Influence of Lewis Acidity on Catalytic Activity of the Porous Alumina for Dehydrofluorination of 1,1,1,2-Tetrafluoroethane to Trifluoroethylene

Article abstract of DOI:10.1007/s10562-014-1409-z

The porous alumina catalysts with different acidity were prepared and tested for dehydrofluorination of 1,1,1,2-tetrafluoroethane to synthesize trifluoroethylene. The XRD, BET, SEM, NH₃-TPD and py-IR techniques were used to characterize the alumina catalysts with different calcination temperatures. The porous θ-Al₂O₃ showed the excellent catalytic performance, with 35.1 % conversion and the selectivity to trifluoroethylene of 99.0 %. The active sites of catalysts for formation of trifluoroethylene are appropriate weak Lewis acid sites, and the strong Lewis acid sites may result in its rapid deactivation, due to the coke or polymerization of trifluoroethylene. Graphical Abstract: Dehydrofluorination of 1,1,1,2-tetrafluoroethane (CF₃CFH₂) is a promising route to synthesize trifluoroethylene over θ-Al₂O₃, the conversion is 35.1 % and the selectivity to trifluoroethylene is 99 % at 450°C. It was suggested that appropriate number of weak Lewis acid sites was beneficial to the catalysis for dehydrofluorination of CF₃CFH₂, the weak Lewis acid sites as the active sites of synthesis of trifluoroethylene. On the other hand, the strong Lewis acid sites easily result in deactivation of catalysts derived from the coke or polymerization of trifluoroethylene.[Figure not available: see fulltext.]

Full text of DOI:10.1007/s10562-014-1409-z

Catal Lett (2015) 145:654–661
DOI 10.1007/s10562-014-1409-z
Influence of Lewis Acidity on Catalytic Activity of the Porous
Alumina for Dehydrofluorination of 1,1,1,2-Tetrafluoroethane
to Trifluoroethylene
•
Wenzhi Jia Qian Wu Xuewei Lang
•
•
•
•
•
Chao Hu Guoqing Zhao Junhui Li
Zhirong Zhu
Received: 21 September 2014 / Accepted: 21 October 2014 / Published online: 19 November 2014
Ó Springer Science+Business Media New York 2014
Abstract The porous alumina catalysts with different
acidity were prepared and tested for dehydrofluorination of
1,1,1,2-tetrafluoroethane to synthesize trifluoroethylene.
The XRD, BET, SEM, NH3-TPD and py-IR techniques
were used to characterize the alumina catalysts with dif-
ferent calcination temperatures. The porous h-Al2O3
showed the excellent catalytic performance, with 35.1 %
conversion and the selectivity to trifluoroethylene of
99.0 %. The active sites of catalysts for formation of tri-
fluoroethylene are appropriate weak Lewis acid sites, and
the strong Lewis acid sites may result in its rapid deacti-
vation, due to the coke or polymerization of
trifluoroethylene.
[1–6]. Nevertheless, the difficulty in separation and purifi-
cation, expensive raw and noble metal catalyst has taken
place in above way. 1,1,1,2-Tetrafluoroethane (CF3CFH2)
once as an alternative has been used widely in the areas of
refrigeration [7], but its global warming potential (GWP) is
over 1300. CF3CFH2 known as a new greenhouse gas [8] has
been replaced eventually by the 2,3,3,3-tetrafluoropropene
(HFO-1234yf) [9]. Thus, the transformation of CF3CFH2 to
other useful product becomes a significant topic. From the
above, catalytic dehydrofluorination of CF3CFH2 to syn-
thesize trifluoroethylene is a promising approach for devel-
opment of new product with high additional value and
disposal issue of the excess CF3CFH2 [10, 11].
Adsorption and tribochemical reaction of CF3CFH2 on
the nascent surfaces of c-Al2O3, ZrO2, SiO2, AlN, and
Si3N4 ceramics were studied by Mori group [12–14] in
recent years. As claimed in the literature, Mg2P2O7 [15,
16], AlF3 [17], Fe2O3-CdO-Al2O3 [18] and Pd/AlF3 [19]
catalyst were used in dehydrofluorination of hydrofluoro-
carbons (HFCs), e.g. CF3CH3, CF2HCH3 and 1, 1-diflu-
orocyclohexane. However, the catalysis research for the
dehydrofluorination of CF3CFH2 is very few until now. It is
disclosed that the catalytic performance is closely related to
catalyst acidity. Teinz et al. [20] reported the dehydroflu-
orination of 3-chloro-1,1,1,3-tetrafluorobutane was selec-
tively catalyzed by strong Lewis acid sites. The influence
of strength of acid sites on formation of vinylidene fluoride
(VDF) in dehydrofluorination of CF3CH3 was investigated
by Li et al. [15, 16]. Also, Okazaki et al. [17] studied the
dehydrofluorination of CF3CH3 over AlF3 catalyst, and the
products distributions were dependent on the acid strength.
However, the relationships between the Lewis acid sites
and activity for dehydrofluorination of CF3CFH2 have not
been clarified clearly up to now. The concepts of acidity
design in catalyst for HFCs dehydrofluorination are
Keywords 1,1,1,2-Tetrafluoroethane Á Trifluoroethylene Á
Dehydrofluorination Á h-Al2O3 Á Lewis acid sites
1 Introduction
Trifluoroethylene (CF2=CHF) is not only used as an impor-
tant fluorine-containing monomer for the synthesis of the
new fluororubber and fluoroplastics, but also used as bio-
logically active compounds. At present, the popular route to
synthesize trifluoroethylene is focused on hydrodechlorina-
tion of trichlorotrifluoroethane or chlorotrifluoroethene
Electronic supplementary material The online version of this
article (doi:10.1007/s10562-014-1409-z) contains supplementary
material, which is available to authorized users.
W. Jia Á Q. Wu Á X. Lang Á C. Hu Á G. Zhao Á J. Li Á
Z. Zhu (&)
Department of Chemistry, Tongji University,
Shanghai 200092, China
e-mail: zhuzhirong@tongji.edu.cn
123

Dehydrofluorination of 1,1,1,2-Tetrafluoroethane to Trifluoroethylene
655
essential in order to develop a new green gashouse con-
version system.
spectrum on a self-supported wafer of sample was also
recorded in the spectral range 1,800–1,400 cm-1 with 64
scans and at a resolution of 4 cm-1. Scanning electron
microscopy (SEM) image of the sample was obtained on a
Hitachi S-4800 (Japan) microscope equipped with an
energy dispersion X-ray (EDX) attachment.
It is well known that aluminas have the various crys-
talline phases such as c, v, j, g, h, e, a. Generally, c phase
alumina performs the high catalytic activity in heteroge-
neous and homogeneous catalysis. h phase alumina is a
common support for total oxidation catalysts, as well as for
some dehydrogenation and hydrogenation catalysts [21],
but few is active species in catalysis. In this work, it was
found for the first time that the porous h-Al2O3 behaved the
excellent catalytic performance for dehydrofluorination of
CF3CFH2 to synthesize trifluoroethylene. The catalysts
were characterized by XRD, BET, SEM/EDX, NH3-TPD
and py-IR techniques. The relationships between structure
and Lewis acid sites of alumina were discussed. The effect
of weak and strong Lewis acid sites of catalysts on catalytic
performance was investigated in detail.
Ammonia temperature-programmed desorption (NH3-
TPD) was conducted on an automatic Altamira-100 Char-
acterization System. 100 mg of catalyst was loaded in a
quartz tublar reactor and was heated from room tempera-
ture to 500 °C and kept for 30 min in a flow of N2
(30 ml min-1). Then it was cooled down to 50 °C. A flow
of NH3 (20 ml min-1) was then introduced for 10 min.
The gaseous or physisorbed NH3 was removed by purging
N2 flow (30 ml min-1) at 80 °C for 1 h. Then the sample
was heated to 600 °C with a ramp of 10 °C min-1. The
desorbed NH3 was monitored continuously via a TCD
detector. The total amounts of desorbed NH3 on the alu-
mina samples are listed in Table 1.
2 Experimental
2.1 Preparation
2.3 Dehydrofluorination of CF3CFH2
The alumina catalysts were prepared by a precipitation
method. A detailed procedure were as follows: an aqueous
solution of NH3ÁH2O (1 M) was added to aqueous solution of
Al(NO3)3Á9H2O and PO-EO surfactant (5 wt%) under stir-
ring until a precipitated slurry was obtained. The pH value of
the suspension was controlled at around 9.0. The resulting
slurry was aged for 2 h and then the solid separated from the
mother liquid, and dried at 100 °C overnight. The solid was
calcined at 600, 900, 950, 1050, 1150, 1200 °C for 3 h,
respectively, with the heating rate of 3 °C min-1. The
obtained catalysts were named as Al2O3-x, where x indicated
the calcination temperature at air. The Physical properties,
amount of acid–base sites of prepared samples with different
calcination temperatures are presented in Table 1.
The dehydrofluorination of CF3CFH2 was carried out in a
fixed-bed continuous-flow metal reactor (15 mm i.d.)
operated in the downflow mode at atmospheric pressure.
The reaction temperature was determined with a thermo-
couple in contact with the catalyst bed. The prepared Al2O3
and the other power catalysts rooted from the commercially
inorganic solid compouds (A. R., Sinopharm Chemical
Reagent Co., Ltd) were shaped by squash techniques, 2 ml
of selected catalyst with particle size of 16–24 mesh were
used for the reaction. Gas flow rates of the CF3CFH2 and
N2 were carefully regulated by mass flow controllers. The
molar ratio of N2/CF3CFH2 was 9 in a total flow rate of
22.5 ml min-1 and the gas hourly space velocity (GHSV)
was 675 h-1. To remove the product HF, the reaction
effluent passed an aqueous KOH solution, then, it was
analyzed by a gas chromatograph (HP-5890) using a HP-
PLOT/Al2O3 column (0.53 mm 9 50 m) with a FID
detector.
2.2 Characterization
X-ray diffraction (XRD) patterns were collected on a Foucs
D8 powder diffractometer operating at 40 kV and 30 mA
using Cu-Ka radiation, in the 2h range from 10o to 80o with
a scan rate of 0.2 min-1. Phase composition and content
were calculated by the Rietveld method using MID-JADE
6.0 and FindIt software. Surface areas of the catalysts were
determined by the modified BET method from the N2
sorption isotherms at 77 K on an automatic NOVA 2200e
apparatus. Fourier transformation infrared (FTIR) spectra
of samples were obtained with a Perkin-Elmer 2000 FT-IR
equipment and a self-supported wafer of sample. Pyridine
(Py) absorbed infrared spectrum (Py-IR) was also con-
ducted at 200 and 400 °C, under a high vacuum. The IR
3 Results and Discussion
3.1 Activity for Dehydrofluorination of CF3CFH2
A series of alkalis, alkaline earth, transition metal, alumi-
num compound, zeolites and heteropolyacid were typically
selected to dehydrofluorination of CF3CFH2 under the
same reaction conditions. The trifluoroethylene yields of
above catalysts at the reaction temperature of 400–500 °C
are shown in Table 2. On the whole, it was found that the
123

656
W. Jia et al.
V (cm3 g-1
)
Amount of
acidic sites
Table 1 Physical properties,
amount of acid sites of the
samples
Samples
Phase
composition
Proportion
(%)
SBET
(m2 g-1
)
Average
pore size
(nm)
(mmol g-1
)
Al2O3-600
Al2O3-900
c
c
h
h
h
e
100
52.4
47.6
100
73.2
26.8
27.1
8.6
207
106
9.08
0.646
0.483
0.362
0.233
17.98
Al2O3-950
89
64
17.88
14.41
0.363
0.226
0.170
0.065
Al2O3-1050
Al2O3-1150
Al2O3-1200
h
e
7
5
3.25
3.20
0.046
0.041
0.006
0.004
a
a
64.3
100
alumina compounds had the high activity. Whereas the
transition metal compounds such as chromium compounds
[22], and the alkalis, molecular sieve and heteropolyacid
had the low activity. Besides, some transition metal com-
pound such as Ni, Fe, Zn and Y possessed the little activity.
Among the alumina compound with classical Lewis acid
properties, it was found that the Al2O3 had the best cata-
lytic performance.
from 675 to 1,680 h-1 in Fig. S1. One can see that the
conversion of CF3CFH2 declines with the increasing of gas
hourly space velocity value, varing from 23.4 to 12.6 % in
the Fig. S1. This phenomenon results from that the con-
tacting times between CF3CFH2 and active sites were
shortened with increasing space velocity.
The polymorph of transitional aluminas including c, v,
j, g, h, e and a, can be produced by calcination of alumina
oxide or hydroxide at different temperature [21]. The dif-
ference in the catalytic activity of these polymorphous
aluminas in acid catalyzed reactions, is mainly associated
to the difference in their structure [23]. Therefore, the
The effect of CF3CFH2 gas hourly space velocity
(GHSV) was studied over Al2O3 catalyst at 450 °C with
CF3CFH2/N2 molar ratio fixed at 9. The gentle tendency of
CF3CFH2 conversion is showed during the GHSV change
Table 2 The activity of solid
Category
Catalysts
Trifluoroethylene yeild/%
acidic and basic catalysts for
dehydrofluorination of 1,1,1,2-
tetreafluoroethane
500 °C
475 °C
450 °C
425 °C
400 °C
Aluminum compound
Al2O3
78.4
40.7
23.3
15.0
16.5
17.2
3.2
65.1
31.8
15.1
8.9
11.2
11.3
1.5
1.1
0
44.3
23.2
6.8
2.3
4.8
5.2
0.8
0.5
0
39.5
16.2
4.3
1.3
2.9
3.6
0
24.8
9.8
1.5
0.4
1.6
1.8
0
AlF3
AlN
AlPO4
CrF3
Transition metal
Cr2O3
NiF2
FeF2
2.3
0
0
ZnF2
0.2
0
0
YF3
0.1
0
0
0
0
Alkalis metal
MgO
1.1
0.8
0.1
0
0.3
0
0.1
0
0
MgF2
0.5
0
Ca(OH)2
NaF
0.1
0
0
0
0.2
0
0
0
0
BaF2
0.1
0
0
0
0
LiF2
0.1
0
0
0
0
Molecular sieve
Heteropolyacid
13X zeolite
HX
5.5
3.2
2.9
1.4
1.6
0.9
0.6
0.7
0.8
0.1
0
0
4.2
0
H3O40PW12ÁxH2O
H3[P(Mo3O10)4]
2.2
0.4
0.5
0.1
0.2
3.1
123

Dehydrofluorination of 1,1,1,2-Tetrafluoroethane to Trifluoroethylene
657
calcination temperature plays an important role on catalytic
activity of alumina, and the activities of alumina with
different calcination temperatures are shown in Fig. 1. The
detectable byproducts from side reactions were very few by
GC analysis, and the selectivity to trifluoroethylene was up
to 99 % for the all alumina catalysts. The initial yield of all
catalyst is gradually reduced with the time on stream
because of coke or polymer on the catalyst surface, then it
almost maintains stable during the 15 h. It can be seen
from Al2O3-600 to Al2O3-1200 in Fig. 1 that the yield of
trifluoroethylene is increased firstly and then decreased.
Al2O3-950 catalyst possesses the best catalytic perfor-
mance, and its yield of trifluoroethylene is 35.1 % during
15 h. However, the activity of Al2O3-1150 and Al2O3-1200
both were almost lost, and their conversion was both about
1.2 %.
Fig. 2 XRD patterns of alumina calcinated at a Al2O3-600, b Al2O3-
900, c Al2O3-950, d Al2O3-1050, e Al2O3-1150 and f Al2O3-1200
3.2 Characterization
agreement with the results reported in literature [25]. From
Al2O3-600 to Al2O3-950 in Table 1, the corresponding to
content of h phase (wt%) in alumina is 0, 47.6 and 100 %.
As a result, the dehydrofluorination performance sequence
is: Al2O3-600 \ Al2O3-900 \ Al2O3-950 (in Fig. 2),
respectively. It is demonstrated that h phase alumina spe-
cies maybe enhance the catalytic performance of catalysts.
Figure 3 shows the N2 adsorption isotherms (Fig. 3a)
and pore size distributions (Fig. 3b) of alumina with dif-
ferent calcination temperature. All isotherms are type IV
according to the IUPAC classification in Fig. 3a. The two
types of pore size distribution are shown in Fig. 3b. For
instance, pore sizes of Al2O3-600 are centered at 7–9 nm,
but the alumina calcined at 900–1,100 °C are centred at
12–18 nm. Other parameters such as surface area, pore
volume, and pore size of the samples are summarized in
Table 1. The surface area and pore volume of alumina
Generally, crystalline phase transformation takes place in
alumina or boehmite with the change of the calcination
temperature [24]. Figure 2 shows the XRD patterns of
alumina under different calcination temperatures. With the
calcinations temperature up to 950 °C, the diffraction peak
at 2 Theta = 66.9o assigned to (440) plane gradually
becomes weak and disappears ultimately. The diffraction
peak at 2 Theta = 32.7o attributed to (002) plane of h-
Al2O3 firstly increases and subsequently decreases as can
be seen from Fig. 2. The proportions of crystalline phase
compositions are summarized in Table 1, which was cal-
culated on the basis of the Scherrer equation (executed by
Jade 6.5 and FindIt software). It was found that the trans-
formation sequence of alumina by thermal decomposition
was via c-Al2O3 ? h-Al2O3 ? e-Al2O3 ? a-Al2O3
crystallite with the increase of calcination temperature, in
80
(a)
(b)
Al2O3-600
Al2O3-900
Al2O3-950
Al2O3-1050
Al2O3-1100
Al2O3-1200
420
360
300
240
180
120
60
70
Al2O3-600
Al2O3-900
Al2O3-950
Al2O3-1050
Al2O3-1150
Al2O3-1200
Al2O3-600
Al2O3-900
Al2O3-950
Al2O3-1050
Al2O3-1150
Al2O3-1200
0.10
0.08
0.06
0.04
0.02
0.00
60
50
40
30
20
10
0
0
0.0 0.2 0.4 0.6 0.8 1.0
5
10 15 20 25 30 35
D / nm
0
2
4
6
8
10 12 14 16
P/P0
Time on steam / h
Fig. 1 Catalytic performance of alumina with different calcination
temperatures
Fig. 3 N2 adsorption isotherms (a) and pore diameters (b) of the
alumina with different calcination temperatures
123

658
W. Jia et al.
declined remarkably with increasing calcination tempera-
ture, indicating that pore structure of Al2O3 was destroyed
during high temperature calcination. In particular, Al2O3-
1150 and Al2O3-1200 mainly in presence of non-porous a-
Al2O3, have very small surface area (\8 m2 g-1) and pore
volume, which usually show no catalytic performance in
many industrial reactions. These facts explain that the
activity of Al2O3-1150 and Al2O3-1200 both are almost
lost, and the low yeild is about 1.2 %.
(weak, medium, strong) exist on transitional alumina. So,
the broad peaks at 157–168, 225 and 303 °C could be
ascribed to the NH3 adsorbed on the weak, moderate and
strong acid sites, respectively. The acid properties of non-
porous Al2O3-1150 and Al2O3-1200 are both nearly lost,
because of their small surface area and pore volume. The
amount of surface acid sites of alumina were also calcu-
lated and listed in Table 1 (entry the seventh column). Note
that the acidic amount of alumina was reduced gradually
with the increase of calcination temperature, meanwhile
accompanied with the change of alumina structure.
The morphology properties of crystalline alumina are
shown in Fig. S2. Al2O3-600 (c phase) is disordered and
flocculated (Fig. S2a). Obviously the large of crystalline
particles present in the sample of Al2O3-1200. As seen in
Fig. S2 (a–f), the pore gap become smaller, and pore
structure of alumina is dramatically destroyed. With the
increasing of calcination temperature, the initial cluster of
alumina related to weak XRD patterns (Fig. 2) is stacking.
Al2O3-1200 (a phase) hardly shows the pore structure with
little surface area. From the SEM images, the conclusion to
the collapse of alumina porous framework under the ele-
vated calcination temperature, is agreed with the results of
N2 adsorption isotherms and pore diameters in Fig. 3.
The acidities of alumina catalysts after calcination with
different temperatures were measured using NH3-TPD
firstly. Figure 4 shows the NH3-TPD profiles of alumina.
The physical sorption NH3 was purged off by N2 gas at
100 °C. With the increasing of calcination temperature, the
TCD signal of desorption NH3 peak decreased, and reached
the minimum for Al2O3-1200 catalyst. Besides, desorption
peak at 168 °C shifted gradually to the lower temperature.
Based on spectroscopic results of previous reports [26], it
was agreed that the three different types of Lewis acid sites
Pyridine adsorption is a well-established technique to
¨
measure Lewis- and Bronsted-acid type in the alumina
materials. To know the distribution of weak sites and
strong acid sites, alumina was outgassed at 200 or 400 °C
prior to pyridine adsorption at room temperature. The py-
IR spectrums of alumina with different calcination tem-
perature are shown in Fig. 5. It was well known that the
wavenumber of the two characteristic bands at 1,452, 1,609
and 1,654 cm-1 (m19b and m8a modes, respectively, of
coordinated Py species) accounted for the strength of the
Lewis acid sites, and the m19b bands at 1,540 cm-1 attrib-
¨
uted to the Bronsted acid sites [27, 28]. Obviously, the
presence of the Lewis at m19b = 1,452 cm-1 and Bronsted
¨
at m19b = 1,540 cm-1 acid sites on the alumina surface are
observed in Fig. 5a, b, and the detailed results can be
summarized in Table 3. Furthermore, the number of Lewis
¨
acid sites on alumina was much more than that of Bronsted
whether the outgassing temperature was 200 or 400 °C in
pretreatment (Fig. 5a, b). High surface free energy of c-
Al2O3 resulted in adsorption of hydroxyl group on alumina
surface, and Al–OH was formed by chemisorption in the
168 oC
(b) 400 oC
o
(a)
200 C
1452
0.1
0.2
1540
1540
1452
(a)
(b)
a)
a)
b)
b)
c)
c)
d)
e)
f)
(c)
d)
e)
(d)
(e)
f)
157 oC
200
(f)
1800 1700 1600 1500 1400 1300
Wavenumber / cm-1
1800 1700 1600 1500 1400 1300
Wavenumber / cm-1
100
300
400
500
Temperature / oC
Fig. 5 Infrared spectra of adsorbed pyridine after desorption at
200 °C (a) and 400 °C (b). a Al2O3-600, b Al2O3-900, c Al2O3-950, d
Al2O3-1050, e Al2O3-1150 and f Al2O3-1200
Fig. 4 TPD curves of NH3 of a Al2O3-600, b Al2O3-900, c Al2O3-
950, d Al2O3-1050, e Al2O3-1150 and f Al2O3-1200
123

Dehydrofluorination of 1,1,1,2-Tetrafluoroethane to Trifluoroethylene
659
¨
alumina surface, corresponding to the weak Bronsted acid
400 °C. Indeed, the porous alumina prepared by precipi-
tation focused on the Lewis acid sites in this work.
D. Dambournet et al. [34] reported the number of Lewis
acid sites was correlated to the specific surface areas, and it
was found that the Lewis acid sites of AlF3 was propor-
tional to its surface areas, which agreed with our results.
Thus, it is further proved that the structure properties of
alumina are responsible for surface Lewis acidity.
sites [29–31]. Digne et al. [32] proposed realistic adsorp-
tion models of hydroxyl group on (110) and (100) surface
of c-Al2O3 using density functional theory (DFT). Gener-
¨
ally, Bronsted acid sites derived from OH group on alu-
mina surface is very weak [33], especially for the alumina
with high calcination temperature, which is a practically
negligible for the measurement by using pyridine probe
molecules. Thus, it could be concluded that Lewis acidic
sites dominantly locate on the surfaces of alumina. The
3.4 Effect of Lewis Acid Sites on Activity
for Dehyrofluorination of CF3CFH2
¨
Lewis and Bronsted acid sites of alumina have declined
simultaneously, with the increasing of calcination temper-
ature. That is because the reduction of surface areas
resulted in the decrease of unsaturated Al(III) sites due to
Lewis acidity, at the elevating of calcination temperature.
EDX analysis of the used h-Al2O3 catalyst confirmed the
existence of the F element on the surface of catalyst. The
results were obtained based on both the weight percentages
(C, 8.88 %; O, 44.75 %; F, 5.25 %; Al, 46.12 %) and
atomic percentages (C, 13.38 %; O, 50.63 %; F, 5.07 %;
Al, 30.92 %) of the detected elements. The partial F ele-
ment was observed for the remained alumina catalyst. It
might be implied that the Al–F bond was effectively
formed on the Lewis acid sites of Al(III) during the cata-
lytic reaction. Halbert group et al. [35, 36] reported the
cleavage of C–F in dehydrofluorination of CF3CH3 (HFC-
143a) and CF2HCH3 (HFC-152a). The dissociation energy
of C–F is 522.0 8.4 kJ mol-1, which is the higher than
414 kJ mol-1 of C–H. In general, C–F cleavage needs a
high activation energy or reaction temperature. It is well
known that the Lewis acid site is considered to activate C–
F bond. Li et al. [15] reported the catalytic dehydrofluri-
nation of CF3CH3 into CF2H2 over Lewis acidic Mg2P2O7
catalyst. It is believed that the first step of the dehydro-
fluoriantion reaction is C–F cleavage. Teinz et al. [20]
reported that C–F bond activation over Lewis acid sites
was the initial step of a dehydrohalogenation reaction.
Therefore, it is reasonable believed that the C–F bond
3.3 Relationships Between Structure and Lewis Acid
Sites
The density of the Lewis acid sites tends to decrease by
increasing the historical calcination temperature of the
alumina (i.e. upon the sequence c ? h ? e ? a, which is
also a sequence of decreasing surface area) [21]. As a
result, the number of acid sites per gram significantly
decreases in this sequence, although catalyst stability
increases. Besides, the specific surface area is tightly
related with distribution of surface acidic sites in many
catalytic reactions [34]. Thus, it is believed that the affinity
of structure toward the surface acid sites is a major decisive
factor in the porous alumina.
To understand the relationships between structure and
Lewis acid sites demonstrated by the various aluminas
more clearly, the integration of py-IR charaterization and
BET results were summarized. Figure 6 shows the depen-
dence of the Lewis acid sites on the specific surface area.
The weak Lewis acid sites closely make an exponential
increase with surface area when the determining tempera-
ture for py-IR is 200 °C, while the strong Lewis acid sites
and surface area nearly turn into a linear proportion law at
1.2
200 oC
1.0
0.8
0.6
0.4
Table 3 The results of properties of acid sites by IR spectra of
absorbed pyridine
¨
Samples
Bronsted acid sites/
Lewis acid sites/
(m19b = 1,452 cm-1
)
(m19b = 1,540 cm-1
)
200 °C
400 °C
200 °C
400 °C
400 oC
0.2
Al2O3-600
Al2O3-900
Al2O3-950
0.21
0.14
0.09
0.08
0.06
0.05
0.03
0.01
0.00
1.06
0.83
0.70
0.41
0.26
0.12
0.19
0.09
0.06
0.04
0.03
0.01
0.0
0
50
100
150
200
Al2O3-1050 0.07
Al2O3-1150 0.02
Al2O3-1200 0.00
Surface area / m2·g-1
Fig. 6 Dependence of the Lewis acid sites detected by pyridine
adsorption on the specific surface area
123

660
W. Jia et al.
activation of CF3FH2 takes place on the Lewis acid sites of
Al(III).
acid sites maybe play the minor promoting role on the
catalysts deactivation.
From the Table 2, it is surprisingly found that the alkalis
¨
metal catalysts and Bronsted acidic catalysts such as het-
The results in Table 4 shows the deactivation rate and
the coke amount of alumina catalysts with different calci-
nation temperature. Herein, trifluoroethylene yield change
with reaction time from 1 to 15 h was calculated, denoted
as deactivation rate. In addition, the weight differences
between the fresh and used catalysts were measured
exactly, reflected to the coke amount. In Table 4, deacti-
vation rate and coke amount both gets low gradually. The
large number of strong acid sites usually is considered as
the dominating reason for superficial coke deposition in
catalysts, which is a main factor leading to deactivation of
catalysts [15, 40, 41]. Drawing on the surface areas in the
BET results, c-Al2O3 (Al2O3-600) is more advantages than
h-Al2O3 (Al2O3-950), whereas h-Al2O3 has higher activity
than c-Al2O3. The large strong Lewis acid sites (0.19 in c-
Al2O3) are the reasons why the trifluoroethylene yeild of c-
Al2O3 is lower than h-Al2O3. In addition, the decline rate
of CF3CFH2 yield for the Al2O3-600 is the fastest in
comparison with these catalysts from Al2O3-600 to Al2O3-
1200. Obviously, the morphology of the used catalysts
turned into black, observed by naked eye. It was indicated
that formation of coke or polymer on the catalyst surface.
In spite of the small amount of strong Lewis acid sites
(only 0.03 and 0.01 in relative peak areas) in the inactive
Al2O3-1150 and Al2O3-1200 catalyst, but they have the
eropolyacid show the very low catalytic activity (below
3 %) for dehydrofluorination of CF3CFH2. It is firmly
suggested that the Lewis acid is closely related to dehy-
drofluorination of CF3CFH2. The alumina compounds with
Lewis acidity of Al(III) sites behave the excellent dehy-
drofluorination performance in the catalyst optimizations
¨
(Table 2). Although the Lewis and Bronsted acid sites both
exist in the alumina catalysts in Fig. 5, the Lewis acid as
the active sites play a key role in the dehydrofluorination of
CF3CFH2.
The catalytic activity of ‘‘transitional’’ aluminas, in
particular c-, h-, e- and a-Al2O3, is undoubtedly mostly
related to the Lewis acidity [37] of a small number of low
coordination surface aluminum ions, associated to the ionic
nature of the surface Al–O bond [28]. It is important to
notice that the effect of Lewis acidity of catalysts on the
activity in some acid catalyzed reactions, for example, the
Re2O7/Al2O3 [38], V2O5/A12O3 [39] catalyst and so on.
The dependence of total Lewis acidity (strong and weak
acidic sites) on yield of trifluoroethylene is shown in
Fig. 7, and their relationships were fitted by nonlinear
Gauss function. It is worthy of noting that the volcanic type
peak emerges. As seen in Fig. 7, the yield of trifluoroeth-
ene is very low with the small Lewis acidic amount. It is
observed that the alumina with the Lewis acid sites of 0.76
has the highest activity for dehydrofluorination of CF3
CFH2 to trifluoroethene. When the Lewis acid sites are too
large, the coke may cause the yield of trifluoroethene
reducing gradually, and the deactivation speed up on the
catalyst surface. Also, the correlation curve between
very low Lewis acid sites of 0.004 and 0.006 mmol g-1
,
respectively. Besides, it was reported by Li et al. [15] that
the weak acid sites are the active sites for dehydrofluori-
nation of CF3CFH2 to CF2=CH2, and the strong acid sites
results in carbon depositon and/or polymerization. In
conclusion, it is suggested that weak Lewis active sites for
dehydrofluorination of CF3CH3 were mainly active sites of
catalysts, and the strong Lewis acid sites selective catalyze
formation of coke or polymer on the catalyst surface.
To understand clearly the reaction over alumina surface,
the process of dehydrofluorination of CF3CFH2 is descri-
bed, in Scheme 1, i.e. dehydrofluorination of CF3CFH2 to
trifluoroethene over weak Lewis acid sites. Conversion of
¨
Bronsted acid sites and trifluoroethene yield is shown in the
¨
Fig. S3, which is fitted by B-Spline function. The Bronsted
40
35
30
25
20
15
10
5
Table 4 The deactivation rate and coke amounts results of alumina
catalysts with different calcination temperature
Catalyst
Deactivation
rate/9102 h-1
Coke
amounts/mg h-1
Al2O3-600
Al2O3-900
Al2O3-950
Al2O3-1050
Al2O3-1100
Al2O3-1200
1.20
1.10
1.00
0.60
0.02
0.02
3.21
2.62
1.90
1.35
0.01
0.01
0
0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4
Total relative Lewis acid sites
Fig. 7 Relationships between total relative Lewis acid sites and the
trifluoroethylene yield
123

Dehydrofluorination of 1,1,1,2-Tetrafluoroethane to Trifluoroethylene
661
4. Ueda W, Tomioka S, Morinkawa Y, Sudo M, Ikawa T (1990)
Chem Lett 19:879
F
C
H
C
F
C
F
H
C
H
F
F
Coke, polymer
F
F
5. Shekar SC, Venugopal A, Rama Rao KS, Sai Prasad PS, Srinivas
R, Kanta Rao P (1998) Stud Surf Sci Catal 113:391
6. Mori T, Yasuoka T, Morikawa Y (2004) Catal Today 88:111
7. Liu ZT, Liu L, Wu J, Lu J, Sun P, Song LP, Liu ZW, Dong WS,
Gao ZW (2007) Ind Eng Chem Res 46:22
F
C
F
H
C
H
F
F
F
C
H
C
Weak L-sites
Strong L-site
Strong
L
F
F
-s
ak L-sites
We
ite
θ-Al2O3 surface
8. Shine KP, Sturges WT (2007) Science 315:1804
9. Henne S, Shallcross DE, Reimann S, Xiao P, Brunner D,
O’Doherty S, Buchmann B (2012) Environ Sci Technol 46:1650
10. Qin LB, Han J, Liu L, Yang XL, Kim HJ, Yu F (2013) Fresenius
Environ Bull 22:1919
11. Huang CQ, Yang B, Yang R, Wei LX, Wang SS, Shan XB, Oi F,
Zhang YW, Sheng LS, Hao LQ, Zhou SK, Wang ZY (2005)
Chem J Chin Univ 26:2314
Scheme 1 Dehydrofluorination of 1,1,1,2-tetrafluoroethane to syn-
thesize trifluoroethene over the Lewis acid sites
trifluoroethene into coke occur over strong Lewis acidic
sites, while maybe directly cause the formation of coke
from CF3CFH2. h-Al2O3 catalyst have a certain amount of
weak Lewis acid sites and low strong Lewis acid sites. It is
explained that the porous h-Al2O3 (Al2O3-950) possesses
the highest activity compared with the other crystalline
alumina.
12. Wu XY, Cong PH, Nanao H, Kobayashi K, Mori S (2002)
Langmuir 18:10122
13. Wu XY, Cong PH, Mori S (2002) Appl Surf Sci 201:115
14. Cong PH, Imai J, Mori S (2001) Wear 24:143
15. Li GL, Nishiguchi H, Ishihara T, Moro-oka Y, Takita Y (1998)
Appl Catal B Environ 16:309
16. Li GL, Ishihara T, Nishiguchi H, Moro-oka Y, Takita Y (1996)
Chem Lett 7:507
17. Okazaki S, Toyota S (1972) Nikkashi 1615
18. Sirlibaev TS, Akramkhodzhaev A, Usmanov KU (1985) J Appl
Chem USSR 58:1541
4 Conclusion
19. Tojo M, Fukuoka S, Tsukube H (2011) Bull Chem Soc Japan
84:333
¨
20. Teinz K, Wuttke S, Borno F, Eicher J, Kemnitz E (2011) J Catal
The Lewis acidity of porous alumina were efficiently
adjusted by altering the calcination temperature, and tested
for dehydrofluorination of 1,1,1,2-tetrafluoroethane to
synthesize trifluoroethylene. There is linear relationship
between the surface area and Lewis acid sites presented in
the prepared alumina catalysts. The strength of Lewis acid
sites on the alumina surface has the important impact on
catalytic dehydrofluorination of CF3CFH2, the weak Lewis
acid sites as the active sites for synthesis of trifluoroeth-
ylene. But, the strong Lewis acid sites easily result in
deactivation of catalysts derived from formation of coke or
polymerization of trifluoroethylene. It is found that the
h-Al2O3 calcined at 950 °C showed the highest activity and
the good stability with time on steam, because of its weak
Lewis acid sites and small number of strong Lewis acid
sites.
282:175
21. Busca G (2014) Catal Today 226:2
22. Jia WZ, Jin LY, Wang YJ, Lu JQ, Luo MF (2011) J Ind Eng
Chem 17:615
23. Sung DM, Ha Kim Y, Park ED, Yie JE (2010) Res Chem In-
termed 36:653
24. Kuo J, Bourell DL (1997) J Mater Sci 32:2687
25. Du XL, Wang YQ, Su XH, Li JG (2009) Powder Technol 192:40
26. Morterra C, Magnacca G (1996) Catal Today 27:497
27. Ramis G, Yi L, Busca G (1996) Catal Today 28:373
28. Busca G (1999) Phys Chem Chem Phys 1:723
29. Sharanda LF, Shimansky AP, Kulik TV, Chuiko AA (1995)
Colloids Surf 105:167
30. Carre S, Tapin B, Gnep NS, Revel R, Magnoux P (2010) Appl
Catal A 372:26
31. Weingarten R, Tompsett GA, Conner JWC, Huber GW (2011) J
Catal 279:174
32. Digne M, Sautet P, Raybaud P, Euzen P, Toulhoat H (2002) J
Catal 211:1
33. Satsuma A, Kamiya Y, Westi Y, Hattori T (2000) Appl Catal A
General 194:253
34. Dambournet D, Eltanamy G, Vimont A, Lavalley JC, Goupil JM,
Demourgues A, Durand E, Majimel J, Rudiger S, Kemnitz E,
Winfield JM, Tressaud A (2008) Chem Eur J 14:6205
35. Neely BD, Carmichael H (1973) J Phys Chem 77:307
36. Noble B, Carmichael H, Bumgardner CL (1972) J Phys Chem
76:1680
Acknowledgments This work was financially supported by
Shanghai Key Basic Research (Grant No. 11JC1412500), CNPC
Inovation Research Funds (2012D-5006-0505) and National Natural
Science Foundation of China (51174277).
37. Dumesic JA, Fripiat JJ (1997) Top Catal 4:1
38. Schekler-Nahama F, Clause O, Commereuc D, Saussey J (1998)
Appl Catal A General 167:237
References
39. Ishida S, Imamura S, Ren F, Tatematsu Y, Fujimura Y (1992)
React Kinet Catal Lett 46:199
40. Bi QY, Qian L, Xing LQ, Tao LP, Lu JQ, Luo MF (2009) J
Fluorine Chem 130:528
´
41. Macias O, Largo J, Pesquera C, Blanco C, Gonzalez F (2006)
Appl Catal A General 314:23
1. Meng BC, Sun ZY, Ma JP, Cao GP, Yuan WK (2010) Catal Lett
138:68
2. Ohnishi R, Wang WL, Ichikawa M (1994) Appl Catal A General
113:29
3. Scott SP, Sweetman M, Thomson J, Fitzgerald AG, Sturrocky EJ
(1997) J Catal 168:501
123