Paper
Catalysis Science & Technology
to their high solubility in polar media, it is often difficult to
separate them from the reaction products, which is problem-
atic in industrial processes. Thus, a water-tolerant solid acid
catalyst with high conversion ability and selectivity is essen-
tial for the esterification and acetalisation of glycerol, where
the active components of the catalyst will remain intact even
in a highly polar reaction mixture at elevated temperatures.
Recently, we reported a mesoporous Zr-SBA-16 catalyst for
the esterification and acetalisation of glycerol and the catalyst
was shown to be very effective in solvent-free conditions.30
Accordingly in the present work, we report an aluminosilicate-
supported iron oxide catalyst for the valorization of glycerol
into its fuel oxygenates via esterification and acetalisation
reactions in solvent-free conditions. Fe incorporation was pre-
viously reported to significantly improve the acid properties
(both in terms of Brönsted and/or Lewis acidity) of Al-SBA-15
materials.31 Hence, improved acidity (and a higher number of
acid sites) has been correlated with better catalytic perfor-
mance in both acetalisation25 and esterification reactions.32
The synthesis procedure and detailed characterization of
Fe/Al-SBA-15 used in this work has been discussed in detail in
earlier reports (see also the experimental section).33,34 Reac-
tion conditions were optimized for the conversion of glycerol
and the role of active metal oxide nanoparticles on product
distribution was emphasized. Finally, catalyst recyclability
studies were performed for both esterification and acetalisation
of glycerol to confirm its excellent stability and reusability.
levulinic acid and the catalyst (0.025–0.050 g) were placed
in an ampoule with continuous stirring (1200 rpm) for
8
h at different temperatures. The resultant mixture
was filtered off, extracted using ethanol and the mono-,
di-(1,2-diacetylglyceride) and triacetylglyceride products were
identified by GC-MS, along with their ratios. The response
factors of the starting material and products were determined
using naphthalene as an external standard. In the acetalisation
with aldehydes, 1 mmol glycerol, 1 mmol aldehyde and the
catalyst (0.1–0.01 g, depending on the aldehyde) were placed
inside an ampoule with stirring (1200 rpm) at 100 °C for 8 h
(12 h in the case of furfural). The resultant mixture was then
filtered off, extracted using ethanol and the products were
identified by GC-MS, along with their ratios. For benzal-
dehyde and furfural, the products were also identified by
1H NMR (D2O). The formation of solketal from glycerol
(1 mmol) and acetone (1 mmol) was carried out in an ampoule
at 100 °C for 8 h under continuous stirring (1200 rpm), over
catalysts (0.1–0.05 g). (2,2-Dimethyl-1,3-dioxolan-4-yl)methanol
and 2,2-dimethyl-1,3-dixan-5-ol were identified as products
by GC-MS.
2.3. Recyclability tests
This test methodology was used for the recycling of all reac-
tions: the catalyst was reused upon reaction completion by
simple centrifugation and separation followed by washing
three times with ethanol and drying prior to reutilization in
the next reaction.
2. Experimental
2.1. Synthesis of Al-SBA-15 and supported Fe/Al-SBA-15
2.4. Analytical methods
The catalysts were prepared according to a previously reported
methodology.34 20 g of P123 template was coated around the
sides of a plastic bottle. 700 mL of HCl solution and the
desired quantity of Al precursor (aluminium isopropoxide, in
order to reach a Si : Al 30 ratio in the synthesis gel) was added
(pH of 1.5) and then mixed until all P123 was dissolved. The
silica precursor used in the study (TEOS) was then slowly
introduced to the solution. The mixture was then left for at
least 24 hours at 100 °C (aging) until a white solid was
formed. The material was then filtered off, dried in an oven
and eventually calcined at 550 °C for 24 h.
Upon reaction completion, the quantitative analysis of
products was performed by GC-MS. Chromatograms were
recorded on a GC-MS turbo system (5975-7820A model)
equipped with a HP-5MS capillary column (30 m × 0.25 mm ×
0.25 μm). NMR spectra were recorded using a Varian Mercury
300 spectrometer. Chemical shifts (δ) are reported in ppm and
were measured relative to the internal reference, D2O (1H).
Esterification and acetalisation (benzaldehyde and
furfural): injector temperature 250 °C, detector temperature
230 °C, 50 °C ramp at 10 °C min−1 until 230 °C, then held
for 20 min.
A typical preparation of the supported iron catalyst was
performed as follows: Al-SBA-15 (0.2 g) was suspended in an
ethanol solution (2 mL) containing previously dissolved
FeCl2·4H2O (100 mg). The mixture was heated in a microwave
at 200 W for 15 min (average temperature 100 °C, 120 °C
maximum temperature reached). The solid was then filtered
off, washed with an excess of ethanol and acetone and dried
overnight at 100 °C. The final catalyst, Fe/Al-SBA-15, was
obtained after calcination of the dried material under air at
400 °C for 2 h.
Retention times (levulinic acid): peak at 9.66 min
levulinic acid, at 12.50 min naphthalene, at 15.99 min
monoacetylglyceride, at 23.07 min diacetylglyceride and at
36.17 min triacetylglyceride.
Retention times (benzaldehyde): peak at 5.20 min benzalde-
hyde, at 12.66 and 12.89 min the diastereoisomer of (2-phenyl-
1,3-dioxolan-4-yl)methanol and at 13.54 min the two diaste-
reoisomers of 2-phenyl-1,3-dioxan-5-ol.
Retention times (furfural): peak at 3.48 min furfural, at 10.32
and 10.60 min the two diastereoisomers of (2-(furan-2-yl)-1,3-
dioxolan-4-yl)methanol and at 10.39 and 11.32 min the other
two diastereoisomers of 2-(furan-2-yl)-1,3-dioxan-5-ol.
Acetalisation (paraformaldehyde and acetone): injector
temperature 250 °C, detector temperature 230 °C, oven
2.2. Typical procedure for catalytic experiments
Glycerol was employed in the various investigated reactions.
In a typical esterification reaction, 1 mmol glycerol, 4 mmol
Catal. Sci. Technol.
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