Oxidative dehydrogenation of propane on magnesium vanadates in the presence of tetrachloromethane

Article abstract of DOI:10.1246/bcsj.75.181

The oxidative dehydrogenation of propane to propylene on active catalysts such as magnesium vanadates (MgV₂O₆, Mg₂V₂O₇, and Mg₃V₂O₈) was studied in the presence and absence of tetrachloromethane (TCM) at 723 K. The reaction rate per unit of catalyst surface on (MgV₂O₆ was about twice those on Mg₂V₂O₇ and Mg₃V₂O₈). The addition of TCM improved the conversion of propane and the reaction rate, while the selectivity to propylene was essentially identical to that in the absence of TCM on three catalysts. The conversion of propane and the corresponding reaction rate increased with increasing partial pressure of TCM (P(TCM)) on (MgV₂O₆, Mg₂V₂O₇, while the selectivity to propylene was insensitive to P(TCM).

Full text of DOI:10.1246/bcsj.75.181

Bull. Chem.
Soc. Jpn.
75
1
The Chemical © 2002 The Chemical Society of Japan
Bull. Chem. Soc. Jpn., 75, 181–186 (2002)
181
Society of Ja-
pan
The Chemical
Society of Ja-
pan
AM
1
Oxidative Dehydrogenation of Propane on Magnesium Vanadates in the
Presence of Tetrachloromethane
Propane Oxidation on Magnesium Vanadates
S. Sugiyama et al.
1
5
002
81
86
Shigeru Sugiyama,* Yutaka Iizuka, Yukinori Konishi, and Hiromu Hayashi
2
1
1
Department of Chemical Science and Technology, Faculty of Engineering, The University of Tokushima,
Minamijosanjima, Tokushima 770-8506
BCSJA8
0
0
8
1
2
1
9
2
009-2673
1272
(
Received August 13, 2001)
3
001
0
The oxidative dehydrogenation of propane to propene on active catalysts such as magnesium vanadates (MgV O ,
2
6
2 2 7 3 2 8
Mg V O , and Mg V O ) has been investigated in the presence and absence of tetrachloromethane (TCM) at 723 K. The
introduction of a small amount of TCM into the feedstream did not influence the selectivity to propene while the conver-
sion of propane was improved on those catalysts. The conversion was enhanced by approximately twice on Mg
upon addition of TCM. It has been shown that the effects of TCM on lattice oxygen in those catalysts mainly control the
enhancement. The formation of an excess amount of the chlorinated species on the surface of the catalysts resulted in a
decrease of the conversion.
2
2 7
V O
001
3.2.3
.5
5
Since magnesium vanadates have been proposed as efficient
catalysts for the oxidative dehydrogenation of butane and pro-
ucts from propane is practically attractive.
1
In the present paper, we report the oxidative dehydrogena-
tion of propane on magnesium meta-, pyro-, and ortho-vana-
dates in the presence and absence of TCM. Further enhance-
ment of the activities for the oxidative dehydrogenation on
those catalysts by the introduction of TCM into the feedstream
will be demonstrated.
2
3–9
pane, extensive papers on those catalysts and the related
10–20
catalysts
cepted that the VwO and/or V–O–V bonds participate in the ac-
tivation of C , resulting in the remarkable activities for the
oxidative dehydrogenation of propane on those catalysts.
have been published. It has been generally ac-
3 8
H
2
1
Most researchers have focused on the combination of vana-
dates and other solid elements to prepare active catalysts.
There are rather few reports on the enhancement of the activi-
ties for the oxidative dehydrogenation of propane by the intro-
duction of gaseous additive into the feedstream. It has been
shown that the activities for the partial oxidation of methane
can be improved on various catalysts by the addition of gas-
eous chlorinated species, such as tetrachloromethane (TCM),
Experimental
Magnesium meta-, pyro-, and ortho-vanadates (MgV
Mg , and Mg , respectively) were prepared from
Mg(OH) and NH VO according to the procedure reported by
2 6
O ,
2
2
V O
7
3 2 8
V O
2
4
3
3
Volta et al. In preparing magnesium meta-vanadate, the resulting
solids were dried at 383 K overnight, followed by the calcination
at 773 K for 6 h and at 873 K for 6 h. In the calcination for the
synthesis of magnesium ortho-vanadate, the calcination tempera-
ture was adjusted at 823 K for 6 h, at 898 K for 49 h, at 913 K for
9 h, at 913 K for 60 h, at 1023 K for 15 h, at 1023 K for 15 h, and
then again at 1073 K for 15 h. The calcination procedure for mag-
nesium pyro-vanadate was given in our previous report. Each
solid was finely ground between calcinations. After the final cal-
cination, XRD patterns of magnesium meta-, pyro-, and ortho-
22–24
into the corresponding feedstream.
Although participation
2
5
of TCM in the gas-phase reaction cannot be excluded, it has
been suggested that the formation of structural or nonstructural
chlorinated species on the catalyst surface would contribute to
the enhanced activities in the partial oxidation with TCM. It
4
27
26,27
seems to be rather strange that there are few reports
on the
effects of TCM on redox behaviors of catalysts since the oxi-
dative dehydrogenation of alkanes should be strongly influ-
enced by the participation of lattice oxygen in the catalysts to
the oxidation. Since TCM is not easily decomposed under am-
vanadates matched MgV
1-0816), and Mg
essentially identical to those reported by Volta et al. ICP analysis
Shimadzu ICPS-5000) of magnesium meta-, pyro-, and ortho-
vanadates found wt%Mg and wt%V to be 11.0 and 46.2, 18.9 and
8.8, and 25.2 and 33.9, respectively, which corresponded to the
calculated values of 10.9 and 45.9, 18.5 and 38.8, and 24.1 and
3.7 for MgV , Mg , and Mg , respectively. Particles
of 0.85–1.70 mm were employed as the catalyst. Surface area and
apparent density of MgV , Mg , and Mg were 2.0
2
O
6
(JCPDS 45-1050), Mg
2 2 7
V O (JCPDS
3
3 2 8
V O (JCPDS 37-0351), respectively, and were
3
(
28
bient conditions and is a suspected human carcinogen and an
29,30
Environmental Protection Agency priority pollutant,
a wide
3
variety of studies on the decomposition of TCM have been car-
ried out in aqueous- and gas-phases. Since the elimination of
TCM as proposed in these techniques requires the input of sub-
3
O
2 6
2
V
2
O
7
3 2 8
V O
31–34
stantial quantities of energy,
the development of decompo-
O
2 6
2
2
V O
2 7
3 2 8
V O
sition methods which produce usable products is desirable
from practical points of view. Since propane conversion pro-
cesses are, at least in principle, attractive for the generation of
precursors for economically important chemicals, the possibil-
ity of decomposing TCM while generating value-added prod-
3
and 1.11, 3.5 and 1.06, and 1.1 m /g and 0.98 g/cm , respectively.
The catalytic experiments were performed in a fixed-bed continu-
ous-flow quartz reactor operated at atmospheric pressure. The re-
actor consisted of a quartz tube, 9 mm i.d. and 35 mm in length,
attached at each end to 4 mm i.d. quartz tubes to produce a total

1
82 Bull. Chem. Soc. Jpn., 75, No. 1 (2002)
Propane Oxidation on Magnesium Vanadates
length of 25 cm. The catalyst charge was held in place in the en-
larged portion of the reactor by two quartz wool plugs. In all ex-
periments, the catalyst was heated to the reaction temperature
while maintaining a continuous flow of helium and was held at
this temperature under a 25 mL/min flow of oxygen for 1 h. No
homogeneous oxidation of propane was observed at 723 K under
the present conditions. The reaction was monitored with an on-
stream Shimadzu GC-8APT gas chromatograph with a TC detec-
tor and integrator (Shimadzu C-R6A). Two columns, one Porapak
Q (6 m × 3 mm) and the other Molecular Sieve 5A (0.2 m × 3
mm), were employed in the analyses. The conversion of propane
was calculated from the products and the propane introduced into
the feed. The selectivities were calculated from the conversion of
propane to each product on a carbon basis. Blank experiments
2
conducted with propane absent from the feed (TCM + O + He)
indicated that TCM undergoes oxidation while producing carbon
oxides. Although the quantities of carbon oxides relative to pro-
pane present were small, all of the data reported were corrected by
performing duplicate experiments with propane absent under oth-
erwise identical values of the process variables. The carbon mass
balances were 100 ± 5%. The reaction rates per unit of surface
area were estimated as the rate (r = FC
and W were flow rate, initial concentration of C
, and catalyst weight) per the catalyst surface area. Powder
X
0 A
0 A
/W, in which F, C , X ,
3 8
H
, conversion of
3 8
C H
X-ray diffraction (XRD) patterns were recorded with a Rigaku
RINT 2500 X, using monochromatized Cu Kα radiation. X-ray
photoelectron spectroscopy (XPS, Shimadzu ESCA-1000AX)
5
1
used Mg Kα radiation. V MAS NMR was obtained with a Bruk-
er AVANCE DSX300, with an external reference of 0.16 M
NaVO
ning rate of 30 kHz.
3
solution at −574.28 ppm at room temperature and a spin-
Fig. 1.
MgV
The oxidative dehydrogenation of propane on
O (Meta-), Mg V O (Pyro-), and Mg V O (Ortho-)
6 2 2 7 3 2 8
2
in the absence (A) and presence (B) of TCM at 723 K.
Reaction conditions: Wt = 0.4, 0.5 and 1.2 g for MgV O ,
2 6
Results and Discussion
Mg
P(C
.17 kPa.
2
V
2
O
7
, and Mg
3
V
2
O
8
, respectively. F = 30 mL/min,
) = 4.1 kPa, P(TCM) = 0, and
Catalytic Activities with and without TCM. In order to
compare the selectivities and to examine the effect of the intro-
duction of TCM into the feedstream for the oxidative dehydro-
genation of propane on three magnesium vanadates, we adjust-
ed the reaction conditions to afford the similar conversion of
propane in the absence of TCM (Fig. 1A). Under these condi-
3
H
8
) = 14.4 kPa, P(O
2
0
2 2 7 3 2 8
proximately twice those on Mg V O and Mg V O (Table 1).
Upon addition of TCM (P(TCM) = 0.17 kPa, Fig. 1B), the
conversion of propane (Fig. 1B) and the reaction rate (Table 1)
were improved, while the selectivity to propene was essential-
ly identical to that in the absence of TCM on three catalysts.
Although deactivation with increasing time-on-stream was
tions, the selectivities to propene on MgV
were essentially identical, while that to CO
rather greater than those on MgV and Mg
tion rate per unit of catalyst surface area on MgV
O
2 6
and Mg
on Mg
. The reac-
was ap-
2 2 7
V O
V O was
3 2 8
2
O
2 6
2 2 7
V O
2 6
O
Table 1. Reaction Rates per Unit of Catalysts Surface Area under Various Reaction
Conditions (P(C
3
H
8
) = 14.4 kPa, F = 30 mL/min, T = 723 K, and 0.75 h on-stream)
Rate/mol min− m−2
1
Catal.
Wt/g
2
P(O )/kPa
P(TCM)/kPa
−
−
−
−
−
−
−
−
−
−
−
−
6
6
6
6
6
6
6
6
6
6
6
6
Meta
Meta
Meta
Meta
Meta
Meta
Pyro
Pyro
Pyro
Pyro
Ortho
Ortho
0.4
0.4
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
1.2
1.2
4.1
4.1
4.1
4.1
4.1
8.2
4.1
4.1
4.1
8.2
4.1
4.1
0
0.17
0
12.5×10
19.8×10
11.0×10
16.1×10
23.6×10
23.5×10
5.3×10
12.4×10
14.5×10
27.8×10
6.9×10
0.17
0.34
0.51
0
0.17
0.34
0.34
0
0.17
12.2×10

S. Sugiyama et al.
Bull. Chem. Soc. Jpn., 75, No. 1 (2002) 183
sometimes observed in the oxidation of alkanes with TCM on
sonable that the activities on magnesium vanadates are greater
24
some catalysts, stable activities on three catalysts continued
up to 6 h on-stream. It is of interest to note that such an im-
provement of the activities with TCM for the oxidative dehy-
2 5
than that on V O due to advantageous hydrogen abstraction
from C on the anionic oxygen species. It is evident that the
3 8
H
anionic oxygen species contribute to the effects of TCM on
magnesium vanadates, although it should be noted that various
factors, partly described below, together with the anionic oxy-
gen species, undoubtedly contribute to the advantageous ef-
2 5
drogenation of propane was not observed on V O catalyst.
Since similar effects of the introduction of TCM were ob-
served on magnesium meta-, pyro-, and ortho-vanadates, it
may be suggested there are similar circumstances in those cat-
51
fects of TCM. It is of interest to note that a few V NMR
peaks are observed from MgV and Mg while just one
signal is observed from Mg , indicating that the effects of
5
1
alysts. It is of interest to note that V MAS NMR revealed
that the signal at approximately −550 ppm was similarly ob-
served from three catalysts together with those at −613 and
O
2 6
2 2 7
V O
3 2 8
V O
TCM may be evident from the synergism of several vanadate
species in the former two magnesium vanadates. Since, for the
three magnesium vanadates examined, the evident influence of
the introduction of TCM on the activity is observed on
−
565 ppm from MgV
Mg (Fig. 2). Volta et al. observed V MAS NMR at a
slower spinning rate of 2.5 kHz to detect the signals at −550
and −615 ppm for Mg and −550 ppm for Mg
while they could not obtain high-resolution NMR from
2 6
O and that at −606 ppm from
5
1
2 2 7
V O
V O
2 2 7
V O
3 2 8
Mg
2
V
2
O
7
and the largest reaction rate in the absence of TCM
, the remainder of this report will be
is obtained on MgV
2 6
O
6
MgV
O
2 6
due to a high quadrupolar interaction. Therefore the
concerned with these two magnesium vanadates.
Effects of the Partial Pressure of TCM. The conversion
of propane and the corresponding reaction rate increased with
5
1
vanadium species in three catalysts, for which a V NMR sig-
nal was observed at approximately −550 ppm, indicate that
the vanadium species possess similar electron densities. This
may contribute to the enhancement of the activities in the pres-
ence of TCM. On the other hand, a V NMR signal at −609
ppm was observed from V , whose activities were not im-
proved by the addition of TCM. The V NMR signal at −609
ppm observed from V indicates that vanadium species in
2 6 2 2 7
increasing P(TCM) on both MgV O and Mg V O , while the
selectivity to propene was essentially insensitive to P(TCM)
(Fig. 3 and Table 1). However, it should be noted that the in-
crements of the conversion of propane and the reaction rate
5
1
2 5
O
5
1
from P(TCM) = 0.17 to 0.34 kPa particularly on Mg
V O
2 2 7
2 5
O
were rather small, probably because the conversion of O
2
the oxide are more anionic than those in three magnesium van-
adates, from which the signal at approximately −550 ppm was
similarly observed. This may reveal that the nearest oxygen
species around the vanadium in magnesium vanadates are
reached approximately 100% at P(TCM) = 0.34 kPa. XRD
patterns of MgV employed in obtaining the results shown
in Fig. 3A but at P(TCM) = 0 and 0.17 kPa (Fig. 4A) were es-
sentially identical to that of fresh MgV , while that used at
P(TCM) = 0.34 kPa (Fig. 4B) showed that the catalyst
2 6
O
2 6
O
2 5
more anionic than that in V O . Therefore it seems to be rea-
2 6 2 2 7
Fig. 3. Effects of P(TCM) on MgV O and Mg V O at
7
23 K.
5
1
Fig. 2. V MAS NMR of V
C), and Mg (D).
2
O
5
(A), MgV
2
O
6
2 2
(B), Mg V O
7
Reaction conditions: as in Fig. 1 except P(TCM) but Wt =
0.5 g.
(
3
V
2
O
8

1
84 Bull. Chem. Soc. Jpn., 75, No. 1 (2002)
Propane Oxidation on Magnesium Vanadates
were insensitive to P(TCM) and were in agreement with refer-
ence patterns for Mg V O
2 2 7
(Fig. 4C). It is of interest to note
that the structure of Mg
2
V O used under the oxygen-limiting
2 7
conditions at P(TCM) = 0.34 kPa is retained even after oxida-
tion, indicating that the effect of the introduction of TCM on
2 2 7
the role of lattice oxygen in Mg V O may be different from
2 6
that in MgV O .
Effects of the Introduction of TCM on Lattice Oxygen.
It has been suggested by various research groups that the ease
of removal of lattice oxygen from magnesium vanadates ex-
plains the great activities for the oxidative dehydrogenation of
4
,35,36
propane.
MgV
of propane was observed in the absence of oxygen on both cat-
alysts. In the absence and presence of TCM on MgV (Figs.
A and B, respectively), the conversion of propane decreased
In order to examine the role of lattice oxygen in
V O
2 2 7
2
O
6
and Mg in the presence of TCM, the conversion
2 6
O
5
with increasing time-on-stream regardless of the addition of
TCM, while the selectivities to the partial oxidation products,
C H and CO, were evidently influenced by the introduction of
3 6
TCM. It should be noted that the conversion of propane in the
absence of TCM was greater than that in the presence of TCM.
In the absence of TCM with Mg (Fig. 5C), the conver-
V O
2 2 7
sion of C and the selectivity to C H decreased sharply and
3
H
8
3 6
increased, respectively, with increasing time-on-stream. In
contrast, the low conversion and the high selectivity to C
continued for 6 h on-stream in the presence of TCM on
Mg (Fig. 5D). These results on both magnesium vana-
dates appear to indicate that lattice oxygens in both MgV
and Mg directly contribute to the conversion of C
Furthermore, the contribution of the lattice oxygen to the con-
version of C is controlled by the introduction of TCM.
XRD patterns of MgV and Mg used without both ox-
ygen and TCM showed that both catalysts were completely
Fig. 4. XRD patterns of MgV
employed in obtaining the results shown in Fig. 3 but after
h on-stream.
A) and (B): MgV
kPa, respectively.
C): Mg used at P(TCM) = 0.34 kPa.
2 6 2 2 7
O and Mg V O previously
3
H
6
6
(
2 2 7
V O
2
O
6
used at P(TCM) = 0.17 and 0.34
2 6
O
(
V
2 2
O
7
2
V
2
O
3 8
H .
7
changed, probably due to the employment of this catalyst un-
der oxygen-limiting conditions. XRD patterns of Mg
previously employed in obtaining the results shown in Fig. 3B
3 8
H
2 2
V O
7
O
2 6
2 2 7
V O
Fig. 5. Effects of TCM on the conversion of C
3
H
8
2 2 2 2 7
in the absence of O on MgV O (A and B) and Mg V O (C and D) at 723 K.
Reaction conditions: Wt = 0.5 g, P(C
3
H
8
) = 14.4 kPa, P(O ) = 0 kPa, and P(TCM) = 0 for (A) and (C) and 0.17 kPa for (B)
2
and (D).
Symbols; Open circle = C
3
H
8
conversion. Closed circle = C
3
H
6
selectivity.
selectivity.
Open square = CO selectivity. Closed square = CO
2

S. Sugiyama et al.
Bull. Chem. Soc. Jpn., 75, No. 1 (2002) 185
Fig. 7. Effects of the chlorinated species on the surface of
the catalysts and/or in gas-phase at 723 K.
Reaction conditions: Wt = 0.5g, F = 30 mL/min, P(C
14.4 kPa, P(O ) = 4.1 kPa, and P(TCM) = 0.17 kPa.
Symbols; Circle = C
Squire = C
Closed symbols: Data with the chlorinated species on the
surface of the catalysts and in gas-phase.
3 8
H )
=
2
3
H
8
conversion.
3
H selectivity.
6
2 6 2 2 7
Fig. 6. XRD patterns of MgV O and Mg V O previously
employed in obtaining the results shown in Fig. 5 but after
h on-stream.
A) and (B): MgV
respectively.
C) and (D): Mg
respectively.
6
Open symbols:Data with the chlorinated species on the
surface of the catalysts.
(
2
O
6
used at P(TCM) = 0 and 0.17 kPa,
(
2 2 7
V O used at P(TCM) = 0 and 0.17 kPa,
Pretreatment with TCM. In order to separate the effects
of gaseous TCM from those of chlorinated species on the sur-
face of the catalysts, pretreatment effects of MgV
Mg with TCM were examined (Fig. 7). In Fig. 7, the
feedstream from 0 to 0.75 and from 2.0 to 3.25 h on-stream
contained C (14.4 kPa), O (4.1 kPa) and TCM (0.17 kPa)
diluted with He. In contrast, C (14.4 kPa) and O (4.1 kPa)
diluted with He were contained into the feedstream from 0.75
to 2.0 and from 3.25 to 4.5 h on-stream. Therefore closed
symbols show data both with the surface chlorinated species
and gaseous TCM, while open symbols show data just with the
2 6
O and
converted to other phases (Figs. 6A and C, respectively), while
MgV and Mg still remained in both catalysts after
propane conversion in the presence of TCM (Figs. 6B and D,
respectively). XRD patterns of Figs. 6A and C showed that
these catalysts after propane conversion without TCM consist-
2 2 7
V O
O
2 6
2 2 7
V O
H
3 8
2
H
3 8
2
ed of Mg1.5VO
and V (JCPDS 45-0946). Oxygen content calculated from
, MgO, and V are 42.3, 39.7, and 29.5 wt%, re-
spectively, and such values are evidently smaller that those
from MgV and Mg (43.2 and 42.7 wt%, respective-
ly). Therefore lattice oxygen in both MgV and Mg is
4
(JCPDS 19-0778), MgO (JCPDS 34-0615),
3 4
O
Mg1.5VO
4
3 4
O
surface chlorinated species on the catalysts. On MgV
7A), the conversions of C in the presence of TCM were al-
ways greater that those in the absence of TCM. However the
effect of the presence of TCM on the selectivity to C was
rather small. On Mg (Fig. 7B), the conversion of C
was similarly influenced by TCM, as observed on MgV
while the selectivity to C was rather insensitive to the pres-
2 6
O (Fig.
O
2 6
V O
2 2 7
3 8
H
O
2 6
2 2 7
V O
removed from the catalyst in the absence of TCM, while it re-
mains in the structure in the presence of TCM. XPS analyses
3 6
H
V O
2 2 7
3 8
H
of MgV O
2 6
and Mg V O
2 2 7
employed in propane conversion in
2 6
O ,
the presence of TCM revealed that no chlorinated species were
formed on the surface. It seems rather strange that the loss of
lattice oxygen from both magnesium vanadates is reduced by
TCM while no TCM residue appears in any form on the sur-
face of the catalysts. It is possible, of course, that a trace
amount of chlorinated species exists on the surface, which can-
not be detected by XPS.
3 6
H
ence or absence of TCM. This may indicate that the presence
of gaseous TCM, which controls the removability of lattice ox-
ygen, is important for the enhancement of the catalytic activi-
ties. The contribution of the surface chlorinated species to the
enhancement by TCM should not be overestimated in the
present systems.

1
86 Bull. Chem. Soc. Jpn., 75, No. 1 (2002)
Propane Oxidation on Magnesium Vanadates
Catal., 177, 343 (1998).
In conclusion, TCM controls the removability of lattice oxy-
gen in MgV
O
2 6
and Mg
2
V
2
O
7
, that is, redox behaviors of these
16 A. Khodakov, B. Olthof, A. T. Bell, and E. Iglesia, J. Cat-
al., 181, 205 (1999).
catalysts. This results in the enhancement of the activities of
both catalysts for the oxidative dehydrogenation of propane. It
is generally accepted that formation of surface chlorinated spe-
cies contributes to the enhancement of the activities for the ox-
idation of alkanes in the presence of TCM. However the
present results reveal that control of removability of lattice ox-
ygen in the catalysts with TCM seems to be important for ac-
tivity improvement.
1
7
P. Viparelli, P. Ciambelli, L. Lisi, G. Ruoppolo, G. Russo,
and J. C. Volta, Appl. Catal. A: Gen., 184, 291 (1999).
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8
1
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This work was partly funded by a Grant-in-Aid for Scientif-
ic Research No.13126215 to HH from the Ministry of Educa-
tion, Science, Sports and Culture, to which our thanks are due.
2
1
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(
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