P. Mäki-Arvela et al.
was operated in Bragg–Brentano diffraction mode, and the
monochromatized Cu–Kα radiation (λ= 1.541874 Å) was
generated with a voltage of 40 kV and a current of 45 mA.
The measured diffractograms were analyzed with Philips
X’Pert HighScore and MAUD [18] programs. The Powder
Diffraction File 2 (PDF-2) database, Inorganic Crystal Struc-
ture Database (ICSD), and Crystallography Open Database
(COD) were used as references [19–21].
with an excess of cyclopentanone (Sigma Aldrich, >99%),
which was also applied as a solvent (60 ml), if not other-
wise stated. The initial valeraldehyde concentration was
0.50 mol/l if not specifically mentioned. The experiments
were performed by adding valeraldehyde, cyclopentanone
and the catalyst into the cold reactor, which was then heated
to 130 °C. The reactor system was equipped with a con-
denser, which exhibited temperature close to zero. Valeral-
dehyde and a part of cyclohexanone were thus condensed
back to the liquid phase. The experiments were carried out
under argon atmosphere. The weight ratio of valeraldehyde
to cyclopentanone in the kinetic experiments was 0.05, while
the amount of catalyst was 1.6 g. The mass ratio of valer-
aldehyde to catalyst was 1.7 being the same as was used in
[1]. Small catalyst particles (below 63 µm) were used under
vigorous stirring (600 rpm) to avoid internal and external
mass transfer limitations. In some experiments mesitylene
(Sigma Aldrich, 97%) was used as a solvent. The products
were analyzed by a GC equipped with HP-5 column (30 m,
di=320 µm, film thickness 0.5 µm) using the following tem-
perature programme: 60 °C (2 min)–8 °C/min–124 °C–4 °C/
min–200 °C–12 °C/min–280 °C (10 min). The reaction
products were identified by GC–MS (Agilent Technologies,
6870N) equipped with DB-1 column (30 m, 250 µm, film
thickness 0.50 µm).
The scanning electron microscopy coupled with an
energy dispersive X-ray analyzer was utilized to study mor-
phology of the fresh catalysts using Zeiss Leo Gemini 1530
microscope combined with secondary electron and back-
scattered electron detectors. Acceleration voltage of 15 kV
was used for X-ray analyzer. In order to perform analysis,
the catalyst was placed as a thin layer on top of the carbon
coating to enhance the conductivity and allow high quality
of magnified images.
The transmission electron microscopy was utilized to
study the structural properties, porosity, metal particle size
and distribution using JEM-1400Plus (by JEOL ltd. Japan)
of 120 kV maximal acceleration voltage. Interpretation of
TEM images and determination of the particles sizes of the
fresh and spent catalyst were done using ImageJ program.
The specific surface area was determined with Sorptom-
eter 1900 (Carlo Erba Instrument) using nitrogen physisorp-
tion. The catalysts were outgassed at 150 °C for 3 h prior to
the measurement. The BET equation was used to calculate
the specific surface area.
CO2 TPD measurements were performed to determine
the concentration of basic sites using Autochem 2010,
Micromeritics instrument. The catalyst, 200 mg, was first
dried at 150 °C for 30 min under helium (AGA, 99.996%)
after which it was cooled to 100 °C. Thereafter CO2 (AGA)
was adsorbed on the catalyst surface during 30 min. The
physisorbed CO2 was flushed from the catalyst surface at
100 °C for 30 min after which the temperature was increased
by 10 °C/min up to 700 °C.
3 Results and Discussion
3.1 Catalyst Characterization Results
XRD results revealed that FeO–CaO–EIM catalyst contained
iron only as Ca2Fe2O5 phase (Table 1; Fig. 2). Ca2Fe2O5 in
based on XRD [23]. On the other hand, metal oxide Fe2O3
particles are threefold smaller than Ca2Fe2O5 (Table 1).
CeO2 [24] and MgO [28] (Table 2). XRD of FeO-MgO-
indicates that iron either is in an amorphous form or it well
dispersed on the support with the particle size below 3 nm,
not being detectable by XRD.
Ammonia TPD was performed with Micromeritics (Auto-
Chem 2910) using helium as a carrier gas. The sample was
dried prior to the measurement at 250 °C for 30 min after
which ammonia (5 vol% in helium, AGA) was adsorbed on
the catalyst for 60 min at 25 °C. Then the gas supply was
stopped and these conditions were hold for 30 min. In the
next step the temperature was increased by 10oC/min to
100 °C and hold at 100 °C for 30 min. The ammonia TPD
was measured using the following temperature programme:
100 °C–10 °C/min–600 °C.
SEM images of different catalysts are depicted in Fig. 3.
(Fig. 3a). FeO–MgO–DP contains plates (Fig. 3b) whereas
105 and 148 nm (Fig. 3c). Particles in FeO–CaO–EIM were
to 600 nm (Fig. 3d). The particle sizes in CaO varied in a
broader range of 50 to 400 nm. These changes can be related
to the presence of different phases in these materials. CaO is
2.3 Kinetic Experiments
Catalytic experiments were typically performed under flow-
ing helium at 130 °C in a glass reactor equipped with a stir-
rer. Typically valeraldehyde (Aldrich, 97%) was reacting
1 3