Surface Properties of Ni/MgO Catalysts
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frequently used catalyst with high activity for the
industrial production of primary amines. However, the
use of Raney nickel may have some disadvantages. For
instance, the preparation of Raney nickel may consume a
great deal of energy and cause environmental pollutions,
since Ni–Al alloy must be prepared first and Al in the
alloy must be leached by a concentrated base. Moreover,
Raney nickel is pyrophoric, and it is usually difficult to
use in a fixed-bed reactor. Thus, it is desirable to
develop more active and selective catalysts for the
hydrogenation of nitriles to amines [3, 13–15].
agglomerations of small particles may occur in the
co-precipitates during drying and calcination procedures,
owing to the high surface tension and chemical bonding
among hydrated particles. Such coagulations may be
avoided in the supercritical fluid drying process, by
removing water at low surface tensions. However, the
supercritical fluid process is expensive, hazardous and
incompatible with many processing apparatuses [27].
Alternatively, a solvent replacing technique of drying
(usually using n-butanol) might be used to effectively
reduce the possibility of formation of chemical bonds
between particles and thus to prevent the formation of hard
agglomerates [28–30]. In particular, this technique has the
advantages of low cost and wide universality.
Supported nickel has been used for the hydrogenation
of nitriles to amines. Silica, silica-alumina, alumina,
zirconia, titania, magnesia, ceria, and carbon were
reported as supports for nickel catalysts [14–20]. Sup-
ports may have strong effect on the activity and selec-
tivity of supported nickel for the hydrogenation of
nitriles to amines, due to their different surface areas,
pore volumes and acid/base properties. For example, the
dispersion of nickel usually increases with surface areas
and the porosity of a support may affect the dispersion
of nickel, resistance to sintering and diffusion of reac-
tants and products [1]. The surface acidity of a support
may promote the formation of secondary and tertiary
amines. The addition of a basic material in the reaction
system may weaken the surface acidity and inhibit the
formation of secondary and tertiary amines. Industrially,
ammonia is usually added to improve the selectivity to
primary amines. The promoting effect of NH3 may come
from: (1) a thermodynamic influence on the reaction
between primary imine and amine, leading to secondary
imine and NH3, (2) a modification of the electronic
properties of the catalytic metal, and (3) a selective
poisoning of surface acid sites responsible for the cou-
pling reactions to by-products [1, 12, 21, 22]. The
decrease of surface acidity of the support usually favors
the formation of primary amines [16, 17, 21–23]. How-
ever, controversies exist in the literature as to the effect
of support on the hydrogenation of nitriles to amines.
Some authors believed that the nature of supports did not
have a significant effect on the selectivity of hydroge-
nation of nitriles [10, 24, 25]. Medina et al. [22] studied
the hydrogenation of acetonitrile over the Ni/MgAlO
catalysts prepared from the Ni/Mg/Al lamellar double
hydroxides (LDH). They found that the introduction of
Mg decreased the surface acidity and increased the
selectivity to the primary amine.
In this work, we prepared the Ni/MgO catalysts with
high loadings. N-butanol was used to replace water in
the samples during the drying process so that water may
be removed from the solution of n-butanol, rather than
removed directly from the samples. Varies techniques
such as X-ray diffraction (XRD), H2 temperature pro-
grammed reduction (TPR), transmission electron
microscopy (TEM), and H2/O2 adsorption were used to
characterize the reducibility, dispersion and particle sizes
of supported nickel. The surface acid/base properties
were determined by the microcalorimetric adsorption of
NH3 and CO2. The microcalorimetric adsorption of H2,
CO and acetonitrile were performed to determine the
properties of nickel surfaces in the catalysts. The cata-
lysts were evaluated by the liquid-phase hydrogenation
of lauronitrile to dodecylamine and the fixed-bed
hydrogenation of toluene to cyclohexane.
2 Experimental
2.1 Preparation of Catalysts
Ni/MgO catalysts with 60% Ni (weight percent) were
prepared by the co-precipitation method. Specifically, an
aqueous solution containing required amount of nickel and
magnesium nitrates was co-precipitated with a solution
containing a slightly excess of sodium carbonate. A green
precipitate was formed, filtered and washed thoroughly by
de-ionized water. Then, the filter cake was divided into two
parts. One was dried directly in an oven at 393 K over-
night, and denoted as Ni/MgO. The other one was added
into n-butanol, heated at 353 K for 12 h and then dried in
an oven at 393 K. The catalyst treated with n-butanol was
denoted as Ni/MgO-B.
Industrial catalysts are mostly high surface area solids,
on which active components are highly dispersed in the
form of small particles [26]. The dispersion of metals on
supports is affected by preparation method and treatment
conditions. Chemical co-precipitation is a widely used
method for preparing supported metal catalysts. However,
A support MgO-B and a catalyst Ni/SiO2-B (60% Ni)
were also prepared for comparison with the n-butanol
treatment procedure. The Raney Ni was an industrial cat-
alyst used by the Feixiang Chemicals Co., Ltd. in China.
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