Vapor phase hydrofluorination of acetylene to vinyl fluoride over La2O3-Al2O3 catalysts

Article abstract of DOI:10.1016/j.jfluchem.2009.03.001

A series of La-doped Al₂O₃ catalysts were prepared and tested for the vapor phase hydrofluorination of C₂H₂ to vinyl fluoride (CH₂CHF, VF). It was found that the La-doped catalyst gave a stable cataly

Full text of DOI:10.1016/j.jfluchem.2009.03.001

Journal of Fluorine Chemistry 130 (2009) 528–533
Contents lists available at ScienceDirect
Journal of Fluorine Chemistry
journal homepage: www.elsevier.com/locate/fluor
Vapor phase hydrofluorination of acetylene to vinyl fluoride over La O -Al O
2
3
2 3
catalysts
a
a
a
a
b
a
a,
Qing-Yuan Bi , Lin Qian , Li-Qiong Xing , Li-Ping Tao , Qiang Zhou , Ji-Qing Lu , Meng-Fei Luo *
a
Zhejiang Key Laboratory for Reactive Chemistry on Solid Surfaces, Institute of Physical Chemistry, Zhejiang Normal University, Jinhua 321004, China
b
Juhua Group Engineering Technology Research Center of National fluoride materials, Quzhou 324004, China
A R T I C L E I N F O
A B S T R A C T
Article history:
A series of La-doped Al O catalysts were prepared and tested for the vapor phase hydrofluorination of
2
3
Received 11 January 2009
Received in revised form 2 March 2009
Accepted 2 March 2009
C
2
H
2
to vinyl fluoride (CH
performance and a higher selectivity to the desired VF and a lower selectivity to coke deposition
compared with the pure Al catalyst. The enhancement in VF selectivity on the La-doped catalyst was
3
due to the elimination of acidic sites on the Al surface by the addition of La , evidenced by NH –
2
CHF, VF). It was found that the La-doped catalyst gave a stable catalytic
2 3
O
Available online 14 March 2009
2
O
3
2
O
3
TPD results, which could also explain the declined selectivity to coke deposition on the catalyst. Raman
result indicated there were two different vibration forms of C–H distortion and C C expansion for the
coke deposition.
Keywords:
Hydrofluorination
Vinyl fluoride
Crown Copyright ß 2009 Published by Elsevier B.V. All rights reserved.
2 3 2 3
La O -Al O catalyst
Coke deposition
Acidic sites
1
. Introduction
conversion and high selectivity to VF for vapor phase hydrofluor-
2 2 2 3
ination of C H . However, since the Al O catalyst has strong
It is well known that vinyl fluoride (VF) is an important fluorine-
acidity, it suffers severe deactivation because of the coke
deposition on the catalyst surface during the reaction [6,7],
particularly for the molecules with high C/H molar ratio [8], such as
alkyne hydrocarbon.
containing monomer, which is usually used to synthesize poly-
vinyl fluoride (PVF), fluoropolymers and other fluorine-containing
fine chemicals. Because PVF has many advantages such as being
resistant to weather, good mechanical strength, chemical inert-
ness, and low permeability to air and water, it has broad
applications and thus attracts much attention in its synthesis.
At present, the main processes of VF synthesis are listed as
follows [1–4]:
To restrain the coke deposition, alkali metals (K, Na) oxide and/
2 3
or alkaline-earth metals (Mg, Ca) oxides were added in the Al O ,
to modify the surface acidity of catalyst [9–11]. Besides, rare-earth
metals are also effective in reducing the coke deposition [12]. For
instance, La
2
O
3
can enhance the stability of Al
2
O
3
catalyst for
reforming of
carbon dioxide reforming of methane [13], CO
2
CHFClCH
3
! CHF ¼ CH
Cl ! CHF ¼ CH
! CHF ¼ CH þ HF
2
þ HCl
(1)
(2)
methane to syngas [14] and catalytic combustion of methane [15].
Budi et al. [16] reported that the presence of La on the surface of
zeolite improved the stability of Cu-ZSM-5 catalyst by reducing the
degree of the copper migration to the external surface of the
CH
2
FCH
2
3
2
þ HCl
CHF
2
CH
2
(3)
(4)
catalyst. Also, La can stabilize
many reactions, as reported in the literature [17–23].
In this work, La-doped Al catalysts were employed in the
vapor phase hydrofluorination of C . The effect of La doping on
the catalytic property of the catalyst was studied.
2 3
g-Al O and enhance its stability for
CH ꢀ CH þ HF ! CHF ¼ CH
2
2 3
O
Considering the atomic efficiency and environmental issue,
reaction (4) is obviously much preferred. The catalysts used in this
reaction mainly include Hg-containing, Cd-containing, Cr-contain-
ing, CuCN, fluorine sulfonic acid and metal chloride compounds.
But these compounds are limited in application due to their strong
2 2
H
2. Results and discussion
2 3 2 2
toxicity [5,6]. An alternative Al O catalyst gives a high C H
2
.1. Influence of reaction temperature and HF/C H molar ratio
2 2
*
Corresponding author. Tel.: +86 579 82282234; fax: +86 579 82282595.
E-mail address: mengfeiluo@zjnu.cn (M.-F. Luo).
Fig. 1 shows the C
products and coke deposition at different reaction temperatures
2 2
H conversion, selectivities to the main
0022-1139/$ – see front matter. Crown Copyright ß 2009 Published by Elsevier B.V. All rights reserved.
doi:10.1016/j.jfluchem.2009.03.001

Q.-Y. Bi et al. / Journal of Fluorine Chemistry 130 (2009) 528–533
529
Table 2
Influence of La content on catalytic behavior of La
2
O
3
2
-Al O
3
catalysts for
a
hydrofluorination of C
2
H
2
to VF. .
La content (mol%)
C
2
H
2
conversion (%)
Selectivity (%)
VF
HFC-152a
Coke deposition
0
1
5
96.1
94.5
92.4
88.0
78.4
84.1
81.1
83.3
19.0
13.9
16.4
15.6
2.1
0.9
0.8
0.8
1
0
a
Reaction temperature: 300 8C.
exerts little function on it. Also, when the HF/C
exceeds 2.5, the conversion of C
that the stoichiometric ratio HF/C
2
H
2
molar ratio
2
2
H hardly changes, due to the fact
2
H
2
needed for the reactions
2 2
(C H to VF and VF to HFC-152a) is 2.
2.2. Influence of La content in the La
2
O
3
-Al
2
O
3
catalyst
Fig. 1. C
2
H
2
conversion, selectivities to the main products and coke deposition at
(1)-Al catalyst.
Table 2 lists the influence of La content on catalytic behavior of
-Al catalysts. It shows that the selectivity to VF is
catalyst to
catalyst, and the selectivity to
coke deposition decreases from 2.1 to 0.9% with increasing La
content. However, the conversion of C declines slightly from
96.1% over the pure Al catalyst to 88.0% over the La (10)-
catalyst. Among the La -Al catalysts, the La (1)-
catalyst gives very high C conversion (94.5%) and the
different reaction temperatures on La
2
O
3
2 3
O
La
2
O
3
2 3
O
enhanced considerably from 78.4% over the Al
84.1% over the La (10)-Al
2 3
O
over the La
Al system studied in the current work. The selectivities to other
unknown and minor products were not discussed in this work. It
can be seen that with increasing reaction temperature, the C
2
O
3
(1)-Al
2
O
3
catalyst. It is a typical profile in the La
2
O
3
-
2
O
3
2 3
O
2 3
O
2
H
2
2
H
2
2
O
3
2 3
O
conversion increases until it gets to a maximum at about 300 8C
and then declines slowly. More interestingly, the highest
selectivity to VF (84.1%) is also obtained at around 300 8C and it
keeps at this level at higher reaction temperature. Meanwhile, the
Al
Al
2
2
O
O
3
3
2
O
3
2
O
3
2 3
O
2
H
2
highest VF selectivity (84.1%). In order to intrinsically compare the
catalytic performance of these catalysts, Table 3 lists the influence
selectivity to the by-product 1,1-difluoroethane (CHF
2
CH
3
, HFC-
of La content on the products selectivities at the 90% of C
2 2
H
1
52a) is approximately 78.2% at 240 8C, but it quickly declines with
conversion over La -Al catalysts. It shows that with
2
O
3
2 3
O
increasing temperature, with a selectivity of 14.9% at 300 8C. The
decline in the selectivity to HFC-152a is due to the fact that HFC-
increasing La content in the catalyst, the selectivity to VF is
enhanced from 66.3 to 88.3%, while the selectivity to HFC-152a
decreases from 32.3 to 9.6%. Also, the coke formation is slightly
suppressed by the La addition. These results (Tables 2 and 3)
1
52a could be decomposed to VF (reaction (3)) at high
temperature. As for the coke deposition, when the reaction
temperature is lower than 300 8C, its selectivity is quite low (ca.
indicate that the addition of a small amount of La into the Al
catalyst can not only keep high C conversion but also enhance
the VF selectivity and reduce the coke deposition.
2 3
O
0
.9%). However, when the temperature rises higher than 300 8C, it
2 2
H
increases quickly. This is due to the enhanced conversion of C
2 2
H ,
accompanied by an increasing formation rate of ethylene, which
could strongly adsorb on the catalyst surface and consequently
form coke deposition. Taking into account of these aspects, we
think that the reaction temperature of 300 8C is appropriate for the
VF synthesis; therefore it is chosen for the rest of the investigation.
2 3 2 3 2 3
2.3. Catalytic stability of Al O and La O (1)-Al O catalysts
Fig. 2 shows the catalytic performances of the pure Al
the La (1)-Al catalysts as a function of reaction time. For the
Al catalyst, as can be seen in Fig. 2(a), the C conversion
2 3
O and
2
O
3
2 3
O
Table 1 lists the influence of HF/C
over the La (1)-Al catalyst. As can be seen in Table 1, the C
conversion, VF and HFC-152a selectivities can be modified by
changing the HF/C molar ratio. The C conversion increases
with increasing HF/C molar ratio, however, the selectivity to VF
2
H
2
molar ratio on the reaction
2
O
3
2 2
H
2
O
3
2
O
3
2
H
2
slightly decreases from the initial value of 96.1% to the final value
of 90.8% during the reaction time of 100 h and has a decreasing
tendency, while the selectivities to VF and HFC-152a have no big
undulation. The selectivity to coke deposition is about 2.1% at the
2
H
2
2 2
H
2 2
H
declines and the selectivity to HFC-152a increases. This is due to
the accelerated formation of HFC-152a, resulting from the further
reaction of VF with HF at a higher content of HF in the feed gas. It is
interesting that the selectivity to coke deposition hardly changes,
indicating that the increasing concentration of HF in the feedstock
beginning and drops to 1.8% after 70 h reaction. For the La
2 3
O (1)-
Al catalyst, as shown in Fig. 2(b), the C conversion keeps
2
O
3
2 2
H
constant (ca. 95.0%) in a time course of 100 h. The selectivity to VF
shows a gentle increase from 81.5 to 85.8%, while those to coke
deposition and HFC-152a decline gently.
Table 1
a
Influence of HF/C
2
H
2
molar ratio on catalytic performance. .
Table 3
Influence of La content on the products selectivities at the 90% of C
over La -Al catalysts.
2 2
H conversion
HF/C ratio
2
H
2
2
C H
2
conversion (%)
Selectivity (%)
2
O
3
2 3
O
VF
HFC-152a
Coke deposition
La content (mol%)
Selectivity (%)
VF
1
2
3
5
6
.5
.5
.5
.0
.0
69.7
94.5
97.8
99.0
99.1
95.5
84.1
70.5
55.0
49.0
2.8
14.9
28.3
43.8
49.3
0.8
0.9
1.0
1.0
1.0
HFC-152a
Coke deposition
0
1
5
66.3
75.0
75.1
88.3
32.2
23.4
23.5
9.6
1.2
0.8
0.8
0.9
10
a
2 3 2 3
Catalyst: La O (1)-Al O . Reaction temperature: 300 8C.

5
30
Q.-Y. Bi et al. / Journal of Fluorine Chemistry 130 (2009) 528–533
2 2 2 3 2 3 2 3
Fig. 2. C H conversion, main products selectivities and coke deposition selectivity at 300 8C on (a) Al O and (b) La O (1)-Al O catalysts with time on stream.
Comparing these two catalysts, it can be concluded that the
initial activity of Al catalyst is high, but it decreases with time
on stream. The selectivity to the desired product VF on La (1)-
Al catalyst is higher than pure Al catalyst. The selectivity to
coke deposition on the pure Al catalyst is much higher than that
on the La (1)-Al catalyst. The difference in catalytic
3 2 3
structural LaAlO [24] emerges. This indicates that the La O
2
O
3
accumulates on the catalyst surface when its content is high. For
the pre-fluorinated catalysts, Fig. 3(b) shows the distinct evolution
2 3
O
2
O
3
2
O
3
3 3
of AlF and LaF phases. For the used catalysts (after 8 h reaction),
2 3
O
2
O
3
2 3
O
behaviors between these two catalysts indicates that the addition
of La may change the surface property of the catalyst, thus alter the
reaction procedures for the formation of VF, HFC-152a and coke
deposition.
2.4. Characterizations
Table 4 lists the properties of the fresh, pre-fluorinated and used
2 3 2 3
La O -Al O catalysts. It is found that surface areas of the fresh
catalysts decrease dramatically with increasing La content, while
those of the pre-fluorinated and used catalysts are not greatly
affected. Compared with the fresh catalyst, the surface areas of the
pre-fluorinated and used catalysts are much smaller. This may be
3 3
due to the formation of AlF and LaF during the pre-fluorination
process, which has much lower surface area than the correspond-
ing oxide. Also, there is no obvious change in the surface areas of
the pre-fluorinated and used catalysts, indicating that the coke
deposited on the catalyst surface barely affects the surface areas of
these catalysts, and the slight deviation in the BET surface areas is
probably due to the error caused by the method of measurement.
Considering the crystallite size of the catalyst, it is found that the
2 3 2 3
crystallite size of the pre-fluorinated La O -Al O catalysts range
from 3.3 to 3.5 nm, implying that these samples are nano-sized
materials.
The XRD patterns of the fresh, pre-fluorinated and used La
catalysts are given in Fig. 3. For the fresh catalysts, as can be
seen in Fig. 3(a), the diffraction peaks at 22.8, 26.6, 40.1 and 44.78
can be attributed to La [15, JCPDS card 83-1355] and these
peaks become sharper with increasing La content whereas
diffraction peaks assigned to Al become weaker correspond-
2 3
O -
2 3
Al O
2 3
O
2 3
O
ingly. Also, a solid solution phase ascribed to perovskite crystal
Table 4
Properties of fresh, pre-fluorinated and used La
2
O
3
-Al
2
O
3
catalysts.
Crystallite size of
2
ꢁ1
)
La content
BET surface area (m
g
(mol%)
pre-fluorinated
catalysts (nm)
Fresh
Pre-fluorinated
catalysts
Used
catalysts
catalysts
0
1
5
282
240
199
169
32
30
30
29
36
37
33
29
3.3
3.3
3.5
3.4
2 3 2 3
Fig. 3. XRD patterns of (a) fresh, (b) pre-fluorinated and (c) used La O -Al O
1
0
catalysts.

Q.-Y. Bi et al. / Journal of Fluorine Chemistry 130 (2009) 528–533
531
3
NH –TPD experiments were performed in order to obtain
information of the acidity of these catalysts. Fig. 5 presents the
desorption traces for the pre-fluorinated La
typical profile shows that there is a desorption peak
a peak
can be ascribed to the NH
the peak to the NH adsorbed on the strong acidic sites [26]. The
2
O
3
-Al
2
O
3
catalysts. A
a
at 135 8C and
b
at 363 8C, the latter of which is wider and bigger. The peak
adsorbed on the weak acidic sites and
a
3
b
3
peak position does not shift with increasing La content, indicating
that the nature of acid centers keeps unchanged. But the area of the
peak
b decreases with increasing La content in the catalyst,
implying a decline in the total amount of the strong surface acidic
sites.
Nano-sized AlF
Lewis acids [27–30]. In contrast, LaF
3
is known to be one of the most effective solid
is slightly alkalescent. The
3
amount of surface acidic sites could be calculated based on the
relative proportion of the peak area. Relative amount of acidic sites
on these pre-fluorinated La
.34 as the content of La increases from 0 to 10 mol. %. The decline
could be attributed to the fact that LaF species cover some surface
acidic sites provided by AlF , or the relative content of AlF reduces
2 3
(10)-Al O
2 3 2 3
O -Al O catalysts drops from 1.00 to
0
3
2 3 2 3
Fig. 4. Raman spectra of used La O -Al O catalysts.
3
3
in the La-rich catalyst, as in the pre-fluorinated La
catalyst.
2
O
3
Fig. 3(c) clearly shows that the diffraction features of the used
catalysts are almost identical to the corresponding pre-fluorinated
In order to determine the nature of acidic sites, pyridine
adsorption experiments were performed. Fig. 6 shows the IR
catalysts. These results indicate that the LaAlO
almost completely converted to AlF and LaF
fluorination process. However, there is still a weak peak at 14.68
ascribed to Al , implying that the phase transition of Al is
3
and La
2 3
O have
3
3
in the pre-
spectra of adsorbed pyridine on pre-fluorinated La
2 3 2 3
O -Al O
catalysts. Several feature bands are observed at 1454, 1490,
ꢁ
1
2
O
3
2
O
3
1540 and 1625 cm
on these samples, and their intensities
somehow incomplete. The XRD results could explain well the
decline in the surface areas of the pre-fluorinated catalysts, due to
become weaker with increasing La content in the catalysts. The
ꢁ1
bands at 1450, 1490 and 1620 cm could be attributed to pyridine
ꢁ1
the phase transition of La
respectively.
2
O
3
and Al
2
O
3
to LaF
3
and AlF
3
,
adsorbed on Lewis acidic sites; while the band at 1540 cm could
be attributed to pyridine adsorbed on Brønsted acidic sites [31,32].
The IR results indicate that the surface of the pre-fluorinated
Fig. 4 shows the Raman spectra of the used La
2
O
3
-Al
2 3
O
ꢁ1
catalysts. A band at 1335 cm
distortion vibration peak and a band at 1603 cm to the C
can be attributed to the C–H
2 3 2 3
La O -Al O catalysts mainly consist of Lewis acidic sites.
ꢁ1
C
Furthermore, the relative amount of these sites declines with
increasing La content in the catalysts, which is in agreement with
expansion vibration peak, which are both due to Raman vibration
of coke deposition [25]. These two peaks become weaker with
increasing La content in the catalyst, indicating that the amount of
coke deposition on the catalyst surface reduces. This result is in
good agreement with the results listed in Table 2. But there are no
Raman characteristic peaks for Al and La oxide compounds or their
fluorides, which may be related either to the strong fluorescent
effect of Al and La or to the carbon deposition that may cover their
oxide or fluoride compounds.
the NH
In the current study, the crystallite size of obtained pre-
fluorinated La -Al catalysts are nano-scaled (Table 4). There-
fore, they can provide sufficient Lewis acidic sites, as shown in
Fig. 6. The catalytic properties of the La -Al catalysts are
closely related to the surface acidity, since the adsorption of
3
–TPD experiments (Fig. 5).
2
O
3
2 3
O
2
O
3
2 3
O
Fig. 5. NH
3
–TPD profiles of pre-fluorinated La
2
O
3
-Al
2
O
3
catalysts.
2 3 2 3
Fig. 6. IR spectra of pyridine adsorption on pre-fluorinated La O -Al O catalysts.

5
32
Q.-Y. Bi et al. / Journal of Fluorine Chemistry 130 (2009) 528–533
organic substances (including acetylene) mainly occurs on the
surface acidic sites of the catalyst [7]. A high surface density of
acidic sites will certainly enhance the initial reactivity, however,
the enhancement in reactivity also results in the accelerated
consecutive reaction between the VF and HF to further produce
HFC-152a, as well as the coke deposition, as can be seen in the case
first heated up to 550 8C and kept for 30 min in flow of Ar
ꢁ
1
(30 mL min ), then it was cooled down to 80 8C. A flow of NH
3
ꢁ
1
(20 mL min ) was then introduced for 60 min. The gaseous or
ꢁ1
physisorbed NH
1 h, thenthe sample was heated to680 8Cwitharampof10 8C min
The desorbed NH was monitored continuously via a TCD detector.
3
was removed by Ar flow (30 mL min ) at 80 8C for
ꢁ1
.
3
of pure Al
2
O
3
(Tables 2 and 3 and Fig. 2). For the La-doped Al
2
O
3
The FTIR spectra of pyridine adsorption on the pre-fluorinated
catalysts were recorded on a Nicolet NEXUS 670 spectrometer in the
catalyst, although the initial reactivity is suppressed due to the
decline in surface density of acidic sites, the consecutive reaction of
VF with HF, and the coke deposition are also inhibited. This could
explain the enhancement in the selectivity to the desired VF and
the drop in the selectivities to the by-product HFC-152a and coke
deposition.
ꢁ
1
range 1800–1400 cm . The pre-fluorinated catalysts were dried in
a hot air oven for 1 h at 100 8C prior to pyridine treatment. A self-
supported pellet of catalyst was brought in contact with pyridine
directly. Then the sample was kept in a hot air oven at 120 8C for 1 h
to remove physisorbed pyridine. After cooling the catalyst sample to
room temperature, the IR spectrum was recorded in the spectral
ꢁ
1
ꢁ1
3
. Conclusions
range 1800–1400 cm with 256 scans and at a resolution of 4 cm
using KBr background at room temperature.
A series of La
2
O
3
-Al
2
O
3
catalysts with different La contents were
to
and high selectivity to VF was
obtained over a pre-fluorinated La (1)-Al catalyst, detailed
with 94.5% of C conversion and 84.1% of VF selectivity and only
.9% of coke deposition selectivity at 300 8C, with a HF/C molar
ratio of 2.5. Furthermore, this catalyst gave a better stability
compared with the pure Al . LaF played an important role in the
catalytic performance by modifying the surface acidic property of
the catalyst, which led to considerable enhancement of
selectivity to VF and a slight decline in C conversion over
the La-doped Al catalyst.
prepared and tested for vapor phase hydrofluorination of C
VF. The high activity to C
2
H
2
4.3. Catalyst activation (pre-fluorination)
2 2
H
2
O
3
2
O
3
Prior to use, the fresh catalyst was subject to a pre-fluorination
process in order to activate the catalyst. The pre-fluorination was
carried out in a stainless steel tubular reactor with an inner
diameter of 1 cm and a length of 30 cm. 3 mL of the fresh catalyst
(20–40 mesh) was loaded in the reactor and dried at 300 8C for 1 h
2 2
H
0
2 2
H
2
O
3
3
ꢁ
1
in N
2
(30 mL min ). Then the N
2
flow was stopped and a mixture
ꢁ
1
ꢁ1
a
of HF (80 mL min ) and N
2
(10 mL min ) was introduced at
2
H
2
260 8C for 1.5 h and subsequently at 350 8C for 2 h. The fresh
catalyst after the activation process was denoted as the pre-
fluorinated catalyst.
2 3
O
4
. Experimental
4.4. Hydrofluorination reaction
4.1. Catalyst preparation
The hydrofluorination reactions were carried out in the same
The La
2
O
3
-Al
2
O
3
catalysts were prepared using a deposition-
reactor soon after the catalyst activation, under atmospheric
pressure. 3 mL of the in situ pre-fluorinated catalyst was used.
precipitation (DP) method. A detailed process is as follows: an
aqueoussolutionofLa(NO
room temperature, then an aqueous solution of (NH
3
)
3
was mixedwitha Al
2
O
3
ꢂH
2
Opowderat
CO (1 M)
Flow rates of C
mass flow controllers. The molar ratio of HF/C H
2
H
2
and HF gases were carefully controlled using
was 2.5 and the
4
)
2
3
2 2
ꢁ1
was added drop-wise to the mixture under stirring until the pH was
brought to about 8.0. The resulting mixture was aged for 1 h and
then the solid was separated from the mother liquid. It was washed
with deionized water and dried at 120 8C overnight, followed by a
calcination at 400 8C for 4 h. The La contents in the catalysts were 0,
GHSV was 900 h . The gaseous products were analyzed by a gas
chromatograph (Shimadzu GC-2014) equipped with a flame
ionization detector (FID) and a HP GS-GASPRO capillary column.
After hydrofluorination reaction, the catalyst was denoted as the
used catalyst.
1
, 5 and 10 mol. %, and the catalystsweredenotedasAl
Al , La (5)-Al and La (10)-Al , with the number in the
parenthesis representing the La content in the catalyst.
2 3 2 3
O , La O (1)-
O
2 3
O
2 3
O
2 3
O
2 3
O
2 3
4.5. Coke deposition calculation
In vapor phase hydrofluorination of C
of C could be decomposed into carbon and ethylene (reaction
2
5)), and this ethylene could also react with HF to produce CH CH F
2 2
H to VF, a small quantity
4.2. Catalyst characterizations
2 2
H
(
3
Surface areas of the catalysts were determined by the modified
(reaction (6)).
BET method from the N
sorb-1 apparatus.
X-ray diffraction (XRD) patterns were collected on a PANalytical
X’Pert PROMPD powder diffractometer operated at 40 kV and
2
sorption isotherms at 77 K on an Auto-
CH ꢀ CH ! CH
2
¼ CH
2
þ 2C
CH
(5)
(6)
CH
2
¼ CH
2
þ HF ! CH
3
2
F
4
0 mA, using Cu Ka radiation. The catalyst was scanned in a 2u
Furthermore, the deposited coke species include mostly carbon
and small amount of polymerized C and other unsaturated
hydrocarbons. So the selectivity to coke deposition could be
calculated as follows:
ꢁ1
range from 10 to 908 with a scan rate of 0.38 min . The phase
compositions of the catalysts were identified with reference to the
power diffraction data files (JCPDS). The crystallite size of pre-
fluorinated samples was calculated by full curve fitting, using Jade
2
H
2
½
Selectivity to coke depositionꢃ ¼ 2 ꢄ ð½Selectivity toC
þ ½Selectivity to CH
2
H
4
ꢃ
6
.5 software.
Raman spectra were obtained on a Renishaw RM1000 confocal
3
CH
2
FꢃÞ
microscope with exciting wavelength of 514.5 nm under ambient
conditions, which were used to get the information of coke
deposition over the used catalysts.
Acknowledgements
3
Temperature-programmed desorption of ammonia (NH –TPD)
was employed to determine the strength of acidic sites and its
distribution of the pre-fluorinated catalysts. The sample (0.1 g) was
This work is financially supported by the National Science
Foundation of China (Grant No. 20873125). The authors are also

Q.-Y. Bi et al. / Journal of Fluorine Chemistry 130 (2009) 528–533
533
[
15] F.X. Yin, S.F. Ji, B.H. Chen, Z.L. Zhou, H. Liu, C.Y. Li, Appl. Catal. A 310 (2006) 164–
grateful to Prof. Zhao-Yin Hou from the Institute of Catalysis,
173.
3
Zhejiang University, for the NH –TPD analysis.
[
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