipicts TG/DTA curves for various samples
predried at 110 °C. The weight losses below 250 °C are
0.85 and 2.46%, for ZrO2 and S/ZrO2, respectively, which
are attributed to the evolution of water vapor. The weight
losses between 610 and 660 °C are very small for both sam-
ples while the losses above 660 °C are negligible and 2.7%,
indicating the slight decomposition of sulfate group in the
S/ZrO2 sample.
two samples. Sulfation of ZrO2 causes an enormous in-
crease of the surface area with concomitant decrease of
pore diameter, pore volume and particle size. These results
are comparable to the literature reports.22,33,35
FT-IR study
Fig. 3 illustrates the FT-IR spectra of ZrO2 and S/ZrO2.
With ZrO2, the band at 1625 cm-1 is ascribed to the bending
vibration mode of the adsorbed water while that at 1550
cm-1 is assigned to the –OH vibration mode.37 After modifi-
cation of ZrO2 with sulfuric acid, the band at 998 cm-1 is as-
signed to the S-O symmetric stretching n1 whereas those
bands of 1027, 1073, 1138, and 1228 cm-1 are attributed to
the splitting of the S-O asymmetric stretching n3, which
implys the existence of sulfate species as bidentate com-
plexes coordinated to ZrO2.21,38 Sohn et al.21 observed a
sharp band at 1364-1390 cm-1 in the FT-IR spectra of self-
Fig. 4. Thermal analysis patterns: (A) TG curves; (B)
DTA curves. (a) ZrO2; (b) S/ZrO2.
Fig. 3. FT-IR spectra of various samples: (a) ZrO2; (b)
S/ZrO2.

318 J. Chin. Chem. Soc., Vol. 56, No. 2, 2009
Hsu et al.
The DTA curves of the two samples show endother-
mic peaks below 250 °C, implying the removal of physisor-
bed water. In addition, small peaks around 630 °C are ob-
served due to a small extent of phase transition from tetra-
gonal to monoclinic form since it corresponds to a constant
weight region in the TG results.
6. For pure ZrO2 two relatively small H2 uptake signals are
observed at 460 and 610 °C in fair agreement with the liter-
ature,34 in which the former one was proposed to arise from
elimination of lattice oxygen, leading to the formation of
anionic vacancies while the latter one was associated with
the bulk reduction or hydride production. In the case of
S/ZrO2 only one peak appears at high temperature of 710
°C. As no corresponding peak is found for pure ZrO2, this
peak is assigned to the reduction of sulfate species as re-
ported by other investigators.40,41 According to the above
results and those of XRD, TG/DTA, and TPR studies, it is
noteworthy that sulfation of ZrO2 causes the stabilization
of tetragonal structure as well as the resistance of ZrO2 re-
duction with H2 gas.
TPD results
The catalyst acidity and basicity can be determined
with TPD of ammonia and carbon dioxide, respectively.
Fig. 5 shows the TPD of ammonia profiles from various
samples. For ZrO2, the curve reveals a small and broad
peak. The S/ZrO2 sample exhibits a much larger peak, which
rises remarkably to a maximum at ~200 °C and thereafter
declines. All samples exhibit a small shoulder peak at 600
°C exactly when the heating program was switched off.
The is possibly due to the effect of increasing then decreas-
ing temperature because a TCD detector was used in moni-
toring desorbed ammonia.39 The acid amount was esti-
mated from the peak area of TPD plots in association with
calibration data. In this way, both the acid amount and acid
strength follow the order of S/ZrO2 >> ZrO2. It was pointed
out that the acid sites are correlated to the Zr4+ cation and
the acid strength is enhanced due to several factors such as
the induction effect of S=O group in the sulfate species as
well as the valency, the electronegativity, and coordination
number of Zr4+ cation.22 According to the TPD plots of car-
bon dioxide (not shown), both catalysts possess quite low
bascity. The data are listed in Table 1.
2-Propanol dehydration
So far, the catalytic conversion of aliphatic alcohols
has attracted considerable interest. The dehydration prod-
ucts, olefins and ethers, are formed on acid sites, whereas
the dehydrogenation products, aldehydes or ketones, are
produced via both acid and base sites. Consequently, the
dehydration rate enhances with the catalyst acidity while
the ratio of the dehydrogenation rate to the dehydration rate
is parallel to the catalyst basicity.1,42 In this study the dehy-
dration products include propene and diisopropyl ether
(DIPE), which are formed on the acid sites. Similar results
were reported for this reaction over a variety of cata-
lysts.15,16,20 Propene is produced via intramolecular E1
mechanism, whereas DIPE is obtained by intermolecular
TPR analysis
The catalyst reduction behavior was determined by
the TPR technique. The TPR profiles are displayed in Fig.
Fig. 5. Ammonia TPD profiles for various samples: (a)
ZrO2; (b) S/ZrO2.
Fig. 6. H2 TPR profiles for various samples: (a) ZrO2;
(b) S/ZrO2.

Dehydration of Aliphatic Alcohols over Sulfated Zirconia
J. Chin. Chem. Soc., Vol. 56, No. 2, 2009 319
The above reaction pathway is a combination of parallel
and consecutive reactions in accordance with other re-
ports.13,16 As revealed in Table 1, increasing temperature
enhances the catalytic activity. In addition, a rise of temper-
ature favors the propene selectivity, which is attributed to
reduction of DIPE formation caused by further reaction of
DIPE to propene.
Table 2. Catalytic results of 2-propanol. W/F, 0.008 h; Time-on-
stream, 30 min
Selectivity (mol%)a
Temperature Conversion
Catalyst
(°C)
(mol%)
Propene
DIPE
ZrO2
250
150
165
180
200
0.58
21.5
27.6
48.4
78.6
100
69.3
71.5
82.0
98.0
0
S/ZrO2
30.7
28.5
18.0
2.0
The DIPE selectivity in many runs is not small enough
to be neglected under our operating conditions. To simplify
the kinetic analysis, only the kinetic parameters for the ini-
tial conversion of 2-propanol to form propene are calcu-
lated. It is known that this reaction follows the first order
kinetics.43,44 Accordingly, the following equation is uti-
lized:
a DIPE, diisopropylether
substitution reaction. No acetone is produced for all reac-
tion runs since these catalysts own weak basicity.
The 2-propanol conversion and the product selectiv-
ity are calculated on the basis of converted 2-propanol. Ta-
ble 2 summaries the results of 2-propanol dehydration over
pure zirconia and sulfated zirconia. In the temperature
range between 150 and 200 °C, ZrO2 exhibits no catalytic
activity, whereas S/ZrO2 shows drastically higher activity.
The remarkable activity difference among the two catalysts
is attributed to their relative acid amount and surface area
as well as crystalline structure. As mentioned earlier, sulfa-
tion of zirconia induces the structural stabilization of tetra-
gonal phase, which is known to associate with the catalyst
activity. Moreover, such a process enhances the catalyst
acid amount and retards the particle aggregation, leading to
smaller particle size and larger surface area (Table 1). All
these factors result in the activity trend of S/ZrO2 >> ZrO2.
The space time W/F is the ratio of catalyst weight (g)
to the feed rate (g/h). Fig. 7 shows the evolution of propene
to DIPE molar ratio as a function of the space time at 180
°C. The initial molar ratios is 3.2 over S/ZrO2 obtained by
extrapolating to zero value of W/F; it refers to the initial se-
lectivity ratios of propene to DIPE. The fact that this ratio
increases with increasing the space time implies propene to
be a primary and secondary product. The reaction network
(Scheme I) is thus shown as follows:
dxp/d(W/F) | W/F®0 = kp
The symbols xp and kp refer to the mole percentage of pro-
pene and the apparent rate constant, respectively. kp is the
slope of the tangent line to the curve in the plot of xp versus
W/F. Hence the rate constant kp is obtained at zero space
time. With S/ZrO2, the values of kp are 33.4, 83.1, 200, and
369 h-1 at 150, 165, 180, and 200 °C, respectively. Fig. 8
shows the Arrhenius plots for the conversion of 2-propanol
to propene. The activation energy (Ea) and Arrhenius fre-
quency factor (A) are 81.0 kJ/mol and 3.60 ´ 1011 h-1 for
2-propene formation on S/ZrO2. For the sake of compari-
sion, the activation energies in the literature were reported
to be 30.66-177.66 kJ/mol on ZrO2-TiO2 catalysts,45 139.5
kJ/mol on LaY zeolite,14 and 31.33-32.89 kJ/mol on 8-10
wt.% sulfuric acid modified TiO2-SiO2,46 76.74 and 89.28
kJ/mol on chromia and alumina pillared montmorillonite
pillared at 500 °C, respectively.44
Scheme I
Fig. 7. The propene/DIPE molar ratio as a function of
the space time over S/ZrO2 at 180 °C.

320 J. Chin. Chem. Soc., Vol. 56, No. 2, 2009
Hsu et al.
1-Butanol dehydration
remarkably the catalytic activity. However, the effect of
temperature on the product selectivity is not pronounced.
The DBE selectivity diminishes slightly with a rise of tem-
perature, whereas the t-2B selectivity reveals the opposite
trend. Different mechanisms (E1, E2 or ElcB) were pro-
posed to explain the product distribution of 1B, c- and t-2B
in the 1-butanol dehydration.32 For this reaction over strong
acidic catalysts, the intramolecular dehydration yields 1B
through an E1 mechanism and then 1B isomerizes quickly
to give the major products of 2B isomers with c-2B to t-2B
molar ratio being close to 1. In the case of amphoteric or ba-
sic catalysts, the intramolecular dehydration occurs via an
E2 or E1cB mechanism and 1B is the main product. In the
present work, the product distribution from 1-butanol con-
version (Table 3) clearly demonstrates that 1B was formed
on the strong acid catalysts of S/ZrO2 through E1 mecha-
nism.
The conversion of 1-butanol was performed at atmo-
spheric pressure and in the temperature range of 150-300
°C. The products are 1-butene (1B), cis- and trans-2-butene
(c- & t-2B), and dibutylether (DBE). No aldehyde or ke-
tone was detected. 1B is formed via intramolecular dehy-
dration while DBE is produced by intermolecular substitu-
tion reaction. c- and t-2B are secondary products, formed
by isomerization of 1B. As reported previously,32 the fol-
lowing Scheme II illustrates the reaction network.
Scheme II
Under our reaction conditions, DBE is the minor
product with its selectivity smaller than 10 mol% for most
of the reaction runs. Consequently, for the kinetic analysis
the conversion of 1-butanol is treated solely as the forma-
tion of 1B and 2B isomers by neglecting DBE. Therefore,
the first order kinetics is applied to this reaction and the fol-
lowing equation is derived.
The 1-butanol conversion and the product selectivity
are calculated with respect to converted 1-butanol. Table 3
presents catalytic results at 0.031 h space time and 30 min
time-on-stream. Pure zirconia exhibits little activity even at
the highest temperature of 300 °C. In contrast, S/ZrO2 pos-
sesses much higher activities, which follows the same trend
as that in 2-propanol reaction. The activity difference is in
line with the catalyst acidity and surface area. A compari-
sion between 2-propanol and 1-butanol conversion clearly
reveals that, as expected, the secondary alcohol of 2-pro-
panol exhibits much higher activity (Table 2 & 3).
–ln (1-x) = k (W/F)
where x and k refer to the 1-butanol conversion and the ap-
parent rate constant, respectively. The symbols W and F
represent the catalyst weight (g) and the feed rate (g/h), re-
spectively. Fig. 9 shows the plots of –ln (1-x) as a function
It is apparent that increasing temperature enhances
Fig. 9. Plots of –ln(1-x) versus W/F for 1-butanol de-
hydration over S/ZrO2. (o) 150 °C; (o) 165 °C;
(à) 180 °C; (+) 200 °C.
Fig. 8. Arrhenius plot for the formation of propene
from 2-propanol over S/ZrO2.

Dehydration of Aliphatic Alcohols over Sulfated Zirconia
J. Chin. Chem. Soc., Vol. 56, No. 2, 2009 321
Table 3. Catalytic results of 1-butanol dehydration. W/F, 0.031 h; Time-on-stream, 30 min
Selectivity (mol%)a
c-2B
t-2B
Temperature
Conversion
(mol%)
Catalyst
(°C)
1B
c-2B
t-2B
DBE
ZrO2
300
150
165
180
200
0.91
4.20
21.5
37.8
59.8
71.1
22.5
21.3
20.7
18.3
16.9
29.3
31.0
31.1
31.1
12.0
33.8
33.9
38.7
45.1
0
1.41
0.87
0.92
0.80
0.69
S/ZrO2
14.4
13.8
9.5
5.5
a 1B, 1-butene; t-2B, t-2-butene; c-2B, c-2-butene; DBE, dibutylether
of the space time W/F over S/ZrO2. Straight lines passing
through the origin verify that this reaction is first order and
their slopes equal the rate constant k. The values of k for
this reaction on S/ZrO2 are 1.63, 7.55, 14.5, and 30.3 h-1 at
150, 165, 180, and 200 °C, respectively. Fig. 10 shows the
Arrhenius plots for the dehydration of 1-butanol. The val-
ues of Ea and A are 94.4 kJ/mol and 9.60 ´ 1011 h-1, respec-
tively. The reported activation energies were 93.2 and 96.6
kJ/mol on HZSM-5 and amorphous aluminosilicate, re-
spectively.47 With 2-butanol dehydration over the S/ZrO2/
g-Al2O3 catalyst, two activation energies were reported,
i.e., 15 kJ/mol for the high temperature range (~150-325
°C) and 46 kJ/mol for the lower temperature range (75 to
~150 °C).23
S/ZrO2 possess weak basicity. In addition sufated zirconia
calcined at 600 °C mainly exhibits the crystalline structure
of tetragonal phase, which favors the catalytic conversion.
In the reaction of 2-propanol and that of 1-butanol, the cat-
alytic activity and the product selectivity are affected by the
nature of alcohols, the catalyst property, and the reaction
condition. 2-Propanol shows much higher activity than 1-
butanol. With both alcohols, the conversion enhances with
increasing the catalyst acidity and surface area as well as
the reaction temperature. In addition, propene and 1-butene
are formed on the catalyst acid sites via E1 elimination and
the alkene selectivities increase with an increase of reac-
tion temperature.
ACKNOWLEDGEMENTS
CONCLUSION
We would like to express our gratitude to the National
Science Council of the Republic of China for financial
support.
The physico-chemical properties of sulfated zirconia
depend on the source and the amount of sulfate ion as well
as the preparation condition. In this work, sulfation of ZrO2
induces remarkable increase of the catalyst surface area
and acid amount with concomitant decrease of the pore vol-
ume, the pore diameter, and the particle size. Both ZrO2 and
Received October 22, 2008.
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