2
H. Pan et al. / Journal of Molecular Catalysis A: Chemical 399 (2015) 1–9
autoclave and heated at 493 K for 8 h, and then further purified by
CHO
NO2
CH2OH
NH2
Pt Catalyst
298 K, Solvent, H2
twice solvothermal treatment in DMF (N,N-dimethylformamide) at
resulting green powder was finally dried overnight at 373 K in oven
for further use.
R
R
The 5 wt.% Pt/MIL-101 catalyst was prepared via a facile impreg-
nation method [24]: MIL-101 was impregnated with an ethanolic
solution containing H2PtCl6 and stirred for 4–6 h. Then, the mix-
ture was evaporated to remove excess solvent, followed by drying
at 373 K overnight. The Pt precursor was reduced in an aqueous
solution of sodium formate at 368 K for 2 h and then washed by
plenty of water to remove chlorine anion. Finally, the sample was
dried at 373 K overnight for further use. The 35AS was prepared
using an ultrasonic impregnation method according to Ref. [38].
Procedure for preparing the 5 wt.% Pt/35AS catalyst was similar to
that of the Pt/MIL-101 catalyst.
Pt Catalyst
R
R
Scheme 1. Liquid-phase hydrogenation of benzaldehyde, nitrobenzene and their
derivatives with Pt/MIL-101 or Pt/35AS catalyst.
which were constructed by the link of terephthalic acid and the ver-
port [8,24–36]. For instance, Au nanoparticles, Pd nanoparticles, Pt
nanoparticles and some bimetallic metals supported on MIL-101
exhibited good performances in hydrogenation [8,24–27], oxida-
In our previous work, Pt/MIL-101 catalyst was proved to be effi-
cient and recyclable in asymmetric hydrogenation of ␣-ketoesters
after chirally modified with cinchona alkaloids and also showed
comparable performance to commercial Pt/C and Pt/Al2O3 catalysts
[24].
The other concern is a kind of inorganic mesoporous com-
posites, Al2O3@SBA-15, which was obtained by coating alumina
inside mesoporous channels of SBA-15 through different meth-
ods. Al2O3@SBA-15 composites can not only take advantage of
mesoporous materials SBA-15 with large specific surface area and
uniform mesopore channel, but also exhibit properties not found
in Al2O3 alone. To be most important, Al2O3@SBA-15 supported Pt
catalysts have been proved to be superior to pristine Al2O3 sup-
ported one in enantioselective hydrogenation of ␣-ketoesters after
chirally modified with cinchona alkaloids as well [37,38].
extend application of the Pt/MIL-101 and Pt/35AS (35AS denotes
the Al2O3@SBA-15 composites where Al2O3 loading is 35 wt.%)
catalysts in liquid-phase hydrogenation of nitrobenzene and ben-
zaldehyde and their derivatives (Scheme 1). Influences of support
and solvent on catalytic performance were investigated. Mainly due
to high hydrophobicity of MIL-101, the Pt/MIL-101 catalyst was
more active than the Pt/35AS catalyst in water for the liquid-phase
hydrogenation of nitrobenzene, benzaldehyde and their deriva-
tives.
2.2.2. Catalyst characterization
XRD patterns of samples were collected on
a Bruker
D8 Advance instrument using Cu-K␣ radiation. The nitrogen
adsorption–desorption isotherms were measured at 77 K on a
Quantachrome Autosorb-3B system, after the samples were evacu-
ated for 10 h at 473 K. The Brunauer–Emmett–Teller (BET) specific
surface area was calculated using adsorption data in the relative
pressure range from 0.05 to 0.35. The pore size distribution curves
were calculated from the analysis of the adsorption branch of the
isotherm using the Barrett–Joiner–Halenda (BJH) algorithm. The
TEM images were taken on an FEI Tecnai G2-TF30 microscope at
an acceleration voltage of 300 kV. The SEM images were taken on
a Hitachi S4800 electromicroscope with an acceleration voltage of
20 kV. The composition of samples was characterized by energy
dispersive X-ray spectroscopy (EDX) using Horiba EMAX spec-
troscopy. The degree of dispersion and the mean particle size (cubic
model) were estimated from the measured CO uptake, assuming a
cross-sectional area for a surface platinum atom of 8.0 × 10−20 m2
and a stoichiometric factor of one, using the nominal platinum con-
centrations. The TG analysis of the samples was conducted from
ambient temperature to a required temperature under nitrogen
atmosphere with Mettler Toledo TGA/SDTA851e apparatus. The Pt
loading on samples was detected with a Thermo Elemental IRIS
Intrepid II XSP inductively coupled plasma–atomic emission spec-
troscopy (ICP–AES).
2.3. Catalytic tests
For liquid-phase hydrogenation with the Pt/MIL-101 catalyst,
0.04 g or 0.05 g catalyst was pretreated under a hydrogen flow
(40 mL/min) at 503 K for 2 h before use; while for the Pt/35AS
catalyst involved hydrogenation, 0.05 g catalyst was used after pre-
treated under the similar conditions at 673 K for 2 h. The catalyst
was then transferred to a 100 mL autoclave and mixed with sol-
vent and substrate. The reaction began when hydrogen (4.0 MPa)
was introduced with stirring at 298 K. The reaction was stopped
after a proper time and products were analyzed by GC–FID (GC-
2014, Shimadzu) equipped with a capillary column (DM-WAX,
30 m × 0.25 mm × 0.25 m).
2. Experimental
2.1. Materials
Chloroplatinic acid hydrate (H2PtCl6·6H2O) (Pt ≥ 37%), tereph-
thalic acid and chromium nitrate (Cr(NO3)3·9H2O) were purchased
from Shanghai Experiment Reagent Co., Nitrobenzene and its
derivatives were purchased from Aladdin and used as received.
Benzaldehyde was of analytical grade and used as received and its
derivatives were purchased from Alfa Aesar and used as received.
3. Results and discussion
2.2. Catalyst preparation and characterization
3.1. Characterization of Pt catalysts
2.2.1. Catalyst preparation
The MIL-101 support and the Pt/MIL-101 catalyst were char-
acterized by XRD, N2 sorption, SEM and TEM. The XRD pattern of
Pt/MIL-101 catalyst demonstrates that the structure of the MIL-
101 was well kept after Pt nanoparticles depositing (Fig. 1a). N2
adsorption–desorption isotherms of MIL-101 and Pt/MIL-101 are
MIL-101 was synthesized according to Ref. [19] with traditional
hydrothermal method. Briefly, terephthalic acid (1.66 g, 10 mmol),
Cr(NO3)3·9H2O (4.00 g, 10 mmol), 5 M aqueous HF (2 mL, 10 mmol)
and deionized water (48 mL), were placed in a 200 mL Teflon-linear