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CATTOD-8780; No. of Pages9
ARTICLE IN PRESS
2
M. Stekrova et al. / Catalysis Today xxx (2013) xxx–xxx
Table 1
OH
Iron loading determined by energy dispersive X-ray microanalysis.
O
+
+
Fe (wt%)
Catalyst
Nominal loading
SEM-EDXA
pinocarveol
isopinocamphone
3
2
Fe-Beta-25
Fe-Beta-150
Fe-Beta-300
5
3
2
4.1
3.1
1.1
O
OH
OH
a spectral resolution equal to 2 cm−1. Spectral bands at 1545 and
1450 cm−1, were used to identify, respectively, Brønsted (BAS) and
Lewis acid sites (LAS). The amounts of BAS and LAS were calculated
from the intensities of the corresponding spectral bands using the
molar extinction coefficients reported by Emeis [14].
- H2O
alpha-pinene
oxide
2-methyl-5-(propan-2-
ylidene)cyclohex-2-enol
p-cymene
trans-carveol
1
6
4
5
2.2. Catalytic tests
O
O
+
Isomerisation of ␣-pinene oxide over the parent materials (H-
Beta zeolites) and over Fe modified beta zeolites with varying
SiO2/Al2O3 ratios of 25, 150 and 300 was carried out in the liq-
uid phase using a batch-mode operated glass reactor. In a typical
experiment the initial concentration of ␣-pinene oxide and the
catalyst mass were 0.02 mol/l and 75 mg, respectively, using N,N-
dimethylacetamide as a solvent (VL = 100 ml) at 140 ◦C. The kinetic
experiments were performed under the following conditions to
avoid external mass transfer limitation: the catalysts particle size
below 90 m and the stirring speed of 390 rpm. The catalyst was
activated in the reactor at 250 ◦C under an inert argon atmosphere
for 30 min before the reaction. The samples were taken at different
time intervals and analyzed by GC. The products were confirmed
by GC–MS and NMR.
campholenic aldehyde
fencholenic aldehyde
8
7
Fig. 1. Reaction scheme of ␣-pinene oxide 1 isomerisation to trans-carveol 4 and
2-methyl-5-(propan-2-ylidene) cyclohex-2-enol 5 and p-cymene 6 (product of sub-
sequent dehydration), to isopinocamphone 2 and pinocarveol 3 and to campholenic
7 and fencholenic 8 aldehydes.
N-methylpyrrolidone as a solvent being 46% at total conversion of
␣-pinene oxide [13].
The aim of the current work was selective synthesis of trans-
carveol over heterogeneous beta zeolites with different silica to
alumina ratio in proton and iron modified forms.
In order to study the reaction in the presence of trace amounts of
a homogeneous catalyst, a few additional experiments were per-
formed. As a homogeneous catalyst FeCl3·6H2O was applied in a
typical experiment at 140 ◦C using 0.02 mol/l ␣-pinene oxide as a
reactant in 100 ml of DMA. The amount of iron was 3.7 mmol in
100 ml of solution, which corresponds to about 9 wt% leaching of
iron from 3 wt% Fe Beta-150.
2. Experimental
2.1. Catalyst synthesis and characterisation
The proton forms of zeolites with different silica to alumina ratio
were supplied by Zeolyst International. The evaporation impreg-
nation method using aqueous solutions of ferric nitrate was used
for preparation of the catalysts: Fe-Beta-25, Fe-Beta-150 and Fe-
Beta-300. The number in the catalyst code indicates the SiO2/Al2O3
molar ratio in the zeolite structure. Water solutions of ferric nitrate
were used for preparation of Fe modified beta zeolite catalysts. The
mixtures were stirred for 24 h at 60 ◦C. The other steps of synthe-
sis were evaporation, drying at 100 ◦C overnight and calcination at
450 ◦C for 4 h.
The characterisation of catalysts was carried out using scanning
electron microscopy, energy dispersive X-ray microanalysis, nitro-
gen adsorption and FTIR spectroscopy using pyridine as a probe
molecule.
The scanning electron microscope (Zeiss Leo Gemini 1530) was
used for determining the crystal morphology of the proton forms
and Fe-modified zeolites.
3. Results and discussion
3.1. Catalyst characterisation results
The morphology (shape and size) of the parent and Fe modified
zeolite catalysts was studied by scanning electron microscopy. The
beta zeolites exhibit circular form. Fe modification of all three zeo-
lites did not influence the parent crystal morphology. The energy
dispersive X-ray micro analysis (EDXA) results shown in Table 1 are
somewhat lower than nominal loading in case of Fe-Beta-300 and
Fe-Beta-25 zeolite catalysts.
Iron loading was determined by EDX-microanalysis for cata-
lysts Fe-Beta-150 after the isomerisation to test if leaching of iron
occurred during the reaction. A slight decrease of iron content
(below 9%) was observed in the spent Fe-Beta-150 (2.85 wt% of iron)
in comparison to the fresh one (3.1% of iron) indicating that iron was
not significantly leached during isomerisation of ␣-pinene oxide in
DMA at 140 ◦C during 3 h reaction time.
The surface area was determined by nitrogen adsorption using
Carlo Erba Sorptomatic 1900 instrument. The samples were out-
gassed at 150 ◦C for 3 h. Dubinin’s equation was used to calculate
the surface areas. The pore size distribution was obtained from
Barrett–Joiner–Halenda correlation.
The acidity of prepared catalysts was measured by infrared
spectroscopy (ATI Mattson FTIR) using pyridine (≥99.5%, a.r.) as
a probe molecule for qualitative and quantitative determination
of both Brønsted and Lewis acid sites. The samples were pressed
into thin self-supported wafers (10–25 mg). The pellets were pre-
treated at 450 ◦C for 1 h prior to the measurements. Pyridine was
first adsorbed for 30 min at 100 ◦C and then desorbed by evacuation
at different temperatures (250, 350, and 450 ◦C) to obtain distribu-
tion of acid sites strengths. All spectra were recorded at 100 ◦C with
The specific surface areas of the proton form zeolites and Fe
modified zeolite catalysts determined by nitrogen adsorption and
calculated by Dubinin’s method are summarised in Table 2. The
highest surface area of proton form zeolite was determined for
H-Beta-25, being however comparable with surface area of H-Beta-
300. The loading of iron on zeolites causes the decrease of the
surface area. Among iron modified zeolites the highest specific sur-
face area was determined for Fe-Beta-300, catalyst with the lowest
content of iron.
Please cite this article in press as: M. Stekrova, et al., H- and Fe-modified zeolite beta catalysts for preparation of trans-carveol from ␣-pinene
Stekrova
