Plasmochemical preparation of NiO-Al2O3 catalysts

Article abstract of DOI:10.1023/A:1011658000578

NiO-Al₂O₃ catalysts were prepared by hydrogen bombardment of aluminum hydroxide impregnated with nickel chloride. After bombardment for 2 h, the material was found to contain nickel aluminum spinel with a heavily distorted structure.

Full text of DOI:10.1023/A:1011658000578

Inorganic Materials, Vol. 37, No. 9, 2001, pp. 947–949. Translated from Neorganicheskie Materialy, Vol. 37, No. 9, 2001, pp. 1114–1116.
Original Russian Text Copyright © 2001 by Normatov, Shermatov, Mirsaidov.
Plasmochemical Preparation of NiO–Al O Catalysts
2
3
I. Sh. Normatov, N. Shermatov, and U. Mirsaidov
Nikitin Institute of Chemistry, Academy of Sciences of Tajikistan,
ul. Aini 299/2, Dushanbe, 734063 Tajikistan
Received June 21, 2000; in final form, March 14, 2001
Abstract—NiO–Al O catalysts were prepared by hydrogen bombardment of aluminum hydroxide impreg-
2
3
nated with nickel chloride. After bombardment for 2 h, the material was found to contain nickel aluminum
spinel with a heavily distorted structure.
INTRODUCTION
with hydrogen for 40 min at L/d = 30. The material was
found to consist of boehmite and nickel oxide, as also
evidenced by the IR spectrum, which showed absorp-
Stimulation of chemical reactions by physical
means is widely used in the technology of inorganic
materials and makes it possible to notably raise the tions at 420, 460, 560, and 1080 cm , attributable to
–
1
reaction rate. Among the underlying mechanisms of the
physicochemical processes involved is the generation
of various structural defects [1, 2], which is of particu-
lar importance in catalysis and catalyst fabrication. For
example, the presence of a distorted spinel phase in
Fe O –Al O materials enhances their catalytic activity
NiO and AlO(OH) (Fig. 3).
1
2
3
2
3
for oxidation of ammonia [3].
H O
The purpose of this work was to prepare NiO–Al O
2
2
3
catalysts by plasma synthesis.
EXPERIMENTAL
Al(OH) supports were prepared as described in [4].
3
2
The specific surface area of the supports (130 m /g)
was determined by oxygen adsorption measurements in
vacuum, using an electronic balance with a sensitivity
–
5
of 5 × 10 g.
After impregnation with a nickel chloride solution
and drying, the support was transferred to the holder of
an rf plasma reactor (Fig. 1).
d
2
L
Atomic hydrogen was generated by passing hydro-
gen gas through an rf discharge between two elec-
trodes, one connected to the feeder of an LGD-12 rf
generator (1.275 GHz), and the other grounded. The
distance between the center of the discharge region and
the support could be varied by moving the latter. In this
way, we were able to vary the activation power. The
support was bombarded with hydrogen atoms at L/d =
H O
2
3
1
5 and 30.
The support temperature during bombardment was
monitored by two Chromel–Alumel thermocouples.
RESULTS AND DISCUSSION
Fig. 1. Schematic of the experimental setup: (1) quartz reac-
tor, (2) rf generator, (3) holder; L is the distance from the
center of the discharge region to the support, and d is the
reactor diameter.
Figure 2a shows the x-ray pattern of the support
impregnated with nickel chloride and then bombarded
0
020-1685/01/3709-0947$25.00 © 2001 MAIK “Nauka/Interperiodica”

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48
NORMATOV et al.
(a)
4
00
600
800
1000
1200
Wavenumber, cm–1
Fig. 3. IR absorption spectrum of the support impregnated
with nickel chloride and then bombarded with hydrogen for
4
0 min.
NiAl O
AlO(OH)
2
4
NiO
γ-Al O
2
3
(b)
(c)
6
00
700
800
900
Wavenumber, cm–1
Fig. 4. IR absorption spectrum of the support impregnated
with nickel chloride and then bombarded with hydrogen for
1
20 min.
Hydrogen bombardment leads to the dehydration of
aluminum hydroxide and boehmite formation. Water
absorption by nickel chloride, promoted by hydrogen
bombardment, leads to the formation of nickel hydrox-
ide. The thermal energy supplied by hydrogen activates
water removal, leading to the formation of NiO.
1
0
20
30
40
θ, deg
The x-ray pattern shown in Fig. 2a contains reflec-
tions from orthorhombic boehmite with lattice parame-
ters a = 4.41 ± 0.05 Å, b = 9.41 ± 0.05 Å, and c =
Fig. 2. X-ray pattern of the support impregnated with nickel
chloride and then bombarded with hydrogen for (a) 40 min at
L/d = 30, (b) 80 min at L/d = 15, and (c) 120 min at L/d = 15.
2
.845 ± 0.05 Å.
After hydrogen bombardment at L/d = 15 (increased
Therefore, the process can be described by the reac- hydrogen flow and, accordingly, processing power), the
tion scheme
material consisted of NiAl O and γ-Al O (Fig. 2b).
2 4 2 3
Hi
Clearly, the formation of γ-Al
AlO(OH)
spinel originates from the diffusion of Ni atoms to the
distorted structure of boehmite.
2
O
3
is the final stage of
∑i
the process Al(OH)3
Al O . The
2
3
Al(OH) + NiCl
AlO(OH) + NiO + 2HCl,
3
2
where
H indicates the atomic hydrogen flow.
i
∑
INORGANIC MATERIALS Vol. 37 No. 9 2001

PLASMOCHEMICAL PREPARATION OF NiO–Al O CATALYSTS
949
2
3
The increased hydrogen flow leads to the reduction
Increasing the hydrogen flow leads to rapid reduc-
of nickel chloride. The energy supplied by bombard- tion of nickel chloride and Ni indiffusion into the dis-
ment enhances the mobility of nickel atoms. The diffu- torted structure of boehmite. This process and the trans-
sion of Ni and the transformation of boehmite into formation of boehmite into γ-Al O under bombard-
2
3
γ-Al O culminate in the formation of a strongly dis- ment culminate in the formation of a heavily distorted
2
3
torted spinel phase with a = 7.88 Å.
spinel phase.
Increasing the bombardment duration to 120 min
increases the amounts of NiO, γ-Al O , and NiAl O
REFERENCES
2
3
2
4
(
Fig. 2c).
1
2
3
. Boldyrev, V.V., Voronin, A.L., Lyakhov, N.Z., and Kani-
mov, B.K., Inorganic Reactions in High-Power Electron
Figure 4 shows the IR absorption spectrum of the
Beams, Zh. Vses. Khim. O–va. im. D. I. Mendeleeva,
support impregnated with nickel chloride for 8 h and
then bombarded with hydrogen for 120 min. The bands
at 600 and 880 cm are due to γ-Al O , and the band at
1
990, vol. 35, no. 5, pp. 540–545.
. Mekhanokhimicheskii sintez v neorganicheskoi khimii
(Mechanochemical Synthesis in Inorganic Chemistry),
Avvakumov, E.G., Ed., Novosibirsk: Nauka, 1991,
pp. 5–32.
. Eliseeva, A.S., Belov, B.A., Pechkin, S.V., et al., Fine-
Particle Metal Oxides: Preparation, Properties, and
Application in Catalysts, Ceramics, and Composites,
Trudy mezhdunarodnogo simpoziuma po teoreticheskoi i
prikladnoi khimii (Proc. Int. Symp. on Theoretical and
Applied Chemistry), Riga: Zinatne, 1991, pp. 165–167.
–
1
2
–
4
3
25 cm–1 is characteristic of AlO tetrahedra in the
8
structure of nickel aluminum spinel.
CONCLUSION
Our IR absorption and x-ray diffraction data demon-
2
mixtures leads to the formation of orthorhombic boeh-
mite at an intermediate stage.
strate that hydrogen bombardment of NiCl + Al(OH)3
4. Karyakin, Yu.V. and Angelov, I.I., Chistye khimicheskie
veshchestva (Pure Chemical Substances), Moscow:
Khimiya, 1974, p. 26.
INORGANIC MATERIALS Vol. 37 No. 9 2001