Full Papers
areas (SBET) of the catalysts were calculated from N2 physisorption
data obtained at 77 K by using a Micromeritics Tristar 3000 appara-
tus. Prior to the physisorption experiments, the samples were evac-
uated at 473 K for at least 12 h. The amount of Ni surface atoms
was determined by hydrogen chemisorption measurements. The
catalyst was activated at 3008C for 1 h in a flow of H2 and evacuat-
ed at 3008C for 1 h in vacuum (<5 mm Hg; 1 mmHg=133.3 Pa). It
was then flushed for 1 h in a flow of He, cooled to 358C, and evac-
uated again for 1 h (<5 mmHg). H2 adsorption (chemisorption and
physisorption) was measured at 358C over the pressure range
from 0.5 to 415 mmHg. Next, physisorbed H2 was removed by out-
gassing the sample for 2 h at 358C (<5 mmHg), and another iso-
therm (physisorption) was measured. The difference between the
two isotherms gave the H2-chemisorption isotherm. The concentra-
tion of chemisorbed hydrogen on the metal was determined by
extrapolating the differential isotherm to zero H2 pressure, and this
value was used to calculate the Ni dispersion. By assuming cubic
crystals, the average nickel crystallite size was calculated by using
Equation (5), wherein SNi was the Ni metal surface area in m2 gꢀ1
and 1Ni was the metal density (8.908 gmꢀ3).[33]
Keywords: biomass · heterogeneous catalysis · lignin · nickel ·
synthesis design
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d ¼ 5=ðSNi1NiÞ
ð5Þ
HAADF-STEM, STEM-EDX mapping, and EELS analyses were per-
formed by using two FEI Titan “cubed” electron microscopes, both
operated at 300 kV. The first was equipped with a Super-X high
solid-angle EDX detector, the second with a GIF Quantum spec-
trometer and electron monochromator, set to provide a 250 meV
energy resolution for EELS. For imaging, the convergence semian-
gle, a, was 22 mrad, whereas the HAADF-STEM collection semian-
gle was 50 mrad. For EELS, the convergence semiangle was
18 mrad and the collection semiangle was approximately
100 mrad. The samples were prepared for TEM investigation by
crushing the powder with ethanol in a mortar and placing several
drops of the suspension onto a holey carbon grid. Diffraction pat-
terns were collected a Huber G670 Guinier diffractometer (CuKa1 ra-
diation, curved Ge(111) monochromator, transmission mode, image
plate). H2-TPR was performed in a tubular reactor by using MS de-
tection under the following conditions: sample weight 100 mg,
heating rate 108Cminꢀ1, flow rate 12 mLminꢀ1, and 5 vol% H2 in
He. TGA of the spent catalyst was performed with a TGA Q500 ana-
lyzer from TGA Instruments. The sample was heated under O2 at
38Cminꢀ1 to 608C, kept at this temperature for 30 min, heated at
108Cminꢀ1 to 8008C and kept at this temperature for 30 min. The
relative weight loss between 60 and 8008C was used as a measure
of the amount of carbon deposits on the catalyst.
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Acknowledgements
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[7] E. A. Borges da Silva, M. Zabkova, J. D. Araujo, C. A. Cateto, M. F. Bar-
This work was performed in the framework of an IAP-PAI network
from BELSPO (Federal Agency). W.S. and S.T. acknowledge fund-
ing from the Research Foundation—Flanders (FWO). S.V.d.B. ac-
knowledges the Institute for the Promotion of Innovation through
Science and Technology in Flanders (IWT-Vlaanderen) for a doctor-
al fellowship. J.D. thanks Methusalem CASAS for funding. We are
grateful to I. Cuppens and G. G. Rangel for ICP-AES analysis, G.
Vanbutsele for help with N2 physisorption analysis, W. Vermandel
for H2-TPR measurements, and Dr. M. Jacquemin for help with H2
chemisorption analysis.
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