Low cost and non-surfactant synthesis of fluorinated alumina modified with magnesium for condensation of aniline to diphenylamine

Article abstract of DOI:10.1016/j.jfluchem.2011.11.010

Fluorinated alumina was modified with different alkaline and alkaline earth metals. And fluorinated alumina modified with magnesium was found to show the best reactivity and selectivity for condensation of aniline to diphenylamine (DPA) under fix-bed cont

Full text of DOI:10.1016/j.jfluchem.2011.11.010

Journal of Fluorine Chemistry 135 (2012) 373–378
Contents lists available at SciVerse ScienceDirect
Journal of Fluorine Chemistry
journal homepage: www.elsevier.com/locate/fluor
Short communication
Low cost and non-surfactant synthesis of fluorinated alumina modified with
magnesium for condensation of aniline to diphenylamine
a
b,
Chunming Zheng , Xiaohong Sun *
a
State Key Laboratory of Hollow-fiber Membrane Materials and Membrane Processes, School of Environmental and Chemical Engineering, Tianjin Polytechnic University,
Tianjin 300160, PR China
b
Key Laboratory of Advanced Ceramics and Machining Technology, Ministry of Education, School of Materials Science and Engineering, Tianjin University, Tianjin 300072, PR China
A R T I C L E I N F O
A B S T R A C T
Article history:
Fluorinated alumina was modified with different alkaline and alkaline earth metals. And fluorinated
alumina modified with magnesium was found to show the best reactivity and selectivity for
condensation of aniline to diphenylamine (DPA) under fix-bed continuous flow reaction conditions.
Various characterizations involving X-ray diffraction, nitrogen-adsorption measurements, inductive
coupled plasma emission spectrum as well as infrared spectrum has integrally testified the structure of
fluorinated alumina modified with magnesium. The preparation of fluorinated alumina modified with
magnesium was simply convenient and, importantly, environmentally benign for non-surfactant needed
in comparison with H-beta zeolite. Meanwhile, the catalyst even exhibited higher conversion of aniline
than H-beta zeolite. Such alumina-based catalyst can be readily recovered for at least 5 times, while the
conversion of aniline and productivity for DPA was almost maintained during the reaction.
ß 2011 Elsevier B.V. All rights reserved.
Received 12 September 2011
Received in revised form 3 November 2011
Accepted 19 November 2011
Available online 28 November 2011
Keywords:
Alumina
Fluorinated
Magnesium
Diphenylamine
Condensation of aniline
1
. Introduction
Diphenylamine (DPA) is an important chemical additive for the
individual solid catalysts but also on the number of their active
sites and the corresponding acid strength [1,13]. In this work, we
first developed and prepared fluorinated alumina modified with
magnesium via a simple method instead of surfactant-assisted
hydrothermal synthesis of H-beta zeolite for production of DPA.
The fluorinated alumina is a solid acid catalyst consisting of rich
Bronsted and Lewis acid sites with three dimensional mesoporous
networks and it was readily prepared by fluorination of the certain
alumina with a high surface area and pore volume [14,15]. Such
fluorinated alumina modified with magnesium catalysts are rare to
date. This incorporation provides simple and eco-friendly access by
reactants in condensation of aniline, which gives rise to
unexpected high catalytic performance for acid reaction in
comparison with H-beta zeolite.
synthesis of rubber chemicals, dyes, and stabilizer for polymers,
etc. [1]. Among all the preparation methods for DPA, condensation
of aniline in the presence of H-beta zeolite as solid acid catalyst
was most widely implemented on relatively large scales [2,3].
Ordinarily, H-beta zeolite is synthesized with organic surfactant,
such as tetraethyl ammonium hydroxide, in strict hydrothermal
conditions [4]. Hence, the synthesis processes are often compli-
cated, costly and environmentally unfriendly [5,6].
A cleaner process for solid acid without by-products is of great
significance for the economical preparation and industrial
application of acid catalysis [7]. The same sustainable approaches
to the production of DPA have also stimulated the use of eco-
friendly, highly active heterogeneous catalysts as alternatives
2. Results and discussion
[
8,9]. Any solid acid catalyst, as effective as H-beta zeolite in
condensation of aniline, are potentially applicable for the efficient
conversion of aniline, and the preparation of the catalysts should
be easy, non-corrosive and non-synthetic organic surfactant to be
needed, allowing for regeneration of the catalyst with low energy
consumption [10–12]. The catalytic performance for condensation
of aniline to DPA depends not only on the structure of the
2
.1. Catalyst characterization
For the catalytic performance of the individual catalysts
depends on the structure of the solid [1], the powder XRD
characterization of fluorinated alumina modified magnesium with
different fluorine content was analyzed. Their diffraction patterns
are given in Fig. 1. Detailed meaning of abbreviations for different
catalysts could be seen in Section 4.1. From Fig. 1; effective
modification of alumina with fluorine could be observed. The
diffraction patterns of the catalysts were similar to pure alumina
*
Corresponding author. Tel.: +86 022 27406141; fax: +86 022 27406114.
E-mail address: sunxh@tju.edu.cn (X. Sun).
0022-1139/$ – see front matter ß 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.jfluchem.2011.11.010

3
74
C. Zheng, X. Sun / Journal of Fluorine Chemistry 135 (2012) 373–378
FMA-20
FMA-10
FMA-20
FMA-10
FMA-05
Alumina
FMA-05
Alumina
1
0
20
30
40
50
60
70
80
0
10
20
30
40
50
2
Theta / [deg.]
Pore size (nm)
Fig. 1. X-ray diffraction pattern of different fluorine content (ammonium fluoride)
Fig. 2. Variation, with respect to fluorine content, of BJH pore distribution curves of
fluorinated alumina modified with magnesium.
fluorinated alumina modified with magnesium.
sample except for high fluorine content of FMA-20. The typical
found in our work. For the fluorination method used in this
manuscript is almost the same with Rodriguez, and the fluorine
content is low (10 wt%), all these results suggest that effective
diffraction peaks of the
g
-AlF
3
ꢀH
2
O could be observed (2u = 14.78;
2
5.08 and 29.78) [10]; and the signals of catalyst pattern with high
fluorine content (2
u
= 31.58 and 52.88) assigned to
3
modification of alumina with fluorine while AlF also could not be
AlF1.65(OH)1.35ꢀnH
2
O [16]; meanwhile; small additional peaks
= 17.28 and 62.08) are identical with the typical pattern of
NH AlF [14]. When catalysts with fluorine content lower than
3 wt%; the XRD technique does not allow to get any information
17]. There are two kinds of explanation for the fluorination
mechanism of alumina by NH F. One is the formation of (NH AlF
over fluorinated alumina by the following reaction:
detected by XRD analysis [16,20].
(
(
2u
Since the catalytic performance of the individual catalysts also
depends on the porous structure of the solid [1], the differences in
the surface area and pore size distributions of the catalyst with
different fluorine contents has been compared, the physical
properties and pore geometry of these materials are given in
Table 1 and Fig. 2, respectively. From Table 1, the solids lose surface
area when the fluorine content increases. Fig. 2 shows that most of
the pores are in the 8–30 nm size range and the distribution is
relatively narrow. When the fluorine contents increase, the pore
4
)
3
6
1
[
4
4
)
3
6
Al3þ þ 6NH
þ 3Hþ
4
F ! ðNH
4
Þ
3
AlF
6
þ 3NH
3
size distribution broadened compared with the alumina. The N
2
(
NH
) AlF
4 3 6
transformed into (NH
4
)AlF
4
,
g
-AlF
3
and finally
a
-AlF
3
adsorption–desorption isotherms of the alumina without fluorine
and FMA-20 (14.5 wt%) are presented in Fig. 3. The desorption step
respectively at 573, 773 and 873 K [18]. However, the other
mechanism also raised that the formation of AlF by NH F to be the
result of consecutive reactions between Al(OH) and HF, leading to
Al(OH) F, Al(OH)F O,
and other intermediates as AlF1.65(OH)1.35ꢀnH
or in a general formula AlF3ꢁX(OH) [19].
The presence of (NH AlF and AlF3ꢁX(OH)
content of FMA-20 catalyst suggest that AlF
according to both mechanisms in agreement with Rodriguez et al.
10]. However, the concentration of the NH F solution used for
impregnation controls the Al /NH F ratio, which influences the
proportion of these intermediate phases at last. And the above
intermediate phases are amorphous and well dispersed at the
surface of alumina support [16]. Rodriguez et al. also found that
XPS analysis could get results with low fluorine content (>2 wt%)
while XRD technique did not allow to get any information when
fluorine content was lower than 13 wt%. The same results also
is slightly displaced to a higher p/p
more fluorine content. Both the modification in the pores size
distribution and the change of desorption p/p value indicate an
0
value for the support with
3
4
3
2
2
2
0
increase of the pores diameters induced by the fluorination. Above
textural properties of the catalyst indicates that pores are
penetrate into the body of the catalyst particles and the pore
volume resides at the internal of the catalyst, the similar even
larger porous structure is favourable to the condensation of aniline
compared with the H-beta zeolite [21]. From Table 1, the difference
between the fluorine content expected and the actual fluorine
content indicates that some fluorine is lost during the preparation,
which could be explained by an increasingly difficulty for reaction
of fluorine with the surface aluminum atoms [12,22,23]. From
powder XRD patterns of Fig. 1, even ammonium fluoride is
maintained on the catalyst during the drying and sublimated
X
4
)
3
6
X
in high fluorine
could be formed
3
[
4
2
O
3
4
Table 1
Chemical analysis and textural properties of different fluorine content fluorinated alumina modified with magnesium.
2
Catalyst
Elemental content (wt%)
Surface area (m /g)
Pore vol. (mL/g)
Average pore size (nm)
Fluorine
Magnesium
a
None
0
0
379
373
359
306
285
289
295
278
1.04
0.98
0.95
0.92
0.91
0.89
0.96
0.93
10.6
10.8
10.9
11.3
11.8
12.3
12.2
12.9
FMA-02
FMA-05
FMA-08
FMA-10
FMA-12
FMA-15
FMA-20
1.92
4.35
6.76
7.93
10.2
13.7
15.1
0.76
0.73
0.76
0.77
0.71
0.77
0.74
a
Pure alumina carrier without any modification.

C. Zheng, X. Sun / Journal of Fluorine Chemistry 135 (2012) 373–378
375
7
6
5
4
3
2
1
00
00
00
00
00
00
00
alumina
FMA-10
Alumina
FMA-15
FMA-20
FMA-20
B
B
1650
L+B
L
L
L
1450
1
700
1600
1550
1500
1400
0
0.2
0.4
0.6
0.8
1.0
-
1
Wavenumber (cm )
Relative pressure (P/P0)
Fig. 4. Pyridine adsorption spectra of different fluorine content (ammonium
fluoride) fluorinated alumina modified with magnesium L: band corresponding to
Lewis sites, B: band corresponding to Bronsted acid sites, L + B: band corresponding
to Lewis and Bronsted acid sites.
Fig. 3.
N
2
adsorption–desorption isotherm at ꢁ195 8C for the alumina and
fluorinated (20 wt%) alumina modified with magnesium (0.75 wt%) catalysts.
during calcination. The catalytic performance of the individual
catalysts also relates to the number of these fluorinated active sites
and the corresponding acid strength, to distinguish the Bronsted
and Lewis acid sites, typical infrared spectra of pyridine adsorbed
on the fluorinated alumina modified with magnesium catalysts are
shown in Fig. 4.
transformation of pseudoboehmite occurred during the calcination
process, which contains water in the structure [26]. From Table 2,
the catalyst activity and selectivity of pure alumina are poor. After
the fluorination process, the catalytic performances increased
dramatically, the concentration of Bronsted acid sites and Lewis
acid sites of this catalyst is the highest among all the catalysts. The
production of DPA depends not only on the structure of the
heterogeneous catalysts but also on proper number of acid sites
with medium acid strength [1]. During the fluorination of alumina,
new Bronsted and Lewis acid sites will produce with new
For the pyridine adsorption FT-IR spectra of pure alumina
ꢁ
1
shown in Fig. 4, peaks at 1447, 1594 cm are representative of
Lewis acidity [16]. For the spectra of fluorinated alumina, peaks at
ꢁ1
1
543 and 1637 cm due to pyridinium ions reveal the presence of
Bronsted acidity [14]. Evidence of this acidity is also shown by the
generated intermediates phases, such as (NH
4
)
3
AlF
6
, AlF3ꢁX(OH)
X
,
ꢁ
1
band at about 1490 cm , which is attributed to Lewis and
Bronsted sites [24]. Increasing the fluorine content leads to an
increase in Bronsted and Lewis acidity, as evidenced by the
, and AlF O. The mobility of the protons of close OH groups is
3
ꢀnH
2
probably increased for hydroxide ions were substituted by fluoride
ions. Very mobile hydrogen could be also generated for the
ꢁ
1
ꢁ1
increase in the peak at 1543 cm and 1447 cm . Fig. 4 shows that
the number of Bronsted and Lewis acid sites is reduced after rising
with increasing of fluorine content. This occurs because portions of
the surface hydroxyl groups of alumina are replaced by fluoride
ions, which increases the electronegativity of the surface and
consequently the acidity of the remaining hydroxyl groups [16,25].
formation of AlF3ꢁX(OH)
gem-fluoride ions. In addition, adjacent hydrated AlF
X
due to the strong inductive effect of the
ꢀnH O results
3
2
in even stronger acid sites [10]. By addition of fluorine content,
Moreno et al. evidenced that the total number of Bronsted acid
sites increases, especially the medium and strong Bronsted acid
sites [14]. These increased Bronsted acid sites, especially medium
ones, are very suitable for the production of DPA [1]. Therefore,
fluorination of alumina could improve the catalytic activity for this
reaction. These results suggests that fluorinated compounds such
2.2. Catalytic studies
Catalytic performance and related acid properties obtained for
the catalysts modified with different alkaline, alkaline earth metals
and H-beta zeolite at 350 8C are given in Table 2.
As is shown in Table 2, pure alumina shows low concentration
of Bronsted acid sites and Lewis acid sites, since incomplete
as (NH
4
)
3
AlF
6
, AlF3ꢁX(OH)
X
, and AlF
3
ꢀnH
2
O are important catalytic
active intermediates [16]. With the modification of different
alkaline and alkaline earth metals, both conversion and selectivity
results of fluorinated alumina strongly depends on the type of the
metals while the catalyst modified with magnesium showed the
Table 2
a
Catalytic performance and related acid properties of fluorinated alumina modified with different alkaline, alkaline earth metals and H-beta zeolite.
b
Element
Metal content (wt%)
Metal content (mmol/g)
Lewis sites (mmol/g)
Bronsted sites (mmol/g)
Aniline conversion (%)
DPA selectivity (%)
Li
0.22
0.72
1.20
0.75
1.25
4.30
–
0.31
0.31
0.31
0.31
0.31
0.31
–
0.35
0.31
0.28
0.42
0.37
0.35
0.43
0.26
0.37
0.23
0.19
0.11
0.26
0.21
0.17
0.29
0.13
0.33
28.6
19.0
12.8
30.5
24.0
20.6
28.4
22.4
28.2
96.7
95.5
94.5
95.7
91.6
87.9
88.5
68.5
95.1
Na
K
Mg
Ca
Ba
c
F
d
None
–
–
e
H-beta
–
–
a
ꢁ1
The reaction proceeded at 350 8C for 4 h, LHSV = 0.2 h with H
2
at atmosphere pressure, fluorine content 10 wt%.
b
c
Theoretical contents of alkaline and alkaline earth metals macerated on the fluorinated alumina.
Alumina modified with fluorine (10 wt%).
d
e
Pure alumina calcined from pseudoboehmite in a stream of air at 550 8C for 4 h.
H-beta (Si/Al = 12.5), calcined in a stream of ammonia (5%) in nitrogen at 350 8C followed by ion-exchange with NaNO
3
and further calcination in a stream of air at 500 8C.

3
76
C. Zheng, X. Sun / Journal of Fluorine Chemistry 135 (2012) 373–378
100
6
5
4
3
2
1
0
0
0
0
0
0
cavities in intersections of the fluorinated alumina would allow for
the formation of bulky intermediates, products or coke precursors,
which increased the catalytic activity. The high catalytic activity and
selectivity is also related to a proper number and strength of acid
sites [27,28]. The presence of strong acid sites is responsible for the
formation of by-products and thus for a lower selectivity of aniline
condensation [1]. Since the mol ratio of alkaline and alkaline earth
metaladdedinthefluorinatedaluminawas thesame (0.31 mmol/g),
only the alkalinity of metals varies from magnesium, lithium to
calcium, sodium, barium and potassium, so these metals could
preferentially cover and neutralize nearly the same amount
Bronsted acid sites (0.29 mmol/g) with different alkalinity. There-
fore, these alkaline and alkaline earth metals affected the strong
Bronstedacidsitesgreatly, making strongBronstedacidsiteschange
to medium even weak Bronsted acid sites, and the overall
concentration of Bronsted acid sites decreased (Table 2). This also
has been confirmed by Moreno et al. [14]. Through IR characteriza-
9
8
0
0
70
6
0
0
5
10
15
20
Content of F (wt %)
Fig. 5. Catalytic performance of different fluorine content (ammonium fluoride)
fluorinated alumina modified with magnesium.
3
tion by adsorption of d -acetonitrile, we also found that the catalytic
6
5
4
3
2
1
0
0
0
0
0
0
0
100
activity decreased with the enhanced alkalinity of metals, but the
decline of the catalytic selectivity is not obvious, which indicates
that the condensation of aniline was rather close to the thermody-
namic equilibrium value. The decrease in the concentration of acid
sites in catalysts influences only their activity, and the selectivity to
diphenylamine was influenced by the strength of the acid sites.
Strong acid sites favour not only the desired aniline condensation
but also the formation of side products [1]. Modification with strong
base cations, suchas calcium, sodium, barium or potassium, reduced
the strong Bronsted acid sites intensively, which reduced the
formation of side products, thereby the catalytic selectivity of DPA
increased. The modification with these strong base cations reduced
not only the strength of the acid sites, but also the concentration of
Bronsted acid sites, compared with weak base cations, such as
magnesium and lithium, the concentration of acid sites also
evidenced the same results by the method from Witchterlova
et al. in Table 2 [29]. There is another article also raised the similar
conclusion [1]. With the combined adjusting of fluorine and
different alkaline and alkaline earth metals, the type of acid sites
was greatly influenced, andthe catalytic selectivityforcondensation
of aniline to DPA was little changed. And the concentration of acid
sites affects the catalytic activity intensively.
9
8
7
0
0
0
0
6
2
80
300
320
340
360
380
400
Temperature (ºC)
Fig. 6. Effect of temperature on catalytic performance of the fluorinated (10 wt%)
alumina modified with magnesium (0.75 wt%) catalyst. Reaction condition:
ꢁ
1
2
reaction temperature = 350 8C, LHSV = 0.2 h with H at atmosphere pressure.
best catalytic performances, even higher than H-beta zeolite. On the
other hand, fluorinated alumina modified with sodium, potassium,
or barium showed significantly lower activity. These differences in
the catalytic activity can be probably related to the substantial
different structures of the individual catalysts and to their acidic
properties [1,27]. The alumina with high surface area and large pore
diameterwas used inthe catalyst, and it seems thatthis specific pore
structure is appropriate for the synthesis of diphenylamine. Larger
In order to see the influence of the fluorine content to the FMA
catalysts on catalyst performance, the alumina is loaded with
different fluorine contents, and then change concentration of the
maceration extract, the suspended liquid is mixed slowly under
the room temperature, appraise the performance of the catalysts
under equal conditions. The results are shown in Fig. 5. From Fig. 5,
6
5
4
3
2
1
0
0
0
0
0
0
100
60
50
40
30
20
10
100
90
80
70
60
9
8
0
0
70
6
0
(
a)
(b)
0
10
20
30
40
50
60
0
1
2
3
4
5
Reaction Time (h)
Recycling Times
Fig. 7. Catalytic performance of the fluorinated (10 wt%) alumina modified with magnesium (0.75 wt%) with a changes of catalytic activity, and b recycling test. Reaction
ꢁ
1
2
condition: reaction temperature = 350 8C, LHSV = 0.2 h with H at atmosphere pressure.

C. Zheng, X. Sun / Journal of Fluorine Chemistry 135 (2012) 373–378
377
the catalysts modified with different fluorine contents have
different conversion rate and selectivity of DPA. With increasing
of fluorine content, the activity of FMA catalyst is reduced after
rising. The catalyst has the best activity when fluorine content is in
All the chemicals were procured from Tianjin Chemical Corp.,
China (analytical grade) and used without further purification. For
the typical catalyst preparation process, a certain weight of
alkaline or alkaline earth metal nitrate and alumina were blended
using 60 mL distilled water in 400 mL glass beakers with 4 h for
agitation. Then they were put into ovens with the temperature of
80 8C to dry the water, followed by calcinations at 550 8C in the
presence of air for 4 h. The repetitious modifications for one
catalyst were the same as above. The percentages indicate the
weight of elements (fluorine and metals) to the weight of alumina.
For example, F(10%)–Mg(0.75%)/alumina (short for FMA-10)
denotes that 4 g alumina was first impregnated by 0.78 g of
ammonium fluoride which contains 0.4 g fluorine. After drying at
90 8C for 12 h and calcination at 550 8C for 4 h, it was then
impregnated by 0.33 g of magnesium nitrate which contains
0.031 g magnesium. The repetitious drying and calcination process
for the catalyst were the same as above. The catalyst was pressed
with the pressure of 15 t when all the modifications were finished.
Then using sieves granular catalysts with 20–40 mesh can be
obtained for experiments.
1
0 wt%. The high activity of the catalyst may relate to the fact that
the catalyst has better acid distribution [1]. The modification of
ammonium fluoride and magnesium changes the acid distribution
of alumina, makes the catalyst have the suitable acid intensity for
production of DPA. The modification also reduces the formation of
the accessory substances, avoids the deposit of coke, and improves
the performance of the FMA catalyst at last [30]. Since the
thermodynamic equilibrium of condensation of aniline to DPA
could be affected by reaction temperature, the catalytic behaviour
for the aniline condensation as a function of the temperature was
researched, and the results were given in Fig. 6. From Fig. 6, the
conversion is controlled by the thermodynamic equilibrium when
the reaction temperature is higher than 350 8C. Finally, it could be
concluded that under such conditions the reaction is not
thermodynamically limited and that higher conversions could
be obtained by increasing the contact time [31]. Attempt could
therefore be made to correlate the catalytic activity patterns to
some physico-chemical characterization.
4.2. Characterization methods
For the most active catalyst, FMA-10, the stability and
reusability of their catalytic performance in condensation of
aniline to DPA was tested, the results are given in Fig. 7.
From the entire test showed in Fig. 7a, the activity of catalyst
obtained by impregnation of support was increasing for the first
X-ray powder diffraction (XRD) patterns of the dry samples
were performed on D/max 2500 diffractometer with Cu K
radiation ( = 0.154 nm). Typically, the data were collected from
108 to 808 with a resolution of 0.28. N adsorption–desorption
a
l
2
3
0 h, and then the catalyst showed stable work. Through the
isotherms were obtained at ꢁ196 8C on a Micromeritics Tristar
3000 sorptometer. Samples were outgassed at 150 8C for a
minimum 12 h prior to analysis. The experimental data were
further processed by the BET equation for surface areas and by the
BJH model for pore size distributions. The acidities of pure alumina,
fluorinated alumina modified with magnesium and commercial H-
Beta zeolite catalysts were measured by means of FT-IR analysis of
chemisorbed pyridine on a Magna Model 560 spectrophotometer
(Nicolet, U.S.A.). The samples were calcined at 500 8C and then
exposed to liquid pyridine at 80 8C for 4 h and then kept at room
temperature overnight so as to allow the base to permeate the
samples. The concentrations of Bronsted and Lewis sites were
reaction of more than 60 h, the conversion of aniline and selectivity
of DPA do not have great change, which indicates that the stability
of the catalyst is good [13]. Moreover the catalyst is reusable for at
least five catalytic runs only under the calcination at 500 8C for 4 h
before the recycling test (Fig. 7b). Fig. 7b shows activities and
selectivities obtained after calcination and by charging a new
continuous flow reaction system. The slight decrease observed in
activity could therefore be due to a feeble poisoning of the catalyst
surface and the lost of fluorine content [22].
3
. Conclusions
estimated by the adsorption of d
same FT-IR methods. The samples were activated at 500 8C
overnight under vaccum, then exposed to d -acetonitrile with a
partial pressure of about 1000 Pa. The adsorption was for 1 h
followed by desorption to vacuum for another 0.5 h. The fluorine
and magnesium contents have been determined for catalysts
calcined at 550 8C on a Thermo Jarrell-Ash ICP-9000 inductive
coupled plasma emission spectrometer.
3
-acetonitrile followed by the
In this report we successfully elaborated the preparation of
fluorinated alumina simply and eco-friendly modified with
different alkaline and alkaline earth metals. With the modification
of magnesium, fluorinated alumina showed the higher catalytic
activity and selectivity for condensation of aniline to diphenyl-
amine than other alkaline, alkaline earth metals and the H-beta
zeolite. The function of magnesium was studied in detail. It could
decrease the strong acid sites of fluorinated alumina without
influencing the concentration of total acid sites. The high catalytic
performance of fluorinated alumina with magnesium is greatly
related to the pore geometry with high surface area, large pore size
and high concentration of acid sites with an intermediate acid
strength. A proper number of acid sites with an intermediate acid
strength could be controlled easily using the combination
adjusting of the fluorine and magnesium. The catalyst could at
least maintain its catalytic performance for 65 h and reuse for 5
times at the reaction temperature of 350 8C.
3
4.3. Catalytic activity measurements for condensation of aniline to
diphenylamine
The reactor system was a fixed-bed, vertical, flow-type reactor
made of stainless steel tube of 40 cm in length and 8 mm in
diameter. The stainless steel reactor was heated to the requisite
temperature with the help of a tubular furnace controlled by a
digital temperature controller cum indicator. The quantity of
modified alumina used in each run was 1 g with the mesh of 20–40.
The catalyst was placed in the middle of the reactor and supported
by a thin layer of glass wool under it. The raw stuff of aniline was
fed into the reactor by a syringe pump that could be operated at
different flow rates under atmospheric pressure. The experimental
conditions including different granular size and space velocity was
performed, and the best reaction conditions could be considered as
belonging to the chemical kinetic regime with proper granular size
of the catalysts and space velocity of the condensation reaction.
The effects of the reaction temperature and time were investigated.
4
. Experimental
4
.1. Synthesis of fluorinated alumina modified with different alkaline
and alkaline earth metals
2
Pseudoboehmite (
pore diameter 10.6 nm) is used as the precursor of
a
-AlOOH, BET surface area 379 m /g, average
-Al (short
g
2 3
O
for alumina) after calcination at 550 8C in the presence of air for 4 h,
which was provided by the catalyst factory of Nankai University.

3
78
C. Zheng, X. Sun / Journal of Fluorine Chemistry 135 (2012) 373–378
[
[
12] S. Jongpatiwut, N. Rattanapuchapong, T. Rirksomboon, S. Osuwan, D.E. Resasco,
Catal. Lett. 122 (2008) 214–222.
13] L.L. Qu, R. Prins, J. Catal. 207 (2002) 286–295.
The products were condensed in a water-cooled condenser at
hourly intervals and analyzed in a SP-502 gas chromatograph
(
0
Shanghai Hongtu Instruments Co. Ltd., China) equipped with
.25 mm ꢂ 50 m capillary column.
[14] M. Moreno, A. Rosas, J. Alcaraz, M. Hernandez, S. Toppi, P. Da Costa, Appl. Catal. A:
Gen. 251 (2003) 369–383.
[15] L.H. Ding, Z.S. Zhang, Y. Zheng, Z. Ring, J.W. Chen, Appl. Catal. A: Gen. 301 (2006)
2
41–250.
Acknowledgments
[16] L.M. Rodriguez, J. Alcaraz, M. Hernandez, M. Dufaux, Y. Ben Taarit, M. Vrinat, Appl.
Catal. A: Gen. 189 (1999) 53–61.
[
[
[
[
17] J.L. Delattre, P.J. Chupas, C.P. Grey, A.M. Stacy, J. Am. Chem. Soc. 123 (2001) 5364–
We gratefully acknowledge the financial support of the
Provincial-College Cooperation Foundation of Yunnan Province,
China(Grant No. 2005YX39). We would also like to thank Dr
Haisheng Zeng, Dr Jixin Chen and Dr Fuxiang Zhang for the
installation of equipment and valuable discussions. Our deepest
gratitude goes to Prof. Naijia Guan and Prof. Minglin Guo for their
help in writing and in-depth discussions on the mechanism.
5365.
18] P.O. Scokard, S.A. Selim, J.P. Damon, P.G. Rouxhet, J. Colloid Interface Sci. 70 (1979)
209–222.
19] F.P. Kerkhof, J.C. Oudejans, J.A. Moulin, E.R.A. Natulewiez, J. Colloid Interface Sci.
77 (1980) 120–130.
20] N. Boz, N. Degirmenbasi, D.M. Kalyon, Appl. Catal. B: Environ. 89 (2009) 590–596.
[21] R. Luque, J.M. Campelo, D. Luna, J.M. Marinas, A.A. Romero, Micropor. Mesopor.
Mater. 84 (2005) 11–20.
[
[
22] P.J. Chupas, C.P. Grey, J. Catal. 224 (2004) 69–79.
23] Y.X. Feng, N. Yin, Q.F. Li, J.W. Wang, M.Q. Kang, X.K. Wang, Catal. Lett. 121 (2008)
References
97–102.
[24] H. Kim, J.J. Lee, S.H. Moon, Appl. Catal. B: Environ. 44 (2003) 287–299.
[
[
1] M. Hronec, Z. Cvengrosova, J. Cejka, Appl. Catal. A: Gen. 255 (2003) 197–202.
2] K. Othmer, Encyclopedia of Chemical Technology, fourth ed., John Wiley & Son
Inc., New York, 1993.
[25] C. Stosiek, G. Scholz, S.L.M. Schroeder, E. Kemnitz, Chem. Mater. 22 (2010) 2347–
2356.
[26] P. Raybaud, M. Digne, R. Iftimie, W. Wellens, P. Euzen, H. Toulhoat, J. Catal. 201
(2001) 236–246.
[27] Y.N. Wang, X.W. Guo, C. Zhang, F.L. Song, X.S. Wang, H.O. Liu, X.C. Xu, C.S. Song,
W.P. Zhang, X.M. Liu, X.W. Han, X.H. Bao, Catal. Lett. 107 (2006) 209–214.
[28] G. Kostrab, M. Lovic, I. Janotka, M. Bajus, D. Mravec, Appl. Catal. A: Gen. 335 (2008)
74–81.
[29] B. Wichterlova, Z. Tvaruzkova, Z. Sobalik, P. Sarv, Micropor. Mesopor. Mater. 24
(1998) 223–233.
[3] V.D. Stytsenko, T.D. Hyu, V.A. Vinokurov, Kinet. Catal. 48 (2007) 292–297.
[4] C.S. Cundy, P.A. Cox, Micropor. Mesopor. Mater. 82 (2005) 1–78.
[5] J. Cejka, B. Wichterlova, Catal. Rev. Sci. Eng. 44 (2002) 375–421.
[6] X.J. Meng, B. Xie, F.S. Xiao, Chin. J. Catal. 30 (2009) 965–971.
[7] T. Tajima, T. Fuchigami, J. Synth. Org. Chem. Jpn. 64 (2006) 406–414.
[8] T. Krahl, E. Kemnitz, J. Fluorine Chem. 127 (2006) 663–678.
[9] M. Verziu, M. Florea, S. Simon, V. Simon, P. Filip, V.I. Parvulescu, C. Hardacre, J.
Catal. 263 (2009) 56–66.
[30] J.M. Campelo, D. Luna, R. Luque, J.M. Marinas, A.A. Romero, J.J. Calvino, M.P.
Rodriguez-Luque, J. Catal. 230 (2005) 327–338.
[31] N.A. Sanchez, J.M. Saniger, J.B.D. Caillerie, A.L. Blumenfeld, J.J. Fripiat, J. Catal. 201
(2001) 80–88.
[
10] L.M. Rodriguez, J. Alcaraz, M. Hernandez, Y. Ben Taarit, M. Vrinat, Appl. Catal. A:
Gen. 169 (1998) 15–27.
11] J.C. Xia, D.S. Mao, B. Zhang, Q.L. Chen, Y.H. Zhang, Y. Tang, Catal. Commun. 7 (2006)
[
3
62–366.