S. Sandesh et al.
co-workers [13] reported hydrotalcite as an active catalyst
using dimethyl formamide as a solvent. Mg/Al/Zr mixed
oxide catalyst has also been used as a base catalyst with
high glycerol carbonate yield but excess of dimethyl car-
bonate has been utilized [14]. KF/hydroxyapatite has been
reported as a catalyst for transesterification of glycerol with
dimethyl carbonate [15]. Recently, NaOH/c-Al2O3 has also
been used for the same reaction but the leaching of ionic
Na species was observed with successive reuse of the
catalyst [16].
(synthesized by combustion method using aluminum
nitrate and urea) and c-Al2O3, SiO2, H-beta zeolite, ZnO
(zinc nitrate was decomposed at high temperature), ZrO2
(synthesized by zirconium oxy chloride) and carbon.
Moreover, the catalysts with different KF content were
prepared by loading KF (in the range 1–24 mmol) on
c-alumina. In a typical procedure, 10 ml of aqueous solu-
tion containing 17 mmol KF was mixed with 1 g of support
under vigorous stirring at room temperature for 2 h fol-
lowed by the evaporation of water at 80 °C in a water bath.
Then the catalyst was dried in an oven at 120 °C overnight
and calcined under air at 600 °C for 4 h. After calcination,
the catalyst was placed in 50 ml distilled water, stirred well
and filtered to remove any physisorbed KF present on the
support, and dried at 120 °C. Different KF loaded Al2O3
catalysts are designated as XKF/Al2O3, where X is the
mmol loading of KF (measured by AAS). The alumina
used was in gamma form unless otherwise stated. Other
solid base catalysts like CaO and MgO were calcined at
850 °C before use and MgAl hydrotalcite (HTc) was syn-
thesized by literature method [24].
KF/Al2O3 was first reported as a solid base catalyst by
Ando et al. [17, 18]. This catalyst has been successfully
applied to a variety of organic transformations such as
aldol condensation [19], transesterification [20], Michael
addition [21] and Tishchenko reaction [22]. Hattori co-
2-
workers [23] reported the formation of K3AlF6 and AlO4
type of phases by the interaction of KF on alumina support
with the formation of OH- species on the catalyst surface.
In the current work, the transesterification reaction of
glycerol with dimethyl carbonate has been investigated
using KF impregnated on different oxide and non-oxide
supports like a- and c-Al2O3, SiO2, zeolite beta, ZnO, ZrO2
and carbon to understand the KF and support interaction.
All the synthesized catalysts have been characterized by
XRD, AAS, N2 adsorption and CO2-TPD measurements.
The physicochemical properties of the catalyst has been
correlated with the activity and selectivity of catalysts. The
catalytic activity of KF/Al2O3 catalyst has also been
compared with conventional solid base catalysts such as
MgO, CaO and hydrotalcite.
2.3 Catalyst Characterization
The powder X-ray diffraction (XRD) patterns were recor-
ded for all the catalysts on a Bruker D2 phaser X-ray dif-
fractometer using Cu Ka radiation with high resolution
Lynxeye detector. All the samples were scanned in the 2h
range of 5°–60° with step size of 0.02°/min.
The specific surface areas of the catalysts were mea-
sured by N2 physisorption at liquid nitrogen temperature on
Quantachrome Nova 1000 at 77 K and determined by using
the standard BET method on the basis of adsorption data.
Basicity of the samples was measured by the tempera-
ture programmed desorption of CO2 (CO2-TPD) using
Quantachrome Autosorb iQ (automated gas sorption ana-
lyser). The sample was preheated at 300 °C under the flow
of He for 3 h, then cooling to 80 °C. Later, the CO2 from a
stream of He (10 % CO2) was fed into the sample for
30 min. Then the sample was purged with He at 100 °C for
1 h in order to eliminate physisorbed CO2. A TPD analysis
was carried out from ambient temperature to 600 °C at a
heating rate of 10 °C/min. CO2 concentration in the
effluent stream was monitored by using a thermal con-
ductivity detector (TCD) and the areas under the peaks
were integrated to determine the amount of CO2 desorbed.
TCD calibration was performed by passing known volumes
of CO2.
2 Experimental
2.1 Materials
Glycerol, dimethyl formamide (DMF), potassium fluoride,
zinc nitrate, zirconium oxy chloride, activated charcoal
(carbon source), aluminum nitrate, urea, calcium oxide
(CaO), magnesium oxide (MgO), magnesium nitrate,
sodium hydroxide pellets and sodium carbonate were
purchased from Merck India Ltd. Pseudoboehmite (alu-
mina source) and H-beta zeolite (SAR = 25) were kindly
donated by Su¨d-Chemie India Pvt Ltd. Fumed silica as a
silica source was purchased from Alfa Aeser. Dimethyl
carbonate (DMC) was purchased from SRL Chemicals Pvt
Ltd. All the chemicals were of research grade and used
without any further purification.
The KF concentration on alumina support was deter-
mined by analyzing potassium content (sample dissolved in
aqua regia) from Perkin Elmer AAnalyst 200 atomic
absorption spectrophotometer (AAS) using potassium
nitrate as a reference standard. Surface density (SD) of
2.2 Catalyst Preparation
KF was loaded on different supports by the wet impreg-
nation method. Supports used in this study were a-Al2O3
123