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Chemistry Letters Vol.35, No.1 (2006)
New Class of Catalysts for the Ammoxidation of Propane to Acrylonitrile
over Nickel–Molybdenum Mixed Nitrides
Huimin Zhang, Zhen Zhao,ꢀ Chunming Xu, and Aijun Duan
State Key Laboratory of Heavy Oil Processing, China University of Petroleum, Beijing, 102249, P. R. China
(Received September 22, 2005; CL-051215; E-mail: zhenzhao@cup.edu.cn)
Nickel–molybdenum mixed nitride catalysts were first re-
hot distilled water, and dried in an oven at 383 K (12 h). The re-
sulting solid was ground by hand and heated at 573 K for 2 h,
then ground and calcined in air again at 773 K for 2 h. The ma-
terials were used in the subsequent synthesis of Ni–Mo bimetal-
lic nitrides.
ported for the ammoxidation of propane to acrylonitrile. It was
found that the mixed nitrides exhibited high activity and selec-
tivity to acrylonitrile. The mixed nitride catalyst with 1.0 of
Ni/Mo atomic ratios showed the best catalytic properties for
propane ammoxidation. The highest yield of acrylonitrile was
28.5% at the propane conversion of 68.4% at 773 K.
The Ni–Mo mixed nitride catalysts and pure Ni3Mo3N cat-
alyst were prepared by temperature-programmed reaction of the
precursors obtained above with ammonia using a fixed-bed mi-
croreactor, a quartz tube with an inner diameter of 15 mm. Typ-
ically, about 3 g of precursor particles with 20–60 mesh was
heated under flowing ammonia gas (400 mL/min). The temper-
ature was increased from room temperature to 573 K in 28 min,
and from 573 to 973 K in 360 min; finally, the temperature was
maintained at 973 K for 120 min. The nitrided Ni–Mo samples
were cooled to room temperature in flowing ammonia gas and
then passivated in a stream of 1% O2/N2 (v/v) for 12 h. Pure
Mo2N catalyst was also prepared by temperature-programmed
reaction of MoO3 and NH3.
Activity tests were carried out in a laboratory stainless steel
fixed-bed reactor operating at atmospheric pressure. One g of
catalyst was loaded, shaped in particles having size ranging from
20 to 40 mesh. The following reaction conditions were used: the
feed composition 2 mol % propane, 15% ammonia, 15% oxygen,
remainder helium; the total flow rate of 14.5 mL/min. The reac-
tor outlet was kept at 443 K. Feed and products were analyzed
on-line using a gas chromatograph (SP-2100), equipped with
FID detector and a methaniser. A Porapak Q column, 60–80
mesh (2 m ꢁ 3 mm), was used for the seperation of CO, CO2,
C2H4, C3H6, C3H8, acetonitrile, acrolein, and acrylonitrile.
The precursors and the Ni–Mo mixed nitrides were
analyzed by the X-ray diffraction (XRD), using a Shimadzu
XRD-6000 diffractometer with a Cu Kꢀ radiation source for
phase identification.
Figure 1 shows the X-ray diffraction patterns of the precur-
sors with various Ni/Mo ratios. The crystalline phases of the
precursors were mainly composed of MoO3, verified by the
peaks at 2ꢁ ¼ 23:7, 25.8, and 27.4ꢂ (JCPDS Card 85-2405)
and NiMoO4, verified by the peaks at 2ꢁ ¼ 28:8, 32.6, and
43.9ꢂ (JCPDS Card 33-0948). Figure 2 shows X-ray diffraction
patterns for the Ni–Mo nitride catalysts with different Ni/Mo
atomic ratios prepared under the above established conditions.
As shown in Figure 2, the diffraction peaks of MoO3 and
NiMoO4 disappeared after the precursors were nitrided. The
crystalline phases of the prepared catalysts were mainly com-
posed of Mo2N and Ni3Mo3N. The XRD peaks of Mo2N were
detected at 2ꢁ ¼ 26:0, 37.8, 43.9, and 63.3ꢂ;13,14 the diffraction
peaks at 2ꢁ ¼ 40:9, 45.5, and 72.8ꢂ could be ascribed to
Ni3Mo3N.13
Direct conversion of alkanes to produce high value products
for the chemical industry constitutes an arduous and stimulating
scientific and technological challenge. Among the most signifi-
cant industrial applications in this field is the production of
acrylonitrile (ACN) through the propane ammoxidation process.
The acrylonitrile, as one kind of the most important chemical in-
termediates, is used extensively in the manufacture of fibers,
polymers, such as styrene–acrylonitrile (SAN) and acryloni-
trile–butadiene–styrene (ABS), and other valuable chemicals.
Many catalysts have been tested for the ammoxidation of
propane to acrylonitrile, and the most effective ones fall into
two main classes:1 they are either VMoxMy mixed oxides (M
is most often Bi or Te) or VSbxMy mixed oxides (M are elements
used as a promoter such as W, Te, Nb, Sn, Bi, Al, and Ti). The
highest acrylonitrile yields to date (about 60%)2–4 have already
been obtained on laboratory scale from propane using a Mo–
V–Nb–Te–Ox catalyst among VMoxMy mixed oxides. V–Sb
mixed oxides also have been reported to yield 34–40%
ACN.5,6 In addition, several other mixed oxides, such as Bi–
Mo,7 P–V,8 and Fe–Sb,9 are also active in the conversion of pro-
pane to acrylonitrile. However, the yield of ACN does not ex-
ceed 20%.10 With the exception of the above mixed oxides, a
few other catalytic materials are used in the propane ammoxida-
tion to acrylonitrile. Recently, the vanadium–aluminum oxyni-
trides have been first reported for the propane ammoxidation
process by Florea et al.,11 and the catalysts yield up to 30%
ACN,12 which present the opportunity for the mixed metal
oxynitrides or nitrides used in the ammoxidation of propane to
acrylonitrile.
This paper is the first to report that the Ni–Mo mixed nitride
catalysts were used in the process of propane ammoxidation to
acrylonitrile.
The Ni–Mo oxides were used as precursors for Ni–Mo ni-
tride catalysts. The precursors were prepared by the co-precipi-
tation from a solution of nickel nitrate to which a solution of am-
monium molybdate tetrahydrate was added stepwise. Tempera-
tures of co-precipitation were 323 K. The mixed oxide precur-
sors with various Ni/Mo ratios and the pure NiMoO4
precursor were obtained by varying pH values of the solution
during precipitation and aging periods. The Ni–Mo mixed oxides
were obtained at a pH of 5.5 and pure NiMoO4 was obtained at a
pH of 7.5. The obtained hot precipitate was filtered, washed with
The results of propane ammoxidation over the prepared cat-
alysts at 773 K are listed in Table 1. The pure Mo2N or Ni3Mo3N
catalyst did not show high activity for propane ammoxidation
Copyright Ó 2006 The Chemical Society of Japan