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holding at 323 K for 1 h with a 10% N2O/Ar flow of 20 sccm. Final-
ly, full TPR was performed under a 20% H2/Ar flow of 25 sccm until
TPR investigations indicate that the reduction of Fe was not
complete at either reduction temperature. In situ FTIR spec-
troscopy with NO as the probe molecule further showed that
Fe2+ active sites are generated after reduction at 543 K instead
of that at 483 K. In conclusion, we have found promotion ef-
fects of Fe in two forms: firstly, the coimpregnated Fe in-
creased the Cu dispersion and reaction rates substantially in
what may be called a structural promotion effect; secondly,
the partially reduced Fe can act as a cocatalyst and convert fur-
furyl alcohol selectively to 2-methylfuran, which is responsible
for the shift of the reaction selectivity after the addition of Fe.
1123 K at 10 KminÀ1
.
In situ diffuse reflectance UV/Vis spectroscopy
Diffuse reflectance UV/Vis spectroscopy was performed by using
a flow cell and a Jasco V550 UV/Vis spectrometer. The in situ flow
cell was made of U-shaped quartz round tube with a UV window
made of square quartz tube (Quartz Plus, Inc.). Typically, 100 mg of
the catalyst was loaded into the flow cell at the window. Other
auxiliary systems (a heating system and gas flow control system)
were used to perform the in situ UV/Vis spectroscopy study. All the
spectra were measured at RT with inert gas flowing through the
sample bed.
Experimental Section
Catalyst preparation
In situ FTIR spectroscopy
The Cu-Fe/SiO2 catalysts were prepared by an incipient wetness
coimpregnation method at a liquid to solid ratio of 1 mLgÀ1. First
Cu(NO3)2·xH2O (99.999%, Sigma–Aldrich) and Fe(NO3)3·9H2O
(99.999%, Sigma–Aldrich) were dissolved in deionized water, and
silica gel (high-purity grade, Sigma–Aldrich) was then added into
the aqueous solution. After drying at RT for 12 h, the mixture was
transferred to an oven at 393 K for 12 h. The dried catalyst was
then calcined at 773 K for 5 h at a ramping rate of 2 KminÀ1. Final-
ly, the catalyst was reduced under 50 sccm H2 for 4 h. The reduc-
tion temperature was determined from the results of the TPR ex-
periments. The Cu loading was 1 wt% in all the catalysts, and the
atomic ratios of Cu/Fe are 1:0, 9:1, and 7:1. Additionally, 1 wt% Fe/
SiO2 was prepared using the same procedure for comparison.
The FTIR measurements were performed by using an in situ diffuse
reflectance infrared Fourier transform (DRIFT) cell with ZnSe win-
dows (15ꢂ2 mm, Harrick Sci.). The IR cell consisted of a cell body,
sample holder, and aluminum heating block. Approximately 50 mg
of the catalyst sample was required to load into the sample holder
as a pellet. Appropriate gases could be fed through the sample by
using mass flow controllers (Brooks 5850E series). IR spectra were
collected by using a FTIR spectrometer (Nicolet Nexus 470). The IR
spectral data were analyzed by using OMNIC software. The catalyst
sample was pretreated with He at 573 K (5 KminÀ1 ramping rate)
for 4 h to remove moisture and other surface contaminants. After
cooling to RT, the sample was reduced at 483 or 543 K (2 KminÀ1
ramping rate) under 20% H2/He at 50 sccm for 2 h. After cooling
to RT under a He flow, the catalyst was treated with 2% NO/He at
10 sccm. IR spectra were collected every 3 min once the NO/He
flow started.
Catalyst characterization
Morphology characterization
XRD analysis was performed by using a Bruker D8 X-ray powder
diffractometer with monochromatic CuKa1 line (l=1.540 ꢁ). SEM
images were obtained by using a Zeiss CrossBeam Auriga 60 FIB-
SEM. N2 adsorption experiments were performed by using a 3Flex
surface characterization analyzer. BET surface areas were calculated
by using the MicroActive for 3Flex software.
Catalyst evaluation
The reactivity of the catalysts was tested in a flow reactor made of
9/16’’ ID stainless-steel tubing. Typically, 50 mg of catalyst was
loaded in the middle of reactor between two quartz wool layers.
Freshly distilled furfural (99%, Sigma–Aldrich) or furfuryl alcohol
(98%, Sigma–Aldrich) was fed into the reactor by using a pump
(NE-1000, New Era Pump System Inc.) and syringe (Hamilton) from
the top of the tubing along with the reduction gas flow. The reac-
tor was heated by using a furnace, and all the gas lines were wrap-
ped with heating tapes and heated to the same temperature as
the reactor to ensure an isothermal reaction system. All the prod-
ucts were collected and analyzed by using online GC (GC 2014,
Shimadzu) equipped with an HP-INNOWax capillary column.
TPR
The reducibility of the Cu-Fe/SiO2 catalysts was determined by
using H2-TPR. In each measurement, ꢀ100 mg of catalyst sample
was loaded into a U-shaped quartz tube reactor. The catalyst was
heated to 773 K at 10 KminÀ1 under a 20% O2/Ar flow of 25 sccm
and held for 1 hour. After cooling under an Ar flow to RT, the cata-
lyst sample was then heated to 1123 K at 10 KminÀ1 under a 20%
H2/Ar flow of 25 sccm. The TPR experiments were performed by
using an Altamira AMI-200 apparatus.
Acknowledgements
We gratefully acknowledge funding from Air Liquide. The authors
thank Dr. Na Ji, Dr. Jason Loiland, Dr. Young Jin Kim, Bahar Ipek,
and Edward Schreiner for their help and suggestions.
N2O preoxidized TPR
N2O preoxidized TPR was performed in the same setup as used for
H2-TPR. Approximately 100 mg of material was placed in a U-
shaped quartz tube reactor. Cu/SiO2 was first reduced at 483 K in
20% H2/Ar flow of 25 sccm. For comparison, Cu-Fe/SiO2 was re-
duced at 483 or 543 K. After the reduction, the material was
cooled to 323 K under an Ar flow followed by N2O oxidation to
convert Cu metal to CuI species. N2O oxidation was finished after
Keywords: biomass
· copper · hydrogenation · iron ·
supported catalysts
&
ChemCatChem 2016, 8, 1 – 8
6
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