X.-H. Lu et al. / Journal of Molecular Catalysis A: Chemical 396 (2015) 196–206
197
nickel-based Ni–Al catalysts are commonly used. However, these
inductively coupled plasma (ICP) analysis. Using a similar proce-
dure, nickel or other metals was impregnated onto the supports
inclusive of three SiO2 sources, ␥-Al O , SiO –Al O (1:1), TiO2
Ni–Al catalysts show a narrow activation temperature (generally
◦
1
30–180 C), and a low selectivity of fully hydrogenated alicyclic
2
3
2
2
3
amines. The drawbacks are mainly correlated with high nickel
content and low dispersion on the carrier, so reducing the nickel
content and improving the effective utilization are of particular
importance. Meanwhile, in the catalytic hydrogenation reaction,
the solvent has a great influence on the reaction rate and selectivity.
Some studies have concluded that [37,38], for the similar struc-
tures solvent, the solubility of hydrogen in the solvent may affect
the rate of heterogeneous catalytic hydrogenation, and the solvent
may affect the adsorption of hydrogen on the catalyst surface in the
catalytic hydrogenation reaction.
or activated carbon. Finally, the dried samples were calcined at
given temperatures for 3 h in the flowing air, and then reduced by
hydrogen at desired temperatures for 3 h. The resultant catalysts
were designated as n%M/SiO -1–3 (silica sources: 1—aerosil-200
2
silica, 2—Ludox AS-40 colloidal silica, 3—Ludox HS-40 colloidal
silica), n%M/Al O , n%M/SiO –Al O , n%M/TiO , n%M/C, where n%
2
3
2
2
3
2
was the weight percent of metals. The 10%Ni/SiO -1 modified with
2
four modifiers (a—sesbania powder, b—activated carbon, c— n-
octyltrimethylammonium bromide, d—glucose) was designated as
10%Ni/SiO -1a, -1b, -1c, -1d, respectively. The XRF results have
2
To date, only one report has approached highly selective ‘one-
step’ catalytic hydrogenation from nitro aromatics to alicyclic
amines [39], which can completely skip the synthesis, separa-
tion and transformation of aromatic amine intermediates, and
meet the requirements of energy-saving green chemistry. The
present work reports the synthesis, structure and catalytic activ-
ity of the supported Ni catalysts for highly efficient one-step
liquid phase hydrogenation of nitro-aromatic compounds with
nitro groups and aromatic rings. The present study is focused on
the catalytic hydrogenation from 1,5-dinitronaphathlene to 1,5-
diaminodecahydronaphathlene. Under optimal conditions, almost
shown that the Ni content of all 10%Ni/oxides catalysts prepared
by impregnation method are in the range of 9.95–10.0 wt%.
2.3. Characterization of catalysts
The X-ray diffraction (XRD) analysis was carried out using a
Rigaku D/MAX-IIIC diffractometer with Ni-filtered Cu-K␣ radiation
operating at 30 kV and 25 mA. The scanning conditions were as fol-
◦
◦
lows: divergence slit, 1.0 ( ); scattering slit, 1.0 ( ); receiving slit,
◦
◦
0.3 (mm); scanning range, 5–65 2ꢀ; scanning speed, 2 /min.
Autosorb-1 was used to determine the N2 adsorption–desorption
properties of the samples. The Brunauer–Emmett–Teller (BET) spe-
cific surface area was calculated using the BET equation in the rela-
tive pressure between 0.05 and 0.25. The Barrett–Joyner–Halenda
(BJH) method was used to calculate the pore volume. Prior to the
1
00 mol% of the substrate conversion with a high selectivity of the
product up to 95.3% is achieved over the most active catalyst, which
is encouraging. Furthermore, some factors affecting the reaction
are revealed through conducting a number of reactions and wide
characterizations.
◦
measurements, the samples were degassed at 300 C under a vac-
−
2
uum of 10 mbar for 10 h. The morphology and size of crystals
were imaged with a JEOL JSM-6510A scanning electron micro-
scope (SEM). The temperature programmed H2 reduction (TPR)
2
. Experimental
was carried out in a N2 flow of 50 ml/min (10 vol% H ), from room
temperature to 600 C at a heating rate of 10 C/min. A thermal con-
ductivity detector (TCD) was used to monitor the H2 consumption.
2
2
.1. Materials
◦
◦
Raney Ni (99.5%), Ni (NO ) ·6H O (98%), RuCl ·xH O (Ru
3
2
2
3
2
Before starting the TPR procedure, the sample was pretreated at
4
8–42%), PdCl (Pd 59–60%), Al O (98%), TiO2 (99%), C (acti-
2 2 3
◦
2
00 C for 30 min in a N flow of 100 ml/min and then cooled down
2
vated carbon) (97%) were purchased from Shanghai Aladdin
Chemical Co. The sesbania powder (98%) was purchased from
Shangdong Dongming Sesbania Gum Factory and n-octyltrimethyl
ammonium bromide (98%) was purchased from Wuhan wdsil-
icone Co. The main reagent used in the hydrogenations were
to room temperature. The X-ray photoelectron spectroscopy (XPS)
spectra were recorded on a VG ESCALAB MK II spectrometer, using
a monochromatic Mg-K␣ radiation, operating at a constant trans-
mission energy pass (80 eV). The C1s photoelectron peak (binding
energy of 284.6 eV with an accuracy of ± 0.05 eV) was used as
an energy reference. Shirley background was subtracted in the
least-square fitting. The peak shape was fixed to a mixture of 20%
Lorentzian and 80% Gaussian with an asymmetric parameter of 0.
1
,5-dinitronaphthalene (99.0%, Shanghai) was directly used as
received. The freshly distilled solvents included methanol, dioxane,
ethyl acetate, tetrahydrofuran (THF) and cyclohexane.
2.2. Preparation of catalysts
2.4. Catalytic activity test
A solution of Ni (NO ) ·6H O or precious metal chlorides was
The
catalytic
one-step
hydrogenations
of
1,5-
3
2
2
impregnated onto various supports like ␥-Al O , TiO , activated
dinitronaphthalene(1,5-DNN)with nitro groups and aromaticrings
to 1,5-diaminodecahydronaphthalene (1,5-DADHN) were carried
out in a batch autoclave (100 ml) under desired temperatures
and H2 pressures. As illustrated in Scheme 1, the hydrogenated
products were mainly consisted of 1,5-diaminonaphthalene (1,5-
DAN), 1,5-DADHN, and others (some cracked byproducts). The
reactant 1,5-DNN (1.0 g) was dissolved in the solvent (methanol,
dioxane, ethyl acetate, THF or cyclohexane) (9.0 g) under magnetic
stirring (the stirring rate of 250 r/min), to which the reduced
catalyst (100 mg) was added. Once the desired temperature and
pressure was reached, the reaction was thought to start. Several
hours later, the reaction was stopped, then the reactor was cooled
down to ambient temperature and H2 was released. The solid
catalyst was then recovered by filtration, washed several times
with tetrahydrofuran (THF) and dried for next use. The liquid
filtrate was quantitatively analyzed by GC-2010 equipped with
a flame ionization detector (FID) and a DB-1 capillary column
2
3
2
carbon, three SiO2 sources (aerosil-200 silica, Ludox AS-40 and
Ludox HS-40 colloidal silica), and modified aerosil-200 silica with
modifiers. Note that ␥-Al O3 was obtained by calcining pseu-
2
◦
doboehmite precursor in air at 550 C for 2 h. The supported
catalysts were prepared through the following procedure. Typ-
ically, 2 g of aerosil-200 silica was dispersed into the solution
consisted of Ni (NO ) ·6H O (1.082 g) and distilled water (30 g).
3
2
2
Then, to the above mixture, one solution of 0.27 g sesbania pow-
der dissolved in 20 ml of ethanol was slowly dripped while stirring.
◦
Subsequently, the resulting mixture was heated to 70–80 C accom-
panied by stirring, until water had been completely evaporated
◦
◦
◦
off. The green solid was dried at 100 C for 12 h, calcined at 400 C
for 3 h in the flow of air, and then reduced by hydrogen at 400 C
for 3 h in a tubular reactor. The resultant catalyst was desig-
nated as 10%Ni/SiO -1a, in which the nickel content was 10 wt%
2
determined by X-ray fluorescence (XRF) analysis, or 10 wt% by