G Model
CATTOD-10044; No. of Pages12
ARTICLE IN PRESS
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C.P. Jiménez-Gómez et al. / Catalysis Today xxx (2016) xxx–xxx
Copper chromite catalyst is traditionally used in industrial
hydrogenation of furfural; however, the presence of chromium
the development of more sustainable environmentally Cr-free
based catalysts as alternative to the industrial catalyst. Thus, it has
been reported in the literature the use of Cu [13–25], Ni [21,25,26],
Co [21], Pd [23,25], Pt [27,28] or Au [29] as active phase for the
centration of 0,3 M, and the adequate amounts of Cu(II) and Ce(IV)
salts to obtain the desired Cu/Ce molar ratios. An aqueous solution
of NaOH (0.3 M) was slowly added to the copper/cerium solution
until pH 11 to precipitate both copper and cerium hydroxides
[40,41]. Thereafter, the precipitate was aged at 60 ◦C for 4 h, and
then at room temperature for 12 h. The solid was filtered and
washed with water until reach a neutral pH to ensure the removal
of Na+ species. Finally, the solid was dried overnight and calcined
at 400 ◦C for 1 h, with a rate of 2 ◦C min−1
.
The catalytic activity, mainly the selectivity, of catalysts in FUR
hydrogenation is directly related to the hydrogenating capacity of
the active phase. Thus, noble metals, such Pd, Pt or Ni, favor the
opening of furanic ring leading to hydrocarbons, such as butane
and pentane [25,26,30], while catalysts with lower hydrogenat-
ing capacity, or larger contact time, give rise to furan, which is
also a building block for the synthesis of tetrahydrofuran, pirrol or
thiophene [7]. The use of an active phase with even lower hydro-
genating capacity, such as Cu, avoids the carbon atom loss during
have a high industrial interest. Thus, FOL is used in the manufacture
ceutical and agrochemical products [1], while MF is a promising
biofuel component [1,5,32] although also displays other applica-
The design of a suitable catalytic system is a challenge in hetero-
geneous catalysis. In the case of catalysts used in the hydrogenation
of furfural, they can be classified in two groups: those that use sup-
ports, such as Al2O3, SiO2 [25,26], or mesoporous MCM-41 silica
[13], with high thermal, chemical or mechanical stability where
the active phase is highly dispersed, and metal nanoparticles (Cu)
interacting with metal oxides, such as MgO [15,16] or ZnO [14].
This interaction modifies the electronic density of the metal species,
and the formation of nanoparticles favors the availability of a high
amount of active sites.
It is well recognized that ceria (CeO2) displays a high ability to
store and release oxygen by the presence of two kinds of oxygen
species: surface oxygen, which is favored for CeO2 with lower parti-
cle size, and bulk oxygen, typical of larger particles, which provides
interesting properties for oxidation process [34,35]. Nevertheless,
the use of Cu/CeO2 catalysts has been previously reported in hydro-
favoring the reduction of copper oxide to Cu0 at lower tempera-
tures, as previously reported in the preferential oxidation of CO
to CO2 [35,39], by comparing ceria with other supports, such as
SiO2 [13], MgO [15] and ZnO [14]. In this sense, the decrease of the
reduction temperature is a key factor to obtain small Cu0 particles,
thus the sintering effect is minimized, which is also avoided by the
strong copper-ceria interaction [36]. Moreover, the relatively low
reaction temperature can limit this sintering effect. The present
research studies the catalytic activity and stability of Cu/CeO2 cat-
alysts in the furfural hydrogenation in gas phase. In addition, the
influence of experimental parameters, such as Cu/Ce molar ratio,
reaction temperature and contact time, on the catalytic perfor-
mance has been also evaluated.
The reduction temperature was estimated by taking into
account the profile of the H2 temperature programmed reduction
(H2 TPR) curves, and it was maintained for 1 h in order to ensure
the full reduction of copper species. Samples were labeled as Cu-
CeO2-x, where x is the Cu/Ce molar ratio.
2.2. Characterization methods
Powder XRD patterns were collected on a X’Pert Pro MPD auto-
mated diffractometer (PANalytical B.V.) equipped with a Ge (1 1
1) primary monochromator (strictly monochromatic CuK␣1 radi-
ation) and an X’Celerator detector with a step size of 0.017◦.
Diffractograms were recorded between 10◦ and 70◦ in 2 with
a total measuring time of 30 min. The particle sizes of CeO2 and
Cu◦ and the lattice strain were estimated by the Williamson-Hall
method, using the equation B cos = (K /D) + (2 sin ), where is
the Bragg angle, B is the full width at half maximum (FWHM) of the
XRD peaks, K is the Scherrer constant, is the wavelength of the X
ray and the lattice strain [42]. The cell parameters were obtained
from Rietveld method by using the XPert HighScore Plus software.
Raman spectra were recorded in a Jobin Yvon Horiba Raman
dispersive spectrometer with a variable power He-Ne laser source
(632.8 nm) with an input power of 0.9 nm using a 10 × objective for
every wavelength. The detector is a CDD Peltier-cooled detector.
H2 temperature-programmed reduction (H2-TPR) experiments
were carried out using 0.080 g of catalyst previously treated with a
He flow (35 mL min−1) at 100 ◦C for 30 min. After cooling to room
temperature, the H2 consumption was studied between this tem-
perature and 800 ◦C, by using an Ar/H2 flow (48 mL min−1, 10 vol.%
of H2) and a heating rate of 10 ◦C min−1. Water formed in the reduc-
tion process was removed with an isopropanol-liquid nitrogen trap
and a cold finger (−80 ◦C). The H2 consumption was measured with
an on-line gas chromatograph (Shimadzu GC-14A) provided with
a TCD, and quantified by calibration with pure CuO as reference
standard (Aldrich), assuming a total reduction of CuO to Cu0.
The carbon content, after the catalytic test, in spent cata-
lysts was determined by elemental analysis with a LECO CHN
932 analyzer. The textural parameters were evaluated from nitro-
gen adsorption–desorption isotherms at −196 ◦C, as determined
by an automatic ASAP 2020 Micromeritics apparatus. Prior to
measurements, samples were outgassed at 200 ◦C and 10−4 mbar
gen molecule cross section of 16.2 Å2. Pore size distribution was
determined using the density functional theory (DFT).
Metal surface area and dispersion were evaluated by N2O titra-
tion [43]. This method is based on the formation of a monolayer
of Cu2O by oxidation of superficial Cu0 with a N2O flow, according
to the reaction: 2Cu0 + N2O → Cu2O + N2. Before analysis, the CuO
phase is reduced under a 10 vol.% H2/Ar flow (48 mL min−1) and a
rate of 5 ◦C min−1, until 220 ◦C for CuCe-x catalysts and 350 ◦C for Cu
catalyst, during 1 h. Then, samples were purged under a He flow and
cooled down to 60 ◦C. The oxidation of Cu0 to Cu+ is carried out by
chemisorption of N2O (5 vol.% N2O/He) at 60 ◦C during 1 h. Later, the
catalyst was again purged with an Ar flow and cooled to room tem-
perature. After this, the reduction of Cu2O to metallic Cu was carried
2. Experimental
2.1. Synthesis of catalysts
The precursors of Cu/CeO2 catalysts were synthesized using a
co-precipitation method from aqueous solutions of Cu(NO3)2·3H2O
(Aldrich, 99%) and Ce(NO3)4 3H2O (Aldrich, 99%) with a total con-
Please cite this article in press as: C.P. Jiménez-Gómez, et al., Gas-phase hydrogenation of furfural over Cu/CeO2 catalysts, Catal. Today