M.R. Altıokka et al. / Journal of Molecular Catalysis A: Chemical 385 (2014) 18–25
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Table 1
Physical and chemical properties of tonsil earth obtained from Ravin Company.
2.4. Esterification reactions
The catalytic experiments were carried out in a stirred batch
reactor at reflux conditions. In a typical experiment, dioxane as the
solvent and one of the reactant were placed in the reactor. A known
amount of catalyst was added and the reactor contents were well
mixed. After a steady value of desired temperature was attained,
the second reactant was added and this was taken as zero time
for the run. Two milliliters of liquid sample was withdrawn from
the reactor at regular intervals for analysis and immediately trans-
ferred to a crucible in an ice bath in order to ensure that no further
reaction took place.
Physical/chemical characteristics
Value
Apparent bulk density g/l
550
Free moisture (2 h, 110 ◦C) %
Loss on ignition (predried, 2 h, 1.000 ◦C)
pH (10% suspension, filtered)
Acidity mg KOH/g
∼10
8.0
2.2–4.8
4.5
3.07%; MgO: 2.3%; CaO: 1.1%; Na2O:08%, K2O:2.2%. Other physical
and chemical properties of tonsil earth are also given in Table 1.
The Merck quality of 12-tungstophosphoric acid (DTP) and 12-
tungstosilicic acid (DTS) were used as the HPA. The other catalyst,
Amberlyst-15, was purchased from Aldrich. Butyl alcohol (>99.5%)
was obtained from Fluka. Formic acid (>99.5%) and dioxane, as the
solvent, were supplied by Merck.
Formic acid, in the reaction mixture, was determined by titration
with 0.1 N standard sodium hydroxide solutions with phenolphtha-
lein as an indicator.
3. Results and discussion
3.1. Characterization of catalysts
2.2. Catalyst preparation
3.1.1. FTIR
The primary structures of supported HPAs (Proton form) were
identified by comparing their FT-IR absorbance bands to those of
bulk DTP, DTS and tonsil (Fig. 1). Bulk DTP in Fig. 1(d) shows the
characteristic IR bands at ca. 1080 cm−1 (P–O in central tetrahe-
dral), 983 cm−1 (terminal W = O), and 890 and 797 cm−1 (W–O–W)
associated with the asymmetric vibrations in the Keggin polyanion
(Fig. 1(d and e)) which matches very well with that of the finding of
Loading of 20% DTP and DTS on tonsil earth was realized first.
After finding that the catalyst containing DTP, between them, has
higher activity the catalyst having 10%, 20% and 30% of DTP on
tonsil earth were prepared by the incipient wetness impregnation
method [17]. In this method, a known amount of tonsil earth was
dried in an oven at 120 ◦C for 1 h. The measured heteropoly acid
(HPA) was dissolved in methanol forming a homogeneous solu-
tion. The methanolic HPA solution was slowly added to the tonsil
earth with constant stirring with the help of glass rod. Initially, sup-
ports were in powdered form; however, upon subsequent addition
of methanolic HPA solution on them they form a paste or wet cake.
Further kneading of the paste for 10 min yielded a dry free flowing
powder. The preformed catalyst was dried in an oven at 120 ◦C for
1 h and then calcined at 275 ◦C for 3 h. The prepared catalysts were
kept in desiccators for experiments.
2.3. Catalyst characterization
The crystallinity and the phase purity of synthesized sam-
ples were analyzed by X-ray diffraction (XRD) patterns by
using X-ray diffractometer (Rigaku Rind 2000, Japan), and Cu-
˚
K␣ (1.54 A) radiation. XRD was performed within 2ꢀ range of
10◦–70◦.
The BET (Brunauer–Emmett–Taller) specific surface area was
obtained from N2 adsorption–desorption isotherm measured
at 77 K in an automatic adsorption apparatus (ASAP2010;
micrometritics). N2 vapor adsorption data was obtained at
the vapor pressure range (P/Po) of 0.03–0.3. The specific sur-
face area was calculated by using multipoint BET method.
The pore size distributions were also determined by the
BJH (Barret–Joyner–Halenda) method using the N2 desorption
isotherm. Prior to measurement, samples were degassed at 275 ◦C
for 2 h.
FTIR studies of the catalysts were conducted by using a Bruker
IFS-66 single channel Fourier transform spectrophotometer. Thin
wafers were prepared by mixing 0.004 g of the catalysts with
0.196 g of KBr.
Thermal analysis was carried out using a NETZSCH STA 409
PC/PG thermal analyzer. The samples with mass of about 10 mg
were placed in alumina crucible .The measurements were per-
formed in dynamic nitrogen atmosphere with the flow rate of
50 mL min−1, in the temperature range of 20–750 ◦C with a heating
Fig. 1. FITR spectra of (a) pure tonsil, (b) 20% DTP/T, (c) 20% DTS/T, (d) pure DTP (e)
pure DTS.
rate of 10 ◦C min−1
.