Benzaldehyde Hydrogenation in Water
Catalyst Preparation and Characterization
hydes in water complemented our previous findings that
were observed on the Pt/FDU-15 catalyst for the chiral hy-
drogenation of ethyl pyruvate in acetic acid. In this case, it
afforded constant activity and enantioselectivity after the
25th cycle.[41] The entrapment of the Pt nanoparticles in the
porous resol matrices and the p-donating interaction with
benzene rings would prevent effectively the agglomeration
and leaching of Pt nanoparticles during reactions[45] so that
the Pt particles can be stabilized and recycled smoothly. In
addition, as discussed above, the high hydrophobicity of
FDU-14 mesopolymers with a pure organic framework may
also contribute to the high performance in water.
Pt/FDU-14 (5 wt.%) was prepared according to literature.[41,42] FDU-14
was impregnated with an aqueous solution of platinum precursor and
stirred for 4–6h. Then the mixture was evaporated to remove the excess
water, followed by drying at 353 K overnight, and finally reduced in an
aqueous solution of sodium formate.
X-ray diffraction patterns were recorded on a Bruker D8 ADVANCE in-
strument with CuKa radiation. The nitrogen sorption isotherms were mea-
sured at 77 K on a Belsorp-max system. The Brunauer–Emmett–Teller
(BET) specific area was calculated by using adsorption data in the rela-
tive pressure range from 0.05 to 0.35. The pore-size distribution curves
were calculated from the analysis of the adsorption branch of the iso-
therm by using the BJH algorithm. Transmission electron microscopy
images were taken on an FEI Tecnai G2 Spirit at an acceleration voltage
of 120 kV. Thermogravimetric analysis (TGA) to investigate the hydro-
phobic property of the catalyst was performed in a N2 atmosphere from
303 K to 423 K with a heating rate of 2 KminÀ1 by using a METTLER
TOLEDO TGA/SDTA851e apparatus. CO chemisorption of samples was
measured at 313 K on a CHEMBET-3000 pulse chemisorption analyzer
after the sample was pretreated in a hydrogen flow at 573 K (673 K for
Pt/alumina) for 2h. 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 8.0ꢁ10À20 m2 and a
stoichiometric factor of one by using nominal platinum concentrations.
Conclusions
In conclusion, the Pt nanoparticles entrapped in the meso-
pores of FDU-14 mesopolymer were confirmed to work
well as an efficient catalyst for the liquid-phase hydrogena-
tion of various benzaldehydes under mild conditions. With
regard to the benzaldehyde hydrogenation on the Pt/FDU-
14 catalyst, water is a better choice of solvent in contrast to
conventional solvents like ethanol. The Pt/FDU-14 catalyst
gave the highest activity of about 5700 molmolÀ1 hÀ1 for the
3-fluorobenzaldehyde hydrogenation in water at ambient
temperature and showed a good reusability. Compared with
the commercial Pt/Al2O3 catalyst, the Pt/FDU-14 catalyst
showed superior performance, particularly for the para-sub-
stituted benzaldehydes, which is mainly owing to its hydro-
phobic character. The results obtained in the hydrogenation
of benzaldehydes with various groups substituted at differ-
ent positions of the phenyl ring indicate that the electron-
rich benzaldehydes are easily activated by the Pt/FDU-14
catalyst.
The catalyst preparation procedure has now been further
improved to prepare the Pt catalyst with a smaller and
more-uniform particle size. Those Pt particles confined in
the mesopores of the FDU-14 mesopolymer are expected to
be more efficient in relevant hydrogenation reactions. The
results obtained in this study also imply that the FDU-type
mesopolymer can be applicable for supporting other noble
metal particles such as Pd, Ru, and Au, resulting in useful
catalysts for the Heck coupling reaction or redox reactions
of unsaturated compounds containing C=C bonds.
General Procedures for Liquid-phase Hydrogenation of Benzaldehydes
For a standard hydrogenation, the molar ratio of catalyst/substrate is
about 5.85ꢁ10À4. Pt/FDU-14 or Pt/alumina (5 wt.% ) was pretreated in a
hydrogen flow (40 mLminÀ1) at 573 or 673 K, respectively, for 2h before
use. The catalyst was then mixed with the benzaldehyde (21 mmol) and
solvent (20 mL) and then transferred to an autoclave with magnetic stir-
ring (1200 rpm). The hydrogenation reaction started at ambient tempera-
ture after hydrogen (4.0 MPa) was introduced. The reaction was stopped
after a period of time and then the products were analyzed by GC (GC-
2014, Shimadzu Co.) equipped with an FID and a capillary column (DM-
WAX, 30 mꢁ0.25 mmꢁ0.25 mm).
Recycling
The recycle experiment was also carried out in water. The detailed proce-
dures are as follows. After the each run, the catalyst (50 mg) was centri-
fuged, washed with ethanol several times, and finally naturally dried in
air overnight. Fresh reactant (21 mmol), water (20 mL), and hydrogen
(4.0 MPa) were then charged to the autoclave together with the recov-
ered catalyst to carry out the next run reaction.
Acknowledgements
This work was supported by the NSFC (20703018), Shanghai Rising-star
Program (08QA1402700), STCSM (08JC1408700), the Doctoral Program
of Higher Education Research (20070269023), 973 Program
(2006CB202508), and Shanghai Leading Academic Discipline Project
(B409). X. Li especially thanks Prof. Dr. Jianliang Xiao in the Chemistry
Department of Liverpool University, Liverpool, UK for valuable discus-
sion and language polishing.
Experimental Section
Materials
Benzaldehyde, hydrogen hexachloroplatinate (IV) hexahydrate
(H2PtCl6·6H2O), sodium formate, and other chemicals were of analytical
grade and used as received. 2-Methoxybenzaldehyde (98%), 3-methoxy-
benzaldehyde (98%), 4-methoxybenzaldehyde (98%), 3-fluorobenzalde-
hyde (97%), 4-fluorobenzaldehyde (98%), 2-chlorobenzaldehyde (98%),
3-chlorobenzaldehyde (97%), and 4-chlorobenzaldehyde (98%) were
purchased from Alfa Aesar and used as received. A commercial Pt/alu-
mina (5 wt.%) was also purchased from Alfa Aesar. The FDU-14 meso-
polymers were synthesized according to the literature.[38]
[1] X. F. Wu, J. K. Liu, X. H. Li, A. Zanotti-Gerosa, F. Hancock, D.
[3] J. Li, Y. M. Zhang, D. F. Han, G. Q. Jia, J. B. Gao, L. Zhong, C. Li,
[4] A. Ramanathan, D. Klomp, J. A. Peters, U. Hanefeld, J. Mol. Catal.
A 2006, 260, 62.
Chem. Asian J. 2009, 4, 699 – 706
ꢀ 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
705