4
32
J Am Oil Chem Soc (2016) 93:431–443
Guerrero-Perez et al. reported the direct conversion of
in three crystallographic forms: α-Bi Mo O , β-Bi Mo O
9
2
3
12
2
2
glycerol to ACN in the presence of ammonia and oxygen
over mixed oxides containing V, Sb and Nb. The highest
ACN yield of 48 % is the subject of some debate [9, 10].
With respect to the possibility of choosing the catalyst and
reaction conditions independently, Liebig et al. studied the
two step conversion of glycerol to ACN with AC as an inter-
mediate. They obtained an overall yield in ACN of 40 % at
full glycerol conversion in an integrated tandem reactor pro-
cess [5]. Whereas, the first step (the dehydration of glycerol
to AC) has been widely studied [3], very little attention has
been paid so far to the AC ammoxidation reaction.
and γ-Bi MoO . However, there is no agreement on which
2 6
phase is active and selective for the ammoxidation reaction.
Kolchin et al. [19] and German et al. [20] stated that the
activity follows the β > α > γ sequence for propene oxidation
and ammoxidation, while Monnier and Keulks [21] claimed
the order is γ > β > α (for propene oxidation), whereas Burr-
ington and Grasselli [22] found that this order is β = α > γ
for selective oxidation of propene. Furthermore, Carson et
al. [23] suggested that there is a synergy effect between the α
and the γ phases leading to better activity and selectivity for
an intimate equimolar mixture.
A few AC ammoxidation catalysts are known in the litera-
ture. However, considering a tandem reaction with glycerol
dehydration as the first step, the catalyst of the second step
should be—at least—water-tolerant. The As–Fe–O, Fe O –
Among the several compositions of multicomponent
Bi–Mo–Ox catalysts tested for propylene ammoxidation to
acrylonitrile, Co Ni Fe BiK P Mo O with silica
4.5 2.5
3
0.07 0.5
12 55
(17.5 wt%) as a binder is reported to show a high activity
for acrylonitrile production with 80 % yield [18]. Therefore,
we focused in the present study on the ammoxidation of AC
to ACN over a multicomponent bismuth molybdate cata-
lyst with the above composition. This MC catalyst contains
mainly two kinds of promoters, namely (1) bivalent metals,
i.e., Co and Ni and (2) a trivalent metal, i.e., Fe. Therefore,
to study the effects of bivalent and trivalent metal cations,
a series of multicomponent (MC) catalysts was synthesized
and screened for the AC ammoxidation reaction to ACN.
Furthermore, the reaction parameter optimization was per-
formed using the design of experiments methodology.
2
3
Bi O –P O , and Fe–Sb–O mixed oxides were tested for AC
2
3
2 5
ammoxidation in the presence of water. The As–Fe–O mixed
oxide catalyst gave the highest ACN yield of 87.1 % at 400 °C
[11]. However, the use of arsenic should be definitely avoided
in an industrial process due to obvious toxicity issues.
Studying the ammoxidation reaction, Oka et al. [12]
found an AC conversion rate 1000 times higher than that
of propylene at 400 °C over a Fe O –Bi O –P O catalyst
2
3
2
3
2
5
in the presence of 51 % water (exhibiting a 40 % yield of
ACN from AC). Liebig et al. reported a Fe–Sb–O catalyst
for the AC ammoxidation reaction. The highest yield of
3
6 % in ACN was reported at 400 °C with around 86.8 %
water in the feed [5].
With respect to the relatively low yields (<40 %)
obtained in the ammoxidation of AC in the presence of
water over specifically designed catalysts, we decided to
focus our study on the multicomponent (MC) BiMoOx-
type catalysts. This kind of catalyst is well-known for its
high performances in the oxidation and ammoxidation of
olefins [13–15]. Bismuth phosphomolybdate was the first
multicomponent catalyst of this family commercialized
by SOHIO for propylene ammoxidation, with an ACN
yield of 65 % at full conversion. Since the initial commer-
cialization, several generations of improved catalysts with
enhanced yields were developed by addition of promot-
ers such as trivalent transition metals (especially Fe) [16],
bivalent transition metals (i.e., Co and Ni) [17] and alkalis
Experimental Section
Catalyst Synthesis
The multicomponent Bi–Mo catalyst has as a general for-
II III
II
mula M M BiMo O where M is a bivalent metal and
M
7
3
12
x
III
is a trivalent metal. Therefore, the catalysts were syn-
thesized according to two groups: group (1) with different
II
M cations such as Co, Ni and Mg and group (2) with dif-
III
ferent M cations such as Fe, Cr and Al.
These multicomponent catalysts were prepared accord-
ing to the co-precipitation method described in SOHIO pat-
ent [18] and their theoretical compositions are summarized
in Table 1.
(
notably K) [18].
A typical synthesis procedure was as follows:
Despite their high activity and selectivity in oxidation/
Bi(NO ) ·5H O (Sigma Aldrich) was dissolved in a 5 M
3
3
2
ammoxidation reactions, it is still not clear how multicom-
ponent bismuth molybdate catalysts show such high perfor-
mances, due to their complex compositions and structures. It
is known that these multicomponent catalysts comprise three
major parts: the first one is bismuth molybdate, the second
nitric acid solution at room temperature. When all the bis-
muth nitrate was dissolved, the appropriate amounts of
Ni(NO ) 6H O (Fluka), Co(NO ) 6H O (Sigma Aldrich),
3
2·
2
3 2·
2
and Fe(NO ) 9H O (Acros Organics) were added to the
3
2·
2
solution. In a second flask, the appropriate amount of
(NH ) Mo O 4H O (Sigma Aldrich) was dissolved in
3+
one is the trivalent metal molybdate (Fe ) and the third one
is a mixture or a solid solution of divalent metal molybdates
4
6
7
27·
2
80 mL of water with minimum heating at 50 °C before the
appropriate amount of KNO (Sigma Aldrich) and H PO
4
2
+ 2+ 2+
(
of Co , Ni or Mg ) [14, 15]. Bismuth molybdate exists
3
3
1
3