CHEMSUSCHEM
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Catalyst syntheses
Procedure for synthesizing sulfonic acid-functionalized silica
gel
Sulfonic acid-functionalized silica gel was synthesized by grafting
using a modification of a published procedure.[26] Silica gel (2 g)
was added to toluene (20 mL) and heated to 1158C with stirring
for 1 h. Then, 3-mercaptopropyltrimethoxysilane (10.0 mmol, 2.0 g)
was added and the stirring was continued at the same tempera-
ture for 24 h. The solid was filtered, washed with water (5ꢃ20 mL),
and dried under ambient conditions overnight. It was then re-sus-
pended in 33% H2O2 (35 mL) and stirred for 1 h in a closed vessel
at 608C. Note that oxidizing at this elevated temperature is advan-
tageous in preparing these materials.[27] The solid was then filtered,
and the cake was washed and re-suspended in 35 mL of 10% w/w
H2SO4(aq) and stirred for another hour at room temperature. The
final product was then filtered, washed with water (4ꢃ20 mL) and
dried under ambient conditions overnight.
Figure 8. FT-IR spectrum of SBA-15-SO3H after removing surfactant.
into solution, and gives excellent yields and 100% selectivity
after 4 h at 1108C. Its activity and selectivity are much higher
than those of sulphonated macroporous acidic resins such as
Amberlyst 70. As the supply of furfural and biobutanol contin-
ue to increase, this catalyst and the related simple catalytic bu-
tanolysis route are good candidates for applications in bio-
refineries.
Procedure for synthesizing propylsulfonic acid-functionalized
mesoporous silica (SBA-15-SO3H)
SBA-15-SO3H was synthesized following the co-condensation pro-
cedure described by Melero and coworkers.[28] The template, Plur-
onic 123 (4 g), was dissolved with stirring in 2m HCl solution
(125 g) at room temperature. The solution was heated to 408C and
the required amount of TEOS added and stirred for 45 min. After
this pre-hydrolysis period the required amount of MPTMS and 33%
H2O2 (20 mL) were added. The resulting mixture was stirred at
408C for 20 h and then aged without stirring for 24 h at 1008C.
The molar ratio of TEOS to MPTMS was 9:1. The solid product was
then filtered and air-dried. The template was extracted with excess
ethanol under reflux for 24 h (300 mLgÀ1), followed by washing
with ethanol and drying at 1008C.
Experimental Section
Materials and instrumentation
Furfuryl alcohol (98% for GC), 1-butanol (99.8% for HPLC grade)
and tetradecane (>99% for GC) were supplied by Sigma Aldrich.
The silica gel for the synthesis of the functionalized mesoporous
silica gels (SBA-15-SO3H), was supplied by Biosolve (60 ꢂ, 0,063–
0,200 mm). Tetraethoxysilane (TEOS, purity 98%), 3-mercaptopro-
pyltrimethoxysilane (MPTMS, purity 85%), poly(ethylene oxide)-
poly(propylene oxide)-poly(ethylene oxide) block copolymer Plur-
onic 123, and ethanol were supplied by Sigma Aldrich and used
as-received.
The other catalysts tested were Amberlyst 70 and Amberlyst 35
(sulphonated macroporous polystyrene/divinylbenzene resin,
Rohm and Haas), sulfonic acid-functionalized hypercrosslinked
polystyrene resins in bead form (D5081 and D5082, Purolite Inter-
national), niobium oxide hydrate (Nb2O5·nH2O) niobium oxide cal-
cined at 4008C, sulfonic acid-functionalized carbon, H-ZSM5 zeo-
lites in protonic form (nominal Si/Al ratio of 55, Zeolyst Internation-
al), and ferrierite in ammonium form (nominal Si/Al ratio of 55,
Shell). The ammonium form was converted to the protonic form
by heating to 5008C at 58CminÀ1 and calcining at this temperature
for 4 h.
All experiments were carried out under reflux in a round-bottom
flask equipped with a condenser and a heating plate, and analyzed
by an Interscience Trace GC-8000 gas chromatograph with a 100%
dimethylpolysiloxane capillary column (VB-1, 30 mꢃ0.325 mm).
When needed, by-products were identified by (GC-MS). FT-IR spec-
tra were collected using a Bruker spectrometer. Morphology and
size of the particles were determined by scanning electron micros-
copy (SEM) using an ESEM microscope (Philips, XL30) operating at
25 kV. The filtration procedure as a test for active species leaching
is described in detail elsewhere.[25]
Procedure for catalytic reaction
The SBA-15-SO3H catalyst (0.050 g; 2.3 mol% based on furfuryl al-
cohol) and 2.04 mmol of furfuryl alcohol were added to 5.0 g of 1-
butanol in a round bottom flask and placed under reflux at 1108C.
Tetradecane was used as internal standard. Reactant conversion
and product yields were monitored by GC.
Acknowledgements
P.D.C. thanks Prof. Giuseppe Alonzo (University of Palermo and
president of Italy’s CRA) for co-mentoring on the conclusion of
her PhD.
Keywords: alcohols · biomass · esterification · heterogeneous
catalysis · solid acids
[1] B. Kamm, P. R. Gruber, M. Kamm, Biorefineries—Industrial Processes and
Products, Wiley-VCH, Weinheim, 2006.
[2] P. Demma Carꢀ, M. Pagliaro, A. Elmekawy, D. R. Brown, P. Verschuren,
N. R. Shiju, G. Rothenberg, Catal. Sci. Technol. 2013, 3, 2057–2061.
[4] C. Caro, K. Thirunavukkarasu, M. Anil Kumar, N. R. Shiju, G. Rothenberg,
ꢁ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
ChemSusChem 2014, 7, 835 – 840 839